EP1601612A2 - Procede pour produire des nanocristaux et nanocristaux ainsi obtenus - Google Patents

Procede pour produire des nanocristaux et nanocristaux ainsi obtenus

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Publication number
EP1601612A2
EP1601612A2 EP04775831A EP04775831A EP1601612A2 EP 1601612 A2 EP1601612 A2 EP 1601612A2 EP 04775831 A EP04775831 A EP 04775831A EP 04775831 A EP04775831 A EP 04775831A EP 1601612 A2 EP1601612 A2 EP 1601612A2
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EP
European Patent Office
Prior art keywords
group
temperature
nanocrystals
precursor
precursor mixture
Prior art date
Legal status (The legal status 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 status listed.)
Withdrawn
Application number
EP04775831A
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German (de)
English (en)
Inventor
Erik C. Scher
Mihai Buretea
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Nanosys Inc
Original Assignee
Nanosys Inc
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Filing date
Publication date
Application filed by Nanosys Inc filed Critical Nanosys Inc
Publication of EP1601612A2 publication Critical patent/EP1601612A2/fr
Withdrawn legal-status Critical Current

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    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
    • C30B29/60—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape characterised by shape
    • C30B29/605—Products containing multiple oriented crystallites, e.g. columnar crystallites
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B19/00—Selenium; Tellurium; Compounds thereof
    • C01B19/007—Tellurides or selenides of metals
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B21/00—Nitrogen; Compounds thereof
    • C01B21/06—Binary compounds of nitrogen with metals, with silicon, or with boron, or with carbon, i.e. nitrides; Compounds of nitrogen with more than one metal, silicon or boron
    • C01B21/0632—Binary compounds of nitrogen with metals, with silicon, or with boron, or with carbon, i.e. nitrides; Compounds of nitrogen with more than one metal, silicon or boron with gallium, indium or thallium
    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B7/00—Single-crystal growth from solutions using solvents which are liquid at normal temperature, e.g. aqueous solutions
    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B7/00—Single-crystal growth from solutions using solvents which are liquid at normal temperature, e.g. aqueous solutions
    • C30B7/005—Epitaxial layer growth
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2002/00—Crystal-structural characteristics
    • C01P2002/30—Three-dimensional structures
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2002/00—Crystal-structural characteristics
    • C01P2002/70—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data
    • C01P2002/72—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data by d-values or two theta-values, e.g. as X-ray diagram
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/01—Particle morphology depicted by an image
    • C01P2004/04—Particle morphology depicted by an image obtained by TEM, STEM, STM or AFM
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/10—Particle morphology extending in one dimension, e.g. needle-like
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/30—Particle morphology extending in three dimensions
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/54—Particles characterised by their aspect ratio, i.e. the ratio of sizes in the longest to the shortest dimension
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/60—Particles characterised by their size
    • C01P2004/64—Nanometer sized, i.e. from 1-100 nanometer

Definitions

  • the present invention relates to the field of semiconductor nanocrystals and to a process for preparing same.
  • Nanocrystals have gained a great deal of attention for their interesting and novel properties in electrical, chemical, optical and other applications.
  • Such nanomaterials have a wide variety of expected and actual applications, including use as semiconductors for nanoscale electronics, optoelectronic applications in emissive devices, e.g., nanolasers, LEDs, etc., photovoltaics, and sensor applications, e.g., as nanoChemFETS.
  • nanocrystals While commercial applications of the molecular, physical, chemical and optical properties of nanocrystals are beginning to be realized; commercially viable processes for the production of a wide variety of nanocrystals have been limited. Both the starting materials used and the conditions under which the nanocrystals are grown are commercially prohibitive.
  • the chemical reaction used to produce nanocrystals involves nanocrystal nucleation and growth. Lack of control over the nucleation event and growth phase in synthetic process has prevented the production of a wide variety of nanocrystal types.
  • Nanocrystals of semiconductors are traditionally formed by the fast injection of pyrophoric precursors into hot coordinating solvents.
  • U.S. Patent No. 6,225,198 Bl to Alivisatos et al. the foil disclosure of which is hereby incorporated by reference in its entirety for all purposes, discloses a process for the formation of rod-shaped II- VI semiconductor nanocrystals.
  • a cold solution (-10 °C ) of a Group II metal and Group VI element is injected into a binary surfactant mixture heated to temperatures around 360 °C to initiate nanocrystal nucleation, which reduces the reaction temperature to around 300 °C.
  • the nanocrystals are grown at temperatures about 50-70 °C lower than the nucleation temperature. A variation in temperature drop of as little as 5 °C leads to different growth rates and different size, shape and structure nanocrystals can result.
  • the present invention relates to processes for producing nanocrystals.
  • An embodiment comprises: contacting a metal precursor with a mixture comprising a coordinating solvent to form a first precursor mixture; heating the first precursor mixture to a first temperature; contacting the first precursor mixture with a second precursor mixture comprising one of a Group V and Group VI compound to form a reaction mixture at a second temperature; and heating the reaction mixture at a third temperature to grow nanocrystals; whereby the second temperature is no more than about 15 °C lower than the first temperature.
  • the second temperature is no more than about 10 °C, 7 °C, 5 °C, 3 °C or 1 °C lower than the first temperature.
  • a further embodiment of the present invention comprises: contacting a metal precursor with a mixture comprising a coordinating solvent and a metal catalyst to form a first precursor mixture; heating the first precursor mixture to a first temperature; contacting the first precursor mixture with a second precursor mixture comprising one of a Group V and Group VI compound to form a reaction mixture at a second temperature; and heating the reaction mixture at a third temperature to grow nanocrystals; whereby the second temperature is no more than about 15 °C lower than the first temperature.
  • the second temperature is no more than about 10 °C, 7 °C, 5 °C, 3 °C or 1 °C lower than the first temperature.
  • Another embodiment of the present invention relates to a composition of rod-shaped DI-V nanocrystals having at least about 50% hexagonal crystal structure and an aspect ratio of at least about 4:1.
  • the composition of rod-shaped HI-V nanocrystals has at least about 70%, 80%, 90% or 95% hexagonal crystal structure and an aspect ratio of at least about 4:1.
  • FIG. 1 is a flow chart depicting the traditional process of producing nanocrystals.
  • FIG. 2(a)-(b) are flowcharts depicting the preparation of the first precursor mixture in accordance with the present invention.
  • FIG. 3(a)-(b) are flowcharts depicting the preparation of the second precursor mixture in accordance with the present invention.
  • FIG. 4 is a flow chart depicting the process of producing nanocrystals in accordance with the invention.
  • FIG. 5 depicts a pyramid-shaped II- VI or ITI-V type nanocrystal 500 having cubic crystal structure with four faces 502-508.
  • FIG. 6 depicts a tetrapod-shaped II- VI or ILT.-V type nanocrystal 600 having cubic crystal structure in the center pyramid region 500 and hexagonal crystal structure in the four arms 602-608.
  • FIG. 7 depicts a rod-shaped H-VI or JJLI-V type nanocrystal 700.
  • FIG. 8a is a Transmission Electron Microscope (TEM) micrograph of rod-shaped CdSe nanocrystals, produced in accordance with the present invention.
  • FIG. 8b shows an X-ray diffraction (XRD) pattern taken of the rod- shaped CdSe nanocrystals. The x-axis is in degrees 2 ⁇ and x-ray source is Cu- K ⁇ radiation.
  • FIG. 9 is a series of three TEM micrographs showing the production of tetrapod-shaped CdSe nanocrystals in accordance with the present invention.
  • FIG. 10 shows the XRD patterns for samples of tetrapods with different arm lengths taken from four different nanocrystal syntheses.
  • the variables include the reaction mixture temperature, the concentration of precursor compounds, the molar ratio of the precursor compounds and the concentration and type of surfactant and coordinating solvent.
  • the inventors have discovered that a minimum, reproducible and predictable temperature change between the first and second temperatures affords maximum control and reproducibility in nanocrystal synthesis. This control has allowed for the production of a wide range of nanocrystal types and shapes, including shaped nanocrystal types that were not possible using previous processes known in the art.
  • FIG. 1 illustrates the traditional process of producing CdSe nanocrystals.
  • the process comprises mixing, 106, a surfactant, 102, and a phosphine oxide, 104, and heating, 108, the mixture to produce a precursor mixture, 110.
  • the process further comprises contacting, 118, simultaneously, a cadmium salt, 116, cooled below room temperature, and a selenium-phosphine complex, 114, also cooled below room temperature, to form a reaction mixture, 120, at a second temperature.
  • the second temperature is at least about 30 °C to about 70 °C lower than the first temperature.
  • the term "about" includes the specified number ⁇ 5%.
  • “about 400 °C” includes 380-420 °C.
  • the reaction mixture is further processed by heating, 122, the reaction mixture to form nanocrystals and isolating, 124, the nanocrystals, to produce a nanocrystal composition, 126.
  • the present invention comprises a process for producing nanocrystals of II- VI or TJJ-V semiconductors, which offers control over the nanocrystal nucleation event and growth phase, and in turn the shape and size of the nanocrystal, by minimizing the temperature change between the first and second temperatures.
  • Examples of II- VI or jJJ-V semiconductor nanocrystals made according to the present invention include: any combination of an element from Group II, such as Zn, Cd and Hg, with any element from Group VI, such as S, Se, Te, Po, of the Periodic Table; and any combination of an element from Group DX such as B, Al, Ga, hi, and Tl, with any element from Group V, such as N, P, As, Sb and Bi, of the Periodic Table.
  • Specific examples include, but are not limited to ZnS, ZnSe, ZnTe, CdS, CdSe, CdTe, GaN, GaP, GaAs, InN, InP and As nanocrystals.
  • the present invention also allows for control over the resulting shape and size of the nanocrystals. Examples of shapes that are made according to the invention include, but are not limited to, spheres, rods, arrowheads, teardrops and tetrapods.
  • Nanocrystals made in accordance with the present invention will optionally be subjected to further processing.
  • surface chemistry modifications are optionally made to the nanocrystals of the present invention.
  • surface modification include, but are not limited to, the addition of coating layers and the addition of shells over the nanocrystals of the present invention.
  • the coating layers and/or shells can be any material, for example, semiconductor materials, or the like.
  • Such processing steps are known to one of skill in the art, see, for example, U.S. Patent Nos. 6,201,229 Bl and 6,322,901 Bl, the foil disclosures of which are hereby incorporated by reference in their entirety for all purposes.
  • the metal precursor can be any metal compound that comprises an element from Group II or Group HJ of the periodic table, such as a metal oxide, metal salt or organometallic complex.
  • Metal oxides for use in the present invention include oxides of the elements Zn, Cd, Hg, B, Al, Ga, In and Tl. Examples of metal oxides include but are not limited to CdO, ZnO, Al O 3 and fr ⁇ O .
  • Metal salts for use in the present invention include salts of the elements Zn, Cd, Hg, B, Al, Ga, In and Tl.
  • metal salts include, but are not limited to, metal halides, metal carboxylates, metal carbonates, metal sulfates and metal phosphates, such ZnF 2 , ZnCl 2 , ZnBr 2 , Znl 2 , Zn(acetate) 2 , ZnSO , CdF 2 , CdCl 2 , CdBr 2 , Cdl 2 , Cd(acetate) 2 , Cd(OH) 2 , Cd(NO 3 ) 2 , Cd(BF 4 ) 2 , CdSO 4 , CdCO 3 , A1F 3 , A1C1 3 , AlBr 3 , A1I 3 , Al(OH) 2 (CO 2 CH 3 ), AlNH 4 (SO 4 ) 2 , Al(OH) 3 , Al(NO 3 ) 3 , Al(ClO 4 ) 3 , AlPO 4 , Al 2 (SO 4 ) 3 , GaF 3 , GaCl
  • Organometallic complexes for use in the present invention include any organometallic complex of the elements Zn, Cd, Hg, B, Al, Ga, In and Tl.
  • organometallic complexes include, but are not limited to, complexes between Group II or Group HI elements and alkyl, haloalkyl, alkenyl, alkynyl, aryl, alkoxyl, alkenoxyl and aryloxyl groups.
  • organometallic complexes include, but are not limited to, dialkylzinc, dialkylcadmium, dialkylmercury, trialkylaluminum, trialkylgallium and trialkylindium, including Zn(CH 3 ) 2 , Zn(CH 2 CH 3 ) 2 , Cd(CH 3 ) 2 , Cd(CH 2 CH 3 ) 2 , Hg(CH 3 ) 2 , Hg(CH 2 CH 3 ) 2 , A1(CH 3 ) 3 , A1(CH 2 CH 3 ) 3 , Ga(CH 3 ) 3 Ga(CH 2 CH 3 ) 3 , h (CH 3 ) 3 and h (CH 2 CH 3 ) 3 .
  • Coordinating solvents for use in the present invention include solvents that can coordinate to metals and have boiling points greater than 150 °C. Preferably, the solvent has a decomposition temperature above 300 C.
  • N is not pentavalent under conditions of present invention, and therefore, X cannot exist if N is Y and N is bonded to three R groups.
  • Alkyl is used herein to refer to any branched or unbranched saturated hydrocarbon chain with 4 to 40 carbon atoms.
  • Haloalkyl is used herein to refer to alkyl chains substituted by any number of halogen atoms such as CI, F, Br and I. Examples include perfluorooctyl (-C 8 F 1 ) and pentadecafluorooctyl (-CH 2 CF 15 ).
  • coordinating solvents include but are not limited to trioctylamine, trihexylphosphine, trihexylphosphine oxide, trioctylphosphine, trioctylphosphine oxide, tridecylphosphine, tridecylphosphine oxide, tridodecylphosphine, tridodecylphosphine oxide, tritetradecylphosphine, tritetradecylphosphine oxide, trihexadecylphosphine, trihexadecylphosphine oxide, and trioctadecylphosphine, trioctadecylphosphine oxide.
  • the mixture comprising a coordinating solvent, 202 optionally further comprises a surfactant.
  • Surfactant is used herein to refer to any molecule that interacts dynamically with the surface of a II- VI or IU-V semiconductor nanocrystal.
  • a surfactant is understood to act dynamically with a nanocrystal surface if the surfactant is capable of removing and/or adding molecules to the nanocrystal, or alternatively, if the surfactant is capable of adhering, adsorbing or binding to the nanocrystal surface.
  • the surfactants include alkylcarboxcylic acids, alkylamines, alkylamine oxides, sulphonates, sulphonic acids, phosphonates, phosphonic acids, phosphinic acids, phosphine oxides and polymers thereof.
  • Examples include hexylphosphonic acid, octylphosphonic acid, decylphosphonic acid, dodecylphosphonic acid and phosphonate esters and polymers of the phosphonic acids, including dimers, trimers, tetramers, pentamers, hexamers, heptamers, etc. of the phosphonic acid.
  • the first precursor mixture, 204 further comprises a metal catalyst, 250.
  • the metal catalyst facilitates nanocrystal nucleation and/or growth.
  • Metal catalysts for use in the present invention include, but are not limited to, colloidal metal nanoparticles.
  • Metal nanoparticles for use in the invention include any metal nanoparticles that facilitate the anisotropic growth of II- VI or HI-V semiconductor nanocrystals, for example, gold.
  • metals for use in the present invention include any of the transition metals from the Periodic Table, including, but not limited to, copper, silver, nickel, palladium, platinum, cobalt, rhodium, iridium, iron, ruthenium, osmium, manganese, chromium, molybdenum, tungsten, vanadium, niobium, tantalum, titanium, zirconium and hafiiium.
  • the metal nanoparticles can be any shape, preferably spheres, and have sizes in the range of about 1 to about 50 nanometers.
  • the first precursor mixture, 204 is heated, 206, to a first temperature, which is sufficient enough to initiate nanocrystal synthesis.
  • the first temperature is about 200 to 500 °C.
  • the first temperature is about 250 to 450 °C.
  • the first temperature is about 290 to 400 °C.
  • the first precursor mixture heated to a first temperature, 208 is used in the nanocrystal synthesis immediately, or alternatively, there is a time delay, 210, wherein the first precursor mixture is held for a period of time at the first temperature before using it further.
  • the period of time is in the range of about 5 minutes to about 12 hours.
  • the first precursor mixture heated to a first temperature, 208 is cooled, 212, to a temperature of about 0 °C to about 100 °C and then optionally heated, 214, to form the first precursor mixture at the first temperature, 208.
  • FIG. 2b illustrates another embodiment of the present invention.
  • a surfactant such as hexylphosphonic acid and a metal precursor such as CdO react to form a Cd- hexylphosphonic acid precursor complex.
  • the first precursor mixture, 204 is optionally heated, 218.
  • the metal precursor complex, 226, is further optionally isolated, 220, by cooling the metal precursor mixture and/or adding a solvent, for example methanol, capable of precipitating the metal precursor complex.
  • the process comprises the steps of purifying, 222, and drying, 224, the metal precursor complex, 226.
  • Heating, 228, the first precursor mixture, 204, to a first temperature forms the first precursor mixture at a first temperature, 208.
  • FIG. 3a illustrates another embodiment of the present invention.
  • a second precursor mixture, 302 comprises one of a Group V and Group VI compound, 304.
  • Group V compound is used herein to refer to any compound that comprises a Group V element of the Periodic Table. Elements from Group V of the Periodic Table include N, P, As, Sb and Bi.
  • Group V compounds include, but are not limited to, N(TMS) 3 , P(TMS) 3 , As(TMS) 3 , Sb(TMS) 3 and Bi(TMS) 3 , wherein TMS refers to the trimethylsilyl group - Si(CH 3 ) 3 ; N(CH 3 ) 3 , N(CH 2 CH 3 ) 3 , P(CH 3 ) 3 , P(CH 2 CH 3 ) 3 , As(CH 3 ) 3 , As(CH 2 CH 3 ) 3 , Sb(CH 3 ) 3 , Sb(CH 2 CH 3 ) 3 , Bi(CH 3 ) 3 and Bi(CH 2 CH 3 ) 3 .
  • TMS refers to the trimethylsilyl group - Si(CH 3 ) 3 ; N(CH 3 ) 3 , N(CH 2 CH 3 ) 3 , P(CH 3 ) 3 , P(CH 2 CH 3 ) 3 , As(CH 3 ) 3 , As(CH
  • Group VI compound is used herein to refer to any compound that comprises a Group VI element of the Periodic Table. Elements from Group VI of the Periodic Table include O, S, Se, Te and Po. Examples of Group VI compounds include, but are not limited to, elemental chalcogens such as S, Se, Te and Po.
  • the second precursor mixture, 302 optionally further comprises a coordinating solvent, 217, for example, a trialkylphosphine oxide such as trioctylphosphine oxide or tritetradecylphosphine oxide.
  • the second precursor mixture further comprises a surfactant, 216, for example, hexylphosphonic acid.
  • the second precursor mixture, 302 comprises no coordinating solvent, 217, or surfactant, 216.
  • the second precursor mixture, 302 comprises about 70-100%» Group V or VI precursor compound.
  • the amount of coordinating solvent, 217, and optional surfactant, 216, used is such that when the second precursor mixture, 302, contacts the first precursor mixture heated to a first temperature, 208, and forms a reaction mixture at a second temperature, as described below, the second temperature is not more than about 15 °C lower than the first temperature.
  • the second precursor mixture, 302 is optionally heated, 310, to form a second precursor mixture at a temperature about 25 to 400 °C, 312.
  • the second precursor mixture, 302 is heated to a temperature such that when it contacts the first precursor mixture heated to a first temperature, 208, and forms a reaction mixture at a second temperature, as described below, the second temperature is not more than about 15 °C lower than the first temperature.
  • FIG. 3b illustrates a further embodiment of the present invention.
  • a fractional amount of second precursor mixture, 302 is optionally diluted with surfactant, 216, and coordinating solvent, 217, to form a diluted second precursor mixture, 318.
  • the diluted second precursor mixture, 318 comprises a different concentration of Group V or Group VI compound, 304, than the second precursor mixture, 302.
  • the diluted second precursor mixture, 318 has the same volume as the second precursor mixture, 302.
  • the present invention allows for changing the molar ratio between the two elements in II- VI and HI-V type semiconductor nanocrystals, without losing control, predictability and reproducibility over the nanocrystal synthesis. This process of dilution can be repeated any number of times.
  • Varying the fractional amounts of second precursor mixture, 302 produces any number of diluted second precursor mixtures, all having varying concentrations of Group V or Group VI compound, 304, but all having constant volume.
  • heating, 316, the diluted second precursor mixture, 318 forms a diluted second precursor mixture at a temperature about 25 to 400 °C, 320.
  • the molar ratio between the two elements in II- VI and HI-V type semiconductor nanocrystals is varied by changing the amount and/or concentration of metal precursor, used in the first precursor mixture.
  • the amount and/or concentration of metal precursor used and the concentration of the Group V or Group VI compound used in the second precursor mixture are both varied.
  • FIG. 4 illustrates a further embodiment of the present invention.
  • Contacting, 402, the first precursor mixture, 208, with a second precursor mixture, 312, or optionally, a diluted second precursor mixture, 320 forms a reaction mixture at a second temperature, 404.
  • the contacting, 402 can be performed by any means known to one of ordinary skill in the art.
  • the second precursor mixture is rapidly injected into the first precursor mixture.
  • the second temperature is no more than about 15 °C lower than the first temperature, alternatively, the second temperature is no more than about 10 °C, 7 °C, 5 °C, 3 °C, or 1 °C lower than the first temperature.
  • there is no temperature change meaning the first and second temperatures are equal.
  • the process further comprises heating, 408, the reaction mixture, 404, at a third temperature to form a reaction mixture at a third temperature, 410, and to grow nanocrystals.
  • the third temperature can be any temperature that allows for the controlled growth of nanocrystals in a predetermined and defined crystal structure.
  • the nanocrystals are grown at a temperature of about 100 to about 450 °C.
  • the reaction mixture is heated at the third temperature for a period of time to grow the nanocrystals.
  • the length of time for the heating, 408, is in the range of about one minute to about one hour.
  • the process shown in FIG. 4 further comprises contacting, 412, the reaction mixture heated to a third temperature, 410, with additional second precursor mixture, 312, or optionally, diluted second precursor mixture, 320.
  • the additional second precursor mixture can be added all at once.
  • the additional second precursor mixture or diluted second precursor mixture can be added in a series of additions.
  • the additional second precursor mixture or diluted second precursor mixture can be added slowly and constantly over the course of the heating, 408.
  • the process shown in FIG. 4, further comprises isolating, 414, the nanocrystal composition, 416, from the reaction mixture.
  • the isolating can be performed by any method known to one of ordinary skill in the art.
  • One example of isolating comprises cooling the reaction mixture to room temperature, adding a sufficient amount of polar solvent, such as methanol, isopropanol or acetone and collecting the nanocrystals by any method such as filtration or centrif ⁇ gation.
  • the nanocrystals can be separated by size and shape.
  • the nanocrystals have a narrow size and shape distribution and require no size or shape separation.
  • the nanocrystals in composition 416 vary not more than about 20% in size.
  • the nanocrystals in composition 416 vary not more than about 15%, 10% or 5% in size. Not more than about 20% of the nanocrystals in composition 416 have varying shape. Alternatively, not more than about 15 >, 10% or 5% of the nanocrystals in composition 416 have varying shape.
  • Nanocrystals can be separated according to size and shape by any method known to one of skill in the art.
  • the nanocrystals can be separated according to size by passing a composition of nanocrystals through filters having progressively smaller pores. Filters can have pore sizes in the range of about 100 nm to about 10 ⁇ m.
  • the nanocrystals can be separated using shape selective precipitation. The addition of a different polarity solvent to a solution of nanocrystals precipitates less soluble nanocrystals, while the shapes that are more soluble remain in solution.
  • Controlling the temperature change between the first and second temperatures allows for precise control over the temperature of the reaction mixture, and thus precise control over the crystal structure in which the nanocrystals will nucleate and grow.
  • the controlled temperature change also allows for a wider range of suitable first temperatures because the second temperature remains sufficiently high to grow the nanocrystals in the desired crystal structure after the reaction mixture is formed.
  • the wider range of first temperatures allows for the use of a wider variety of reagents, coordinating solvents and surfactants, thus reducing manufacturing costs.
  • Producing II- VI type nanocrystals in an anisotropic shape depends on nucleating and/or growing the material in a particular crystal structure.
  • Anisotropic is used herein to mean nanocrystals having properties that differ according to the direction of measurement.
  • anisotropic rod- shaped nanocrystals have anisotropic aspect ratios of about 2:1 to about 10:1 or greater.
  • An aspect ratio of 2: 1 for a rod-shaped nanocrystal means the length of the rod is 2 times the width of the rod.
  • FIG. 5 wherein rod-shaped nanocrystal, 500, has length, 504, and width, 502.
  • Aspect ratio can be measured by any method known to one of skill in the art, for example, High Resolution or Low Resolution Transmission Electron Microscopy (HRTEM or TEM, respectively), scanning electron microscopy (SEM) or atomic force microscopy (AFM).
  • Crystal structure is used herein to mean the geometric arrangement of the points in space at which the atoms of the nanocrystal occur.
  • CdSe like other LT-VI nanocrystals, forms hexagonal and cubic crystal structures.
  • FIG. 6 depicts a nanocrystal, 600, in a pyramid-shape, resulting from nucleation and/or growth in the cubic crystal structure, with four faces, 602, 604, 606, and 608.
  • a higher temperature is required to nucleate CdSe and other IJ-VI nanocrystals in the hexagonal crystal structure than the cubic crystal structure.
  • it also requires a higher temperature to grow CdSe and other nanocrystals in the hexagonal crystal structure than in the cubic crystal structure.
  • the crystal structure of the nanocrystal can be determined by any process known to one of skill in the art and includes, but is not limited to, X-ray crystallography, transmission electron microscopy (TEM), scanning electron microscopy (SEM) and solid state nuclear magnetic resonance (SSNMR). Preferably, X-ray crystallography or TEM is used.
  • a further embodiment of the present invention comprises a process for producing anisotropic rod-shaped II- VI and JH-V nanocrystals.
  • the process comprises contacting a first precursor mixture heated to a first temperature, with a second precursor mixture to form a reaction mixture at a second temperature.
  • the first and second temperatures are sufficiently high to nucleate and/or grow II- VI or UI-V nanocrystals in the hexagonal crystal structure.
  • the reaction mixture is then heated to a third temperature, which is also sufficiently high to grow the II- VI or HI-V nanocrystals in the hexagonal crystal structure.
  • the second temperature is no more than about 15 °C lower than the first temperature, alternatively, the second temperature is no more than about 10 °C, 7 °C, 5 °C, 3 °C, or 1 °C lower than the first temperature. Alternatively, there is no temperature change, meaning the first and second temperatures are equal.
  • the present invention comprises a process for producing tetrapod-shaped II- VI and HI-V nanocrystals.
  • the process comprises contacting a first precursor mixture, which is heated to a first temperature, with a second precursor mixture to form a reaction mixture at a second temperature.
  • the first and second temperatures are sufficiently high to nucleate II- VI and HI-V nanocrystals in the cubic crystal structure.
  • the reaction mixture is then heated to a third temperature, which is sufficiently high to grow the H-VI and HI-V nanocrystals in the hexagonal crystal structure.
  • the second temperature is no more than about 15 °C lower than the first temperature, alternatively, the second temperature is no more than about 10 °C, 7 °C, 5 °C, 3 °C, or 1 °C lower than the first temperature.
  • there is no temperature change meaning the first and second temperatures are equal.
  • this process results in a tetrapod-shaped nanocrystal, 700, having 4 rod-shaped arms, 702, 704, 706, and 708 (each having hexagonal crystal structure) extending from each corresponding face, 602, 604, 606, and 608 of the center of the nanocrystal, 600 (each having cubic crystal structure).
  • FIG. 8a is a Transmission Electron Microscope (TEM) micrograph of rod-shaped CdSe nanocrystals, produced in accordance with the present invention.
  • the micrograph shows the nanocrystals have rod shape with uniform length and aspect ratio.
  • FIG. 8b shows an X-ray diffraction (XRD) pattern taken of the rod-shaped CdSe nanocrystals.
  • the XRD pattern shows the nanocrystals are formed in the hexagonal crystal structure.
  • FIG. 9 is a series of three TEM micrographs showing the production of tetrapod-shaped nanocrystals over time in accordance with the present invention.
  • the series of micrographs shows the precise control the process of the present invention offers over the length of the arms on each tetrapod.
  • the reaction progresses as shown from top to bottom and shows increasing length of the tetrapod arms.
  • FIG. 10 shows the XRD patterns for samples of tetrapods taken over time during the nanocrystal synthesis.
  • the bottom XRD patterns show that early on in the process, the nanocrystals have a larger portion of the cubic crystal structure present.
  • each XRD pattern moves up on the graph
  • This data confirms the nanocrystals nucleate in the cubic crystal structure, forming the pyramid shaped center, but the nanocrystals grow in the hexagonal crystal structure to produce the rod-shaped arms of the tetrapods.
  • Another embodiment of the present invention comprises a process for producing rod-shaped HI-V nanocrystals with at least about 50% hexagonal crystal structure and aspect ratio of at least about 4:1.
  • the rod- shaped HI-V nanocrystals have at least about 60%, 70%, 80%, 90% or 95% hexagonal crystal structure and aspect ratio of at least about 4:1.
  • the process comprises contacting a metal precursor comprising a Group HI element of the Periodic Table, with a mixture comprising a coordinating solvent, and a metal catalyst to form a first precursor mixture.
  • the process further comprises heating the first precursor mixture to a first temperature.
  • the first temperature is sufficiently high to nucleate and/or grow HI-V nanocrystals in the hexagonal crystal structure.
  • the process further comprises contacting the first precursor mixture with a second precursor mixture comprising a Group V compound to form a reaction mixture at a second temperature, and heating the reaction mixture at a third temperature to grow nanocrystals.
  • the second temperature is no more than about 15 °C lower than the first temperature, and at no time does the temperature drop below that which is required to grow the HI-V nanocrystals in the hexagonal crystal structure.
  • Another embodiment of the present invention therefore, relates to a composition of rod-shaped HI-V nanocrystals having at least about 50%) hexagonal crystal structure and an aspect ratio of at least about 4:1.
  • the composition of rod-shaped HI-V nanocrystals have at least about 60%, 70%, 80%, 90% or 95%> hexagonal crystal structure and aspect ratio of at least about 4:1. It is preferable to produce rod-shaped nanocrystals having no cubic crystal structure, because the areas having cubic crystal structure act as stacking faults such that the shape of the nanocrystal is not a straight rod but a zigzag-shaped rod. This zigzag shape can adversely affect the optical and electronic properties of the nanocrystal.
  • the percentage of crystal structure for a particular nanocrystal can be determined by any method known to those of ordinary skill in the art. For example, measuring the amount of the nanocrystal in one crystal structure to the total amount of the nanocrystal, or by measuring the ratio of crystal structure in the produced nanocrystal to that of a nanocrystal pure in one crystal structure determines the percentage of crystal structure.
  • X-ray diffraction patterns of nanocrystals pure in crystal structure are known to those of ordinary skill in the art and can be made, for example, theoretically, in silico or experimentally.
  • the nanocrystals of the present invention have usefol optical and electronic properties that can be applied in a variety of devices.
  • devices include, but are not limited to electrooptic devices, such as white light sources, light emitting diodes (LED), photorefractive devices, RF filters, such as those for optical data storage, communication and photovoltaic devices, such as those for solar energy conversion.
  • the nanocrystals are deposited on a substrate, for example, an electrode, or sandwiched between two or more substrates.
  • substrates for use in the present invention include, but are not limited to silicon and other inorganic semiconductors, for example, ZnO, TiO and In 2 O 3 -SnO 2 (ITO); polymers such as semiconductive polymers, for example, polyphenylenevmylene; and glass, such as ITO-coated glass.
  • the nanocrystals can be deposited neat or as a mixture comprising the nanocrystals.
  • the mixture further comprises materials that include, but are not limited to electrooptical and semiconductive organic and inorganic molecules and polymers.
  • molecules and polymers include, but are not limited to amines, such as triarylamines and polymers or dendrimers thereof; inorganic semiconductors, such as GaAs, InP and TiO ; polyarylenes, such as polythiophene, polypyrrole, polyphenylene, and polyfluorene, and polyarylvinylenes, such as polyphenylenevmylene and polythienylvinylene.
  • Nanocrystals are deposited as a single layer or as multilayers.
  • a layer comprises only one type of nanocrystal, for example, H-VI rods.
  • a layer comprises two or more different types of nanocrystals.
  • a layer comprises two, three, four, five, six, seven, eight, nine, ten, etc. different types of nanocrystals.
  • a layer comprises H-VI rods, H-VI tetrapods and HI-V rods.
  • each layer comprises the same type of nanocrystal.
  • each layer comprises a different type of nanocrystal.
  • Layer thickness is about 10 nm to about 1000 ⁇ m. Preferably, the layer thickness is about 50 ⁇ m to about 100 ⁇ m. Layer thickness can be measured by any method known to one of ordinary skill in the art, for example, atomic force microscopy (AFM) or scanning electron microscopy (SEM).
  • AFM atomic force microscopy
  • SEM scanning electron microscopy
  • the nanocrystals are oriented on the electrode surface in one direction. Alternatively, the nanocrystals are randomly oriented.
  • the nanocrystals are oriented by any method known to those of skill in the art. For example, the nanocrystals are oriented under an applied electrical, optical or magnetic field, or the nanocrystals are oriented mechanically by fluid flow orientation.
  • the following examples are illustrative, but not limiting, of the method and compositions of the present invention. Other suitable modifications and adaptations of the variety of conditions and parameters normally encountered in nanocrystal synthesis and which are obvious to those skilled in the art are within the spirit and scope of the invention.
  • High quality CdSe rods were prepared by admixing about 0.74g octadecylphosphonic acid (ODPA), about 3.23g of trioctylphosphine oxide (TOPO) and about 0.095g of CdO into a 3-neck flask.
  • the flask was degassed and about 1.5 lg of trioctylphosphine (TOP) was added to form a first precursor mixture, hi a separate flask, a selenium precursor mixture (Se:TOP) was prepared with about 10%) selenium by weight.
  • About 0.1 lg Se:TOP mixture was added to about 0.41g of TOP for a total weight of about 0.52g.
  • the first precursor mixture was heated to about 320 °C.
  • the new selenium precursor mixture with additional TOP was injected into the heated first precursor mixture to nucleate CdSe nanocrystals and form the reaction mixture.
  • the temperature of the reaction mixture dropped to about 315 °C upon injection.
  • the reaction mixture was heated at about 315 °C for about 15 minutes to produce high quality wurzite CdSe rods.
  • High quality CdTe tetrapods were prepared by admixing about 0.40g octadecylphosphonic acid (ODPA), about 3.63g of trioctylphosphine oxide (TOPO) and about 0.050g of CdO into a 3-neck flask. The flask was degassed by heating under vacuum and about 1.50g of trioctylphosphine (TOP) was added to form a first precursor mixture. In a separate flask, a tellurium precursor mixture (Te:TOP) was prepared with about 10% tellurium by weight. About 0.16g Te:TOP mixture was added to about 0.39g of TOP for a total weight of about 0.55g.
  • ODPA octadecylphosphonic acid
  • TOPO trioctylphosphine oxide
  • CdO CdO
  • the first precursor mixture was heated to about 320 °C.
  • the new tellurium precursor mixture with additional TOP was injected into the heated first precursor mixture to nucleate CdTe nanocrystals and form the reaction mixture.
  • the temperature of the reaction mixture dropped to about 315 C upon injection.
  • the reaction mixture was heated at about 315 °C for about 15 minutes to produce high quality CdTe tetrapods.

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Abstract

L'invention concerne un procédé pour produire des nanocristaux. Le procédé comprend la mise en contact d'un précurseur métallique au moyen d'un mélange, comprenant un solvant de coordination et éventuellement un tensioactif et un catalyseur métallique, ce qui permet de former un premier mélange précurseur. Le procédé comprend également le chauffage du premier mélange précurseur à une première température et la mise en contact du mélange précurseur et d'un second mélange précurseur qui peut être un précurseur du groupe V ou du groupe VI, ce qui forme un mélange de réaction à une deuxième température. Le procédé comprend, de plus, le chauffage du mélange de réaction à une troisième température permettant de faire croître les nanocristaux, l'écart de température entre les deux premières températures ne devant pas dépasser 15 °C.
EP04775831A 2003-03-11 2004-03-10 Procede pour produire des nanocristaux et nanocristaux ainsi obtenus Withdrawn EP1601612A2 (fr)

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