WO2023034268A1 - Method for fabricating silicon quantum dots - Google Patents

Method for fabricating silicon quantum dots Download PDF

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Publication number
WO2023034268A1
WO2023034268A1 PCT/US2022/041993 US2022041993W WO2023034268A1 WO 2023034268 A1 WO2023034268 A1 WO 2023034268A1 US 2022041993 W US2022041993 W US 2022041993W WO 2023034268 A1 WO2023034268 A1 WO 2023034268A1
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perhydridosilane
recited
quantum dots
solution
dopant
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PCT/US2022/041993
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French (fr)
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Ramez Ahmed ELGAMMAL
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The Coretec Group Inc.
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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B33/00—Silicon; Compounds thereof
    • C01B33/02—Silicon
    • C01B33/021—Preparation
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B33/00—Silicon; Compounds thereof
    • C01B33/02—Silicon
    • C01B33/021—Preparation
    • C01B33/027—Preparation by decomposition or reduction of gaseous or vaporised silicon compounds other than silica or silica-containing material
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
    • C09K11/00—Luminescent, e.g. electroluminescent, chemiluminescent materials
    • C09K11/08—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials
    • C09K11/59—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials containing silicon
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2002/00—Crystal-structural characteristics
    • C01P2002/02—Amorphous compounds
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/30—Particle morphology extending in three dimensions
    • C01P2004/32—Spheres
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/80—Compositional purity

Definitions

  • Quantum dots are semiconductor particles that are typically from 1 to 10 nanometers in size. They have optical and electronic properties that differ from larger particles because of quantum mechanics. For instance, when quantum dots are illuminated by ultraviolet light, an electron can be excited from the valence band to the conductance band. The excited electron can drop back into the valence band, releasing energy as light. The color of that light depends on the energy difference between the bands. Applications for quantum dots include optoelectronics, photonics, single-electron transistors, solar cells, LEDs, lasers, single-photon sources, batteries, and more.
  • Silicon quantum dots may be of greater interest than crystalline silicon quantum dots due to higher photoluminescence efficiency.
  • a variety of approaches exist for fabricating silicon quantum dots such as laser ablation, plasma synthesis, chemical vapor deposition, electrochemical etching, Zintl salt oxidation, silicon halide reduction, decomposition of silicon precursors, and metallothermal reduction if silica.
  • some of these approaches have not been well-explored and/or have been unable to produce amorphous silicon quantum dots or produce them with size dispersions necessary in many optical applications.
  • a method according to an example of the present disclosure includes dispersing perhydridosilane in a miscible solvent to form a perhydridosilane solution, and energizing the perhydridosilane solution.
  • the energizing causes formation of silicon quantum dots from the perhydridosilane.
  • the perhydridosilane is selected from Si n H2n+2 , Si n H2n, and combinations thereof.
  • the perhydridosilane is selected from trisilane, cyclohexasilane, and combinations thereof.
  • the perhydridosilane is cyclohexasilane.
  • the silicon quantum dots are amorphous.
  • the miscible solvent is selected from terpenes, long chain alkenes of six or more carbon atoms, alkyl ether with at least eight carbon atoms, aryl ether with at least eight carbon atoms, oleic acid, oleylamine, trialkyl phosphines, and combinations thereof.
  • in the perhydridosilane solution has a concentration of perhydridosilane that is 0.1 M to 2.0M.
  • the dispersing includes injecting the perhydridosilane into the solution.
  • the perhydridosilane solution includes surfactant molecules, the surfactant molecules binding to surfaces of the silicon quantum dots.
  • the energizing is selected from heating, sonication, and combinations thereof.
  • the energizing includes heating at a temperature of 60 - 400 °C and at a pressure of 1 - 5 atm.
  • the energizing includes sonication at a temperature of -20 - 40°C and at a pressure of 1 - 5 atm.
  • the perhydridosilane solution includes at least one dopant selected from a boron dopant, a phosphorous dopant, a lithium dopant, and combinations thereof.
  • the dopant is the boron dopant and is selected from organoborane, alkyl boranes, organoborate, haloborane, and combinations thereof.
  • the dopant is the phosphorous dopant and is selected from phosphine, alkyl phosphine, aryl phosphine, organophosphates, halophosphine, and combinations thereof.
  • the dopant is the lithium dopant and is selected from methyl lithium, butyl lithium, t-butyl lithium, lithium bromide and combinations thereof.
  • the perhydridosilane includes a surface modifier selected from alkene, alkyne, propargyl amine, and combinations thereof.
  • a method includes dispersing cyclohexasilane in a miscible solvent to form a silane solution having a concentration of 0.1M to 2.0M, and heating the silane solution at a temperature of 60 - 400 °C and at a pressure of 1 - 5 atm. The heating causing formation of amorphous silicon quantum dots from the cyclohexasilane.
  • a method according to an example of the present disclosure includes dispersing perhydridosilane in a miscible solvent to form a perhydridosilane solution having a concentration of 0.1M to 2.0M, and sonicating the perhydridosilane solution, the sonicating causing formation of amorphous silicon quantum dots from the perhydridosilane.
  • the present disclosure may include any one or more of the individual features disclosed above and/or below alone or in any combination thereof.
  • Figure 1 illustrates a mechanism of thermochemical decomposition of perhydridosilane to form amorphous quantum dots.
  • Figure 2 illustrates hot injection of cyclohexasilane into a solvent to form amorphous quantum dots.
  • Figure 3 illustrates a mechanism of thermochemical decomposition of cyclohexasilane with surfactant to form amorphous quantum dots.
  • Figure 4 illustrates a mechanism of thermochemical decomposition of perhydridosilane with a boron doping agent to form doped amorphous quantum dots.
  • Figure 5 illustrates a mechanism of thermochemical decomposition of cyclohexasilane with a boron doping agent to form doped amorphous quantum dots.
  • Figure 6 illustrates a mechanism of thermochemical decomposition of perhydridosilane with a phosphorous dopant to form doped amorphous quantum dots.
  • Figure 7 illustrates a mechanism of thermochemical decomposition of cyclohexasilane with a phosphorous dopant to form doped amorphous quantum dots.
  • Figure 8 illustrates a mechanism of thermochemical decomposition of perhydridosilane with a lithium dopant to form doped amorphous quantum dots.
  • Figure 9 illustrates a mechanism of thermochemical decomposition of cyclohexasilane with a lithium dopant to form doped amorphous quantum dots.
  • Figure 10 illustrates a mechanism of thermochemical decomposition of perhydridosilane with a surface modifier to form surface-modified amorphous quantum dots.
  • Figure 11 illustrates a mechanism of thermochemical decomposition of cyclohexasilane with a surface modifier to form surface-modified amorphous quantum dots.
  • Figure 12 illustrates a mechanism of thermochemical decomposition of perhydridosilane with an alkene surface modifier to form surface-modified amorphous quantum dots.
  • Figure 13 illustrates a mechanism of thermochemical decomposition of perhydridosilane with an alkyne modifier to form surface-modified amorphous quantum dots.
  • like reference numerals designate like elements where appropriate and reference numerals with the addition of one-hundred or multiples thereof designate modified elements that are understood to incorporate the same features and benefits of the corresponding elements.
  • Perhydridosilane has a general formulae Si n H2n+2 or Si n H2n, where n is 3-8 and the molecule is linear, branched, or cyclic.
  • SiX4 silicon halides
  • perhydridosilane facilitates the fabrication of pure silicon quantum dots that have only silicon and hydrogen on the surface, which are chemically labile and can be readily functionalized to form silicon-carbon bonds.
  • the perhydridosilane is processed in a solution phase.
  • An example method includes dispersing the perhydridosilane in a miscible solvent to form a perhydridosilane solution.
  • the perhydridosilane solution is then energized to induce decomposition of the perhydridosilane and formation of the amorphous quantum dots.
  • One example methodology of the energizing is thermal energizing by heating to a temperature of 60°C to 400°C and at a pressure of 1 atm to 5 atm. The heating causes a decomposition reaction and formation of silicon quantum dots from the perhydridosilane.
  • the mechanism of thermochemical decomposition of perhydridosilane is shown in Figure 1.
  • a linear silane of formula Si n H2n+2 may condense to form a polysilane.
  • the polysilane acts as a source of growth of a silicon quantum dot by release of H2.
  • a cyclic silane of formula Si n H2n may ring-open and form an analogous polysilane that generates silicon quantum dots upon release of H2.
  • the selected perhydridosilane is a liquid at 23 °C and is miscible in the selected solvent.
  • the processing temperature of 60°C to 400°C maintains the amorphous character of the resulting silicon quantum dots, and the silicon precursor contains only silicon and hydrogen so that pure silicon quantum dots are produced that only have silicon and hydrogen.
  • the selected perhydridosilane is cyclohexasilane (SieH ).
  • Example solvents include non-polar high boiling solvents, such as but not limited to, terpenes (e.g. squalene), long chain alkenes (e.g. 1 -octadecene), long chain alkenes of six or more carbon atoms, alkyl ether with at least eight carbon atoms, aryl ether with at least eight carbon atoms (e.g. dioctyl ether or diphenylether), oleyl derivatives (e.g. oleic acid or oleylamine), or trialkyl phosphines (e.g. trioctylphosphine).
  • Solvents may coordinate to cyclohexasilane or its ring- opened intermediate or there may be no interaction. Coordination may stabilize reactive intermediates and influence particle growth, size, and morphology.
  • the reaction may be carried out in a vessel that is suitable for the process temperatures and pressures.
  • the reaction time may be in the range of 1 hour to 36 hours
  • the concentration of cyclohexasilane (or other perhydridosilane) in the solvent is 0.1 M to 2 M
  • the reaction temperatures is 60°C to 400°C
  • the pressure in the vessel is from 1 atm to 5 atm.
  • Another example thermal methodology involves hot-injection and may utilize the same process parameters as above for concentration, temperature, pressure, and solvent type.
  • the solvent is pre-heated to the proscribed temperature range above and the perhydridosilane is added rapidly to the hot solvent.
  • this produces highly mono-disperse quantum dots due to rapid reaction and crystal growth and is limited by Ostwald ripening.
  • this methodology allows use of solid perhydridosilane (at 23 °C), which can be rapidly added in the solid state and then melt in the heated solvent for reaction.
  • Additional agents or processing aids may also be added to the solution in the examples herein.
  • a surfactant may be added to bind to the surfaces of the quantum dots.
  • the surfactant molecules may direct the growth of the quantum dots, facilitate the decomposition, and/or cap the quantum dots.
  • surface groups may affect the photophysics of the quantum dots, and surfactants may thus be used to modulate light emission wavelength.
  • Figure 3 illustrates the reaction involving surfactant and the resulting molecules on the surfaces of the quantum dots.
  • sonic energizing may be used (sonochemical processing).
  • the perhydridosilane solution is subjected to sonication.
  • Sonication may facilitate surface functionalization of the silicon quantum dots.
  • sonication of cyclohexasilane facilitates an increase in kinetic energy and concomitant increase in silicon quantum dot growth.
  • the sonication may be conducted for 10 minutes to 4 hours, with a perhydridosilane solution concentration of 0.1 M to 2 M at a temperature of -20°C to 40°C at ambient pressure (generally about 0.7 atm to about 1 atm).
  • the amorphous silicon quantum dots can also be doped by inclusion of dopants during processing. Doping levels may in general range from 0.01 at% to 5 at%, although some dopants may be higher.
  • dopants of interest may include boron dopants, phosphorous dopants, and/or lithium dopants.
  • Figures 4 and 5 illustrate mechanisms of boron doping of linear and cyclic perhydridosilanes, respectively.
  • Example boron dopants may include, but are not limited to, those that are soluble in the chosen solvent, such as organoboranes (B(CH3)3), alkyl boranes, organoborates, such as (B(OEt)3), or haloboranes, such as BF3 or BBn.
  • organoboranes B(CH3)3)
  • alkyl boranes such as (B(OEt)3)
  • haloboranes such as BF3 or BBn.
  • Figures 6 and 7 illustrate mechanisms of phosphorous doping of linear and cyclic perhydridosilanes, respectively.
  • Example phosphorous dopants may include, but are not limited to, phosphines, such as P(CH3)3, alkyl phosphines, aryl phosphines, such as PPI13, organophosphates, such as P(OEt)3, or halophosphines, such as PBn.
  • Doping levels for phosphorous may range from 0.01 at% to 5 at%.
  • FIGs 8 and 9 illustrate mechanisms of lithium doping of linear and cyclic perhydridosilanes, respectively.
  • Example lithium dopants may include, but are not limited to, alkyl lithium, such as methyl lithium, butyl lithium, and t-butyl lithium.
  • the solvent is tetrahydrofuran
  • lithium bromide (LiBr) may be used.
  • Doping levels for lithium may range from 0.01 at% to 20 at%. Lithiation of silicon quantum dots may be of interest in lithium- ion batteries and other industries.
  • the perhydridosilane solution may include a surface functionalization modifier.
  • the surface functionalization modifier is selected from alkene, alkyne, propargyl amine, and combinations thereof.
  • Figures 10 and 11 illustrate mechanisms of surface modification of the silicon quantum dots. Further examples shown in Figures 12 and 13 demonstrate mechanisms of surface modification of the silicon quantum dots using general alkene or alkyne rather than propargyl amine that is shown in Figure 10 and 11.

Abstract

A method includes dispersing perhydridosilane in a miscible solvent to form a perhydridosilane solution, and energizing the perhydridosilane solution, such as by heating at a temperature of 60 – 400 °C and at a pressure of 1 – 5 atm. The energizing causes formation of silicon quantum dots from the perhydridosilane.

Description

METHOD FOR FABRICATING SILICON QUANTUM DOTS
BACKGROUND
[0001] Quantum dots are semiconductor particles that are typically from 1 to 10 nanometers in size. They have optical and electronic properties that differ from larger particles because of quantum mechanics. For instance, when quantum dots are illuminated by ultraviolet light, an electron can be excited from the valence band to the conductance band. The excited electron can drop back into the valence band, releasing energy as light. The color of that light depends on the energy difference between the bands. Applications for quantum dots include optoelectronics, photonics, single-electron transistors, solar cells, LEDs, lasers, single-photon sources, batteries, and more.
[0002] Fabrication of silicon quantum dots presents several challenges for commercialization. Hydrogen-terminated amorphous silicon quantum dots may be of greater interest than crystalline silicon quantum dots due to higher photoluminescence efficiency. A variety of approaches exist for fabricating silicon quantum dots, such as laser ablation, plasma synthesis, chemical vapor deposition, electrochemical etching, Zintl salt oxidation, silicon halide reduction, decomposition of silicon precursors, and metallothermal reduction if silica. However, some of these approaches have not been well-explored and/or have been unable to produce amorphous silicon quantum dots or produce them with size dispersions necessary in many optical applications.
SUMMARY
[0003] A method according to an example of the present disclosure includes dispersing perhydridosilane in a miscible solvent to form a perhydridosilane solution, and energizing the perhydridosilane solution. The energizing causes formation of silicon quantum dots from the perhydridosilane.
[0004] In a further embodiment of any of the foregoing embodiments, the perhydridosilane is selected from SinH2n+2 , SinH2n, and combinations thereof.
[0005] In a further embodiment of any of the foregoing embodiments, the perhydridosilane is selected from trisilane, cyclohexasilane, and combinations thereof.
[0006] In a further embodiment of any of the foregoing embodiments, the perhydridosilane is cyclohexasilane.
[0007] In a further embodiment of any of the foregoing embodiments, the silicon quantum dots are amorphous. [0008] In a further embodiment of any of the foregoing embodiments, the miscible solvent is selected from terpenes, long chain alkenes of six or more carbon atoms, alkyl ether with at least eight carbon atoms, aryl ether with at least eight carbon atoms, oleic acid, oleylamine, trialkyl phosphines, and combinations thereof.
[0009] In a further embodiment of any of the foregoing embodiments, in the perhydridosilane solution has a concentration of perhydridosilane that is 0.1 M to 2.0M.
[0010] In a further embodiment of any of the foregoing embodiments, the dispersing includes injecting the perhydridosilane into the solution.
[0011] In a further embodiment of any of the foregoing embodiments, the perhydridosilane solution includes surfactant molecules, the surfactant molecules binding to surfaces of the silicon quantum dots.
[0012] In a further embodiment of any of the foregoing embodiments, the energizing is selected from heating, sonication, and combinations thereof.
[0013] In a further embodiment of any of the foregoing embodiments, the energizing includes heating at a temperature of 60 - 400 °C and at a pressure of 1 - 5 atm.
[0014] In a further embodiment of any of the foregoing embodiments, the energizing includes sonication at a temperature of -20 - 40°C and at a pressure of 1 - 5 atm.
[0015] In a further embodiment of any of the foregoing embodiments, the perhydridosilane solution includes at least one dopant selected from a boron dopant, a phosphorous dopant, a lithium dopant, and combinations thereof.
[0016] In a further embodiment of any of the foregoing embodiments, the dopant is the boron dopant and is selected from organoborane, alkyl boranes, organoborate, haloborane, and combinations thereof.
[0017] In a further embodiment of any of the foregoing embodiments, the dopant is the phosphorous dopant and is selected from phosphine, alkyl phosphine, aryl phosphine, organophosphates, halophosphine, and combinations thereof.
[0018] In a further embodiment of any of the foregoing embodiments, the dopant is the lithium dopant and is selected from methyl lithium, butyl lithium, t-butyl lithium, lithium bromide and combinations thereof.
[0019] In a further embodiment of any of the foregoing embodiments, the perhydridosilane includes a surface modifier selected from alkene, alkyne, propargyl amine, and combinations thereof.
[0020] A method according to an example of the present disclosure includes dispersing cyclohexasilane in a miscible solvent to form a silane solution having a concentration of 0.1M to 2.0M, and heating the silane solution at a temperature of 60 - 400 °C and at a pressure of 1 - 5 atm. The heating causing formation of amorphous silicon quantum dots from the cyclohexasilane.
[0021] A method according to an example of the present disclosure includes dispersing perhydridosilane in a miscible solvent to form a perhydridosilane solution having a concentration of 0.1M to 2.0M, and sonicating the perhydridosilane solution, the sonicating causing formation of amorphous silicon quantum dots from the perhydridosilane.
[0022] The present disclosure may include any one or more of the individual features disclosed above and/or below alone or in any combination thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] The various features and advantages of the present disclosure will become apparent to those skilled in the art from the following detailed description. The drawings that accompany the detailed description can be briefly described as follows.
[0024] Figure 1 illustrates a mechanism of thermochemical decomposition of perhydridosilane to form amorphous quantum dots.
[0025] Figure 2 illustrates hot injection of cyclohexasilane into a solvent to form amorphous quantum dots.
[0026] Figure 3 illustrates a mechanism of thermochemical decomposition of cyclohexasilane with surfactant to form amorphous quantum dots.
[0027] Figure 4 illustrates a mechanism of thermochemical decomposition of perhydridosilane with a boron doping agent to form doped amorphous quantum dots.
[0028] Figure 5 illustrates a mechanism of thermochemical decomposition of cyclohexasilane with a boron doping agent to form doped amorphous quantum dots.
[0029] Figure 6 illustrates a mechanism of thermochemical decomposition of perhydridosilane with a phosphorous dopant to form doped amorphous quantum dots.
[0030] Figure 7 illustrates a mechanism of thermochemical decomposition of cyclohexasilane with a phosphorous dopant to form doped amorphous quantum dots.
[0031] Figure 8 illustrates a mechanism of thermochemical decomposition of perhydridosilane with a lithium dopant to form doped amorphous quantum dots.
[0032] Figure 9 illustrates a mechanism of thermochemical decomposition of cyclohexasilane with a lithium dopant to form doped amorphous quantum dots.
[0033] Figure 10 illustrates a mechanism of thermochemical decomposition of perhydridosilane with a surface modifier to form surface-modified amorphous quantum dots. [0034] Figure 11 illustrates a mechanism of thermochemical decomposition of cyclohexasilane with a surface modifier to form surface-modified amorphous quantum dots.
[0035] Figure 12 illustrates a mechanism of thermochemical decomposition of perhydridosilane with an alkene surface modifier to form surface-modified amorphous quantum dots.
[0036] Figure 13 illustrates a mechanism of thermochemical decomposition of perhydridosilane with an alkyne modifier to form surface-modified amorphous quantum dots.
[0037] In this disclosure, like reference numerals designate like elements where appropriate and reference numerals with the addition of one-hundred or multiples thereof designate modified elements that are understood to incorporate the same features and benefits of the corresponding elements.
DETAILED DESCRIPTION
[0038] Disclosed are methods for fabricating amorphous silicon quantum dots from perhydridosilane compounds via thermochemical or sonochemical decomposition. Perhydridosilane has a general formulae SinH2n+2 or SinH2n, where n is 3-8 and the molecule is linear, branched, or cyclic. In comparison to silicon halides (SiX4) and other silicon-containing precursors, perhydridosilane facilitates the fabrication of pure silicon quantum dots that have only silicon and hydrogen on the surface, which are chemically labile and can be readily functionalized to form silicon-carbon bonds.
[0039] The perhydridosilane is processed in a solution phase. An example method includes dispersing the perhydridosilane in a miscible solvent to form a perhydridosilane solution. The perhydridosilane solution is then energized to induce decomposition of the perhydridosilane and formation of the amorphous quantum dots. One example methodology of the energizing is thermal energizing by heating to a temperature of 60°C to 400°C and at a pressure of 1 atm to 5 atm. The heating causes a decomposition reaction and formation of silicon quantum dots from the perhydridosilane. Without wishing to be bound, the mechanism of thermochemical decomposition of perhydridosilane is shown in Figure 1. For instance, a linear silane of formula SinH2n+2 may condense to form a polysilane. The polysilane acts as a source of growth of a silicon quantum dot by release of H2. Similarly, a cyclic silane of formula SinH2n may ring-open and form an analogous polysilane that generates silicon quantum dots upon release of H2.
[0040] For solution processing, the selected perhydridosilane is a liquid at 23 °C and is miscible in the selected solvent. The processing temperature of 60°C to 400°C maintains the amorphous character of the resulting silicon quantum dots, and the silicon precursor contains only silicon and hydrogen so that pure silicon quantum dots are produced that only have silicon and hydrogen.
[0041] As an example, the selected perhydridosilane is cyclohexasilane (SieH ). Example solvents include non-polar high boiling solvents, such as but not limited to, terpenes (e.g. squalene), long chain alkenes (e.g. 1 -octadecene), long chain alkenes of six or more carbon atoms, alkyl ether with at least eight carbon atoms, aryl ether with at least eight carbon atoms (e.g. dioctyl ether or diphenylether), oleyl derivatives (e.g. oleic acid or oleylamine), or trialkyl phosphines (e.g. trioctylphosphine). Solvents may coordinate to cyclohexasilane or its ring- opened intermediate or there may be no interaction. Coordination may stabilize reactive intermediates and influence particle growth, size, and morphology.
[0042] The reaction may be carried out in a vessel that is suitable for the process temperatures and pressures. For example, the reaction time may be in the range of 1 hour to 36 hours, the concentration of cyclohexasilane (or other perhydridosilane) in the solvent is 0.1 M to 2 M, the reaction temperatures is 60°C to 400°C, and the pressure in the vessel is from 1 atm to 5 atm.
[0043] Another example thermal methodology involves hot-injection and may utilize the same process parameters as above for concentration, temperature, pressure, and solvent type. As shown in Figure 2, the solvent is pre-heated to the proscribed temperature range above and the perhydridosilane is added rapidly to the hot solvent. In general, this produces highly mono-disperse quantum dots due to rapid reaction and crystal growth and is limited by Ostwald ripening. Additionally, this methodology allows use of solid perhydridosilane (at 23 °C), which can be rapidly added in the solid state and then melt in the heated solvent for reaction.
[0044] Additional agents or processing aids may also be added to the solution in the examples herein. For instance, a surfactant may be added to bind to the surfaces of the quantum dots. The surfactant molecules may direct the growth of the quantum dots, facilitate the decomposition, and/or cap the quantum dots. Moreover, surface groups may affect the photophysics of the quantum dots, and surfactants may thus be used to modulate light emission wavelength. Without wishing to be bound, Figure 3 illustrates the reaction involving surfactant and the resulting molecules on the surfaces of the quantum dots.
[0045] Alternative to thermal energizing, sonic energizing may be used (sonochemical processing). For example, the perhydridosilane solution is subjected to sonication. Sonication may facilitate surface functionalization of the silicon quantum dots. For example, sonication of cyclohexasilane facilitates an increase in kinetic energy and concomitant increase in silicon quantum dot growth. In general, the sonication may be conducted for 10 minutes to 4 hours, with a perhydridosilane solution concentration of 0.1 M to 2 M at a temperature of -20°C to 40°C at ambient pressure (generally about 0.7 atm to about 1 atm).
[0046] The amorphous silicon quantum dots can also be doped by inclusion of dopants during processing. Doping levels may in general range from 0.01 at% to 5 at%, although some dopants may be higher. For example, dopants of interest may include boron dopants, phosphorous dopants, and/or lithium dopants. Figures 4 and 5 illustrate mechanisms of boron doping of linear and cyclic perhydridosilanes, respectively. Example boron dopants may include, but are not limited to, those that are soluble in the chosen solvent, such as organoboranes (B(CH3)3), alkyl boranes, organoborates, such as (B(OEt)3), or haloboranes, such as BF3 or BBn.
[0047] Figures 6 and 7 illustrate mechanisms of phosphorous doping of linear and cyclic perhydridosilanes, respectively. Example phosphorous dopants may include, but are not limited to, phosphines, such as P(CH3)3, alkyl phosphines, aryl phosphines, such as PPI13, organophosphates, such as P(OEt)3, or halophosphines, such as PBn. Doping levels for phosphorous may range from 0.01 at% to 5 at%.
[0048] Figures 8 and 9 illustrate mechanisms of lithium doping of linear and cyclic perhydridosilanes, respectively. Example lithium dopants may include, but are not limited to, alkyl lithium, such as methyl lithium, butyl lithium, and t-butyl lithium. Alternatively, if the solvent is tetrahydrofuran, lithium bromide (LiBr) may be used. Doping levels for lithium may range from 0.01 at% to 20 at%. Lithiation of silicon quantum dots may be of interest in lithium- ion batteries and other industries.
[0049] In further examples, the perhydridosilane solution may include a surface functionalization modifier. For example, the surface functionalization modifier is selected from alkene, alkyne, propargyl amine, and combinations thereof. Figures 10 and 11 illustrate mechanisms of surface modification of the silicon quantum dots. Further examples shown in Figures 12 and 13 demonstrate mechanisms of surface modification of the silicon quantum dots using general alkene or alkyne rather than propargyl amine that is shown in Figure 10 and 11.
[0050] Although a combination of features is shown in the illustrated examples, not all of them need to be combined to realize the benefits of various embodiments of this disclosure. In other words, a system designed according to an embodiment of this disclosure will not necessarily include all of the features shown in any one of the Figures or all of the portions schematically shown in the Figures. Moreover, selected features of one example embodiment may be combined with selected features of other example embodiments.
[0051] The preceding description is exemplary rather than limiting in nature. Variations and modifications to the disclosed examples may become apparent to those skilled in the art that do not necessarily depart from this disclosure. The scope of legal protection given to this disclosure can only be determined by studying the following claims.

Claims

CLAIMS What is claimed is:
1. A method comprising: dispersing perhydridosilane in a miscible solvent to form a perhydridosilane solution; and energizing the perhydridosilane solution, the energizing causing formation of silicon quantum dots from the perhydridosilane.
2. The method as recited in claim 1 , wherein the perhydridosilane is selected from SinH2n+2 , SinH2n, and combinations thereof.
3. The method as recited in claim 1, wherein the perhydridosilane is selected from trisilane, cyclohexasilane, and combinations thereof.
4. The method as recited in claim 3, wherein the perhydridosilane is cyclohexasilane.
5. The method as recited in claim 1, wherein the silicon quantum dots are amorphous.
6. The method as recited in claim 1, wherein the miscible solvent is selected from terpenes, long chain alkenes of six or more carbon atoms, alkyl ether with at least eight carbon atoms, aryl ether with at least eight carbon atoms, oleic acid, oleylamine, trialkyl phosphines, and combinations thereof.
7. The method as recited in claim 1, wherein in the perhydridosilane solution has a concentration of perhydridosilane that is 0.1M to 2.0M.
8. The method as recited in claim 1, wherein the dispersing includes injecting the perhydridosilane into the solution.
9. The method as recited in claim 1, wherein the perhydridosilane solution includes surfactant molecules, the surfactant molecules binding to surfaces of the silicon quantum dots.
10. The method as recited in claim 1, wherein the energizing is selected from heating, sonication, and combinations thereof.
11. The method as recited in claim 10, wherein the energizing includes heating at a temperature of 60 - 400 °C and at a pressure of 1 - 5 atm.
12. The method as recited in claim 10, wherein the energizing includes sonication at a temperature of -20 - 40°C and at a pressure of 1 - 5 atm.
8
13. The method as recited in claim 1, wherein the perhydridosilane solution includes at least one dopant selected from a boron dopant, a phosphorous dopant, a lithium dopant, and combinations thereof.
14. The method as recited in claim 1, wherein the dopant is the boron dopant and is selected from organoborane, alkyl boranes, organoborate, haloborane, and combinations thereof.
15. The method as recited in claim 1, wherein the dopant is the phosphorous dopant and is selected from phosphine, alkyl phosphine, aryl phosphine, organophosphates, halophosphine, and combinations thereof.
16. The method as recited in claim 1, wherein the dopant is the lithium dopant and is selected from methyl lithium, butyl lithium, t-butyl lithium, lithium bromide and combinations thereof.
17. The method as recited in claim 1, wherein the perhydridosilane includes a surface modifier selected from alkene, alkyne, propargyl amine, and combinations thereof.
18. A method comprising: dispersing cyclohexasilane in a miscible solvent to form a silane solution having a concentration of 0.1M to 2.0M; and heating the silane solution at a temperature of 60 - 400 °C and at a pressure of 1 - 5 atm, the heating causing formation of amorphous silicon quantum dots from the cyclohexasilane.
19. A method comprising: dispersing perhydridosilane in a miscible solvent to form a perhydridosilane solution having a concentration of 0.1M to 2.0M; and sonicating the perhydridosilane solution, the sonicating causing formation of amorphous silicon quantum dots from the perhydridosilane.
9
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