Hindered piperidine derivative-functionalized silicon nanoparticles

Abstract

The composition contains silicon nanoparticles having a hindered piperidine derivative free radical scavenger on the surface of the silicon nanoparticles. A process for making silicon nanoparticles having a hindered piperidine derivative free radical scavenger on the surface of the silicon nanoparticles, the process comprising producing silicon nanoparticles using a VHFLPP process and collecting the silicon nanoparticles in a capture fluid as they are made, wherein the hindered piperidine derivative free radical scavenger is provided in the capture fluid before, during, or after collecting the silicon nanoparticles such that the silicon nanoparticles and the hindered piperidine derivative free radical scavenger are present together in the capture 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. [Background technology]

[0002] Introduction The emergence of nanotechnology is bringing about a paradigm shift in many technological fields because the properties of many materials change at nanoscale dimensions. For example, reducing the dimensions of some structures to the nanoscale can increase the surface area to volume ratio, thus resulting in changes in the electrical, magnetic, reactive, chemical, structural, and thermal properties of the material. Nanomaterials can already be found in commercial applications and will be present in a wide range of technologies in the coming decades, including computers, photovoltaics, optoelectronics, medicine / pharmaceuticals, building materials, military applications, and many others.

[0003] Silicon nanoparticles are of particular interest. A key feature of small silicon nanoparticles (average size less than 10 nanometers (nm)) is that they exhibit photoluminescence in the visible and near-infrared when stimulated by shorter wavelengths of light (such as ultraviolet light). This is thought to arise from quantum confinement effects that occur when the nanoparticle diameter is smaller than the exciton diameter, resulting in bandgap bending (i.e., an increase in the gap). Researchers have shown how the bandgap energy (measured in electron volts) of nanoparticles varies as a function of the nanoparticle diameter.

[0004] Although silicon is an indirect bandgap semiconductor in bulk, silicon nanoparticles with an average size of less than 10 nm are comparable to direct bandgap materials, made possible by interface trapping of excitons. Direct bandgap materials can be used in optoelectronic applications as silicon quantum dot materials. Silicon quantum dots are particularly desirable over other quantum dot materials because they do not require environmentally unfriendly components such as lead, selenium, cadmium, indium, or arsenic. Another intriguing property of nanomaterials is their reduced melting point, which follows from the surface phonon instability theory. Researchers have shown that the melting point of nanomaterials formed from nanoparticles varies as a function of the nanoparticle diameter.

[0005] It would be desirable to develop silicon nanoparticle technologies, and in particular silicon quantum dot technologies, to control the optical properties of silicon quantum dots. It would be 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

[0006] The present invention provides a method for modifying 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 the silicon quantum dots with a piperidine derivative free radical scavenger. Some researchers have demonstrated the ability to red-shift the emission wavelength of silicon quantum dots by as much as 70 nanometers by complexing aromatic organic ligands on the surface of silicon quantum dots. See Zhou et al., Nano Lett. 2015, 15, 3657-3663 and Li et al., Phys. Chem. Chem. Phys., 2014, 16, 19275-19281. Blue-shifting the luminescence emission of silicon quantum dots is even more surprising than such results.

[0007] A further surprising advantage is the present invention's discovery that functionalizing the surface of silicon nanoparticle quantum dots with a piperidine derivative free radical scavenger dramatically reduces the time required to passivate the silicon nanoparticles, thereby reducing the time required to produce air-stable silicon nanoparticles containing silicon quantum dots. A still further advantage is that the present invention provides a process for preparing such functionalized silicon nanoparticles in a continuous process by functionalizing the silicon nanoparticles as they are produced and dispersed in a capture fluid. The silicon nanoparticles can then be passivated in the capture fluid. This process typically takes several days at 60 degrees Celsius (°C), 85% relative humidity (RH), and 101 kilopascals (atmospheric pressure), but when functionalized with a piperidine derivative free radical scavenger, can occur within a few hours under the same conditions.

[0008] In a first aspect, the present invention is a composition comprising silicon nanoparticles, wherein the silicon nanoparticles comprise a hindered piperidine derivative free radical scavenger on the surface of the silicon nanoparticles.

[0009] In a second aspect, the present invention is a process for making silicon nanoparticles having a hindered piperidine derivative free radical scavenger on the surface of the silicon nanoparticles, the process comprising generating the silicon nanoparticles using a very high frequency low pressure plasma (VHFLPP) process and collecting the silicon nanoparticles in a capture fluid as they are made, wherein the hindered piperidine derivative free radical scavenger is provided in the capture fluid before, during, 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 explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic diagram of a VHFLPP configured to prepare samples herein. [Figure 2] FIG. 1 shows the photoluminescence emission (PL) spectra of samples 1-3 when excited at 365 nm with different passivation / aging times. [Figure 3] FIG. 1 shows photoluminescence excitation (PLE) spectra of Samples 1 to 3. [Figure 4] FIG. 1 shows UV-Vis absorbance spectra as a function of passivation / aging time for Samples 1-3. [Figure 5] FIG. 1 shows photoluminescence (PL) of samples 4 to 6. [Figure 6] FIG. 1 shows photoluminescence excitation (PLE) spectra of Samples 4 to 6. [Figure 7] FIG. 1 shows UV-Vis absorbance spectra of Samples 4 to 6. [Figure 8] FIG. 1 shows photoluminescence emission spectra (PL) of Samples 4 to 6. [Figure 9] FIG. 1 shows photoluminescence excitation (PLE) spectra of Samples 4 to 6. [Figure 10] FIG. 1 shows the UV-Vis absorbance spectra of Samples 9 and 10. [Figure 11] FIG. 1 shows photoluminescence emission spectra (PL) of Samples 9 and 10. [Figure 12] FIG. 1 shows photoluminescence excitation spectra (PLE) of Samples 9 and 10. DETAILED DESCRIPTION OF THE INVENTION

[0011] Products identified by trade names refer to compositions available under those trade names as of the priority date of this document.

[0012] "Multiple" means two or more. "And / or" means "and, or as an alternative." All ranges are inclusive of the endpoints unless otherwise indicated.

[0013] "Cx~Cy", "C x ~C y "," "C x~y " are interchangeable and refer to compositions having a number of carbon atoms ranging from x to y.

[0014] "Silicon nanoparticles" refer to silicon-based particles having an average particle size of less than 1 micrometer, typically 100 nanometers (nm) or less, but also having an average particle size of 1 nm or greater. Dynamic light scattering or transmission electron microscope image analysis are common methods for determining the average particle size of silicon nanoparticles. Silicon nanoparticles include silicon quantum dots.

[0015] "Silicon-based" refers to a composition that includes silicon. Silicon-based materials generally contain 40 percent (%) or more silicon atoms or a combination of silicon and oxygen atoms relative to the total atoms in the material, and can 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 and oxygen atoms.

[0016] "Silicon quantum dots" refer to silicon nanoparticles that have a crystalline silicon structure and exhibit photoluminescence when exposed to light. Typically, silicon quantum dots have an average particle size in the range of 1 to 10 nanometers, preferably in the range of 1 to 6 nanometers, and more preferably in the range of 1 to 5 nanometers. Silicon quantum dots are characterized by the fact that they emit light when exposed to light having a wavelength in the wavelength range of 300 to 477 nanometers, which corresponds to blue light and ultraviolet light.

[0017] In one aspect, the present invention is a composition comprising silicon nanoparticles that include 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 can include other components in addition to the silicon nanoparticles. The silicon nanoparticles preferably include, and can be, silicon quantum dots.

[0018] The hindered piperidine derivative free radical scavengers may be the same or may be a combination of, or may be more than one hindered piperidine derivative free radical scavengers. Desirably, the hindered piperidine derivative free radical scavengers are non-aromatic, meaning that they do not contain an aromatic ring. Examples of suitable piperidine derivative free radical scavengers include any one or more combinations selected from the group consisting of bis(1,2,2,6,6-pentamethyl-4-piperidyl)sebacate, bis(1-octyl-2,2,6,6-tetramethyl-4-piperidyl)sebacate, bis(2,2,6,6-tetramethyl-4-piperidyl)sebacate, and 4-hydroxy-2,2,6,6-tetramethylpiperidine 1-oxylbenzoate.

[0019] The hindered piperidine derivative free radical scavenger is present on the surface of the silicon nanoparticle, thereby "functionalizing" the silicon nanoparticle. The hindered piperidine derivative free radical scavenger can be chemically bonded to the silicon nanoparticle, such as by a covalent bond. However, it is desirable that there be no aromatic conjugation between the hindered piperidine derivative free radical scavenger and the silicon nanoparticle. 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 nanoparticle. The hindered piperidine derivative free radical scavenger-functionalized silicon nanoparticles may not contain any conjugated organic groups at all. The present invention also encompasses hindered piperidine derivative-functionalized silicon nanoparticles in which the hindered piperidine derivative-functionalized free radical scavenger adheres to the surface of the silicon nanoparticle without chemically bonding to the silicon nanoparticle. The non-chemical adhesion can occur through electrostatic attraction or any other non-chemical bonding means.

[0020] In addition to the hindered piperidine derivative free radical scavenger, the silicon nanoparticles can further comprise a passivating group on their surface. The passivating group can be any group or a combination of two or more groups that protects the silicon nanoparticles from decomposition when exposed to oxygen and moisture in the air. For example, the silicon nanoparticles can comprise 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 the air.

[0021] The functionalized hindered piperidine derivative silicon quantum dots surprisingly exhibit a blue shift in luminescence emission wavelength (i.e., a shift to shorter wavelength emission) compared to identical silicon quantum dots that are not functionalized hindered piperidine derivatives. Furthermore, the formation of an oxide passivation coating on the surface of the functionalized hindered piperidine derivative silicon nanoparticles surprisingly occurs when exposed to air at 60 degrees Celsius (°C), 85% relative humidity (RH), and 101 kilopascals (atmospheric pressure) for only a few hours, sufficient to protect the silicon nanoparticles from decomposition, rather than for several days when passivated in a trapping fluid.

[0022] In a second aspect, the present invention is a method for preparing the hindered piperidine derivative-functionalized silicon nanoparticles of the first aspect. The method includes producing silicon nanoparticles using a high frequency, low pressure plasma (VHFLPP) process, collecting the silicon nanoparticles in a trapping fluid as they are produced, the trapping fluid having a hindered piperidine derivative free radical scavenger dispersed therein. When the silicon nanoparticles enter the trapping fluid, the hindered piperidine derivative free radical scavenger adheres to the surface of the silicon nanoparticles while they are in the trapping fluid. The hindered piperidine derivative free radical scavenger is as described herein above.

[0023] VHFLPP is a commonly known process for making nanoparticles, and in the present application, the silicon nanoparticles include silicon quantum dots. The VHFLPP process provides better control over particle size and size distribution when producing nanoparticles than other processes that provide nanoparticles. Examples of VHFLPP processes are taught in the prior art, including U.S. Patent Application Publication No. 2013 / 0189446, U.S. Patent Application Publication No. 2012 / 0326089, and WO 2020 / 205850. A basic description of the VHFLPP process follows.

[0024] The VHFLPP process uses a gas stream containing at least one nanoparticle precursor flowing through a quartz tube at a pressure less than 13,333 Pascals (Pa). To produce silicon nanoparticles, the nanoparticle precursor is or includes a silicon-containing material typically selected from the group consisting of silane, disilane, halogen-substituted silanes, halogen-substituted disilanes, C1-C4 alkyl silanes, C1-C4 alkyl disilanes, and mixtures of any combination thereof. The gas stream can contain additional precursors (dopants), typically containing 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 to 50 volume percent (vol%) of the gas stream composition. The remainder of the gas stream is primarily one or a combination of more inert gases, such as argon (Ar), helium (He), neon (Ne), krypton (Kr), xenon (Xe), and radon (Rn).

[0025] Two concentric ring electrodes, typically copper ring electrodes separated from one another with one ring electrode "upstream" (relative to the gas flow) relative to the other, are placed around the outside of the quartz tube. A plasma is generated within the quartz tube by powering the upstream ring electrode with a radio frequency source while grounding the other ring electrode. The radio frequency is very high (typically in the 30-500 megahertz range) and typically coupled to a power in the 80-1000 watt range.

[0026] The nanoparticle precursors decompose, nucleate, and grow into nanoparticles as they flow through the plasma, which has a pressure of 6666 Pascals (Pa) or less, preferably 667 Pa or less, while typically 133 Pa or more.

[0027] The nanoparticles continue to flow in the gas stream, exiting the quartz tube through an orifice and entering a collection chamber. While the gas stream is flowing, the collection chamber is at a pressure less than 13.33 Pascals (Pa). When the gas stream is not flowing, the collection chamber typically contains 6.67 x 10 -5 The pressure is in Pa.

[0028] A trapping fluid reservoir containing the trapping fluid is present within the collection chamber, and a gas stream is directed toward the trapping fluid. The distance between the surface of the trapping fluid and the orifice of the quartz tube is desirably in the range of 5 to 50 orifice diameters. The gas stream containing the nanoparticles impinges on the surface of the trapping fluid, thereby introducing the nanoparticles into the trapping fluid. During the VHFLPP process, the nanoparticles collect in the trapping fluid. Typically, to aid in the dispersion of the nanoparticles in the trapping fluid, the trapping fluid is agitated (e.g., stirred or subjected to ultrasonic agitation) during nanoparticle collection, and / or the reservoir containing the trapping fluid is rotated during nanoparticle collection. After trapping is complete, it is also useful to sonicate the trapping fluid containing the nanoparticles to promote dispersion of the nanoparticles.

[0029] The capture fluid should have a sufficiently low vapor pressure so that it remains largely intact in the reservoir in the collection chamber during the VHFLPP process. The capture fluid is desirably non-aqueous. Examples of suitable capture fluids include mineral oil, silicone oils (e.g., polydimethylsiloxane (PDMS), phenylmethyl-dimethylcyclosiloxane, tetramethyltetraphenyltrisiloxane, and pentaphenyltrimethyltrisiloxane), fluorocarbons, and alkylene oxide oils. The capture fluid may also be a blend of two or more fluids. Further desirable properties and examples of suitable capture fluids are taught in paragraphs

[0070] to

[0077] of WO 2020 / 205850, the teachings of which are incorporated herein by reference as desirably applied to the capture fluids of the present invention.

[0030] The silicon nanoparticles are functionalized with a hindered piperidine derivative free radical scavenger while in the capture fluid. Such 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 attaches to the surface of the silicon nanoparticles, functionalizing the silicon nanoparticle surface. The hindered piperidine derivative free radical scavenger is provided in the capture fluid before, during, and / or after collecting the silicon nanoparticles, so that the silicon nanoparticles and the hindered piperidine derivative free radical scavenger are present together in the capture fluid. For example, when the silicon nanoparticles are collected in the capture fluid during the VHFLPP process, the capture fluid may contain a hindered piperidine derivative free radical scavenger. Alternatively, or in addition, the hindered piperidine derivative free radical scavenger can be added to the capture fluid containing the silicon nanoparticles after the silicon nanoparticles are collected in the capture fluid and before exposing the silicon nanoparticles to air. Desirably, sufficient hindered piperidine derivative free radical scavenger is provided to achieve a concentration of hindered piperidine derivative free radical scavenger of 0.1 weight percent (wt. %) or greater, preferably 0.5 wt. % or greater, 1.0 wt. % or greater, 2.0 wt. % or greater, 3.0 wt. % or greater, 4.0 wt. % or greater, or even 5.0 wt. % or greater, based on the combined weight of the hindered piperidine derivative free radical scavenger and scavenging fluid, while typically 10 wt. % or less, 9 wt. % or less, 8 wt. % or less, 7 wt. % or less, 6 wt. % or less, or even 5 wt. % or less.

[0031] The trapping fluid can provide a protective medium for the storage and controlled passivation of hindered piperidine derivative-functionalized silicon nanoparticles. Silicon nanoparticles can rapidly degrade when directly exposed to moist air. However, moisture and oxygen slowly penetrate the trapping fluid and react with the silicon nanoparticle surface to form oxides. The oxide layer can be generated in a controlled manner by exposing the silicon nanoparticles in the trapping fluid to moist air at a controlled temperature. Once passivated, the silicon nanoparticles can be isolated from the trapping fluid without the risk of rapid decomposition. One method for passivating silicon nanoparticles in a trapping fluid is to subject the nanoparticles and trapping fluid to a temperature preferably above 25°C, typically at or near 65°C, in air (preferably at 85% relative humidity) for a certain period of time. The passivation process generally takes 12 to 72 hours or more, and in some cases can take 168 hours or longer without the hindered piperidine derivative free radical scavenger. However, it has been discovered that passivation of hindered piperidine derivative-functionalized silicon nanoparticles can occur within just a few hours. Determine when passivation has occurred by examining the photoluminescence emission intensity of the particles in a Fluorolog FL-3 instrument using excitation and emission slit widths of 2 nm and an integration time of 0.1 sec / nm. Excite the particles with light of 365 nm wavelength. Passivation is complete when the peak emission wavelength no longer changes significantly. The peak emission intensity is typically 60 x 10 at the peak emission wavelength when measured in a Fluorolog FL-3 instrument. 6 When the change in peak emission wavelength is less than 10 nm per day, the peak emission wavelength is considered to stop changing significantly and passivation is considered to be complete.

[0032] The hindered piperidine derivative-functionalized silicon nanoparticles can be isolated from the capture fluid, preferably after passivation. Methods for isolating the hindered piperidine derivative-functionalized silicon nanoparticles from the capture fluid include, for example, a combination of filtration and decantation with centrifugation. If the hindered piperidine derivative-functionalized silicon nanoparticles are passivated, they can be isolated from the capture fluid in air. If the hindered piperidine derivative-functionalized silicon nanoparticles are not passivated before isolation from the capture fluid, they should be isolated in an inert atmosphere, such as dry nitrogen or a dry noble gas atmosphere.

[0033] It is possible to recycle or reuse the capture fluid in the VHFLPP process. That is, nanoparticles can be collected in the same capture fluid for multiple runs of the VHFLPP process. Typically, the nanoparticles are isolated from the capture fluid before reusing the capture fluid, but this is not necessary. For example, nanoparticles can be collected in the capture fluid, passivated, and then isolated from the capture fluid (e.g., by filtration or centrifugation). The remaining capture fluid can then be used in a subsequent VHFLPP process.

[0034] The VHFLPP process can be performed as a continuous or pulsed process. A continuous VHFLPP process uses a constant, continuous radio frequency (RF) signal 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. The amplitude-modulated signal typically operates between 1 and 50 kHz as a square wave wave function multiplied by a continuous VHF sinusoidal waveform. The advantages of the pulsed process include using pulse energy to control the size of the nanoparticles produced by controlling the residence time the nanoparticle precursor is exposed to the high-power plasma as it passes through the VHF glow discharge. In a continuous VHF plasma process (non-modulated), nanoparticle size can be controlled by the concentration of the nanoparticle precursor—the silicon concentration in the case of silicon nanoparticles—and the residence time of the precursor through the VHF plasma. [Example]

[0035] In the following examples, the following VHFLPP settings and procedures are used:

[0036] Configuring VHFLPP Figure 1 shows a schematic diagram of the VHFLPP set up for this example. Samples are prepared in an inert environment, such as a nitrogen-purged glovebox 1. Connected to the glovebox 1 is a vacuum loadlock 2. Opening the vacuum loadlock seal 2a between the gas-purged glovebox and the vacuum loadlock allows samples to be transferred from the inert-gas-purged glovebox to the vacuum loadlock. A roughing pump 2b is in fluid communication with the vacuum loadlock. A rack and pinion arm 2c allows items to be transferred between the loadlock 2 and a main capture chamber 4. The vacuum loadlock is separated from the main capture chamber 4 by a gate valve 3. When gate valve 3 is open, the vacuum loadlock is in fluid communication with the main capture chamber. When gate valve 3 is closed, the vacuum loadlock 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 connected to a roughing pump (Ebara 1000 with a pumping speed of 5,000 liters / min). The main capture 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 with an inner diameter of 7 millimeters, an outer diameter of 9.6 millimeters, and a length of 23 centimeters. Extending through the seal into the main capture chamber is the trapped fluid reservoir holder 7, which holds the trapped fluid reservoir 6. The trapped fluid reservoir holder allows the user to position the trapped fluid reservoir at a desired distance from the dielectric discharge tube orifice. The dielectric discharge tube orifice can be moved toward or away from the dielectric discharge tube orifice to allow for positioning at a greater distance. During operation of the VHFLPP process, a gas flow comprising a precursor gas(es) and an inert carrier gas(es) enters the inlet end 5a of the dielectric discharge tube 5, passes through the dielectric discharge tube, and enters the main collection chamber 4 through the dielectric discharge tube orifice 5b. The diameter of the dielectric tube orifice is desirably adjustable so that the pressure ratio of (discharge tube pressure) / (main collection chamber pressure) is 500 or greater.The dielectric discharge tube has two electrodes 8a and 8b of a double-ring copper electrode 8 around it.

[0037] Operation of the VHFLPP process Silicon nanoparticles are produced using the VHFLPP process and the setup described above in this specification as follows: In a glove box, a trapping fluid is placed in a trapping fluid reservoir, and octadecene or a hindered piperidine derivative is placed in the trapping fluid, as shown for the specific example. The trapping fluid is transferred into the load lock through the load lock barrier. The load lock is sealed and evacuated to a pressure of less than 2.67 Pa using a roughing pump. A high vacuum pump is used to pump 6.67 x 10 -5 The main capture chamber is evacuated to a pressure of less than 6.67 x 10 Pa. Gate valve 3 is opened, and rack-and-pinion transfer arm 2c is used to transfer the capture fluid reservoir from the load lock onto the capture fluid reservoir holder 7 in the main capture chamber. Gate valve 3 is closed, and the pressure in the main capture chamber is reduced to 6.67 x 10 Pa. -5 Lower the pressure to below 1 Pa. Move the trapping fluid reservoir holder to position the trapping fluid reservoir the desired distance below the dielectric discharge tube orifice. Rotate the trapping fluid reservoir holder (and therefore the trapping fluid reservoir) at a speed of 12 revolutions per minute.

[0038] A gas stream is supplied to end 5a of the dielectric discharge tube by metering the desired gases. Each example below specifies the composition of the desired gases that make up the stream and their relative flow rates. The gases are supplied together to end 5a of the dielectric discharge tube to create a gas flow through the tube.

[0039] Ultra-high frequency plasma 9 is generated in the dielectric discharge tube between electrodes 8a and 8b by applying a sine wave to the electrodes while flowing a gas stream through the dielectric discharge tube. The sine wave is generated using a Tektronix AFG3252 function generator and an Electronic and Innovation 3200L Class A radio frequency amplifier connected to the electrodes. The sine wave between the electrodes generates a capacitively coupled ultra-high frequency (frequency between 90 and 500 megahertz) plasma in the dielectric discharge tube. The frequency source is adjusted to provide maximum power coupled to the plasma while minimizing the drive amplitude of the sine wave. The coupled power density of the plasma is 130 watts per square centimeter (W / cm). 2 ) is greater than.

[0040] Silicon nanoparticles are formed in the plasma, exit the dielectric discharge tube through orifice 5b, and are collected in the trapping fluid in the trapping fluid reservoir.

[0041] Once the silicon nanoparticles have been collected, the transfer arm is used to return the trapping fluid reservoir containing the silicon nanoparticles to the inert glovebox through the load lock. The trapping fluid and silicon nanoparticles are transferred to a glass vial and sealed with a polytetrafluoroethylene cap and electrical tape. The glass vial is removed from the glovebox and sonicated for 30 minutes using a benchtop ultrasonic bath (40 kHz) to help disperse any agglomerated particles.

[0042] The silicon nanoparticles are passivated by placing the silicon nanoparticle-coated solid substrate while in the trapping fluid at an aging temperature and humidity as reported herein below for an aging time.

[0043] Photoluminescence (PL) spectrum of the sample Silicon nanoparticles emit light when exposed to ultraviolet radiation only if they have a particle size in the 1-10 nanometer range. Therefore, observing the emission is one way to confirm that the silicon nanoparticles are silicon quantum dots. The following procedure is used to detect and characterize the emission for the samples described herein below.

[0044] Samples were prepared by adding a portion of the silicon nanoparticles in the trapping fluid, in the form of a dispersion, to a poly(methyl methacrylate) cuvette with a 1-centimeter (cm) path length. The cuvette was placed in the sample holder of a Horiba Fluorolog-3 spectrophotometer (FL3-22), which contained a 450-watt xenon excitation lamp that irradiated the sample after passing through a dual-grating (1200 grooves / mm with a 330-nm blaze) excitation spectrometer to select the excitation wavelength. Excitation photons entered the sample compartment and were directed toward the sample. The sample compartment had forward-facing optics for measuring the sample's photoluminescence emission at approximately 45 degrees relative to the excitation photons. Emission photons were directed into a dual-grating (1200 grooves / mm with a 500-nm blaze) emission spectrometer and projected onto a Hamamatsu R928P photomultiplier tube. The emission signal was corrected for the grating and detector specifications (from the vendor). The excitation and emission slits were 2 nm, and the integration time was 100 ms / nm. Photoluminescence emission and excitation spectra are measured using an FL3-22 instrument. The PL spectrum is typically measured using an excitation wavelength of 365 nm and scanning the emission wavelength. The emission wavelength is set constant (e.g., 700 nm), and the excitation wavelength is scanned from 280 to 550 nm while measuring the signal intensity at the selected emission wavelength. The photoluminescent excitation (PLE) spectrum is measured.

[0045] Sample absorbance spectrum The absorbance of the sample is measured as follows. In Examples 1, 2, and 3, a dual-beam spectrophotometer, Shimadzu UV2600i, was used. A 1-cm path-length poly(methacrylate) cuvette containing a sample dispersion of silicon nanoparticles in a trapping fluid was placed in the path of one beam (sample beam). A 1-cm path-length poly(methacrylate) cuvette containing only the trapping fluid was placed in the path of the other beam (reference beam). Deuterium and tungsten-halogen traps excite the sample and reference over wavelengths from 280 to 800 nm with a 1-nm bandwidth. Transmitted light was focused onto a silicon diode using Czerny-Turner optics. The absorption of excitation photons by the nanoparticles in the sample at each wavelength was plotted to obtain the absorbance spectrum of the sample.

[0046] For Examples 4-8, absorbance spectra are collected in a similar manner using a Shimadzu UV-1800 spectrophotometer.

[0047] Absorbance spectra were not measured for Examples 9-12, but can be collected in a similar manner as for any of the other Examples.

[0048] sample Prepare the following samples according to the procedure above and the parameters in the table below. Sample characterization is included in the table below. Table 1 lists the elements used to make each sample.

[0049] [Table 1]

[0050] Table 2 lists the parameters for preparing the samples. Table 3 identifies additional parameters used in preparing the samples. A brief description of each sample is provided before Table 2.

[0051] 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.

[0052] Sample 2: The capture fluid is a light mineral oil containing 5 wt% octadecene. Sample 2 is a comparative example to Sample 3.

[0053] Samples 3 and 10: The capture fluid is a light mineral oil containing 5 wt. % HPD 1. Sample 3 is prepared under similar conditions as Samples 1 and 2. Sample 10 is half the mass of Sample 9, and 5 wt. % HDP 1 was added before exposure to air, but after Sample 9 was sonicated at 40 kilohertz for 10 minutes.

[0054] Samples 4 and 5: The capture fluid is a light mineral oil containing 5 wt. % octadecene. The sample is sonicated at 40 kHz for 20 minutes and split into two samples, one designated Sample 4 and one designated Sample 5, before passivation. Sample 4 is passivated. 5 wt. % HPD 1 is added to Sample 5, and Sample 5 is sonicated for an additional 30 minutes before passivation.

[0055] Sample 6: The capture fluid for Sample 6 is a light mineral oil containing 5 wt% HPD 2. This sample has similar processing conditions as Sample 4 (comparative).

[0056] Samples 7 and 8: For Sample 7, the capture fluid is a light mineral oil containing 5 wt% HPD 1. The sample is sonicated at 40 kilohertz for 20 minutes and split into two samples, one designated Sample 7 and one designated Sample 8. Sample 7 is passivated for 3 days at 25°C and 50% relative humidity. Sample 8 is passivated for 3 days at 60°C and 85% relative humidity. The difference between Sample 7 and Sample 8 is the temperature and relative humidity for passivation.

[0057] [Table 2]

[0058] [Table 3] * mVpp = millivolts peak-to-peak

[0059] Table 4 contains a summary of the photoluminescence properties of the samples. Table 4 includes the properties of each example measured after different passivation aging times. The terms in Table 4 are as follows:

[0060] PL λ peak: the peak wavelength of the maximum emission photoluminescence intensity of silicon nanoparticles measured after passivation during the aging time when excited at 365 nm.

[0061] λ FWHM: full width at half maximum of the emitted photoluminescence of silicon nanoparticles in the trapping fluid when excited at 365 nm, measured after passivation during the aging period.

[0062] PL emission intensity (×10 6 Counts): Peak photoluminescence intensity of silicon nanoparticles in the trapping fluid measured after passivation during an aging period when excited at 365 nm in the PL1 peak (excitation and emission monochromator slit width of 2 nm and integration time of 0.1 s / nm).

[0063] Eg: Optical band gap from peak photoluminescence emission photoluminescence spectrum of silicon nanoparticles in the trapping fluid measured after passivation during the aging time when excited at 365 nm.

[0064] σEg: standard deviation of the optical band gap from the peak photoluminescence emission spectrum of silicon nanoparticles in the trapping fluid measured after passivation during the aging time when excited at 365 nm.

[0065] [Table 4]

[0066] The data in Table 4 reveal that the hindered piperidine derivatives induce a dramatic blue shift in the photoluminescence of the silicon quantum dots they coat. Additional information about the samples is evident from the spectra in Figures 2-12.

[0067] Figure 2 shows the photoluminescence emission (PL) spectra of Samples 1 (Si nanoparticles deposited directly in mineral oil), 2 (Si nanoparticles deposited directly in octadecene (5 wt%) in mineral oil (MO)), and 3 (Si nanoparticles deposited directly in HPD 1 (5 wt%) in mineral oil (MO)) when excited at 365 nm with different passivation / aging times. As can be seen in Figure 1, silicon nanoparticles deposited in mineral oil containing HPD 1 molecules have a significant blue shift in emission after 1 day of passivation / aging and increase in emission intensity much more rapidly than samples trapped in mineral oil (Sample 1) or octadecene in mineral oil (Sample 2). The PL intensity achieved by the sample trapped in HPD 1 reaches a maximum after 3 days of passivation / aging, while silicon nanoparticles trapped in mineral oil alone require 7 days of passivation / aging to reach similar PL values.

[0068] Figure 3 shows 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 scanning the excitation wavelength while recording the intensity values ​​of the emission detector. Figure 3 shows that the PLE of HDP 1-treated silicon nanoparticles is significantly altered compared to particles treated with mineral oil or octadecene in mineral oil.

[0069] Figure 4 shows UV-Vis absorbance spectra as a function of passivation / aging time for three samples of silicon nanoparticles trapped and passivated in mineral oil (Sample 1), octadecene (Sample 2), and HPD 1 (Sample 3). These spectra reveal a large deviation in absorbance from particles passivated / aged with HPD 1 compared to the other fluids.

[0070] Figure 5 shows the photoluminescence (PL) spectra of silicon nanoparticles trapped in 5 wt% octadecene in mineral oil (Sample 4), half of Sample 4 to which 5 wt% HPD 1 had been added before exposure to air (Sample 5), and 5 wt% HPD 2 in mineral oil (Sample 6), all of which were passivated / aged at 60 °C and 85% RH for 3 days. The emission spectra of the two samples containing the hindered piperidine derivative (Sample 5 and Sample 6) were blue-shifted compared to the spectrum of the sample without the hindered piperidine derivative (Sample 4), and the emission intensity after 3 days was at least two times greater with the hindered piperidine derivative than with octadecene. All samples were excited at 365 nm with 2 nm slit widths and 0.1 s / nm integration times for the excitation and emission monochromators.

[0071] Figure 6 shows photoluminescence excitation (PLE) spectra for the same samples shown in Figure 5 (Samples 4, 5, and 6). For each of these spectra, the emission monochromator was set to the peak emission wavelength, and then the excitation wavelength was swept while recording the PL emission intensity (displayed as PLE intensity on the y-axis of Figure 6). Both the emission and excitation monochromator slit widths were set to 2 nm, and the integration time was 0.1 s / nm for all spectra. As shown in Figure 5, it is clear that exposing silicon nanoparticles to the hindered piperidine derivative before exposure to air dramatically increases the PLE intensity after just a few days of passivation / aging compared to unexposed silicon nanoparticles.

[0072] Figure 7 shows the UV-Vis absorbance spectra of silicon nanoparticles trapped in octadecene (Sample 4) passivated / aged at 60 °C and 85% RH for 1, 2, and 3 days, and then trapped in octadecene to which HPD 1 was added before being exposed to air (Sample 5). The absorbance of the nanoparticles exposed to HPD 1 blue-shifts much more rapidly than the nanoparticles treated with octadecene alone.

[0073] Figure 8 shows the photoluminescence emission spectra (PL) for silicon nanoparticles trapped in 5 wt% HPD 1 in mineral oil and then exposed to air (Sample 7), and for silicon nanoparticles subjected to a passivation / aging process at 60 °C and 85% RH (Sample 8). Sample 8 was Sample 7 divided in half by mass before exposure to air. The slit widths of the emission and excitation monochromators were set to 2 nm, and the integration time was 0.1 s / nm for each spectrum. The emission spectra reveal that passivation / aging of the HPD 1 silicon nanoparticles at high temperature and humidity accelerates the photoluminescence emission intensity of the sample.

[0074] Figure 9 shows the photoluminescence excitation (PLE) spectra of the same samples (Samples 7 and 8) shown in Figure 8. For each of these spectra, the emission monochromator was set to the peak emission wavelength, and then the excitation wavelength was swept while recording the PL emission intensity (displayed as PLE intensity on the y-axis of Figure 8). Both the emission and excitation monochromator slit widths were set to 2 nm, and the integration time was 0.1 s / nm for all spectra. It is clear from Figure 8 that exposing the hindered piperidine derivative-treated silicon nanoparticles to high temperature and humidity conditions (the passivation / aging process) results in a much more rapid increase in the photoluminescence properties of the nanoparticles.

[0075] Figure 10 shows the UV-Vis absorbance spectra of silicon nanoparticles trapped in 5 wt% HPD 1 in mineral oil and split in half by mass to undergo room temperature aging (Sample 7), and silicon nanoparticles passivated / aged at 60 °C and 85% RH (Sample 8) over 1, 2, and 3 days. The absorbance of the passivated / aged nanoparticles shifts significantly to the blue over 3 days compared to nanoparticles exposed to room temperature and humidity conditions.

[0076] Figure 11 shows the photoluminescence emission spectra (PL) of silicon nanoparticles trapped in mineral oil (Sample 9) and then split in half by mass and trapped in a fresh sample with 5 wt% HPD1 added before air exposure (Sample 10). Both samples were then passivated / aged at 60 °C and 85% RH for up to 7 days (Sample 9) and 10 days (Sample 10). The slit widths of the emission and excitation monochromators were set to 2 nm, and the integration time was 0.1 s / nm for each spectrum. It is clear that adding HDP1 molecules to silicon nanoparticles trapped in mineral oil before exposing the sample to air results in an initial blue shift in the emission spectrum and a much more rapid increase in emission intensity compared to samples not exposed to the hindered piperidine derivative. This demonstrates the feasibility of adding a treatment agent to silicon nanoparticles before air exposure, resulting in optical properties similar to those of nanoparticles deposited directly in a trapping fluid containing the treatment molecule.

[0077] Figure 12 shows the photoluminescence excitation spectra (PLE) of Samples 9 and 10. For each of these spectra, the emission monochromator was set to the peak emission wavelength, and then the excitation wavelength was swept while the PL emission intensity (displayed as PLE intensity on the y-axis of Figure 12) was recorded. Both the emission and excitation monochromator slit widths were set to 2 nm, and the integration time was 0.1 s / nm for all spectra.

Claims

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

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

3. 3. The composition comprising silicon nanoparticles of claim 1 or claim 2, wherein the silicon nanoparticles do not contain aromatic conjugation between the hindered piperidine derivative free radical scavenger and the silicon nanoparticles.

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

5. The composition comprising silicon nanoparticles according to any one of claims 1 to 4, wherein the free radical scavenger is one or any combination of two or more selected from the group consisting of bis(1,2,2,6,6-pentamethyl-4-piperidyl)sebacate, bis(1-octyl-2,2,6,6-tetramethyl-4-piperidyl)sebacate, bis(2,2,6,6-tetramethyl-4-piperidyl)sebacate, and 4-hydroxy-2,2,6,6-tetramethylpiperidine 1-oxylbenzoate.

6. 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. 1. A process for making silicon nanoparticles having a hindered piperidine derivative free radical scavenger on a surface of the silicon nanoparticles, the process comprising producing the silicon nanoparticles using a VHFLPP process that collects the silicon nanoparticles in a capture fluid as they are made, 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. 8. The process of claim 7, wherein the free radical scavenger is one or any combination of two or more selected from the group consisting of bis(1,2,2,6,6-pentamethyl-4-piperidyl)sebacate, bis(1-octyl-2,2,6,6-tetramethyl-4-piperidyl)sebacate, bis(2,2,6,6-tetramethyl-4-piperidyl)sebacate, and 4-hydroxy-2,2,6,6-tetramethylpiperidine 1-oxylbenzoate.

9. 9. The process of claim 7 or claim 8, wherein the hindered piperidine derivative free radical scavenger is non-aromatic.

10. 10. The process of any one of claims 7 to 9, wherein the process further comprises passivating the silicon nanoparticles in the trapping fluid by exposing the trapping fluid containing the silicon nanoparticles to a moisture-containing atmosphere, optionally at a temperature above 25°C, for a period of time to produce passivated silicon nanoparticles having surface-bound hindered piperidine derivative free radical scavengers.

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