Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F9/00—Making metallic powder or suspensions thereof
  • B22F9/16—Making metallic powder or suspensions thereof using chemical processes
  • B22F9/30—Making metallic powder or suspensions thereof using chemical processes with decomposition of metal compounds, e.g. by pyrolysis
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B82—NANOTECHNOLOGY
  • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
  • B82Y20/00—Nanooptics, e.g. quantum optics or photonic crystals
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
  • C23C16/04—Coating on selected surface areas, e.g. using masks
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
  • C23C16/44—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the method of coating
  • C23C16/448—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the method of coating characterised by the method used for generating reactive gas streams, e.g. by evaporation or sublimation of precursor materials
  • C23C16/4486—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the method of coating characterised by the method used for generating reactive gas streams, e.g. by evaporation or sublimation of precursor materials by producing an aerosol and subsequent evaporation of the droplets or particles
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
  • C23C16/44—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the method of coating
  • C23C16/48—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the method of coating by irradiation, e.g. photolysis, radiolysis, particle radiation
  • C23C16/483—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the method of coating by irradiation, e.g. photolysis, radiolysis, particle radiation using coherent light, UV to IR, e.g. lasers
• • 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
  • C30B29/02—Elements
• • 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
• • G—PHYSICS
  • G02—OPTICS
  • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
  • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
  • G02F1/35—Non-linear optics
  • G02F1/355—Non-linear optics characterised by the materials used
  • G02F1/3556—Semiconductor materials, e.g. quantum wells

Definitions

• the present invention relates to a method of producing metal quantum dots.
• the method enables metal quantum dots of uniform size to be produced which can be used in providing very regular metal layers.
• Quantum dots are defined as small particles whose linear dimension in all three directions is less than the de Broglie wavelength of the electrons or holes. Such particles can have a greatly modified electronic structure from the corresponding bulk material.
• methods of producing quantum dots have focussed on semiconductor material for use in the field of optoelectronics.
• a paper describing semiconductor quantum dots and some of their properties has been published in Angewandte Chemie International Edition (English) 1993, 32, at pages 41- 53: "semiconductor q-particles: chemistry in the transition region between solid state and molecules" by Horst Weller.
• a number of methods of producing semiconductor quantum dots have also been tried and these have been centred on the generation of colloids or inverse micelles or on "smokes”.
• the present invention provides a method of producing metal quantum dots, which method comprises providing a solution in an evaporable solvent of the metal in chemically combined form, passing the solution through an electrostatic capillary nozzle to form droplets of the solution in a chamber, irradiation of the droplets within the chamber with photons and removing the evaporable solvent from the droplets to form metal particles.
• the method starts with a solution in an evaporable solvent of the chosen metal in chemically combined form.
• the evaporable solvent is volatile in the sense that the solvent is evaporable under the reaction conditions used and may be water or an organic solvent whose nature is not important.
• the metal is typically present in the form of a salt, preferably a salt with a volatile anion such as nitrate or chloride.
• a wide variety of metals may be used indeed almost any metal which produces positive ions in solution such as Ag, Ni, Fe or Co.
• the solution may contain polyphosphate as stabiliser, for example in the form of sodium polyphosphate which has an average chain length of about 15 PO " 3 units.
• Polyphosphate is well suited for the stabilisation of nanometre size particles, because the chain is strongly bound by metal ions on to the particle surface. It causes electrostatic repulsion between particles because of its charge, and also keeps them apart sterically because of its chain length.
• Other frequently used stabilisers are thiols.
• the starting solution may contain an organic polymer which encapsulates the metal particle.
• organic polymers in solution or dispersion in the volatile liquid, are suitable and known to those working in the field. Examples of suitable polymers include polyvinyl alcohol, polyvinyl acetate, polymethyl methacrylate and polycarbonate. With each of the above examples of stabilisers, particle aggregation whilst in solution is prevented.
• the polyphosphate or organic polymer binds the dried particles into a film.
• the solution is converted into droplets, and ideally the size of these droplets is made as nearly uniform as possible.
• an electrostatic capillary nozzle is used in which a jet of aerosol droplets can be formed by the electrostatic deformation of a meniscus of the starting solution.
• the droplet size can be controlled by varying the flow rate from a reservoir and the voltage applied to the nozzle.
• the droplets emerge from the nozzle into a chamber preferably under low-pressure conditions and are irradiated preferably using a laser.
• the volatile solvent is evaporated off to leave the desired particles of metal.
• the particles are encapsulated in the polymer.
• the size of the resulting particles or quantum dots depends on two factors: the concentration of the chemically combined metal in the starting solution; and the size of the formed droplets. Both these variables are readily controlled and pre- determined either experimentally or theoretically to provide quantum dots of desired size, which is typically less than 25 nm, and preferably in the range 1 to 20 nm.
• FIG. 1 An example of a spray nozzle assembly which may be used to generate the desired droplet size is shown in Figure 1.
• the assembly consists of a reaction chamber 7 which is an evacuable chamber having inlet and outlet ports for the introduction and circulation, if desired, of a gas, e.g. nitrogen or argon.
• a capillary nozzle member 3 which may be a conventional capillary tube, projects into an upper region of the reaction chamber 7 and is connected to a reservoir 2 of the solution to be issued as an aerosol.
• the capillary nozzle member 2 which is preferably a metal capillary of stainless steel or platinum for example, is also connected to a voltage supply 1 for raising the voltage potential of the nozzle member so that it is positive with respect to a substrate 5 Iocated along the base of the reaction chamber 7.
• a laser 8 is positioned outside of the chamber 7 so as to irradiate the aerosol 4 formed at the nozzle 2 or in the region of Rayleigh Taylor cone.
• the chamber 7 may be substantially transparent to the laser light or may have a window (not shown) which is transparent.
• the positive potential is applied to the nozzle member 3 and the solution delivered from the reservoir 2 to the nozzle member 3 at a minimum permissible pressure.
• the aerosol droplets 4 formed fall from the nozzle member 3 under the effect of gravity and the applied voltage potential to the substrate 5 beneath.
• the laser 8 having an energy density preferably greater than 10 3 Wm 2 at a wavelength less than 700 nm.
• the solvent is evaporated leaving quantum dots of the element metal on the substrate 5.
• the assembly may be used to coat a static substrate or altematively could be used in a continuous process for the coating of a moving liner substrate such as a tape. In these circumstances the rate of movement of the tape must be matched to the arrival rate of the particles.
• the assembly can also be used to "write" a structure with the particles, such as a wave guide. Since the droplets are highly charged, they can be focussed and deflected in any conventional manner to control the deposition site of the particles on the substrate.
• a single layer of quantum dots may be deposited on the substrate. Also, the layer(s) of quantum dots may coalesce on the substrate to form a continuous thin film.
• the resulting particles will have some forward momentum, and are deposited on the substrate placed under the nozzle.
• the particles also can be dispersed into a liquid carrier, e.g. a solution of the aforementioned polymers, which may then be coated onto a substrate, e.g. by spin coating and dried.
• Example 1 A starting solution was prepared consisting of 10 3 M silver nitrate which is diluted with methanol. The solution was supplied to the electrostatic spray nozzle assembly shown in Figure 1 , operated at 1-10 keV, so as to generate aerosol droplets of diameter 0.1 to 10 ⁇ m. The Rayleigh Taylor cone and the aerosol were illuminated using a He-Ne laser (633 nm) having 1mW output power with a beam having a cross-section at the nozzle of around 1mm 2 .
• a starting solution was prepared consisting of 10 "3 M silver nitrate, the solution also containing 1 M sodium hexametaphosphate and was diluted with methanol.
• the solution was supplied to the electrostatic spray nozzle assembly operated as 1-10 keV so as to generate aerosol droplets of diameter 0.1 to 10 ⁇ m.
• the aerosol was illuminated as described in Example 1.
• the methanol evaporated off to give particles of Ag with the hexametaphosphate forming an inorganic polymer which encapsulated the particles and formed a polyphosphate film containing the particles.
• Altemative stabilisers or polymers such as polyvinyl alcohol have been used, with similar results.
• Example 3 A starting solution was prepared consisting of 10 "1 M nickel chloride in water which was then diluted with methanol to provide a 10 '3 M solution. As described above the solution was supplied to the nozzle assembly which was held at a potential of 1-10 keV, preferably 4 keV, thereby generating aerosol droplets of the desired diameter and irradiated. The methanol evaporated off to give particles of nickel. The same method has also been employed with nickel nitrate.
• a starting solution was prepared consisting of 10 "1 M iron nitrate in water which was then diluted with methanol to provide a 10 3 M solution.
• the solution was supplied to the electrostatic capillary nozzle which was held at a positive potential >3 keV.
• the resultant aerosol was irradiated as described earlier using a He-Ne laser.
• the methanol evaporated off to give particles of iron which oxidised after exposure to air to form iron oxide particles.
• the same method has also been employed using cobalt nitrate to produce cobalt oxide quantum dots.
• Metal particles of the size described above have applications in many industries. For example, ferromagnetic material becomes superparamagnetic when made into fine particles. Such a material retains a high magnetic permeability but shows no hysteresis, remanence or coercivity and can be usefully employed in miniature inductors, and electric motors etc. as magnetic losses can be eliminated. Also fine metal particles can be used in dyes for plastics, glasses or ceramics for example. Moreover, very non-linear optical properties can be obtained with sub 10 nm metal particles for example. Other and further applications of metal particles manufactured by the method described herein are envisaged.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• Materials Engineering (AREA)
• Organic Chemistry (AREA)
• Metallurgy (AREA)
• Chemical Kinetics & Catalysis (AREA)
• General Chemical & Material Sciences (AREA)
• Mechanical Engineering (AREA)
• Nonlinear Science (AREA)
• Crystallography & Structural Chemistry (AREA)
• Optics & Photonics (AREA)
• Nanotechnology (AREA)
• Biophysics (AREA)
• Life Sciences & Earth Sciences (AREA)
• Health & Medical Sciences (AREA)
• Toxicology (AREA)
• Dispersion Chemistry (AREA)
• General Physics & Mathematics (AREA)
• Physical Or Chemical Processes And Apparatus (AREA)
• Inorganic Compounds Of Heavy Metals (AREA)
• Manufacture Of Metal Powder And Suspensions Thereof (AREA)
• Physical Vapour Deposition (AREA)
• Physical Deposition Of Substances That Are Components Of Semiconductor Devices (AREA)
• Chemically Coating (AREA)

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Citations (2)

• 1995
  • 1995-07-27 GB GBGB9515439.9A patent/GB9515439D0/en active Pending
• 1996
  • 1996-07-29 WO PCT/GB1996/001853 patent/WO1997004906A1/en not_active Ceased
  • 1996-07-29 JP JP9507367A patent/JPH11510314A/ja not_active Ceased
  • 1996-07-29 US US09/000,272 patent/US5965212A/en not_active Expired - Fee Related
  • 1996-07-29 EP EP96925896A patent/EP0871557B1/en not_active Expired - Lifetime
  • 1996-07-29 DE DE69604089T patent/DE69604089T2/de not_active Expired - Fee Related
  • 1996-07-29 ES ES96925896T patent/ES2137720T3/es not_active Expired - Lifetime

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