SEMICONDUCTOR NANOPARTICLE CONTAINING AgAuTe COMPOUND AS MAIN COMPONENT

Abstract

The present invention relates to a semiconductor nanoparticle containing an AgAuTe compound comprising Ag, Au, and Te as essential constituent elements. The AgAuTe compound constituting the semiconductor nanoparticle is represented by the following formula. The semiconductor nanoparticle according to the present invention contains 90 atomic% or more of the AgAuTe compound. The semiconductor nanoparticle according to the present invention has an improved light absorption characteristic in the long wavelength range and can suitably support applications in the near-infrared range and the short-wave infrared range. Specifically, the semiconductor nanoparticle according to the present invention has an absorption edge wavelength on the long wavelength side of the absorption spectrum of 1200 nm or greater. AgxAuyTez (In the formula, x, y, and z represent the number of atoms of Ag, Au, and Te, respectively, and 0.25 ≤ z / (x + y) ≤ 1 holds true. In addition, y / (x + y + z) > 0.10 also holds true.)

Description

Semiconductor nanoparticles based on AgAuTe compounds

[0001] The present invention relates to semiconductor nanoparticles containing an AgAuTe compound as a main component, and more particularly to semiconductor nanoparticles that have optical semiconductor properties, particularly good light absorption properties in the long wavelength region.

[0002] When semiconductors are made into nanoscale particles, they exhibit a quantum confinement effect and exhibit a band gap that corresponds to the particle size. Therefore, by adjusting the band gap by controlling the composition and particle size of the semiconductor nanoparticles, it becomes possible to arbitrarily set the emission wavelength and absorption wavelength. Semiconductor nanoparticles that utilize this property are also called quantum dots (QDs), and are expected to be used in various technical fields. Examples of applications of semiconductor nanoparticles that are being considered include light-emitting elements and fluorescent materials used in display devices and marker substances for detecting biological substances.

[0003] This is because semiconductor nanoparticles have the ability to control the emission wavelength by adjusting the particle size as described above, and also have a sufficiently narrow and stable emission peak width compared to organic dyes. Furthermore, in addition to being able to control the absorption wavelength, semiconductor nanoparticles also have the properties of high quantum efficiency and a high absorption coefficient. Due to these properties, semiconductor nanoparticles are also being considered for use in photoelectric conversion elements and light-receiving elements mounted on solar cells, various optical sensors, etc.

[0004] In particular, semiconductor nanoparticles are expected to be applied to the light receiving elements of optical sensors that are compatible with the near-infrared region (NIR) and short-wave infrared region (SWIR). Optical sensors that can handle light in these long wavelength regions are installed in LIDAR (Light Detection and Ranging) and SWIR image sensors. LIDAR is a remote sensing system for autonomous driving automobiles, drones, ships, etc., and has become an important device in the recent development of autonomous driving technology. Recently, LIDAR has also been applied to facial recognition technology and augmented reality (AR) technology in smartphones, tablets, etc. Furthermore, SWIR image sensors are a device whose demand is expected to increase in the future in fields such as food inspection, agriculture, and drones.

[0005] Until now, silicon thin films have often been used as light-receiving elements in sensors for optical devices such as those described above. However, sensors based on silicon thin films have a significant drop in sensitivity in the long wavelength range of 900 nm or longer, making them unsuitable for the above applications. Therefore, there is hope for the development of light-receiving elements that use semiconductor nanoparticles.

[0006] Several semiconductor compounds have been investigated for the composition of semiconductor nanoparticles. Semiconductor compounds with absorption wavelengths in the long wavelength region of the near infrared region (NIR) or short wave infrared region (SWIR) include PbS, PbSe, CdHgTe, and Ag. ２ S, Ag ２ Se, Ag ２ Te, AgInSe ２ , AgInTe ２ , CuInSe ２ , CuInTe ２ Metal chalcogenide compounds such as InAs and InAs are known (Patent Documents 1 to 4). The present applicant has also disclosed nanoparticles of a semiconductor compound mainly composed of an AgAuS-based compound (Patent Document 5).

[0007] Japanese Patent Application Laid-Open No. 2004-243507 Japanese Patent Application Laid-Open No. 2004-352594 Japanese Patent Application Laid-Open No. 2017-014476 International Publication No. WO2020 / 054764 Japanese Patent No. 7269591

[0008] Although the above-mentioned semiconductor compounds have light absorption characteristics in the desired wavelength range, many of them have obstacles when considering applications such as the display devices and markers for detecting biological substances mentioned at the beginning. For example, the European RoHS Directive (Restriction of the use of certain hazardous substances in electrical and electronic equipment) restricts the use of Pb in electrical and electronic equipment from the perspective of environmental impact. Therefore, semiconductor nanoparticles made of compounds containing Pb as a metal component are unlikely to be widely used in the electrical and electronic fields. Furthermore, when considering the use of semiconductor nanoparticles in biological fields, it is also difficult to use compounds containing heavy metals such as Cd and Hg.

[0009] Furthermore, while the semiconductor compounds described above have photoresponsiveness in the long-wavelength region, there is a growing demand for compounds with absorption wavelengths on the longer wavelength side. Recent advances in autonomous driving technology for automobiles have been remarkable, and it is necessary to support autonomous driving levels (levels 4 and 5) that do not require a human driver. In this case, it is important for LIDAR to have a response in the longer wavelength region, which is less susceptible to the influence of sunlight and natural light. Therefore, quantum dot technology is still in the research stage. Therefore, semiconductor nanoparticles that can exhibit response in the longer wavelength region while taking practicality into consideration are needed.

[0010] The present invention has been made under the above-mentioned background, and proposes semiconductor nanoparticles made of a novel semiconductor compound that take into consideration practicality in compliance with various regulations and have suitable optical semiconductor properties. In particular, the present invention proposes semiconductor nanoparticles that have improved optical absorption properties in the long wavelength region compared to conventional methods and can be suitably used in the near infrared region (NIR) and short wave infrared region (SWIR).

[0011] To solve the above-mentioned problems, the present inventors focused on the AgAuS ternary compound related to the prior art (Patent Document 5) by the applicant of the present application. Ag and Au are metals that can be used favorably from the viewpoint of regulatory compliance, such as environmental impact and toxicity, and AgAuS compounds are semiconductor compounds that can exhibit optical semiconductor properties. However, AgAuS compounds have absorption wavelengths that are somewhat on the low wavelength side, leaving issues with photoresponse in the infrared region (NIR) and shortwave infrared region (SWIR). In this regard, the applicant's prior art shifts the absorption wavelength to the long wavelength side by adding a metal such as In to the AgAuS compound to form an AgAuS-based multi-component compound.

[0012] The present inventors have come up with the idea of ​​using Te (tellurium), a chalcogen element with a larger mass than S (sulfur), as the chalcogen element of a semiconductor compound, in contrast to the above-mentioned conventional techniques. This is because it is believed that by using a chalcogen element with a larger mass than S, the orbital energy difference between each metal element and the chalcogen element is reduced when a compound is formed, thereby shifting the photoresponsivity to the longer wavelength side. The present inventors then investigated the formation of nanoparticles of AgAuTe compounds, which are chalcogen compounds of Ag and Au, and their optical properties.

[0013] According to the studies by the present inventors, it has been confirmed that nanoparticles mainly composed of AgAuTe compounds have absorption wavelengths in the long wavelength region compared to AgAuS compounds and AgAuSe compounds containing Se as a chalcogen element. Furthermore, the AgAuTe compounds studied by the present inventors can form relatively highly crystalline and stable nanoparticles. However, it has been confirmed that the composition of AgAuTe compounds, particularly the Au content, affects their dispersibility as nanoparticles. Based on these study results, the present inventors discovered semiconductor nanoparticles made of AgAuTe compounds with a suitable composition and conceived the present invention.

[0014] That is, the present invention, which solves the above-mentioned problems, is semiconductor nanoparticles containing an AgAuTe compound represented by the following formula, which is composed of Ag, Au, and Te as essential constituent elements, and which contain the AgAuTe compound in an amount of 90 atomic % or more.

[0015] (wherein x, y, and z are the numbers of Ag, Au, and Te atoms, respectively, and 0.25≦z / (x+y)≦1. Also, y / (x+y+z)>0.10.)

[0016] The structure of semiconductor nanoparticles containing an AgAuTe compound as a main component according to the present invention and a method for producing the same will be described in detail below.

[0017] A. Structure of the Semiconductor Nanoparticles According to the Present Invention A-1. Chemical Composition of the Semiconductor Nanoparticles As described above, the semiconductor nanoparticles according to the present invention contain an AgAuTe compound as a major component (90% by mass or more). Therefore, Ag and Au are essential elements as metal elements (transition metal elements) constituting the AgAuTe compound. Te is an essential and characteristic chalcogen element of the present invention. As described above, Te is an element with a large mass among chalcogen elements such as S and Se. The use of Te provides effective response in both the near-infrared region (NIR) and the short-wave infrared region (SWIR).

[0018] The AgAuTe compound constituting the semiconductor nanoparticles according to the present invention has Ag, Au, and Te atoms in a ratio of x, y, and z, respectively. ｘ Au ｙ Te ｚ It can be expressed as follows. With regard to the composition of the AgAuTe compound, the value of y / (x + y + z), which is the atomic ratio of Au in the compound, is y / (x + y + z) > 0.10. That is, the Au content of the AgAuTe compound of the present invention is greater than 10 atomic %, and AgAuTe compounds with an Au content of 10 atomic % or less are excluded from the present invention. The details of the reason for excluding Au contents of 10 atomic % or less are not clear, but according to the studies of the present inventors, it has been confirmed that nanoparticles of AgAuTe compounds with low Au contents are prone to aggregation and have poor dispersibility. The atomic ratio of Au, y / (x + y + z), is preferably 0.11 or more, more preferably 0.12 or more.

[0019] The upper limit of the atomic ratio y / (x+y+z) of Au is preferably 0.35 or less, and more preferably 0.20 or less, because within this range, a stable AgAuTe compound with good crystallinity is obtained.

[0020] Furthermore, Te is contained in the AgAuTe compound so as to perform charge compensation for Ag and Au. In this case, the number z of Te atoms in the AgAuTe compound satisfies 0.25≦z / (x+y)≦1. The number z of Te atoms is more preferably 0.3≦z / (x+y+z)≦0.7, even more preferably 0.3≦z / (x+y+z)≦0.5, and particularly preferably 0.3≦z / (x+y+z)≦0.4.

[0021] The proportion of Ag in the AgAuTe compound of the present invention is the remainder of the above proportions of Au and Te. The value of x / (x+y+z), which is the atomic ratio of Ag, is preferably 0.3 or more and 0.6 or less.

[0022] The composition of the AgAuTe compound described above refers to the overall composition of the AgAuTe compound in the semiconductor nanoparticles. The AgAuTe compound applied to the present invention may be composed of a single phase or multiple phases. ｘ Au ｙ Te ｚ ) can have several specific chemical compositions depending on the valence of Ag, Au, and Te. ３ AuTe ２ (x=3, y=1, z=2) and AgAuTe ２ Compounds with stoichiometric compositions such as (x = 1, y = 1, z = 2) can be synthesized. The AgAuTe compound in the semiconductor nanoparticles of the present invention is composed of compounds with these stoichiometric compositions in a single phase or in multiple phases. In addition, compounds that do not have the above-mentioned stoichiometric composition may be included. It is sufficient that x, y, and z are within the above-mentioned ranges in the entire AgAuTe compound in the semiconductor nanoparticles. However, the AgAuTe compound that constitutes the semiconductor nanoparticles of the present invention is highly crystalline and often includes compounds with the above-mentioned stoichiometric composition.

[0023] The semiconductor nanoparticles according to the present invention are primarily composed of AgAuTe compounds, with 90 atomic % or more of the AgAuTe compound. The semiconductor nanoparticles may consist solely of AgAuTe compounds. Semiconductor nanoparticles preferably contain 95 atomic % or more of the AgAuTe compound. The semiconductor nanoparticles according to the present invention may contain elements other than the AgAuTe compound (Ag, Au, Te). For example, the constituent elements of the solvent used to synthesize the AgAuTe compound or elements contained in the precursors of the raw materials Ag, Au, and Te may be contained in the semiconductor nanoparticles. Elements that may be contained in addition to the essential constituent elements Ag, Au, and Te include C, P, S, Se, Cl, Br, and I. The content of these elements in the semiconductor nanoparticles is acceptable as long as it is less than 10 mass %. The composition values ​​of the compounds and elements shown here are values ​​related to the semiconductor nanoparticles and do not include the content of the protective agent and its constituent elements, which will be described later.

[0024] A-2. Structure of the Semiconductor Nanoparticles According to the Present Invention As described above, the AgAuTe compound applied to the present invention is composed of a single phase or multiple phases. Semiconductor nanoparticles composed of multiple phases can have a so-called core-shell structure. An example of a core-shell structure is a structure in which a core (core compound) is an AgAuTe compound containing Ag, Au, and Te, and a shell (shell compound) is a compound having a different composition from the core compound or a compound not containing any of Ag, Au, and Te, and the shell compound covers at least a portion of the surface of the core compound. A specific example is a semiconductor nanoparticle composed of a core compound made of an Au-rich AgAuTe compound and a shell compound made of an Ag- and Te-rich AgAuTe compound that covers at least a portion of the surface of the core compound. Note that "Au-rich" means that the composition ratio of Au in the compound is 50 atomic % or more, and "Ag- and Te-rich" means that the total composition ratio of Ag and Te in the compound is 50 atomic % or more. Furthermore, the semiconductor nanoparticles may not necessarily have a regular combination of multiple phases like the core-shell structure described above, but may have a structure in which multiple phases with different compositions are randomly distributed.

[0025] The shape of the semiconductor nanoparticles according to the present invention may be spherical, cubic, or rod-shaped. The spherical or cubic semiconductor nanoparticles preferably have an average particle size of 2 nm or more and 20 nm or less. The particle size of the semiconductor nanoparticles is related to the band gap adjustment effect due to the quantum confinement effect. The above average particle size is preferable for achieving favorable light absorption characteristics through band gap adjustment. The average particle size of the semiconductor nanoparticles can be obtained by observing a plurality of semiconductor nanoparticles (preferably 100 or more) using an electron microscope such as a TEM, measuring the particle size of each particle, and calculating the particle number average. The particle size can be measured as the average value of the major axis and minor axis.

[0026] Furthermore, a scanning transmission electron microscope (scanning TEM) can be suitably used in analyzing the composition and structure of the semiconductor nanoparticles according to the present invention. In particular, a high-angle annular dark-field scanning transmission microscope (HAADF-STEM) can provide a scattering image that reflects the compositional information of the nanoparticles, and by combining it with an energy dispersive X-ray spectrometer (EDX) or the like, it is possible to understand the distribution of Ag, Au, and Te and the composition of the entire nanoparticles.

[0027] A-3. Optical Semiconductor Properties of Semiconductor Nanoparticles According to the Present Invention As described above, the band gap of semiconductor nanoparticles is adjusted by the quantum confinement effect depending on the particle size, and the light absorption characteristics change. The semiconductor nanoparticles according to the present invention preferably have an absorption edge wavelength of 1200 nm or more on the long-wavelength side of their absorption spectrum. This allows the semiconductor nanoparticles to have absorptivity and responsiveness to light in the visible light to near-infrared region. In a more preferred embodiment, the present invention can provide semiconductor nanoparticles having an absorption edge wavelength of 1300 nm or more on the long-wavelength side of their absorption spectrum.

[0028] A-4. Use of the semiconductor nanoparticles according to the present invention By coating and supporting the semiconductor nanoparticles according to the present invention on an appropriate substrate or carrier, they can be used in various applications such as the above-mentioned optical sensor elements. There are no particular limitations on the structure, shape, or dimensions of the substrate or carrier. Examples of substrates in the form of a plate or foil or film include glass, quartz, silicon, ceramics, or metal. In addition, examples of granular or powdered carriers include ZnO, TiO ２ , W.O. ３ , SnO ２ , In ２ O ３ , Al ２ O ３ The semiconductor nanoparticles may be supported on the inorganic oxide support and then fixed to a substrate.

[0029] Furthermore, when semiconductor nanoparticles are applied to or supported on a substrate or carrier, a solution, slurry, or ink in which semiconductor nanoparticles are dispersed in an appropriate dispersion medium is often used, as described above. Chloroform, toluene, cyclohexane, hexane, or the like can be used as the dispersion medium for this solution. Dipping and spin coating methods can be used as methods for applying the semiconductor nanoparticle solution, and various methods such as dropping, impregnation, and adsorption can be used as methods for supporting the semiconductor nanoparticles.

[0030] The semiconductor nanoparticles according to the present invention preferably contain a protective agent to suppress aggregation during their synthesis or when dispersed in a dispersion medium as described above. This protective agent is preferably at least one of alkylamines having an alkyl chain carbon number of 4 to 20, alkenylamines having an alkenyl chain carbon number of 4 to 20, alkylcarboxylic acids having an alkyl chain carbon number of 3 to 20, alkenylcarboxylic acids having an alkenyl chain carbon number of 3 to 20, and alkanethiols having an alkyl chain carbon number of 4 to 20. These protective agents bond to the surface of the semiconductor nanoparticles to coat at least a portion of them, suppressing aggregation of the semiconductor nanoparticles in the dispersion and forming a uniform solution. Furthermore, adding a protective agent to the reaction system together with the raw materials in the semiconductor nanoparticle synthesis process allows the synthesis of nanoparticles with a suitable average particle size. The protective agent can be any of the alkylamines, alkenylamines, alkylcarboxylic acids, alkenylcarboxylic acids, and alkanethiols, either singly or in combination.

[0031] B. Method for Producing Semiconductor Nanoparticles According to the Present Invention Next, a method for producing semiconductor nanoparticles according to the present invention will be described. ２ Based on this concept, the semiconductor nanoparticles according to the present invention are mainly composed of AgAuTe compounds in which Au is doped into Te. ｘ Au ｙ Te ｚ ) is Ag ２ It is believed that this can be produced by adding Au to nanoparticles of Te. However, the AgAuTe compound used in the present invention must contain more than 10 atomic % of Au (y / (x+y+z)>0.10). According to the investigations of the present inventors, Ag ２ In the method of adding Au to Te nanoparticles, it is difficult to synthesize a compound that satisfies the above-mentioned condition of the Au content.

[0032] The present inventors have found that the synthesis of an AgAuTe compound with an optimized Au content requires that compounds of the respective constituent elements Ag, Au, and Te be used as precursors (Ag precursor, Au precursor, Te precursor), which are introduced into the same reaction system and heated simultaneously to cause a reaction. Below, a method for producing semiconductor nanoparticles using this AgAuTe compound synthesis method will be described.

[0033] B-1. Raw materials (Ag precursor, Au precursor, Te precursor) The raw materials Ag precursor, Au precursor, and Te precursor are Ag salts or Ag complexes, and Au salts or Au complexes, respectively. The Ag precursor and Au precursor are preferably salts or complexes containing monovalent Ag and monovalent Au.

[0034] The Ag precursor is preferably an Ag salt or an Ag complex. The Ag precursor is preferably a salt or complex containing monovalent Ag. Specific examples of suitable Ag precursors include silver acetate (Ag(OAc)), silver nitrate, silver carbonate, silver oxide, silver oxalate, silver chloride, silver iodide, silver (I) cyanide, and silver diethyldithiocarbamate.

[0035] As the Au precursor, an Au salt or an Au complex is used. The Au precursor is preferably a salt or complex containing monovalent Ag. However, as the Au precursor, a salt or complex containing trivalent Au can also be used. This is because, during the synthesis process of semiconductor nanoparticles, trivalent Au is reduced to monovalent Au by the solvent or the coexisting Te precursor, etc. A specific example of a suitable Au precursor is chloro(dimethylsulfide)gold(I) ((CH ３ ) ２ SAuCl), Au resinate (C １０ H １８ Au ２ S ２ : CAS 68990-27-2), gold(I) iodide, gold(I) sulfite, chloroauric acid(III), gold(III) acetate, gold(I) cyanide, gold(III) cyanide, 1,10-phenanthroline gold(III), etc.

[0036] The Te compound that can be used as a Te precursor is tellurium oxide (TeO ２ ), telluric acid (Te(OH) ６), sodium tellurite (Na ２ TeO ３ Te compounds such as tetraethoxysilane, ...

[0037] B-2. Formation of a reaction system of an AgAuTe compound When synthesizing an AgAuTe compound, the above-described Ag precursor, Au precursor, and Te precursor are mixed to form a single reaction system, which is then reacted. At this time, the Ag precursor, Au precursor, and Te precursor that have been prepared separately may be mixed sequentially. At this time, the order of mixing is not particularly limited. Alternatively, a mixture of an Ag precursor and an Au precursor that will become the metal components of the AgAuTe compound may be prepared as a metal source precursor, and the metal source precursor and the Te precursor may be mixed to form a reaction system.

[0038] The synthesized AgAuTe compound (Ag ｘ Au ｙ Te ｚ The atomic ratio (x, y, z) of each element in the Ag precursor and the Au precursor can be adjusted by adjusting the ratio of the amounts of the Ag precursor and the Au precursor charged. The ratio of the amounts of the precursors charged to obtain a suitable AgAuTe compound is preferably set so that the ratio (a / b, hereinafter sometimes referred to as the Ag charge ratio) is 1.0 or more and 6.0 or less, and more preferably 2.0 or more and 5.0 or less, where a is the number of Ag atoms in the Ag precursor and b is the number of Au atoms in the Au precursor.

[0039] The amount of the Te precursor added to the reaction system can be set within a relatively wide range relative to the amounts of Ag and Au added, because even if excess Te is present in the reaction system, it has little effect on the composition of the AgAuTe compound.

[0040] As described above, the semiconductor nanoparticles of the present invention preferably have a protective agent bonded to the AgAuTe compound. Therefore, it is preferable to add a protective agent to the above-mentioned reaction system together with the Ag precursor, the Au precursor, etc. As the protective agent, it is preferable to add at least one of alkylamines having an alkyl chain carbon number of 4 to 20, alkenylamines having an alkenyl chain carbon number of 4 to 20, alkylcarboxylic acids having an alkyl chain carbon number of 3 to 20, alkenylcarboxylic acids having an alkenyl chain carbon number of 3 to 20, and alkanethiols having an alkyl chain carbon number of 4 to 20.

[0041] Although the reaction system for synthesizing semiconductor nanoparticles can produce nanoparticles without a solvent, it is preferable to use a solvent. When a solvent is used, octadecene, tetradecane, oleic acid, oleylamine, dodecanethiol, or a mixture thereof can be used.

[0042] B-3. ​​AgAuTe Compound Synthesis Conditions AgAuTe compound nanoparticles are synthesized by heating a reaction system consisting of an Ag precursor, an Au precursor, a Te precursor, and a protective agent. The heating temperature (reaction temperature) is 40°C or higher and 200°C or lower. Below 40°C, the synthesis reaction is difficult to proceed. On the other hand, above 200°C, there is a risk that Au alone will form nanoparticles, and a compound with the desired composition will not be produced. The average particle size of the semiconductor nanoparticles increases with increasing reaction temperature, but within the above temperature range, it rarely exceeds the preferred average particle size. A more preferred reaction temperature is 50°C or higher and 100°C or lower.

[0043] The reaction time (heating time) can be adjusted depending on the amount of raw materials charged, but is preferably 5 minutes or more and 120 minutes or less. The reaction time is more preferably 10 minutes or more, and even more preferably 15 minutes or more. It is preferable to stir the reaction system during the synthesis reaction of semiconductor nanoparticles.

[0044] After the synthesis reaction of the semiconductor nanoparticles is completed, the reaction system is cooled as necessary, and the semiconductor nanoparticles are recovered. At this time, a non-solvent alcohol (ethanol, methanol, etc.) is added to precipitate the nanoparticles, or the semiconductor nanoparticles are precipitated and recovered by centrifugation or the like, and the particles are further washed with alcohol (ethanol, methanol, etc.) and then uniformly dispersed in a good solvent such as chloroform.

[0045] As described above, the present invention relates to novel semiconductor nanoparticles whose main component is an AgAuTe compound. The semiconductor nanoparticles according to the present invention have favorable optical semiconductor properties and are also practical in consideration of usage regulations, etc. The photoresponsive properties of the semiconductor nanoparticles according to the present invention are capable of responding to long wavelength regions of the near-infrared region (NIR) and short-wave infrared region (SWIR).

[0046] TEM images of semiconductor nanoparticles of Example 1 (AgAuTe), Reference Example 1 (AgAuS), and Reference Example 2 (AgAuSe) synthesized according to the first embodiment. Measurement results of absorption spectra of semiconductor nanoparticles of Example 1 (AgAuTe), Reference Example 1 (AgAuS), and Reference Example 2 (AgAuSe) synthesized according to the first embodiment. TEM image of AgAuTe semiconductor nanoparticles synthesized by adjusting the Ag feed ratio according to the second embodiment. XRD diffraction pattern of AgAuTe semiconductor nanoparticles synthesized by adjusting the Ag feed ratio according to the second embodiment. Measurement results of absorption spectra of AgAuTe semiconductor nanoparticles synthesized by adjusting the Ag feed ratio according to the second embodiment. TEM image of AgAuTe semiconductor nanoparticles synthesized by adjusting the reaction temperature according to the third embodiment. XRD diffraction pattern of AgAuTe semiconductor nanoparticles synthesized by adjusting the reaction temperature according to the third embodiment. Measurement results of absorption spectra of AgAuTe semiconductor nanoparticles synthesized by adjusting the reaction temperature according to the third embodiment.

[0047] First Embodiment: Hereinafter, an embodiment of the present invention will be described. In this embodiment, semiconductor nanoparticles made of an AgAuTe compound were synthesized, and their appearance and crystalline structure were confirmed. Then, absorption spectrum measurement was performed to confirm the absorption wavelength. At this time, as a comparison with the AgAuTe compound (Example 1), semiconductor nanoparticles made of an AgAuS compound (Reference Example 1) and an AgAuSe compound (Reference Example 2) were synthesized, and their absorption wavelengths were compared.

[0048] Example 1: In the synthesis of AgAuTe compound nanoparticles in this embodiment, a mixture of Ag precursor and Au precursor, which are the metal components, was prepared in advance as a metal source precursor, and then the metal source precursor and the Te precursor were mixed and reacted to synthesize semiconductor nanoparticles.

[0049] 0.3 mmol of silver acetate (Ag(OAc)) was used as the Ag precursor, and 0.3 mmol of chloro(dimethylsulfide)gold (AuS(CH)) was used as the Au precursor. ３ ) ２ A methanol solution containing 0.1 mmol of tellurium oxide (TeO) was dissolved and mixed in 3.0 mL of oleylamine (OLA) as a solvent. The pressure was reduced to remove the methanol, and a solution of the metal source precursor was prepared (Ag charge ratio = 3). ２ 0.2 mmol of tetrahydrofuran (Te) was dissolved in 0.5 mL of 1-dodecanethiol (DDT), a solvent and protective agent, and heated at 100° C. for 5 minutes in a nitrogen atmosphere to prepare a Te precursor solution.

[0050] The metal source precursor solution was injected into the Te precursor solution using a syringe, and the reaction temperature was set to 100°C, followed by stirring for 15 minutes while heating. After the reaction was completed, the mixture was allowed to cool for 10 minutes, and then centrifuged at 4000 rpm for 5 minutes to separate the supernatant from the precipitate. Then, 4 cm of ethanol was added to the supernatant as a poor solvent. ３ The mixture was added to cause precipitation, and the mixture was centrifuged at 4000 rpm for 5 minutes, and the precipitate was collected to obtain AgAuTe compound nanoparticles.

[0051] The AgAuTe compound nanoparticles obtained by the above procedure were dissolved in 3 cm of chloroform. ３This dispersion was transferred to a sample bottle, and the atmosphere was replaced with nitrogen, and then the bottle was stored in a refrigerator in a dark place.

[0052] Reference Example 1: Nanoparticles of an AgAuS compound using S as a chalcogen element that forms a compound with Ag and Au were synthesized as follows.

[0053] 0.3 mmol of silver acetate as the Ag precursor, 0.1 mmol of chloro(dimethylsulfide)gold(I) as the Au precursor, and 0.2 mmol of thiourea as the S precursor were placed in a test tube, and 2.9 mL of oleylamine as a solvent and 0.1 mL of 1-dodecanethiol as a protective agent were added.

[0054] After the air was replaced with nitrogen as described above, the mixture was stirred for 10 minutes at a reaction temperature of 150°C using a hot stirrer. After the reaction was completed, the mixture was allowed to cool for 30 minutes and then centrifuged at 4000 rpm for 5 minutes to separate the supernatant and precipitate. Further centrifugation and purification were performed to obtain a dispersion of nanoparticles of the AgAuS compound.

[0055] Reference Example 2: Nanoparticles of an AgAuSe compound in which Se is used as a chalcogen element that forms a compound with Ag and Au were synthesized as follows.

[0056] 0.075 mmol of silver acetate (Ag(OAc)) as the Ag precursor, 0.025 mmol of chloro(dimethylsulfide)gold(I) as the Au precursor, and 0.20 mmol of selenourea as the Se precursor were placed in a test tube, to which 2.9 mL of oleylamine (OLA) as the solvent and 0.1 mL of 1-dodecanethiol (DDT) as the protective agent were added.

[0057] A stirrer was placed in a test tube containing the above raw materials and solvent, and the mixture was purged with nitrogen three times, followed by stirring with a hot stirrer for 10 minutes while heating at a reaction temperature of 50°C. After the reaction was completed, the mixture was allowed to cool for 20 minutes, then transferred to a small test tube and centrifuged at 4000 rpm for 5 minutes to separate the supernatant from the precipitate.

[0058] Then, 4 cm of methanol was added to the supernatant as a poor solvent. ３The mixture was added to form a precipitate, which was then centrifuged at 4,000 rpm for 5 minutes to recover the precipitate. ３ After adding and dispersing, the mixture was centrifuged under the same conditions to remove by-products and the solvent, and the AgAuSe compound nanoparticles were purified.Further centrifugation and purification were performed to obtain a dispersion of AgAuS compound nanoparticles.

[0059] [TEM Observation and Measurement of Average Particle Size] TEM observation was performed on each of the semiconductor nanoparticles of Example 1 (AgAuTe), Reference Example 1 (AgAuS), and Reference Example 2 (AgAuSe). TEM images of each of the manufactured semiconductor nanoparticles are shown in FIG. 1 (see the scale bar of each photograph for magnification). Each TEM image confirmed that approximately spherical nanoparticles had been synthesized. Then, based on the TEM images, the average particle size of the nanoparticles of each composition was measured and calculated. In the particle size measurement, the particle sizes of all measurable nanoparticles included in the TEM images were determined, and the average particle size was calculated.

[0060] [Composition Analysis of Semiconductor Nanoparticles] EDX analysis was performed in addition to the above TEM observation to analyze the composition of the nanoparticles. Table 1 shows the measurement results of the composition of each semiconductor nanoparticle. In this embodiment and each of the following embodiments, the results of the composition analysis are expressed in atomic % relative to the total nanoparticles. Table 1 also shows the ratio (y / (x+y+z)) of the number of Au atoms to the total number of Ag atoms (x), Au atoms (y), and chalcogen element (Te, S, Se) atoms (z), calculated based on the composition analysis results.

[0061]

[0062] [Absorption Spectrum Measurement] Next, the absorption spectrum was measured for each of the semiconductor nanoparticles of Example 1 (AgAuTe), Reference Example 1 (AgAuSe), and Reference Example 2 (AgAuS). The absorption spectrum was measured using a UV-visible spectrophotometer (Agilent 8453, manufactured by Agilent Technologies Inc.) in the wavelength range of 400 nm to 1600 nm. The measurement results of the absorption spectrum of each of the semiconductor nanoparticles produced in this embodiment are shown in FIG. 2.

[0063] 2, it can be seen that the semiconductor nanoparticles of Example 1 (AgAuTe), in which Te is used as the chalcogen element, have an absorption edge wavelength on the longer wavelength side compared to the semiconductor nanoparticles of Reference Example 1 (AgAuS) and Reference Example 1 (AgAuSe), in which S and Se are used as the chalcogen elements. The absorption edge wavelengths of each semiconductor nanoparticle were 1400 nm for Example 1 (AgAuTe), 750 nm for Reference Example 1 (AgAuS), and 950 nm for Reference Example 2 (AgAuSe). It was confirmed that the AgAuTe semiconductor nanoparticles, in which Te, which has a large mass, is used as the chalcogen element, have suitable photoresponse characteristics in the long wavelength region.

[0064] Second embodiment: In this embodiment, AgAuTe semiconductor nanoparticles of various compositions were synthesized by adjusting the feeding ratio of Ag and Au. Also, in this embodiment, chloroauric acid (HAuCl) was used as the Au precursor. ４ ) was applied to prepare a metal source precursor. At this time, AgAuTe semiconductor nanoparticles were synthesized by keeping the total amount of the metal source precursor constant, varying the Ag charging ratio (Ag / Au:(a / b)) among them to 0.33, 1.0, 3.0, 4.7, and 7.0, and keeping the Te content (number of moles of Te precursor charged) constant (0.2 mmol). The synthesis conditions for the semiconductor nanoparticles were the same as those in the first embodiment, except for the Au precursor and Ag charging ratio.

[0065] Then, TEM observation and EDX analysis were performed in the same manner as in Embodiment 1. A TEM analysis image of the AgAuTe semiconductor nanoparticles synthesized in this embodiment is shown in Figure 3. Table 2 also shows the results of composition analysis by EDX analysis.

[0066]

[0067] In this embodiment, solid particle synthesis can be confirmed at any feed ratio. However, as shown in Figure 3, nanoparticles with an Ag feed ratio of 7.0 exhibited extremely high agglomeration tendency, making it difficult to maintain the state of independent particles. These nanoparticles had an Au atomic ratio (y / (x + y + z)) of 0.07, which was 0.1 or less. Furthermore, for nanoparticles with Ag feed ratios of 7.0, 4.7, 3.0, and 1.0, the Au atomic ratio (y / (x + y + z)) tends to increase as the Ag feed ratio decreases.

[0068] On the other hand, nanoparticles with an Ag loading ratio of 0.33 contain almost no Au and are essentially in the form of an AgTe compound. The reason why nanoparticles with a high loading of Au contain no Au is unclear, but the inventors speculate as follows. Specifically, during synthesis, the raw material Au ions (trivalent) react with organic components in the system to produce some reduced Au particles (zerovalent). These Au particles are separated and removed from the target AgAuTe by centrifugation after the synthesis reaction. If a large number of Ag ions are present, the Au ions are consumed in the production of AgAuTe particles, but if the concentration of Ag ions is low, the reduction reaction of Au precedes. It is speculated that if a large number of zerovalent Au particles are produced in the reaction solution, the autocatalytic reaction of the Au particles sequentially reduces the Au ions, resulting in the reduction of the Au used to form AuAgTe particles, resulting in the formation of nanoparticles not containing Au.

[0069] [Confirmation of Crystallinity of AgAuTe Nanoparticles] Next, XRD analysis was performed on the AgAuTe nanoparticles synthesized in this embodiment to confirm their crystallinity. The XRD analyzer was a Smart-Lab-3K manufactured by Rigaku Corporation, with CuKα radiation as the characteristic X-ray and a rate of 1° / min as the analysis condition. Figure 4 shows the XRD diffraction patterns of samples of the AgAuTe nanoparticles of this embodiment produced with Ag loading ratios of 7.0, 4.7, 3.0, and 1.0.

[0070] From FIG. 4, among the AgAuTe nanoparticles synthesized in this embodiment, the diffraction patterns of the samples with Ag loading ratios of 7.0, 4.7, and 3.0 are ３ AuTe ２ The diffraction peaks of these AgAuTe nanoparticles were sharp and had narrow half-widths, and those with Ag loading ratios of 4.7 and 3.0 exhibited particularly good crystallinity. From these results, it is believed that suitable AgAuTe nanoparticles require an Au atomic ratio (y / (x+y+z)) of more than 0.1.

[0071] Furthermore, no clear peak was observed for the sample with an Ag loading ratio of 1.0, which is thought to be because the AgAuTe nanoparticles in this sample were particles consisting of crystallites with a size of several nanometers or less, or amorphous particles.

[0072] [Absorption Spectrum Measurement] The absorption spectrum of the AgAuTe nanoparticles synthesized in this embodiment was measured. The method for measuring the absorption spectrum was the same as in the first embodiment. The measurement results are shown in Figure 5. The values ​​of the absorption edge wavelength calculated from the measurement results are shown in Table 3.

[0073]

[0074] Referring to FIG. 5 and Table 3, the samples with Ag charge ratios of 7.0, 4.7, and 3.0 have particularly large absorption edge wavelengths. Although nanoparticles with an Ag charge ratio of 0.33 also have responsiveness on the long wavelength side of 1000 nm or more, their absorption edge wavelengths are smaller than those of nanoparticles with Ag charge ratios of 7.0, 4.7, and 3.0. These nanoparticles do not contain Au. Considering the above-mentioned TEM observation results, AgAuTe semiconductor nanoparticles that have good dispersibility, can maintain a single particle state, and have good responsiveness in the long wavelength region have Ag charge ratios of 4.7 (Au atomic ratio 0.107) and 3.0 (Au atomic ratio 0.156). These AgAuTe semiconductor nanoparticles are predicted to exhibit particularly effective responsiveness in both the near-infrared region (NIR) and the short-wave infrared region (SWIR).

[0075] Third Embodiment: In this embodiment, AgAuTe nanoparticles were synthesized by varying the heating temperature (reaction temperature) after mixing a metal source precursor and a Te precursor to form a reaction system. A metal source precursor (Ag charge ratio 3.0) was prepared using the same Ag precursor and Au precursor as in the second embodiment, and mixed with a Te precursor (Te 0.2 mmol) to form a reaction system. Then, the reaction was carried out at heating temperatures of 50°C and 70°C to synthesize semiconductor nanoparticles. The operations other than the reaction temperature were the same as in the second embodiment.

[0076] Figure 6 is a TEM image of AgAuTe nanoparticles synthesized in this embodiment. Figure 6 also shows a TEM image of AgAuTe nanoparticles synthesized in the second embodiment (Ag charge ratio 3.0, reaction temperature 100°C). The sample with a reaction temperature of 50°C is a fine particle with weak contrast. By increasing the reaction temperature to 70°C or 100°C, the contrast of the particles becomes clearer. The results of composition analysis by EDX analysis, which was performed simultaneously with TEM observation, are shown in Table 4.

[0077]

[0078] It can be seen from Table 4 that there is no significant difference in the composition of the AgAuTe nanoparticles synthesized in this embodiment. It is believed that the reaction temperature does not have a significant effect on the composition of the AgAuTe nanoparticles.

[0079] Figure 7 shows the XRD diffraction pattern of the AgAuTe nanoparticles synthesized in this embodiment. The conditions for the XRD analysis were the same as those in the second embodiment. Figure 7 also shows the diffraction pattern of the AgAuTe nanoparticles synthesized in the second embodiment (Ag charge ratio 3.0, reaction temperature 100°C). All samples showed Ag ３ AuTe ２ The diffraction pattern can be identified as follows: However, the sample with a reaction temperature of 50°C has a broad peak, indicating that the sample has lower crystallinity than the sample with a reaction temperature of 100°C. Considering the above TEM observation results, it was confirmed that increasing the reaction temperature increases the crystallinity.

[0080] 8 shows the measurement results of the absorption spectrum of the AgAuTe nanoparticles synthesized in this embodiment. As can be seen from FIG. 8, there was little difference in the absorption spectrum of the AgAuTe nanoparticles synthesized in this embodiment, and the absorption edge wavelength was near 1400 nm in all cases. From the results of the composition analysis above, there was little difference in the composition of the AgAuTe nanoparticles depending on the reaction temperature. It can also be said that there was little difference in the absorption characteristics depending on the reaction temperature.

[0081] As described above, semiconductor nanoparticles made of the AgAuTe compound according to the present invention can exhibit excellent optical semiconductor properties. Furthermore, this AgAuTe compound is designed to comply with usage regulations and avoid the use of heavy metals. The semiconductor nanoparticles according to the present invention are expected to be applied to light-emitting elements and fluorescent materials used in display devices and marker substances for detecting biological substances, as well as photoelectric conversion elements and photodetectors mounted in solar cells and optical sensors. In particular, the present invention aims to improve light absorption characteristics in the long wavelength regions of the near-infrared region (NIR) and shortwave infrared region (SWIR). Therefore, the present invention is particularly useful for photodetectors applied to LIDAR and SWIR image sensors, among the above-mentioned optical elements, in which responsiveness in the near-infrared region is important.

Claims

1. Semiconductor nanoparticles containing an AgAuTe compound represented by the following formula, which is composed of Ag, Au, and Te as essential constituent elements, and which contain 90 atomic % or more of the AgAuTe compound. (In the formula, x, y, and z are the numbers of Ag, Au, and Te atoms, respectively, and 0.25≦z / (x+y)≦1. Also, y / (x+y+z)>0.10.) 2. The semiconductor nanoparticles according to claim 1, wherein in the AgAuTe compound, 0.1≦x / (x+y+z)≦0.

6.

3. The semiconductor nanoparticles according to claim 1 or 2, which contain 99 atomic % or more of the AgAuTe compound.

4. The semiconductor nanoparticles according to claim 1 or 2, which have a spherical or cubic shape and an average particle size of 2 nm or more and 20 nm or less.

5. The semiconductor nanoparticle according to claim 1 or 2, wherein the AgAuTe compound comprises: a core compound made of an Au-rich AgAuTe compound; and a shell compound made of an Ag and Te-rich AgAuTe compound covering at least a portion of the surface of the core compound.

6. Semiconductor nanoparticles according to claim 1 or 2, having at least one of the following protective agents bonded to the surface: alkylamines having an alkyl chain carbon number of 4 to 20, alkenylamines having an alkenyl chain carbon number of 4 to 20, alkylcarboxylic acids having an alkyl chain carbon number of 3 to 20, alkenylcarboxylic acids having an alkenyl chain carbon number of 3 to 20, and alkanethiols having an alkyl chain carbon number of 4 to 20.

7. The semiconductor nanoparticles according to claim 1 or 2, having an absorption edge wavelength on the long wavelength side of the absorption spectrum of 1,200 nm or more.

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