Synthesis of SWIR absorbing InAs quantum dots with narrow size dispersion

Abstract

A method of synthesising large InAs quantum dots comprises: providing small InAs quantum dots in a reaction vessel; providing a In-Zn-As feedstock; heating the reaction vessel to a growth temperature; adding the In-Zn-As feedstock to the reaction vessel at a growth addition rate while maintaining the growth temperature.

Description

Infrared (IR) imaging allows the visualisation of features that are undetectable to the human eye and has wide-ranging applications, including consumer, industrial, and health. Quantum dots (QDs) have the potential for improvements over current silicon-based photodetectors and InGaAs photodetectors in terms of efficiency and spectral tunability in the short-wavelength infrared (SWIR), as well as the potential for reduced costs and scalable fabrication allowing high volume applications in automotive sensing, machine vision, and consumer electronics. IR photodetectors based on QDs have shown exceptional promise, offering numerous benefits such as solution processability, wavelength tunability, high responsivity and lower cost. Current state-of-the-art focuses on the use of PbS QDs in a photodiode structure that can be monolithically integrated onto CMOS read-out integrated circuits. InAs QDs exhibit comparable optical properties and can be efficiently size-tuned to absorb NIR and SWIR wavelengths. Methods of synthesising high quality InAs QDs, adapted from the synthesis of InP QDs, have been developed to produce InAs QDs that absorb in the NIR (~940 nm). However, reliable synthetic protocols to produce InAs QDs that absorb further into the NIR and the SWIR are yet to be realised. Current synthesis methods for colloidal InAs QDs cannot maintain a narrow size distribution during the growth of the particles to the desired sizes (i.e. 5 to 15 nm corresponding to first excitonic absorbance maxima in the region of 1200-2500 nm wavelength). Commonly what is observed is that as the size of the dot increases beyond a certain size the growth becomes impaired or imbalanced and the narrow size distribution broadens, resulting in ill-defined absorption spectra as reflected by an increase in the absorption HWHM and peak:valley ratio. It is an object of the present invention to address the foregoing challenges with the provision of InAs quantum dots for IR absorption, particularly NIR and SWIR. SUMMARY OF THE INVENTION A first aspect of the present invention relates to a method of synthesising large InAs quantum dots, the method comprising: providing small InAs quantum dots in a reaction vessel; providing a In-Zn-As feedstock; heating the reaction vessel to a growth temperature; adding the In-Zn-As feedstock to the reaction vessel at a growth addition rate while maintaining the growth temperature. The methods disclosed herein provide high quality pluralities of large colloidal InAs quantum dots without the need for further size focussing. By high quality, it is meant that the pluralities of large colloidal InAs quantum dots have low polydispersity (i.e. low HWHM, high PA / ratio, and high %Trough). Advantageously, the methods described herein provide control over the morphology of the InAs quantum dots that are to be provided, producing isotropic ortetrapodal InAs quantum dots. Providing the small InAs quantum dots may comprise preforming the small InAs quantum dots, optionally the preforming comprising: providing an In carboxylate; providing a Zn-As feedstock; heating the In carboxylate to a Zn-As addition temperature; adding the Zn-As feedstock to the In carboxylate while maintaining the Zn-As addition temperature; and heating the mixture of In carboxylate and Zn-As feedstock to a conversion temperature and maintaining the conversion temperature for a conversion period to provide small InAs quantum dots. Alternatively, pre-forming the small InAs quantum dots may be undertaking by any suitable technique known in the art. The small InAs quantum dots may be provided by forming the small InAs quantum dots in situ. In other words, the small InAs quantum dots are formed before producing the large InAs quantum dots, preferably directly before producing the InAs quantum dots and / or within the reaction vessel in which growth to large InAs quantum dots is to occur. Forming the small InAs quantum dots in situ may comprise: providing an initial portion of the In-Zn-As feedstock within the reaction vessel; heating the reaction vessel to a pre-growth temperature and maintaining the pre-growth temperature for a pre-growth period prior to heating to the growth temperature; and converting at least a portion of the In-Zn-As feedstock within the reaction vessel to the small InAs quantum dots as the reaction vessel is heated. Providing the In-Zn-As feedstock may comprise: providing a mixture of In carboxylate and Zn carboxylate; providing an As feedstock; heating the mixture of In carboxylate and Zn carboxylate to an As addition temperature; and adding the As feedstock to the mixture of In carboxylate and Zn carboxylate while maintaining the As addition temperature. It has been found that providing the indium and arsenic in these sources moderates their reactivity, allowing for more controlled growth of the large InAs quantum dots and improving the quality of the resulting plurality of large InAs quantum dots. Providing the In-Zn-As feedstock may comprise: providing an In carboxylate; providing a Zn-As feedstock; heating the In carboxylate to a Zn-As addition temperature; and adding the Zn-As feedstock to the In carboxylate while maintaining the Zn-As addition temperature. It has been found that forming a Zn-As feedstock prior to adding to the In carboxylate improves the suitability of the In-Zn-As feedstock for synthesis of large InAs quantum dots. Providing the Zn-As feedstock may comprise: providing a Zn carboxylate; providing an As feedstock; heating the Zn carboxylate to an As addition temperature; and adding the As feedstock to the Zn carboxylate while maintaining the As addition temperature. The method may further comprise monitoring the peak absorption wavelength of the InAs quantum dots within the reaction vessel and ceasing addition of the In-Zn-As feedstock when a target peak absorption wavelength is achieved. In this way, large InAs quantum dots of particular sizes (and suitable for particular applications) may be targeted. The ln:As molar ratio in the In-Zn-As feedstock may be from 1:1 to 10:1, preferably from 1.5:1 to 8:1, more preferably from 2:1 to 6:1, most preferably from 3:1 to 4:1. The Zn:As molar ratio in the In-Zn-As feedstock may be from 1:5 to 5:1, preferably from 1:3 to 3:1, more preferably from 1:2 to 2:1, most preferably about 1:1. The ln:Zn:As molar ratio in the In-Zn-As feedstock is expressed as x:y:z, wherein: x is the quantity of In and has a value from 1 to 10; y is the quantity of Zn and has a value from 0.2 to 5; and z is the quantity of As and has a value of about 1. In particular embodiments, x has a value of from 3 to 7, y has a value of from 1 to 3, and z has a value of about 1. Alternatively or additionally: x has a value of about 3, y has a value of about 1, z has a value of about 1; or x has a value of about 5, y has a value of about 1, z has a value of about 1; or x has a value of about 5, y has a value of about 2, z has a value of about 1; or x has a value of about 5, y has a value of about 3, z has a value of about 1; or x has a value of about 7, y has a value of about 2, z has a value of about 1. In-Zn-As feedstocks with the foregoing molar ratios have been found to be particularly effective in producing high quality large InAs quantum dots. The method may further comprise providing additives to the reaction vessel, optionally the additives being selected from carboxylic acids (such as myristic, isostearic, or oleic acids), amines (such as octadecylamine or trioctylamine), additional sources of In (such as In carboxylates as described herein), additional sources of Zn (such as Zn carboxylates as described herein), and sources of chloride (such as tetrachloroethylene and zinc chloride). Such additives have been found to have beneficial effects on the quality of the large InAs quantum dots produced. The additives may amines (such as octadecylamine and trioctylamine) and additional sources of Zn (such as zinc carboxylates). Such additives stabilise the InAs quantum dots in the reaction solution. In particular embodiments, the additives comprise isostearic acid, octadecylamine, In carboxylate, and Zn isostearate. Optionally, the additives further comprise a source of chloride (such as tetrachloroethylene and zinc chloride). Such sources of chloride are believed to further stabilise the growing InAs quantum dots and are particularly beneficial for the production of tetrapodal InAs quantum dots. In embodiments, the growth temperature is from 220 to 380 °C, preferably from 240 to 360 °C, more preferably from 260 to 340 °C, most preferably from 280 to 320 C, such as about 300 °C. The growth addition rate may be constant. In embodiments, the growth addition rate is: (i) from 1 to 15 mL / hr, preferably from 2 to 10 mL / hr, most preferably from 3 to 8 mL / hr; and / or (ii) from 0.1 to 1 mmol / hr of As, preferably from 0.2 to 0.7 mmol / hr of As, most preferably from 0.3 to 0.6 mmol / hr of As, such as about 0.35 mmol / hr of As. In some embodiments, the growth addition rate is: (i) in mL / hr and from 0.1 to 2 times the initial volume (in mL), preferably from 0.2 to 1 times the initial volume (in mL), more preferably from 0.3 to 0.6 times the initial volume (in mL); and / or (ii) in mmol / hr of As and from 0.01 to 0.24 times the initial volume (in mL), preferably from 0.02 to 0.12 times the initial volume (in mL), more preferably from 0.03 to 0.07 times the initial volume (in mL). In particular embodiments, the growth temperature is constant, such as about 300 °C, about 320 °C, about 340 °C or about 360 °C. In such embodiments, the growth addition rate may be constant, such as: (i) from 1 to 2 mL / hr, from 3 to 5 mL / hr, from 9 to 11 mL / hr, or from 12 to 15 mL / hr; and / or (ii) from 0.06 to 0.1 mmol / hr of As, from 0.1 to 0.4 mmol / hr of As, from 0.5 to 0.7 mmol / hr of As; or from 0.7 to 1 mmol / hr of As. Alternatively, or additionally, the constant growth addition rate in such embodiments may be: (i) in mL / hr and from 0.05 to 0.45 times the initial volume (in mL), from 0.3 to 0.6 times the initial volume (in mL), from 1.0 to 1.5 times the initial volume (in mL), or from 1.8 to 2.2 times the initial volume (in mL). (ii) in mmol / hr and from 0.005 to 0.03 times the initial volume (in mL), from 0.02 to 0.06 times the initial volume (in mL), from 0.08 to 0.11 times the initial volume (in mL), or from 0.11 to 0.14 times the initial volume (in mL). In embodiments, the growth temperature is about 300 °C and the growth addition rate is selected from: (i) from 1 to 2 mL / hr; (ii) being in mL / hr and from 0.05 to 0.45 times the initial volume (in mL); (iii) from 0.06 to 0.1 mmol / hr of As; and (iv) being in mmol / hr and from 0.005 to 0.03 times the initial volume (in mL). In embodiments, the growth temperature is about 320 °C and the growth addition rate is selected from: (i) from 3 to 5 mUhr; (ii) from 0.3 to 0.6 times the initial volume (in mL); (iii) from 0.1 to 0.4 mmol / hr of As; and (iv) from 0.02 to 0.06 times the initial volume (in mL). In embodiments, the growth temperature is about 340 °C and the growth addition rate is selected from: (i) from 9 to 11 mL / hr; (ii) from 1.0 to 1.5 times the initial volume (in mL); (iii) from 0.5 to 0.7 mmol / hr of As; and (iv) from 0.08 to 0.11 times the initial volume (in mL). In embodiments, the growth temperature is about 360 °C and the growth addition rate is selected from: (i) from 12 to 15 mL / hr; (ii) from 1.8 to 2.2 times the initial volume (in mL); (iii) from 0.7 to 1 mmol / hr of As; and (iv) from 0.11 to 0.14 times the initial volume (in mL). In embodiments, the growth addition rate is: (i) from 6 to 50 mL / hr, preferably from 8 to 40 mL / hr, more preferably from 10 to 30 mL / hr, most preferably from 15 to 20 mL / hr; and / or (ii) from 0.6 to 6 mmol / hr of As, preferably from 0.8 to 5 mmol / hr of As, more preferably from 1 to 3.5 mmol / hr of As, most preferably from 1.5 to 2.5 mmol / hr of As. The growth addition rate may increase over the course of the reaction. Increasing the growth addition rate is particularly effective for producing tetrapodal InAs quantum dots. In particular embodiments: (i) the growth addition rate (in ml_ / hr) is maintained at from 0.05 to 0.4 times the volume of the reaction (in mL), preferably from 0.1 to 0.3 times the volume of the reaction (in mL), such as about 0.2 times the volume of the reaction (in mL); and / or (ii) the growth addition rate (in mmol / hr of As) is maintained at from 0.005 to 0.05 times the volume of the reaction (in mL), preferably from 0.01 to 0.04 times the volume of the reaction (in mL), such as about 0.02 times the volume of the reaction (in mL). The growth temperature is increased over the course of the reaction. For example, the growth temperature is increased in increments of 5 °C. in embodiments, the growth temperature increases from 270 to 300 °C, such as from 280 to 300 °C. A second aspect of the present invention relates to plurality of InAs quantum dots obtained or obtainable by the method of the first aspect of the present invention. A third aspect of the present invention relates to a plurality of InAs quantum dots with a peak absorbance of between 750 nm and 3000 nm, preferably from 800 nm to 2500 nm, more preferably from 900 nm to 2000 nm, further preferably from 1000 nm to 1800 nm, most preferably from 1200 nm to 1600 nm. The plurality of InAs quantum dots may have a HWHM of less than 100 meV, preferably less than 80 meV, more preferably less than 60 meV, further preferably less than 50 meV, yet further preferably less than 40 meV, most preferably less than 30 meV. The plurality of InAs quantum dots may have a peak:valley ratio of greater than 1, preferably greater than 1.3, more preferably greater than 1.6, further preferably greater than 2, yet further preferably greater than 2.2, still further preferably greater than 2.4, or most preferably greater than 2.7. The quantum dots may have isotropic morphology. Alternatively, the quantum dots may have tetrapodal morphology. A fourth aspect of the present invention relates to an IR photodetector comprising a plurality of InAs quantum dots according to the second or third aspects of the present invention. DESCRIPTION OF THE DRAWINGS Fig. 1 is of a typical photoabsorbance spectrum annotated to show how Peak:Valley ratio (PA / ), % Trough, and HWHM are derived. Fig. 2 is a block diagram for the synthesis of large InAs quantum dots beginning from small InAs quantum dots: - Step 101 is the provision of small InAs quantum dots, - Step 102 is heating to an nth growth temperature, - Step 103 is the provision of a In-Zn-As feedstock, - Step 104 is the addition of the In-Zn-As feedstock at an nth growth addition rate while maintaining the nth growth temperature, and - Step 105 is cooling and isolation of the large InAs quantum dots. The dashed arrow indicates that steps 102 and 104 may be repeated, heating to an n+1 growth temperature. Fig. 3 is a block diagram for the synthesis of small InAs quantum dots: - Step 201 is the provision of an In carboxylate, - Step 202 is heating to a ZnAs addition temperature, - Step 203 is the provision of a ZnAs feedstock, - Step 204 is the addition of the ZnAs feedstock, - Step 205 is heating to a conversion temperature for a conversion period, and - Step 101 is the provision of small InAs quantum dots. Fig. 4 is a block diagram for the synthesis of a In-Zn-As feedstock: - Step 201 is the provision of an In carboxylate, - Step 202 is heating to a ZnAs addition temperature, - Step 203 is the provision of a ZnAs feedstock, - Step 204 is the addition of the ZnAs feedstock, - Step 301 is maintaining the temperature for a period to form In-Zn-As feedstock, and - Step 103 is the provision of the In-Zn-As feedstock. Fig. 5 is a block diagram for the synthesis of a In-Zn-As feedstock: - Step 401 is the provision of a mixture of In carboxylate and Zn carboxylate, - Step 402 is heating to an As addition temperature, - Step 403 is the addition of As feedstock, and - Step 404 is the provision of an In-Zn-As feedstock. Fig. 6 is a block diagram for the synthesis of a ZnAs feedstock: - Step 501 is the provision of a Zn carboxylate, - Step 502 is heating to an As addition temperature, - Step 503 is the addition of As feedstock, and - Step 203 is the provision of a ZnAs feedstock. Fig. 7 is a series of photoabsorption spectra for Examples 1 to 4. Each spectrum follows the progress of large InAs quantum dot synthesis for one example, with off-set traces being shown for different volumes of In-Zn-As feedstock added. Fig. 8 is a TEM image of isotropic InAs quantum dots formed in Example 4. Fig. 9 is a photoabsorption spectrum for the final quantum dots of Example 4. Fig. 10 is a plot of peak photoabsorption wavelength against mmol of As added over the duration of Example 4. Fig. 11 is a TEM image of tetrapodal InAs quantum dots formed in Example 5. Fig. 12 is a photoabsorption spectrum for the final quantum dots of Example 5. Fig. 13 is a plot of peak photoabsorption wavelength against mmol of As added over the duration of Example 5. Fig. 14 is a TEM image of tetrapodal InAs quantum dots formed in Example 6. Fig. 15 is a photoabsorption spectrum for the final quantum dots of Example 6. Fig. 16 is a plot of peak photoabsorption wavelength against mmol of As added over the duration of Example 6. Fig. 17 is a TEM image of tetrapodal InAs quantum dots formed in Example 7. Fig. 18 is a photoabsorption spectrum for the final quantum dots of Example 7. Fig. 19 is a plot of peak photoabsorption wavelength against mmol of As added over the duration of Example 7. Fig. 20 is a TEM image of tetrapodal InAs quantum dots formed in Example 8. Fig. 21 is a photoabsorption spectrum for the final quantum dots of Example 8. Fig. 22 is a plot of peak photoabsorption wavelength against mmol of As added over the duration of Example 8. Figs. 23A and 23B detail the experiments performed as part of Example 9. Fig. 24 shows absorbance spectra of large InAs quantum dots with a peak absorbance of over 1600 nm produced at different In-Zn-As feedstock addition rates in Example 11. Fig. 25 shows representative STEM images of the InAs quantum dots produced in Example 11 using the intermediate In-Zn-As feedstock addition rate of 4.8 mUhr. Fig. 26 is a photoabsorption spectrum for the final quantum dots of Example 12. Fig. 27 is a plot of peak photoabsorption wavelength against mmol of As added over the duration of Example 12. Fig. 28 is a photoabsorption spectrum for the final quantum dots of Example 13. Fig. 29 is a plot of peak photoabsorption wavelength against mmol of As added over the duration of Example 13. Fig. 30 is a photoabsorption spectrum for the final quantum dots of Example 14. Fig. 31 is a plot of peak photoabsorption wavelength against mmol of As added over the duration of Example 14. DEFINITIONS AND ABBREVIATIONS By “InAs quantum dots” it is meant colloidal InAs quantum dots that are formed in solution using a ‘bottom up’ approach and typically having surface ligands. The InAs quantum dots may comprise indium and arsenic, but may include further elements as dopants. Alternatively, the InAs quantum dots may consist essentially of, or consist of, indium and arsenic. It will be understood that the ratio of indium to arsenic will be present in approximately equimolar amounts, but that the ratio may be varied. For example, the quantum dots may contain a molar ratio of ln:As of from 3:1 to 1:2, optionally from 2:1 to 1:1, from 1.7:1 to 1.2:1, or from 1.6:1 to 1.4:1, such as about 1.5:1. By small InAs quantum dots it is meant InAs quantum dots that have a peak absorbance below 750 nm. By large InAs quantum dots it is meant InAs quantum dots that have a peak absorbance in the NIR or SWIR range. In embodiments, the large InAs quantum dots have a peak absorbance of between 750 nm and 3000 nm, preferably from 800 nm to 2500 nm, more preferably from 900 nm to 2000 nm, further preferably from 1000 nm to 1800 nm, most preferably from 1200 nm to 1600 nm. References to “NIR” herein are references to “near infrared”, corresponding to light with a wavelength below 1 pm (e.g. from 0.7 to 1 pm). References to “SWIR” herein are references to “short wavelength infrared”, corresponding to light with a wavelength of 1 to 3 pm. References to “ODE” herein are references to 1-octadecene. References to “TOP” herein are references to trioctylphosphine. References to “TOPO” herein are references to trioctylphosphine oxide. References to “Ma” herein are references to myristate, used as a ligand. References to “Ac” herein are references to acetate, used as a ligand. References to “room temperature” herein will be understood to be references to ordinary temperatures, such as a temperature of about 20°C. Due to the shape of the quantum dots’ first excitonic absorption peak, it is not possible to accurately define their full-width-at-half maximum. Accordingly, a number of other measures are used as indicators of the polydispersity of these quantum dots. In general, a narrow particle size distribution is indicated by a high peak-to-valley ratio, a high % trough, and a narrow half-width-half-maximum. These measures are defined below, with reference to Fig. 1. Peak-to-valley ratio (Peak:Valley ratio or P / V) refers to the ratio of the peak to valley of the first excitonic absorption peak. Peak-to-valley ratio is a measure of how disperse the plurality of quantum dots is, with a larger ratio indicating a narrower size dispersion. % Trough is a measure of the depth of the valley behind the first excitonic absorption peak. A higher % Trough indicates the presence of fewer smaller-than-median quantum dots having a smaller-than-median absorption wavelength and can be calculated as follows: %Trough = 1-(V / P) x 100 Half-width-at-half-maximum (HWHM) is a measure of the width of the first excitonic absorption peak at half its maximum, taken towards higher wavelengths. A lower HWHM indicates a narrower size dispersion. Particle sizes were determined using scanning transmission electron microscopy (STEM). Determining the particle sizes comprised selecting a representative sample of quantum dots, measuring the major (largest) and minor (smallest) dimension for each quantum dot, and taking the mean to be the average size of each individual quantum dot. The average sizes of each individual quantum dot were then averaged to provide a mean particle size and standard deviation for the plurality of quantum dots. By ‘tetrapodal morphology’ it is meant that the quantum dots possess four limbs extending from a central point. The limbs are equally spaced (e.g. with angles between the limbs being approximately 109.5 degrees) and, preferably, are of approximately equal length. DETAILED DESCRIPTION Synthesis of Large InAs Quantum Dots The present invention relates to a method of producing large InAs quantum dots with improved control over particle size and size distribution. The method comprises the steps of providing small InAs quantum dots (101) in a reaction vessel, providing a In-Zn-As feedstock (103), heating the reaction vessel to a growth temperature (102), and adding the In-Zn-As feedstock to the reaction vessel at a growth addition rate while maintaining the growth temperature (104). The large InAs quantum dots may then be cooled and isolated (105). The small InAs quantum dots are preferably provided in a solvent. Any suitable high-boiling solvent that is able to disperse the small InAs quantum dots may be used. Typical solvents include Lewis base type coordinating solvents, such as a phosphine (e.g. TOP), a phosphine oxide (e.g. TOPO), an amine (e.g. oleylamine, hexadecylamine, and dodecylamine), non-coordinating organic solvents (e.g. alkanes and alkenes, such as squalane, squalene, and 1-octadecene), or heat transfer fluids (such as (such as hydrogenated terphenyl (e.g. Therminol® 66), mixtures of biphenyl and diphenyl oxide (e.g. Dowtherm™), ethers, and xylene). Preferred solvents are squalane and 1-octadecene Preferably, the boiling point of the solvent is high so as to permit the use of higher temperatures. Without wishing to be bound by theory, it is believed that the use of higher temperatures provides a plurality of large InAs quantum dots with improved size distribution. Preferably, the boiling point of the solvent is in excess of 200 °C, in excess of 220 °C, in excess of 240 °C, in excess of 260 °C, in excess of 280 °C, or in excess of 300 °C. The solvent is preferably anhydrous and degassed prior to heating to the reaction temperature. Degassing may be performed to remove volatiles (such as low boiling solvents or dissolved gases) before or after addition of the small InAs quantum dots by heating the solvent to an intermediate temperature, such as 120°C, under a reduced pressure. Any reaction vessel suitable for the materials used and the temperatures and pressures applied during the synthesis may be used. Preferably the synthesis is performed under an inert atmosphere, such as nitrogen or argon. Preferably, the synthesis is performed under anhydrous conditions. It has been found that size, quality, and morphology of the quantum dots may be controlled by tuning of the composition of the In-Zn-As feedstock, the rate of addition of the In-Zn-As feedstock to the reaction vessel, and the reaction temperature. The In-Zn-As feedstock may be as described herein under “Provision of In-Zn-As Feedstocks”. By tuning the growth addition rate, the concentration of indium and arsenic in the solution relative to the concentration of existing nuclei (e.g. InAs quantum dots) may be controlled so that the reaction remains in the growth regime (as opposed to the nucleation regime) and the resulting InAs quantum dots have a low polydispersity. Unexpectedly, it has been found that controlling the growth addition rate also has a strong influence on the morphology of the InAs quantum dots. It will be understood that the concentration of free indium and arsenic in the reaction solution is dependent on the concentration of indium and arsenic in the In-Zn-As feedstock and the overall volume of the solution in the reaction vessel. The growth addition rate may be from 1 to 50 mL / hr, preferably from 2 to 40 mL / hr, more preferably from 3 to 30 mL / hr, further preferably from 5 to 25 mL / hr, most preferably from 10 to 20 mL / hr. Alternatively, the growth addition rate is defined in terms of the mmol of As added to the reaction vessel. In such embodiments, the growth addition rate may be from 0.1 to 6 mmol / hr of As, preferably from 0.2 to 5 mmol / hr of As, more preferably from 0.3 to 3.5 mmol / hr of As, further preferably from 0.5 to 3 mmol / hr of As, most preferably from 1 to 2.5 mmol / hr of As. In some embodiments, the growth addition rate is from 1 to 15 mL / hr, preferably from 2 to 10 mL / hr, most preferably from 3 to 8 mL / hr, such as about 3.3 mL / hr. Alternatively, the growth addition rate may be from 0.1 to 1 mmol / hr of As, preferably from 0.2 to 0.7 mmol / hr of As, most preferably from 0.3 to 0.6 mmol / hr of As, such as about 0.35 mmol / hr of As. It will be understood that the growth addition rate may scale linearly with the initial volume of the reaction (i.e. the initial volume of solution within the reaction vessel). In embodiments, the growth addition rate (in mL / hr) may be from 0.1 to 2 times the initial volume (in mL), preferably from 0.2 to 1 times the initial volume (in mL), more preferably from 0.3 to 0.6 times the initial volume (in mL). In embodiments, the growth addition rate (in mmol / hr of As) may be from 0.01 to 0.24 times the initial volume (in mL), preferably from 0.02 to 0.12 times the initial volume (in mL), more preferably from 0.03 to 0.07 times the initial volume (in mL). For example, if a reaction has an initial volume of about 7 mL, an appropriate growth addition rate may be about 3.5 mL / hr (or 0.35 mmol / hr of As), whereas if a reaction has an initial volume of 18 mL, an appropriate growth addition rate may be about 5 mL / h (or 0.5 mmol / hr of As). Without wishing to be bound by theory, it is thought that these conditions are particularly effective for producing isotropic InAs quantum dots. In other embodiments, the growth addition rate is from 6 to 50 mL / hr, preferably from 8 to 40 mL / hr, more preferably from 10 to 30 mL / hr, most preferably from 15 to 20 mL / hr. Alternatively, the growth addition rate may be from 0.6 to 6 mmol / hr of As, preferably from 0.8 to 5 mmol / hr of As, more preferably from 1 to 3.5 mmol / hr of As, most preferably from 1.5 to 2.5 mmol / hr of As. In embodiments, the growth addition rate increases throughout the course of the reaction, either gradually or in a stepwise fashion. When increased in a stepwise fashion, the growth addition rate may be increased when 20 to 30% of the total In-Zn-As feedstock has been added, when 30 to 40% of the total In-Zn-As feedstock has been added, and when 40 to 70% of the In-Zn-As feedstock has been added. The growth addition rate may be varied such that the rate scales linearly with the volume of solution present in the reaction vessel at the time the addition is made. In other words, as the volume within the reaction vessel increases over time, so too does the addition rate. In embodiments, the growth addition rate (in mL / hr) may be maintained at from 0.05 to 0.4 times the volume (in mL), preferably from 0.1 to 0.3 times the volume (in mL), such as about 0.2 times the volume (in mL). In embodiments, the growth addition rate (in mmol / hr of As) may be maintained at from 0.005 to 0.05 times the volume (in mL), preferably from 0.01 to 0.04 times the volume (in mL), such as about 0.02 times the volume (in mL). Without wishing to be bound by theory, it is thought that these conditions are particularly effective for producing tetrapodal InAs quantum dots. Alternatively, the growth addition rate remains constant throughout the course of the reaction. The growth temperature may be between 220 and 380 °C. Preferably the growth temperature is between 240 and 360 °C, more preferably the growth temperature is between 260 and 340 °C, most preferably the growth temperature is between about 280 and 320 °C, such as about 300 °C. In embodiments, the growth temperature is greater than about 220 °C, greater than about 240 °C, greater than about 260 °C, greater than about 280 °C, greater than about 300 °C, greater than about 320 °C, greater than about 340 °C, or greater than about 360 °C. In embodiments, the growth temperature is lower than about 380 °C, lower than about 360 °C, lower than about 340 °C, lower than about 320 °C, lower than about 300 °C, lower than about 280 °C, or lower than about 260 °C. As is shown by the dashed arrow in Fig. 2, the method may further comprise increasing the growth temperature to which the reaction vessel is heated. The growth temperature may be increased in a gradual (i.e. undergoing substantially constant change) or a stepwise fashion (i.e. heating to and maintaining the higher temperature for a period). In embodiments, the initial growth temperature is as described herein, and is increased in increments of from 1 to 20 °C, preferably in increments of from 2 to 10 °C, most preferably in increments of about 5 °C. For example, the initial temperature may be about 280 °C and is increased to about 285 °C, then to about 290 °C, then to about 295 °C, and then to about 300 °C. In embodiments, the initial growth temperature is as described herein, and is gradually increased by a temperature of from 10 to 50 °C, preferably from 15 to 30 °C, most preferably about 20 °C. For example, the initial temperature may be about 280 °C and may be increased gradually to about 300 °C. Further additives may be included in the reaction vessel. For example, carboxylic acids (such as myristic, isostearic, or oleic acids), amines (such as octadecylamine or trioctylamine), additional sources of In (such as In carboxylates as described herein), additional sources of Zn (such as Zn carboxylates as described herein), and sources of chloride (such as tetrachloroethylene and zinc chloride). Preferred additives are zinc isostearate and sources of chlorides (such as tetrachloroethylene and zinc chloride). Without wishing to be bound by theory, these additives appear to stabilise the growing nuclei, thereby improving the quality of the resulting quantum dots. It will be understood that the additional sources of In and Zn are additional to the InZnAs feedstock (i.e. are not further portions of the InZnAs feedstock). The method may further comprise monitoring the peak absorption wavelength of the InAs quantum dots within the reaction vessel and ceasing addition of the In-Zn-As feedstock when a target peak absorption wavelength is achieved. The method may further comprise the isolation of the large InAs quantum dots. Any suitable isolation technique, or combination or techniques, may be used, such as precipitation, centrifugation, and filtration. Provision of Pre-Formed Small InAs Quantum Dots The small InAs quantum dots may be pre-formed and added to the reaction vessel. As shown in Fig. 3, synthesising the small InAs quantum dots may comprise providing an In carboxylate (201); providing a Zn-As feedstock (203); heating the In carboxylate to a Zn-As addition temperature (202); adding the Zn-As feedstock to the In carboxylate (204); and heating the mixture of In carboxylate and Zn-As feedstock to a conversion temperature and maintaining the conversion temperature fora conversion period (205) to provide the small InAs quantum dots (101). Alternatively, large InAs quantum dots as described herein may be used in place of the small InAs quantum dots, such that they are grown larger. The In carboxylate may be any suitable In carboxylate. Particular carboxylates are In myristate, In isostearate, In acetate, and mixed In carboxylates, such as In myristate:acetate. In embodiments, the In carboxylate may comprise ln(Ma)3-x(Ac)x, wherein 0 <x <3, such as x being about 1.5. The In carboxylate may be dissolved in a solvent. Particular solvents that may be used are those defined herein under “Synthesis of Large InAs Quantum Dots”. Further additives may be included, for example, carboxylic acids (such as myristic, isostearic, or oleic acids) or amines (such as octadecylamine or trioctylamine). The Zn-As feedstock may be as described herein under “Provision of ZnAs Feedstocks” The Zn-As addition temperature may be in the range of from room temperature to 140 °C, preferably from 40 to 120 °C, more preferably from 60 to 100 °C, most preferably about 80 °C. In embodiments, the Zn-As addition temperature may be greater than room temperature, greater than 40 °C, greater than 60 °C, greater than 80 °C, greater than 100 °C, or greater than 120 °C. In embodiments, the Zn-As addition temperature may be less than 140 °C, less than 120 °C, less than 100 °C, less than 80 °C, less than 60 °C, or less than 40 °C. The Zn-As feedstock may be added to the In carboxylate instantaneously. Alternatively, the Zn-As feedstock may be added to the In carboxylate over a period of from 10 seconds to 240 minutes, preferably from 1 minute to 120 minutes, more preferably from 10 to 90 minutes, yet more preferably from 45 to 75 minutes, most preferably about 60 minutes. The conversion temperature may be between 220 and 350 °C. Preferably the conversion temperature is between 240 and 320 °C, more preferably the conversion temperature is between 260 and 300 °C, most preferably the conversion temperature is about 280 °C. In embodiments, the conversion temperature is greater than about 220 °C, greater than about 240 °C, greater than about 260 °C, greater than about 280 °C, greater than about 300 °C, or greater than about 320 °C. In embodiments, the conversion temperature is lower than about 350 °C, lower than about 320 °C, lower than about 300 °C, lower than about 280 °C, or lower than about 260 °C. The conversion period may be from 10 seconds to 240 minutes, preferably from 1 minute to 120 minutes, more preferably from 10 to 90 minutes, yet more preferably from 45 to 75 minutes, most preferably about 60 minutes. In Situ Provision of Small InAs Quantum Dots The small InAs quantum dots may be formed in situ. In other words, they may be produced in the reaction vessel. A suitable way that this may be done is providing an initial portion of the In-Zn-As feedstock within the reaction vessel; heating the reaction vessel to a pre-growth temperature and maintaining the pre-growth temperature for a pre-growth period prior to heating to the growth temperature; and converting at least a portion of the In-Zn-As feedstock within the reaction vessel to the small InAs quantum dots. The conversion occurs as the reaction vessel is heated to the pre-growth temperature and / or at the pre-growth temperature. Further conversion may occur as the reaction vessel is heated to the growth temperature. The In-Zn-As feedstock may be as described herein under “Provision of In-Zn-As Feedstocks”. Further additives may be included in the reaction vessel. For example, carboxylic acids (such as myristic, isostearic, or oleic acids), amines (such as octadecylamine or trioctylamine), additional sources of In (such as In carboxylates as described herein), or additional sources of Zn (such as Zn carboxylates as described herein). The pre-growth temperature may be between 220 and 350 °C. Preferably the pregrowth temperature is between 240 and 320 °C, more preferably the pre-growth temperature is between 260 and 300 °C, most preferably the pre-growth temperature is about 300 °C. In embodiments, the pre-growth temperature is greater than about 220 °C, greater than about 240 °C, greater than about 260 °C, greater than about 300 °C, or greater than about 320 °C. In embodiments, the pre-growth temperature is lower than about 350 °C, lower than about 320 °C, lower than about 300 °C, or lower than about 260 °C. In embodiments, the pre-growth temperature is lower than the growth temperature. The pre-growth period may be from 1 to 120 minutes, optionally from 2 to 60 minutes, further optionally from 5 to 30 minutes, such as about 10 minutes. In embodiments, the pre-growth temperature and period is simply the time taken to heat the contents of the reaction vessel to the reaction temperature. Provision of In-Zn-As Feedstocks As shown in Fig. 5, the In-Zn-As feedstock may be provided by providing a mixture of In carboxylate and Zn carboxylate (401); providing an As feedstock; heating the mixture of In carboxylate and Zn carboxylate to an As addition temperature (402); and adding the As feedstock to the mixture of In carboxylate and Zn carboxylate while maintaining the As addition temperature (403). The In carboxylate may be any suitable In carboxylate. Particular carboxylates are In myristate, In isostearate, In acetate, and mixed In carboxylates, such as In myristate:acetate. In embodiments, the In carboxylate may comprise ln(Ma)3-x(Ac)x, wherein 0 <x <3, such as x being about 1.5. The Zn carboxylate may be any suitable Zn carboxylate. Particular carboxylates are Zn myristate, Zn isostearate, Zn acetate, and mixed Zn carboxylates. The In carboxylate and / or Zn carboxylate may be dissolved in a solvent. Particular solvents that may be used are those defined herein under “Synthesis of Large InAs Quantum Dots”. Further additives may be included, for example, carboxylic acids (such as myristic, isostearic, or oleic acids) or amines (such as octadecylamine or trioctylamine). The As feedstock may comprise any suitable As compound. Suitable As compounds include As trialkylsilyls having the formula As(SiR13)3 and As trialkylgermanium compounds having the formula As(GeR13)3. R1 may be any suitable alkyl group, for example -Ci-ealkyl or -Ca-ecycloalkyl, optionally with substitutions. In embodiments, R1 may be selected from methyl, ethyl, n-propyl, / so-propyl, n-butyl, / so-butyl, sec-butyl, ferf-butyl, and combinations thereof. Preferably, R1 is -Ci-3alkyl. Most preferably, R1 is a methyl group. The As compound may be dissolved in a solvent to form the As feedstock. Particular solvents that may be used are those defined herein under “Synthesis of Large InAs Quantum Dots”. The As addition temperature may be in the range of from room temperature to 140 °C, preferably from 40 to 120 °C, more preferably from 60 to 100 °C, most preferably about 80 °C. In embodiments, the As addition temperature may be greater than room temperature, greater than 40 °C, greater than 60 °C, greater than 80 °C, greater than 100 °C, or greater than 120 °C. In embodiments, the As addition temperature may be less than 140 °C, less than 120 °C, less than 100 °C, less than 80 °C, less than 60 °C, or less than 40 °C. The As feedstock may be added to the In carboxylate and Zn carboxylate instantaneously. Alternatively, the As feedstock may be added to the In carboxylate and Zn carboxylate over a period of from 10 seconds to 240 minutes, preferably from 1 minute to 120 minutes, more preferably from 10 to 90 minutes, yet more preferably from 45 to 75 minutes, most preferably about 60 minutes. Alternatively, as shown in Fig. 4, the In-Zn-As feedstock may be provided by providing an In carboxylate (201); providing a Zn-As feedstock (203); heating the In carboxylate to a Zn-As addition temperature (202); and adding the Zn-As feedstock to the In carboxylate (204) while maintaining the Zn-As addition temperature (301). The In carboxylate may be any suitable In carboxylate. Particular carboxylates are In myristate, In isostearate, In acetate, and mixed In carboxylates, such as In myristate:acetate. In embodiments, the In carboxylate may comprise ln(Ma)3-x(Ac)x, wherein 0 <x <3, such as x being about 1.5.The In carboxylate may be dissolved in a solvent. Particular solvents that may be used are those defined herein under “Synthesis of Large InAs Quantum Dots”. Further additives may be included, for example, carboxylic acids (such as myristic, isostearic, or oleic acids) or amines (such as octadecylamine or trioctylamine). The Zn-As feedstock may be as described herein under “Provision of ZnAs Feedstocks” The Zn-As addition temperature may be in the range of from room temperature to 140 °C, preferably from 40 to 120 °C, more preferably from 60 to 100 °C, most preferably about 80 °C. In embodiments, the Zn-As addition temperature may be greater than room temperature, greater than 40 °C, greater than 60 °C, greater than 80 °C, greater than 100 °C, or greater than 120 °C. In embodiments, the Zn-As addition temperature may be less than 140 °C, less than 120 °C, less than 100 °C, less than 80 °C, less than 60 °C, or less than 40 °C. The Zn-As feedstock may be added to the In carboxylate instantaneously. Alternatively, the Zn-As feedstock may be added to the In carboxylate over a period of from 10 seconds to 240 minutes, preferably from 1 minute to 120 minutes, more preferably from 10 to 90 minutes, yet more preferably from 15 to 60 minutes, most preferably about 30 minutes. The ln:As ratio in the In-Zn-As feedstock may be from 1:1 to 10:1, preferably from 1.5:1 to 8:1, more preferably from 23:1 to 6:1, most preferably from 3:1 to 4:1, such as about 3.4:1. The Zn:As ratio in the In-Zn-As feedstock may be from 1:5 to 5:1, preferably from 1:3 to 3:1, more preferably from 1:2 to 2:1, most preferably about 1:1. The ln:Zn:As ratio in the In-Zn-As feedstock may be expressed as x:y:z, wherein: x is the quantity of In and has a value from 1 to 10; y is the quantity of Zn and has a value from 0.2 to 5; and z is the quantity of As and has a value of about 1. Alternatively, x is from 1.5 to 8, y is from 0.33 to 3, and z is about 1. Further alternatively, x is from 2 to 6, y is from 0.5 to 2, and z is about 1. Yet further alternatively, x is from 3 to 4 (such as about 3.4), y is 1, and z is about 1. The In-Zn-As feedstock may have an As concentration of from 0.01 to 1 M, preferably from 0.05 to 0.5 M, more preferably from 0.05 to 0.2 M, most preferably from 0.08 to 0.15 M, such as about 0.1 M. Without wishing to be bound by theory, it is believed that these ratios of In to As and Zn to As lead to improved size distribution at larger InAs quantum dot sizes while allowing the formation of both isotropic and tetrapodal InAs quantum dots depending on the process conditions applied. Provision of Zn-As Feedstocks As shown in Fig. 6, providing the Zn-As feedstock may comprise: providing a Zn carboxylate (501); providing an As feedstock; heating the Zn carboxylate to an As addition temperature (502); and adding the As feedstock to the Zn carboxylate while maintaining the As addition temperature (503). Without wishing to be bound by theory, it is believed that combination of the Zn and As to form the Zn-As feedstock prior to mixing with the In carboxylate moderates the reactivity of these precursors (whether forming small InAs quantum dots or a In-Zn-As feedstock), thereby improving the quality of the resulting plurality of large InAs quantum dots. The Zn carboxylate may be any suitable Zn carboxylate. Particular carboxylates are Zn myristate, Zn isostearate, Zn acetate, and mixed Zn carboxylates. The Zn carboxylate may be dissolved in a solvent. Particular solvents that may be used are those defined herein under “Synthesis of Large InAs Quantum Dots”. Further additives may be included, for example, carboxylic acids (such as myristic, isostearic, or oleic acids) or amines (such as octadecylamine or trioctylamine). The As feedstock may comprise any suitable As compound. Suitable As compounds include As trialkylsilyls having the formula As(SiR1s)3 and As trialkylgermanium compounds having the formula As(GeR13)3. R1 may be any suitable alkyl group, for example -Ci-ealkyl or -Cs-ecycloalkyl, optionally with substitutions. In embodiments, R1 may be selected from methyl, ethyl, n-propyl, / so-propyl, n-butyl, / so-butyl, sec-butyl, fert-butyl, and combinations thereof. Preferably, R1 is -Cvsalkyl. Most preferably, R1 is a methyl group. The As compound may be dissolved in a solvent to form the As feedstock. Particular solvents that may be used are those defined herein under “Synthesis of Large InAs Quantum Dots”. The As addition temperature may be in the range of from room temperature to 140 °C, preferably from 40 to 120 °C, more preferably from 60 to 100 °C, most preferably about 80 °C. In embodiments, the As addition temperature may be greater than room temperature, greater than 40 °C, greater than 60 °C, greater than 80 °C, greater than 100 °C, or greater than 120 °C. In embodiments, the As addition temperature may be less than 140 °C, less than 120 °C, less than 100 °C, less than 80 °C, less than 60 °C, or less than 40 °C. The As feedstock may be added to the In carboxylate and Zn carboxylate instantaneously. Alternatively, the As feedstock may be added to the In carboxylate and Zn carboxylate over a period of from 10 seconds to 240 minutes, preferably from 1 minute to 120 minutes, more preferably from 10 to 90 minutes, yet more preferably from 45 to 75 minutes, most preferably about 60 minutes. Specific Conditions for Isotropic InAs Quantum Dots One or more of the following conditions may be used to produce large isotropic InAs quantum dots: (i) the small quantum dots are produced in situ, (ii) the In-Zn-As feedstock has an As concentration of from 0.01 to 1 M, preferably from 0.05 to 0.5 M, more preferably from 0.05 to 0.2 M, most preferably from 0.08 to 0.15 M, such as about 0.1 M; (iii) the ln:Zn:As ratio in the In-Zn-As feedstock may be expressed as x:y:z, wherein: x is the quantity of In and has a value from 3 to 7, such as from 5 to 7; y is the quantity of Zn and has a value from 1 to 3; and z is the quantity of As and has a value of about 1; (iv) the growth addition rate is from 1 to 15 mL / hr, such as from 3 to 5 mL / hr, from 9 to 11 mL / hr, or from 12 to 15 mL / hr; (v) the growth addition rate is from 0.1 to 1.8 mmol / hr of As, such as from 0.3 to 0.6 mmol / hr of As, from 0.9 to 1.3 mmol / hr of As, or from 1.2 to 1.8 mmol / hr of As; (vi) the growth addition rate (in ml_ / hr) is from 0.1 to 2 times the initial volume (in mL), preferably from 0.2 to 1 times the initial volume (in mL), more preferably from 0.3 to 0.6 times the initial volume (in mL); (vii) the growth addition rate (in mmol / hr of As) is from 0.01 to 0.24 times the initial volume (in mL), preferably from 0.02 to 0.12 times the initial volume (in mL), more preferably from 0.03 to 0.07 times the initial volume (in mL); (viii) the growth addition rate is constant; (ix) the growth temperature is from 280 to 380 °C, such as about 300 °C, about 320 °C, about 340 °C, or about 360 °C; (x) the solvent is squalene or octadecene; and (xi) the reaction solution comprises zinc isostearate. In particular embodiments, the In-Zn-As feedstock has an As concentration of from 0.01 to 0.5 M and the molar ratio ln:Zn:As may be expressed as x:y:z, wherein: x is the quantity of In and has a value from 5 to 7; y is the quantity of Zn and has a value from 1 to 3; and z is the quantity of As and has a value of about 1, and one of the following sets of reaction conditions is applied: - the growth temperature is about 300 °C and the growth addition rate is from 1 to 2 mL / hr; - the growth temperature is about 300 °C and the growth addition rate (in mL / hr) is from 0.05 to 0.45 times the initial volume (in mL); - the growth temperature is about 300 °C and the growth addition rate is from 0.06 to 0.1 mmol / hr of As; the growth temperature is about 300 °C and the growth addition rate (in mmol / hr) is from 0.005 to 0.03 times the initial volume (in mL); - the growth temperature is about 320 °C and the growth addition rate is from 3 to 5 mL / hr; - the growth temperature is about 320 °C and the growth addition rate (in mL / hr) is from 0.3 to 0.6 times the initial volume (in mL); - the growth temperature is about 320 °C and the growth addition rate is from 0.1 to 0.4 mmol / hr of As; the growth temperature is about 320 °C and the growth addition rate (in mmol / hr) is from 0.02 to 0.06 times the initial volume (in mL); the growth temperature is about 340 °C and the growth addition rate is from 9 to 11 mL / hr; - the growth temperature is about 340 °C and the growth addition rate (in mL / hr) is from 1.0 to 1.5 times the initial volume (in mL); - the growth temperature is about 340 °C and the growth addition rate is from 0.5 to 0.7 mmol / hr of As; the growth temperature is about 340 °C and the growth addition rate (in mmol / hr) is from 0.08 to 0.11 times the initial volume (in mL); the growth temperature is about 360 °C and the growth addition rate is from 11 to 15 mL / hr; - the growth temperature is about 360 °C and the growth addition rate (in mL / hr) is from 1.8 to 2.2 times the initial volume (in mL); - the growth temperature is about 360 °C and the growth addition rate is from 0.7 to 1 mmol / hr of As; - the growth temperature is about 360 °C and the growth addition rate (in mmol / hr) is from 0.11 to 0.14 times the initial volume (in mL). Specific Conditions for Tetrapodal InAs Quantum Dots One or more of the following conditions may be used to produce large isotropic InAs quantum dots: (i) the small quantum dots are produced in situ, (ii) the small quantum dots are pre-formed; (iii) the In-Zn-As feedstock has an As concentration of from 0.01 to 1 M, preferably from 0.05 to 0.5 M, more preferably from 0.05 to 0.2 M, most preferably from 0.08 to 0.15 M, such as about 0.1 M; (iv) the ln:Zn:As ratio in the In-Zn-As feedstock may be expressed as x:y:z, wherein: x is the quantity of In and has a value from 1 to 5, such as about 1; y is the quantity of Zn and has a value from 1 to 5, such as about 3; and z is the quantity of As and has a value of about 1; (iv) the growth addition rate is from 6 to 50 mL / hr, preferably from 8 to 40 mL / hr, more preferably from 10 to 30 mL / hr, most preferably from 15 to 20 mL / hr; (v) the growth addition rate is from from 0.6 to 6 mmol / hr of As, preferably from 0.8 to 5 mmol / hr of As, more preferably from 1 to 3.5 mmol / hr of As, most preferably from 1.5 to 2.5 mmol / hr of As; (vi) the growth addition rate increases over the course of the reaction, optionally such that the growth addition rate (in mL / hr) is maintained in a range from 0.05 to 0.4 times the volume (in mL), preferably from 0.1 to 0.3 times the volume (in mL), such as about 0.2 times the volume (in mL). Alternatively, the growth addition rate (in mmol / hr of As) may be from 0.005 to 0.05 times the volume (in mL), preferably from 0.01 to 0.04 times the volume (in mL), such as about 0.02 times the volume (in mL); (vii) the growth temperature is from 280 to 320 °C, such as about 300 °C; (viii) the solvent is squalene or octadecene; (ix) the reaction solution comprises zinc isostearate; (x) the reaction solution comprises TCE or zinc chloride. Large InAs quantum dots may be produced using one or more of the following conditions wherein the growth addition rate increases over the course of the reaction: - The In-Zn-As feedstock has an As concentration of from 0.01 to 1 M, preferably from 0.05 to 0.5 M, more preferably from 0.05 to 0.2 M, most preferably from 0.08 to 0.15 M, such as about 0.1 M; - The ln:Zn:As ratio in the In-Zn-As feedstock may be expressed as x:y:z, wherein: x is the quantity of In and has a value from 3 to 7, such as about 3.4; y is the quantity of Zn and has a value of about 1; and z is the quantity of As and has a value of about 1; - The growth temperature is from 280 to 320 °C, such as from 280 to 300 °C; - The reaction solution comprises zinc isostearate; and - The reaction solution comprises TCE or zinc chloride. In one preferred embodiment, the growth addition rate increases in a stepwise fashion as follows: Firstly at a rate of from 5 to 13 mL / hr; Secondly at a rate of from 13 to 17 mL / hr; Thirdly at a rate of from 17 to 20 mL / hr; and Fourthly at a rate of from 20 to 25 mL / hr. In another preferred embodiment, the growth addition rate is maintained (in mL / hr) in a range from 0.05 to 0.4 times the volume (in mL), preferably from 0.1 to 0.3 times the volume (in mL). In another preferred embodiment, the growth addition rate (in mmol / hr of As) is maintained at from 0.005 to 0.05 times the volume (in mL), preferably from 0.01 to 0.04 times the volume (in mL), In another preferred embodiment, the growth addition rate increases in a stepwise fashion as follows: Firstly at a rate of from 5 to 15 mL / hr; Secondly at a rate of from 15 to 20 mL / hr; Thirdly at a rate of from 20 to 28 mL / hr; and Fourthly at a rate of from 28 to 35 mL / hr. Large InAs quantum dots may also be produced using one or more of the following conditions wherein the growth temperature increases over the course of the reaction: - The In-Zn-As feedstock has an As concentration of from 0.01 to 1 M, preferably from 0.05 to 0.5 M, more preferably from 0.05 to 0.2 M, most preferably from 0.08 to 0.15 M, such as about 0.1 M; - The ln:Zn:As ratio in the In-Zn-As feedstock may be expressed as x:y:z, wherein: x is the quantity of In and has a value from 3 to 7, such as about 3.4; y is the quantity of Zn and has a value of about 1; and z is the quantity of As and has a value of about 1; and - The growth addition rate is from 5 to 40 mL / hr, preferably from 10 to 20 mL / hr, such as about 13.5 mL / hr. In preferred embodiments the temperature increases in a stepwise fashion as follows: Firstly a temperature of about 280 °C; Secondly at a temperature of about 285 °C; Thirdly at a temperature of about 290 °C; Fourthly at a temperature of about 295 °C; and Fifthly at a temperature of about 300 °C. Pluralities of InAs Quantum Dots The present invention also relates to pluralities of InAs quantum dots obtained or obtainable by the foregoing methods. The pluralities of InAs quantum dots may have a peak absorbance of between 750 nm and 3000 nm, preferably from 800 nm to 2500 nm, more preferably from 900 nm to 2000 nm, further preferably from 1000 nm to 1800 nm, or most preferably from 1200 nm to 1600 nm. The peak absorbance may be greater than 750 nm, optionally greater than 800 nm, optionally greater than 900 nm, optionally greater than 1000 nm, optionally greater than 1200 nm, optionally greater than 1600 nm, optionally greater than 1800 nm, optionally greater than 2000 nm, or optionally greater than 2500 nm. The peak absorbance may be lower than 3000 nm, optionally lower than 2500 nm, optionally lower than 2000 nm, optionally lower than 1600 nm, optionally lower than 1200 nm, optionally lower than 1000 nm, optionally lower than 900 nm, or optionally lower than 800 nm. As will be understood, the plurality of InAs quantum dots may be a plurality of large InAs quantum dots as defined herein. The pluralities of InAs quantum dots may have a HWHM of less than 100 meV, preferably less than 80 meV, more preferably less than 60 meV, further preferably less than 50 meV, yet further preferably less than 40 meV, or most preferably less than 30 meV. The pluralities of large InAs quantum dots may have a HWHM of more than 30 meV, optionally more than 40 meV, further optionally more than 50 meV, further optionally more than 60 meV, or further optionally more than 80 meV. The pluralities of large InAs quantum dots may have a HWHM in the range of 30 to 100 meV, optionally in the range of 40 to 80 meV, or further optionally in the range of 50 to 60 meV. The pluralities of InAs quantum dots may have a peak:valley ratio of greater than 1, greater than 1.2, greater than 1.3, greater than 1.5, greater than 1.7, greater than 2, greater than 2.2, greater than 2.4, or greater than 2.6. The pluralities of large InAs quantum dots may have a peak:valley ratio of less than 3, less than 2.6, less than 2.4, less than 2.2, less than 2, less than 1.7, less than 1.5, less than 1.3, less than 1.2, or less than 1.1. The pluralities of large InAs quantum dots may have a peak:valley ratio in the range of from 1.1 to 3, from 1.2 to 2.6, from 1.3 to 2.4, from 1.5 to 2.2, or from 1.7 to 2. The plurality of InAs quantum dots may have a % Trough of greater than 0, greater than 9, greater than 16, greater than 23, greater than 33, greater than 41, greater than 50, greater than 55, greater than 58, or greater than 62. The plurality of large InAs quantum dots may have a % Trough of less than 67, less than 62, less than 58, less than 55, less than 50, less than 41, less than 33, less than 23, less than 17, or less than 9. The plurality of large InAs quantum dots may have a % Trough in the range of from 9 to 67, from 17 to 62, from 23 to 58, from 33 to 55, or from 33 to 41. In embodiments, the InAs quantum dots have isotropic morphology. In particular, they may have a tetrahedral morphology. Without wishing to be bound by theory, it is believed that isotropic quantum dots have more efficient packing, allowing for increased densities of quantum dots in films and devices (compared to tetrapodal quantum dots). In alternative embodiments, the InAs quantum dots have tetrapodal morphology. Without wishing to be bound by theory, it is believed that tetrapodal quantum dots have a higher absorption per quantum dot; improved carrier transport (e.g. along the limbs), with transport being directional and having fewer hopping events; and longer exciton lifetimes due to delocalisation (all compared to isotropic quantum dots). IR Photodetectors and Other Devices Comprising Pluralities of InAs Quantum Dots The present invention also relates to IR photodetectors comprising a plurality of large InAs quantum dots as described herein. The present invention also relates to other optoelectronic devices comprising a plurality of large InAs quantum dots as described herein. In embodiments, the devices comprise a single plurality of large InAs quantum dots (e.g. all of the same size or morphology). Alternatively, the devices comprise two or more pluralities of large InAs quantum dots (e.g. a mixture of tetrapodal and isotropic InAs quantum dots). EXAMPLES Preparation of Indium Carboxylate A mixed indium carboxylate is used in the following syntheses of InAs quantum dots. The mixed indium carboxylate comprising mixed indium acetates and myristates, with a molecular weight of 541.1 g / mol and an empirical stoichiometry of ln(Ma)i.48(Ac)i,52 (i.e. comprising 21% indium by mass). The mixed indium carboxylate is converted to indium myristate in situ during the degassing step at elevated temperature. Degassed Therminol 66 (7.594 kg) was charged to a 20 L reactor and heated to 35 °C, followed by addition of myristic acid (4.050 kg). Indium acetate (2.352 kg) was added and the mixture degassed at 200 rpm for 2 hours. The agitation was increased to 250 rpm and the temperature increased to 140 °C for 2 hours under vacuum, with acetic acid being collected in a distillation head. The reaction temperature was maintained for a further 4 hours under vacuum, after which the reaction mixture being golden-coloured and turbid. The reaction mixture was allowed to settle before half of the mixture was transferred to a 30L filter and stirred with acetone (14.004 kg) to induce precipitation. A further charge of acetone (14.004 kg) is added before the second half of the reaction mixture is transferred to the filter. The precipitates were collected and washed with acetone (6 by 4.86 kg), with resuspension between filtrations. The precipitate is dried to constant mass via nitrogen purge (at 0.5 bar for 1 hour), under vacuum for 8 hours, and finally in a vacuum oven at 50 °C and 10 mbar. Reaction Sampling Aliquots for absorption spectroscopy were obtained as follows. Using a nitrogen filled syringe equipped with a suitable needle, 0.2-0.3 mL of tetrachloroethylene (TCE) was taken into the syringe, followed by approx. 0.1 mL of the reaction solution. The contents of the syringe were then expelled via a 0.1 micron syringe filter into 2 mL TCE in a 1 cm pathlength cuvette. TCE was added to make the contents the appropriate fill level for measurement. Unless stated otherwise, the formation of quantum dots in the following examples was tracked using this methodology. Example 1 Preparation of Small InAs Quantum Dot Solution Zinc isostearate (1.9 g) and ODE (3.25 mL) were charged to a 100 mL 3-neck round bottomed flask equipped with a magnetic stirrer. The B19 necks were sealed with rubber septa, a B24-to-flex adaptor fitted to the central neck and a thermocouple pierced through the rubber septum to make contact with the solvent. The flask was heated to 120°C and evacuated for 1 hour before being backfilled with nitrogen and cooled to 80°C. Tris(trimethylsilyl)arsine in ODE (0.5M; 6 mL) was added dropwise over 1 hour at 80°C and then cooled to room temperature. In parallel, indium carboxylate (3.23 g), myristic acid (0.418 g) and ODE (100 mL) were charged to a 250 mL 3-neck round bottomed flask equipped with a magnetic stirrer. The B19 necks were sealed with rubber septa, a B24-to-flex adaptor fitted to the central neck and a thermocouple pierced through the rubber septum to make contact with the solvent. The flask was heated to 120°C and evacuated for 1 hour before being backfilled with nitrogen. The flask was opened under positive nitrogen pressure and octadecylamine (1.6 g) charged to the flask. Once sealed, the flask was evacuated at 120°C for 1 hour before being backfilled with nitrogen and cooled to 80°C. The above prepared Zn-As solution was added to the flask dropwise over 1 hour. Following addition, the reaction was heated to 280°C for 1 hour, and then cooled to room temperature. Preparation of In-Zn-As Solution Indium carboxylate (15 g), oleic acid (9.5 mL), zinc isostearate (2.4 g) and ODE (80 mL) were charged to a 500 mL 3-neck round bottomed flask equipped with a magnetic stirrer. The B19 necks were sealed with rubber septa, a B24-to-flex adaptor fitted to the central neck and a thermocouple pierced through the rubber septum to make contact with the solvent. The flask was heated to 120°C and evacuated for 1 hour before being backfilled with nitrogen and cooled to 80°C. Tris(trimethylsilyl)arsine in ODE (0.5M; 19 mL) was added dropwise over 1 hour at 80°C and then cooled to room temperature. Growth of Large InAs Quantum Dots A clean dry 500 mL 3-neck round bottom flask, equipped with a magnetic stirrer, was sealed with rubber septa on the B19 and B24 central neck and a B19-to-flex adaptor fitted to the remaining neck. A thermocouple was pierced through the rubber septum and positioned such that it reached to the bottom of the flask near to the stirrer bar. An inert atmosphere was created in the flask by three evacuation / nitrogen backfill cycles. The small InAs quantum dot solution (20 mL) was transferred via syringe and the flask heated to 120°C and evacuated for 1 hour. The flask was backfilled with nitrogen and a syringe filled with In-Zn-As feedstock positioned to add through the central neck. At 120°C, a few drops of In-Zn-As feedstock were added, followed by the flask being heated to 280°C. At 260°C the In-Zn-As feedstock addition started at a rate of 3.6 mL / hour. After 23 mL of In-Zn-As feedstock addition, the feed was stopped and the reaction cooled to room temperature. The next day, the reaction was heated to 285°C and 36.5 mL of In-Zn-As feedstock was added at a rate of 3.6 mL / hr. The temperature was increased to 290°C and a further 44.5 mL of In-Zn-As feedstock was added at the same rate. The temperature was then increased to 295'C and a further 48.5 mL of In-Zn-As feedstock was added at the same rate. The temperature was then increased to 300°C and a further 36.5 mL of In-Zn-As feedstock was added so that a total of 189 mL of In-Zn-As feedstock had been added. The reaction mixture was then cooled to 120°C. Octanoic acid (2.5 mL) was added to the reaction mixture and the temperature maintained at 120°C for 1 hour before being cooled to 80°C. Toluene (90 mL) was added and the temperature lowered to 60°C after which octanol (90 mL) was added and the reaction mixture cooled to room temperature, transferred to a large Schlenk tube and taken into a nitrogen filled glove box. The diluted reaction mixture was transferred to large centrifuge tubes and centrifuged at 6000 ref for 10 minutes. The supernatant was decanted to a large bottle and the grey solids discarded. Isopropyl alcohol (IPA; 600 mL) was added to the supernatant to precipitate the quantum dots, which were collected by centrifugation (6000 ref, 10 mins) and redispersed in octane (60 mL). Further purification was effected by precipitation with IPA (120 mL) and the solids collected by centrifugation, washed with acetone (30 mL) and dried. The final solids were dissolved in octane (90 mL), centrifuged (6000 ref, 10 min) and filtered through a 0.2 micron syringe filter. Final yield 2.1 g. Thermogravimetric data showed that the sample contained 83% InAs by mass with the remainder being organic ligands. The C18:C14:C8 ratio determined by gas chromatography-flame ionisation detector (GC-FID) was 0.25:1:0.88. Absorption spectra taken throughout the growth are presented in Fig. 7 and a table of spectral data presented in Table 1. Table 1 Vol Feed stock added, mL Reaction Temperature, °C Amax (nm) Peak:Valley HWHM, meV Small InAs quantum dots 675 1.63 98.4 0.2 280 675 1.62 98.9 23 280 1005 1.82 69.3 47.1 295 1170 1.82 64.1 105 300 1372 1.52 62.8 189 300 1400 1.21 53 after octanoic acid 120 1408 1.26 55.2 isolated RT 1405 1.09 57.3 Example 2 Preparation of Small InAs Quantum Dot Solution The small InAs quantum dot solution was prepared as in Example 1. Preparation of In-Zn-As Solution Zinc isostearate (9.0 g) and trioctylamine (6 mL) were charged to a 250 mL 3-neck round bottomed flask equipped with a magnetic stirrer. The B19 necks were sealed with rubber septa, a B24-to-flex adaptor fitted to the central neck and a thermocouple pierced through the rubber septum to make contact with the solvent. The flask was heated to 120°C and evacuated for 2 hours before being backfilled with nitrogen and cooled to 80°C. Tris(trimethylsilyl)arsine in ODE (0.5 M; 27 mL) was added dropwise over 30 minutes at 80°C and then cooled to room temperature. In parallel, indium carboxylate (24.7 g), oleic acid (15.6 mL), trioctylamine (10.5 mL) and ODE (52.5 mL) were charged to a 500 mL 3-neck round bottomed flask equipped with a magnetic stirrer. The B19 necks were sealed with rubber septa, a B24-to-flex adaptor fitted to the central neck and a thermocouple pierced through the rubber septum to make contact with the solvent. The flask was heated to 120°C and evacuated for 4 hours before being backfilled with nitrogen and cooled to 80°C. The above prepared Zn-As solution was added to the flask dropwise over 30 minutes and the temperature maintained for a further 30 minutes before cooling to room temperature. Growth of Large InAs Quantum Dots A clean dry 500 mL 3-neck round bottom flask, equipped with a magnetic stirrer, was sealed with rubber septa on the B19 and B24 central neck and a B19-to-flex adaptor fitted to the remaining neck. A thermocouple was pierced through the rubber septum and positioned such that it reached to the bottom of the flask near to the stirrer bar. An inert atmosphere was created in the flask by three evacuation / nitrogen backfill cycles. The small InAs quantum dot solution (20 mL) was transferred via syringe and the flask heated to 120°C and evacuated for 1 hour. The flask was backfilled with nitrogen and a syringe filled with In-Zn-As feedstock positioned to add through the central neck. At 120°C, a few drops of In-Zn-As feedstock were added, followed by the flask being heated to 280°C. At 260°C the In-Zn-As feedstock addition started at a rate of 3.0 mL / hr. The reaction was cooled to room temperature after 20 mL had been added. The next day the reaction was heated to 285°C, addition of In-Zn-As feedstock started at 260°C at 3.0 mL / hr and continued. After the addition of 31 mL of In-Zn-As feedstock, the temperature was increased to 290°C, after addition of a further 37 mL of In-Zn-As feedstock the temperature was increased to 295°C, after addition of a further 43 mL of In-Zn-As feedstock the temperature was increased to 300°C. When a total of 142 mL had been added, the addition was stopped and the reaction cooled to 120°C. Octanoic acid (8 mL) was added to the reaction mixture and the temperature maintained at 120°C for 1 hour before being cooled to 80°C. Toluene (80 mL) was added and the temperature lowered to 60°C after which octanol (80 mL) was added and the reaction mixture cooled to room temperature, transferred to a large Schlenk tube and taken into a nitrogen filled glove box. The diluted reaction mixture was transferred to large centrifuge tubes and centrifuged at 6000 ref for 10 minutes. The supernatant was decanted to a large bottle and the grey solids discarded. IPA (400 mL) was added to the supernatant to precipitate the quantum dots, which were collected by centrifugation (6000 ref, 10 mins) and redispersed in octane (90 mL). Further purification was effected by precipitation with IPA (150 mL) and the solids collected by centrifugation washed with acetone (30 mL) and dried. The final solids were dissolved in octane (90 mL), centrifuged (6000 ref, 10 min) and filtered through a 0.2 micron syringe filter. Final yield: 2.7 g. Thermogravimetric data showed that the sample contained 78% InAs by mass with the remainder being organic ligands. The C18:C14:C8 ratio determined by GC-FID was 0.26:1:1.68. Absorption spectra taken throughout the growth are presented in Fig. 7 and a table of spectral data presented in Table 2. Table 2 Vol Feed stock added, mL Reaction Temperature, °C Amax (nm) Peak:Valley HWHM, meV Small InAs quantum dots 675 1.63 98.4 0.9 280 697 1.77 107 19.7 280 1005 1.9 67 37 290 1133 1.78 65.4 43.2 295 1170 1.76 58.8 114 300 1372 1.37 50 142 300 1408 1.33 48.7 after octanoic acid 120 1405 1.32 48.1 isolated RT 1408 1.36 44.9 Example 3 Preparation of In-Zn-As Solution Zinc isostearate (15.0 g) and trioctylamine (20 mL) were charged to a 250 mL 3-neck round bottomed flask equipped with a magnetic stirrer. The B19 necks were sealed with rubber septa, a B24-to-flex adaptor fitted to the central neck and a thermocouple pierced through the rubber septum to make contact with the solvent. The flask was heated to 120°C and evacuated for 5 hours before being backfilled with nitrogen and cooled to 80°C. Tris(trimethylsilyl)arsine in ODE (0.5 M; 45 mL) was added dropwise over 30 minutes at 80°C and then cooled to room temperature. In parallel, indium carboxylate (61.8 g), oleic acid (39 mL), trioctylamine (25 mL) and squalane (130 mL) were charged to a 500 mL 3-neck round bottomed flask equipped with a magnetic stirrer. The B19 necks were sealed with rubber septa, a B24-to-flex adaptor fitted to the central neck and a thermocouple pierced through the rubber septum to make contact with the solvent. The flask was heated to 130°C and evacuated for 5 hours before being backfilled with nitrogen and cooled to 80°C. The above prepared Zn-As solution was added to the flask dropwise over 30 minutes and the temperature maintained for a further 30 minutes before cooling to room temperature. The next day the flask was heated to 80°C and evacuated for 5 hours, backfilled with nitrogen and cooled to room temperature. In Situ Preparation of Small InAs Quantum Dot Solution and Growth of Large InAs Quantum Dots Zinc isostearate (0.264 g), octadecylamine (0.114 g) and squalane (5 mL) were charged to a 250 mL 3-neck round bottomed flask equipped with a large rugby ball shaped magnetic stirrer. The centre B24 and one B19 neck were sealed with rubber septa, a B19-to-flex adaptor fitted to the other B19 neck and a thermocouple pierced through the B19 rubber septum to make contact with the solvent The flask was heated to 130°C and evacuated for 1 hour before being backfilled with nitrogen and cooled to 70°C. In-Zn-As feedstock (1.854 mL @ 18.54 mL / hr) was added through the centre septum via a syringe and the mixture stirred at 70°C for 15 minutes. The temperature was increased to 320°C and at 300°C, a few drops of In-Zn-As feedstock were added manually and addition started at 3.34 mL / hr. After 10.13 mL In-Zn-As feedstock had been added, addition was stopped and the reaction cooled to room temperature. The next day a few drops of In-Zn-As feedstock were added and the reaction mixture heated to 320°C. At 300°C the addition was restarted at 3.34 mL / hr. After 23.46 mL of In-Zn-As feedstock had been added, the addition was stopped and the reaction cooled to 120°C. Octanoic acid (1 mL) was added, the reaction stirred at 120°C for 1 hr and then cooled to 80°C. Toluene (13 mL) and octanol (13 mL) were added and the reaction mixture cooled to room temperature, transferred to a large Schlenk tube and taken into a nitrogen filled glove box. The diluted reaction mixture was transferred to centrifuge tubes and centrifuged at 6000 ref for 10 minutes. The supernatant was decanted to a bottle and the grey solids discarded. IPA (1.5 vol equivalent) was added to the supernatant to precipitate the quantum dots which were collected by centrifugation (6000 ref, 10 mins) and redispersed in octane (10 mL). Further purification was effected by precipitation with IPA (16 mL) and the solids collected by centrifugation washed with acetone (5 mL) and dried. The final solids were dissolved in octane (10 mL), centrifuged (6000 ref, 10 min) and filtered through a 0.2 micron syringe filter. Final yield: 0.54 g. Thermogravimetric data showed that the sample contained 76% InAs by mass with the remainder being organic ligands. Absorption spectra taken throughout the growth are presented in Fig. 7 and a table of spectral data presented in Table 3. Table 3 Vol Feed stock added, mL Reaction Temperature, °C Amax (nm) Peak:Valley HWHM, meV 2.7 320 932 2.58 62.7 4.2 320 1007 2.65 56.6 6.4 320 1091 2.48 51.3 10.1 320 1212 2.49 46.0 23.19 320 1443 1.78 42.1 after octanoic acid 120 1450 1.71 44.3 isolated RT 1451 1.64 44.8 Example 4 Preparation of In-Zn-As Solution Zinc isostearate (6.0 g) and trioctylamine (4 mL) were charged to a 250 mL 3-neck round bottomed flask equipped with a large rugby ball shaped magnetic stirrer. The B19 necks were sealed with rubber septa, a B24-to-flex adaptor fitted to the central neck and a thermocouple pierced through the rubber septum to make contact with the solvent. The flask was heated to 120°C and evacuated for 2.5 hours before being backfilled with nitrogen and cooled to 80°C. 0.5 M Tris(trimethylsilyl)arsine in ODE (9 mL) was added dropwise over 30 minutes at 80°C, stirred for a further 30 minutes and then cooled to room temperature. In parallel, indium carboxylate (12.36 g), oleic acid (7.8 mL), trioctylamine (5 mL) and squalane (23 mL) were charged to a 250 mL 3-neck round bottomed flask equipped with a large rugby ball shaped magnetic stirrer. The B19 necks were sealed with rubber septa, a B24-to-flex adaptor fitted to the central neck and a thermocouple pierced through the rubber septum to make contact with the solvent. The flask was heated to 130°C and evacuated for 4 hours before being backfilled with nitrogen and cooled to 80°C. The above prepared Zn-As solution was added to the flask dropwise over 30 minutes and the temperature maintained for a further 30 minutes before cooling to room temperature. The next day the flask was heated to 80°C and evacuated for 5 hours, backfilled with nitrogen and cooled to room temperature. In Situ Preparation of Small InAs Quantum Dot Solution and Growth of Large InAs Quantum Dots Zinc isostearate (0.18 g), octadecylamine (0.114 g) and squalane (5 mL) were charged to a 250 mL 3-neck round bottomed flask equipped with a large rugby ball shaped magnetic stirrer. The center B24 and one B19 neck were sealed with rubber septa, a B19-to-flex adaptor fitted to the other B19 neck and a thermocouple pierced through the B19 rubber septum to make contact with the solvent. The flask was heated to 130°C and evacuated for 1 hour before being backfilled with nitrogen and cooled to 70°C. In-Zn-As feedstock (1.854 mL @ 18.54 mL / hr) was added through the center septum via syringe and the mixture stirred at 70°C for 15 minutes. The temperature was increased to 320°C by heating at maximum setting (10 min ramp time) and at 300°C, a few drops of In-Zn-As feedstock were added manually and addition started at 3.34 mL / hr. After addition of 26.0 mL, the addition was stopped and the reaction cooled to 120°C. Octanoic acid (1 mL) was added, the reaction stirred at 120°C for 1hr and then cooled to 80°C. Toluene (13 mL) and octanol (13 mL) were added and the reaction mixture cooled to room temperature, transferred to a large schlenk tube and taken into a nitrogen filled glove box. The diluted reaction mixture was transferred to centrifuge tubes and centrifuged at 6000 ref for 10 minutes. The supernatant was decanted to a bottle and the grey solids set to one side. IPA (1.5 vol equivalent) was added to the supernatant to precipitate the quantum dots which were collected by centrifugation (6000 ref, 10 mins) and redispersed in octane (10 mL). The grey solids were washed with octane (3 x 10 mL) and the washings combined. The product was obtained by precipitation with acetone (2 vol equivalents), collected by centrifugation (6000 ref, 10 mins) and dispersed in octane (10 mL). The octane solutions were combined and further purification was affected by precipitation with acetone (2 vol equivalents) and the solids collected by centrifugation washed with acetone (5 mL) and dried. The final solids were dissolved in octane (10 mL), centrifuged (6000 ref, 10 min) and filtered through a 0.2 micron syringe filter. Final yield: 0.41 g. Absorption spectra taken throughout the growth are presented in Fig. 7 and a table of spectral data presented in Table 4. Table 4 Vol Feed Stock added, mL Reaction Temperature, °C Amax (nm) Peak:Valley HWHM, meV 2.7 320 919 2.41 64.8 7.2 320 1100 2.35 51.4 10.2 320 1183 2.44 44.2 18.7 320 1350 2.11 42.5 26.0 320 1449 1.73 38.1 after octanoic acid 120 1448 1.76 37.1 isolated RT 1440 1.76 38.1 TEM imaging (Fig. 8) shows that the InAs quantum dots are isotropic. The absorption spectrum, and tracking of the 1st excitonic absorption peak position with the mmol of arsenic added are provided in Figs. 9 and 10 respectively. Example 5 Preparation of In-Zn-As Solution Zinc isostearate (28.5 g) and trioctylamine (19 mL) were charged to a 250 mL 3-neck round bottomed flask equipped with a large rugby ball shaped magnetic stirrer. The B19 necks were sealed with rubber septa, a B24-to-flex adaptor fitted to the central neck and a thermocouple pierced through the rubber septum to make contact with the solvent. The flask was heated to 120°C and evacuated for 6 hours before being backfilled with nitrogen and cooled to 80°C. 0.5 M tris(trimethylsilyl)arsine in squalane (85.5 mL) was added dropwise over 30 minutes at 80°C, stirred for a further 30 minutes and then cooled to room temperature. In parallel, indium carboxylate (78.28 g), isostearic acid (51.3 mL), trioctylamine (33.25 mL) and squalane (166.25 mL) were charged to a 2L 3-neck round bottomed flask equipped with a large rugby ball shaped magnetic stirrer. The B19 necks were sealed with rubber septa, a B24-to-flex adaptor fitted to the central neck and a thermocouple pierced through the rubber septum to make contact with the solvent. The flask was heated to 120°C and evacuated for 6 hours before being backfilled with nitrogen and cooled to 80°C. The above prepared Zn-As solution was added to the flask dropwise over 30 minutes and the temperature maintained for a further 30 minutes before cooling to room temperature. The next day, the flask was heated to 80C and evacuated for 5 hours before being backfilled with nitrogen and cooled to room temperature. Growth of Large Tetrapodal InAs Quantum Dots Indium carboxylate (1.14 g), isostearic acid (0.78 mL), zinc isostearate (1.416 g), and squalane (30 mL) were charged to a 500 mL 3-neck round bottomed flask equipped with a large rugby ball shaped magnetic stirrer. The center B24 and one B19 neck were sealed with rubber septa, a B19-to-flex adaptor fitted to the other B19 neck and a thermocouple pierced through the B19 rubber septum to make contact with the solvent. The flask was heated to 120°C and evacuated for 2 hours before being backfilled with nitrogen. Octadecylamine (0.684 g) was added to the flask through the central neck and flask was and evacuated at 120°C for 30 minutes before being backfilled with nitrogen and cooled to 100°C. In-Zn-As feedstock (8.1 mL @ 16.2 mL / hr) was added through the central septum via a syringe. The temperature was increased to 320°C by heating at maximum setting (10 min ramp time) and at 295°C, a few drops of feedstock were added manually and addition started at 10.8 mL / hr. The addition rate of the In-Zn-As feedstock was increased in step-wise fashion over the course of the reaction, with the following addition rates being used for each portion of In-Zn-As feedstock: Cumulative Volume of In-Zn-As Feedstock added (mL) Addition rate applied (mL / hr) 48.5 10.8 73 16.2 90 19.8 197 23.4 After the cumulative addition of 197 mL of In-Zn-As feedstock, the addition was stopped and the reaction cooled to 120°C. Octanoic acid (10 mL) was added, the reaction stirred at 120°C for 1 hour and then cooled to 60°C. The reaction mixture was transferred to a large Schlenk tube containing 220 mL chloroform and taken into a nitrogen-filled glove box. The diluted reaction mixture was transferred to centrifuge tubes and centrifuged at 6000 ref for 10 minutes. The supernatant was decanted to a bottle and the grey solids set to one side. IPA (1.5 vol equivalent) was added to the supernatant to precipitate the quantum dots which were collected by centrifugation (6000 ref, 10 mins) and redispersed in chloroform (40 mL). The product was obtained by precipitation with acetone (1.5 vol equivalents) and IPA (1.5 vol equivalents), collected by centrifugation (6000 ref, 10 mins). The final solids were washed twice with 10 mL of acetone and dried before re-dispersing in octane (40 mL). The final octane solution was centrifuged (6000 ref, 10 min) and filtered through a 0.2 micron syringe filter. Final yield: 5.07 g. Thermogravimetric analysis showed that the sample contained 77 % InAs by mass with the remainder being organic ligands. TEM imaging (Fig. 11) shows that the InAs quantum dots are tetrapodal. The absorption spectrum, and tracking of the 1st excitonic absorption peak position with the mmol of arsenic added are provided in Figs. 12 and 13 respectively. Example 6 The small InAs quantum dot solution was prepared as in Example 1 and the In-Zn-As feedstock was prepared as in Example 5 Growth of Large Tetrapodal InAs Quantum Dots A clean dry 2L 3-neck round bottom flask, equipped with a large rugby ball shaped magnetic stirrer, was sealed with rubber septa on the B19 and B24 central neck and a B19-to-flex adaptor fitted to the remaining neck. A thermocouple was pierced through the rubber septum and positioned such that it reached to the bottom of the flask near to the stirrer bar. An inert atmosphere was created in the flask by three evacuation / nitrogen backfill cycles, using heat to dry the flask. The small InAs quantum dot solution (89 mL) was transferred via syringe and the flask was heated to 110°C and evacuated for 2 h. The flask was backfilled with nitrogen and a polyethylene tube primed with In-Zn-As feedstock and controlled by a peristaltic pump was positioned to add through the central neck. At 120°C, a few drops of In-Zn-As feedstock were added, followed by the flask being heated to 280°C. At 270°C the feedstock addition started at a rate of 13.56 mL / h. The temperature of the reaction mixture was increased in step-wise fashion over the course of the reaction, with the following temperatures being used for each portion of the In-Zn-As feedstock: Cumulative Volume of In-Zn-As Feedstock added (mL) Temperature applied (°C) 81* 270 to 280 125 285 155 290 177 295 540 300 *the reaction was cooled to room temperature overnight following this initial addition, after which the reaction was resumed at the new temperature of 285°C. When a total of 540 mL had been added, the addition was stopped and the reaction cooled to 120°C. The next day, the reaction was reheated to 90°C and half the batch (-315 mL) was transferred to an evacuated, dry 1L three neck flask, containing a rugby ball shaped magnetic stirrer. Octanoic acid (15.5 mL) was added to the reaction mixture and the temperature maintained at 120°C for 1 hour before being cooled to 80°C. Toluene (165 mL) was added and the temperature lowered to 60°C after which octanol (165 mL) was added and the reaction mixture cooled to room temperature, transferred to a large Schlenk tube and taken into a nitrogen filled glove box. The diluted reaction mixture was transferred to large centrifuge tubes and centrifuged at 6000 ref for 10 minutes. The supernatant was decanted to a large bottle and the grey solids discarded. IPA (970 mL) was added to the supernatant to precipitate the quantum dots, which were collected by centrifugation (6000 ref, 10 mins) and redispersed in octane (120 mL). The same procedure was repeated with the second half of the batch and the quantum dots were combined in glass bottle. Further purification was affected by precipitation with acetone (480 mL) and the solids collected by centrifugation, washed with acetone (40 mL) and dried. The final solids were dissolved in octane (240 mL), centrifuged (6000 ref, 10 min) and filtered through a 1 micron syringe filter. The final yield was 13.4 g. Thermogravimetric data showed that the sample contained 81% InAs by mass with the remainder being organic ligands. The C18:C14:C8 ratio determined by GC-FID was 0.3:1:0.97. TEM imaging (Fig. 14) shows that the InAs quantum dots are tetrapodal. The absorption spectrum, and tracking of the 1st excitonic absorption peak position with the mmol of arsenic added are provided in Figs. 15 and 16 respectively. Example 7 The small InAs quantum dot solution was prepared as in Example 1 and the In-Zn-As feedstock was prepared as in Example 5 Preparation of 1M ZnCh-Octanol Solution Zinc chloride powder (1.36 g) was weighed into a 28 mL glass vial. The vial was sealed with a rubber septum and evacuated for 2 - 3 minutes followed by being backfilled with nitrogen gas. This evacuation / backfill cycle was repeated three more times. Under a flow of nitrogen, nitrogen-sparged 1-octanol (10 mL) was added to the vial via a syringe. The vial was evacuated carefully until bubbling ceased before being backfilled with nitrogen and sonicated for a minimum of 30 minutes or until all of the zinc chloride had dissolved. Once a clear, colourless solution was obtained the vial was stored under a nitrogen flow for later use. Growth of Large Tetrapodal InAs Quantum Dots A clean, dry 500 mL 3-neck round bottom flask, equipped with a large rugby ball shaped magnetic stirrer, was sealed with rubber septa on the B19 and B24 central neck and a B19-to-flex adaptor fitted to the remaining neck. A thermocouple was pierced through the rubber septum and positioned such that it reached to the bottom of the flask near to the stirrer bar. An inert atmosphere was created in the flask by three evacuation / nitrogen backfill cycles. Small InAs quantum dot solution (15 mL) was transferred via a syringe and the flask heated to 110°C and evacuated for 2 hours. The flask was backfilled with nitrogen and a syringe filled with In-Zn-As feedstock positioned to add through the central neck. At 120°C, a few drops of feedstock were added, followed by the flask being heated to 280°C. The temperature of the reaction mixture and addition rate of the In-Zn-As feedstock were varied over the course of the reaction, with the following temperatures and addition rates being adopted after addition of the indicated volume of In-Zn-As feedstock: Cumulative Volume of In-Zn-As Feedstock added Temperature applied (°C) Addition rate applied (mL / hr) (mL) 9.36* 260 to 280 2.25 Addition of zinc chloride solution 21.36 200 to 280 18 39.36 280 13.5 78.46 285 13.5 86.56** 290 13.5 105.86 200 to 290 13.5 *the reaction was cooled to room temperature overnight following this initial addition. The next day the flask was evacuated at 120°C for 30min then backfilled with nitrogen. 1M ZnCh-octanol solution (0.3 mL) was added via a syringe and the solution heated to 150°C and stirred for 1 hour. The solution was then heated to 280°C. At 200°C the feedstock addition was resumed. **the reaction was cooled to room temperature overnight following this addition. The addition was then stopped and the reaction cooled. At 100°C, nitrogen sparged 1-octanol (55 mL) and dry nitrogen sparged toluene (55 mL) was added and the mixture transferred to a dry inert Schlenk tube and taken into the glovebox for workup. The contents of the Schlenk tube was decanted to 6 x 50 mL centrifuge tubes. After centrifugation (6000 ref, 10 minutes) the supernatant was decanted to a 500 mL bottle and the solids discarded. Dry IPA (240 mL) was added to the bottle to precipitate the dots. The solids were collected by centrifugation (6000 ref, 10 minutes) and the light brown supernatant discarded. The black solids were dissolved in octane (40 mL), reprecipitated by addition of IPA (75 mL) and collected by centrifugation (6000 ref, 10 min). The light coloured supernatant was discarded and the solid allowed to dry before being re-dissolved in octane (60mL), centrifuged (6000 ref, 10min) and filtered (0.1 micron syringe filter) into a bottle for storage. Thermogravimetric analysis showed that the sample contained 70 % InAs by mass with the remainder being organic ligands. TEM imaging (Fig. 17) shows that the InAs quantum dots are tetrapodal. The absorption spectrum, and tracking of the 1st excitonic absorption peak position with the mmol of arsenic added are provided in Figs. 18 and 19 respectively. Example 8 The In-Zn-As feedstock was prepared as in Example 5. Growth of Large Tetrapodal InAs Quantum Dots Indium carboxylate (1.14 g), isostearic acid (0.78 mL), zinc isostearate (1.416 g), and squalane (30 mL) were charged to a 500 mL 3-neck round bottomed flask equipped with a large rugby ball shaped magnetic stirrer. The center B24 and one B19 neck were sealed with rubber septa, a B19-to-flex adaptor fitted to the other B19 neck and a thermocouple pierced through the B19 rubber septum to make contact with the solvent. The flask was heated to 120°C and evacuated for 2 hour before being backfilled with nitrogen. Octadecylamine (0.684 g) was added to the flask through the central neck and flask was and evacuated at 120°C for 30 minutes before being backfilled with nitrogen and cooled to 100°C. In-Zn-As feedstock (8.1 mL @ 16.2 mL / hr) was added through the center septum via a syringe. The temperature was increased to 320°C by heating at maximum setting (10 min ramp time) and at 295°C, a few drops of feedstock were added manually and addition started at 10.8 mL / hr. The addition rate of the In-Zn-As feedstock was increased in step-wise fashion over the course of the reaction, with the following addition rates being used for each portion of In-Zn-As feedstock: Cumulative Volume of In-Zn-As Feedstock added (mL) Addition rate applied (mL / hr) 41 10.8 75 18.9 125 25 211 30 After the cumulative addition of 197 mL of In-Zn-As feedstock, the addition was stopped and the reaction cooled to 120°C. Octanoic acid (10.7 mL) was added, the reaction stirred at 120°C for 1 hr and then cooled to 60°C. The reaction mixture was transferred to a large Schlenk tube containing 220 mL chloroform and taken into a nitrogen-filled glove box. The diluted reaction mixture was transferred to centrifuge tubes and centrifuged at 6000 ref for 10 minutes. The supernatant was decanted to a bottle and the grey solids set to one side. IPA (1.5 vol equivalent) was added to the supernatant to precipitate the quantum dots which were collected by centrifugation (6000rcf, 10 mins) and redispersed in chloroform (40 mL). The product was obtained by precipitation with acetone (1.5 vol equivalents) and IPA (1.5 vol equivalents), collected by centrifugation (6000 ref, 10 mins). The final solids were washed twice with 10mL of acetone and dried before re-dispersing in octane (40 mL). The final octane solution was centrifuged (6000 ref, 10 min) and filtered through a 0.2 micron syringe filter. Final yield: 5.2 g. Thermogravimetric analysis showed that the sample contained 76 % InAs by mass with the remainder being organic ligands. TEM imaging (Fig. 20) shows that the InAs quantum dots are tetrapodal. The absorption spectrum, and tracking of the 1st excitonic absorption peak position with the mmol of arsenic added are provided in Figs. 21 and 22 respectively. Example 9 The procedure of Examples 3 and 4 was repeated, varying the stoichiometry and concentration of the In-Zn-As feedstock, the reaction temperature, feedstock addition rate, and what additives were present. The details of these repetitions and the characteristics of the resulting isotropic InAs quantum dots are shown in Figs. 23A and 23B. The results show that well-defined isotropic InAs quantum dots could be achieved by matching the In-Zn-As addition rate to the reaction temperature for a range of feedstocks, with higher addition rates being required at higher temperatures. In addition, zinc isostearate was found to stabilize the nuclei, allowing for lower addition rates to be used. Example 10 InAs quantum dots with a peak absorption of 1450 nm were prepared as described in Example 4. At the end of the reaction, 16 mL of reaction solution was homogenized at 80 °C and transferred to a new flask containing pre-degassed (130 °C, 40 min), zinc isostearate (1.9 g), and squalane (2 mL) under nitrogen. The reaction mixture was heated to 340 °C. At 320 °C addition of 5:2:1 ln:Zn:As feedstock commenced at a rate of 4.8 mUhr. The growth was monitored by periodically taking aliquots for absorption measurements. After 4.8 mL was added, the feed rate was lowered to 2.8 mL / hr and continued until a total of 8.8 mL was added after which the addition stopped, the reaction cooled rapidly using compressed air to 280 °C, and then allowed to cool naturally to 120 °C. At 120 °C octanoic acid (1 mL) was added and the reaction stirred to 1 hour then cooled to 80 °C. The warm reaction mixture was transferred to an inert Schlenk tube containing dry degassed chloroform (25 mL) and taken into a glove box. The contents of the Schlenk tube were decanted into 2 x 50 mL centrifuge tubes and centrifuged at 6000 rpm for 10 mins. The supernatant transferred to 4 x 50 mL centrifuge tubes and the solids discarded. To the supernatant, isopropanol (1.5 vol equivalents was added to precipitate the dots. The solid product was collected by centrifugation at 6000 rpm for 10 minutes. The light coloured supernatant was discarded and the black solids redissolved in chloroform (5 mL total) and precipitated by addition of isopropanol (20 mL) and acetone (10 mL). The solids were collected by centrifugation, the colourless supernatant discarded. A final dissolution / re-precipitation cycle with octane (8 mL) / acetone (10 mL) was carried out, the product collected by centrifuge (6000 rpm / 10 min), washed with acetone (3 mL) three times, dried before being dissolved in octane (8 mL) and filtered (0.2 pm syringe filter) into a vial. Example 11 The procedure of Example 10 was repeated at varying In-Zn-As feedstock feed rates, as set out in the table below: Feed rate (mL / hr) Abs nm Trough % HWHM meV starting material 1447 35.9 43.1 2.4 1607 8.6 48.0 4.8 1618 21.6 38.0 7.2 1655 3.2 41.5 It can be seen that the high quality isotropic InAs quantum dots were produced using the intermediate addition rate of 4.8 ml_ / hr, which is the same scaled rate as was used to produce the initial InAs quantum dots with an absorption peak centred on 1450 nm. Overlain absorbance spectra are shown in Fig 24 and representative STEM images of the InAs quantum dots formed at the intermediate addition rate of 4.8 mL / hr are shown in Fig. 25. Example 12 The In-Zn-As feedstock was prepared as in Example 5. Growth of Large Tetrapodal InAs Quantum Dots without Reaction Sampling Indium carboxylate (0.19 g), isostearic acid (0.13 mL), zinc isostearate (0.236 g), and squalane (5 mL) were charged to a 250 mL 3-neck round bottomed flask equipped with a large rugby ball shaped magnetic stirrer. The center B24 and one B19 neck were sealed with rubber septa, a B19-to-flex adaptor fitted to the other B19 neck and a thermocouple pierced through the B19 rubber septum to make contact with the solvent. The flask was heated to 130°C and evacuated for 1 hour before being backfilled with nitrogen and cooled to 120°C. Octadecylamine (0.114 g) was added to the flask through the central neck and flask was and evacuated at 120°C for 30 minutes before being backfilled with nitrogen and cooled to 100°C. In-Zn-As feedstock (1.35 mL @ 2.7 mL / hr) was added through the central septum via a syringe. The temperature was increased to 320°C by heating at maximum setting (10 min ramp time) and at 295°C, a few drops of feedstock were added manually and addition started at 1.8 mL / hr. The addition rate of the In-Zn-As feedstock was increased in step-wise fashion over the course of the reaction, with the following addition rates being used for each portion of In-Zn-As feedstock: Cumulative Feedstock volume (mL) Addition Rate (mL / hr) 7.5 1.8 20.7 3.15 25.1 4.16 After the addition of 25.1 mL, the addition was stopped and the reaction cooled to 120°C. Octanoic acid (1.25 mL) was added, the reaction stirred at 120°C for 1hr and then cooled to 60°C. The quantum dots were isolated following the method outlined in Example 5. As is shown in Figs. 26 and 27, growth was slower and the first excitonic wavelength reached only 1317 nm before losing definition and a significant decrease in quantum dot quality (e.g. %Trough). The final shape of the absorption spectrum did not have the characteristic tetrapodal features. This highlights the role of chloride sources, such as TCE, in controlling the growth rate of quantum dots. Example 13 Preparation of In-Zn-As Solution Zinc isostearate (9.0 g) and trioctylamine (6 mL) were charged to a 250 mL 3-neck round bottomed flask equipped with a magnetic stirrer. The B19 necks were sealed with rubber septa, a B24-to-flex adaptor fitted to the central neck and a thermocouple pierced through the rubber septum to make contact with the solvent. The flask was heated to 120°C and evacuated for 2 hours before being backfilled with nitrogen and cooled to 80°C. Tris(trimethylsilyl)arsine in squalene (0.5 M; 27 mL) was added dropwise over 30 minutes at 60°C and then cooled to room temperature. In parallel, indium carboxylate (24.7 g), oleic acid (15.6 mL), trioctylamine (10.5 mL) and squalene (52.5 mL) were charged to a 500 mL 3-neck round bottomed flask equipped with a magnetic stirrer. The B19 necks were sealed with rubber septa, a B24-to-flex adaptor fitted to the central neck and a thermocouple pierced through the rubber septum to make contact with the solvent. The flask was heated to 120°C and evacuated for 4 hours before being backfilled with nitrogen and cooled to 60°C. The above prepared Zn-As solution was added to the flask dropwise over 30 minutes and the temperature maintained for a further 30 minutes before cooling to room temperature. Growth of Tetrapodal InAs Quantum Dots with TCE Indium carboxylate (0.19 g), isostearic acid (0.13 mL), zinc isostearate (0.236 g), and squalane (5 mL) were charged to a 250 mL 3-neck round bottomed flask equipped with a large rugby ball shaped magnetic stirrer. The center B24 and one B19 neck were sealed with rubber septa, a B19-to-flex adaptor fitted to the other B19 neck and a thermocouple pierced through the B19 rubber septum to make contact with the solvent. The flask was heated to 130°C and evacuated for 1 hour before being backfilled with nitrogen and cooled to 120°C. Octadecylamine (0.114 g) was added to the flask through the central neck and flask was and evacuated at 120°C for 30 minutes before being backfilled with nitrogen and cooled to 100°C. In-Zn-As feedstock (1.35 mL @ 2.7 mL / hr) was added through the central septum via a syringe. The temperature was increased to 320°C by heating at maximum setting (10 min ramp time) and at 295°C, a few drops of feedstock were added manually and addition started at 1.8 mL / hr. After 8 mL the feedstock addition was stopped and the reaction was cooled to room temperature. Next day, the reaction mixture was heated back to 320°C and at 295°C, 2.5 pL anhydrous TCE in 47.5 pL degassed squalane was added. Then the feedstock addition was started at the rate of 2.7 mL / hr. The addition rate of the In-Zn-As feedstock was increased in step-wise fashion over the course of the reaction, with the following addition rates being used for each portion of In-Zn-As feedstock: Cumulative Feedstock volume (mL) Addition Rate (mL / hr) 8 1.8 19.2 2.7 31 3.3 64.5 4 After the addition of 64.5 mL, the addition was stopped and the reaction cooled to 120°C. Octanoic acid (3 mL) was added, the reaction stirred at 120°C for 1 hr and then cooled to 60°C. The quantum dots were isolated following the method outlined in Example 5. The absorption spectrum of the final tetrapodal InAs quantum dots is shown in Fig. 28, with tracking of the 1st excitonic absorption peak position with the mmol of arsenic shown in Fig. 29. Example 14 The In-Zn-As feedstock was prepared as in Example 13. Growth of Tetrapodal InAs Quantum Dots with Addition of TCE Indium carboxylate (0.19 g), isostearic acid (0.13 mL), zinc isostearate (0.236 g), and squalane (5 mL) were charged to a 250 mL 3-neck round bottomed flask equipped with a large rugby ball shaped magnetic stirrer. The center B24 and one B19 neck were sealed with rubber septa, a B19-to-flex adaptor fitted to the other B19 neck and a thermocouple pierced through the B19 rubber septum to make contact with the solvent. The flask was heated to 130°C and evacuated for 1 hour before being backfilled with nitrogen and cooled to 120°C. Octadecylamine (0.114 g) was added to the flask through the central neck and flask was and evacuated at 120°C for 30 minutes before being backfilled with nitrogen and cooled to 100°C. In-Zn-As feedstock (1.35 mL @ 2.7 mL / hr) was added through the central septum via a syringe. The temperature was increased to 320°C by heating at maximum setting (10 min ramp time) and at 295°C, a few drops of feedstock were added manually and addition started at 1.8 mL / hr. After 1.9 mL of feedstock added, 5 pL anhydrous TCE in 95 pL degassed squalane was added and the reaction continued with the feedstock addition rate of 1.8 mL / h. After 7.6 mL of feedstock added, further 5 pL anhydrous TCE in 95 pL degassed squalane was added. After the addition of 20.2 mL, the addition was stopped and the reaction cooled to 120°C. Oleic acid (2 mL) was added, the reaction stirred at 120°C for 1 hour and then cooled to 60°C. The quantum dots were isolated following the method outlined in Example 5. The absorption spectrum of the final tetrapodal InAs quantum dots is shown in Fig. 30, with tracking of the 1st excitonic absorption peak position with the mmol of arsenic shown in Fig. 31. Clauses of the Invention Clause 1. A method of synthesising large InAs quantum dots, the method comprising: providing small InAs quantum dots in a reaction vessel; providing a In-Zn-As feedstock; heating the reaction vessel to a growth temperature; adding the In-Zn-As feedstock to the reaction vessel at a growth addition rate while maintaining the growth temperature. Clause 2. The method of clause 1, wherein providing the small InAs quantum dots comprises preforming the small InAs quantum dots, optionally the preforming comprising: providing an In carboxylate; providing a Zn-As feedstock; heating the In carboxylate to a Zn-As addition temperature; adding the Zn-As feedstock to the In carboxylate while maintaining the Zn-As addition temperature; and heating the mixture of In carboxylate and Zn-As feedstock to a conversion temperature and maintaining the conversion temperature for a conversion period to provide small InAs quantum dots. Clause 3. The method of clause 1, wherein providing the small InAs quantum dots comprises forming the small InAs quantum dots in situ. Clause 4. The method of clause 3, wherein forming the small InAs quantum dots in situ comprises: providing an initial portion of the In-Zn-As feedstock within the reaction vessel; heating the reaction vessel to a pre-growth temperature and maintaining the pre-growth temperature for a pre-growth period prior to heating to the growth temperature; and converting at least a portion of the In-Zn-As feedstock within the reaction vessel to the small InAs quantum dots as the reaction vessel is heated. Clause 5. The method of any one of the preceding clauses, wherein providing the In-Zn-As feedstock comprises: providing a mixture of In carboxylate and Zn carboxylate; providing an As feedstock; heating the mixture of In carboxylate and Zn carboxylate to an As addition temperature; and adding the As feedstock to the mixture of In carboxylate and Zn carboxylate while maintaining the As addition temperature. Clause 6. The method of any one of clauses 1 to 4, wherein providing the In-Zn-As feedstock comprises: providing an In carboxylate; providing a Zn-As feedstock; heating the In carboxylate to a Zn-As addition temperature; and adding the Zn-As feedstock to the In carboxylate while maintaining the Zn-As addition temperature. Clause 7. The method of any one of clauses 2 to 6, wherein providing the Zn-As feedstock comprises: providing a Zn carboxylate; providing an As feedstock; heating the Zn carboxylate to an As addition temperature; and adding the As feedstock to the Zn carboxylate while maintaining the As addition temperature. Clause 8. The method of any one of the preceding clauses, further comprising monitoring the peak absorption wavelength of the InAs quantum dots within the reaction vessel and ceasing addition of the In-Zn-As feedstock when a target peak absorption wavelength is achieved. Clause 9. The method of any one of the preceding clauses, wherein the ln:As molar ratio in the In-Zn-As feedstock is from 1:1 to 10:1, preferably from 1.5:1 to 8:1, more preferably from 2:1 to 6:1, most preferably from 3:1 to 4:1. Clause 10. The method of any one of the preceding clauses, wherein the Zn:As molar ratio in the In-Zn-As feedstock is from 1:5 to 5:1, preferably from 1:3 to 3:1, more preferably from 1:2 to 2:1, most preferably about 1:1. Clause 11. The method of any one of the preceding claims, wherein the ln:Zn:As molar ratio in the In-Zn-As feedstock is expressed as x:y:z, wherein: x is the quantity of In and has a value from 1 to 10; y is the quantity of Zn and has a value from 0.2 to 5; and z is the quantity of As and has a value of about 1. Clause 12. The method of clause 11, wherein: x has a value of from 3 to 7 y has a value of from 1 to 3 z has a value of about 1 Clause 13. The method of clause 12, wherein: x has a value of about 3, y has a value of about 1, z has a value of about 1; or x has a value of about 5, y has a value of about 1, z has a value of about 1; or x has a value of about 5, y has a value of about 2, z has a value of about 1; or x has a value of about 5, y has a value of about 3, z has a value of about 1; or x has a value of about 7, y has a value of about 2, z has a value of about 1. Clause 14. The method of any one of the preceding clauses, further comprising providing additives to the reaction vessel, optionally the additives being selected from carboxylic acids (such as myristic, isostearic, or oleic acids), amines (such as octadecylamine or trioctylamine), additional sources of In (such as In carboxylates as described herein), additional sources of Zn (such as Zn carboxylates as described herein), and sources of chloride (such as tetrachloroethylene and zinc chloride). Clause 15. The method of clause 14, wherein the additives comprise amines (such as octadecylamine and trioctylamine) and additional sources of Zn (such as zinc carboxylates). Clause 16. The method of clause 14, wherein the additives comprise isostearic acid, octadecylamine, In carboxylate, and Zn isostearate. Clause 17. The method of clause 16, wherein the additives further comprise a source of chloride (such as tetrachloroethylene and zinc chloride). Clause 18. The method of any one of the preceding clauses, wherein the growth temperature is from 220 to 380 °C, preferably from 240 to 360 °C, more preferably from 260 to 340 °C, most preferably is from 280 to 320°C, such as about 300 °C. Clause 19. The method of any one of the preceding clauses wherein the growth addition rate is constant, the growth addition rate being: (i) from 1 to 15 mL / hr, preferably from 2 to 10 mL / hr, most preferably from 3 to 8 mL / hr; and / or (ii) from 0.1 to 1 mmol / hr of As, preferably from 0.2 to 0.7 mmol / hr of As, most preferably from 0.3 to 0.6 mmol / hr of As, such as about 0.35 mmol / hr of As; and / or (ill) in mL / hr and from 0.1 to 2 times the initial volume (in mL), preferably from 0.2 to 1 times the initial volume (in mL), more preferably from 0.3 to 0.6 times the initial volume (in mL); and / or (iv) in mmol / hr of As and from 0.01 to 0.24 times the initial volume (in mL), preferably from 0.02 to 0.12 times the initial volume (in mL), more preferably from 0.03 to 0.07 times the initial volume (in mL). Clause 20. The method of any one of the preceding claims, wherein the growth temperature is constant, such as about 300 °C, about 320 °C, about 340 °C or about 360 °C. Clause 21. The method of clause 20, wherein the growth addition rate is constant. Clause 22. The method of clause 21, wherein the growth addition rates is from 1 to 2 mL / hr, from 3 to 5 mL / hr, from 9 to 11 mL / hr, or from 12 to 15 mL / hr. Clause 23. The method of clause 21, wherein the growth addition rates is in ml_ / hr and from 0.05 to 0.45 times the initial volume (in mL), from 0.3 to 0.6 times the initial volume (in mL), from 1.0 to 1.5 times the initial volume (in mL), or from 1.8 to 2.2 times the initial volume (in mL). Clause 24. The method of clause 21, wherein the growth addition rates is from 0.06 to 0.1 mmol / hr of As, from 0.1 to 0.4 mmol / hr of As, from 0.5 to 0.7 mmol / hr of As; or from 0.7 to 1 mmol / hr of As. Clause 25. The method of clause 21, wherein the growth addition rates is in mmol / hr and from 0.005 to 0.03 times the initial volume (in mL), from 0.02 to 0.06 times the initial volume (in mL), from 0.08 to 0.11 times the initial volume (in mL), or from 0.11 to 0.14 times the initial volume (in mL). Clause 26. The method of clause 20, wherein the growth temperature is about 300 °C and the growth addition rate is selected from: (i) from 1 to 2 mL / hr; (ii) being in mL / hr and from 0.05 to 0.45 times the initial volume (in mL); (iii) from 0.06 to 0.1 mmol / hr of As; and (iv) being in mmol / hr and from 0.005 to 0.03 times the initial volume (in mL). Clause 27. The method of clause 20, wherein the growth temperature is about 320 °C and the growth addition rate is selected from: (i) from 3 to 5 mL / hr; (ii) from 0.3 to 0.6 times the initial volume (in mL); (iii) from 0.1 to 0.4 mmol / hr of As; and (iv) from 0.02 to 0.06 times the initial volume (in mL). Clause 28. The method of clause 20, wherein the growth temperature is about 340 °C and the growth addition rate is selected from: (i) from 9 to 11 mL / hr; (ii) from 1.0 to 1.5 times the initial volume (in mL); (iii) from 0.5 to 0.7 mmol / hr of As; and (iv) from 0.08 to 0.11 times the initial volume (in mL). Clause 29. The method of clause 20, wherein the growth temperature is about 360 °C and the growth addition rate is selected from: (i) from 12 to 15 mL / hr; (ii) from 1.8 to 2.2 times the initial volume (in mL); (iii) from 0.7 to 1 mmol / hr of As; and (iv) from 0.11 to 0.14 times the initial volume (in mL). Clause 30. The method of any one of clauses 1 to 19, wherein the growth addition rate is: (i) from 6 to 50 mL / hr, preferably from 8 to 40 mL / hr, more preferably from 10 to 30 mL / hr, most preferably from 15 to 20 mL / hr; and / or (ii) from 0.6 to 6 mmol / hr of As, preferably from 0.8 to 5 mmol / hr of As, more preferably from 1 to 3.5 mmol / hr of As, most preferably from 1.5 to 2.5 mmol / hr of As. Clause 31. The method of any one of clauses 1 to 19 and 30, wherein the growth addition rate increases over the course of the reaction, optionally wherein: (i) the growth addition rate (in ml_ / hr) is maintained at from 0.05 to 0.4 times the volume of the reaction (in mL), preferably from 0.1 to 0.3 times the volume of the reaction (in mL), such as about 0.2 times the volume of the reaction (in mL); and / or (ii) the growth addition rate (in mmol / hr of As) is maintained at from 0.005 to 0.05 times the volume of the reaction (in mL), preferably from 0.01 to 0.04 times the volume of the reaction (in mL), such as about 0.02 times the volume of the reaction (in mL). Clause 32. The method of any one of clauses 1 to 19, 30, and 31, wherein the growth temperature is increased over the course of the reaction. Clause 33. The method of clause 32, wherein the temperature is increased in increments of 5 °C. Clause 34. The method of clause 32 or 33, wherein the growth temperature increases from 270 to 300 °C, such as from 280 to 300 °C. Clause 35. A plurality of InAs quantum dots obtained or obtainable by the method of any one of clauses 1 to 34. Clause 36. A plurality of InAs quantum dots with a peak absorbance of between 750 nm and 3000 nm, preferably from 800 nm to 2500 nm, more preferably from 900 nm to 2000 nm, further preferably from 1000 nm to 1800 nm, most preferably from 1200 nm to 1600 nm, optionally being obtained or obtainable by the method of any one of clauses 1 to 29. Clause 37. The plurality of InAs quantum dots of clause 36, wherein the plurality of large InAs quantum dots has a HWHM of less than 100 meV, preferably less than 80 meV, more preferably less than 60 meV, further preferably less than 50 meV, yet further preferably less than 40 meV, most preferably less than 30 meV. Clause 38. The plurality of InAs quantum dots of clause 36 or clause 37, wherein the plurality of large InAs quantum dots has a peak:valley ratio of greater than 1, preferably greater than 1.3, more preferably greater than 1.6, further preferably greater than 2, yet further preferably greater than 2.2, still further preferably greater than 2.4, or most preferably greater than 2.7. Clause 39. The plurality of InAs quantum dots of any one of clauses 36 to 38, wherein the quantum dots have isotropic morphology. Clause 40. The plurality of InAs quantum dots of any one of clauses 36 to 38, wherein the quantum dots have tetrapodal morphology. Clause 41. An IR photodetector comprising a plurality of InAs quantum dots according to any one of clauses 35 to 40.

Claims

1. A method of synthesising large InAs quantum dots, the method comprising:providing small InAs quantum dots in a reaction vessel;providing a In-Zn-As feedstock;heating the reaction vessel to a growth temperature;adding the In-Zn-As feedstock to the reaction vessel at a growth addition rate while maintaining the growth temperature.

2. The method of claim 1, wherein providing the small InAs quantum dots comprises preforming the small InAs quantum dots, the preforming comprising:providing an In carboxylate;providing a Zn-As feedstock;heating the In carboxylate to a Zn-As addition temperature;adding the Zn-As feedstock to the In carboxylate while maintaining the Zn-As addition temperature; andheating the mixture of In carboxylate and Zn-As feedstock to a conversion temperature and maintaining the conversion temperature for a conversion period to provide small InAs quantum dots.

3. The method of claim 1, wherein providing the small InAs quantum dots comprises forming the small InAs quantum dots in situ.

4. The method of claim 3, wherein forming the small InAs quantum dots in situ comprises:providing an initial portion of the In-Zn-As feedstock within the reaction vessel;heating the reaction vessel to a pre-growth temperature and maintaining the pre-growth temperature for a pre-growth period prior to heating to the growth temperature; andconverting at least a portion of the In-Zn-As feedstock within the reaction vessel to the small InAs quantum dots.

5. The method of any one of the preceding claims, wherein providing the In-Zn-As feedstock comprises:providing a mixture of In carboxylate and Zn carboxylate;providing an As feedstock;heating the mixture of In carboxylate and Zn carboxylate to an As addition temperature; andadding the As feedstock to the mixture of In carboxylate and Zn carboxylate while maintaining the As addition temperature.

6. The method of any one of claims 1 to 4, wherein providing the In-Zn-As feedstock comprises:providing an In carboxylate;providing a Zn-As feedstock;heating the In carboxylate to a Zn-As addition temperature; andadding the Zn-As feedstock to the In carboxylate while maintaining the Zn-As addition temperature.

7. The method of any one of claims 2 to 6, wherein providing the Zn-As feedstock comprises:providing a Zn carboxylate;providing an As feedstock;heating the Zn carboxylate to an As addition temperature; andadding the As feedstock to the Zn carboxylate while maintaining the As addition temperature.

8. The method of any one of the preceding claims, further comprising monitoring the peak absorption wavelength of the InAs quantum dots within the reaction vessel and ceasing addition of the In-Zn-As feedstock when a target peak absorption wavelength is achieved.

9. The method of any one of the preceding claims, wherein the ln:As molar ratio in the In-Zn-As feedstock is from 1:1 to 10:1, preferably from 1.5:1 to 8:1, more preferably from 2:1 to 6:1, most preferably from 3:1 to 4:1.

10. The method of any one of the preceding claims, wherein the Zn:As molar ratio in the In-Zn-As feedstock is from 1:5 to 5:1, preferably from 1:3 to 3:1, more preferably from 1:2 to 2:1, most preferably about 1:1.

11. The method of any one of the preceding claims, wherein the ln:Zn:As molar ratio in the In-Zn-As feedstock is expressed as x:y:z, wherein:x is the quantity of In and has a value from 1 to 10;y is the quantity of Zn and has a value from 0.2 to 5; andz is the quantity of As and has a value of about 1.

12. The method of any one of the preceding claims, further comprising providing additives to the reaction vessel, optionally the additives being selected from carboxylic acids (such as myristic, isostearic, or oleic acids), amines (such as octadecylamine or trioctylamine), additional sources of In (such as In carboxylates as described herein), additional sources of Zn (such as Zn carboxylates as described herein), and sources of chloride (such as tetrachloroethylene and zinc chloride).

13. The method of any one of the preceding claims, wherein the growth temperature is from 220 to 380 °C, preferably from 240 to 360 °C, more preferably from 260 to 340 °C, most preferably from 280 to 320°C, such as about 300 °C.

14. The method of any one of the preceding claims wherein the growth addition rate is:(i) from 1 to 15 mL / hr, preferably from 2 to 10 mL / hr, most preferably from 3 to 8 mL / hr; and / or(ii) from 0.1 to 1 mmol / hr of As, preferably from 0.2 to 0.7 mmol / hr of As, most preferably from 0.3 to 0.6 mmol / hr of As, such as about 0.35 mmol / hr of As; and / or(iii) in mL / hr and from 0.1 to 2 times the initial volume (in mL), preferably from 0.2 to 1 times the initial volume (in mL), more preferably from 0.3 to 0.6 times the initial volume (in mL); and / or(iv) in mmol / hr of As and from 0.01 to 0.24 times the initial volume (in mL), preferably from 0.02 to 0.12 times the initial volume (in mL), more preferably from 0.03 to 0.07 times the initial volume (in mL).

15. The method of any one of the preceding claims, wherein the growth temperature is constant, such as about 300 °C, about 320 °C, about 340 °C or about 360 °C.

16. The method of claim 15, wherein the growth addition rate is constant, such as:(i) from 1 to 2 mL / hr, from 3 to 5 mL / hr, from 9 to 11 mL / hr, or from 12 to 15 mL / hr; and / or(ii) from 0.06 to 0.1 mmol / hr of As, from 0.1 to 0.4 mmol / hr of As, from 0.5 to 0.7 mmol / hr of As; or from 0.7 to 1 mmol / hr of As; and / or17. The method of claim 15, wherein the growth addition rate is constant, such as:(i) being in mL / hr and from 0.05 to 0.45 times the initial volume (in mL), from 0.3 to 0.6 times the initial volume (in mL), from 1.0 to 1.5 times the initial volume (in mL), or from 1.8 to 2.2 times the initial volume (in mL); and / or(ii) being in mmol / hr and from 0.005 to 0.03 times the initial volume (in mL), from 0.02 to 0.06 times the initial volume (in mL), from 0.08 to 0.11 times the initial volume (in mL), or from 0.11 to 0.14 times the initial volume (in mL).

18. The method of any one of claims 1 to 14, wherein the growth addition rate is:(i) from 6 to 50 mL / hr, preferably from 8 to 40 mL / hr, more preferably from 10 to 30 mL / hr, most preferably from 15 to 20 mL / hr; and / or(ii) from 0.6 to 6 mmol / hr of As, preferably from 0.8 to 5 mmol / hr of As, more preferably from 1 to 3.5 mmol / hr of As, most preferably from 1.5 to 2.5 mmol / hr of As.

19. The method of any one of claims 1 to 14 and 18, wherein the growth addition rate increases over the course of the reaction, optionally wherein:(i) the growth addition rate (in ml_ / hr) is maintained at from 0.05 to 0.4 times the volume of the reaction (in mL), preferably from 0.1 to 0.3 times the volume of the reaction (in mL), such as about 0.2 times the volume of the reaction (in mL); and / or(ii) the growth addition rate (in mmol / hr of As) is maintained at from 0.005 to 0.05 times the volume of the reaction (in mL), preferably from 0.01 to 0.04 times the volume of the reaction (in mL), such as about 0.02 times the volume of the reaction (in mL).

20. The method of any one of claims 1 to 14, 18, and 19, wherein the growth temperature is increased over the course of the reaction.

21. A plurality of InAs quantum dots with a peak absorbance of between 750 nm and 3000 nm, preferably from 800 nm to 2500 nm, more preferably from 900 nm to 2000 nm, further preferably from 1000 nm to 1800 nm, most preferably from 1200 nmto 1600 nm, optionally being obtained or obtainable by the method of any one of claims 1 to 20.

22. The plurality of InAs quantum dots of claim 21, wherein the plurality of large 5 InAs quantum dots has a HWHM of less than 100 meV, preferably less than 80 meV, more preferably less than 60 meV, further preferably less than 50 meV, yet further preferably less than 40 meV, most preferably less than 30 meV.

23. The plurality of InAs quantum dots of claim 21 or claim 22, wherein the plurality 10 of large InAs quantum dots has a peak:valley ratio of greater than 1, preferably greater than 1.3, more preferably greater than 1.6, further preferably greater than 2, yet further preferably greater than 2.2, still further preferably greater than 2.4, or most preferably greater than 2.7.15 24. The plurality of InAs quantum dots of any one of claims 21 to 23, wherein thequantum dots have isotropic morphology or have tetrapodal morphology.

25. An IR photodetector comprising a plurality of InAs quantum dots according to any one of claims 21 to 24.

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