Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B82—NANOTECHNOLOGY
  • B82B—NANOSTRUCTURES FORMED BY MANIPULATION OF INDIVIDUAL ATOMS, MOLECULES, OR LIMITED COLLECTIONS OF ATOMS OR MOLECULES AS DISCRETE UNITS; MANUFACTURE OR TREATMENT THEREOF
  • B82B1/00—Nanostructures formed by manipulation of individual atoms or molecules, or limited collections of atoms or molecules as discrete units
• • 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
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
  • B22F1/05—Metallic powder characterised by the size or surface area of the particles
  • B22F1/054—Nanosized particles
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F9/00—Making metallic powder or suspensions thereof
  • B22F9/16—Making metallic powder or suspensions thereof using chemical processes
  • B22F9/18—Making metallic powder or suspensions thereof using chemical processes with reduction of metal compounds
  • B22F9/24—Making metallic powder or suspensions thereof using chemical processes with reduction of metal compounds starting from liquid metal compounds, e.g. solutions
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B82—NANOTECHNOLOGY
  • B82B—NANOSTRUCTURES FORMED BY MANIPULATION OF INDIVIDUAL ATOMS, MOLECULES, OR LIMITED COLLECTIONS OF ATOMS OR MOLECULES AS DISCRETE UNITS; MANUFACTURE OR TREATMENT THEREOF
  • B82B3/00—Manufacture or treatment of nanostructures by manipulation of individual atoms or molecules, or limited collections of atoms or molecules as discrete units
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B82—NANOTECHNOLOGY
  • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
  • B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B32/00—Carbon; Compounds thereof
  • C01B32/90—Carbides
  • C01B32/914—Carbides of single elements
  • C01B32/956—Silicon carbide
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F2998/00—Supplementary information concerning processes or compositions relating to powder metallurgy
  • B22F2998/10—Processes characterised by the sequence of their steps

Definitions

• the present invention relates to methods for the mechanochemical preparation of stable passivated nanoparticles, made of e.g. silicon or germanium.
• a nanoparticle is a microscopic particle with at least one dimension less than 100 nanometer (nm). Nanoparticles have recently been at the forefront of biomedical, optical, and electronics research because they can exhibit fundamentally new behavior when their sizes fall below the critical length scale associated with any given property.
• a bulk material is generally considered to have uniform physical properties throughout regardless of its size, but at the nano- scale the properties of materials change as the percentage of atoms at the surface of the material becomes significant. Below the micrometer scale, size-dependent properties are observed such as quantum confinement in semiconductor particles, surface plasmon resonance in some metal particles, and supermagnetism in magnetic materials.
• Quantum confinement occurs when electrons and holes in a semiconductor are restricted in one or more dimensions.
• a quantum dot is confined in all three dimensions, a quantum wire is confined in two dimensions, and a quantum well is confined in one dimension. That is, quantum confinement occurs when one or more of the dimensions of a nanocrystal is made very small so that it approaches the size of an exciton in bulk crystal, called the Bohr exciton radius.
• An exciton is a bound state of an electron and an imaginary particle called an electron hole in an insulator or semiconductor.
• An exciton is an elementary excitation, or a quasiparticle of a solid.
• a quantum dot is a structure where all dimensions are near the Bohr exciton radius, typically a small sphere.
• a quantum wire is a structure where the height and breadth is made small while the length can be long.
• a quantum well is a structure where the height is approximately the Bohr exciton radius while the length and breadth can be large. Quantum confinement effects at very small crystalline sizes can cause silicon and germanium nanoparticles to fluoresce, and such fluorescent silicon and germanium nanoparticles have great potential for use in optical and electronic systems as well as biological applications.
• Silicon and germanium nanoparticles may be used, e.g., in optical switching devices, photovoltaic cells, light emitting diodes, lasers, and optical frequency doublers, and as biological markers.
• the photoluminescence (PL) mechanism in silicon and germanium nanoparticles is also influenced by the nature and bonding state of the particle surface.
• the direct band gap semiconductor has a vertically aligned conduction and valence band. Absorption of a photon is obtained if an empty state in the conduction band is available for which the energy and momentum equals that of an electron in the valence band plus that of the incident photon. Photons have little momentum relative to their energy since they travel at the speed of light. The electron therefore makes an almost vertical transition on the E-k diagram.
• the conduction band is not vertically aligned to the valence.
• a phonon is a particle associated with lattice vibrations and has a relatively low velocity close to the speed of sound in the material. Phonons have a small energy and large momentum compared to that of photons. Conservation of both energy and momentum can therefore be obtained in the absorption process if a phonon is created or an existing phonon participates.
• the minimum photon energy that can be absorbed is slightly below the band gap energy in the case of phonon absorption and has to be slightly above the band gap energy in the case of phonon emission. Since the absorption process in an indirect band gap semiconductor involves a phonon in addition to the electron and photon, the probability of having an interaction take place involving all three particles will be lower than a simple electron-photon interaction in a direct band gap semiconductor.
• a preferred embodiment of the present invention relates to methods of producing stable passivated semiconductor nanoparticles through high energy ball milling of material (such as silicon or germanium) in the presence of a reactive liquid or gaseous medium.
• the present invention provides a method of forming stable, functionalized nanoparticles, comprising the steps of: providing a first material, providing a reactive liquid or gaseous medium, and ball milling the first material in the reactive liquid or gaseous medium to provide ball milled nanoparticles.
• the method includes the use of a reactive liquid or gaseous medium that is selected from the group including: alcohols, aldehydes, alkynes, alkenes, amines, azides, carboxylic acids, ketones, nucleic acids, and solutions of peptides and proteins.
• the first material possesses semi-conductive properties.
• the method can include ball milling with a high energy ball mill.
• the method can include ball milling as a batch operation.
• the method can include ball milling as a continuous operation.
• the functionalized nanoparticles exhibit size-dependent quantum confinement effects including photoluminescence.
• the functionalized nanoparticles are soluble in organic solvents, including but not limited to a reactive medium.
• the functionalized nanoparticles are soluble in aqueous systems, including but not limited to the reactive medium.
• the reactive medium contains polyfunctional molecules including but not limited to dicarboxylic acids and diols such that the polyfunctionalized nanoparticles are further reactive.
• the polyfunctionalized nanoparticles are covalently linked together.
• the functionalized nanoparticles exhibit strong covalent linkages between the first material and the reactive medium.
• the method of the present invention forms stable nanoparticles.
• the method includes providing a first material, providing a reactive liquid or gaseous medium, ball milling the first material in the reactive liquid or gaseous medium to provide a liquid phase and a solid phase.
• the liquid phase preferably contains nanoparticles.
• a stainless steel milling vial is loaded under inert atmosphere with chunks of single-crystal silicon and the reactive organic liquid of choice.
• Stainless steel milling balls are added to the vial, which is then sealed and subjected to HEBM. Ongoing ball-ball and ball-wall impacts during milling impart mechanical energy into the system, and silicon pieces trapped in these collisions fracture, reducing particle size and creating fresh surface.
• This newly created surface is highly reactive and provides sites for direct reaction between the silicon and the reactive organic, resulting in the formation of covalent bonds.
• silicon particle sizes are reduced into the nano-domain via comminution, and the direct surface reaction continues as fresh surface is continually produced via facture.
• milling is preferably performed for a continuous period of 24 hours.
• An advantage of the present invention in addition to producing stable, functionalized nanoparticles in a single mechanochemical step, is that the liquid phase produced by the single mechanochemical step separates the nanoparticles of interest from the larger particles by solubalizing these nanoparticles in the liquid phase.
• the present invention inherently includes a separation technique for the size of particles (nanoparticles) which are of interest from those larger ones which are not of interest.
• the present invention includes a method of forming stable functionalized nanoparticles, comprising providing a first material; providing a reactive medium; and reducing, in the reactive medium, the first material to particles having dimensions of no greater than 100 nm in size, the reactive medium functionalizing the particles in the first material as the particles are formed to provide stable functionalized nanoparticles.
• the first material is mechanically reduced to nanoparticles.
• ball milling is used to mechanically reduce the first material to nanoparticles, though impactors, for example, can instead used to mechanically reduce the first material to nanoparticles.
• the particles have dimensions of no greater than 50 nm. More preferably, the particles have dimensions of no greater than 20 nm. Sometimes, it is preferable that the particles have dimensions of no greater than 5 nm.
• the present invention also includes a method of mechanochemically making stable functionalized nanoparticles, comprising providing a first material; providing a reactive medium; and repeatedly mechanically impacting the first material in the presence of the reactive medium until a desired quantity of nanoparticles is produced, wherein the reactive medium reacts with the first material as the nanoparticles are produced to functionalize the nanoparticles.
• the present invention includes a method of forming stable functionalized nanoparticles, comprising providing a first material; providing a reactive medium; and ball milling said first material in said reactive medium to provide ball milled nanoparticles.
• the present invention includes a method of forming stable functionalized nanoparticles, comprising providing a first material; providing a reactive medium; ball milling said first material in said reactive medium to provide a fluid phase; and wherein in step "c" the fluid phase contains nanoparticles.
• the ball milling also produces a solid phase.
• the reactive medium can be selected from the group consisting of: alcohols, aldehydes, alkynes, alkenes, amines, carboxylic acids, nucleic acids, and solutions of peptides and proteins, azides, ketones, epoxides, amides, esters, amino acids, organic halides, thiols, and carbohydrates, for example.
• the reactive medium is liquid or gaseous.
• the reactive medium is pure liquid, though the reactive medium can comprise a solution.
• the reactive medium can comprise a supercritical fluid solution.
• the functionalization is passivation.
• the nanoparticles possess at least one property from the group consisting of: semiconductive, magnetic, radioactive, conductive, and luminescent properties. It might be advantageous for the nanoparticles to possess at least two properties from the group consisting of: semiconductive, magnetic, radioactive, conductive, and luminescent properties; the nanoparticles can possess phosphorescent and/or fluorescent properties.
• the nanoparticles can target certain cells in a living organism, such as by entering certain cells in a living organism. These cells can comprise cancer cells, endothelial cells and stem cells, for example.
• the nanoparticles comprise can silicon passivated with hydrophilic groups that allow transport through a cell membrane.
• the method nanoparticles can have properties which allow the nanoparticles to act as biological markers.
• the nanoparticles can comprise silicon passivated with hydrophilic groups that allow transport through a cell membrane.
• the nanoparticles can also comprise germanium passivated with hydrophilic groups that allow transport through a cell membrane.
• the nanoparticles can also comprise germanium passivated with hydrophilic groups that allow transport through a cell membrane.
• the ball milling is high energy ball milling.
• the ball milling can be a batch operation or a continuous operation.
• the condensation or radical-chain polymers can comprise, for example, polyamides, polyvinylcholoride, polyethylene, polypropylene, polyimides, or polyethers.
• the first material is altered from an indirect band gap semiconductor to a direct band gap semiconductor through high energy ball milling.
• the present invention includes as well nanoparticles produced by the method of any prior claim.
• Figure 1 is a schematic diagram that illustrates the overall procedure for production of alkyl-passivated silicon nanoparticles, according to the method of the present invention
• Figure 2 is a transmission electron microscope (TEM) image obtained of suspended silicon nanoparticles produced by milling for twenty-four hours in 1-octyne, and wherein a number of nanoparticles are indicated by arrows in the image and can be seen with sizes ranging from 1-4 nm, with few particles in the range of 5-30 nm
• Figures 3 and 4 are enlargements of the two nanoparticles labeled "B" and "C" in
• Figure 5 shows a Fourier transform infrared spectrum obtained from silicon nanoparticles produced by milling for twenty-four hours in 1-octyne, and wherein for analysis, the nanoparticles were isolated from the milling solution by rotary evaporation, and were dissolved in carbon disulfide;
• Figure 11 is a transmission electron micrograph of a narrow size distribution of germanium nanoparticles from Fraction 6;
• Figure 15 shows photoluminescence spectra of various fractions of germanium nanoparticles
• Figure 16 is a low magnification TEM Image of water-soluble germanium nanoparticles featuring larger nanoparticles
• Figure 19 is a UV- Vis absorbance and photoluminescence spectra of germanium nanoparticles in water
• Figure 20 shows a) FTIR spectrum of passivated silicon nanoparticles produced by milling in air b) FTIR spectrum of passivated silicon nanoparticles produced by milling in 1-octyne for 24 hours c) FTIR spectrum of passivated silicon nanoparticles produced by milling in 1-octene for 24 hours d) FTIR spectrum of passivated silicon nanoparticles produced by milling in 1-octaldehyde for 24 hours e) FTIR spectrum of passivated silicon nanoparticles produced by milling in octanoic acid for 24 hours f) FTIR spectrum of passivated silicon nanoparticles produced by milling in 1-octanol for 24 hours;
• Figure 21 shows the resulting structures of silicon nanoparticle surface-bound 1- octyne, 1-octene, 1-octaldehyde, octanoic acid, and 1-octanol;
• Figure 22 shows solubilized passivated nanoparticle concentration against the passivating molecule chain length
• Figure 24 shows emissions of passivated silicon nanoparticles produced by milling in 1-hexyne ( ⁇ ), 1-octyne (A), 1-decyne (•), and 1-dodecyne ( ⁇ ), when excited under 360 nm light.
• the present invention includes a novel procedure for synthesis of stable alkyl- or alkenyl-passivated silicon nanoparticles using high-energy ball milling.
• the high energy ball mill can be a SPEX-type mill.
• the impact energy for SPEX mills ranges within the intervals 0.023 - 0.084 J and 0.069 - 0.252 J for the 4 g and 12 g balls, respectively.
• High energy ball mills like the SPEX models have ball velocities of around 4 m/s, which translates to kinetic energy inputs of 0.012 J/hit or power inputs of 0.24 W/g-ball.
• SPEX type mills and stainless steel vials are commercially available (http ://www. spexsp .com) .
• the vials can be nylon vials made from Nylon 6/6 and of the same dimensions as the commercially available stainless steel vials.
• the main advantage of this mechanochemical approach is the simultaneous production of silicon nanoparticles and the chemical passivation of the particle surface by alkyl or alkenyl groups covalently linked through strong Si-C bonds.
• This invention embodies a novel and successful method for the mechanochemical preparation of stable alkyl- or alkenyl-passivated silicon nanoparticles.
• This green chemistry approach achieves a direct alkylation of the fresh silicon surface without the assistance of an unstable hydrogen-terminated intermediate or the use of any corrosive or toxic chemicals.
• the nanoparticles produced are of notably small sizes for a top-down comminution method, as particles less than 10 nm have been observed. Such sizes are not readily achievable with traditional grinding techniques.
• the exhibited blue fluorescence and obvious Stokes shift indicate that the nanoparticles are largely oxide-free.
• the nanoparticles prepared by this method have proven to be thermally-stable and maintain their fluorescence over periods of months. This method therefore provides a simple and effective way of producing alternatively passivated silicon nanoparticles.
• passivated silicon nanoparticles via high energy ball milling as described above is traditionally performed in a batch- wise method; i.e., the reactants are loaded in a vial, the process proceeds to completion in the closed container, and the products are removed. No material crosses an imaginary boundary surrounding the milling vial.
• the process can be made continuous, or non-batch-wise, by providing an input and output stream to the milling vial such that reactants and products continuously cross an imaginary boundary surrounding the milling vial.
• the continuous production of functionalized nanoparticles in the proposed continuous mechanochemical attrition device can be modeled as a continuous stirred tank reactor (CSTR).
• CSTR continuous stirred tank reactor
• reactants flow in (solvent, coarse silicon chunks), and products flow out (solubilized silicon nanoparticles, solvent, and partially-functionalized silicon particles).
• FIG. 1 The overall procedure for production of alkyl-passivated silicon nanoparticles is illustrated in Figure 1.
• Stainless steel milling balls are added to the vial, which is then sealed and placed in the high-energy ball mill (e.g. SPEX Sample Prep 8000 Series high energy ball mill, www.spexsp.com).
• the milling balls are typically one half inch (1.27 cm) diameter. Other sizes are available. The diameters could be between about 1 - 50 mm.
• High energy ball milling (HEBM) utilizes ball velocities of around 4 m/s, which translate to kinetic energy inputs of 0.012 J/hit, or power inputs of 0.24 W/g-ball.
• Measured values of specific intensity for high energy ball milling have been reported in the range 0.2 - 1.2 W/g, which is much greater than that found in other types of mills such as rotary mills, or other comminutive processes such as grinding.
• the ongoing impacts and collisions of the milling balls (ball-ball and ball- wall impacts) during high energy ball milling impart a significant amount of mechanical energy to the system which cause the silicon pieces to fracture, thus reducing particle size and creating fresh silicon surface.
• the newly-created surface in high energy ball milling is highly reactive and provides sites for direct reaction between the silicon and the reactive medium, preferably and alkene or alkyne. The alkene or alkyne reacts with the silicon surface resulting in the formation of a covalent Si-C bond.
• liquid hydrocarbon phase that now contains functionalized and solublized nanoparticles
• a "sediment" phase that contains a variety of particles, including partially- functionalized and/or partially-comminuted particles.
• the solvent can be easily removed, leaving a distribution of functionalized nanoparticles.
• Figure 2 is a transmission electron microscope (TEM) image obtained of suspended silicon nanoparticles produced by milling for 24 hours in 1-octyne. A number of nanoparticles can be seen with sizes ranging from 1-4 nm, with few particles in the range of 5 to 30 nm.
• the high-resolution TEM images in Figures 3 and 4 show individual single-crystal silicon particles with diameters of approximately 6 nm and 9 nm, respectively. However, the majority of nanoparticles in Figure 2 are even smaller than this, demonstrating that nanoparticles are produced of notably small size for such a top- down method.
• EDS Energy dispersive x-ray spectroscopy
• Figure 5 shows a Fourier transform infrared (FTIR) spectrum obtained on silicon nanoparticles produced by milling for 24 hours in 1-octyne.
• FTIR Fourier transform infrared
• the nanoparticles were isolated from the milling solution by rotary evaporation, and were dissolved in carbon disulfide. Carbon disulfide was chosen as the solvent such that its absorption peaks spectrum would not interfere with those of the nanoparticles' spectrum.
• the infrared spectrum shows clear evidence of an organic layer, as noted by the strong C- H stretching bands in the 2800-3000 cm “1 , as well as C-H vibrational modes at 1374 cm-1 and 717 cm “1 .
• the pronounced peaks and -1257 cm “1 , -806 cm “1 , and -796 cm “1 correspond to Si-C bonds, indicating that the 1-octyne is indeed bound covalently to the surface of the particle.
• NMR Nuclear magnetic resonance spectroscopy
• Figure 6 shows a 13 C ⁇ 1 H ⁇ NMR spectrum
• Figure 7 shows an 1 H NMR spectrum, both obtained on prepared alkyl coated silicon nanoparticles isolated from the milling solvent and dispersed in methylene chloride-d.
• the assignment of CH multiplicities was determined by use of the multipulse distortionless enhancement by polarization (DEPT) sequence in a separate experiment.
• the 13 C spectrum of the nanoparticles clearly shows a uniformity of chemical environment for the alkyl chain, exhibiting a single methyl resonance and a distinct number of methylene chain carbons.
• Figure 8 shows the PL excitation-emission spectrum of alkyl-passivated silicon nanoparticles produced by milling for 8 hours with 1-octyne as the reactive media.
• the particles exhibit an excitation peak at around 327 nm, and an emission peak at around 405 nm.
• Figure 13 is a high resolution transmission electron micrograph of fraction 6 showing approximately 5nm germanium nanoparticles. The lattice fringes are clearly visible on the particles indicating that they are single crystal.
• Figure 14 shows optical absorption spectra of different fractions of germanium nanoparticles. Early fractions (larger particles) show a more pronounced tailing to longer wavelengths.
• Figure 15 shows photoluminescence spectra of various fractions of germanium nanoparticles. Later fractions (smaller particles) show higher energy (shorter wavelength) luminescence in accordance to quantum size effects.
• the solution contained dimethylamino-1-propyne passivated germanium nanoparticles which are soluble.
• the 3-dimethylamino-l-propyne was removed by rotary- evaporation to yield solid nanoparticles.
• Approximately 20ml of distilled water was added to the vial to further dissolve remaining nanoparticles from the residue.
• the water was removed from this fraction by rotary-evaporation to obtain a second batch of dry nanoparticle product.
• This nanoparticle product is soluble in water, methanol or other polar solvents and can be redispersed in those solvents for characterization. Characterization: FTIR spectra were obtained at 1 cm "1 resolution with 1000 scans using a Bruker IFS-55 spectrometer.
• TEM images were taken with a JEOL 2011 TEM using an accelerating voltage of 200 kV.
• EDS data were obtained in the TEM using an Oxford Inca attachment, using a 3 nm beam spot.
• NMR spectra were obtained on a Bruker Avance 300 MHz high resolution NMR spectrometer.
• the excitation-emission spectra and photoluminescence data from the nanoparticles were obtained using a Varian Cary Eclipse spectrofluorimeter. Particles were dissolved in distilled water, and UV- Visible absorbance peaks obtained on a Cary 50 spectrophotometer provided reference peaks for the initial excitation wavelengths used during PL analysis.
• Figure 16 is a low magnification TEM Image of water-soluble germanium nanoparticles featuring larger nanoparticles.
• Figure 17 is a higher magnification image of germanium nanoparticles showing the size of many of the smaller particles.
• Figure 18 is a high resolution image of a single nanoparticle. The lattice fringes of this particle indicate that it is single crystal.
• Figure 19 is a UV- Vis absorbance and photoluminescence spectra of germanium nanoparticles in water.
• the present inventors published a new method for the simultaneous production of silicon nanoparticles and the chemical passivation of the particle surface by alkyl/alkenyl groups covalently linked through Si-C bonds (A. S. Heintz, M. J. Fink, B. S. Mitchell. Adv.
• Stainless steel milling balls are added to the vial, which is then sealed and subjected to HEBM.
• Ongoing ball-ball and ball- wall impacts during milling impart mechanical energy into the system, and silicon pieces trapped in these collisions fracture, reducing particle size and creating fresh surface.
• This newly created surface is highly reactive and provides sites for direct reaction between the silicon and the reactive organic, resulting in the formation of covalent bonds.
• HEBM silicon particle sizes are reduced into the nano- domain via comminution, and the direct surface reaction continues as fresh surface is continually produced via facture.
• milling is preferably performed for a continuous period of 24 hours.
• Figure 20 shows a series of Fourier transform infrared (FTIR) spectra obtained on silicon nanoparticles produced by milling in 1-octyne (spectrum b), 1-octene (spectrum c), 1-octaldehyde (spectrum d), octanoic acid (spectrum e), and 1-octanol (spectrum f).
• FTIR Fourier transform infrared
• Silicon Nanoparticles 1.0 g of silicon pieces of 99.95% purity obtained from Sigma-Aldrich were placed in a stainless steel milling vial along with two stainless steel milling balls, each with a diameter of 1.2 cm and weighing approximately 8.1 g. In a glovebox under nitrogen atmosphere, the vial was loaded, filled with approximately 25 mL of the desired liquid media, and then tightly sealed. For reactive media, 1-octanol > 99% purity, octyl aldehyde > 99% purity, and octanoic acid > 98% purity were all obtained from Sigma-Aldrich.
• Nanoparticle Solubility One of the main advantages of the developed production method is that the passivated silicon nanoparticles become solubilized in the liquid milling medium during milling. This allows for easy collection, and facilitates an initial separation of the passivated nanoparticles by size via sedimentation.
• the chain length of the passivating molecule should have an effect on the solubility of passivated silicon nanoparticles within the milling solution.
• the net intermolecular attractive force between the nanoparticle and the liquid will increase; essentially, the nanoparticle becomes more 'solvent-like' as the passivating molecules become larger.
• the attachment of larger passivating molecules to the nanoparticle surface should allow for the solubilization of larger nanoparticles.
• Figure 22 shows the mass concentration in the milling solution of passivated silicon nanoparticles formed by milling in the presence of alkynes of carbon chain lengths of 6, 8, 10, and 12. As the chain length of the reactive liquid molecule increases, the concentration of nanoparticles in solution increases as well.
• Table 2 lists the process yields for passivated silicon nanoparticles formed by milling in the presence of alkynes of carbon chain lengths of 6, 8, 10, and 12. Yet again, there is an observed increase in the amount of nanoparticles that remain solubilized. Indeed, as the chain length of the passivating molecule is increased, a greater mass of silicon nanoparticles becomes solubilized in the liquid medium.
• Table 2 Process yields of passivated silicon nanoparticles produced by milling in alkynes of various chain lengths.
• the concentration of nanoparticles within the milling solution as presented above only goes to show a greater overall mass of the solubilized nanoparticles, and speaks nothing of their size.
• the relation between the size of the solubilized nanoparticles and passivating molecule chain length can be achieved through a comparison of their optical properties. Recall that the bandgap of a silicon nanoparticle is size-dependent; smaller silicon nanoparticles have larger bandgaps, and will thus luminesce at higher energies.
• Figure 23 shows the emissions of silicon nanoparticle passivated with alkyl molecules of different chain lengths when excited at 420 nm. For ease of comparison in peak location, the emissions have been normalized to unity.
• FIG. 24 shows the emissions of silicon nanoparticle passivated with alkyl molecules of different chain lengths when excited at 360 nm, again normalized to unity. Although narrower emissions are observed due to excitation of the smaller populations, in similar fashion to before a red-shift is observed with increasing passivating molecule chain length.
• a semiconductor material such as silicon or germanium, is altered from an indirect band gap semiconductor to a direct band gap semiconductor through high energy ball milling.
• the reactive medium includes polyfunctionalized nanoparticles that are further reactive in specialized conditions.
• the high energy ball milling apparatus takes the form of a fluidized bed in which the reactive medium carries the silicon or other material to be comminuted into the fluid bed and in doing so provides momentum to the milling balls, causing them to collide.
• the passivation process proceeds as previously described, but the nanoparticles are carried out of the fluidized bed in the spent reactive medium.
• the milling balls are replaced by impactors, which traverse back and forth in an enclosed preferably polymeric vial.
• the silicon (or other material) fractures in the presence of the reactive medium as previously described, except that collisions are between the impactor and the end surface of the vial.
• impactors can be cylindrical and have dimensions of 1 cm in diameter by 3 cm long for example, and be made of any magnetic material such as steel (as the impactors are preferably agitated with electromagnets (the impactors are preferably magnetic because the preferred cryogenic mill (6750 freezer mill produced by SPEX) uses a magnet to make the impactor move back and forth, whereas the SPEX high energy ball mill uses a mechanical motor and swing arm to get the vial moving, the cryomill instead uses magnets to move the impactor)).
• the preferred cryogenic mill (6750 freezer mill produced by SPEX) uses a magnet to make the impactor move back and forth
• the SPEX high energy ball mill uses a mechanical motor and swing arm to get the vial moving
• the cryomill instead uses magnets to move the impactor
• the passivated silicon nanoparticles are formed in a batch- wise operation.
• the passivated silicon nanoparticles are formed and removed from the high energy ball milling apparatus in a continuous manner.

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