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WO2008030110A2 - Procédés de formation de nanoparticules - Google Patents

Procédés de formation de nanoparticules Download PDF

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Publication number
WO2008030110A2
WO2008030110A2 PCT/NZ2007/000246 NZ2007000246W WO2008030110A2 WO 2008030110 A2 WO2008030110 A2 WO 2008030110A2 NZ 2007000246 W NZ2007000246 W NZ 2007000246W WO 2008030110 A2 WO2008030110 A2 WO 2008030110A2
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WO
WIPO (PCT)
Prior art keywords
nanoparticles
group
decomposition
metal
bonding agent
Prior art date
Application number
PCT/NZ2007/000246
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English (en)
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WO2008030110A3 (fr
Inventor
Richard David Tilley
Christopher William Bumby
Original Assignee
Victoria Link Limited
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Victoria Link Limited filed Critical Victoria Link Limited
Priority to US12/439,472 priority Critical patent/US20100139455A1/en
Priority to AU2007293765A priority patent/AU2007293765A1/en
Priority to EP07834850A priority patent/EP2059480A4/fr
Priority to JP2009526561A priority patent/JP2010502540A/ja
Priority to CA002662006A priority patent/CA2662006A1/fr
Publication of WO2008030110A2 publication Critical patent/WO2008030110A2/fr
Publication of WO2008030110A3 publication Critical patent/WO2008030110A3/fr

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    • 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
    • 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
    • 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

Definitions

  • the present invention relates to methods for preparing nanoparticles of group IV elements. It relates particularly to the preparation of nanoparticles of Si, Ge and Sn, and binary and ternary alloys of these elements.
  • the invention relates to quantum dots, also known as nanoparticles or nanocrystals.
  • Nanoparticle is generally invoked to refer to particles that have an average diameter between about 1 run and about 100 nm. Nanoparticles have a size intermediate between individual atoms and macroscopic bulk solids. Nanoparticles that have diameters smaller or comparable to the Bohr exciton radius of the material can exhibit quantum confinement effects. Such effects can alter the optical, electronic, catalytic, optoelectronic, thermal and magnetic properties of the material.
  • nanoparticles exhibit photoluminescence effects that are significantly greater than the photoluminescence effects observed for macroscopic crystals having the same composition. Additionally, these quantum confinement effects may vary as the size and surface chemistry of the nanoparticle is varied. For example, size-dependent discrete optical and electronic transitions exist for nanoparticles of group II- VI semiconductors (e.g., CdSe) and group III- V semiconductors (e.g., InP).
  • group II- VI semiconductors e.g., CdSe
  • group III- V semiconductors e.g., InP
  • the present invention provides a method of preparing nanoparticles of one or more group IV metals or alloys thereof comprising the steps of: reacting, under an inert atmosphere, at atmospheric pressure and with heating, one or more group IV metal precursors with a decomposition-promoting reagent in a liquid reaction medium comprising a high temperature surfactant; adding a surface-bonding agent; and recovering the nanoparticles.
  • the liquid reaction medium may comprise a high temperature solvent and a high temperature surfactant.
  • the group IV metal precursor comprises a compound of the general formula: G(Ar) x Y 4-x ; wherein G is the group IV metal, Ar is aryl, Y is halo and x takes a value that is at least 0 and no greater than 4.
  • the group IV metal precursor comprises a compound of the general formula: G(Ar) y Y 2-y wherein G is the group IV metal, Ar is aryl, Y is halo and y takes a value that is at least 0 and no greater than 2.
  • the decomposition-promoting reagent is selected from one of: a) a strong reducing agent; or b) S, Se 5 Te, P or As or a compound comprising one or more of these elements in a zero valence state.
  • the method of the invention includes a further step of adding a quenching agent prior to adding the surface-bonding agent.
  • the step of adding a quenching agent is prior to adding the surface-bonding agent but after adding the decomposition-promoting reagent.
  • the decomposition-promoting agent is selected from the group consisting of: S; Se; Te; P; As; and compounds comprising one or more of these elements in a zero valence state, and the method includes the step of adding a quenching agent.
  • the surface-bonding agent may also act as the quenching agent.
  • the step of adding the surface-bonding agent is effective to prevent aggregation of the nanoparticles.
  • the surface-bonding agent interacts with the nanoparticles to provide an organic layer surrounding the nanoparticles.
  • the surface-bonding agent is a carboxylic acid, aldehyde, amide or alcohol. More preferably, the surface-bonding agent is a carboxylic acid and, therefore, the resulting nanoparticles are "acid-terminated".
  • the surface-bonding agent comprises an alkenyl or alkynyl moiety.
  • one preferred embodiment of the invention comprises preparing acid-terminated nanoparticles of one or more group IV metals or alloys thereof; preferably acid-terminated nanoparticles of Ge, Si or Sn, or a binary or ternary alloy thereof.
  • the step of reacting includes heating to a temperature between about 100°C and about 400 0 C; more preferably to between about 200 0 C and about 400 0 C; more preferably to about 300 0 C.
  • the method of the invention is complete in less than about 30 minutes. More preferably, the method is complete in less than about 20 minutes.
  • the method includes a further step of purifying the nanoparticles.
  • the method produces nanoparticles with size in the range about 1 nm to about 20 nm, more preferably about 1 nm to about 10 nm.
  • the method produces a monodisperse nanoparticle size distribution such that the nanoparticle diameter has a standard deviation of less than 20% of the mean diameter. More preferably, the method produces a monodisperse nanoparticle size distribution such that the nanoparticle diameter has a standard deviation of less than 5% of the mean diameter.
  • the method produces a solution of nanoparticles having a concentration >1 gl '1 ; more preferably >1 O gI "1 .
  • the method produces nanoparticles with a chemical reaction yield >50%; more preferably >60%.
  • the method produces nanoparticles that produce luminescence in response to optical excitation with a quantum efficiency in excess of 1%. More preferably, the nanoparticles produce luminescence in response to optical excitation with a quantum efficiency in excess of 20%.
  • the method produces nanoparticles with a high degree of crystallinity.
  • G is germanium
  • the crystal structure is substantially that of diamond.
  • the present invention provides nanoparticles of a group IV metal or a group, IV metal alloy prepared substantially according to the method of the invention.
  • the present invention provides a method of preparing chemically functionalised nanoparticles of one or more group IV metals or alloys thereof comprising the steps of: reacting hydrogen-terminated nanoparticles of the group IV metals or alloys thereof with a compound of the formula L-R-N; wherein R is alkyl, alkenyl or aryl, L is a group having the desired functionality and N is a functional group capable of bonding to the hydrogen- terminated nanoparticle surface; and recovering the chemically functionalised nanoparticles.
  • Preferred chemically functionalised nanoparticles include water soluble nanoparticles prepared by reacting hydrogen-terminated nanoparticles with a compound of the formula L-R-N; wherein L is a polar functional group.
  • An alternative embodiment provides biochemically functionalised nanoparticles reacting hydrogen-terminated nanoparticles with a compound of the formula L-R-N; wherein L is a functional group capable of binding to a biological antibody and/or biologically active molecule.
  • the present invention provides chemically functionalised nanoparticles of one or more group IV metals or alloys thereof prepared according to the method of the invention.
  • the present invention provides a method of preparing hydrogen-terminated nanoparticles of one or more group IV metals or alloys thereof; preferably hydrogen-terminated nanoparticles of Ge, Si or Sn, or a binary or ternary alloy thereof; comprising reacting acid-, aldehyde-, alcohol- or amide-terminated nanoparticles of the invention with a hydride reducing agent in the absence of water and oxygen; and recovering the hydrogen-terminated nanoparticles.
  • the hydrogen-terminated nanoparticles are prepared from acid-terminated nanoparticles of the invention.
  • the present invention provides hydrogen-terminated nanoparticles of one or more group IV metals or alloys thereof prepared substantially according to the method f the invention.
  • Nanoparticles of the invention are suitable for incorporation into a matrix of a second material such as a polymeric, ceramic, metallic or other material. They are also suitable for the preparation of devices such as optoelectronic devices, including photovoltaic devices, and biochemical imaging devices.
  • aryl is intended to include optionally substituted aromatic radicals including, but not limited to: phenyl; naphthyl; indanyl; biphenyl; and the like; and optionally substituted heteroaromatic radicals including, but not limited to: pyrimidinyl; pyridyl; pyrrolyl; furyl; oxazolyl; thiophenyl; and the like.
  • alkyl is intended to include optionally substituted straight chain, branched chain and cyclic saturated hydrocarbon groups.
  • alkenyl is intended to include optionally substituted straight chain, branched chain and cyclic mono-unsaturated hydrocarbon groups.
  • alkynyl is intended to include optionally substituted straight chain and branched chain hydrocarbon groups that include a -G ⁇ C- moiety.
  • halo refers to an iodo, bromo, chloro or fluoro group.
  • each of such groups may be independently selected.
  • the term "optionally substituted” is intended to mean that one or more hydrogen atoms in the group is replaced with one or more independently selected suitable substituents, provided that the normal valency of each atom to which the optional substituent/s are attached is not exceeded.
  • nanoparticle As used herein, the terms “nanoparticle”, “nanocrystal” and “quantum dot” refer to any particle less than 100 nanometres in size.
  • nanoparticle may have a higher degree of crystallinity than a nanoparticle
  • references to nanoparticles in this specification should be understood by one skilled in the art to also include nanocrystals and quantum dots.
  • the "size" of a nanoparticle refers to the diameter of the core of the nanoparticle.
  • a nanoparticle will typically comprise a core of one or more first materials and can optionally be surrounded by a shell of a second material.
  • a nanoparticle of the invention will typically comprise a "core" of a group IV metal (such as silicon, germanium or tin) or an alloy thereof and can be optionally surrounded by a “shell” of a second material.
  • the term “core” refers to the central region of the nanoparticle.
  • a core can substantially include a single homogeneous material.
  • a core may be crystalline, polyatomic or amorphous. While a core may be referred to as crystalline, it is understood that the surface of the core may be amorphous or polycrystalline and that this non-crystalline surface layer may extend to a finite depth into the core.
  • the "shell" of a nanoparticle may comprise a layer of either organic or inorganic material or a bi-layer comprising both an inner inorganic layer and an outer organic layer, or vice versa.
  • the shell material may be selected to minimise the number of "dangling bonds" at the surface of the nanoparticle core.
  • the shell material in the nanoparticles of the present invention is generally dictated by the surface-bonding agent employed in the method of the invention.
  • the term "photoluminescence" of nanoparticles refers to the emission of light of a first wavelength (or range of wavelengths) by the nanoparticles following irradiation with light of a second wavelength (or range of wavelengths).
  • the first wavelength (or range of wavelengths) is longer than the second wavelength (or range of wavelengths).
  • the term “quantum efficiency" of the nanoparticles refers to the ratio of the number of photons emitted by the nanoparticles to the number of photons absorbed by the nanoparticles.
  • the term "monodisperse”, with respect to nanoparticles, refers to a population of nanoparticles wherein at least 75% and preferably 100% of the population, (or an integer or non- integer there between) falls within a specified particle size range.
  • 'monodispersed' particles has a standard deviation of less than 20% of the mean diameter and a 'highly monodispersed' population has a standard deviation of less than 5% of the mean diameter.
  • surfactant molecule refers to a molecule containing a non-polar end comprising an alkyl, alkenyl or aryl group or combination thereof and a polar end containing one or more groups selected from: various acids, such as carboxylic, sulfinic, sulfonic, phosphinic and phosphonic acids, and their salts; primary, secondary, ternary or quaternary amines; halides; oxides; sulfides; thiols; phosphines; phosphides; phosphates; and glycols.
  • various acids such as carboxylic, sulfinic, sulfonic, phosphinic and phosphonic acids, and their salts; primary, secondary, ternary or quaternary amines; halides; oxides; sulfides; thiols; phosphines; phosphides; phosphates; and glycols.
  • composition-promoting reagent refers to a compound or material that accelerates a chemical reaction involving a group IV metal precursor compound at a given temperature, such as to yield one or more group IV metals.
  • This invention may also be said broadly to consist in the parts, elements and features referred to or indicated in the specification of the application, individually or collectively, and any or all combinations of any two or more of said parts, elements or features, and where specific integers are mentioned herein which have known equivalents in the art to which this invention relates, such known equivalents are deemed to be incorporated herein as if individually set forth.
  • Figure 1 is a generalised flow diagram of the method of the invention
  • Figure 2 is a flow diagram of one embodiment of the method of the invention.
  • Figure 3 is a flow diagram of an alternative embodiment of the method of the invention.
  • Figure 4a is a transmission electron micrograph of germanium nanoparticles prepared according to the invention.
  • Figure 4b is another transmission electron micrograph of germanium nanoparticles prepared according to the invention.
  • Figure 5 is the X-ray diffraction data for germanium nanoparticles prepared according to the invention.
  • Figure 6 shows electron diffraction by germanium nanoparticles prepared according to the invention;
  • Figure 7 shows the luminescence spectra of germanium nanoparticles prepared according to the invention.
  • Figure 8 is a diagram of typical glassware apparatus useful in a method of the invention.
  • Figure 9a represents a chemically functionalised nanoparticle, having a surface organic layer, prepared according to the invention.
  • Figure 9b represents a hydrogen-terminated nanoparticle prepared according to the invention.
  • Figure 9c shows a carboxylic acid group bound to the surface of an acid-terminated nanoparticle prepared according to the invention.
  • the present invention relates to a method of forming nanoparticles comprising one or more group IV elements.
  • the method comprises forming nanoparticles that include a semiconductor material consisting of one or more of the elements Si, Ge and Sn.
  • the method comprises reacting, in a liquid reaction medium at atmospheric pressure and under an inert atmosphere, one or more group IV metal precursors, with a decomposition-promoting reagent.
  • the reaction is carried out by heating the reaction mixture.
  • the group IV metal precursors are sources of semiconductor material consisting of one or more of Si, Ge and Sn.
  • the decomposition-promoting reagent may be a reducing agent, a polymerising agent, or other suitable substance.
  • the method also includes the use of a high temperature surfactant in the reaction mixture.
  • the method includes the addition of a strongly-interacting surface-bonding agent to the reaction mixture. This surface-bonding agent forms an organic coating on the nanoparticle, preventing aggregation of the nanoparticles during subsequent crystal growth.
  • FIG. 1 The general method of preparing nanoparticles is illustrated in Figure 1. As shown in Figure 1, the method of the invention comprises four main steps:
  • a number of group IV metal precursors are suitable for use in a method of the invention. These include organometallic compounds containing a silicon, germanium or tin atom. Preferably, these organometallic compounds containing the silicon, germanium or tin atoms are tetravalently bonded to a combination of aryl groups and halides following the molecular formula: G(Ar) x Y 4-X where G is the group IV metal, Ar is aryl, Y is halo and x takes a value that is at least 0 and no greater than 4. ; - ⁇ ⁇
  • Such compounds include, but are not limited to: tetraphenylgermane; triphenylchlorogermane; diphenyldichlorogermane; phenyltrichlorogermane; tetraphenylsilane; triphenylchlorosilane; diphenyldichlorosilane; phenyltrichlorosilane; tetraphenylstannane; triphenylchlorostannane; diphenyldichlorostannane; phenyltrichlorostannane; as well as their bromo-, iodo- and fluoro- analogues.
  • the group IV metal precursor species includes a group IV atom divalently bonded to a combination of aryl groups and halides following the molecular formula: G(Ar) y Y 2-y where G is the group IV metal, Ar is aryl, Y is halo and y takes a value that is at least 0 and no greater than 2.
  • Ar is optionally substituted phenyl; more preferably phenyl.
  • the group IV precursor is the phenyl-substituted precursor G(Ph) x Y 4-x . This precursor is particularly preferred when the decomposition-promoting reagent is selected from the group consisting of: S; Se; Te; P; As; and compounds comprising one or more of these elements in a zero valence state (see below).
  • the group IV precursor may be a mixture of different group IV metal precursors, including those having different group IV metals. This can result in alloy or interphase formation in the final nanoparticles.
  • the primary role of the liquid reaction medium is to solvate the group IV metal precursors and the various reagents to ensure a homogenous liquid phase reaction.
  • the liquid reaction medium also provides a barrier to nanoparticle aggregation through the interaction of a high temperature surfactant with the nanoparticle surface. These measures can be effective in producing a high degree of monodispersity of the size of the nanoparticles.
  • liquid reaction medium should be thermally stable at the reaction temperature.
  • the liquid reaction medium comprises a high temperature surfactant and a high temperature solvent.
  • the high temperature surfactant also acts as the high temperature solvent.
  • high temperature means that the surfactant or solvent should be thermally stable under an inert atmosphere at the reaction temperature and have a boiling point in excess of the reaction temperature.
  • the reaction temperature is preferably between about 100°C and about 400 0 C; more preferably between about 200 0 C and about 400°C; more preferably about 300 0 C.
  • the surfactant possesses a molecular structure containing a functional group capable of interacting with the nanoparticle surface. This acts to form a thin layer of solvent material that is weakly bound to the nanoparticle surface. In such a way aggregation of the nanoparticles can be inhibited.
  • Preferred surfactants do not take part in parasitic side-reactions with the reagents or precursors.
  • Suitable surfactants that meet the above criteria may include, but are not limited to compounds of the formulae: R-NH 2 ; R-PH 2 ; R 3 N; R 3 P; R 2 NH; R 2 PH; R 4 N + ; and RE y ; wherein R is alkyl, alkenyl or aryl, E is an ethylene glycol group and N, P and H take their common IUPAC meaning.
  • Preferred high temperature surfactants include oleylamine, hexadecylamine, trioctylamine and trioctylphosphine. These surfactants act as co-ordinating solvents and so need no additional solvent.
  • suitable high boiling point organic solvents include, but are not limited to: alkanes, alkenes, aromatic hydrocarbons and other paraffins; mono- or poly-ethylene glycol ethers; crown ethers; and phenyl ethers.
  • the group IV metal precursor can be introduced into the liquid reaction medium either prior to or subsequent to heating of the liquid reaction medium to the reaction temperature.
  • the liquid reaction medium is heated to the desired reaction temperature under a flow of a suitable inert gas to purge gaseous contaminants from the reaction vessel prior to the introduction of the group IV metal precursor and other reagents.
  • Suitable inert gases are known to those persons skilled in the art. Such gases include, but are not limited to: nitrogen; argon; and helium. Preferably ? , the inert gas is nitrogen.
  • FIG. 8 shows a typical benchtop glassware apparatus suitable for this synthesis.
  • the liquid reaction medium 1 is contained in a three-necked round bottomed flask 2.
  • the temperature is monitored using a thermometer probe 3 housed in a protective glass enclosure 4.
  • the solution is stirred with a magnetic stir bar 5 and heat is applied 6, by a heating mantle, heat bath or similar apparatus.
  • Inert gas is admitted into the flask 2 via the gas inlet 7 and leaves via the outlet 10. Reagents can be added to the flask 2 using a syringe temporarily, admitted at the gas inlet 7.
  • a condenser 8 is also used to cool and condense vapour above the liquid reaction medium 1.
  • the condenser can be water cooled through the water inlet 9 and outlet 9 to an outer glass sheath. This reaction mixture is usually heated to the reaction temperature during step a), although it is possible to heat the mixture to the reaction temperature during step b).
  • the decomposition-promoting reagent is added to the solution of the group IV metal precursor in the liquid reaction medium, typically under conditions of heat and an inert atmosphere.
  • the decomposition-promoting reagent may be injected into the reaction vessel as a solution or suspension, hi a preferred embodiment, the decomposition-promoting reagent is added as a solution in a carrier liquid, which may be the same as that comprising the liquid reaction medium.
  • the decomposition-promoting reagent accelerates the decomposition of the group IV metal precursor at the reaction temperature to the elemental form of the group IV metal — typically Ge or Si or Sn (or alloys of these) as nanoparticles.
  • the generalised reaction scheme is as follows:
  • np indicates nanoparticle formation
  • the decomposition-promoting agent is a strong reducing agent.
  • the decomposition-promoting agent must be able to cleave the substituent-Ge, substituent-Si or substituent-Sn bond.
  • the decomposition-promoting agent must be able to cleave one or more Si-Ph, Sn-Ph or Ge-Ph bonds.
  • This strong covalent bond has previously been assumed to be stable to reductive attack, but the liquid phase method disclosed herein utilises a combination of high reaction temperatures and strong reducing agents to obtain elemental group IV metals from precursors containing Ge- Ph, Si-Ph or Sn-Ph bonds.
  • Example strong reducing agents include, but are not limited to, one or more of: sodium borohydride; lithium borohydride; potassium borohydride; sodium naphthalide; sodium anthracide; lithium naphthalide; lithium anthracide; potassium naphthalide; potassium anthracide; lithium aluminium hydride; sodium aluminium hydride; potassium aluminium hydride; sodium hydride; lithium hydride; potassium hydride; sodium; lithium; potassium; sodium sulfide; lithium sulfide; potassium sulfide; tin dichloride; tin dioleate; tin dibromide; tin di-iodide; sodium amide; sodium azide; and triphenyl phosphine.
  • the decomposition- promoting reagent comprises one or more elements from group V or VI, or a compound comprising one or more of these elements in a zero valence state, wherein the group V or VI elements are selected from the group comprising: sulfur; selenium; tellurium; phosphorus; and arsenic.
  • the decomposition-promoting reagent comprises S or Se (or a compound comprising one of these elements in a zero valence state).
  • S or Se or a compound comprising one of these elements in a zero valence state.
  • np indicates nanoparticle formation
  • the by-products may include: Ph-S-Ph 5 Ph-Cl 5 Ph, Ph-Ph 5 Cl 2 , S and GeS 2 . ; .
  • a quenching agent is typically used in the embodiment of the invention illustrated in Figure 3. However, a quenching agent may also be used in those embodiments wherein the decomposition- promoting reagent is a strong reducing agent.
  • the quenching agent acts to remove excess decomposition-promoting reagent from the reaction mixture, thus eliminating any inhibitory effects this may have on nanoparticle growth.
  • the use of a quenching agent prevents the reaction of any excess decomposition- promoting reagent with the surface-bonding agent which, in some embodiments, is added to the reaction mixture after the quenching agent.
  • the decomposition-promoting reagent is selected from the group consisting of: S; Se; Te; P; As; and compounds comprising one or more of these elements in a zero valence state
  • a quenching agent is preferably added subsequent to precursor decomposition.
  • the decomposition-promoting reagent is selected from one of: a) a strong reducing agent, or b) S, Se, Te, P or As or a compound comprising one or more of these elements in a zero valence state;
  • the quenching reagent is a non-aqueous high boiling point acid.
  • Suitable non-aqueous high boiling point acids include, but are not limited to: carboxylic acids; and compounds containing one or more carboxylic acid groups.
  • the quenching agent may be a hydride reducing agent such as sodium borohydride, lithium borohydride, potassium borohydride, lithium aluminium hydride, sodium aluminium hydride, potassium aluminium hydride, sodium hydride, lithium hydride or potassium hydride.
  • the surface-bonding agent is added to the reaction mixture to prevent aggregation of the nanoparticles.
  • a surface-bonding agent can provide stronger interactions with the nanoparticle surface than those obtained from the high temperature surfactant within the liquid reaction medium. Typically, the surface-bonding agent is added in excess.
  • the surface-bonding agent it is possible to avoid parasitic side-reactions of the surface-bonding agent with the decomposition-promoting reagent by adding the surface-bonding agent after the initial decomposition of the precursor.
  • a second motivation for adding the strongly binding surface- bonding agent after the initial decomposition of the precursor is that very strong bonds between the nanoparticle and the surface-bonding agent may inhibit nanoparticle growth. Notwithstanding this point, it is possible to add the surface-bonding agent to the reaction mixture prior to, or at the same time as, the decomposition-promoting agent.
  • Suitable surface-bonding agents that may be susceptible to reduction as a parasitic side-reaction in those embodiments wherein the decomposition-promoting reagent is a strong reducing agent include, but are not limited to: trioctylphosphine oxide; carboxylic acids; sulfonic acids; phosphonic acids; alcohols; thiols; and other proton-donating compounds.
  • Suitable surface-bonding agents that may be susceptible to parasitic side-reactions in those embodiments wherein the decomposition-promoting reagent is selected from the group consisting of: S; Se; Te; P; As; and compounds comprising one or more of these elements in a zero valence state, include, but are not limited to: primary, secondary and ternary phosphines.
  • the surface-bonding agent comprises an alkenyl or alkynyl moiety
  • the surface-bonding agent may form stable bonds between the group FV metal and carbon at the nanoparticle surfaces
  • the surface-bonding agent comprises a compound of the formula R-N, wherein R is alkyl, alkenyl or aryl and N is a functional group capable of bonding to the surface of the group IV metal nanoparticle.
  • the surface-bonding agent may comprise a bi-functional compound of the formula L-R-N wherein R is alkyl, alkenyl or aryl, L is a group having the desired functionality and N is a functional group capable of bonding to the surface of the group IV metal nanoparticle.
  • the surface-bonding agent is the same as the quenching agent.
  • the excess surface-bonding agent acts to remove excess decomposition-promoting reagent from the reaction mixture.
  • the nanoparticles remain in suspension following the addition of the surface-bonding agent.
  • the particles are typically subject to a purification/recovery step:
  • the nanoparticles are recovered and optionally purified following their preparation according to the methods disclosed above. Recovery and purification may proceed by a number of techniques known to those skilled in the art. Such techniques include, but are not limited to: nanoparticle flocculation and centrifugation; or two phase separation in an appropriate choice of immiscible solvents.
  • An example purification procedure which is illustrative only, is: (a) addition of a flocculent to the reaction mixture;
  • Suitable flocculents include, but are not limited to: distilled or suitably purified water; alcohols including methanol, ethanol, propanol and butanol; methyl formamide; and acetone.
  • Suitable low boiling point solvents include, but are not limited to: toluene; tetrahydrofuran (THF); chloroform; dichloromethane; and liquid alkanes having fewer than 10 carbon atoms.
  • the methods of the present invention lead to the formation of nanoparticles and/or nanocrystals of group IV elements or alloys thereof.
  • the particles may be robust, chemically stable, crystalline, and may be coated by an organic or inorganic passivating layer.
  • the product of the method of the invention is described herein as a nanoparticle or nanocrystal, those persons skilled in the art will appreciate that the group IV metal nanoparticle has a surrounding layer, the composition of which is dependent on the surface-bonding agent.
  • the surface-bonding agent is oleic acid
  • the oleic acid will be bound to the surface as illustrated in Figures 9a and 9c.
  • Figure 9a shows the group IV metal nanoparticle core 70 with the surface-bonding agent 71, which may be a carboxylic acid such as oleic acid, forming a surface organic layer.
  • Figure 9b is a diagram of a hydrogen-terminated group IV metal nanoparticle produced according to one aspect of the present invention.
  • Figure 9c shows a carboxylic acid group, such as that present in oleic acid, binding to the surface of the group IV metal nanoparticle.
  • a further aspect of this invention is the preparation of hydrogen-terminated group IV metal nanoparticles from acid-, aldehyde-, alcohol- or amide-terminated group IV metal nanoparticles grown outside of a glovebox environment.
  • the hydrogen-terminated nanoparticles are prepared from acid- terminated nanoparticles.
  • Suitable hydride reducing agents include, but are not limited to: lithium aluminium hydride; sodium aluminium hydride; potassium aluminium hydride; lithium triethylborohydride; sodium triethylborohydride; sodium borohydride; lithium borohydride; potassium borohydride; hydrogen gas; sodium hydride; potassium hydride; lithium hydride; borane-tetrahydrofuran complex; lithium tri-tert-butoxyaluminium hydride; sodium cyanoborohydride; and di-isobutylaluminum hydride.
  • Suitable inert gases are known to those persons skilled in the art. Such gases include, but are not limited to: nitrogen; argon; and helium. Preferably, the inert gas is nitrogen.
  • the reaction is quenched with an alcohol.
  • Suitable alcohols include, but are not limited to: methanol; ethanol; butanol; and propanol.
  • a further aspect of this invention is the preparation of chemically functionalised group IV metal nanoparticles by the reaction of a specific chemically active species with the surface of the hydrogen-terminated nanoparticles of this invention.
  • the chemically active species may be a compound of the formula L-R-N wherein R is alkyl, alkenyl or aryl, L is a group having the desired functionality and N is a functional group capable of bonding to the hydrogen-terminated nanoparticle surface.
  • water soluble nanoparticles may be produced by reacting the hydrogen-terminated nanoparticles with a compound of the formula L-R-N, wherein L is a polar functional group.
  • biochemically functionalised nanoparticles may be prepared a compound of the formula L-R-N, wherein L is a functional group capable of binding to a biological antibody and/or biologically active molecule.
  • the methods of the present invention, and the resultant nanoparticles incorporate a number of favourable characteristics.
  • the method of the present invention may be carried out in a fumehood or benchtop location.
  • many of the prior art methods require high pressures and/or the use of controlled atmosphere glove-box techniques or other protective environments. This is because the method of the present invention is carried out at atmospheric pressure and uses comparatively benign or non-toxic reactants when compared with many of the prior art methods.
  • the methods described herein are capable of achieving high reaction yields of nanoparticles exceeding 60%. Such yields are achieved through the use of non-hydride decomposition agents, thus obviating the formation of the volatile by-products silane, germane, stannane and derivatives thereof, hi this way, the group IV elements in the precursor species remain within the reaction vessel until completion of the reaction.
  • the reaction terminates at solid phase nanoparticles, and the crystallisation of elemental particles from the reaction solution ensures that the decomposition reaction drives to completion.
  • yield figures given herein refer to the yields from syntheses in the absence of quenching agents, surfactants or surface active material.
  • the nanoparticles require short reaction times, typically less than one hour and more preferably less than 30 minutes.
  • the nanoparticles can be synthesised with solution concentrations in excess of 2 gl "1 and, in preferred embodiments, with concentrations in excess of 10 gl "1 .
  • Such production rates represent a significant improvement over many of the prior art processes.
  • Figures 4a and 4b show transmission electron microscope (TEM) images of germanium nanoparticles prepared according to the methods of the present invention.
  • the scale bar in both photographs is 20 nm. High monodispersity is observed. This is achievable through the homogeneous solution-phase nature of the reaction.
  • Figure 5 shows the X-ray diffraction data of germanium nanoparticles prepared according to the methods of the present invention and demonstrates the high crystallinity of the nanoparticles.
  • the copper peaks observed in the X-ray diffraction data are due to sampling of the TEM grid bars.
  • Preferred embodiments of the invention produce nanoparticles with a diameter standard deviation of less than 20% of mean diameter; more preferably less than 5% of mean diameter.
  • Figure 6 shows the electron diffraction pattern from 8 run germanium nanoparticles prepared according to the methods of the present invention.
  • the nanoparticles of the present invention emit coloured light at wavelengths within the visible spectrum
  • the nanoparticles emit light under optical excitation at near-infrared and infrared wavelengths less than the bandgap of the bulk crystalline material.
  • the wavelength of the light emitted by the nanoparticles may be tuned through manipulation of the nanoparticle size, the chemical make-up of the passivating layer and the chemical composition of the group IV metal or alloy comprising the nanoparticle.
  • the method disclosed herein provides a passivated germanium nanoparticle displaying discrete optical transitions and photoluminescence.
  • Figure 7 shows the typical luminescence (as a function of excitation wavelength) of a solution of germanium nanoparticles.
  • Preferred embodiments of the method of the present invention produce nanoparticles with luminescence having a quantum efficiency >1%, more preferably up to and in excess of 20%.
  • nanoparticles of the present invention have many possible applications, as would be understood by one skilled in the art.
  • the nanoparticles are observed to luminesce in the visible spectrum and may be utilised in the field of biomedical imaging or as a starting material for novel optoelectronic devices.
  • Group IV nanoparticles are of particular interest in the field of biomedical imaging where the long lifetime, high stability and low toxicity of germanium, silicon and tin is highly attractive compared to current alternatives.
  • the nanoparticles of the present invention may be incorporated into biochemical imaging markers.
  • the nanoparticles may have an average particle diameter of between about 1 and about 200 angstroms and will produce nearly monochromatic luminescence within the visible spectrum in response to optical excitation.
  • the biochemical imaging system may include a linker attaching, a biochemically active molecule to the nanoparticle, enabling the tagging of specific chemical compounds.
  • the system may contain more than one type of linker type, with each type of linker being attached to nanoparticles that luminesce at a different and nearly monochromatic, visible wavelength.
  • the nanoparticles of the present invention may be incorporated into optoelectronic materials by a variety of methods, including the deposition of a film of the nanoparticles upon a substrate.
  • the nanoparticles 5 may include, for example, silicon or germanium or an alloy thereof.
  • the nanoparticles may have an average particle diameter of between about 1 and about 200 angstroms.
  • the deposited nanoparticles may be sintered at a temperature between about 300 0 C and 900°C to produce a film of material exhibiting optoelectronic properties, hi certain embodiments, the film may consist of a plurality of nanoparticles resulting in a polycrystalline material. This material may be further used to produce a variety of electronic devices, including photovoltaic devices, infrared emitting devices and light emitting devices.
  • an optoelectronic material may include the incorporation of one or more nanoparticles into a matrix of one or more polymeric species whereby electrons can be transferred to and from the nanoparticles by means of external electronic contacts.
  • the nanoparticles may include silicon or germanium or an alloy thereof. At least one of the nanoparticles may have an average particle diameter of between about 1 nm to about 20 nm.
  • the said nanoparticle-incorporating matrix may be deposited upon a substrate or flexible film. This material may be further used to produce a variety of electronic devices including photovoltaic devices, infrared emitting devices and light emitting devices.
  • the nanoparticles of the present invention may be incorporated into photovoltaic devices for the generation of electrical power from optical and near-infrared radiation. Such devices may include a plurality of nanoparticles.
  • the photovoltaic devices may include electrical contacts at their anode and cathode.
  • the photovoltaic devices may include nanoparticles of a size optimised to provide maximum absorption of an incident solar spectrum.
  • An alternative procedure omits steps (2) and (3) from the procedure described in Example 1 and instead utilises solutions of sulfur in oleylamine and triphenylchlorogermane in oleylamine which are injected into the heated solvent at a temperature between 26O 0 C and 36O°C. The procedure is then followed as from step (5) of Example 1.
  • Step 10 Further dilute precipitate with flocculent and centrifuge. Repeat steps 9-11 until required purity is reached. Steps 9-11 may also be repeated on the supernatant to yield size selective precipitation of nanoparticles
  • step 6 If tetraglyme is used in step 6 a defined quantity of trioctylphosphine may also be added to the flask at this point
  • sodium napthalide breaks down at a temperature close to the boiling point of naphthalene ( ⁇ 220°C), but addition of naphthalene to a mixture containing triphenylchlorogermane and sodium metal at 275 0 C exhibits decomposition of the group IV metal precursor in the time required for the naphthalene to enter the solution, attain thermal equilibrium with its surroundings and then re- volatilise.
  • the reducing agent be homogeneously distributed within the solution.
  • the reducing agent should be fully soluble in the utilised solvent system such that crystallisation occurs from a completely homogeneous distribution of decomposed precursor molecules.
  • this req ⁇ irement may be relaxed, provided the heterogeneity of the distribution of the reducing agent is on a length scale that is comparable with the average diffusion length within the solution for a reduced group IV atom undergoing crystallisation.
  • the thermal breakdown of lithium aluminium hydride to LiH and AlH 3 at temperatures above 200 0 C is not a barrier to its utilisation in the methods of the present invention because the resulting highly disperse emulsion of LiH reacts completely with the precursor prior to aggregation of the insoluble hydride salt to form a homogeneous distribution of precursor decomposition products within the solution. Vigorous stirring can assist the production of a homogeneous distribution of reduced or partially-reduced precursor molecules.

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Abstract

La présente invention concerne un procédé de préparation de nanoparticules d'éléments du groupe IV, notamment de nanoparticules de Si, Ge et Sn, et d'alliages binaires ou ternaires de ces éléments. Le procédé comprend la décomposition en phase de solution d'un ou de plusieurs précurseurs de métaux du groupe IV à température élevée et sous atmosphère inerte à pression atmosphérique, en utilisant un réactif favorisant la décomposition. Un agent de liaison de surface est ajouté au mélange réactionnel afin de former une couche organique entourant les nanoparticules et empêchant l'agrégation.
PCT/NZ2007/000246 2006-09-04 2007-09-04 Procédés de formation de nanoparticules WO2008030110A2 (fr)

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US12/439,472 US20100139455A1 (en) 2006-09-04 2007-09-04 Methods of Forming Nanoparticles
AU2007293765A AU2007293765A1 (en) 2006-09-04 2007-09-04 Methods of forming nanoparticles
EP07834850A EP2059480A4 (fr) 2006-09-04 2007-09-04 Procédés de formation de nanoparticules
JP2009526561A JP2010502540A (ja) 2006-09-04 2007-09-04 ナノ粒子の作成方法
CA002662006A CA2662006A1 (fr) 2006-09-04 2007-09-04 Procedes de formation de nanoparticules

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EP2059480A4 (fr) 2010-05-05
AU2007293765A1 (en) 2008-03-13
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CA2662006A1 (fr) 2008-03-13

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