CA2241183A1

CA2241183A1 - Organically-functionalized monodisperse nanocrystals of metals

Info

Publication number: CA2241183A1
Application number: CA002241183A
Authority: CA
Inventors: James R. Heath; Daniel V. Leff
Original assignee: Individual
Current assignee: University of California
Priority date: 1995-12-28
Filing date: 1996-12-27
Publication date: 1997-07-10
Also published as: EP0914244A4; JP2000504374A; EP0914244A1; AU1743397A; WO1997024224A1

Abstract

Organically-functionalized metal nanoparticles are produced by mixing a metal precursor with an organic surface passivant and reacting the resulting mixture with a reducing agent to generate free metal while binding the passivant to the surface of the free metal to produce organically functionalized metal particles.

Description

W O 97/24224 PCTnUS96/20402 ORGANrCALLY-FUNC~ONAL~ZED MONODrSPERSE ~ANOCRYSTALS OF ~nErALS

FTFT r~ OF THF INVFNTION
This invention relates to metal and metal alloy nanocrystals. In one of its moreparticular aspects, this invention relates to organically-functionalized monodisperse nanocrystals of metals and metal alloys and methods of p~ ion thereof.
B~CKGROUNI) OF THE INVF~TION
Preparations for nanoparticle metal and metal oxide hydrosols are known. The myriad methods for preparing these particles include, but are not limited to: (1) the synthesis of colloidal dispersions of various transition metals (Pt, Pd, Ir, Rh, Os, Au, Ag, Fe, Co, and the like) in aqueous media, stabilized by added polymers as protective colloids; (2) the synthesis of ultr~m~ll metal oxide particles by the combination of water and metal chlorides, 10 hydroxides, or ~t~et~tes, in aqueous media; (3) the synthesis of Ag nanoparticles by the reduction of Ag+ in aqueous media; (4) the formation of colloidal silver and gold in aqueous media by ultrasonic radiation; (5) the formation of colloidal gold in aqueous media by the reduction of a gold salt; and (6) the formation of colloidal platinum and palladium in aqueous media by synthetic routes analogous to those for preparing gold colloids. The fabrication of ~5 large metal cluster complexes with various stoichiometries and ligands (e.g. M55LI2Clx, M =
Rh, Ru, Pt, Au; L = PR3, AsR3, x = 6, 20; R= Ph, t-Bu) is also known.
Nanometer-scale crystallites of various metals and non-metals have received a great deal of attention in the past decade. For such crystallites, the electronic, thermodynamic, and chemical properties depend sensitively on size, shape, and surface composition; therefore, 20 these materials have been marked for a number of technological applications ranging from chemical catalysis, photoelectronics, film growth see~1ing, electronic m~teri~ls7 reprography, xerography, electron microscopy, and others. A major challenge to this field in general and a great barrier to act~ li7ing such applications of these novel particles is the complete control over particle size, morphology, and surface structure. The preparation and isolation of 25 crystallites characterized by well-defined surface compositions, narrow size distributions, and uniform shape is paramount to their success as applied materials. In addition, most of these applications require that the particles be dispersible into some solvent, polymer, or other !

W O 97/24224 PCTrUS96/20402 matrix as a monodisperse (non-aggregated) colloid, and that they exhibit various chemical and thermal stabilitics. Metal particles involved in these various technologies include ferromagnetic materials (e.g. Fe2O3, Co), noble metals (Pd, Pt), coinage metals (Au, Ag), alloys of these metals (e.g. CoxAuy), oxides of these metals (e.g. Ag2O), and others.
To date, there are only a few reports concerning the preparation of organically-functionalized metal nanoparticles. However, the products synthesi7~ cl in these reports are marred by some or all of the following characteristics: 1) the resulting materials are x-ray amorphous (non-crystallinc); 2~ the resulting materials have poor surface compositions; 3) the resulting materials have poor solubility in aqueous and organic media; and 4) the resulting 10 materials have broad relative size distributions (mean diarneter + 50 %). For example, organically-functionalized gold nanocrystals limited to certain "average" sizes, characterized by broad size distributions, and which are not soluble in aqueous media have been disclosed.
P~RTFF ST~TFl\~FNT OF TH~ INVF.NTION
The nanocrystal products of the present invention avoid the previously discussed15 problems. The "as prepared" spherical nanoparticles are crystalline and are characterized by narrow relative size distributions (as low as + 10 %). More importantly, however, is the fact that they are functionalized with well-defined organic groups covalently bound to the particle surface. These organic functional groups may be altered both chemically and with respect to percent coverage on the surface. Such chemistry is tremendously useful in the following 20 ways: 1) the organic functional groups, coupled with the size-dependent curvature of a particle surface, yield varying solubilities as a function of particle size. This fact, along with the size-dependent interactions between particles allows the production of narrow size distributions (ideally to within + .3 nm) over the range of - 1.5 to 10 nm, using specially developed chemical techniques; 2~ the particles may be made highly soluble in aqueous 25 media as well as a variety of organics (:~lk~nes, aromatics, halogenated hydrocarbons, and the like). This leads to the ability to prepare particles on or inside various substrates and matrices (gels, polymers, glasses, porous materials, and the like), 3~ the effect of fractional surface coverages on similar size particles can be used to sterically control chemical approach to a surface to give increased reaction selectivity in certain catalytic processes.

W O 97/24224 PCT~US96/20402 The method for the ~ aLion and isolation of crystallites according to the present invention is characterized by well-defined surface compositions, narrow size distributions, and uniform shape. Also, two- and three-11imen~ional close-packed ordered arrays(superlattices) of these nanocrystals have been fabricated on half-micron length scales.
Catalytically active metals such as Pt, Pd, and Ag and non-catalytically active matals and alloys such as Au and CoxAuy have been prepared.
The present invention provides techniques for the synthesis of various metallic nanocrystal m~t(~.ri~l~ in which the resultant particles are characterized by the following properties: (I) they are soluble and resoluble in various organic media, including organic 10 solutions containing dissolved polymers; (2) they are stable as powders or monodisperse (non-aggregated) colloids under ambient conditions for at least several days; (3) they are stable for months when stored under low temperature conditions as powders or monodisperse (non-aggregated) colloids in solution, (4) they can exist as monodisperse entities (when prepared as organic colloids) which can be readily separated into ~bi~ ily narrow size 15 distributions via various chemical and chromatographic techniques, (5) they can be prepared in at least gram quantities; (6) they may consist of a host of metallic elements prepared as either pure metal particles or alloys, synthesized from the combination of a host of specific metal-conl~inin~ inorganic compounds, phase transfer catalysts, surface passivants, and reducing agents; (7) they are readily dispersed into various matrices or onto various substrates 20 (gels, polymers, glasses, alumina, silica, and the like), (8) can be arranged into two- and three-dimensional close-packed ordered arrays to form 'superlattices' exhibiting novel electronic properties domin~ted by single electron phenomena. Particles that have been prepared and that meet the above criteria include Au, Ag, Pt, Pd, and Co/Au (alloy). Par~icle sizes range from 1 - 20 nm diameter.
Besides the fact that the nanocrystals of the present invention have a host of materials properties not exhibited by any other particle system, a maJor advancement of the technology over existing prior art is the use of covalently-bound organic ligands, which form excellent kinetic and/or thermodynamically stable monolayers on the surfaces of the nanocrystals, as a route toward stabilizing these particles in solution. This enables chemically tailored 30 solubility, monodispersity, and size control to the final metal nanocrystal product. The W O 97/24224 PCTrUS96/20402 ligands in general have a chemical component which interacts with the metal nanocrystal surface, and a chemical component which interacts with the surr~-nn~ling solvent, polymer, matrix, etc. Both components can be modified within the limits of chemical compatibility.
The invention is not limited to simple single component metallic systems. Indeed, for 5 some systems it is difficult to chemically stabilize a bare metal particle through the use of covalent organic lig~ncls However, in that case, alloys of the metal may be made in which a second metal is included. Ideally, this second metal is characterized by a lower surface energy (so it coats the surface of the particle), and is itself readily stabilized by a certain organic ligand. For example, in the Co/Au system, Co has magnetic properties which lend it 10 to potential technological applications. However, it is difficult to find ligands which chemically stabilize a Co nanocrystal. Such ligands are readily found for the Au system, and, furthermore, Au has a lower surface energy. Thus it is possible to prepare Co/Au alloyed nanocrystals which exhibit the ferromagnetic properties of Co but are characterized by the relatively simple surface chemistry of Au.
In general, the organically functionalized metal and metal alloy nanoparticles of the present invention are p~ d by providing a solution or dispersion of a metal precursor, providing a solution of an organic surface passivant, mixing the metal precursor solution or dispersion with the organic surface passivant solution, reacting the resulting mixture with a reducing agent to reduce the metal precursor to free metal while concomitantly binding the organic surface passivant to the resulting free metal surface to produce organically functionalized metal or metal alloy nanoparticles having a particle diameter of 10 - 200A.
In a preferred embodiment of the invention, an organic solution of a phase transfer agent is mixed with the metal pe~;ul~or prior to mixing with the organic surface passivant.
DF~CRIPTION O~ pF<FFFRRFn EMP~ODIMFNTS
An inorganic gold compound such as HAuCI4 is dissolved in H2O to generate a solution cont~ining AuC14- as the active metal reagent. AuC14- is phase transferred from H2O
into an organic phase such as toluene using an excess of a phase transfer reagent or catalyst such as N(C8HI7)4Br. A stoichiometric amount of an alkylthiol such as C6HI3SH dissolved in an organic solvent such as toluene is added to the organic phase. ~xcess reducing agent such as NaBH4 is dissolved in H2O, added to the organic mixture with rapid stirring, and allowed W O 97/24224 PCTrUS96t20402 to continue to stir for several hours. The aqueous layer is removed and discarded. The organic layer is passed through submicron filter paper (no material is removed, and all color passes through the paper). The organically-functionalized metal nanocrystals are precipitated usin~
an alcohol solution such as ethanol kept at low temperature. The f1ltrate is washed with this same alcohol. The particles are re-dissolved in an organic solvent such as toluene, re-precipitated, and re-washed. The particles are finally re-dissolved in an organic solvent such as hexane or toluene.
Au particles with one phase transfer reagent and an alkylamine as the surface passivant can be prepared using an akylamine such as Cl2H2sNH2 or Cl8 H3sNH2 as the 10 surface passivant rather than an akylthiol.
Au particles with no phase transfer reagent and an alkylamine as the surface passivant can be prepared using an akylamine such as Cl2H2sNH2 or Cl8H3sNH2 as the surfacepassivant rather than an akylthiol, and no phase transfer reagent. A small amount of insoluble black solid particulate material is generated during the synthesis. This precipitate is removed 15 by filtration of the two-phase system with submicron filter paper. The precipitation of the organically-functionalized metal nanocrystals then proceeds in the same manner above.
Ag particles with one phase transfer reagent and an alkylthiol as the surface passivant can be prepared using an inorganic silver compound such as AgNO3 or AgCIO4 H2O as the metal source, which, when dissolved in H2O, yields Ag+ as the active metal reagent.
Pt particles with one phase transfer reagent and an alkylamine as the surface passivant can be prepared using an akylamine such as Cl2H2sNH2 or Cl8H35NH2 as the surfacepassivant and an inorganic platinum compound such as H2PtCl6 3H20 as the metal source, which, when dissolved in H2O, yields PtCl6-2 as the active metal reagent.
Pd particles with one phase transfer reagent and an alkylamine as the surface passivant 25 can be prepared using an akylamine such as Cl2H25NH2 or ~l8H3sNH2 as the surface passivant and an inorganic palladium compound such as Na2PdCl6 4H2O as the metal source, which, when dissolved in H2~:), yields PdCl6-2 as the active metal reagent.
Co/Au alloy particles with two phase transfer reagents and an akylthiol as the surface passivant can be prepared as follows.

W O 97124224 PCTrUS96/20402 An inorganic cobalt compound (here CoCl2 H20) is dissolved in E~20 to generate asolution cont~inin~ C~o+2 as the active metal reagent. Co+2 is phase transferred from H2~ into an organic phase such as toluene using an excess of a phase transfer reagent or catalyst such as (C6H5)4BNa. The aqueous layer is removed and the organic layer is washed with H20.
5 An inorganic gold compound such as HAu~14 is dissolved in ~20 to generate a solution cont~ining AuCl4 as the active metal reagent. AuCl4 is phase transferred from H2O into an organic phase such as toluene using an excess of a phase transfer reagent or catalyst such as N(C8H~7)4Br. The aqueous layer is removed and the organic layer is washed with H2O. The two organic solutions are combined to form a mixture of Co+2 and AuCl4. A stoichiometric 10 amount of an alkylthiol such as Cl2H25SH dissolved in toluene is added to the organic mixture. Excess reducing agent such as NaBH4 is dissolved in H2O, added to the organic mixture with rapid stirring, and allowed to continue to stir for several hours. The aqueous layer is removed and discarded. The organic layer is passed through submicron filter paper (no material is removed, and all color passes through the filtcr paper). The organically-15 functionalized alloy nanocrystals are precipitated using an alcohol solution such as ethanolkept at low temperature. The filtrate is washed with this same alcohol. The particles are re-dissolved in an organic solvent such as toluene, re-precipitated, and re-washed. The particles are finally re-dissolved in an organic solvent such as hexane or toluene.
Solubilization of organically-functionalized nanocrvstals in aqueous media can be 20 accomplished as follows.
The nanocrystals are first prepared according to one of the synthetic schemes described above. A concentrated solution (e.g., 6 mg/ml) of the particular nanocrystals is prepared in an organic solvent such as hexane to yield an intensely-colored (e.g., purple brown, etc.) solution. A separate solution consisting of a specific weight % of a soap or 25 detergent molccule in aqueous media is prepared. The term "soap" or "detergent~' is general here and is taken to mean any molecule that has a polar (hydrophilic) ionic region and a nonpolar (hydrophobic) hydrocartion region (e.g., a fatty acid, an alkali metal alkane sulfonate salt, etc.). When dissolved in a~ueous media under the a~plo~ ate conditions, these soaps and d~ gellt~ will form structures called micelles. A micelle is basically any 30 water-soluble aggregate, spontaneously and reversibly formed from amphiphile molecules.

W O g7/24224 PCTAJS96~0402 These aggregates can adopt a variety of three-dimensional structures (e.g., spheres, disks, bilayers, etc.) in which the hydrophobic moieties are segregated from the solvent by self-aggregation. If the hydrophobic portion of the amphiphile is a hydrocarbon chain, the micelles will consist of a hydrocarbon core, with the polar groups at the surface serving to S m~int~in solubility in water. A nonpolar substance is solubilized in the hydrophobic region of these micelle structures. This is precisely the mech~ni~m by which the soap or detergent solution the organically-~unctionalized nanocrystals. A known amount of the nanocrystal solution is added to a known amount of the colorless soap solution, resulting in a two-layer mixture. This mixture is stirred vigorously for a period of at least 12 hours. The color of the 10 organic solution is transferred to the soap solution, and this signifies the solubilization of the metal nanocrystals in the aqueous media. The result is an intensely-colored single-layer solution cont~inin~; a small amount of bulk metal that precipitates during the solubilization process. This metal precipitate is removed by filtration with submicron filter paper. The entire above procedure can be repeated several times in order to repeatedly increase the 15 concentration of the metal nanocrystals in the aqueous media.
One example of a potential application of these m~t~.ri~l~ concerns metal-doped matrices such as metal-doped polymer films. Thin polymer films for exmaple cont~inin~ a high weight percent of metal particles may provide a route to m~teri~l~ with a unique combination of mechanical, dielectric, optical, electric, and even magnetic properties.
20 However, narrow particle size distributions, coupled with uniform distribution of the particles throughout the polymer film is necessary to make these properties microscopically uniform throughout a macroscopic film. Fabricating such a film would involve preparing polymer/solvent/particle solutions with relatively high and adjustable particlelpolymer weight ratios and with the particles existing as monodisperse entities in the solution. The 25 polymer/particle thin film could then be prepared from the solution through various standard spin-coating or evaporation techniques. Other suitable matrices include sol-gels, alumina, and glassy carbon.
A second example of a potential application of these material~ deals with using silver particles in reprography. There are a number of reprographic processes which have stages that 30 intim~tely depend on the nucleation and growth of small silver particles. For example, small W 097124224 PCT~US96/20402 silver particles form the amplification (latent image) center in conventional photographic processes. This latent image center, formed by the action of light on silver halide crystals, acquires catalytic properties that enable it to trigger the reduction of the entire silver halide crystal to metallic silver by the reducing agent of the developer. For this process, uniform particle size distributions lead to uniform film quality, and small particle sizes lead to enhanced film resolution. Also, since gold is frequently used in small quantities as a ~n.~iti7~r for photographic emulsions, the Au particles may be applicable here as well.
A third example of a potential application of these materials pertains to chemical catalysis. In catalytic processes, the size and morphology of the particle is often of great 10 concern as it determines catalytic reactivity and selectivity. Organicaliy-functionalized nanometer-scale particles of catalytically-active metals have extremely high surface areas (a large number of catalytically active sites per particle) and unique size-dependent chemicz~l behavior which enables their application as highly selective catalysts in a variety of homogeneous and heterogeneous catalytic processes from petroleum cracking to polymer 15 synthesis. The Pt, Pd, and Ag particles are applicable here.
Other examples of potential applications include the use of these nanocrystals as functional units in innovative micro and nanoelectronic devices. These applications are based on the idea that two- and three-dimensional close-packed ordered arrays (superlattices) of these nanocrystals will exhibit novel electronic properties ~10min~tecl by single electron 2Q phenomena, due to the quantum confined electronic properties of the individual particles as well as their collective coherence effects.
The following exarnples illustrate specific embodiments of the presnt invention. In the following examples all reactions were performed at room temperature, ambient pressure, and ambient atmosphere.
E~MPLE 1 (a) 150 mg (.380 mmol) of HAuCl4 ~ 3H20) was dissolved by stirring in 25 mL of deionized water to yield a clear, yellow solution;
(b) 0.365g (.667 mmol) of N(C8H~7)4 Br(3) was dissolved by stirring in 25 mL of toluene to yield a clear solution and then added to the rapidly-stirring aqueous solution of the Au salt (solution (a)). An immediate two-layer separation resulted, with an orange/red organic W O 97/24224 PCTAUS96~402 phase on top and an orange-tinted aqueous phase on the bottom. This mixture is vigorously stirred until all color disappeared from the aqueous phase, indicating quantitative transfer of the AuCl4 moiety into the organic phase;
(c) 0.0190 g (.0226 ml; .108 mmoI) of CloH21SH was placed in 25 mL oftoluene and5 then this mixture was added to the rapidly stirring two-phase mixture from (a) and ~b);
(d) 0.151 g (4.00 mmol) of NaBH4 was dissolved in 25 mL of deionized water to yield an effervescent, cloudy solution and then this mixture was added to the rapidly stirring mixture from (a), (b), and (c). There was an instant color change of the organic phase to black/brown and then quickly (1 minute) to dark purple. After 10 mimltes~ the aqueous layer 10 became clear and colorless. The reaction was continued at room temperature and room pressure (kept open to ambient atmosphere) for ~ 12 hour while rapidly stirring. Once the reaction time was f1nished, the aqueous phase was separated and discarded, and the dark purple organic phase was reduced in volume to _ S mL ~3y rotary evaporation. To this 5 ml toluene/particle solution was added 350 mL of methanol and this mixture was cooled to 15 -60~C for twelve hours. The dark purple/black precipitate was then vacuum filtered using 0.65 ,um nylon filter paper, washed with an excess of methanol (200 ml), and dried on a vacuum line to give ~ 60 mg of dry product. This 60 mg of particles was re-dissolved in 50 ml of toluene, re-precipitated, and re-washed by the procedure described just previously, to yield 40 mg of dry product. The particles were finally either stored as a powder in the freezer 20 or at room temperature, or they were re-dissolved in a ~ el-~d amount of an organic solvent (e.g., hexane, toluene, chloroforrn, etc.) to yield a solution with a concentration ranging from 1-30 mg/ml. These solutions were either stored in the freezer or at room temperature.
The nanoparticles were characterized by the following: (a) X-ray diffraction (XRD):
This characterization, performed on a powder of the particles, showed that the particles were 25 crystalline with diffraction pea'lcs like those of fcc Au ~except for the bro~ ning at finite size). The main reflections were: (111) at 2(~ = approx. 64.6~, (311) at 2~) = approx. 38.2~, (200) at 2(~) = approx. 44.4~, (220) at 2(~) = approx. 64.6~, (311) at 2~) = approx. 77.5~, (222) at 2~ = approx. 81.8~. Also, using diffraction peal~ line-width bro~lenin~. the average domain size was determined to be 70 ~ 7 A; (b) Ultraviolet-visible spectroscopy (UV/vis):
30 This characterization, performed on dilute hexane or toluene solutions of the nanoparticles, showed one main, broad absorption feature at ~maX = 521 nm; (c) infrared spectroscopy (IR):
This characterization, performed on a film of solid particles that were deposited on an NaCl window by evaporation of several drops of a particle/hexane solution, showed the standard C-C and C-H stretches, as well as those for the thiol group. The stretches were in the regions of 2950-2750 crn~l, and 750-650 cm~l; (d) Nuclear magnetic resonance spectroscopy (NMR):
This characterization, performed on concentrated particle/CDC13 solutions (10 mg/ml), showed three broad multiplets at ~ = 1.50, 1.30, and .90 ppm, with intensities of roughly 2:2:1. These peaks are superimposed on a fourth, very broad signal in the range of â = 2.1 -.60 ppm; (f) Tr~n~mi~ion electron miscroscopy (TEM): This characterization, performed on 10 samples prepared by evaporating a drop of a dilute particle/hexane solution onto an amorphous carbon-coated Cu TEM grid, yielded TEM micrographs of the particles which indicated that the particles were predominantly spherical in morphology, that they were present with a broad size distribution ( c~ ~ 20 %), and that the average domain size was ~ 65 A; (g) X-ray photoelectron spectroscopy (XPS): This characterization, performed on a 15 uniform film of nanoparticles (several micrometers thick) supported on nylong filter paper, showed the ap~lo~liate signals for gold (5P3/2, 4f7/2, 4fs/2, 4ds/2~ 4d3/2, and 4P3/2 at ~ 59, 84, 87, 336, 355, and 548 eV, respectively), carbon (ls at ~ 285.3 eV), and Oxygen (ls at ~ 531.8 eV). Also observed were signals for Br (3P3/2 peak at 183.5 eV, 3Pl~2 peak at 189.5 eV, and 3d peak at # 68.0 ev). The peak positions, line shapes, and peak-to-peak distance of the Au 20 4f doublet are the standard measure of the gold oxidation state. The ginding energies for the Au 4f doublet are 83.5(3) and 87.2(3) eV (peak-to-peak distance of 3.7 eV). These mcasurements are con~iet~ni with the Au~ oxidation state; (h) Elemental analysis (EA): The analyses yielded 77.06 % Au, 2.99 % S, 2.86 % H, and 17.14 % C. The corresponding Au: S
molar ratio of the nanoparticles was 4.20:1, and the C:Il and C:S ratios are those of neat 25 decanethiol, within experimental uncertainties; (i) Dir~~ lial sc~nning calorimetry (DSC):
This characterization, performed on a 6 mg sample (dry powder) of nanoparticles, showed a broad, endothermic transition beginning at ~ 95~ C and peaking at 120 ~ C (18 J/g).; (j) Thermogravimetric analysis (TGA): This characterization, performed on a 5 mg sample (dry powder) of nanoparticles, showed a mzl~im~l rate of weight loss at approximately 235~ C.
30 The total weight loss was found to be consistent with the total amount of bonded ligands W O 97/24224 PCT~US96/20402 found by element~l analysis; (k) Solubility tests: This characterization, performed on dry powder samples of nanoparticles yiedled excellent solubility in hexane, toluene, chloroform, dichloromethane, pyridine, benzene, and several other organic solvents. M~hllulll solubility was found to be in the range 20 - 30 mg/ml.

(a) 112 mg (.284 mmol) of HAuCl43H2O(3) was dissolved by stirring in 25 mL of deionized water to yield a clear, yellow solution, (b) 0.363 g (.666 mmol) of N(C8HI7)4Br~2) was dissolved by stirring in 25 mL of toluene to yield a clear solution and then added to the rapidly-stirring aqueous solution of the 10 Au salt (solution (a)). An immediate two-layer separation resulted, with an orange/red organic phase on top and an orange-tinted aqueous phase on the bottom. This mixture is vigorously stirred until all color disappeared from the aqueous phase, indicating quantitative transfer of the AuCl4 moiety into the organic phase;
(c3 0.57~ g (3.10 mmol) of Cl2~2sNH2(s) (dodecylamine) was placed in 25 mL of 15 toluene and then this mixture was added to the rapidly stirring two-phase mixture from ~a) &
(b). Upon the addition of this solution, the aqueous layer immediately became beige/murky white;
(d) 0.1 65g (4.86 mmol) of NaBH4 was dissolved in 25 mL of deionzaed water to yield an effervescent, cloudy solution and then this mixture was added to the rapidly stirring 20 mixture from (a), (b), and ~c). There was an instant color change of the organic phase to black/brown and then quickly (1 minute) to dark purple. After 10 mimltec, the aqueous layer becarne clear and colorless. The reaction was continued at room temperature and room pressure (kept open to arnbient atmosphere) for ~ 12 hour while rapidly stirring. Once the reaction time was finished, the aqueous phase was sc~ d and discarded, and the dark 25 purple organic phase was reduced in volume to ~ 5 mL by rotary evaporation. To this 5 mi toluene/particle solution was added 350 mL of methanol and this mixture was cooled to -60~
C for twelve hours. The dark purple/black precipitate was then vacuum filtered using 0.65 llm nylon filter paper, washed with an excess of methanol (200 ml), and dried on a vacuum line to give ~ 60 mg of dry product. This 60 mg of particles was re-dissolved in 50 ml of 30 toluene, re-precipitated, and re-washed by the procedure described just previously, to yield 60 W O 97/24224 PCTAUS96/204~2 mg of dry product. The particles were finally either stored as a powder in the freezer or at room temperature, or they were re-dissolved in a preferred amount of an organic solvent (e.g., hexane, toluene, chloroform, etc.) to yield a solution with a concentration ranging from 1-30 mg/ml. These solutions were either stored in the freezer or at room temperature. When stored S as powders at room telllp~ ul~, the particles exhibit a certain degree a metastability. That is, the particles are unstable with respect to particle aggregation and quickly lose their solubility over a matter of a few days.
The nanoparticles were characterized by the following: (a) X-ray diffraction (~RD):
This characterization, performed on a powder of the particles, showed that the particles were 10 crystalline with diffraction peaks like those of fcc Au {except for the broz~ ing at finite size). The main reflections were: (111) at 2~ approx. 38.2~, (200) at (~) = approx. 44.4~, (220) at 2~ approx. 64.6~, (311) at 2~3 = approx. 77.5~, (222) at 2~) = approx. 81.8~. Also, using diffraction peak line-width bro~lening, the average domain size was determined to be 26 + 3 ~; (b) Ultraviolet-visible spectrscopy (UV/vis): This characterization, performed on 15 dilute hexane or toluene solutions of the nanoparticles, showed one main, broad absorption feature at ?~.ma,~ = 517 nm; (c) infrared spectroscopy (IR): This characterization, performed on a film of solid particles that were deposited on an NaCl window by evaporation of several drops of a particle/hexane solution, showed dodecylamine bands in the regions from ~ 3310-2990 cm~l(N-H stretch), ~ 3000-2850 cm-l (C-H allphatic stretch), ~ 1700-1300 cm (N-H
20 band (~ 1600 cm~l and CH2 scissor (~ 1450 cm~l), ~ 1100-1050 cm~~ (C-N stretch), and ~
900-700 cm~~ H wag); (d) Nuclear magnetic resonance spectroscopy (NMR): This characterization, performed on concentrated particles/CDC13 solutions (10 mg/ml), showed three broad multiplets at ~ =1.56,1.35, and 85 ppm, with intensities of roughly 2:2:1. These peaks are supcrimposed on a fourth, very broad signal in the range of ~ = 2.0 - .50 pp; (e) 25 Mass spcctroscopy (MS): This characterization, performed on solid samples, showed the typical fragmentation pattern of straight-chain primary amines as well as molecular ion peaks of the amines. MS (Auxdodecylaminey),m/e (%); 30(100%) [-CI2 NH2~+, 185 (M+, 4%)[Cl2H27NJ+; (f) Tr~nsmi~ion electron microscopy (TEM): This characterization, performed on samples prepared by evaporating a drop of a dilute particle/hexane solution onto an 30 amorphous carbon-coated Cu TEM grid, yielded TEM micrographs of the particles which CA 0224ll83 l998-06-23 W O 97/24224 PCT~US96/20402 indicated that the particles were predominantly spherical in morphology, that they were present with a broad size distribution (c~ ~ 20 %), and that the average domain size was ~ 30 A; (g) X-ray photoelectron spectroscopy (XPS): This characterization, performed on a ~ uniform film of nanoparticles (several micrometers thick) supported on nylon filter paper, 5 showed the appropriate signals for gold (5P3/2 4f'7/2 4fs/2 4ds/2 4d3/2 and 4P3n at ~ 59, 84, 87, 336,366, and 548 eV, respectively), carbon (ls at ~ 285.3 eV), and Oxygen (ls at ~ 531.8 eV). Also observed were signals for Br (3P3/2 peak at 183.5 eV, 3PIn peak at 189.5 eV, and 3d peak at ~ 68.0 ev). The peak positions, line shapes, and peak-to-peak distance of the Au 4f doublet are the standerd measure of the gold oxidation state. The binding energies for the 10 Au 4f doublet are 83.5(3) and 87.2(3) eV (peak-to-peak distance of 3.7 eV). These measurements are consistant with the Au~ oxidation state; (h) Elemental analysis (EA): The analyses yielded 89.12 % Au, .79 % N, 2.00 % H, and 9.20 % C. The corresponding Au:N
molar ratio of the nanoparticles was 7.9:1, and the C:H and C:N ratios are those of neat dodecylamine, within ~ c~ ental uncertainties; (i) Dirr~ e.llial sc~nning calorimetry 15 (DSC): This characterization, performed on a 7 mg sample (dry powder) of nanoparticles, showed a broad, exothermic transition(s) e~ten~lin~; from ~ 50 ~C to 130 ~C, which includes a relatively sharp endothermic feature centered at 90 ~C (7 J/g)., G)Therrnogravimetric analysis (TGA): This characterization, performed on a 5 mg sample (dry powder) of nanoparticles, showed a m~im~l rate of weight loss at approximately 250~C. The total 20 weight loss was found to be consistent with the total amount of bonded ligands found by el~ment~l analysis, (k) Solubility tests: This char~rteri~tion~ performed on dry powder samples of nanoparticles yielded excellent solubility in hexane, toluene, chloroform, dichloromethane, pyridine, benzene, and several other organic solvents. Maximum solubility was found to be in the range of 22 - 30 mg/ml.

The process of EXAMPLE 2 was repeated except that no phase transfer reagent was used, a small amount of insoluble black-solid particulate material was generated during the ~, synthesis, and this precipitate was removed by filtration of the two-phase system with submicron filter paper just before the precipitation step. That is, the insoluble precipitate was 30 removed by filtration of the two-phase system with .66 micron filter paper. The aqueous CA 0224ll83 l998-06-23 W O 97/24224 PCT~US96/20402 phase was then separated and discarded, and the dark-purple organic phase was reduced in volume to ~ 5 mL by rotary evaporation. The particles were then precipitated, re-precipitated, and stored in the manner described in EXAMPLE 2.
Particle composition, size, and properties may be varied by means of the following changes: the variation of the metal precursor used, the variation of phase transfer reagents used or their omission from the synthetic procedure, the variation of one or more surface passivants used, the variation of the reducing agent used, or the variation of some of the reactant molar ratios, or any combination thereof.
The nanoparticles were charactarized by the following:
10 (a) X-ray diffraction (XRD): This characterization, performed on a powder of the particles, showed that the particles waee crystalline with diffraction peaks like those of fcc Au (except for the broadening at finite size). The main raflections were: (111) at 2~) = approx. 38.2~, (200) at 2(~ = approx. 44.4~, (220) at 2~ = approx. 64.6~, (311) at 2~) = approx. 77.5~, (222) at 2(~) = approx. 81.8~. Also, using diffraction peak line-widthi bro~lening, the average 15 domain size was determined to be 55 + 7 A; ~b) Ulkaviolet-visible spectroscopy (IJV/vis):
This characteli~Lion, performed on dilute hexane or toluene solutions of the nanoparticles, showed one main, broad absorption feature at ~maX = 525 nm; (c) infrared spectroscopy (IR):
This characterization, performed on a film of solid particles that were deposited on an NaCl window by evaporation of several drops of a particle/hexane solution, showed dodecylamine 20 bands in the regions from ~ 3310-2990 cm~~ (N-H stretch), ~ 3000-2850 cm~' (C-H aliphatic stretch), ~ 1700-1300 cm~l (N-H bend ~ 1600 cm~l and CH2 scissor ~ 1450 cm~~ 1100-1050 cm~l (C-N stretch), and ~ 900-700 cm~l (N-H wag), (d) Nuclear magnetic resonance speckoscopy (NMR): This characterization, performed on concenkated particle/CDCl3 solutions (10 mg/ml~, showed three broad multiplets at ~ 1.54, 1.32, and .85 ppm, with 25 intensities of roughly 2:2:1. These peaks arr superimposed on a fourth, very broad signal in the ran~e of ~ 2.0 - .50 ppm; (a) Mass spectroscopy (MS): This characterization, performed on solid samples, showed the typical fragmentation pattern of straight-chain primary amines as well as molecular ion peaks of the amines. MS (Auxdodecylaminey), m/e (%): 30(100%) L-CH2N~2]+, 185 (M+, 4%) [Cl2H27N~+; (f) Tr~n~mi~ion eleckon microscopy (TEM): This 30 characterization, performed on samples prepared by evaporating a drop of a dilute W O 97/24224 PCTrUS96/2040Z

particle/hexane solution onto an amorphous carbon/coated Cu TEM grid, yielded TEM
micrographs of the particles which indicated that the particles were predomin~ntly spherical in morphology, that they were present with a broad size distribution (~ ~ 20 %), and that the average domain size was ~ 50 A; (g) X-ray photoelectron spectroscopy (XPS3: ThisS characterization, performed on a uniform film of nanoparticles (several micrometers thick) supported on nylon filter paper, showed the ap~ iate signals for gold (5P3/2 4f'7~24f5~2 4ds/2 4d3n and 4P3n at ~ 59, ~4, 87, 336, 366, and 548 eV, respectively), carbon (ls at ~
285.3 eV), and Oxygen (ls at ~ 531.8 eV). Signals for Br (3P3/2 peak at 183.5 eV, 3PI/2 peak at 189.5 e~, and 3d peak at ~ 68.0 ev) were not observed. The peak positions, line shapes, 10 and peak-to-peak distance of the Au 4f doublet are the standard measure of the gold oxidation state. The binding energies for the Au 4f doublet are 83 5(3) and 87.2(3) eV (peak-to-peak distance of 3.7 eV). These measurements are consistent with the Au~ oxidation state: (h) Elemental analysis (EA): The analyses yielded 9Q.58 % Au, .75 % N, 1.69 % H, and 9.51 %
C. The corresponding Au:N molar ratio of the nanoparticles was 8.6:1, and the C:H and (~:N
15 ratios are those of neat dodecylamine, within experimental uncertainties; (i) Differential sc~nnin~ calorimetry (DSC): This characterization, performed on a 8 mg sample (dry powder) of nanoparticles, showed a strong, broad, exothermic transition beginning at ~ 50 ~C with a relatively sharp, and relatively endothermic feature peaking near 110~C (4 J/g); (j) Thermogravimetric analysis (TGA): This characterization, performed on a 5 mg sample (dry 20 powder) of nanoparticles, showed a m~xim~l rate of weight loss at approximately 250~C.
The total weight loss was found to be consistent with the total amount of bonded ligands found by elemental analysis; (k) Solubility tests: This characterization, performed on dry powder samples of nanoparticles yielded excellent solubility in hexane, toluena, chloroform, dichloromethane, pyridine, benzene, and several other organic solvents. Maximum solubility 25 was found to be in the range of 22-30 mglml.

(a) 547 mg of (C8HI7)4NBr (phase transfer reagent) was dissolved in 10 ml of toluene and sonnicated for 2 minlltes;
(b) 119 mg of Co~126H2O was dissolved in 15 ml of H2O by sonnication for 15 30 minutes;
!

(c) The toluene and aqueous solutions from steps (a) and (b), respectively, werecombined and stirred together for 15 minutes, which resulted in a blue-colored toluene layer.
The aqueous phase was then separated from the organic phase and discarded, (d) 98 mg of HAuCl4 was dissolved in 15 ml H2O and then mixed with a 137 mg (C8I-II7)4NBr in 20 ml toluene solution. The AuCl4 ions were transferred from the aqueous to the toluene phase (organic Phase color becomes red/orange) and then the aqueous phase was separated and discarded, (e) The two solutions of metal precursors (1:2 Au:Co molar ratio) in toluene (solutions from step (c) and (d)) were merged and stirred for S minutes;
(f) 0.36 ml of Cl2H25SI~ (surface passivant) was added to the toluene solution from (e) and stirred for 2 minutcs. The mixture tured blue/gray in color;
(g) A solution of 283 mg NaBH4 (re~ cing agent) in 3 ml H20 was added to the toluene phase from step (f) and the reaction was allowed to proceed for 6 hours while stirring.
Then, the black-colored toluene phase was separated from the aqueous phase and rotary 15 evaporated down to 5 ml. The concentrated solution was put in a freezer for 12 hours and then filtered, while cold, to remove phase transfer reagent that had crystallized out of the organic phase solution. The nanoparticles, still dissolved in the organic phase, were then precipitated by the addition of 300 ml of methanol. The particles/toleune/methanol solution was sonnicated for 10 min and then filtered through 0.2 ~Lm nylon filter paper. The filtrate 20 was clcar and the particles were black. The weight of residue on the filter paper was 41 mg.
This residue was re-dissolved in 5 ml toluene, and the solution was sonnicated for 15 minutes and filtered. Then, the particles were precipitated again (using 200 ml of methanol) and filtered. The weight of the re-soluble, final residue was 20 mg. The particles were finally either stored as a powder in the freezer or at room temperature, or they were re-dissolved in a 25 preferred amount of an organic solvent (e.g., hexanc, toluene, chloroform, etc.) to yield a solution with a concentration ranging from 1-30 rng/ml. These solutions were either stored in the freezer or at room temperaturc.
The nanoparticles were characterized by the following materials characterizationtechniques:

W O 97/24224 PCTrUS96~0402 (a) X-ray diffraction (XRD): This characterization, performed on a powder of the particles, showed that the particles were crystalline with diffraction peaks like those of fcc Au (except for the bro71(1enin~ at finite size). The main reflections were: (111) at 2(~) ~ approx. 38.2~, - (200) at 2~3 ~ approx. 44.4~, (220) at 2~ ~ approx. 64.6~, (311 ~ at 2(~ ~ approx. 77.5~, (222) S at 2~) ~ approx. 81.8~. Cobalt reflections were masked by those of gold. Also, using diffraction peak line-width broa~lenin~, the average domain size was determined to be 30 + 5 A; (b) Ultraviolet/visible spectroscopy (W/vis); This characterization, performed on dilute hexane or toluene solutions of the nanoparticles, showed one main, broad absorption feature at ~maX = 520 nm; (c) Infrared spectroscopy (IR): This characterization, performed on a film of solid particles that were deposited on an NaCl window by evaporation of several drops of a particle/hexane solution, showed ~e standard C-C and C-H stretches, as well as those for the thiol group. The stretches were in the regions of 2950-2750 cm~t, 1500-1200 cm~l, and 750-650 cm~l, (d) Trzln~mi~ion electron microscopy (TEM): This characterization, perforrned on samples prepared by evaporating a drop of a dilute particle/hexane solution onto an amorphous carbon-coated Cu TEM grid, yielded TEM micrographs of the particles which indicated that the particles were predominantly spherical in morphology, that they were present with a relatively narrow size distribution (~ ~ 10%), and that the average domain size was ~ 30 A; (e) X-ray, photoelectron spectroscopy (XPS): This characterization, performed on a uniform film of nanoparticles (several micrometers thick) supported on nylon f1lter paper, showed the a~propliate signals for gold (5P3n 4~7n~4fsnt 4dsn 4d3n and 4P3n at ~ 59, 84, 87, 336, 366, and 548 eV, respectively), carbon (ls at ~ 285.3 eV), and Oxygen (ls at ~
531.8 eV). The peak positions, line shapes, and peak-to-peak distance of the Au 4f doublet are the standard measure of the gold oxidation state. The binding energies for the Au 4f doublet are 83.5(3) and 87.2(3) eV (peak-to-peak distance of 3.7 eV). These measurements are consistent with the Au oxidation state. Also observed were the signals for cobalt (3s at 57 ev; 2p3/2 and 2pl/2 at 779 ev and 794 ev, respectively) and sulfur (2p3/2 and 2pl/2 at 163 ev and 164 ev, respectively). An analysis of the XPS data revealed that the Co/Au alloy was comprised of about 3% Co and 97% Au; (f) Solubility tests: This characterization, performed on dry powder samples of nanoparticles yielded excellent solubility in hexane, toluene, W O 97/24224 PCT~US96/20402 chloroform, dichloromethane, pyridine, benzene, and several other organic solvents.
Maximum solubility was found to be in the range of 20 - 30 mg/ml.

(a) lOg of DD~B was dissolved in 104 ml of toluene and sonnicated for 10 minut~s;
(b) 11 9 mg of CoCl26H~O was dissolved in the DDAS/toluene solution and sonnicated for 5 hours to dissolve all of the Co salt in the toluene. The CoCl2/DDAB/toluene solution had a typical cobalt blue color, (c) 98 mg HAuCl4 was dissolved in 15 ml H2O and mixed with a 13 7 mg (C8HI7)4NBr in 20 ml toluene solution. The AuCl4 ions were transferred from the aqueous to 10 the toluene phase (organic phase color becomes red/orange) and then the aqueous phase was separated and discarded;
(d) The two solutions (from steps (b) and (c)) of metal precursors (1:2 Au:Co molar ratio) in toluene werc merged and stirred for 5 minutes. The solution had a dark green color;
(e) 0.18 ml of Cl2H25SH (surface passivant) was added to the toluene solution from 15 (d) and stirred for 2 minutes. The solution turned blue again;
(f) A solution of 283 mg NaBH4 (reducing agent) in 3 ml H2O was added to the toluene phase resulting from step (a), and the reaction was allowed to proceed for 5 hours while stirring. After 5 hours of reaction time, the toluene phase was diluted with 200 ml a toluene and washed with 500 ml of H2O. A viscous, white DDAB/water emulsion was 20 formed and allowed to precipitate out of the thiol-capped Au/Co particles/toluene solution.
The black particle/toluene solution was then separated and rotary evaporated to a concentrated 10 ml solution. 500 ml of methanol was then added to precipitate the particles.
The particles/toluene/methanol solution was sonnicated for 30 min and then filtered through a 0.2 ~m nylon filter paper. The filtrate was clear and the particles were black. The weight of 25 residdue on the filter paper was 69 mg. The residue was re-dissolved in 100 ml of toluene by sonnication for 15 minutes and the solution was then filtered. 31 mg of the residue were not dissolved. The toluene solution was rotary evaporated down to 5 ml and the particles were precipitated again by addition of 3~0 ml of methanol and 15 mim-tes sonnication. After filtering, the weight of the resoluble, final residue was 21 mg. The particles were finally 30 either stored as a powder in the freezer or at room temperature, or they were re-dissolved in a W O 97124224 PCTnJS96~0402 preferred amount of an organic solvent (e.g., hexane, toluene, chloroforrn, etc.) to yield solution with a concentration ranging from 1-30 mg/ml. These solutions were either stored in the freezer or at room temperature.
- The nanoparticles synthe~i7ed by the above procedures were characterized by the following materials characterization techniques:
(a) X-ray diffraction (XRD): This characterization, perforrned on a powder of the particles, showed that the particles were crystalline with diffraction peaks like those of fcc Au (except for the bro~ ning at finite size). The main reflections were: (111) at 2~) = approx. 38.2~, (200) at 2~ = approx. 44.4~, (220) at 2(~ = approx. 64.6~, (311) at 2~) = approx. 77.5~, (222) at 2~) = approx. 81.8~. Cobalt reflections were masked by those of gold. Also, using diffraction peak line-width broadening, the average domain size was deterrnined to be 15 + 2 A; (b) Ultraviolet-v;sible spectroscopy (IJV/vis): This characterization, performed on dilutc hexane or toluene solutions of the nanoparticles, showed one main, broad absorption feature at ~a~ = 517 nm; (c) Infrared spectroscopy (IR): This characterization, perforrned on a film S of solid particles that were deposited on an NaCl window by evaporation of several drops of a particle/hexane solution, showed the standard C-C and C-H stretches, as well as those for the thiol group. The stretches were in the regions of 2950-2750 cm~l, 1500-1200 cm~l, and 750-450 cm~l; (d) Tr~n~mi~ion electron microscopy (TEM): This characterization, performed on samples pL~l)al~d by evaporating a drop of a dilute particle/hexane solution onto an arnorphus carbon/coated Cu TEM grid, yielded TEM micrographs of the particles which indicated that the particles were predominently sphericaal in morphology, that they were present with a relatively narrow size distribution (~ ~ 7%), and that the average domain size was ~ l S ~; (e) X-ray photoelectron spectroscopy (XPS): This characterization, performed on a uniform film of nanoparticles (several micrometers thick) supported on nylon filter paper, showed the appropriate signals for gold (5P3n 4f7/24fs/2 4dsn 4d3/2 and 4P3n at ~ 59, 84, 87, 336, 366, and 548 eV, respectively), carbon (ls at ~ 285.3 eV), and Oxygen (ls at ~ 531.8 eV). The peak positions, line shapes, and peak-to-peak distance of the Au 4f doublet are the standard measure of the gold oxidation state. The binding energies for the Au 4f doublet are 83.5(3) and 87.2(3) eV (peak-to-peak distance of 3.7 eV). These measurements are consistent with the Au~ oxidation state. Also observed were the signals for cobali (3s at 57 ev; 2p3n and W O 97/24224 PCT~US96/20402 2PI/2 at 779 ev and 794 ev, respectively~ and sulfur (2p3/2 and 2p~/2 at 163 ev and 164 ev, respectively). An analysis of the XPS data revealed that the Co/Au alloy was comprised of about 2% Co and 98% Au; (f) Solubility tests: This chara~ aLion, performed on dry powder samples of nanoparticles yielded excellent solubility in hexane, toluene, chloroform, 5 dichloromethane, pyridine, benzene, and several other organic solvants. Maximum solubility was found to be in the range of 20 - 30 mg/ml.

(a) Dodecanethiol-functionalized Ag nanocrystals (average domain size of 3 nm) were first prepared according to the procedure of EXAMPLE 1, except that AgNO3 was used as the 10 metal source and dodecanethiol was used as the thiol;
(b) A 6 mg/ml solution of the Dodecanethiol-functionalized Ag nanocrystals was prepared by dissolving 24 mg of particles in 4 ml of hexane to yield an intensely-colored (dark brown) solution;
(c) A separate solution (micelle solution) consisting of 20 g of sodium dodecylsulfate (SDS) dissolved in 300 ml of deionized H2O was prepared. This yielded a 6.25 weight percent solution of SDS in ~I2O; (d) 1 ml of the 6 mg/ml Ag particle/hexane solution was added to 20 ml of the 6.25 weight percent solution of SDS in H2O resulting in a two-layer mixture (organic layer on top and aqueous layer on the bottom). This mixture was stirred vigorously for a period of 6 hours. The dark-brown color of the organic solution is transferred 20 to the aqueous micelle solution to yield an amber-colored single phase system (no two layar separation exists anymore). This signifies the solubilization of the metal nanocrystals in the aqueous media. As a by-product of this solubilization procedure, a small amount of bulk metal precipitates. This metal precipitate was removed by filtration with .65 micron nylon filter paper to yield 1 mg of black, insoluble particulate m~t( ri~l. The entire above procedure 25 was repeated several times in order to increase the concentration of the metal nanocrystals in the aqueous media. A concentration of .1~ mg/mi (.01 wt. % Ag) was ultimately achieved here.
The aqueous solutions of nanoparticles were characterized by the following techniques: (a) Ultraviolet-visible spectroscopy (W/vis): This char~ct~ri7~tion, performed on 30 dilute particle/hexane/SDS/watar solutions, showed one main, broad absorption featurre at W O 97/24224 PCT~US96~0402 ~max = 450 nm (this represents the characteristic optical signature of monodisperse silver colloids); (b) Tr~n~mi~.~ion electron microscopy (Tl~M): This characterization, performed on samples prepared by evaporating a drop of a dilute particle/hexane/Sl~S/water solution onto an amorphous carbon-coated Cu TEM grid, yielded T~M micrographs of the particles which 5 indicated that the particles were present with the same structural properties (e.g., shape, size, and size distribution) as those of the original dodecanethiol/functionalized Ag nanocrystals used for solubilization. Specifically, this analysis showed that the particles were predominantly spherical in morphology, that they were present with a relatively narrow size distribution (cs ~10%), and that the average domain size was ~ 30 ~.

(a~ 225 mg (,510 mmol) of H2PtCl85H2O(6) was dissolveed by stirring in 25 mL o~
deionized water to yield a clear, orange-yellow solution;
(b) 0.620 g (1.13 mmol) of N(C8HI7)4Br(8) was dissolved by stirring in 25 mL of toluene to yield a clear solution and then added to the rapidly-stirring aqueous solution of the Pt salt (solution (a~). An immediate two-layer separation resulted, with an orange/red organic phase on top and an orange-yellow (tinted) aqueous phase on the bottom. This mixture is vigorously stirred until all color disappeared from the aqueous phase, indicating qll~ntit~tive transfer of the PtCl6-2 moiety into the organic phase;
(c) .095 g (.511 mmol) of Cl2H25NH2(6) (dodecylamine) was placed in 25 mL of toluene and then this mixture was added to the rapidly stirring two-phase mixture from (a) and (b). Upon the addition of this solution, the aqueous layer immediately became beige/white, (d~ 0.212 g (5.61 mmol) of NaBH4 was dissolved in 25 mL of deionized water to yield an effervescent, cloudy solution and then this mixture was added to the rapidly stirring mixture from (a), (b) and ~c). There was an instant color change of the organic phase to black/brown and then quickly (1 minute) to dark brown. After 5 mimlte,c~ the aqueous layer became clear and colorless. The reaction was continued at room temperature and room pressure (kept open to ambient atmosphere) for ~ 12 hour while rapidly stirring. Once the reaction time was fmished, the aqueous phase was separated and discarded, and the dark-brown organic phase was rduced in volume to ~ 5 mL by rotary evaporation. To this 5 ml tolune/particle solution was added 350 mL of methanol and this mixture was cooled to -60~C

W O 97/24224 PCTrUS96/20402 for twelve hours. The dark-brown precipitate was then vacuum filtered using 0.65 ~lm nylon filter paper, washed with an excess of methanol (220 ml), and dried on a vacuum line to give ~ 55 mg of dry product. This 55 mg of particles was re-dissolved in 50 ml of toluene, re-precipitated, and re-washed by the procedure described just previously, to yield 47 mg of dry product. The particles were finally either stored as a powder in the freezer or at room temperature, or they were re-dissolved in a pl~r~ d amount of an organic solvent (e.g., hexane, toluene, chloroform, and the like) to yield a solution with a concentration ranging from 1-30 mg/ml. These solutions were either stored in the freezer or at room temperature.
The nonoparticles characterized by the following:
10 (a) X-ray diffraction (XRD): This characterization, performed on a powder of the particles, showed that the particles were crystalline with diffraction peaks like those of fçc Pt (except for the broadening at finite size). The main reflections were: (111) at 2(~) = approx. 38.2~, (200) at 2(~ += approx. 44.4~, (220) at 2~) = approx. 64.6~, (311) at 2~ = approx. 77.5~, (222) at 2~) = approx. 81.8~. Also, using diffraction peak line-width bro~ ning, the average 15 domain size was determined to be 30 + 4A; (b) Ultraviolet-viswible spectroscopy (UV/vis):
This characterization, performed on dilute hexane or toluene solutions of the nanoparticles, did not show an absorption feature in the visible spectrum between 300 - 800 nm (this is as expected because Pt is not a 'one-electron' metal); (c) infrared spectroscopy (~R): This characterization, perforrned on a film of solid particles that were deposited on an NaCI
20 window by evaporation of several drops of a particle/hexane solution, showed dodecylamine bands in the regions from ~ 3310-2990 cm~~ H stretch), ~ 3000-2850 cm~l (C-H aliphatic stretch), ~ 1700-1300 cm~l (N-H bend ~ 1600 crn~' and CH2 scissor ~ 1450 cm~'), ~ 1100-1050 crn~l (C-N stretch), and ~ 900-700 crn~l (N-H wag), (d) Nuclear magnetic resonance spectroscopy (NMR): This characterization, performed on concentrated particle/CDC13 25 solutions (10 mg/ml), showed three broad multiplets at o = 1.56, 1.3~, and .87 ppm, with intensities of roughly 2:2: 1. These peaks are superimposed on a fourth, very broad signal in the range of o = 2.1 - .55 ppm; (e) Tr~n~mi~sion electron microscopy (TEM): Thischaracterization, perforrned on samples prepared by evaporating a drop of a dilute particle/hexane solution onto an amorphous carbon-coated Cu TEM grid, yielded TEM
30 micrographs of the particles which indicated that the particles were predominantly spherical W O 97~24224 PCT~US96~0402 in morphology, that they were present with a relatively narrow size distribution (~ ~ 15%), and that the average domain size was ~ 26A; (f) Solubility tests: This characterization, per~ormed on dry powder samples of nanoparticles yielded excellent solubility hexane, toluene, chloroform, dichloromethane, pyridine, benzene, and several other organic solvents.
5 Maximum solubility was found to be in the range of 25-30 mg/ml.

(a) 197 mg (.450 mmol) of Na2PdCI84H2O(8) was dissolved by stirring in 25 mL of deionized water to yield a clear, gray/black solution;
(b) 0.494 g (.900 mmol) of N(C8HI7)4Br(8) was dissolved by stirring in 25 mL of 10 toluene to yield a clear solution and then added to the rapidly-stirring aqueous solution of the Pd salt (solution (a)). An immediate two-layer separation resulted. This mixture is vigorously stirred until all color disappeared from the aqueous phase, indicating quantitative transfer of the PtCl8-2 moiety into the organic phase (black);
(c) .086 g (.465 mmol) of C12H2sNH2 (8) (dodecylamine) was placed in 25 mL of 15 toluene and then this mixture was added to the rapidly stirring two-phase mixture from (a) &
(b). Upn the addition of this solution, the aqueous layer immediately became beige/white;
(d) 0.171 g (4.52 m~nol) of NaB~4 was dissolved in 25 mL of deionized water to yield an effervescent, cloudy solution and then this mixture was added to the rapidly stirring mixture from (a), (b), and (c). There was an instant color charlge of the organic phase to dark 20 black. After 5 miml1~s, the aqueous layer became clear and colorless. The reaction was continued at room temperature and room pressure (kept open to ambient atmosphere) for ~ 12 hour while rapidly stiring. Once the reaction time was finished, the aqueous phase was separated and discarded, and the dark-black organic phase was reduced in volume to ~ S mL
by rotary evaporation. To this S ml toluene/particle solution was added 350 mL of methanol 25 and this mixture was cooled to -60~C for twelve hours. The dark-black precipitate was then vacuum filtered using 0.65 ~m nylon filter paper, washed with an excess of methanol (200 ml), and dried on a vacuum line to give ~ 50 mg of dry product. This 50 mg of particles was re-dissolved in 50 ml of toluene, re-precipitated, and re-washed by the procedure described just previously, to yield 39 mg of dry product. The particles were finally either stored as a 30 powder in the freezer or at room temperature, or they were re-dissolved in a preferred amount W O 97/24224 PCTrUS96/20402 of an organic solvent (e.g., hexane, chloroform, etc.) to yield a solution with a concentration ranting from 1-30 mg/ml. These solutions were either stored in the freezer or at room temperature.
The nanoparticles were characterized by the following:
(a) X-ray diffraction ~XRD): This characterization, performed on a powder of the particles, showed that the particles were crystalline with diffraction peaks like those of fcc Pd (except for thc bro~(lçning at finite size). The main reflections were: (111) at 2 ~) = approx. 38.2~, (200) at 2(~ = approx. 44.4~, (220) at 2~ = approx. 77.5~, (311) at 2'~ = approx. 77.5~, (222) at 2(~) = approx. 81.8~. Also, using diffraction peak line-width broadening, the average lO domain size was determined to be 20 ~ 3 A, (b) Ultraviolet-visible spectroscopy (uV/vis):
This characterization, performed on dilute hexane or toluene solutions of the nanoparticles, did not show an absorption feature in the visible spectrum between 300 - 800 nm (this is as expected because Pd is not a 'one-electron' metal); (c) Infrared spectroscropy (IR): This characterization, performed on a f1lm of solid particles that were deposited on an NaCI
15 window by evaporation of several drops of a particle/hexane soution, showed dodecylamine bands in the regions from ~ 3310 - 2990 cm~l (N-H stretch), ~ 3000-2850 cm~l (C-H aliphatic strech), ~ 1700-1300 cm~l (N-H bend (~ 1600 cm~l CH2 scissor (~ 1450 cm~~ l lO0-1050 cm~l (C-H stretch), and ~ 900-700 cm~ H wag); (d) Nuclear magnetic resonance spectroscopy (NMR): This characterization, per~ormed on concentrated particle/CDCl3 20 solutation (10 mg/ml), showed three broad multiplets at ~ = 1.54, 1.36, and 192 ppm, with intesities of roughtly 2:2:1. These peaks are superimposed on a fourth, very broad signal in the range of ~ = 2.1-.60 ppm; (e) Tr~n~mi~ion electron microscopy (TEM): This characterization, perforrned on samples prepared by evaporating a drop of a dilute particle/hexane solutation onto an amorphous carbon-coated Cu TEM grid, yielded T~M
25 micrographs of the particles which indicated that the particles were predominatly spherical in morphology, that they were present with a relatively narrow size distribution (~ ~ 10%), and that the average domain size was ~18 ~; (f) Solubility tests: This characterization, performed on dry powder samples of nanoparticles yielded excellent solubility hexane, toluene, chloroform, dichloromethane, pyridine, benzene and several other organic solvents.
30 Maximum solubility was found to be in the range of 25 -3 0 mg/ml.

W 097/24224 PCT~US96/20402 (a) 10 mg of dodecanethiol-capped Ag nanocrystals prepared according to the procedure of Example 6 and having an average domain size of approximately 30 ~ was added to 10 mg of polystyrene and then mixed with 2 ml of toluene (effectively a 50 % by weight Ag film because the toluene evaporates during spin coating procedures);
(b) the 2 ml mixture from (a~ was then spin coated onto a glass substrate (whichcontained patterned Al electrodes) at a rate of 3600 RPM, to generate a thin metal nanocrystal-doped polymer thin film;
(c) After evaporating a top Al electrode onto the thin film, dielectric, optical and film 10 thickness measurements were carried out.
The film thickness was measured by profilometry to be 20 llm. The dielectric measurements of the metal nanocrystal-doped polymer thin film yielded unique dielectric values as copared to the 'pure' or un-doped polymer. The dielectric characteristics for the un-doped polymer thin filme were: a) dielectric constant = 2; b) breadown voltage - 12 kv/mm.
15 The dielectric characteristics for the metal nanocrystal-doped polymer thin film were: a) dielectric constaIlt - 15; b) breadown voltate - 1.2 kv/mm. As can be seen, the dielectric constant of the doped film increases by about a factor of lû. There is one broad absorption feature at ~maX = 465 nm. This feature is shifted to the red of that expected for just the nanoparticles in solution themselves (i.e. particles not part of a doped polymer film).
The fabrication methods discussed above may be used to prepare a range of novel metal nanocrystal-doped polymer thin film structures ~tili7ing a variety of polymers (e.g., polystyrene, PMMA, conducting polymers, etc.) and a single kind of metal nanocrystal, or any combination of different metal nanocrystals. These include, but are not limited to:
org~nic~lly-functionalized Ag nanocrystal single or multilayer films; organically-25 functionalized Au nanocrystal single or multilayer films; organically-functio~li7Pd Pt nanocrystal single or multilayer films, organically-functionalized Pd nanocrystal single or multilayer films; organically-fimctionalized Au/Co nanocrystal single or multilayer films; any combination therein of the organically-functionalized metal nanocrystals (e.g., a multilayer structure with an Ag/AulAg nanocrystal configuration or Ag/Pt/Au nanocrystal configuration, W O 97/24224 PCT~US96/20402 etc.); any variable stoichlomekic combination of the organically-functionalized metal nanocrystals (e.g., a 20% Ag /20% Au / 10% Pt nanocyrstal / 50% polymer configuration).

(a) dodecylamine-capped Pt nanocrystals were prepared and characterized according 5 to the procedure of Example 7. The particles used here for catalysis had an average domain size of approximately 25 A; (b) 10 ml of a 10 mg/ml solution of dodecylamine-capped Pt nanocrystals prepared as in (a), above, was combined with 125 ml of clean hexane in a reaction flask. The air was purged from this mixture through three freeze-pump-thaw vacuum cycles over the course of S hours; (c) H2(g) was bubbled through the evacuated 10 solution in the reaction flask from (b) for 12 hours; (d) The I~2(g) flow was stopped, the initial pressure of ~--I2(g) in the reaction vessel was measured with an in-line mercury manometer (P
H2(g) = 665 torr)~ and then the flask was completely sealed; (e) .5 ml of l-hexene was injected into the reaction vessel via a 3 cc syringe that had been purged with H2(g); (f) The reaction mixture was vigorously stirred for 5 hours, and the pressure drop of H2(g) was monitored over 15 this time interval. Control experiments (no Pt-catalyst was added~ were also carried out in an analogous fashion.
Where no Pt nanocrystals were added, the pressure of H2(g) remains constant at the initial value of 662 torr over the course of 250 minutes. This indicates that no reaction took placc (i.c., no conversion of l-hexene to hexane occurred). Where an aliquot of a hexane 20 solution of dodecylamine-functionalized Pt nanocrystals (avg. diameter ~ 25 ~) was initially added, the pressure of H2(g) initially decreases in a logarithmic fashion and then reaches some stcady-state value (the conversion of l-hexene to hexane is presumably complete within about 75 minutes or the catalyst is used up).
Any lo-lOOA Pt and Pd nanocrystals functionalized with amine surface groups that25 will bind to the particles such as dodecylamine, octadecylarnine, or pyridine can be used to produce similar results.
Although the present invention has been described with reference to ~ rer~ed embo-liment~, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.

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Claims

What is claimed is:

1. A method for preparing organically functionalized nanocrystals of metals and metal alloys comprising the steps of:
(a) providing a solution or dispersion of one or more metal salts;
(b) providing a solution of a non-metallic organic surface passivant;
(c) mixing said one or more metal salts with said non-metallic organic surface passivant;
(d) reacting the resulting mixture with a reducing agent to reduce said one or more metal salts to free metal while concomitantly binding said non-metallic organic surface passivant to the resulting free metal surface;
thereby providing organically functionalized metal and metal alloy nanocrystals having a particle diameter of 1-20 nanometers.

2. The method of claim 1 which additionally comprises the steps of providing an organic solution of a phase transfer agent and mixing said phase transfer agent with said one or more metal salts prior to mixing with said non-metallic organic surface passivant.

3. (This claim has been cancelled.)

4. (This claim has been cancelled.)

5. (This claim has been cancelled.)

6. The method of either claim 1 or claim 2 wherein at least one of said metal salts is a transition metal salt.

7. The method of claim 6 wherein said transition metal salt is a salt of Au, Ag, Pt, Pd, Co, or Ni.

8. (This claim has been cancelled.)

9. (This claim has been cancelled.)

10. (This claim has been cancelled.)

11. The method of claim 2 wherein said phase transfer agent is a molecule containing both polar and non-polar functionality.

12. The method of claim 2 wherein said phase transfer agent is a molecule having the ability to form micelles or inverted micelles.

13. The method of claim 2 wherein said phase transfer agent is an amphiphilic molecule.

14. The method of claim 13 wherein said amphiphilic molecule is a member selected from the group consisting of alcohols, ethers, esters, fatty acids, phospholipids, polyphosphate esters, polyethers, alkylammonium salts, tetraalkylboron alkali metal compounds, alkali metal soaps and detergents, and nitrogen-containing aromatic compounds.

15. The method of claim 2 wherein said phase transfer agent is a zwitterion molecule.

16. The method of either claim 1 or claim 2 wherein said non-metallic organic surface passivant is a compound of the formula R-X, wherein R is a member selected from the group consisting of alkyl, aryl, alkynyl, and alkenyl groups, and X is a group which can bind to said free metal surface via strong or weak interactions.

17. The method of either claim 1 or claim 2 wherein said non-metallic organic surface passivant is a member selected from the group consisting of thiols, phosphines, oxyphosphines, disulfides, amines, oxides, and amides.

18. (This claim has been cancelled.)

19. The method of either claim 1 or claim 2 wherein said reducing agent is a member selected from the group consisting of sodium borohydride, sodium cyanoborohydride, sodium citrate, lithium aluminum hydride, K, and NaK.

20. A method for preparing a metal nanocrystal-doped matrix or a metal alloy nanocrystal-doped matrix comprising:
providing organically functionalized metal or metal alloy nanocrystals prepared according to the method of either claim 1 or claim 2;
providing a matrix; and combining said organically functionalized metal or metal alloy nanocrystals with said matrix.

21. The method of claim 20 wherein said matrix is a polymer solution.

22. The method of claim 21 wherein said polymer solution and said organically functionalized metal or metal alloy nanocrystals are combined by spin coating.

23. The method of claim 21 wherein the polymer comprising said polymer solution is a member selected from the group consisting of polystyrene, polymethylmethacrylate, polyethers, polypropylene, and polyethylene.

24. The method of claim 21 wherein the solvent comprising said polymer solution is a member selected from the group consisting of alcohols, ketones, ethers, chloroform, TCE, and dichloromethane.

25. The method of claim 20 wherein said matrix is a sol-gel.

26. The method of claim 20 wherein said matrix is alumina.

27. The method of claim 20 wherein said matrix is glassy carbon.

28. The product of the method of claim 1.

29. The product of the method of claim 2.

30. A method for converting 1-hexene to hexane which comprises reacting 1-hexene with hydrogen in the presence of an organically functionalized metal nanocrystal catalyst prepared by the steps of:
(a) providing a solution of a Pt or Pd salt;
(b) mixing said Pt or Pd salt solution with an organic solution of a phase transfer agent;
(c) providing a solution of an amine surface passivant selected from the group consisting of dodecylamine, octadecylamine, and pyridine;
(d) mixing the organic phase resulting from step (b) with said amine surface passivant solution; and (e) reacting the resulting mixture of step (d) with a reducing agent to reduce said Pt or Pd salt to free Pt or Pd while concomitantly binding said amine surface passivant to the resulting free Pt or Pd surface.