Hindered piperidine derivative functionalized silicon nanoparticles

Abstract

A composition containing silicon nanoparticles having a hindered piperidine derivative free radical scavenger on the surface of the silicon nanoparticles. A process for preparing silicon nanoparticles having a hindered piperidine derivative radical scavenger on the surface of the silicon nanoparticles, the process comprising producing silicon nanoparticles using a VHFLPP process that collects the silicon nanoparticles in a trapping fluid when preparing the silicon nanoparticles, and wherein a hindered piperidine derivative free radical scavenger is provided in the trap fluid before, during and / or after collecting the silicon nanoparticles such that the silicon nanoparticles and the hindered piperidine derivative free radical scavenger are present together in the trap fluid.

Description

Technical Field

[0001] The present invention relates to silicon quantum dots having hindered piperidine derivative free radical scavengers on their surfaces and methods for making the same.

[0002] introduction

[0003] The advent of nanotechnology has led to paradigm shifts in many technological fields, as the properties of many materials change at the nanoscale. For example, reducing the dimensions of some structures to the nanometer scale can increase the surface-to-volume ratio, leading to changes in the material's electrical, magnetic, reactive, chemical, structural, and thermal properties. Nanomaterials are already found in commercial applications and are likely to be present in a wide variety of technologies over the coming decades, including computing, photovoltaics, optoelectronics, medicine / pharmaceuticals, structural materials, military applications, and many others.

[0004] Silicon nanoparticles are of particular interest. An important feature of small silicon nanoparticles (average size less than 10 nanometers (nm)) is that they photoluminesce in the visible and near-infrared when excited by shorter wavelength light, such as ultraviolet light. This is believed to be caused by a quantum confinement effect that occurs when the diameter of the nanoparticle is smaller than the excitation radius, resulting in a bending of the energy band gap (i.e., an increase in the energy band gap). Researchers have shown that the band gap energy (measured in electron volts) of nanoparticles varies depending on the diameter of the nanoparticle.

[0005] Although silicon is an indirect bandgap semiconductor in the bulk, silicon nanoparticles with an average size of less than 10 nm can simulate direct bandgap materials, which can be achieved by interface capture of excitons. Direct bandgap materials can be used as silicon quantum dot materials in optoelectronic applications. Silicon quantum dots are particularly desirable relative to other quantum dot materials because they do not require environmentally unfriendly components such as lead, selenium, cadmium, indium or arsenic. Another interesting property of nanomaterials is the melting point reduction that follows the surface phonon instability theory. Researchers have shown that the melting point of nanomaterials formed by nanoparticles varies according to the diameter of the nanoparticles.

[0006] It is desirable to develop silicon nanoparticle technology, particularly silicon quantum dot technology, to control the optical properties of silicon quantum dots. It is particularly desirable to be able to control the optical properties of fully passivated silicon quantum dots that are stable to exposure to air. Summary of the Invention

[0007] The present invention provides a method for changing the optical properties of silicon quantum dots. Surprisingly, the present invention provides a method for blue-shifting the luminescence emission of silicon quantum dots by functionalizing the surface of silicon quantum dots with piperidine derivative free radical scavengers. Some researchers have demonstrated the ability to red-shift the emission wavelength of silicon quantum dots by up to 70 nanometers by complexing aromatic organic ligands onto the surface of silicon quantum dots. See Zhou et al., Nano Lett. 2015, Vol. 15, pp. 3657-3663 and Li et al., Phys. Chem. Chem. Phys., 2014, Vol. 16, pp. 19275-19281. The blue-shift of the luminescence emission of silicon quantum dots is surprising compared to such results.

[0008] An even more surprising benefit is the present invention's discovery that functionalizing the surface of silicon nanoparticle quantum dots with a piperidine derivative free radical scavenger significantly reduces the time required to passivate the silicon nanoparticles, thereby reducing the time required to produce air-stable silicon nanoparticles (including silicon quantum dots). Even more beneficially, the present invention provides a method for preparing such functionalized silicon nanoparticles in a continuous process by functionalizing the silicon nanoparticles as they are prepared and dispersed into a capture fluid. The silicon nanoparticles can then be passivated in the capture fluid, a process that typically takes several days at 60 degrees Celsius (°C) and 85% relative humidity (RH) at 101 kilopascals pressure (atmospheric pressure), but once functionalized with a piperidine derivative free radical scavenger, can occur within a few hours under the same conditions.

[0009] In a first aspect, the present invention is a composition comprising silicon nanoparticles, wherein the silicon nanoparticles comprise a hindered piperidine derivative radical scavenger on a surface of the silicon nanoparticles.

[0010] In a second aspect, the present invention is a method for preparing silicon nanoparticles having a hindered piperidine derivative free radical scavenger on the surface of the silicon nanoparticles, the method comprising using a very high frequency low pressure plasma (VHFLPP) method to produce the silicon nanoparticles, the VHFLPP method collecting the silicon nanoparticles in a capture fluid as the silicon nanoparticles are prepared, and wherein the hindered piperidine derivative free radical scavenger is provided in the capture fluid before, during and / or after collecting the silicon nanoparticles and before exposing the silicon nanoparticles to air, such that the silicon nanoparticles and the hindered piperidine derivative free radical scavenger are present together in the capture fluid. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 A schematic diagram of the VHFLPP apparatus used to prepare the samples herein is shown.

[0012] Figure 2Shown are the photoluminescence emission (PL) spectra of samples 1 to 3 at different passivation / aging times when excited at 365 nm.

[0013] Figure 3 Photoluminescence excitation (PLE) spectra of samples 1 to 3 are shown.

[0014] Figure 4 Shown are the UV-Vis absorption spectra of samples 1 to 3 as a function of passivation / aging time.

[0015] Figure 5 The photoluminescence emissions (PL) of samples 4 to 6 are shown.

[0016] Figure 6 Photoluminescence excitation (PLE) spectra of samples 4 to 6 are shown.

[0017] Figure 7 UV-Vis absorption spectra of samples 4 to 6 are shown.

[0018] Figure 8 Photoluminescence emission (PL) spectra of samples 4 to 6 are shown.

[0019] Figure 9 Photoluminescence excitation (PLE) spectra of samples 4 to 6 are shown.

[0020] Figure 10 The UV-Vis absorption spectra of samples 9 and 10 are shown.

[0021] Figure 11 The photoluminescence emission spectra (PL) of samples 9 and 10 are shown.

[0022] Figure 12 Photoluminescence excitation (PLE) spectra of samples 9 and 10 are shown. DETAILED DESCRIPTION

[0023] Products identified by their trade names refer to compositions available under those trade names at the priority date of this document.

[0024] "A plurality of" means two or more. "And / or" means "and, or as an alternative." Unless otherwise indicated, all ranges are inclusive.

[0025] "Cx to Cy", "C x -C y ”, “C x-y ” are used interchangeably and refer to compositions having a number of carbon atoms in the range of x to y.

[0026] "Silicon nanoparticles" refers to silicon-based particles having an average particle size of less than 1 micron, typically 100 nanometers (nm) or less, and an average particle size of 1 nm or greater. Dynamic light scattering or transmission electron microscopy image analysis are common methods for determining the average particle size of silicon nanoparticles. Silicon nanoparticles include silicon quantum dots.

[0027] "Silicon-based" refers to compositions that contain silicon. Silicon-based materials typically contain 40 percent (%) or more, and may contain 50% or more, 60% or more, 70% or more, 80% or more, 90% or more, or even 100% silicon atoms, or a combination of silicon atoms and oxygen atoms, based on all atoms in the material.

[0028] "Silicon quantum dots" refer to silicon nanoparticles that have a crystalline silicon structure and photoluminesce when exposed to light. Typically, the average particle size of silicon quantum dots ranges from 1 to 10 nanometers, preferably from 1 to 6 nanometers, and more preferably from 1 to 5 nanometers. Silicon quantum dots are characterized by luminescence when exposed to light with a wavelength in the range of 300 to 477 nanometers, corresponding to blue and ultraviolet light.

[0029] In one aspect, the present invention provides a composition comprising silicon nanoparticles comprising a hindered piperidine derivative free radical scavenger on the surface of the silicon nanoparticles, thereby forming hindered piperidine derivative functionalized silicon nanoparticles. The composition can consist of silicon nanoparticles or contain other components in addition to silicon nanoparticles. The silicon nanoparticles desirably include and can be silicon quantum dots.

[0030] The hindered piperidine derivative free radical scavenger can be the same, or can be a combination or more than one hindered piperidine derivative free radical scavenger. Ideally, the hindered piperidine derivative free radical scavenger is non-aromatic, which means that they do not contain aromatic rings. Examples of suitable piperidine derivative free radical scavengers include any one or more than one selected from the group consisting of: bis(1,2,2,6,6-pentamethyl-4-piperidinyl) sebacate; bis(1-octyl-2,2,6,6-tetramethyl-4-piperidinyl) sebacate; bis(2,2,6,6-tetramethyl-4-piperidinyl) sebacate; and 4-hydroxy-2,2,6,6-tetramethylpiperidinyl 1-oxybenzoate.

[0031] The hindered piperidine derivative free radical scavenger is on the surface of the silicon nanoparticles, thereby "functionalizing" the silicon nanoparticles. The hindered piperidine derivative free radical scavenger can be chemically bonded to the silicon nanoparticles, such as by covalent bonding. However, it is desirable that there is no aromatic conjugation between the hindered piperidine derivative free radical scavenger and the silicon nanoparticles. That is, it is desirable that the hindered piperidine derivative free radical scavenger functionalized silicon nanoparticles do not contain conjugated functional groups in the hindered piperidine derivative directly bonded to the silicon nanoparticles. The hindered piperidine derivative free radical scavenger functionalized silicon nanoparticles may be completely free of conjugated organic groups. The present invention also encompasses hindered piperidine derivative functionalized silicon nanoparticles, wherein the hindered piperidine derivative functionalized free radical scavenger adheres to the surface of the silicon nanoparticles without being chemically bonded to the silicon nanoparticles. Adhesion without chemical bonding can occur by electrostatic attraction or any other non-chemical bonding means.

[0032] In addition to the hindered piperidine derivative free radical scavenger, the silicon nanoparticles may also include a passivating group on their surface. The passivating group can be any group or combination of more than one group that protects the silicon nanoparticles from decomposition when exposed to oxygen and moisture in air. For example, the silicon nanoparticles may include an oxide coating on their surface in combination with the hindered piperidine derivative free radical scavenger. The oxide coating protects the silicon nanoparticles from decomposition when exposed to oxygen and moisture in air.

[0033] The hindered piperidine derivative-functionalized silicon quantum dots surprisingly exhibit a blue shift in the luminescence emission wavelength (i.e., a shift toward shorter wavelength emission) relative to the same silicon quantum dots that are not functionalized with the hindered piperidine derivative. Furthermore, the formation of an oxide passivation coating on the surface of the hindered piperidine derivative-functionalized silicon nanoparticles occurs surprisingly well: when the silicon nanoparticles are passivated at 101 kilopascals (atmospheric pressure) in a trapping fluid at 60 degrees Celsius (°C) and 85% relative humidity (RH), the silicon nanoparticles are protected from decomposition upon exposure to air for only a few hours, rather than several days.

[0034] In a second aspect, the present invention provides a method for preparing hindered piperidine derivative functionalized silicon nanoparticles of the first aspect. The method comprises using a very high frequency low pressure plasma (VHFLPP) method to produce the silicon nanoparticles, wherein the silicon nanoparticles are collected in a capture fluid during the preparation of the silicon nanoparticles, and wherein the capture fluid has a hindered piperidine derivative free radical scavenger dispersed therein. When the silicon nanoparticles enter the capture fluid, the hindered piperidine derivative free radical scavenger adheres to the surface of the silicon nanoparticles in the capture fluid. The hindered piperidine derivative free radical scavenger is as described above.

[0035] VHFLPP is a commonly known method for producing nanoparticles, and in this case, silicon nanoparticles, including silicon quantum dots. When producing nanoparticles, the VHFLPP method offers greater control over particle size and size distribution than other methods for producing nanoparticles. Examples of VHFLPP methods are described in the prior art, including US2013 / 0189446, US2012 / 0326089, and WO2020 / 205850. Below is a basic description of the VHFLPP method.

[0036] The VHFLPP method uses a gas stream containing at least one nanoparticle precursor, which flows through a quartz tube at a pressure below 13,333 Pascals (Pa). To produce silicon nanoparticles, the nanoparticle precursor is or comprises a silicon-containing material, typically selected from the group consisting of silane, disilane, halogen-substituted silanes, halogen-substituted disilanes, C1 to C4 alkylsilanes, C1 to C4 alkyldisilanes, and mixtures of any combination thereof. The gas stream may contain additional precursors (dopants), typically comprising a component or any combination of components selected from the group consisting of halogens, germanium, boron, phosphorus, and nitrogen. The combined concentration of the nanoparticle precursor and dopant in the gas stream typically ranges from 0.1 volume percent (vol%) to 50 vol%, relative to the gas stream composition. The remainder of the gas stream is primarily an inert gas or a combination of more than one inert gas, such as argon (Ar), helium (He), neon (Ne), krypton (Kr), xenon (Xe), and radon (Rn).

[0037] Concentrically and externally of the quartz tube are two ring electrodes, typically copper, spaced apart, with one ring electrode positioned "upstream" (relative to the gas flow) relative to the other. Plasma is generated within the quartz tube by powering the upstream ring electrode with an RF source while grounding the other ring electrode. RF is a very high frequency (typically ranging from 30 MHz to 500 MHz) and is coupled to a power typically ranging from 80 watts to 1000 watts.

[0038] When the nanoparticle precursor flows through the plasma, it decomposes, nucleates and grows into nanoparticles.The pressure of the plasma is 6666 Pascal (Pa) or less, preferably 667 Pa or less, and typically 133 Pa or greater.

[0039] The nanoparticles continue to flow in the airflow and leave the quartz tube through the orifice into the collection chamber. When the airflow is flowing, the pressure in the collection chamber is less than 13.33 Pascals (Pa). When the airflow is not flowing, the pressure in the collection chamber is typically 6.67×10 -5 Pa.

[0040] The capture fluid reservoir that comprises capture fluid is positioned at collecting chamber, and wherein air-flow is directed to capture fluid.The distance between the surface of capture fluid and the orifice of quartz tube is ideally in the scope of 5 to 50 orifice diameters.The surface of the air-flow collision capture fluid that contains nanoparticles, thereby nanoparticles are introduced in the capture fluid, and nanoparticles gather in the capture fluid during the process of VHFLPP method.Usually, in order to help nanoparticles are dispersed in the capture fluid, during nanoparticle collection, stir (for example, stir or stand ultrasonic agitation) capture fluid and / or make the reservoir that contains capture fluid rotate during nanoparticle collection.After capture is finished, the capture fluid that contains nanoparticles is carried out ultrasonic treatment and also helps to promote the dispersion of nanoparticles.

[0041] The capture fluid should have sufficiently low vapor pressure to keep substantially intact in the reservoir in the collection chamber in the VHFLPP method. The capture fluid is ideally non-aqueous. The example of a suitable capture fluid includes mineral oil, and silicone oil (such as polydimethylsiloxane (PDMS), phenylmethyl-dimethylcyclosiloxane, tetramethyltetraphenyltrisiloxane and pentaphenyltrimethyltrisiloxane), fluorocarbons and alkylene oxide oils. The capture fluid can be a blend of more than one fluid. Other desired properties and examples of suitable capture fluids are proposed in paragraphs

[0070] to

[0077] of WO2020 / 205850, and these teachings are incorporated herein by reference because they are ideally suitable for the capture fluid of the present invention.

[0042] Silicon nanoparticles are functionalized with a hindered piperidine derivative free radical scavenger in a capture fluid. This functionalization occurs simply by having the silicon nanoparticles and the hindered piperidine derivative free radical scavenger present together in the capture fluid. The hindered piperidine derivative free radical scavenger adheres to the surface of the silicon nanoparticles to functionalize the silicon nanoparticle surface. Before, during, and / or after collecting the silicon nanoparticles, the hindered piperidine derivative free radical scavenger is provided in the capture fluid so that the silicon nanoparticles and the hindered piperidine derivative free radical scavenger are present together in the capture fluid. For example, when collecting silicon nanoparticles in a capture fluid during a VHFLPP method, the capture fluid may contain the hindered piperidine derivative free radical scavenger. Alternatively or in addition, the hindered piperidine derivative free radical scavenger may be added to the capture fluid containing the silicon nanoparticles after the silicon nanoparticles have been collected in the capture fluid and before the silicon nanoparticles are exposed to air. Ideally, sufficient hindered piperidine derivative free radical scavenger is provided to obtain a concentration of 0.1 weight percent (wt%) or more, preferably 0.5 wt% or more, 1.0 wt% or more, 2.0 wt% or more, 3.0 wt% or more, 4.0 wt% or more, and even 5.0 wt% or more, while typically 10 wt% or less, 9 wt% or less, 8 wt% or less, 7 wt% or less, 6 wt% or less, and even 5 wt% or less of the hindered piperidine derivative free radical scavenger, based on the combined weight of the hindered piperidine derivative free radical scavenger and the capture fluid.

[0043] The capture fluid can provide a protective medium for the storage and controlled passivation of hindered piperidine derivative-functionalized silicon nanoparticles. If directly exposed to humid air, the silicon nanoparticles will degrade rapidly. However, by exposing the silicon nanoparticles in the capture fluid to humid air at a controlled temperature, an oxide layer can be formed in a controlled manner because moisture and oxygen slowly penetrate the capture fluid and react with the silicon nanoparticle surface to form oxides. Once passivated, the silicon nanoparticles can be separated from the capture fluid without the risk of rapid degradation. One way to passivate the silicon nanoparticles in the capture fluid is to subject the nanoparticles and the capture fluid to a temperature preferably greater than 25°C, typically 65°C or close to 65°C, in air (preferably at 85% relative humidity) for a period of time. In the absence of hindered piperidine derivative free radical scavengers, the passivation process typically takes 12 to 72 hours or even longer, and in some cases takes 168 hours or longer. However, it has been found that passivation of hindered piperidine derivative-functionalized silicon nanoparticles can occur in a few hours or less. The passivation was complete by examining the photoluminescence emission intensity of the particles using a Fluorolog FL-3 instrument with an excitation and emission slit width of 2 nm and an integration time of 0.1 sec / nm. The particles were excited with light of 365 nm wavelength. Passivation was complete when the peak emission wavelength no longer changed significantly. The peak emission intensity at the peak emission wavelength, as measured using the Fluorolog FL-3 instrument, was typically greater than 60 × 10 6 When the change in peak emission wavelength was less than 10 nm / day, the peak emission wavelength was considered to have stopped changing significantly, and passivation was considered complete.

[0044] The hindered piperidine derivative functionalized silicon nanoparticles can be separated from the capture fluid, preferably after passivation. Methods for separating the hindered piperidine derivative functionalized silicon nanoparticles from the capture fluid include, for example, filtration and centrifugal decantation. If the hindered piperidine derivative functionalized silicon nanoparticles have been passivated, separation from the capture fluid can be performed in air. If the hindered piperidine derivative functionalized silicon nanoparticles have not been passivated prior to separation from the capture fluid, separation should be performed in an inert atmosphere such as dry nitrogen or a dry noble gas atmosphere.

[0045] In the VHFLPP method, the capture fluid can be recycled or reused. That is, for the multiple operations of the VHFLPP method, nanoparticles can be collected in the same capture fluid. Usually, before the capture fluid is reused, the nanoparticles are separated from the capture fluid, but this is not required. For example, the nanoparticles can be collected in the capture fluid, passivated, and then separated (for example, by filtering or centrifuging) from the capture fluid. The remaining capture fluid can then be used for the VHFLPP method subsequently.

[0046] The VHFLPP method can be run as a continuous or pulsed process. A continuous VHFLPP process uses a constant, continuous radio frequency on the upstream ring electrode. In contrast, a pulsed VHFLPP process uses an amplitude-modulated very high frequency (VHF) radio frequency signal applied to the upstream ring electrode. This amplitude-modulated signal typically operates with a square wave function ranging from 1 kHz to 50 kHz, which is multiplied by a continuous VHF sinusoidal waveform. Advantages of the pulsed process include using pulse energy to control the size of the nanoparticles, which are produced by controlling the residence time of the nanoparticle precursors as they are exposed to the high-power plasma while passing through the VHF glow discharge. In a continuous VHF plasma process (non-modulated), the nanoparticle size can be controlled by the concentration of the nanoparticle precursors—in the case of silicon nanoparticles, the concentration of silicon—as well as by the residence time of the precursors in the VHF plasma.

[0047] Example

[0048] For the following examples, the following VHFLPP apparatus and procedure were used.

[0049] VHFLPP device

[0050] Figure 1A schematic diagram of a VHFLPP apparatus according to an embodiment of the present invention is shown. Samples are prepared in an inert environment, such as a glove box 1 purged with nitrogen. Connected to the glove box 1 is a vacuum load lock 2. When the vacuum load lock seal 2a between the gas-purged glove box and the vacuum load lock is opened, the sample can be transferred from the inert gas-purged glove box to the vacuum load lock. A low vacuum pump 2b is in fluid communication with the vacuum load lock. A rack and pinion arm 2c allows items to be moved between the load locks 2 into the main capture chamber 4. The vacuum load lock is separated from the main capture chamber 4 by a gate valve 3. When the gate valve 3 is open, the vacuum load lock is in fluid communication with the main capture chamber. When the gate valve 3 is closed, the vacuum load lock is isolated from the main capture chamber. The main capture chamber is connected to a high vacuum pump 11 via a gate valve 10. The high vacuum pump 11 is a turbomolecular pump (pumping speed of 600 liters / second) supported by a low vacuum pump (Ebara S50 semiconductor pump, pumping speed of 5,000 liters / minute). The main collection chamber is also in fluid communication with the upstream dielectric discharge tube 5 via the dielectric discharge tube orifice 5b. The dielectric discharge tube is a high-purity fused silica tube having an inner diameter of 7 mm, an outer diameter of 9.6 mm, and a length of 23 cm. Extending through a seal into the main collection chamber is a capture fluid reservoir holder 7, which holds the capture fluid reservoir 6. The capture fluid reservoir holder can be moved toward or away from the dielectric discharge tube orifice to allow the user to position the capture fluid reservoir at a desired distance from the dielectric discharge tube orifice. During operation of the VHFLPP process, a gas flow comprising a precursor gas and an inert carrier gas flows into the inlet end 5a of the dielectric discharge tube 5, flows through the dielectric discharge tube, and flows into the main collection chamber 4 through the dielectric discharge tube orifice 5b. The diameter of the dielectric tube orifice is ideally adjustable and can be adjusted to produce a pressure ratio of (discharge tube pressure) / (main collection chamber pressure) of 500 or more. The dielectric discharge tube has two electrodes 8a and 8b of a double-ring copper electrode 8 around its circumference.

[0051] VHFLPP method operation

[0052] Silicon nanoparticles were prepared using the VHFLPP method and apparatus described herein as follows. Within a glove box, a trapping fluid was placed in a trapping fluid reservoir, and as described in the specific examples, octadecene or a hindered piperidine derivative was placed in the trapping fluid. The trapping fluid was transferred through the load lock barrier and into the load lock. The load lock was sealed and evacuated to a pressure of less than 2.67 Pa using a low vacuum pump. The main trapping chamber was evacuated to a pressure of less than 6.67 × 10 -5 Open gate valve 3 and use the rack and pinion transfer arm 2c to transfer the trapping fluid reservoir from the load lock to the trapping fluid reservoir holder 7 in the main trapping chamber. Close gate valve 3 and reduce the pressure of the main trapping chamber to less than 6.67×10 - 5Pa. Move the capture fluid reservoir holder to position the capture fluid reservoir at the desired distance below the dielectric discharge tube orifice. Rotate the capture fluid reservoir holder (and therefore the capture fluid reservoir) at a rate of 12 revolutions per minute.

[0053] The gas flow is fed into the end 5a of the dielectric discharge tube by metering the desired gases. Each of the following examples determines the composition of the desired gases constituting the flow and their relative flow rates. The gases are fed together into the end 5a of the dielectric discharge tube to generate the gas flow through the dielectric discharge tube.

[0054] A very high frequency plasma 9 is generated in a dielectric discharge tube between electrodes 8a and 8b while a gas flow is caused to flow through the dielectric discharge tube by applying a sinusoidal wave to the electrodes. The sinusoidal wave is generated using a Tektronix AFG 3252 function generator and an Electronic and Innovation 3200L Class A RF generator connected to the electrodes. The sinusoidal wave on the electrodes generates a capacitively coupled very high frequency (90 MHz to 500 MHz) plasma in the dielectric discharge tube. The frequency source is tuned to provide maximum power coupled into the plasma while minimizing the driving amplitude of the sinusoidal wave. The coupled power density of the plasma is greater than 130 watts per square centimeter (W / cm 2 ).

[0055] Silicon nanoparticles are formed in the plasma and exit the dielectric discharge tube through the orifice 5b and are collected in the capture fluid in the capture fluid reservoir.

[0056] When the silicon nanoparticles were collected, the capture fluid reservoir containing the silicon nanoparticles was transferred back to the inert glove box via a load lock using a transfer arm. The capture fluid and silicon nanoparticles were transferred to a glass vial and sealed with a Teflon cap and electrical tape. The glass vial was removed from the glove box and sonicated using a benchtop ultrasonic bath (40 kHz) for 30 minutes to help disperse any agglomerated particles.

[0057] The silicon nanoparticles are passivated by placing the silicon nanoparticle-coated solid substrate in a capture fluid at an aging temperature and aging humidity for an aging time as reported below.

[0058] Sample photoluminescence (PL) spectrum

[0059] Silicon nanoparticles emit light when exposed to ultraviolet radiation only when they have a particle size in the range of 1 to 10 nanometers. Therefore, observing the luminescence is a method to confirm that the silicon nanoparticles are silicon quantum dots. The following procedure was used to detect and characterize the luminescence of the samples described below.

[0060] The sample is generated by adding a portion of the silicon nanoparticles (which are in the form of a dispersion) in the trapping fluid to a poly (methyl methacrylate) cuvette with a 1 cm path length. The cuvette is placed in the sample holder of a Horiba Fluorolog-3 spectrophotometer (FL3-22), which includes a 450-watt xenon excitation lamp that illuminates the sample after the sample passes through a double grating (1200 grooves / mm, 330 nm blaze) excitation spectrometer to select the excitation wavelength. The excitation photons enter the sample compartment that holds the sample and are directed to the sample. The sample compartment has forward optics to measure the photoluminescence emission of the sample at approximately 45 degrees relative to the excitation photons. The emitted photons are directed to a double grating (1200 grooves / mm, 500 nm blaze) emission spectrometer and projected onto a Hamamatsu R928P photomultiplier tube. The emission signal is calibrated to the grating and detector specifications (from the supplier). The excitation and emission slits were 2 nm, and the integration time was 100 milliseconds / nm. An FL3-22 instrument was used to measure photoluminescence emission and excitation spectra. Emission (PL) spectra, which are photoluminescence (PL) spectra, typically use an excitation wavelength of 365 nm and sweep emission wavelengths. Photoluminescence excitation (PLE) spectra are measured by setting the emission wavelength constant (e.g., 700 nm) and sweeping the excitation wavelength from 280 nm to 550 nm, while measuring the signal intensity at the selected emission wavelength.

[0061] Sample absorption spectrum

[0062] Measure the absorbance of the sample as follows:

[0063] For Examples 1, 2 and 3, a Shimadzu UV2600i spectrophotometer, which is a dual-beam spectrophotometer, was used. A poly(methacrylate) cuvette with a path length of 1 cm was placed in the path of one beam (sample beam) containing a sample dispersion of silicon nanoparticles in a trapping fluid. A (methacrylate) cuvette containing only a trapping fluid with a path length of 1 cm was placed in the path of another beam (reference beam). Deuterium and tungsten-halogen lamps excited the sample and reference with a 1 nm bandwidth at wavelengths of 280 nm to 800 nm. Transmitted light was focused onto a silicon diode using a Czerny-Turner optical system. The absorption of excitation photons by the nanoparticles in the sample was plotted at each wavelength to obtain the absorption spectrum of the sample.

[0064] For Examples 4 to 8, absorption spectra were collected in a similar manner using a Shimadzu UV-1800 spectrophotometer.

[0065] Absorption spectra were not measured for Examples 9 to 12, but they could be collected in a similar manner to any other Example.

[0066] sample

[0067] The following samples were prepared according to the aforementioned procedure and the parameters in the table below. Characterization of the samples is included in the table below. Table 1 lists the elements used to prepare each sample.

[0068] Table 1

[0069]

[0070] Table 2 lists the parameters used to prepare the samples. Table 3 identifies additional parameters used in preparing the samples. A brief description of each sample is provided before Table 2.

[0071] Samples 1 and 9: The capture fluid is light mineral oil. Sample 1 is a comparative example of Sample 3. Sample 9 is a comparative example of Sample 10.

[0072] Sample 2: The capture fluid is light mineral oil with 5 wt% of octadecene. Sample 2 is a comparative example of Sample 3.

[0073] Samples 3 and 10: The capture fluid was light mineral oil with 5 wt% HPD 1. Sample 3 was prepared under similar conditions to Samples 1 and 2. Sample 10 was half the mass of Sample 9, with HDP 1 added at 5 wt% before exposure to air but after sonicating Sample 9 at 40 kHz for 10 minutes.

[0074] Samples 4 and 5: The trapping fluid was light mineral oil with 5 wt% octadecene. The sample was sonicated at 40 kHz for 20 minutes and split into two samples, one for Sample 4 and one for Sample 5, before passivation. Sample 4 was passivated. 5 wt% of HPD 1 was added to Sample 5, and Sample 5 was sonicated for an additional 30 minutes before passivation.

[0075] Sample 6: The capture fluid for Sample 6 was light mineral oil with 5 wt% HPD 2. This sample had similar processing conditions as Sample 4 (Comparative Example).

[0076] Samples 7 and 8: For Sample 7, the trapping fluid was light mineral oil with 5 wt% HPD 1. The sample was sonicated at 40 kHz for 20 minutes and split into two samples, one for Sample 7 and one for Sample 8. Passivated Sample 7 was cured at 25°C and 50% relative humidity for 3 days. Passivated Sample 8 was cured at 60°C and 85% relative humidity for 3 days. The difference between Samples 7 and 8 is the passivation temperature and relative humidity.

[0077]

[0078]

[0079] Table 4 contains a summary of the photoluminescence properties of the samples. Table 4 contains the properties of each example measured after different passivation aging times. The terms in Table 4 are as follows:

[0080] PL λ peak: the peak wavelength of the maximum emission photoluminescence intensity of silicon nanoparticles measured after a passivation aging time when excited at 365 nm.

[0081] λ FWHM: Full width at half maximum of the emitted photoluminescence of the silicon nanoparticles in the trapping fluid when excited at 365 nm, measured after a passivation aging time.

[0082] PL emission intensity (×10 6 Counts): Peak photoluminescence intensity of the silicon nanoparticles in the trapping fluid measured after a passivation aging time when excited at 365 nm at the PL 1 peak (excitation and emission monochromator slit widths of 2 nm, integration time of 0.1 sec / nm).

[0083] Eg: Optical band gap of the photoluminescence spectrum of the peak photoluminescence emission from silicon nanoparticles in the trapping fluid when excited at 365 nm, measured after a passivation aging time.

[0084] σEg: standard deviation of the optical band gap of the peak photoluminescence emission spectrum of the silicon nanoparticles in the trapping fluid when excited at 365 nm, measured after a passivation aging time.

[0085] Table 4

[0086]

[0087]

[0088] The data in Table 4 reveal that the hindered piperidine derivatives induce a significant blue shift in the photoluminescence of the silicon quantum dots to which they are coated. Figure 2-12 Additional information about the sample is evident in the spectra.

[0089] Figure 2 Shown are the photoluminescence emission (PL) spectra of samples 1 (Si nanoparticles deposited directly into mineral oil), 2 (Si nanoparticles deposited directly into octadecene (5 wt %) in mineral oil (MO), and 3 (Si nanoparticles deposited directly into HPD 1 (5 wt %) in mineral oil (MO)) when excited at 365 nm at different passivation / aging times. Figure 1As can be seen, silicon nanoparticles deposited in mineral oil containing HPD 1 molecules have a significant emission blue shift after the first day of passivation / aging and increase emission intensity much faster than the sample trapped in mineral oil (sample 1) or the sample trapped in octadecene in mineral oil (sample 2). While silicon nanoparticles trapped in mineral oil alone require 7 days of passivation / aging to reach similar PL values, the PL intensity achieved by the sample trapped with HPD 1 reaches a maximum within 3 days of passivation / aging.

[0090] Figure 3 Shown are the photoluminescence excitation spectra of samples 1, 2, and 3. This was measured by placing an emission monochromator near the PL emission peak and then sweeping the excitation wavelength while recording the intensity values ​​of the emission detector. Figure 3 A significant change in the PLE of silicon nanoparticles treated with HDP 1 compared to particles treated with mineral oil or octadecene in mineral oil is shown.

[0091] Figure 4 Shown are UV-Vis absorption spectra of three samples of silicon nanoparticles trapped and passivated in mineral oil (sample 1), octadecene (sample 2), and HPD 1 (sample 3) as a function of passivation / aging time. These spectra reveal a large deviation in absorbance for particles passivated / aged with HPD 1 compared to the other fluids.

[0092] Figure 5 Shown are the photoluminescence emissions (PL) of silicon nanoparticles trapped in 5 wt% octadecene in mineral oil (sample 4), 5 wt% HPD 1 added to half of sample 4 before exposure to air (sample 5), and 5 wt% HPD 2 in mineral oil (sample 6), all passivated / aged for three days at 60°C and 85% RH. The emission spectra of the two samples with hindered piperidine derivatives (samples 5 and 6) are blue-shifted relative to the spectrum of the sample without hindered piperidine derivatives (sample 4), and the emission intensity after three days is at least 2-fold higher with hindered piperidine derivatives relative to octadecene. All samples were excited at 365 nm with 2 nm slit widths for the excitation and emission monochromators and an integration time of 0.1 s / nm.

[0093] Figure 6 Shows Figure 5 Photoluminescence excitation (PLE) spectra of the same samples shown in Figure 4 (sample 4, sample 5, and sample 6). For each of these spectra, the emission monochromator was set at the peak emission wavelength, and the excitation wavelength was scanned (at Figure 6 The PLE intensity is shown on the y-axis in Figure 1). For all spectra, the emission and excitation monochromator slit widths were set to 2 nm, and the integration time was 0.1 s / nm. Figure 5 In Figure 5, it is apparent that exposing silicon nanoparticles to hindered piperidine derivatives prior to exposure to air significantly increases the PLE intensity within only a few days of passivation / aging relative to unexposed silicon nanoparticles.

[0094] Figure 7 Shown are UV-Vis absorption spectra of silicon nanoparticles trapped in octadecene (sample 4) and then HPD1 added to silicon nanoparticles trapped in octadecene before exposure to air (sample 5) after passivation / aging at 60°C and 85% RH for 1, 2, and 3 days. The absorbance of the nanoparticles exposed to HPD 1 blue-shifts much faster than that of the nanoparticles treated with octadecene alone.

[0095] Figure 8 Shown are photoluminescence emission (PL) spectra of silicon nanoparticles trapped in 5 wt% HPD 1 in mineral oil and then exposed to air (Sample 7), as well as during passivation / aging at 60°C and 85% RH (Sample 8). Sample 8 is Sample 7 mass-split in half before exposure to air. For each spectrum, the emission and excitation monochromator slit widths were set to 2 nm, with an integration time of 0.1 s / nm. It is evident from the emission spectra that passivating / aging the HPD 1 silicon nanoparticles at elevated temperature and humidity accelerates the sample's photoluminescence emission intensity.

[0096] Figure 9 Shows Figure 8 Photoluminescence excitation (PLE) spectra of the same samples (samples 7 and 8) shown in Figure 2. For each of these spectra, the emission monochromator was set at the peak emission wavelength, and the excitation wavelength was scanned (in the range of 0 to 100 nm) while recording the PL emission intensity. Figure 8 The PLE intensity is shown on the y-axis in Figure 1). For all spectra, the emission and excitation monochromator slit widths were set to 2 nm, and the integration time was 0.1 s / nm. Figure 8 As is evident in Figure 2, it is apparent that exposing hindered piperidine derivative treated silicon nanoparticles to elevated temperature and humidity conditions (passivation / aging process) results in a much faster increase in the photoluminescent properties of the nanoparticles.

[0097] Figure 10 Shown are UV-Vis absorption spectra of silicon nanoparticles trapped in 5 wt% HPD 1 in mineral oil, split in half by mass and subjected to room temperature aging (Sample 7) and passivation / aging at 60°C and 85% RH (Sample 8) for 1, 2, and 3 days. Relative to the nanoparticles exposed to room temperature and humidity conditions, the absorbance of the passivated / aged nanoparticles shifted significantly to the blue within three days.

[0098] Figure 11Shown are the photoluminescence emission spectra (PL) of silicon nanoparticles trapped in mineral oil (sample 9) and a new sample of sample 9 split in half by mass and with the addition of 5 wt% of HPD 1 before exposure to air (sample 10). The two samples were then passivated / aged at 60°C and 85% RH for up to 7 days (sample 9) and 10 days (sample 10). For each spectrum, the emission and excitation monochromator slit widths were set to 2 nm and the integration time was 0.1 s / nm. It is clear that the addition of HDP 1 to the silicon nanoparticles trapped in mineral oil before exposure to air results in an initial blue shift in the emission spectrum and a much faster increase in emission intensity for the sample not exposed to the hindered piperidine derivative. This illustrates the possibility of adding a treating agent to the silicon nanoparticles before exposure to air and obtaining similar optical properties to the nanoparticles deposited directly into the trapping fluid containing the treating molecule.

[0099] Figure 12 The photoluminescence excitation (PLE) spectra of samples 9 and 10 are shown. For each of these spectra, the emission monochromator was set at the peak emission wavelength, and then the excitation wavelength was scanned (at Figure 12 The PLE intensity is shown on the y-axis in Figure ). For all spectra, the emission and excitation monochromator slit widths were set to 2 nm, and the integration time was 0.1 s / nm.

Claims

1. A composition comprising silicon nanoparticles, wherein the silicon nanoparticles comprise a hindered piperidine derivative free radical scavenger on the surface of the silicon nanoparticles.

2. The composition comprising silicon nanoparticles according to claim 1, wherein the silicon nanoparticles comprise silicon quantum dots.

3. The composition comprising silicon nanoparticles according to claim 1 or claim 2, wherein the silicon nanoparticles are free of aromatic conjugation between the hindered piperidine derivative free radical scavenger and the silicon nanoparticles.

4. The composition comprising silicon nanoparticles according to any one of claims 1 to 3, wherein the hindered piperidine derivative radical scavenger is non-aromatic.

5. The composition comprising silicon nanoparticles according to any one of claims 1 to 4, wherein the radical scavenger is one or any combination of more than one selected from the group consisting of: bis(1,2,2,6,6-pentamethyl-4-piperidinyl) sebacate; bis(1-octyl-2,2,6,6-tetramethyl-4-piperidinyl) sebacate; bis(2,2,6,6-tetramethyl-4-piperidinyl) sebacate; and 4-Hydroxy-2,2,6,6-tetramethylpiperidinyl 1-oxybenzoate. 6 . The composition comprising silicon nanoparticles according to claim 1 , wherein the silicon nanoparticles further comprise an oxide in combination with the hindered piperidine derivative on the surface of the silicon nanoparticles.

7. A method for preparing silicon nanoparticles having a hindered piperidine derivative free radical scavenger on the surface of the silicon nanoparticles, the method comprising using a VHFLPP method to produce the silicon nanoparticles, the VHFLPP method collecting the silicon nanoparticles in a capture fluid as they are prepared, and wherein the hindered piperidine derivative free radical scavenger is provided in the capture fluid before collecting the silicon nanoparticles and / or after collecting the silicon nanoparticles and before exposing the silicon nanoparticles to air, such that the silicon nanoparticles and the hindered piperidine derivative free radical scavenger are present together in the capture fluid.

8. The method according to claim 7, wherein the free radical scavenger is one or more than one selected from the group consisting of: bis(1,2,2,6,6-pentamethyl-4-piperidinyl) sebacate; bis(1-octyl-2,2,6,6-tetramethyl-4-piperidinyl) sebacate; bis(2,2,6,6-tetramethyl-4-piperidinyl) sebacate; tetramethyl-4-piperidinyl) sebacate; and 4-hydroxy-2,2,6,6-tetramethylpiperidinyl 1-oxybenzoate.

9. The process according to any one of claims 7 to 8, wherein the hindered piperidine derivative free radical scavenger is non-aromatic.

10. The method according to any one of claims 7 to 9, wherein the method further comprises the following steps: The silicon nanoparticles in the capture fluid are passivated by exposing the capture fluid containing the silicon nanoparticles to a moisture-containing atmosphere for a period of time, optionally at a temperature above 25 degrees Celsius, to produce passivated silicon nanoparticles having surface-bound hindered piperidine derivative radical scavengers.

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