Direct deposition of nanoparticles onto solid substrates in a trapped fluid

Abstract

The method for directly coating silicon nanoparticles onto a solid substrate is further characterized by using a VHFLPP process to collect the silicon nanoparticles in a capture fluid as they are made, and immersing the solid substrate in the capture fluid while collecting the silicon nanoparticles.

Description

[Technical Field]

[0001] The present invention relates to a method for depositing nanoparticles onto a solid substrate in a trapping fluid during the production of the nanoparticles. [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, which occur when the nanoparticle diameter is smaller than the exciton radius, 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] There are applications where it is desirable to have silicon nanoparticles coating the surface of an article. For example, displays and photovoltaics often benefit from having quantum dot material (such as silicon quantum dots) coating the surface of a glass substrate.

[0006] A challenge in obtaining such articles is that a binder is typically required that is applied to the substrate and / or nanoparticles to adhere the nanoparticles to the substrate, and the binder can interfere with the performance properties of the resulting coated substrate, such as preventing light transmission through the quantum dot coated glass substrate.

[0007] Another challenge is efficiently coating multiple surfaces of a three-dimensional substrate. In producing silicon nanoparticles, it is possible to deposit silicon nanoparticles directly onto a solid substrate surface from a nanoparticle beam. However, this process is line-of-sight deposition, in which only the top surface exposed to the nanoparticle beam is coated with silicon nanoparticles, while the side surfaces of the substrate remain essentially uncoated, requiring subsequent passage of the side surfaces under the nanoparticle beam to coat them. It would be desirable to be able to coat multiple, preferably all, surfaces of a substrate with silicon nanoparticles at once.

[0008] Yet another challenge is to efficiently passivate silicon nanoparticles as they are coated onto a substrate. Unpassivated silicon nanoparticles are unstable to exposure to oxygen and moisture and therefore must be maintained in an inert atmosphere until passivated. It would be desirable to have a process that allows for coating a solid substrate with silicon nanoparticles from a nanoparticle beam directly as the silicon nanoparticles are made, and further allows for easy handling of the silicon nanoparticle-coated substrate without concern for maintaining it in an inert atmosphere until passivated.

[0009] It would advance the art of preparing solid substrates coated with silicon nanoparticles to provide a process that (a) coats a solid substrate with silicon nanoparticles from a nanoparticle beam, resulting in more uniform silicon nanoparticle deposition than is achieved by directly exposing the solid substrate to a nanoparticle beam, and (b) coats the surface of the solid substrate without requiring a separate step of applying an adhesion promoter to the substrate, ideally without requiring any adhesion promoter at all. Furthermore, it would be desirable if the method (c) could simultaneously coat multiple surfaces of the solid substrate with quantum dots from the nanoparticle beam, including surfaces other than the one directly exposed to the nanoparticle beam containing silicon nanoparticles, and / or (d) allowed for direct coating of the solid substrate with silicon nanoparticles from the nanoparticle beam as the silicon nanoparticles are produced, and further allowed for easy handling of the silicon nanoparticle-coated substrate without concern for maintaining it under an inert atmosphere until passivated. Summary of the Invention

[0010] The present invention provides a process for applying nanoparticles onto a solid substrate that (a) coats a solid substrate with silicon nanoparticles from a nanoparticle beam, resulting in more uniform silicon nanoparticles than would be achieved by directly exposing the solid substrate to a nanoparticle beam, and (b) coats the surface of the solid substrate without requiring a separate step of applying an adhesion promoter to the substrate, ideally without requiring any adhesion promoter at all. Furthermore, process (c) allows for simultaneous coating of multiple surfaces of the solid substrate with quantum dots from the nanoparticle beam, including surfaces other than the one directly exposed to the nanoparticle beam containing silicon nanoparticles, and / or (d) allows for direct coating of the solid substrate with silicon nanoparticles from the nanoparticle beam as the silicon nanoparticles are made, and further allows for easy handling of the silicon nanoparticle-coated substrate without concern for maintaining it under an inert atmosphere until passivated.

[0011] The present invention is the result of the discovery that when a solid substrate is placed in a trapping fluid of a very high frequency, low pressure plasma (VHFLPP) process, silicon nanoparticles disperse in the trapping fluid and coat multiple surfaces of the solid substrate, even beyond the surface directly facing the nanoparticle beam impinging on the trapping fluid. Such placement of silicon nanoparticles on the solid substrate surface is continuous with the process of creating silicon nanoparticles, thereby eliminating the need for a separate step of creating silicon nanoparticles and then disposing them on the solid substrate surface. The newly created silicon nanoparticles tend to coat the solid substrate surface without the need for a separate binder. Indeed, the newly created silicon nanoparticles have reactive sites on their surface that can react with functional groups on some solid substrate surfaces, thereby chemically bonding the nanoparticles to the solid substrate surface. For example, Si-OH functional groups on the surface of a glass substrate can react with newly created silicon nanoparticles to bond them to the glass substrate surface. Furthermore, the trapping fluid protects the silicon nanoparticles on the substrate from air and moisture, allowing handling of the freshly coated substrate without providing an inert atmosphere beyond the trapping fluid the coated substrate was created in. The silicon nanoparticles can then be passivated directly in the trapping fluid, making the silicon nanoparticle-coated substrate stable against removal from the trapping fluid.

[0012] It is noteworthy that nanoparticle beams containing silicon nanoparticles can be used to directly coat solid substrates in a VHFLPP process without immersing the solid substrate in a trapping fluid. However, as shown in the Examples section below, the result is a less uniform coating than that achieved by immersing the solid substrate in a trapping fluid. Furthermore, the coated solid substrate must then be immersed in a trapping fluid or maintained in an inert atmosphere until the silicon nanoparticles are passivated or decompose.

[0013] In a first aspect, the present invention is a method for directly coating silicon nanoparticles onto a solid substrate, the method comprising a VHFLPP process of collecting silicon nanoparticles in a capture fluid as the silicon nanoparticles are made, the process being further characterized by immersing the solid substrate in the capture fluid during collection of the silicon nanoparticles.

[0014] The methods of the present invention are useful for producing solid substrates coated with silicon nanoparticles, including silicon quantum dots, that are useful for the further manufacture of articles such as optical displays, photovoltaics, and other photoactive articles. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a schematic diagram of the VHFLPP setup used to prepare the examples herein. DETAILED DESCRIPTION OF THE INVENTION

[0016] Products identified by trade names refer to compositions available under those trade names as of the priority date of this document.

[0017] "Multiple" means two or more. "And / or" means "and, or as an alternative." All ranges are inclusive of the endpoints unless otherwise indicated.

[0018] "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.

[0019] "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.

[0020] "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.

[0021] "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.

[0022] The present invention is a method for directly depositing silicon nanoparticles onto a solid substrate in the trapping fluid of a very high frequency, low pressure plasma (VHFLPP) process. VHFLPP is a commonly known process for producing nanoparticles, and in this 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.

[0023] 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).

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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 preferably non-aqueous. Examples of suitable capture fluids include mineral oil, silicone oil (e.g., polydimethylsiloxane (PDMS), phenylmethyl-dimethylcyclosiloxane, tetramethyltetraphenyltrisiloxane, and pentaphenyltrimethyltrisiloxane), fluorocarbon, and alkylene oxide oil. 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.

[0029] The trapping fluid can provide a protective medium for storing and controlling passivation of the nanoparticles after they are created. 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, so an oxide layer can be formed 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 risk of rapid decomposition. One method for passivating silicon nanoparticles in a trapping fluid is to subject the nanoparticles and trapping fluid to temperatures greater than 25°C, typically at or near 65°C, in air (preferably at 85% relative humidity) for a period of time, typically 12 to 72 hours; the period can be even longer than 72 hours. In some instances, this period can be 168 hours or longer. Longer periods can result in a greater degree of oxidation of the silicon nanoparticle surface, especially in fluids with low oxygen and moisture permeability.

[0030] The capture fluid can contain additives dissolved or dispersed therein. Desirable additives can include surface modifiers that attach to the surface of the nanoparticles when they are collected. The surface modifier can make the nanoparticles more compatible with the capture fluid or some other medium with which the nanoparticles need to be combined, can make the surface of the nanoparticles reactive for further chemical reaction, or can impart both compatibility and reactivity. Examples of additives that can be included in the capture fluid include hydrocarbons (such as 1-alkenes) to aid in dispersing nanoparticles in hydrophobic media, oligoglycols (such as allyl ethers) to aid in dispersing nanoparticles in hydrophilic media, terminal olefins containing functional groups such as alcohols, carboxylates, and amines, as well as protected versions of these for post-passivation conversion and extraction, and fluorocarbons with terminal olefins to aid in dispersing nanoparticles in fluoropolymers.

[0031] 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.

[0032] 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. 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.

[0033] The method of the present invention comprises collecting silicon nanoparticles in a capture fluid as they are produced, and immersing a solid substrate in the capture fluid while collecting the silicon nanoparticles. A surprising discovery made in the present invention is that the solid substrate can be present in the capture fluid during the VHFLPP process, resulting in deposition of nanoparticles from the capture fluid onto the surface of the solid substrate. The capture fluid provides a medium in which the newly produced silicon nanoparticles can disperse and then adhere to multiple surfaces of the solid substrate in the capture fluid.

[0034] The solid substrate is solid at 25 degrees Celsius (°C). The solid substrate remains solid when in the trapping fluid. The solid substrate can be a single item such as a film, block, plate, ball, pellet, or any other shaped object. Alternatively, the solid substrate can be one of multiple solid items (substrates) in the trapping fluid, such as multiple pellets, granules, powder particles, or any shaped item. That is, the trapping fluid can contain multiple solid substrates at once, or it can contain a single solid substrate. When multiple solid items (substrates) are present in the trapping fluid, nanoparticles tend to deposit on the surface of more than one, typically all, of the solid items (substrates) during the method of the present invention. The method of the present invention is particularly useful for simultaneously disposing nanoparticles on the surface of multiple solid items.

[0035] In the broadest scope of the present invention, the solid substrate can be any composition, provided that it is solid at 25°C when in the capture fluid of the process. For example, the solid substrate can be or include glass, plastic, ceramic, metal, carbon, or salt. Glass refers to non-crystalline, amorphous solid materials, including volcanic and silicate glasses, such as soda-lime glass, borosilicate glass, lead glass, and aluminosilicate glass. Plastic refers to thermoplastic and / or thermoset polymeric materials, including polyethylene (including linear low-density polyethylene and low-density polyethylene), polypropylene, polystyrene, polyurethane, polyacrylic, polyester, polycarbonate, and polyimide. Ceramics refer to materials such as boron nitride, alumina, aluminum nitride, ceria, silica, titania, and zirconia. Metals include iron, nickel, cobalt, copper, chromium, manganese, and vanadium.

[0036] Any one or a combination of two or more variations of the VHFLPP process described above can be used in the present method. For example, it may be desirable to agitate the trapping fluid and / or rotate the trapping fluid reservoir during collection of the silicon nanoparticles. The trapping fluid can be any of the trapping fluids described above, including silicone oil or mineral oil. It may be desirable to include an additive dispersed in the trapping fluid. The additive can modify the surface of the silicon nanoparticles and / or the surface of the solid substrate. For example, the trapping fluid can contain a compatibilizing agent that binds to the surface of the silicon nanoparticles as they enter the trapping fluid, increasing their compatibility and / or reactivity with the solid substrate. Desirably, the silicon nanoparticles are silicon quantum dots. The method can include passivating the silicon nanoparticles. As described above, passivation desirably involves subjecting the nanoparticles in the trapping fluid to a temperature greater than 25°C, typically at or near 65°C, in air (preferably at a relative humidity of 85%) for a period of time, typically 12 to 168 hours. An oxide coating is formed on the nanoparticles in the trapping fluid during the passivation process, and the oxide layer protects the silicon nanoparticles from destructive rapid oxidation upon removal from the trapping fluid and exposure to air. Passivation of the silicon nanoparticles occurs even while the silicon nanoparticles are on the surface of a solid substrate.

[0037] The method of the present invention can include isolating the silicon nanoparticle-coated solid substrate formed in the capture fluid of the method from the capture fluid. After passivation of the silicon nanoparticles, separating the silicon nanoparticle-coated solid substrate from the capture fluid can be done in air without special precautions. If the silicon nanoparticles are not passivated in the capture fluid, isolation of the silicon nanoparticle-coated solid substrate should be done in an inert atmosphere with controlled amounts of oxygen and moisture to avoid catastrophic oxidation of the silicon nanoparticles. The inert atmosphere may be moisture- and oxygen-free, or may contain just enough to allow slow oxidation of the silicon nanoparticle surface and passivate the silicon nanoparticles in a controlled manner. In the broadest scope of the present invention, isolation of the silicon nanoparticle-coated solid substrate can be done by any means, such as decantation, filtration, and / or physically removing the silicon nanoparticle-coated solid substrate from the capture fluid.

[0038] The method of the present invention provides a solid substrate coated with silicon nanoparticles. A silicon nanoparticle-coated solid substrate is a solid substrate having silicon nanoparticles attached to its surface. This method generally provides a coating on multiple surfaces (or a larger area of ​​the substrate's surface) rather than just one side of the solid substrate directed toward the silicon nanoparticle-containing nanoparticle beam. In this way, or in addition, the silicon nanoparticle coating tends to be more uniform across the entire surface of the solid substrate than with deposition methods other than a trapping fluid. The nanoparticles are typically dispersed to some extent in a trapping fluid before coating the solid substrate, which not only allows for coating of all sides of the solid substrate but also facilitates penetration into cavities in the solid substrate to coat the interior surfaces. [Example]

[0039] In the following examples, the following VHFLPP settings and procedures are used:

[0040] Configuring VHFLPP Figure 1 shows a schematic diagram of the VHFLPP setup for this example. Samples are prepared in an inert environment, such as a nitrogen-purged glovebox 1. A vacuum loadlock 2 is connected to the glovebox 1. 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 a turbomolecular pump (pumping speed 600 liters / second) assisted by a roughing pump (Ebara S50 semiconductor pump with a pumping speed of 5,000 liters / minute). The main capture chamber is also in fluid communication with the upstream dielectric discharge tube 5 through 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 into the main capture chamber through the seal is the trapped fluid reservoir holder 7, which holds the trapped fluid reservoir 6. The trapped fluid reservoir holder can be moved toward or away from the dielectric discharge tube orifice to allow the user to position the trapped fluid reservoir at a desired distance from the dielectric discharge tube orifice. During operation of the VHFLPP process, a gas stream comprising precursor gas(es) and 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 preferably 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.

[0041] Operation of the VHFLPP process Silicon nanoparticles are fabricated 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 a solid substrate 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 below 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.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] The silicon nanoparticle-coated solid substrate is isolated from the transfer fluid and passivated. For coated pellets and powders, a syringe filter (0.22 micrometer polytetrafluoroethylene filter, available from CELLTREAT under product code 229778) with a 30 milliliter syringe is used to isolate the silicon nanoparticle-coated substrate. The silicon nanoparticle-coated substrate and capture fluid are loaded into the syringe, and while holding the silicon nanoparticle-coated substrate, the plunger is depressed to drive the fluid through the syringe filter. The silicone nanoparticle-coated substrate is rinsed with toluene to remove residual capture fluid, and then dried at 25-110°C for several hours, optionally under a flow of inert gas. For larger objects, such as glass sheets, the silicon nanoparticle-coated substrate is removed from the capture fluid using tweezers or a spatula, rinsed with toluene, and optionally dried at 25-110°C for several hours, optionally under a flow of inert gas.

[0047] Identification of silicon nanoparticles by photoluminescence Silicon nanoparticles emit light when exposed to ultraviolet radiation only if they have a particle size in the 1-10 nanometer range, so observing the emission is one way to confirm that the silicon nanoparticles are silicon quantum dots.

[0048] In a dark room or dark space, the silicon nanoparticle-coated substrate sample is exposed to ultraviolet light using a handheld UVA LED flashlight (Waveform Lighting's realUV 5-watt LED flashlight) to expose the silicon nanoparticles to 365-nanometer light. The flashlight is held approximately 0.3-0.5 meters from the silicon nanoparticle-coated substrate sample. The presence or absence of luminescence is assessed by visually observing the luminescence from the silicon nanoparticle-coated substrate. Observing the luminescence confirms the presence of silicon quantum dots. Notably, all of the samples described below exhibit bright luminescence, thereby confirming that the solid substrate is coated with silicon quantum dots.

[0049] 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.

[0050] [Table 1]

[0051] Each Example (Ex) uses a solid substrate identified below in the capture fluid: Comparative Example (Comp Ex) A uses only a solid substrate in the capture fluid reservoir, and no capture fluid.

[0052] Glass solid substrate Example (Ex) 1 - Glass Beads A capture fluid consisting of 5.7 grams (g) of glass beads (silica beads, 30-40 course, Potters Industries) in 6 g of capture fluid (light mineral oil) is used.

[0053] Example 2 - Glass Beads A capture fluid consisting of 7.5 g of glass beads (silica beads, 30-40 course, Potters Industries) in 12 g of capture fluid (light mineral oil) is used.

[0054] Example 3 - Glass Beads A capture fluid consisting of 10 g of glass beads (silica beads, 30-40 course, Potters Industries) in 10 g of capture fluid (light mineral oil) is used.

[0055] Example 4 - Hollow Glass Spheres A capture fluid consisting of 0.61 g of hollow glass spheres (9-13 micrometer average size available from Millipore Sigma as catalog number 440345) in 12 g of capture fluid (light mineral oil) is used.

[0056] Example 5 - Glass Plates: A capture fluid consisting of 0.715 g of glass coverslip (borosilicate glass coverslip (Corning Glass coverslip No. 1, 22 millimeter square, catalog number 2865-22), Corning) in 7.15 g of capture fluid (light mineral oil) is used.

[0057] Polymer Solid Substrate Example 6 - Low Density Polyethylene Powder A capture fluid consisting of 1.63 g of low density polyethylene powder (Polyethylene Powder, Low Density, 500 micrometers, CAS No. 9002-88-4, manufactured by Alfa Aesar) in 12 g of capture fluid (light mineral oil) is used.

[0058] Ceramic Solid Substrate Example 7 - Boron Nitride / Silicone Core / Shell Particles. A capture fluid consisting of 0.67 g of boron nitride / silicone core / shell particles in 11 g of capture fluid (light mineral oil) is used. The boron nitride / silicone core / shell particles are prepared as follows: 16.8 weight percent (wt%) of 20 mm 2Polydimethylsiloxane (cSt / sec) was mixed with h-BN spherical agglomerates (Saint-Gobain CTS7M) in a Thinky ARE-310 planetary mixer at 2000 revolutions per minute for four cycles per minute to coat the BN particles with silicone. The silicone-coated BN particles were placed in a glass vial with only one open end, a NW25 vacuum port at the open end, and an internal glass baffle. A vacuum was applied to the glass vial to achieve an internal pressure of 0.7866 Pa and hold for 10 minutes. Ultra-high purity argon gas (99.999%) was metered into the glass vial at a rate of 50 standard cubic centimeters per minute using a mass flow controller until the vial pressure reached 35.46 Pa. The glass vial was rotated at a rate of 15 revolutions per minute to rotate the BN particles inside it. A very high frequency (133 MHz) radio frequency signal was applied to a copper coil surrounding the outside of the rotating glass vial, generating a capacitively coupled AR discharge inside the glass vial. The very high frequency plasma power was adjusted to 138 watts and applied for 130 minutes, after which the plasma and argon gas flow were stopped and the glass vial was vented to the atmosphere. The particles inside had a BN core with a silicone / SiOx surface coating. The particles were removed from the glass vial, rinsed with deionized water, and dried at 120°C for 24 hours. Diamond ATR-IR spectroscopy confirmed that the BN particle surfaces were coated with silicone. Visual observation of the particles revealed that their color changed from bright white to pale yellow.

[0059] metal solid substrate Example 8 - Iron Powder. A scavenging fluid consisting of 7.4 g of iron powder (iron particles / powder, -70 mesh (less than 212 micrometers), CAS number 7439-89-6, manufactured by Acros Organics) in 10.4 g of scavenging fluid (light mineral oil) is used.

[0060] Example 9 - Iron Powder. A scavenging fluid consisting of 3.4 g of iron powder (iron particles / powder, -70 mesh (less than 212 micrometers), CAS number 7439-89-6, manufactured by Acros Organics) in 10 g of scavenging fluid (light mineral oil) is used.

[0061] Example 10 - Nickel Powder A capture fluid consisting of 1.4 g of nickel powder (iron particles / powder, -50+100 mesh CAS number 7440-02-0, manufactured by Alfa Aesar) in 8.4 g of capture fluid (light mineral oil) is used.

[0062] Carbon solid substrate Example 11 - Graphite Rod. Use a capture fluid consisting of 2.93 g of graphite rod (a random mixture of 2.0 millimeter diameter 2B Mr Pen and 0.7 millimeter diameter 2B NEOX rods (lengths ranging from 0.2 to 4 centimeters, available from Amazon.com) in 12 g of capture fluid (light mineral oil).

[0063] Comparison sample Comparative Example A - Coated graphite rod without trapping fluid. Example 11 was repeated, except that the 12 g of trapping fluid was omitted. Instead, the graphite rod was placed in a trapping reservoir on the trapping fluid reservoir holder, but no trapping fluid was present. During the process, the graphite rod was directly exposed to a gas stream containing silicon nanoparticles. After coating with silicon nanoparticles, the trapping fluid reservoir was removed from the deposition chamber through the load lock and placed in a nitrogen-purged glove box. 12 g of mineral oil was added to the trapping fluid reservoir to cover the coated graphite rod, and the trapping fluid reservoir was removed from the glove box and exposed to an atmosphere at 60°C and 85% relative humidity for 7 days.

[0064] Comparative Example B - Coated hexagonal boron nitride rod without trapping fluid. A 2.69 g hexagonal boron nitride (h-BN) rod (GE Advanced Ceramics Plug#: 130689, International Publication No. 143503, 3.175 mm diameter, variable length from 3 to 30 mm) was placed in a trapping reservoir on a trapping fluid reservoir holder without any trapping fluid present. During the process, the h-BN rod was directly exposed to a gas stream containing silicon nanoparticles. After coating with silicon nanoparticles, the trapping fluid reservoir was removed from the deposition chamber through the load lock and placed in a nitrogen-purged glove box. 12 g of mineral oil was added to the trapping fluid reservoir to cover the coated graphite rod, and the trapping fluid reservoir was removed from the glove box and exposed to an atmosphere at 60 °C and 85% relative humidity for 7 days.

[0065] Comparative Example C - Glass beads coated without trapping fluid. Five grams of glass beads (silica beads, 30-40 course, Potters Industries) were placed in the trapping reservoir on the trapping fluid reservoir holder, but no trapping fluid was present. During the process, the glass beads were directly exposed to a gas stream containing silicon nanoparticles. After coating with silicon nanoparticles, the trapping fluid reservoir was removed from the deposition chamber through the load lock and placed in a nitrogen-purged glove box. 12 grams of mineral oil was added to the trapping fluid reservoir to cover the coated graphite rod, and the trapping fluid reservoir was removed from the glove box and exposed to an atmosphere at 60°C and 85% relative humidity for 7 days.

[0066] Comparative Example D - Low-density polyethylene powder coated without trapping fluid. 0.6 g of low-density polyethylene powder (polyethylene powder, low density, 500 micrometers, CAS No. 9002-88-4, manufactured by Alfa Aesar) was placed in a trapping reservoir on a trapping fluid reservoir holder, but no trapping fluid was present. During the process, the polyethylene powder was directly exposed to a gas stream containing silicon nanoparticles. After coating with silicon nanoparticles, the trapping fluid reservoir was removed from the deposition chamber through the load lock and placed in a nitrogen-purged glove box. 12 g of mineral oil was added to the trapping fluid reservoir to cover the coated graphite rod, and the trapping fluid reservoir was removed from the glove box and exposed to an atmosphere at 60°C and 85% relative humidity for 7 days.

[0067] Comparative Example E - Low-density polyethylene beads coated without trapping fluid. 1 g of low-density polyethylene beads (polyethylene beads, low density, 1-3 mm, CAS No. 9002-88-4, Sigma-Aldrich) was placed in the trapping reservoir on the trapping fluid reservoir holder, but no trapping fluid was present. During the process, the polyethylene beads were directly exposed to a gas stream containing silicon nanoparticles. After coating with silicon nanoparticles, the trapping fluid reservoir was removed from the deposition chamber through the load lock and placed in a nitrogen-purged glove box. 12 g of mineral oil was added to the trapping fluid reservoir to cover the coated graphite rod, and the trapping fluid reservoir was removed from the glove box and exposed to an atmosphere at 60 °C and 85% relative humidity for 7 days.

[0068] Table 2 shows the process parameters for the VHFLPP process for each example. The gas flow composition is generated by integrating the listed gases at specific flow rates into the inlet end 5a of the dielectric discharge tube. The deposition time is the time the process generates silicon nanoparticles.

[0069] Table 3 shows the power and passivation parameters for the VHFLPP process. Drive amplitude is reported in millivolts peak-to-peak (mVpp).

[0070] Each sample luminesces when exposed to ultraviolet light, thereby confirming that they are solid substrates coated with silicon quantum dots. None of the samples require an adhesion promoter to adhere the silicon quantum dots to the solid substrate. Furthermore, each of the examples exhibits uniform luminescence, demonstrating a uniform coating of silicon quantum dots.

[0071] In particular, Comparative Example A emits light non-uniformly on the graphite rod, indicating a non-uniform coating. In contrast, Example 10 emits light uniformly on the graphite rod, indicating a uniform coating. Comparative Example A and Example 10 demonstrate that coating in a trapping fluid achieves a more uniform coating of silicon nanoparticles. Comparative Examples B-E, which were coated with silicon quantum dots separately from the trapping fluid, also exhibit non-uniform light emission, evidence of a non-uniform coating of the quantum dots. Comparison of the Examples and Comparative Examples reveals that coating a solid substrate while immersed in a trapping fluid results in a more uniform coating of the solid substrate with quantum dots than coating the solid substrate away from the trapping fluid.

[0072] These examples demonstrate the successful coating of various solid substrates with silicon nanoparticles, particularly silicon quantum dots, by a direct coating method in which the solid substrate is in a trapping fluid, the silicon nanoparticles are directed directly into the trapping fluid as they are produced, and no adhesion promoter is required. The examples also illustrate the successful passivation of silicon quantum dots on the surface of a solid substrate without the need to remove the silicon quantum dots from the trapping fluid or to maintain the silicon quantum dots in an inert atmosphere while in the trapping fluid.

[0073] [Table 2]

[0074] [Table 3]

Claims

1. 1. A method for directly coating silicon nanoparticles onto a solid substrate, comprising a VHFLPP process of collecting silicon nanoparticles in a capture fluid as the silicon nanoparticles are made, the process being further characterized by immersing the solid substrate in the capture fluid while collecting the silicon nanoparticles.

2. The method of claim 1 , wherein the solid substrate is a single item and / or one of a plurality of items.

3. 3. The method of claim 1, wherein the solid substrate is selected from the group consisting of glass, plastic, ceramic, metal, carbon, and salt.

4. The method of any one of claims 1 to 3, wherein the silicon nanoparticles are silicon quantum dots.

5. The method of any one of claims 1 to 4, wherein the capture fluid is selected from silicone oil, mineral oil, or a solution of silicone oil or mineral oil with additional dispersing additives.

6. 6. The method of claim 1, wherein the trapping fluid further comprises a compatibilizer that binds to the surface of the nanoparticles when they enter the trapping fluid, increasing the compatibility and / or reactivity of the nanoparticles with the solid substrate.

7. 7. The method of claim 1, wherein the trapping fluid reservoir is rotated and / or the trapping fluid is agitated as the silicon nanoparticles are created and dispersed in the silicon fluid during the VHFLPP process.

8. 8. The method of any one of claims 1 to 7, further comprising aging the solid substrate in the trapping fluid, optionally in a moisture-containing atmosphere, at a temperature greater than 25°C for a period of one hour or more to passivate the silicon nanoparticles by forming an oxide coating on the silicon nanoparticles in a controlled manner.

9. The method of any one of claims 1 to 8, further comprising separating the silicon nanoparticle coated solid substrate from the capture fluid.

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