WO2008118422A1 - Nanocristaux d'oxyde métallique : préparation et utilisations - Google Patents

Nanocristaux d'oxyde métallique : préparation et utilisations Download PDF

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Publication number
WO2008118422A1
WO2008118422A1 PCT/US2008/003878 US2008003878W WO2008118422A1 WO 2008118422 A1 WO2008118422 A1 WO 2008118422A1 US 2008003878 W US2008003878 W US 2008003878W WO 2008118422 A1 WO2008118422 A1 WO 2008118422A1
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WIPO (PCT)
Prior art keywords
nanocrystals
film
oxide
organic
dispersion
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PCT/US2008/003878
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English (en)
Inventor
Stephen O'brien
Limin Huang
Zhuoying Chen
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The Trustees Of Columbia University In The City Of New York
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Application filed by The Trustees Of Columbia University In The City Of New York filed Critical The Trustees Of Columbia University In The City Of New York
Publication of WO2008118422A1 publication Critical patent/WO2008118422A1/fr
Priority to US12/566,135 priority Critical patent/US20100135937A1/en

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Definitions

  • This invention was made with government support under award number DMR- 0213574 of the MRSEC program of the National Science Foundation, by the SRC under a CSR (Cross Disciplinary Research) award, and relied on equipment supported by the NSEC program of the National Science Foundation under Award Number CHE-Ol 17752, and by a CAREER award, DMR-0348938.
  • the government has certain rights in the invention.
  • Nanoparticles including metal oxides are of considerable interest. Accordingly, methods of preparation have been studied. For example, U.S. Pat. No. 6,262,129 describes methods of preparation of metal nanoparticles (e.g., cobalt) using surfactants, wherein the metal nanoparticles have comparatively narrow size distributions.
  • metal nanoparticles e.g., cobalt
  • Non-chemical methods including Pulsed Laser Deposition (PLD) 14"20 ' 26'27 and magnetron sputtering, 21 "23 have successfully deposited well crystalline epitaxial BaTiO 3 thin films on different substrates. Some of these epitaxial films provide well-behaved electrical and optical properties and they have been employed for the fabrication of dynamic random access memories (DRAM), electro-optical devices and thin film capacitors.
  • PLD Pulsed Laser Deposition
  • DRAM dynamic random access memories
  • Chemical approaches have also been widely studied in the synthesis of BaTiO 3 due to the desire to understand fundamentally the relationship between the particle size and ferroelectricity and to reduce the cost to produce ferroelectric nanostructures. Chemical approaches also offer an advantage for potential nanocrystal self-assembly. Chemical approaches for the synthesis Of BaTiO 3 nanostructures include sol-gel processing, 28"33 coprecipitation, 36"39 ' 35 pyrolysis 40"42 and hydrolysis 43"44 of metal lo-organic or bimetallic alkoxide precursors, hydrothermal 43"51 or solvothermal 52"53 synthesis and peptide templates assisted room temperature synthesis.
  • nanocrystal 54 Most can be classified as aqueous synthesis and only a few of them 52"54 are considered nonaqueous (non-hydrolytic). In nonaqueous synthesis, it is generally easier to control the nanocrystal size distribution for uniform nanocrystals. In certain cases the nanocrystals are prepared with surface capping ligands. 43"44 ' 50 ' 55 Without surface capping ligands aggregation is a major problem which creates difficulties for physical property measurements, although nanocrystals can be temporally dispersed into solvent by strong sonication. With surface bound ligands, nanocrystals can be well dispersed into solvents and functional ized by conjugation of functional groups to surface ligands or by ligand exchange. Furthermore, uniform and well-dispersed nanocrystals could be used in self-assembly, to create nanocrystal superlattices that have potentially interesting collective opto-electronic properties. 3607
  • Mesoporous structures include porous inorganic and inorganic/organic hybrid ultra high surface materials for catalysis, surface functionalization, and electronic/optoelectronic use.
  • the technological backbone is a process of forming high surface area mesostructured materials (materials containing pores with diameters between 2 and 50 nm). See for example U.S. Pat. No. 7,176,245 by SBA Materials Inc.
  • Capacitors are the devices which can store charge (hence energy) in a small area. Typically capacitors are either electrochemical type (where electrolyte ions store energy) or solid state type (where electrons store energy). Energy storage ability of a capacitor depends upon it's capacitance per unit area and the voltage it can sustain. Capacitance depends upon the dielectric constant of the material used (as insulating layer) and surface area of material where charge is stored.
  • Ultracapacitors are based on a structure that contains an electrical double layer. In a double layer, the effective thickness of the "dielectric" is exceedingly thin — on the order of nanometers — and that, combined with the very large surface area, is responsible for their extraordinarily high capacitances in practical sizes. Ultracapacitors can have power densities (energy density stored / delivered per unit time) which are 10 to 100 times higher than conventional batteries. They can also have a very nigh number of charge-discharge cycles, millions or more compared to 200-1000 recharges for most commercially available rechargeable batteries. The efficiency of ultracapacitors compared to batteries is also high. Ultracapacitors offer promise for hybrid automotive engines, starter batteries, consumer electronics, and UPS power supplies. SUMMARY
  • Metal oxide nanocrystalline forms methods of preparation of the nanocrystalline forms, stable dispersions of the nanocrystalline forms and methods of preparation thereof, uses for the nanocrystalline forms and dispersions thereof, including films incorporating the nanocrystalline forms, methods of formation of films including the use of dispersions of the nanocrystalline forms, and uses for the films, are disclosed and claimed herein.
  • a nanocrystalline form of a metal oxide comprising a plurality of nanocrystals, the plurality of nanocrystals having a narrow size distribution and an average particle diameter ranging from about 1 nm to about 100 nm, the nanocrystals comprising a metal oxide of formula M ' X O Z .
  • a mixed metal oxide of the perovskite type of formula M 2 M 3 O 3 or a complex mixed metal oxide of the formula M 4 x M 5 y O z , wherein all of M 1 - M 3 are independently selected ions of metallic elements, are provided.
  • the nanocrystals can be uncapped and uncoated, or can be capped or coated with an organic coating material.
  • the narrow size distribution is a monodisperse size distribution, for example having a monodispersity of ⁇ 10%.
  • a method of preparation of the metal oxide nanocrystalline form comprising contacting an metalorganic precursor, wherein the metalorganic precursor comprises a single metallic element or more than one metallic element, and a liquid substance comprising an alcohol at an elevated temperature of less than about 350°C, to provide the plurality of metal oxide nanocrystals having a narrow size distribution.
  • a reagent can be put in contact with the metalorganic precursor and liquid substance, following application of the elevated temperture, to provide a plurality of metal oxide nanocrystals.
  • the metal oxide precursor solution can be formed using a metalorganic compound including a single metallic element or including a plurality of metallic elements.
  • a substantially homogeneous dispersion of the nanocrystalline form, or a substantially homogeneous dispersion of a nanocrystalline form prepared by an inventive method, in a liquid is provided.
  • methods of preparation of substantially homogeneous dispersions are provided. The dispersions can be stable over a period of time.
  • films including the inventive nanocrystals, or including nanocrystals prepared by an inventive method, or using an inventive dispersion or a dispersion prepared by an inventive method are provided.
  • the films can include various matrix materials, such as organic, inorganic, or mixed organic/inorganic matrix materials, in combination with the metal oxide nanocrystals.
  • the films can have high dielectric constants.
  • the films can have various physical properties that are substantially unchanged from the properties of the respective types of nanocrystals from which the films are formed.
  • inventive nanocrystals or thin films incorporating inventive nanocrystals can be incorporated into various devices such as capacitors, ultracapacitors, semiconductor devices, optoelectronic devices, and display devices.
  • Figure 1 shows TEM and XRD analysis of as synthesized 6 -10 nm BaTiO 3 nanocrystals capped with decanoic acid (case I), a) Overview; b) selected area electron diffraction (SAED); c) XRD powder patterns. All reflections can be assigned to the BaTiO 3 phase (JCPDS No. 31 -174); d) high resolution TEM (HRTEM) image of an individual nanocrystal on the ⁇ 1 1 1 > zone axis. ; e) HRTEM image of an individual nanocrystal on the ⁇ 100> zone axis; f) power spectrum (PS) of (d); g) PS of (e).
  • HRTEM high resolution TEM
  • PS power spectrum
  • Figure 2 shows TEM and XRD analysis of as synthesized 3 - 5 nm BaTiO 3 nanocrystals capped with oleic acid (case II).
  • HRTEM high resolution TEM
  • PS power spectrum
  • Figure 3 shows TEM and XRD analysis of as synthesized IO - 20 nm BaTiO 3 nanoparticle and nanorod mixture capped with oleyl alcohol (case III), a) Overview; b) a typical nanoparticle; c) a typical nanorod; d) selected area electron diffraction (SAED); e) XRD powder patterns. All reflections can be assigned to the BaTiO 3 phase (JCPDS No. 31 -174).
  • Figure 4 shows IR studies of four samples: (a) benzyl alcohol (99.8% Aldrich);
  • Figure 5 shows a 1 H- NMR spectrum of a filtered bimetallic (Ba, Ti) metalorganic precursor solution.
  • Figure 6 shows XRD patterns Of BaTiO 3 nanocrystals synthesized in a solvothermal process using metal barium and titanium isopropoxide as a precursor.
  • the solvthermal process were carried out under different alcohols and alcohol mixture (a) ethanol; (b) 95% ethanol; (c) ethanol + isopropanol (volume ratio of 1 : 1); and (d) isopropanol.
  • Figure 7 shows XRD patterns Of BaTiO 3 nanocrystals synthesized in a solvothermal process using BaTi ethylhexano-isoproxide as a precursor.
  • the solvthermal process were carried out under different alcohols (a) ethanol and KOH; (b) 95% ethanol;
  • Figure 8 shows TEM images Of BaTiO 3 nanocrystals synthesized in a solvothermal process using different alcohols and BaTi metalorganic sources, (a) ethanol; (b) isopropanol; (c) 95% ethanol; (d) ethanol + isopropanol. (a-d) metal barium and titanium isopropoxide as a precursor, (e) isopropanol; and (f) 95% ethanol. (e,f) BaTi ethylhexano-isoproxide as a precursor.
  • Figure 9 shows photographic images of oleic acid coated BaTiO 3 nanocrystals with different sizes dispersed in hexane to afford homogeneous, and transparent/semitransparent nanocrystal suspension.
  • FIG 10 shows Scanning Electron Microscopy (SEM) images Of BaTiO 3 (BT) thin films composed of the nanocrystals with two different sizes, respectively (top-view).
  • the films were prepared by spin-coating of a hexane suspension of the oleic acid coated nanocrystals.
  • Various film thickness can be achieved applying multiple spin-coating (inset, cross-sectional view).
  • Figure 11 shows: (a) Photo image of a stable ethanol solution Of BaTiO 3 nanocrystals; (b) TEM image of corresponding individual BaTiO 3 nanocrystals; (c,d) BaTiO 3 nanocrystal thin film by multiple spin-coating (five coatings), top view and cross-sectional view, respectively.
  • Figure 12 shows the thermal stability Of BaTiO 3 nanocrystal thin films at different temperatures, as discussed below. There is no diffraction peak sharpening for samples annealed at temperatures lower than 600 0 C. Significant peak sharpening can be observed at a higher temperature of 800 0 C, indicating the crystal growth.
  • Figure 13 shows polarization-electric field curve based on the C-V measurement of the BaTiO 3 nanocrystal ( ⁇ 8nm in diameter) thin film (five coatings).
  • Figure 14 shows several images: (a) SEM image of a micro-patterned BaTiO 3 nanocrystal thin films prepared by MIMIC with a micro-patterned PDMS stamp; (b) High-resolution SEM image Of BaTiO 3 nanocrystal thin film prepared by spin-coating, showing that the thin film is composed of nanocrystals with a uniform size of ⁇ 10 nm; (c) Tapping mode AFM image of the BaTiO 3 nanocrystal thin film. All these films were prepared on n-Si substrates with native oxide layers.
  • Figure 15 shows frequency dependence (1 KHz to 100 KHz) of the dielectric constant and dielectric loss of the nanocrystal BaTiO 3 108 nm thin film at room temperature.
  • a nanoparticle is a physical form of a solid material wherein the individual particle dimensions are of the order of nanometers (10 ⁇ 9 meters), ranging up to no more than about 1 micron ( 10 ⁇ 6 meters) in average diameter, typically less than 100 nm (10 ⁇ 7 meters).
  • a "nanocrystal” is a nanoparticle composed of a single crystal domain or a nanocomposite of multiple crystal domains within an individual nanoparticle.
  • the nanocrystals disclosed and claimed herein are composed of a metal oxide or a mixed metal oxide, or combinations thereof, as defined.
  • a nanocrystal herein can be composed of a member of the perovskite family of minerals or of other members of this class of metal oxides of the general formula M 2 M 3 O 3 wherein M 2 and M 3 are metal ions.
  • M 2 and M 3 are metal ions.
  • Examples include barium titanate (BaTiO 3 ) and lead titanate (PbTiO 3 ).
  • a nanocrystal can be composed of a binary metal oxide of the general formula M ' X O ⁇ wherein M 1 is a metal ion. Examples include zinc oxide, zirconium oxide, and titanium oxide.
  • a nanocrystal can be composed of a complex metal oxide of the general formula M 4 x M 5 y O z wherein M 4 and M 5 are metal ions.
  • a nanocrystal can also include ions of additional metallic elements other than the predominant metal ions selected from M 1 - IVp as defined above in a crystal lattice of the metal oxide, mixed metal oxide, or complex mixed metal oxide. Examples include ions of zirconium, yttrium, or rare earth metals. Accordingly, a nanocrystal can include both the metallic elements making up the bulk oxide, and can also include dopants of various ions of other metallic elements, or can include metal oxide forms where more than a single type of metallic element can occupy a particular crystal site.
  • nanocrystals of (cobalt, manganese)-doped zinc oxide include the binary oxide zinc oxide, but additionally containing ions of cobalt and manganese in various proportions. All such compositions of this type are included in the disclosed subject matter.
  • a nanocrystal can have an average diameter of about 1 to about 100 nm.
  • a collection or plurality of a particular type of nanocrystal composed of a type of material, referred to herein as a "nanocrystalline form" of that type of material, for example a material prepared by a disclosed method, can have a narrower size distribution within this range of sizes.
  • the nanocrystals can be predominantly of a size of about 2-3 nanometers, or about 10-20 nanometers.
  • the range of individual particle sizes can be monodisperse, indicating a normal distribution of particle sizes around a mean.
  • a nanocrystalline form having a narrow size distribution, a monodisperse size distribution, or both, can provide uniform sample properties.
  • Nanocrystalline forms wherein the size distribution is narrow, and can be monodisperse, for example with a monodispersity of ⁇ 10%.
  • the average nanocrystal particle size in a particular sample is tunable using the methods herein, such that nanocrystalline forms of various compositions, average particle diameters, and particle size distributions can be prepared by these methods.
  • the solid nanoparticles, nanocrystals herein need not be of any particular shape. Nanocrystals can be roughly spherical, or can be elongate, or can form regular or irregular polyhedra.
  • An “average particle diameter” as the term is used herein refers to a numerical average of x, y, and z orthogonal axes that, when not all equal as in a roughly spherical nanocrystal, are defined with x being the longest dimension of the particle.
  • a nanocrystal can be "uncoated” and “uncapped”, that is, not having a distinct surface layer composed of a different material, such as an organic material.
  • a nanocrystal can be “coated” or “capped”, meaning that the layer of the material on the surface of each nanocrystal can include other materials in addition to the bulk material of the crystalline phase.
  • the term “capped nanocrystal” refers to an inventive nanocrystal wherein the nanocrystal is covered with a molecular layer of one or more organic compounds, that it bonded to the surface of the metal oxide nanocrystal, typically by non-covalent interactions.
  • a “coated” nanocrystal includes a capped nanocrystal as well as including an inventive metal oxide nanocrystal where more than a single molecular layer covers the nanocrystal surface; a coated nanocrystal can have many molecular layers of an organic compound or a mixture of organic compounds on its surface.
  • the terms “capped” and “coated” refer to nanocrystals having on the surface an "organic coating material” that is not volatile to any great extent and which requires heating to a relatively high temperature, such as in sintering, to remove the organic material.
  • the nanocrystals can be capped with a "ligand,” which refers to an organic molecule capable of complexing, or forming typically non-covalent bonds with, an inorganic molecular entity.
  • a nanocrystal for example barium titanate
  • a ligand such as oleic acid, a hydrophobic long chain with a carboxyl end group.
  • An “uncapped” or “uncoated” nanocrystal can have a dry surface, or can have a surface wetted with a volatile liquid such as an alcohol or water, wherein the volatile liquid can be removed if necessary without resorting to elevated temperatures, for example temperatures over 100 0 C.
  • An "uncapped” or “uncoated” nanocrystal also includes a nanocrystal wherein a surface layer of the metal oxide also includes metal alkoxide or metal hydroxide groups, or a layer of a volatile solvent such as an alcohol or ether.
  • a "metallic element” as the term is used herein refers to the identity of the element in any chemical form, i.e., a metallic element is an element classified as metallic (i.e., not a non-metal such as oxygen, etc.) which can be in the form of an elemental metal (zero-valent) or can be in form of a salt or complex of a metal (metal ion).
  • a metallic element in metallic form refers to the unoxidized metal
  • a metallic element in salt or complex form refers to the metal in chemical combination with other elements, such as forming ionic bonds with other elements.
  • the compound barium titanate comprises two metallic elements barium and titanium, each element being in a salt or complex form, namely in an oxide form wherein each metal is in an elevated oxidation state, i.e., an oxidation state of + 1 or higher.
  • a “metal oxide”, “mixed (or doped) metal oxide”, or “complex mixed metal oxide” can each include various species wherein the metal ion, although comprising an identical metallic element, is in a different oxidation state in distinct species, and thus is composed with a different stoichiometry.
  • a “manganese oxide” herein can include manganese(II) oxide (MnO), manganese(III) oxide (Mn 2 O 3 ), manganese dioxide (manganese(IV) oxide, MnO 2 ), manganese trioxide (manganese(VI) oxide, MnO 3 ), manganese(VII) oxide (Mn 2 O 7 ), any other stable manganese oxide, or a combination; an "iron oxide” can include FeO and Fe 3 O 4 , or any other stable oxides, or a combination.
  • a "rare earth” metallic element comprises the elements of the lanthanides, elements 57-71 , as is well known in the art.
  • a "metalorganic precursor” or a solution thereof refers to a molecular composition including at least one metallic element that can be reacted with a liquid comprising an alcohol, such as 95% ethanol, or isopropanol, or an isopropanol-water mixture, or an alcohol-water mixture containing an alkali, to provide nanocrystals.
  • metalorganic precursors include metal alkoxides, metal carboxylates such as metal acetates, and metal complexes such as metal acetoacetonates.
  • Metalorganic precursors can be present as solutions in solvents of various types to provide a metalorganic precursor solution.
  • a metalorganic precursor solution can be contacted with an alcohol or a liquid comprising an alcohol and optionally, water and/or an alkali, at an elevated temperature of less than about 350 0 C, to provide a nanocrystalline form.
  • This process can be termed a "solvothermal" process, as it involves solvents and heat.
  • the nanocrystalline form can be recovered in solid form by contact with a reagent. Alternatively, the nanocrystalline form can be handled as a stable dispersion in a liquid medium.
  • the nanocrystalline form can be uncapped and uncoated, i.e., lacking organic surface layers.
  • metalorganic precursor solution can include an organic material that provides a capping or coating material. Examples are fatty acids, fatty amines, and fatty alcohols.
  • a “reagent” as the term is used herein refers to a liquid material that tends to induce formation of nanocrystals or separation of nanocrystals from a suspension or dispersion in another liquid material.
  • nanocrystals can be formed by contacting a metalorganic precursor and a liquid comprising an alcohol at an elevated temperature. Following application of the elevated temperature to the reaction mixture, nanocrystals are present in the liquid milieu. The nanocrystals can be collected, such as by centrifugation.
  • addition of a reagent can assist in techniques for recovering the nanocrystals from the reaction mixture, bringing about additional nanocrystal formation or increasing the ease of separation of the nanocrystals, or both.
  • a "dispersion” as the term is used herein refers to a mixture of the plurality of nanocrystals and a liquid wherein the predominant portion of the nanocrystals are suspended in the liquid such that they do not readily precipitate out.
  • a dispersion within the meaning herein is stable for a period of time, which can range from about one hour to about six months.
  • Another term for a dispersion is a "suspension”. A certain amount of precipitation can occur, and the dispersed solid nanocrystals can be caused to precipitate by centrifugation, but under normal gravitational conditions they do not rapidly collect at the bottom of a vessel containing the dispersion.
  • a dispersion can be transparent, or can be opalescent, or cloudy, depending at least in part on the size of the dispersed nanocrystals.
  • the liquid in which the plurality of nanocrystals is dispersed can be an organic solvent, such as a non-polar organic solvent. Examples are hydrocarbons (aliphatic or aromatic), chlorocarbons, and the like.
  • the organic solvent can also be a polar solvent, such as acetone, an alcohol, an ether, or a mixture of a water-miscible solvent and water.
  • the liquid can also be a mixture of various types of organic solvents, and optionally water. Alternatively the liquid can be supercritical carbon dioxide.
  • not prone to aggregation or clumping means herein that the individual nanocrystals do not attract each other such that, for instance, a dispersion of the nanocrystals in a liquid substance is stable over a period of time, the nanocrystals do not rapidly form larger aggregates, and the nanocrystals remain in suspension. It is well known in the art that nanoparticles such as nanocrystals, particularly those that lack capping or coating groups, tend to attach each other and form larger clumps of the material. However, the disclosed nanocrystals, including those that are uncapped and uncoated, have a greater propensity to remain dispersed and distinct than do art nanoparticles.
  • a “copolymer” refers to a polymeric material, as is well known in the art, that includes two or more types of monomers.
  • a “block copolymer” is a copolymer wherein the two or more types of monomers are incorporated within distinct oligomeric moieties, which are bonded to each other to create a copolymer with blocks of each type of monomeric unit.
  • P 123 refers to a triblock copolymer surfactant in the Pluronic® group.
  • a “mesoporous material” refers to a type of porous materials containing ordered pore structure with diameters between 2 and 50 nm, according to IUPAC notation.
  • the matrix is typically amorphous silica oxide (silica) based, but can be composed of other metal oxides.
  • a silica mesoporous material can be prepared by hydrolysis and condensation of tetraethyl orthosilicate templated by supermolecular arrays of surfactant (micellar rods). After the organic-inorganic composites are formed, the organic templates can be removed by thermal treatment or solvent extracting, leaving behind an inorganic matrix with ordered pores and channels corresponding to the original surfactant supermolecular templates.
  • the pore sizes can vary and the channel structure can be one-dimensional or three- dimensional.
  • MCM Mobil Company Materials: MCM-41 , one-dimensional; MCM-48, three-dimensional
  • SBA series Spenta Barbara Amorphous: SBA- 15, one-dimensional; SBA- 16, three-dimensional.
  • Mesoporous materials have order pore structure, high surface area and high porosity, and can be applied to fields such as catalysis, sorption, and electronics. See, for example, U.S. Pat. No. 7, 176,245 and documents cited therein.
  • a type of the nanocrystalline form as the phrase is used herein is meant a particular elemental composition, average particle diameter, particle diameter distribution, and other characteristic attributes of an inventive nanocrystalline form.
  • a film comprising a nanocrystalline form substantially retains” some property "of the respective type of nanocrystalline form", what is meant is that the particular property in question, such as dielectric constant, density, spectral absorption or reflectivity, etc., is not greatly altered, diminished, etc. through the process of incorporation of the nanocrystalline form into the corresponding film.
  • a “matrix” as the term is used herein refers to a solid composition, formed by polymerization or condensation of a "matrix precursor”, which can be a solid or a liquid, that incorporates nanocrystals and is cohesive, holding the nanocrystals embedded in the matrix, which can serve to provide a cohesive film.
  • a “film” as the term is used herein refers to a physical structure wherein the thickness is substantially less than the length or breadth; a film can be flat or can be curved in various forms.
  • a film can coat an underlying structure or surface, such as glass, metal, human skin, plastic, and other types of surfaces.
  • a film can be disposed on a substrate such as a sheet or wafer composed at least in part of silicon, silica, silicon nitride, or diamond.
  • the disclosed subject matter provides a nanocrystalline form of a metal oxide, the form comprising a plurality of nanocrystals, the plurality of nanocrystals having a narrow size distribution and an average particle diameter ranging from about 1 nm to about 100 nm, the nanocrystals comprising a metal oxide of formula M' x O z, a mixed metal oxide of the perovskite type of formula M 2 M 3 O 3 , or a complex mixed metal oxide of the formula M 4 x M 5 y0 z , wherein all of M 1 - M 5 are independently selected ions of metallic elements.
  • the average particle size can range from about 1 nm to about 100 nm, but the distribution of particle sizes around the average in a particular sample or plurality of nanocrystals is narrow. Accordingly, a particular plurality of nanocrystals can have an average particle diameter of, for example, 5 nm, and have virtually no members of that plurality having an individual particle diameter greater than, for example 8 nm, or less than about 2 nm. Thus, although samples of nanocrystals disclosed herein can have an average over an approximately 1 -100 nm size range, within any particular sample, the size range is much smaller.
  • the distribution of individual nanocrystal diameters can be substantially monodisperse, i.e., having a normal distribution around a mean, with a relatively small standard deviation compared to the mean. This deviation can be 10% or less. This implies a relatively uniform set of properties being present among the individual nanocrystals, which provides for relatively uniform bulk physical properties throughout the sample.
  • nanocrystalline forms of a wide variety of compositions and physical parameters such as average particle diameter can be prepared, i.e., the methods are "tunable" to achieve a particular desired result.
  • a metal oxide of formula M' X O Z typically referred to as a "binary metal oxide", wherein M 1 is a metal ion, contains predominantly one metallic element in ionic form.
  • additional ions of other metallic elements can be present in the lattice of the nanocrystalline material, such as dopants.
  • dopants include ions of ions of zirconium, yttrium, or rare earth metals.
  • M 1 in include metallic elements such as titanium, zirconium, hafnium, vanadium, niobium, tantalum, tungsten, manganese, iron, cobalt, nickel, copper, zinc, gallium, indium, tin or cerium.
  • the particular element of a particular metal oxide nanocrystalline form can be combined with oxygen in various stoichiometries; in general, x is 1 to about 3 and z is 1 to about 6. Even for a particular metal M 1 , different compositions with oxygen can exist, for example as in the cases Of Mn 2 O 3 and MnO 2 , both of which are binary metal oxides within the meaning herein. Specific examples of binary metal oxides that can compose a nanocrystalline form of the disclosure are zinc oxide, titanium oxide, and zirconium oxide.
  • a metal oxide of the general formula M 2 M 3 O 3 is referred to a mixed metal oxide of the perovskite type.
  • M 2 and M 3 are independently selected metal ions.
  • perovskite type metal oxides contain predominantly two distinct metallic elements in combination with oxygen in a defined stoichiometry.
  • additional ions of other metallic elements can be present in the lattice of the nanocrystalline material, such as dopants.
  • dopants include ions of ions of zirconium, yttrium, or rare earth metals.
  • M 2 include barium, strontium, calcium, lithium, lead, yttrium, bismuth, lanthanum, or a rare earth metal.
  • Example of M 3 include titanium, zirconium, iron, copper, manganese, cerium, or cobalt.
  • perovskite type metal oxides include barium titanate, strontium titanate, calcium titanate, barium strontium titanate, barium lanthanum, lithium lanthanum titanate, lead titanate, lead zirconium titanate, barium zirconate, lead zirconate, yttrium ferrite, bismuth ferrite, yttrium barium copper oxide, lanthanum manganese oxide, strontium cerium oxide, or a rare earth cobalt oxide.
  • a metal oxide of the general formula M 4 x M 5 y O z is referred to as a complex mixed metal oxide.
  • M 4 and M 3 are independently selected metal ions.
  • the particular element of a particular metal oxide nanocrystalline form can be combined with oxygen in various stoichiometries; in general, x is 1 to about 3, y is 1 to about 5, or z is 3 to about 12, or any combination thereof.
  • M 4 for example, can be indium, lithium, bismuth or yttrium.
  • IVl 3 for example, can be tin, niobium, or iron.
  • Examples of complex mixed metal oxides in nanocrystalline form of the disclosed subject matter include indium tin oxide, lithium niobium oxide, or a garnet.
  • garnet examples include Bi 3 Fe 5 Oi 2 or Y 3 Fe S Oi 2 .
  • additional ions of other metallic elements can be present in the lattice of the nanocrystalline material, such as dopants.
  • dopants include ions of ions of zirconium, yttrium, or rare earth metals.
  • a nanocrystalline form of whichever metal oxide type can include nanocrystals wherein the nanocrystals are uncapped or uncoated, as described above.
  • Uncapped and uncoated nanocrystals are free of relatively non-volatile organic capping (a monomolecular layer) or coating (a thicker than monomolecular layer) materials.
  • Uncapped and uncoated nanocrystals can be used, for example, to form films comprising the nanocrystalline form that are substantially free of organic materials. Such films can be used in various electronic devices such as in dielectric layers, where the presence of organic contaminants is undesirable.
  • Many art forms of uncapped and uncoated nanocrystals are prone to aggregation and clumping, and are difficult to disperse to provide substantially stable and homogeneous dispersions.
  • uncapped and uncoated nanocrystalline forms of the disclosed subject matter are not prone to aggregation or clumping over a period of time, ranging from one hour to about six months.
  • Uncapped and uncoated metal oxide nanocrystalline forms of the disclosed subject matter can be dispersed to form substantially stable and homogeneous dispersions particularly in polar organic solvents such as methanol, ethanol, or isopropanol, optionally containing various amounts of water.
  • Such dispersions can be used to form films and coatings substantially free of organic contaminants, with any need to resort to high temperature techniques such as sintering, which can employ temperatures approaching 600 0 C.
  • Uncapped and uncoated nanocrystals of the disclosed subject matter can have a surface wetted with a volatile liquid such as an alcohol or water, wherein the volatile liquid can be removed if necessary without resorting to elevated temperatures, for example temperatures over 100 0 C, or can include nanocrystals with surface metal alkoxide or metal hydroxide groups, or a layer of a volatile solvent such as an alcohol or ether.
  • a volatile liquid such as an alcohol or water
  • the nanocrystalline forms of the present disclosure can be capped or coated, such as with an organic coating material.
  • an organic coating material such as gold nanoparticles
  • certain nanoparticles such as gold nanoparticles
  • Analogously stabilized metal oxide nanocrystals are termed capped nanocrystals herein, and can include organic coating materials on their surfaces.
  • Organic coating materials typically include long chain organic molecules such as fatty acids, fatty alcohols, and fatty amines.
  • nanocrystals When more than a single molecular layer is present, the nanocrystals are referred to as coated nanocrystals.
  • a coated nanocrystal is necessarily also a capped nanocrystal, but a capped nanocrystal has only the molecular single layer.
  • Nanocrystals that are capped or coated can be found to be stabilized against aggregation or clumping, and also can be more easily dispersed in certain types of liquids, such as non-polar organic solvents including aliphatic and aromatic hydrocarbons.
  • organic coating materials include decanoic acid, oleic acid, oleylamine, and oleyl alcohol. Such coating materials are relatively non-volatile and would require high temperatures to remove.
  • Coated nanocrystals can typically be more readily dispersed in non-polar organic solvents such as hexane or benzene than can uncapped and uncoated nanocrystals. Coated nanocrystals also can suffer no disadvantage in applications where an organic contaminant-free material is not needed, such as in a coating for metal, plastic, glass, skin, or the like.
  • a sunblock formulation wherein zinc oxide nanocrystals are dispersed in a carrier oil or cream base are not negatively affected by the presence of a capping or coating layer on the nanocrystals, and a capping or coating layer may be necessary to achieve good dispersion in the hydrophobic oil or cream.
  • supercritical carbon dioxide generally considered to be equivalent to a non- polar organic solvent in solvating properties, can be a dispersant for nanocrystals, such as coated or capped nanocrystals.
  • a method of preparation of a metal oxide nanocrystalline form comprising contacting an metalorganic precursor, wherein the metalorganic precursor comprises a single metallic element or more than one metallic element, and a liquid substance comprising an alcohol at an elevated temperature of less than about 350 0 C, to provide the plurality of metal oxide nanocrystals having a narrow size distribution.
  • the metalorganic precursor can be a metal alkoxide, a metal carboxylate, or a metal complex such as a metal acetoacetonate.
  • Other metal salts and complexes can be used, such as a bulk metal oxide not in nanocrystalline form that can be dissolved in a suitable solvent.
  • the barium in the preparation of barium titanate in a nanocrystalline form of the present disclosure, can be provided in metalorganic form of an alkoxide, such as a benzoxide, that can be prepared by dissolving barium metal in benzyl alcohol.
  • the barium can be provided in metalorganic form by dissolving bulk barium oxide in an alcohol such as ethanol or isopropanol. This can be mixed with a titanium alkoxide, such as titanium isopropoxide, to provide a bimetallic metalorganic precursor solution that can be heated in the presence of the liquid medium comprising an alcohol to provide a nanocrystalline form of the present disclosure.
  • the reaction mixture of the metalorganic precursor and the liquid substance comprising an alcohol is exposed to a temperature of less than about 350 0 C.
  • the reaction mixture can be exposed to a temperature of about 80-230 0 C to provide a nanocrystalline form.
  • the nanocrystalline form which can be present as a stable dispersion in the reaction mixture medium, can be collected, such as by centrifugation, to provide the nanocrystalline form as a dry powder. Alternatively, it can be handled in that dispersion.
  • a reagent can be added after the step of heating.
  • the reagent can amount to up to about 20% of a volume of the precursor solution.
  • the reagent can include a polar organic solvent such as ethanol, or acetone.
  • the reagent can facilitate recovery or collection of the nanocrystals from the dispersion, such as by centrifugation.
  • the metalorganic precursor can include only a single metallic element.
  • metallic element examples include titanium, zirconium, hafnium, vanadium, niobium, tantalum, tungsten, manganese, iron, cobalt, nickel, copper, zinc, gallium, indium, tin and cerium.
  • the metalorganic precursor includes only titanium as a metallic element in salt or complex form.
  • Other metalorganic precursors including only a single metallic element can include zinc and zirconium.
  • the metalorganic precursor can include two or more metallic elements.
  • the metalorganic precursor can include a first metallic element selected from the group consisting of titanium, zirconium, hafnium, vanadium, niobium, tantalum, tungsten, manganese, iron, cobalt, nickel, copper, zinc, gallium, indium, tin and cerium, and a second metallic element selected from the group consisting of barium, strontium, calcium, lithium, lead, yttrium, bismuth, lanthanum, a rare earth metal, titanium, zirconium, iron, copper, manganese, cerium, and cobalt.
  • the metalorganic precursor comprises barium and titanium salts or complexes.
  • examples include a titanium alkoxide, titanium acetate, or titanium acetoacetonate and a barium alkoxide, barium acetate, or barium acetoacetonate.
  • an embodiment of the disclosed subject matter concerns a method for the preparation of ligand surface-capped nanocrystals Of BaTiO 3 , comprising: dissolving barium metal in an alcohol to provide a barium alcoholate solution; then, contacting the barium alcoholate solution with a solution of a titanium alkoxide to provide a bimetallic precursor solution; then, contacting the bimetallic precursor solution at an elevated temperature for a period of time comprising at least about 24 hours with a solvent/1 igand mixture; then, adding a polar solvent to precipitate the nanocrystals; and lastly, separating the ligand surface-capped nanocrystals from the polar solvent.
  • the elevated temperature can be about 8O 0 C to about 23O 0 C. Due to the presence of volatile alcohols, a temperature at the higher end of this range would be above their boiling point, so the reaction can be carried out under self-generated pressure in a pressure containment vessel. For example, a pressure of about 20 atm to about 30 atm can be used.
  • the reaction mixture can include an organic coating material such that a capped or coated nanocrystalline form is obtained.
  • the organic coating material can include an alkanoic acid, a saturated or unsaturated fatty acid, decanoic acid, oleic acid, an alkylamine, a fatty amine, oleylamine, an alkanol, a fatty alcohol, or oleyl alcohol, or a combination thereof.
  • the Ba benzyl alcoholate reacts with this Ti-O- Ti species to form BaTiO 3 nanoparticles by the Ba 2+ substituting the isopropanol groups. Since the synthesis of the precursor is in the very early stage of the reaction, the precursor is probably a mixture of the Ti-O-Ti species (above) or some intermediate product before forming the Ti-O-Ti species, Ba benzyl alcoholate, and extra benzyl alcohol.
  • Figure 1 shows the TEM and XRD characterizations of 6-10 nm BaTiO 3 nanocrystals capped with decanoic acid (case I).
  • SAED Selected Area Electron Diffraction
  • Figure l (b) and l (c) where BaTiO 3 phase is assigned to the crystal structure and crystallinity is confirmed.
  • An overview TEM image ( Figure I (a)) at low magnification shows non-aggregated BaTiO 3 nanocrystals with average diameter 6-10 nm without any presence of larger particles or agglomerates.
  • HRTEM patterns of individual nanocrystals are shown in Figures l (d) and l(e).
  • Figure 2 shows the TEM and XRD characterizations of 3-5 nm BaTiO 3 nanocrystals capped with oleyl acid (case II). Combining the technique of XRD and SAED ( Figures 2(b) and 2(c)), BaTiO 3 phase is assigned to the crystal structure, even though diffraction peaks in the XRD pattern ( Figure 2(c)) are broadened substantially due to the small crystal size and the organic coating. The low angle background is attributed to the small crystal size, extra organic coatings and solvents, and the possible effect of the glass substrate when the XRD experiment was carried out.
  • FIG. 2(a) An overview TEM image (Figure 2(a)) at low magnification shows non-aggregated BaTiO 3 nanocrystals with average diameter 3-5 nm without any presence of larger particles or agglomerates. HRTEM patterns of individual nanocrystals are shown in Figures 2(d) and 2(f). In Figure 2(d), a representative nanocrystal is oriented in its ⁇ 1 1 1> zone axis and the corresponding power spectrum (PS) is shown in Figure 2(e). Although most of the 3-5 nm BaTiO 3 nanocrystals have a single domain, twinning by sharing one of the (1 1 1 ) planes is also observed and one example is shown in Figure 2(f).
  • PS power spectrum
  • nanocrystals are spherical ( Figure 3(b)), but cubic, elliptical, triangular and rod ( Figure 3(c)) shapes are also observed.
  • the sizes of these particles are around 10-12 nm and the size of these nanorods is around 20 nm in length and 6 nm in width.
  • OLOH case IV
  • nanocrystals with a much smaller size (2-3 nm) are found.
  • Figure 6 shows the typical X-ray diffraction (XRD) patterns of the samples prepared in different alcohol or alcohol mixture using barium and titanium isopropoxide as a precursor. All diffraction peaks can be assigned to the BaTiO 3 phase (JCPDS No. 3 I - 174) without any indication of crystalline byproducts such as BaCO 3 or TiO 2 . The measurement indicates the exclusive presence of a perovskite BaTiO 3 phase in high crystallinity and high purity. The broad diffraction peaks suggest small crystalline sizes on the nanometer scale.
  • XRD X-ray diffraction
  • the crystal sizes decrease in the following order of solvents: ethanol, 95% ethanol > mixed ethanol and isopropanol > isopropanol, which is consistent with the TEM observation.
  • the TEM images ( Figure 8) indicate that the samples consist of individual BaTiO 3 nanocrystals with narrow size distribution and no aggregation, except for that prepared in isopropanol, which show irregular in shape and some extent of aggregation of smaller nanocrystals.
  • BaTiO 3 nanocrystals show more regular and uniform when prepared in mixed ethanol and isopropanol (Fig. 8d) than prepared in sole alcohols (Figs. 8a and 8b).
  • Figure 7 shows the XRD patterns of the samples prepared using BaTi ethylhexano-isoproxide as a source.
  • the measurement indicates the presence of the perovskite BaTiO 3 phase in high crystallinity and high purity.
  • Very trace amount of BaC03 could be detected for the samples prepared in ethanol and isopropanol, but could totally vanish when extending the duration time from 48 hrs to 72 hrs.
  • the diffraction peaks appear sharper as compared with those prepared using metal Ba and titanium isopropoxide as a precursor, showing the formation of larger nanocrystals when using BaTi ethylhexano-isoproxide as a source.
  • the crystal size can further increase (up to -100 nm) by increasing the volume ratio of 95% ethanol/BaTi ethylhexano-isoproxide (1 : l -10: l), while small amount of amorphous phase (tiny and irregular phase) may co-exist as well.
  • alkali such as potassium hydroxide (KOH), or tetrapropylammonium hydroxide (TPAOH)
  • KOH potassium hydroxide
  • TPAOH tetrapropylammonium hydroxide
  • the simple solvothermal process of a BaTi metalorganic source in an alcohol solvent is a versatile method for producing highly crystalline and aggregate -free BaTiO 3 nanocrystals with variable sizes and narrow size distribution.
  • the tunable nanocrystal sizes (5-100 nm) can be realized by using different alcohol solvents and BaTi metalorganic sources, which provide tunable rates of alcoholysis process and further nucleation Of BaTiO 3 nanocrystals.
  • the aggregate-free nature Of BaTiO 3 nanocrystals enables easy modification of the crystal surface with a variety of surface capping agents (e.g. oleic acid), surfactants, or polymers.
  • surface capping agents e.g. oleic acid
  • surfactants e.g. oleic acid
  • polymers e.g. polyethylene glycol dimethacrylate (PET n-butyl)
  • oleic acid-coated BaTiO 3 nanocrystals are highly dissolved in non-polar solvents such as hexane and toluene to obtain homogeneous and transparent/semitransparent suspensions (Figure 9).
  • the BaTiO 3 nanocrystals synthesized in 95% ethanol show higher solubility and stability in polar solvents such as ethanol than those synthesized in anhydrous ethanol, probably because of more surface hydroxy 1 groups and enhanced surface polarity for the crystals prepared in trace amount of water.
  • the suspension can be stable for weeks without precipitation. Only a small number of nanoparticles may be precipitated out in a month, but they can be easily re-dispersed to ethanol using a simple sonication process.
  • a substantially homogeneous dispersion of the nanocrystalline form or a substantially homogeneous dispersion of a nanocrystalline form prepared by a disclosed method, in a liquid are provided.
  • the nanocrystals of the dispersed nanocrystalline form can be uncoated and uncapped, or can be capped or coated, as described above.
  • the liquid can comprise a non-polar organic solvent or a polar organic solvent or a mixture thereof.
  • the liquid can comprise water, or a mixture of water with a water-soluble organic solvent.
  • dispersions can be readily formed in non-polar organic solvent such as hexane or toluene, or a mixture thereof.
  • the liquid can be a polar organic solvent such as ethanol or methanol, or a mixture thereof.
  • the dispersion can be substantially physically stable over a period of time under normal gravitation, such that substantial amounts of precipitation of the nanocrystalline form does not occur over a period of time, which can range from about one hour to about six months.
  • the dispersion can also be substantially chemically stable, wherein decomposition of the nanocrystalline form to another chemical entity in the presence of the liquid does not take place to any great extent.
  • a substantially homogeneous dispersion can include additional ingredients.
  • a dispersion can further include a surfactant, a polymer, a liquid crystal forming material, a phospholipid, or a mixture thereof.
  • a dispersion can include a matrix precursor, that is, a material adapted to form a matrix for the nanocrystalline form, such as upon drying or removal of the liquid substance in formation of a film comprising the nanocrystalline form.
  • a matrix can serve to provide physical cohesiveness to such a film, or to alter the properties of the film, or both.
  • a matrix precursor can be an organic matrix precursor adapted for polymerization for formation of an organic matrix, or an inorganic matrix precursor adapted for formation of an inorganic matrix, or a mixed organic/inorganic matrix precursor adapted for formation of an organic/inorganic matrix, or any mixture thereof.
  • an organic matrix is an organic polymer, such as a poly(methyl methacrylate), a polyurethane, or a block organic copolymer.
  • An example of an inorganic matrix is amorphous silica.
  • An example of an organic/inorganic matrix is an amorphous silica modified with oligomeric or polymeric organic domains.
  • an organic/inorganic matrix can be composed of interpenetrating networks of silica and an organic polymer, or can be composed of a block copolymer comprising organic and inorganic domains.
  • the inorganic domain can be amorphous silica.
  • Si wafer Si wafer
  • flexible substrates e.g. plastic
  • coating spin-coating, dip-coating, and cast-coating
  • Uniform, dense and crack-free BaTiO 3 thin films (50-500 nm in thickness) were prepared by multiple spin-coating of the nanocrystal suspension (either hexane suspension of oleic acid capped nanocrystals or ethanol suspension of uncoated nanocrystals).
  • a thermal treatment at 350-400 0 C was applied to remove the surface oleic acid coatings ( Figure 10).
  • the thin films also show high thermal stability.
  • the XRD results show they can be stable up to 500 0 C with no sign of crystal growth, and only at higher temperature (800 0 C) one can see significant crystal merge and growth in the thin films, according to the extent of diffraction peak sharpening during the thermal treatment at various temperatures (Figure 13).
  • the oleic acid-coated BaTiO 3 nanocrystals also enable an easy incorporation with other media (e.g. polymers, liquid crystals, etc.), which is favorable for BaTiO 3 -based nanocomposite thin film processing and can further improve the basic mesogenic properties of nematic liquid crystals (such as higher clearing temperature, larger birefringence and enhanced dielectric response) when doped at low concentration ( ⁇ I wt%).
  • media e.g. polymers, liquid crystals, etc.
  • various embodiments of the disclosed subject matter include methods of forming a film comprising a plurality of metal oxide nanocrystals, the method comprising disposing a dispersion of the nanocrystal line form or a dispersion of a nanocrystalline form prepared by a method of the disclosed subject matter, or disposing the dispersion of the plurality of nanocrystals, or disposing a dispersion prepared by a method of the disclosed subject matter, on a substrate, then, at least partially removing the liquid substance, and the reagent if present, or the liquid from a dispersion therein, to provide the film disposed on the substrate.
  • a matrix precursor can be included in the dispersion of nanocrystals that is disposed on the substrate such that the matrix precursor can be polymerized to provide the film disposed on the substrate upon removal of liquid materials, wherein the film comprises a matrix.
  • the matrix precursor can be organic, inorganic or organic/inorganic, and can be polymerized to provide a respective matrix composed of an organic, inorganic, or organic/inorganic material.
  • the film formed by removal of the liquid substance thus includes the matrix material in which the plurality of nanocrystals is dispersed or embedded.
  • the matrix formed by polymerization of the matrix precursor can add film strength for greater facility of processing.
  • the substrate upon which the dispersion is disposed and upon which the film is formed by removal of the liquid substance can be an electrically insulating, conductive or semi-conductive material.
  • the substrate can be a flat, curved, or irregular surface, which can be composed of a solid material comprising silicon, silicon nitride, silica, diamond, or an organic plastic.
  • the substrate can be a surface that is to be coated by the dispersion, such as human skin.
  • a plurality of zinc oxide nanocrystals optionally including a matrix material such as a cream, can be disposed on human skin to form a sunscreen protective coating.
  • other materials for example metal or glass, can be coated with a protective layer.
  • the dispersion can be disposed on the substrate by a process comprising spin- coating, dip-coating, cast-coating, printing, or spraying, as are well known in the art.
  • the stability of the dispersion including a dispersion of uncapped and uncoated metal oxide nanocrystals, allows the dispersion to be handled over a period of time without greatly changing in solids content through precipitation of significant portions of the dispersed nanocrystalline solid metal oxide.
  • the liquid substance, and reagent if present, or the liquid if a dispersion therein is used, can be removed from the dispersion, for example by volatilization, leaving the film as a residue upon the substrate surface.
  • liquid materials can be removed at least in part by evaporation or volatilization, or evaporation under a vacuum, or through the application of heat, or any combination thereof.
  • the film can be further processed in substantially dry form on a suitably adapted substrate by heating or sintering the film at any suitable temperature.
  • sintering can be carried out at up to 600 0 C, although lower temperatures can also be used.
  • the substrate is adapted to be stable at a sintering temperature selected.
  • the film comprises, for example, a plurality of uncapped and uncoated nanocrystals, lacking a matrix precursor, or with a matrix precursor that forms a heat-stable inorganic material such as silica
  • a film substantially free of organic material can be obtained without any need to resort to high sintering temperatures to remove organic residues.
  • Organic residues can be undesirable; the residues can, for example, degrade electrical properties of the film.
  • the film can also be substantially free of voids.
  • the nanocrystals can be in direct contact with each other such that a continuous film is obtained and, when a matrix is present, the matrix can also serve to make the film continuous and substantially lacking in voids and defects.
  • the film can be adapted to have a particular proportion of voids; for example the film can be adapted to have 10% voids, or 20% voids. The relative proportion of the voids to the film can be controlled or tuned.
  • the film can have a thickness of about 10 nm to about 1 millimeter.
  • the film can be formed of substantially a single layer of nanocrystals, or can include many layers of nanocrystals in the thickness dimension.
  • the film can be of substantially any length and breadth, depending on the dimensions of the substrate on which it is disposed.
  • the film can have a high dielectric constant or dielectric strength.
  • a high dielectric constant or strength can be a dielectric constant greater than ten.
  • the film can have a dielectric constant of about 80 to about 750.
  • the film of the disclosed subject matter can be composed of a single composition of nanocrystalline form, which can be embedded or disposed in a matrix material, or which can not include a matrix material.
  • An example of a single type of nanocrystalline form is barium titanate.
  • the film can include only the nanocrystalline form having a single component wherein substantially all the nanocrystals are of approximately the same dimension, having a narrow size distribution, or a monodisperse size distribution.
  • the film can include nanocrystals of a single chemical composition, for example barium titanate, but include a mixture of different sizes of the nanocrystals, for example a mixture of barium titanate nanocrystals of two different size profiles, for example a 3-5 nm set and a 10-20 nm set.
  • the film can include more than one type of nanocrystal including a single type of metal oxide, but wherein some nanocrystals are uncapped and uncoated and others in the same film are capped or coated.
  • An example is a film composed of barium titanate and silica, which can be prepared from a dispersion of barium titanate and a matrix precursor including a tetralkylorthosilicate.
  • the liquid can be ethanol, such as 95% aqueous ethanol (azeotrope ethanol).
  • the film can include nanocrystals having compositions including different chemical compositions.
  • a film can include barium titanate crystals, and lead titanate crystals.
  • the film can further include a block co-polymer, such as a block polyethylene- polypropylene or a block copolymer surfactant such as a Pluronic® surfactant, or triblock copolymer surfactant such as Pi 23 of the Pluronic family.
  • a block co-polymer such as a block polyethylene- polypropylene or a block copolymer surfactant such as a Pluronic® surfactant, or triblock copolymer surfactant such as Pi 23 of the Pluronic family.
  • the film can further include an organic component used in generation of a mesoporous material.
  • a mesoporous material is a micro-structured material that can be prepared by hydrolysis and condensation of tetraethyl orthosilicate templated by supermolecular arrays of surfactant (micellar rods). After the organic- inorganic composites are formed, the organic templates can be removed by thermal treatment or solvent extracting, leaving behind an inorganic matrix with ordered pores and channels corresponding to the original surfactant supermolecular templates.
  • the organic compound used in generation of a mesoporous material can include MCM-41 , MCM-48, which are products originally developed by researchers from former Mobil Company, and SBA -15, or SBA- 16, products developed by researchers from University of California Santa Barbara, as are well known in the art.
  • Such films can also be deposited on substrates, which can be flat, curved, or irregular, and can be formed of materials that include silicon, silicon nitride, silica, diamond, or an organic plastic.
  • the film comprising a particular type or types of the nanocrystalline form can substantially retain properties of the respective type of nanocrystalline form, that is, formation of a film or coating of the nanocrystalline form does not eliminate or substantially alter the unique properties that can result from the material being in the nanocrystalline form, as opposed to a standard bulk form not including nanocrystals.
  • An example is electrical properties such as dielectric constant.
  • Other properties of the nanocrystalline form that can be substantially retained by a film formed of the nanocrystals include density properties, spectral properties such as absorption maxima, extinction coefficients, reflectivity parameters, luminescence, or any combination thereof.
  • the film can substantially retain hardness properties or scratch resistance properties of the nanocrystalline form, or can retain thermal properties of the nanocrystalline form
  • the film can include a nanocrystalline form wherein the nanocrystals are uncapped and uncoated, enabling the formation of organic contaminant free films. The absence of the organic contaminants can serve to preserve the properties of the nanocrystalline form in the film.
  • a coating layer can be formed including the nanocrystalline form disclosed and claimed herein, or a nanocrystalline form prepared by a method disclosed and claimed herein.
  • a coating layer can be formed using the dispersion disclosed and claimed herein, or a dispersion prepared by a method disclosed and claimed herein.
  • a coating layer can include an embodiment of the nanocrystalline form of zinc oxide, titanium oxide, or zirconium oxide.
  • a coating layer can further include a monomer adapted for polymerization, or a polymer, or both.
  • a coating layer as disclosed and claimed herein can be adapted for application to human skin.
  • the nanocrystalline form can include zinc oxide
  • the coating layer can include a cream or oil in which the nanocrystalline form is dispersed, that can be applied to human skin to prevent sunburn.
  • the coating layer can be adapted for application to a metal, plastic, or glass surface.
  • the coating layer can include titanium oxide and be adapted for application to a glass surface to alter the transmission or reflection properties of the glass, or to provide a solar self- cleaning glass surface, or both.
  • the coating layer can include a suitable organic, inorganic, or organic/inorganic matrix adapted to provide adhesion to the surface.
  • a metal surface such as an automobile body can be covered with the coating layer as disclosed and claimed herein, wherein a nanocrystalline form of titanium or zirconium oxide is dispersed in an organic polymer adapted to adhere to a metal surface, to provide an automobile paint.
  • nanoparticles may be used in various electronic and/or electro-optic apparatus.
  • Such nanoparticles may include metal oxide nanoparticles having high k dielectric constants, that is, having dielectric constants often or greater.
  • a mechanically and thermally stable thin film of such metal oxide nanoparticles between 10-1000 nm in thickness (or thicker) can be generated on substrates.
  • a film of metal oxide nanoparticles may be referred to as a high k film, that is, a film have a high dielectric constant k.
  • a high dielectric constant can be a dielectric constant greater than about 10. In various embodiments, the film can have a dielectric constant of about 80 to about 750.
  • the high k film may include one or more types of nanoparticles.
  • the nanoparticles in the high k film may be amorphous nanoparticles, crystalline nanoparticles, or a combination of amorphous nanoparticles and crystalline nanoparticles.
  • the nanoparticles may be capped or uncapped.
  • the substrates, on which the high k film may be disposed may include Si, SiO 2 , SiN, silicon- on-insulator, or other wafer known to the semiconductor industry.
  • ultracapacitors offer very high charge densities and short charge/discharge times, plus a very high capacity for recharge without degradation.
  • ultracapacitors make use of very thin films, which can be on the order of nanometers, of high k materials, such as films prepared from the nanocrystalline forms herein.
  • the effective thickness of the "dielectric" of an ultracapacitor is exceedingly thin — on the order of nanometers — and that, combined with the very large surface area, is responsible for their extraordinarily high capacitances in practical sizes.
  • the nanoparticles of the high k film include a metal oxide of one of the many specified compositions stated previously in this disclosure.
  • the various metal oxide compositions for inclusion in the high k film may include binary metal oxides such as, but are not limited to, titanium oxide (TiO 2 ), zirconium oxide (ZrO 2 ), hafnium oxide (HfO 2 ), vanadium oxide (V 2 O 3 ), niobium oxide (Nb 2 Os), tantalum oxide (Ta 2 O 5 ) , tungsten oxide (WO x ), manganese oxide (Mn 3 O 4 ), iron oxide (Fe 3 O 4 ), cobalt oxide (CoO), nickel oxide (NiO), copper oxide (CuO), zinc oxide (ZnO), (cobalt, manganese)- doped zinc oxide, gallium oxide (Ga 2 O 3 ), indium oxide (In 2 O 3 ), tin oxide (SnO 2 ), ceria (CeO 2 ), and combinations thereof.
  • the various metal oxide compositions for inclusion in the high k film may include perovskite ABO 3 structures such as, but are not limited to, barium titanate (BaTiO 3 ), strontium titanate (SrTiO 3 ), calcium titanate (CaTiO 3 ), barium strontium titanate ((Ba 5 Sr)TiO 3 ), barium lanthanum titanate ((Ba ⁇ .
  • perovskite ABO 3 structures such as, but are not limited to, barium titanate (BaTiO 3 ), strontium titanate (SrTiO 3 ), calcium titanate (CaTiO 3 ), barium strontium titanate ((Ba 5 Sr)TiO 3 ), barium lanthanum titanate ((Ba ⁇ .
  • lithium lanthanum titanate (LiLaTiO 3 ), lead titanate (PbTiO 3 ), lead zirconium titanate (Pb(Zr 5 Ti)O 3 ), barium zirconate (BaZrO 3 ), lead zirconate (PbZrO 3 ), yttrium ferrite (YFeO 3 ), bismuth ferrite (BiFeO 3 ), yttrium barium copper oxide (YBCO), lanthanum manganese oxide (LaMnO 3 ), strontium cerium oxide (SrCeO 3 ), rare earth cobalt oxide (RECoO 3 ), and combinations thereof.
  • the various metal oxide compositions for inclusion in the high k film may include other complex metal oxides such as, but are not limited to, indium tin oxide (ITO), lithium niobium oxide (LiNbO 3 ), garnet such as Bi 3 Fe 5 Oi 2 , Y 3 Fe 5 Oi 2 , and combinations thereof.
  • ITO indium tin oxide
  • LiNbO 3 lithium niobium oxide
  • garnet such as Bi 3 Fe 5 Oi 2 , Y 3 Fe 5 Oi 2 , and combinations thereof.
  • the metal oxides may be synthesized as metal oxide nanocrystals using a solvothermal approach.
  • a synthesis approach is based on the solvothermal reaction of a metal oxide precursor (such as metal alkoxides or metal acetylacetonates, or metal acetates) with an alcohol (ethanol, isopropanol, or oleyl alcohol), or the alcohol mixture (e.g. ethanol and isopropanol) or the alcohol with controlled amount of water (0-20 wt% water, e.g. 95% ethanol, azeotropic liquids) at a relatively low temperature (80-230 0 C).
  • a metal oxide precursor such as metal alkoxides or metal acetylacetonates, or metal acetates
  • alcohol ethanol, isopropanol, or oleyl alcohol
  • the alcohol mixture e.g. ethanol and isopropanol
  • controlled amount of water e.g. 95% ethanol, azeotropic
  • suspensions are used where the suspension may be integrated into mixtures containing other components such as organic or inorganic materials.
  • Such suspensions are comparable to solutions, in which the nanoparticle colloid is dispersed into the liquid such that it is similar in properties to a solution. Solutions are stable for prolonged periods of time without change.
  • Processing temperature for generating the oxide nanoparticles may be relatively low, typically less than 250° C. Such processes may produce partially crystallized or amorphous materials that require further thermal treatment, which may lead to a loss of surface coating, aggregation, or precipitation from solution.
  • the metal oxide nanoparticles are initially in the form of a suspension. For example, in a single processing step in ethanol under elevated pressure and temperature may be performed that results in virtually 100% crystalline barium titanate with high purity.
  • the metal oxide nanoparticle suspension may be mixed with another suspension to create a mixture.
  • the second suspension contains a precursor that will allow the generation of a matrix, which may be referred to as a matrix precursor suspension.
  • the matrix precursor suspension may be a precursor for the generation of a matrix composed of one or more of several materials.
  • it may be organic (e.g. a polymer, such as PMMA or block copolymer) or inorganic (e.g. another metal oxide or SiO 2 ) or an organic-inorganic framework containing both block copolymer and SiO?.
  • the mixture of the nanoparticle oxide suspension and the matrix precursor suspensions can be applied onto a substrate in order to create a wet film that can be dried and or thermally processed to create a thin film. Such a process may be broadly referred to as a chemical deposition.
  • the thin film may be patterned and processed using conventional semiconductor processing techniques to form the thin film as a component of an electric device in an integrated circuit.
  • the nanoparticles may be capped with ligands or not capped.
  • the choice of capping or not capping can affect the solvent conditions that may be used in the processing.
  • a suspension mixture that utlilizes non-polar solvents is associated with nanoparticles and non-polar capping groups.
  • An example of an idealized mixture may include BaTiO 3 nanoparticles suspended in ethanol with no ligand capping to be mixed with tetra-ethyl-ortho-silicate, or equivalently tetra-ethoxy-silane, (TEOS), a silica precursor such as, Si(OCH 2 CH 3 ) 4 , also in ethanol.
  • An example of an idealized mixture may include BaTiO 3 nanoparticles suspended in ethanol with no ligand capping to be mixed with TEOS and a block co-polymer, such as block polyethylene- polypropylene (Pluronic surfactant e.g. Pi 23 ), a silica precursor (Si(OCH 2 CH 3 ) 4 ) also in ethanol.
  • An example of an idealized mixture may include BaTiO 3 nanoparticles suspended in ethanol with no ligand capping to be mixed with a silica precursor and organic component used in the generation of a mesoporous material, such as MCM-41 , MCM-48, SBA -15, SBA- 16, etc.
  • identical solvent suspension compatibility can generate a homogeneous mixture suitable for chemical deposition.
  • BaTiO 3 nanocrystal synthesis may be conducted using a one-pot solvothermal approach based on the reaction between a barium titanium metalorganic source and an alcohol at a relatively low temperature of 180-230 0 C and a self-generated pressure of 20-30 atm depending on the alcohols used and the reaction temperature.
  • a BaTiO 3 bimetallorganic precursor may include barium titanium ethylhexano-isoproxide, a commercially available product, or can be prepared by dissolving metal Ba or metal oxide BaO with alcohol (ethanol, isopropanol, benzyl alcohol, oleyl alcohol or their mixture) following by mixing with equimolar quantity of titanium isopropoxides.
  • Simple alcohol such as ethanol or isopropanol or their mixture may be used as a solvent.
  • Addition of controlled amount of water (0-20 wt%) or alkaline (e.g. KOH) to the system can tune the rate of alcoholysis process, thus offering further controls over crystal size and dispersion in polar solvents.
  • the process enables the production of uniform and highly crystallized BaTiO 3 nanocrystals with high yields (> 90%) and tunable sizes ranging from about 4 to 100 nm, depending on the barium titanium source, type of alcohol and the amount of water and alkaline in the system.
  • the process can be scaled up to kilograms of production using a commercially available pressure reactor.
  • the surface of intrinsically aggregate-free BaTiO 3 nanocrystals can be coated and functional ized with a variety of surface capping agents (e.g. oleic acid), surfactants, polymers or phospholipids, using a post-treatment process.
  • Such BaTiO 3 nanocrystals retain good solubility and stability in either non-polar solvents (such as hexane, toluene) or polar solvents (such as ethanol, methanol).
  • the stable and homogeneous nanocrystal suspension enables easy incorporation Of BaTiO 3 nanocrystals to other media (e.g. polymers, liquid crystals), which is favorable for either pure BaTiO 3 nanocrystal thin film processing or BaTiO 3 -based nanocomposite thin film processing on both solid substrates (e.g. Si wafer) or flexible substrates (e.g. plastic) using a variety of available methods including coating (spin-coating, dip-coating, and cast-coating), printing or spraying techniques. Pure BaTiO 3 nanocrystal thin films are stable up to 500 0 C with no sign of crystal merging and growth.
  • media e.g. polymers, liquid crystals
  • BaTiO 3 nanocrystal thin films with a variable thickness ranging from 20 nm to l ⁇ m may be used in various applications.
  • BaTiO 3 nanocrystal thin films may be used as a ferroelectric component, a high dielectric constant, or high dielectric strength component of devices such as in capacitors, ultracapacitors, field-effect transistors, displays and other electronic devices.
  • nanoparticle based films may be implemented in various memory devices such as, but not limited to, non-volatile memory, volatile memory, FRAM, electrically erasable programmable read-only memory (EEPROM), and flash memory.
  • Applications may include implementation in display devices, magnetic devices, giant magnetoresi stance (GMR) devices including magnetoresistive random access memory (MRAM), magnetooptical devices, magnetooptical switching devices, electro-optic switching devices, waveguides, sensors, superconductors, membranes, and transparent conducting films.
  • GMR giant magnetoresi stance
  • MRAM magnetoresistive random access memory
  • magnetooptical devices magnetooptical switching devices
  • electro-optic switching devices waveguides, sensors, superconductors, membranes, and transparent conducting films.
  • Applications may include devices, whose operation is based on properties of a material, for which an input such as electrical or magnetic fields, stress, heat or light yields an output such as charge, current, magnetization, strain, temperature or light as a consequence of a material property intrinsic to the structure of the material.
  • properties include permittivity, permeability, elastic constant, specific heat, refractive index, piezoelectricity, the electro- calorific or magneto-calorific effects, the electro-optic or magneto-optic effect, the photoelastic effect, the pyroelectric effect, the photovoltaic effect, the piezomagnetic effect, thermal expansion, photostriction, superconductivity, the Faraday or Kerr effect.
  • Applications may include implementations in catalysis or in a biological application.
  • nanoparticles may be implemented for an application based on a material device, for a material device based on a property of the material, for a material device based on a property of the material related to the structure of the material, for applications related to processing of a material to provide a desired structure of the material in a device, and for applications to process a material based on the ability to prepare the material from nanosized particles.
  • the family of complex oxide pervoskites possessing the ferroelectric property may be used in transducers and actuators (piezoelectric effect), high-K dielectric capacitors, and memory applications (microelectronics) that may rely on the hysteresis between two stable states of polarization.
  • the investigation of micron to nanoscale ferroelectric materials has prompted a desire for a deeper understanding of how size effects polarization and ferroelectric order and the hypothesized importance of size effects in bulk ferroelectric systems. Contrasting views of the effect of sample size on ferroelectricity can be considered from experimental and theoretical points of view.
  • First principles density-functional theory (DFT) provides a microscopic understanding of ferroelectrics. Theory can be used to calculate the relative stability of competing phases. A new understanding of the theory of bulk polarization along with new levels of theory may provide models for further materials based research.
  • Ferroelectricity the existence of a remnant polarization, is a collective phenomenon influenced by surface and size effects. It is assumed that the macroscopic polarization, P, in the presence of applied electric field, E, is proportional to the displacement x of a set of ions from their position midway along some double well potential. The displacement gives rise to dipoles within the material, which can align to form domains with (P+, P-) or at some angle to the field.
  • the Helmholz free energy, F can be expanded in a power series in the macroscopic order parameter for the polarization, P(T):
  • T C can mark the transition between order and disorder in a ferroelectric material, corresponding to the transition between the ferroelectric and paraelectric phase respectively.
  • Nanocrystals are isolated three dimensional nanometer scale units of materials, typically with symmetrical spherical or geometrical morphology and optimally, a well-formed crystalline core.
  • the concepts of surface capping and solution stabilization have been developed to allow suspensions of nanoparticles to exist as solutions in a variety of aqueous and non-aqueous (organic solvent) media. The field can be aided greatly by the improved understanding of size-dependent scaling laws, which have emerged from fundamental studies in chemical physics and condensed matter physics.
  • a wide variety of approaches for the preparation Of BaTiO 3 nanocrystals, nanowires and nanotubes can be used, including pyrolysis of organometallic precursors, hydrothermal/solvothermal synthesis, coprecipitation and sol-gel processing.
  • the solution-phase decomposition of bimetallic alkoxide precursors in the presence of coordinating ligands can yield well-isolated and single-crystalline BaTiO 3 nanocrystals and nanowires.
  • a synthetic strategy for preparing nano-structured complex oxides that retain ferroelectricity may be applicable to multiple roles in nanoelectronics.
  • a sol-gel processing of bimetallic alkoxide precursor in presence of coordinating ligands such as oleic acid can yield uniform and well-isolated BaTiO 3 nanocrystals.
  • monodispersed transition oxide nanocrystals can be synthesized by direct thermal decomposition of metal acetate in the presence of oleic acid at high temperature.
  • a coordinating agent e.g. oleic acid
  • a versatile synthetic procedure can involve the nucleation-controlled thermal decomposition of barium titanium molecular precursor in presence of oleic acid followed by further crystallization at higher temperature. With the control over the nucleation process and with the crystal surface capped with oleic acid, the resulting barium titanium oxide nanoparticles can be re-dispersed in hexane.
  • Uniform BaTiO 3 nanocrystals may be produced in the form of isolated nanocrystals, continuous and micropatterned thin films by spin-coating or soft lithography (microprinting or micromolding).
  • a high temperature hexagonal BaTiO 3 phase (which exists at 146O 0 C) may be present at room temperature, probably due to cubic/tetragonal symmetries on nanometer scale.
  • This versatile method may enhance the fundamental understanding of size-dependent evolution of ferroelectricity on individual nanocrystals and nanocrystal thin films and provided enhanced flexibility in integrating ferroelectric BaTiO 3 and other types of nanocrystals
  • the film can be paraelectric.
  • the ferroelectricity is not always necessary for materials as long as they have high k dielectric constant.
  • the ferroelectricity is undesirable, for example, high k gate dielectrics for transistor application. Accordingly, the film can be paraelectric but not ferroelectric.
  • Nano-structured thin films of barium titanate can be built from uniform nanoparticles.
  • the nanoparticles can be prepared by a chemical processing, based on thermal decomposition of a bimetallic barium titanium molecular precursor in the presence of oleic acid (a capping group), followed by high-temperature crystallization of this nucleation-controlled intermediate.
  • oleic acid a capping group
  • Such a method offers a versatile way of preparing uniform and monodisperse BaTiO 3 nanocrystals, which can be used as a basis for micropatterned or continuous BaTiO 3 nanocrystal thin films.
  • BaTiO 3 nanocrystals can crystallize with evidence of tetragonal ity.
  • Well-isolated BaTiO 3 nanocrystals smaller than 10 nm, can be prepared with control over aggregation and crystal densities on various substrates such as Si, Si/SiO 2 , Si 3 N 4 /Si, Pt-coated Si substrates and other substrates.
  • BaTiO 3 nanocrystal thin films may be formed with a uniform nanocrystal line grain texture. Electric field dependent polarization measurements show spontaneous polarization and hysteresis, indicating ferroelectric behavior for the BaTiO 3 nanocrystalline films with grain sizes in the range 10-30 nm. Dielectric measurements of the films show dielectric constants in the range 85-90 over the 1 KHz to 100 KHz, with low loss.
  • preparation of a bimetallic barium titanium molecular precursor may include preparing barium titanium glycolate, BTG, (BaTi(C 2 H 4 O 2 ) ⁇ C 2 H 6 O 2 H 2 O).
  • BTG barium titanium glycolate
  • BaTiO 3 nanocrystal synthesis a single bimetallic molecular precursor may be used to ensure a correct stoichiometry of the product.
  • BTG may be first prepared in dry box by mixing BaO, ethylene glycol, 2-propanol and Ti(OPr) 4 . The resulting white powder can be filtered, washed, dried at 6O 0 C and maintained in dry box because of its hygroscopic property.
  • the BTG can be thermally decomposed in presence of oleic acid
  • Thermogravimetric (TG) analysis of BTG (BaTi(C 2 H 4 O 2 MC 2 H 6 O 2 H 2 O) is known to show three weight loss rate maxima at 67 0 C, 12O 0 C, and 36O 0 C, which correspond to the loss of single water molecule, four physically bonded ethylene glycol molecules, and three chemically bonded ethylene glycol molecules in a single BTG molecule, respectively.
  • a thermal decomposition temperature of 36O 0 C can be used, at which three chemically bonded glycoalite ligands can be converted to oxide ligands in which barium titanium oxide starts to form.
  • Oleic acid (OA) can be used as a coordinating agent to mediate the nucleation process.
  • High boiling point solvent trioctylamine (TOA) (bp: 365-367 0 C) can be used as a solvent to achieve such a high temperature.
  • BTG powder 500 mg can be first mixed with OA ( 1 ml) and TOA (12 ml) in a four-neck vessel.
  • the BTG can be heating at 100 0 C in N 2 until the BTG totally dissolves and a light yellowish clear solution is formed.
  • the clear solution can be heated gradually in vacuum at 12O 0 C, 200 0 C and 25O 0 C to remove released ethylene glycol.
  • the solution can be heated at 350-360° C in a N 2 atmosphere for 2 h in the presence of oleic acid and trioctylamine until the solution turns to deep brown color.
  • the barium titanium oxide nanoparticles can be separated by adding ethanol followed by centrifugation and washed by repeated precipitation/re-dispersion with ethanol.
  • the resulting yellowish precipitate with OA coating can be re-dispersed in hexane with original concentration of- 20 mg/ml and a clear orange solution can be obtained for further applications.
  • X-ray diffraction measurement may show that the resulting yellowish precipitate may have an amorphous phase and not crystallized under the previous thermal treatment. In such a case, further high temperature treatment (600° C) can be used to bring the nanoparticles into full crystallization.
  • BaTiO 3 individual nanocrystals and thin films can be formed on different substrates.
  • four different substrate include n-Si wafers with a native oxide layer, p-Si wafers with a SiO 2 layer (400 nm), p-Si wafers with a Si 3 N 4 layer, and Pt(100nm)/Si ⁇ 2 (500 nm)/Si wafers.
  • a clear hexane solution barium titanium oxide nanoparticles diluted by 1 :4 can be micro- printed or micro-molded on the substrates using a polydimethylsiloxane elastomer (PDMS) stamp.
  • PDMS polydimethylsiloxane elastomer
  • a dilute hexane solution can be spin-coated on substrates using a high spin rate (4000 rpm).
  • the original barium titanium oxide nanoparticle solution can be diluted with hexane or with triblock copolymer Pluronic P 123 (EO70PO20EO70) (1 :2-1 : 16 by volume).
  • the original BaTi oxide solution can be spin-coated on substrates with a low spin-rate (1000-2000 rpm).
  • As-prepared thin films can be subjected to 600 0 C calcination in static air to achieve full crystallization.
  • each coating can be dried at 300 0 C before putting down next coating, where the multi-coated thin films can be eventually treated at 600 0 C for 1 hour until fully crystallized.
  • Thin films Of BaTiO 3 individual nanocrystals can be contacted with metal electrodes or electrodes of other conductive materials to form electrical structures in devices and to form test samples of the thin films.
  • a top platinum (Pt) electrode can be deposited by a vapor deposition system, such as a VEECO vapor deposition system with a four-position electron gun.
  • the thin film samples may be maintained at room temperature while the Pt metal is heated by an electron beam to its melting temperature.
  • the Pt vapor can be deposited through an aperture mask onto the thin film samples for 5 to 10 minutes in order to produce electrodes around 800 to 1000 Angstroms thick.
  • the deposition can be carried out under vacuum down to 10 "6 Torr.
  • metals or conductive materials may be applied to thin films Of BaTiO 3 individual nanocrystals to form conductive contact to the thin films using a variety of techniques, such as but not limited to, chemical vapor deposition, thermal evaporation, sputtering, atomic layer deposition, and combinations of various deposition techniques.
  • the BaTiO 3 nanocrystal thin films can be characterized also with scanning electron microscopy (SEM, Hitachi 4700 Hitachi 4700 Field Emission SEM) and atomic force microscopy (AFM, Nanoscope UIa, Digital Instruments).
  • SEM scanning electron microscopy
  • AFM atomic force microscopy
  • BaTiO 3 nanocrystals can be deposited onto a Si substrate and excited with the 488 nm line of an argon-ion laser focused to 2 ⁇ m.
  • Unpolarized Raman scattered light can be collected in backscattering from ⁇ 200 to 1200 cm “1 , with resolution better than 1 cm "1 .
  • top Pt electrodes 0.1 mm in diameter and 50 nm in thickness can be evaporated on top of the films through a shadow mask by electron beam evaporation.
  • Electric field - polarization hysteresis can be measured, for example, using a Radiant Precision Workstation.
  • Frequency dependence of the capacitance and dielectric loss can be measured by a HP4194A Impedance Gain/Phase Analyzer in the low frequency region of 1 KHz to 100 KHz.
  • the XRD patterns show that after 600 0 C treatment, all diffraction peaks can be assigned to BaTiO 3 phase without any indication of other crystalline by-products such as barium carbonate or titanium dioxide.
  • the diffraction peaks are broad, indicating the formation of nanocrystals.
  • the average crystal size can also be calculated as 13.4 nm in average from Debye-Scherrer equation by taking account of the peak broadening at (1 1 1 ) diffraction line (no peak splitting due to symmetry change).
  • the lattice parameter can be estimated to be 4.014 A from the diffraction peaks at (100) and (200) and the ratio of c/a can be estimated to be 1.0032 from the average ratio of diffraction peak ( 1 1 1) vs diffraction peaks at (100), (1 10) and (200), respectively.
  • a high- temperature hexagonal phase can be attributed to a locally stacked hexagonal sequence in cubic-tetragonal crystallites, as a result of nano-sized twins in the cubic-tetragonal matrix.
  • the presence of hexagonal symmetry here can be attributed to the coexistence of cubic/tetragonal phases at nanometer scale.
  • the tetragonal ity in BaTiO 3 nanocrystals together with the presence of the hexagonal symmetry can also be confirmed with a Raman scattering measurement.
  • Raman scattering spectra are more sensitive to short-range ordering structure.
  • the Raman spectra show a small shoulder peak at around 307 cm "1 and a very broad peak at - 710 cm “1 at room temperature, which are characteristic of structural tetragonality (4mm symmetry).
  • temperature-dependent Raman spectra show these two peaks still persist when temperature is raised above a Curie temperature (ferroelectric-paraelectric transition temperature recorded around 125 0 C for bulk BaTiO 3 ), indicating no distinct phase transition for BaTiO 3 on such a small nanometer range.
  • BaTiO 3 thin films may be prepared from nanocrystals.
  • Soft-lithography techniques including micromolding in capillaries (MIMIC) and microcontact printing using PDMS stamps can be successfully applied to pattern a variety of materials (e.g. organic molecules, polymers, proteins, nanoparticles, colloids and metals).
  • BaTiO 3 nanocrystals are micro-patterned using micromolding of a barium titanium oxide nanoparticle solution followed by 600° C crystallization.
  • Figure 14a shows a BaTiO 3 thin film with a micro-pattern, which further shows that the pattern is made Of BaTiO 3 nanocrystals.
  • a variety of patterns can be obtained by choosing PDMS molds with appropriate micropatterns.
  • continuous BaTiO 3 thin films can be prepared by spin-coating of original concentration of the barium titanium oxide nanoparticle solution with relative slow spin rates (1200-2000 rpm) followed by 600 0 C crystallization. Uniform thin films can be obtained with their colors depending on the film thickness.
  • the high-resolution SEM image shows the thin film is composed of uniform BaTiO 3 nanocrystals whose grain size is about 10 nm and visible inter-crystal voids as well, which probably arise form the loss of organic species during the thermal treatment for crystallization.
  • a typical film may contain 10% to 15% porosity. There are a few sporadic larger nanocrystals (-25 nm, less than 1 %) among the small nanocrystals.
  • the crystal size is in good agreement with TEM observation on the powder samples.
  • the tapping-mode AFM image in Figure 14c also confirms the uniformity of the BaTiO 3 nanocrystals in the thin film.
  • the uniformity of the nanocrystals also depends on the substrate used. Experiments show that BaTiO 3 nanocrystals are uniform when dispersed on Si substrates, while they become less uniform on Pt-coated Si substrates.
  • a 100 nm thick Pt coated Si wafer with 500 nm thick SiO 2 layer [Pt(I OO nm)/SiO 2 (500 nm)/Si] can be used as a substrate, where the Pt coating can be used as a bottom electrode and e-beam evaporated Pt dots on top Of BaTiO 3 thin films through a shadow mask can be used as top electrodes.
  • the BaTiO 3 single coating may be full of inter- crystal voids
  • triple or four coatings may be applied on the Pt(IOO nm)/SiO 2 (500 nm)/Si substrates to make the film thicker and denser, so that it can reduce possible electrical shortcut created on the evaporation of top Pt electrodes. Smaller electrode area may be used.
  • the multi-coatings usually afford less uniform nanocrystals and larger crystal size distribution (for instance, the average grain size is around 10-15 nm for triple coatings, and 20-30 nm for four coatings.) Although the less uniformity over micron scale, the low SEM magnification and the optical microscopy show that the BaTiO 3 film is still quite uniform over a macroscopic range except for very few sporadic structural pinholes on the film surface.
  • Representative polarization-electric field hysteresis curves of the BaTiO 3 thin films show obvious hysteresis loops when sweeping the electric field across the films.
  • the film is stable up to an electric field of 700 kV/cm (couples of cycles) and starts to break down when driving the electric field higher than 800 kV/cm.
  • the leaky behavior is believed to originate from the small inter-crystal voids inside the film.
  • the BaTiO 3 thin film becomes thicker and denser after four coatings ( ⁇ 108 nm in thickness, 20-30 nm in grain size), and it shows constant ferroelectric hysteresis loop and can be stable up to an electric field of 900 kV/cm without any sign of breakdown.
  • the remnant polarization value P r and the coercive field value E c of the BaTiO 3 film with four coatings are around I ⁇ C/cm 2 and 90 kV/cm, respectively, compared to the reported single crystal value (P 1 .
  • the shape of the hysteresis loops of the BaTiO 3 films does not show much change after 85O 0 C treatment for 1 h, indicating that ferroelectricity of the tetragonal BaTiO 3 nanocrystals evolves at temperature as low as 600° C.
  • Figure 15 shows dielectric constant and dielectric loss over the frequency range of 1 KHz to 100 KHz for the BaTiO 3 thin film (four coatings).
  • the typical dielectric constant of the thin film is around 85 to 90 with the dielectric loss around 0.03 or below in the whole frequency range. This value is significantly lower than the reported bulk BaTiO 3 ceramics value (1500 at 1 kHz). However it is relatively high when compared to other reported values, taking into consideration (a) -15% porosity in the film and (b) the nanoscale grain size.
  • the dielectric constant increases very slightly while the dielectric loss remains very low (0.03 to 0.04) in the whole frequency region.
  • the dielectric constant is highly anisotropic, due to the fact that the displaced atoms are tightly bound by the ferroelectric displacement along the polar axis (c-axis), while they are relatively free to vibrate in the perpendicular direction. This is not the case for nanocrystalline thin films in which the nanocrystallites are randomly oriented and thus an averaged value of the dielectric constant over the crystallographic axes is predicted.
  • a nucleation-mediated barium titanium oxide intermediate method involving the thermal decomposition of barium titanium organometallic precursors in presence of capping agent oleic acid affords uniform BaTiO 3 nanocrystals after 600 0 C calcinations.
  • This method offers a versatile means of preparing well-isolated, patterned or continuous thin films Of BaTiO 3 nanocrystals on various substrates, and can be easily incorporated with current micro- and nanofabrication processes.
  • the BaTiO 3 nanocrystals are crystallized with some degree of tetragonal ity, which is the source of the ferroelectricity found in such small size range.
  • Electric field dependent polarization measurements show spontaneous polarization and hysteresis, indicating ferroelectric behavior for the BaTiO 3 nanocrystalline films with grain sizes in the range 10-30 nm.
  • Dielectric measurements of the films show dielectric constants in the range 85-90 over the 1 KHz to 100 KHz, with low loss, which may provide enhanced performance in use in thin film capacitance applications or other electronic device applications.
  • a bimetallic precursor solution is prepared by dissolving 1 mmol metallicbarium (99.99% ESPI) in 10 mL anhydrous benzyl alcohol C 6 H 5 CH 2 OH (99.8% Aldrich) in a glovebox at 80°C with stirring until a slightly yellow transparent solution is formed. Then, the transparent solution is cooled down to room temperature and an equimolar quantity of titanium (IV) isopropoxide Ti[OCH(CH 3 ) 2 ] 4 (99.999% Aldrich) is added and mixed at 30-50°C until a white precipitate is formed.
  • the white precipitate (amorphous) is used as the bimetallic precursor in solution without further treatment.
  • the bimetallic precursor solution is then transferred with a syringe out of the glove box and injected immediately through a septum into a preheated (320 °C) solvent/ligand mixture.
  • the solvent/ligand mixture had been preheated to 320°C with stirring under dry nitrogen flow and at ambient pressure.
  • the temperature drops to around 220°C with the boiling of low boiling point benzyl alcohol, which is carried away gradually by the nitrogen flow.
  • the mixture of the white precursor solution, hot oleylamine and carboxylic acid turns from cloudy (right after injection) into a transparent, slightly yellow solution. This is attributed to the high solubility of the precursor in the solvent/ligand mixture.
  • the benzyl alcohol is removed under the N 2 flow, and the temperature of the system achieves its final resting temperature of 320 0 C. This temperature is maintained for 24 hrs to prepare decanoic acid capped 6-10 nm BaTiO 3 nanocrystals;
  • the bimetallic precursor solution is prepared by dissolving 1 mmol metallic barium (99.99% ESPI) in 10 mL anhydrous benzyl alcohol (C 6 H 5 CH 2 OH, 99.8% Aldrich) in a glovebox at 80°C with stirring until a slightly yellow transparent solution is formed. Then, the transparent solution is cooled down to room temperature and an equimolar quantity of titanium (IV) isopropoxide (Ti[OCH(CH 3 ) 2 ] 4 , 99.999% Aldrich) is added and mixed at 30-50 0 C until a white precipitate is formed.
  • an equimolar quantity of titanium (IV) isopropoxide Ti[OCH(CH 3 ) 2 ] 4 , 99.999% Aldrich
  • the white precipitate (amorphous) is used as the bimetallic precursor in solution without further treatment.
  • the bimetallic precursor solution is transferred through a syringe out of the glove box and injected immediately through a septum into a preheated (320 0 C) solvent/ligand mixture.
  • the solvent/ligand mixture had been preheated to 32O 0 C with stirring under dry nitrogen flow and at ambient pressure.
  • the temperature drops to around 22O 0 C with the boiling of low boiling point benzyl alcohol, which is carried away gradually by the nitrogen flow.
  • the mixture of the white precursor solution, hot oleylamine and carboxylic acid turns from cloudy (right after injection) into a transparent, slightly yellow solution. This is attributed to the high solubility of the precursor in the solvent/1 igand mixture.
  • the benzyl alcohol is removed under the N 2 flow, and the temperature of the system reverts to its final resting temperature of 320 0 C. This temperature is maintained at 48 hrs to prepare oleic acid capped 3-5 nm BaTiO 3 nanocrystals.
  • BaTiO j nanoparticles and nanorods with size of 10-20 nm capped with oleyl alcohol (Case 111): BaTiO 3 nanocrystals were also prepared by replacing BzOH by a mixture of 9 mL BzOH and I mL oleyl alcohol (OLOH)
  • Oleylamine (45 mL) is injected through a septum into this precursor solution with no further addition of carboxylic acid. After injection the temperature of the system is brought slowly (2-3 hrs) to 320°C (in both case III and case IV) with stirring under N 2 and rest at this temperature for 24 hrs (case III) or 48 hrs (case IV).
  • BaTiO3 nanocrystals of about 2-3 nanometers diameters (capped with oleyl alcohol and oleylamine) (Case IV): BaTiO 3 nanocrystals were also prepared by replacing BzOH with 10 mL OLOH (case IV). No carboxylic acid is added as a ligand.
  • 2 mmol metallic barium is transferred from a glove box and added to alcohol (10 mL OLOH) with stirring under dry N 2 flow. Then the temperature of this system is elevated to I 8O°C and maintained at this temperature until barium is dissolved into the alcohol and a transparent solution is formed.
  • the BaTiO 3 nanocrystals are collected by adding polar solvents, ethyl alcohol (case I and III) or acetone (case II and IV) for particle precipitation and subsequent centrifugation. Extra solvent and surfactant can be removed and BaTiO 3 nanocrystals are collected by the following way: acetone or ethanol is added to the reaction solution in the volume ration around 3: 1 or greater. With shaking or sonicating, the transparent solution becomes cloudy. This cloudy solution is sonicated for one minute to ensure thorough mixture of polar solvent and solution, then centrifuged at high speed (13.4 Krpm) to collect the precipitate.
  • polar solvents ethyl alcohol
  • acetone case II and IV
  • the precipitate is collected and dispersed in hexane or toluene by shaking or sonication for one to two minutes. This procedure is generally referred as "washing" nanoparticles to remove extra solvent or surface ligands. Then polar solvent can be added into this hexane or toluene solution to "wash” the nanoparticles for the second time if needed. Because the extra solvent and surface ligands, the BaTiO 3 nanoparticles capped with oleic acid or oleyl alcohol need to be “washed” for at least twice or more.
  • the nanocrystals As the nanocrystals are "washed” for more and more times they turn whiter and whiter and the surface ligands can be eventually stripped off, which can affect solubility in non-polar solvents. After washing, the nanocrystal precipitates can be dispersed in to nonpolar solvents such as hexanes or toluene to form a transparent slightly yellow solution with the help of sonication for three to five minutes. The nanocrystals are easily re-dispersed in nonpolar solvents such as hexane or toluene.
  • Powder X-ray Diffraction (XRD) characterizations were carried out on as synthesized nanocrystals. Results are shown in Figures 1 -3 Low magnification conventional TEM is performed on a JEOL l OOCX microscope and High Resolution TEM (HRTEM) is performed on a JEOL JEM 300OF microscope. XRD is performed on an lnel Multipurpose diffracto meter by drop coating particle solution on a glass substrate. IR data ( Figure 4) and NMR data ( Figure 5) of the bimetallic precursor solution are also shown.
  • a reaction between a barium titanium metalorganic source and an alcohol is carried out at a temperature of 80-230 0 C.
  • the reaction takes place in an autoclave where self-generating pressure (20-30 atm) from alcohol vapor at elevated temperatures can enhance the reactivity at the low temperature.
  • the alcohol is a good solvent that can dissolve the barium titanate precursor.
  • the alcohol is also a reactant involved in the alcoholysis process or in the reaction with an organic moiety of the metalorganic source, which is believed to initiate formation of Ba-O-Ti bonds, a crucial step for the nucleation Of BaTiO 3 nanocrystals.
  • the alcohol can also act as a surface modifier to stabilize the nanocrystals by forming ether end groups on the nanocrystal surface. It is also found that trace amount of water such as in 95% ethanol can tune the rate of alcoholysis process, thus offering further controls over the particle size and morphology.
  • Water also can modify the crystal surface with more hydroxyl groups, providing for better solubility Of BaTiO 3 nanocrystals in polar solvents such as ethanol, with no aid from other additives or surfactants.
  • the BaTiO 3 nanocrystals are easily dispersed in ethanol to afford a substantially homogeneous suspension that can be stable up to weeks or longer without precipitation. Only a small number of nanoparticles may precipitate out in a month, but they can be easily re-dispersed in ethanol using sonication.
  • Other nonaqueous processes that take place in high-boiling- point solvents usually produce BaTiO 3 nanocrystals with surface ligands and some contamination from the solvents.
  • the organic coating must be removed by oxidation in order to retain the intrinsic properties of the nanocrystals.
  • the organic residue after the oxidation mainly carbon- rich species
  • the organic residue after the oxidation can become a major contributor to electrical leakage.
  • some voids may be left, resulting in high porosity, that results in a low dielectric constant.
  • the value of the dielectric constant k can be about 90 for a calcined thin film vs. about 750 for a pure BaTiO 3 nanocrystalline thin film.
  • Thin films with voids also have poorer mechanical strength.
  • the simple reaction system containing only a BaTi metalorganic source and a general alcohol can produce high purity, high crystalline BaTiO 3 nanocrystals.
  • the product can be easily collected and cleaned with little or organic residue.
  • the resulting nanocrystals can be easily dispersed in ethanol with no additives or surfactants.
  • the stable dispersion can provide highly pure BaTiO 3 nanocrystalline thin films with minimal contamination from organic ligands or solvents.
  • barium titanate nanocrystals The synthesis of barium titanate nanocrystals is based on the solvothermal process of a BaTi metalorganic source (barium titanate precursor) in an alcohol solvent.
  • the first step of the synthesis was performed in a glove box because of the moisture-sensitive nature of the sources.
  • BaTi ethylhexano-isoproxide a commercially available product, is used as a precursor.
  • the homogeneous solution (or suspension) was transferred to an autoclave and heated in oven at a temperature of between 180 and 22O 0 C with self- generating pressure (20-30 atm) for a desired period of
  • the autoclave was cooled down.
  • the resulting milky suspension was centrifuged, and a white precipitate was collected and re-dispersed in ethanol.
  • the precipitation-dispersion cycle was repeated for three times until the white precipitate was thoroughly washed with ethanol.
  • the BaTiO 3 nanocrystals were suspended in ethanol solvent for storage or further use. The solvothermal process reaches a high yield above 90% based on the recovery from metal barium.
  • the aggregate-free nature Of BaTiO 3 nanocrystals can offer advantages in coating and functional ization of the crystal surface with a variety of surfactants, polymers.
  • a simple solution processing involving the reaction between BaTiO 3 nanocrystals (wet phase) and oleic acid at elevated temperature can provide strong oleic acid binding to the crystal surface, allowing the tailoring of the surface polarity and the crystal solubility in either non-polar solvents (such as hexane, toluene) or polar solvents (such as ethanol, methanol).
  • the BaTiO 3 nanocrystals were first collected from the ethanol suspension by centrifugation, and the wet white precipitate was mixed with access amount of oleic acid and stirred at temperature of 8O 0 C for 1 h to induce strong oleic acid bonding to the crystal surface.
  • the extra amount of oleic acid was washed away with ethanol by repeating a precipitation-dispersion process for three times.
  • the resulting oleic acid-coated nanocrystals were re-dispersed in hexane to obtain a homogeneous and transparent/semitransparent suspension.
  • the stable and homogeneous suspension allows facile film processing and integration with other media.
  • XRD X-ray powder diffraction
  • BaTiO 3 nanocrystal thin films were prepared on Si substrates by spin coating of hexane or ethanol suspension Of BaTiO 3 nanocrystals at a spin rate of -1500 rpm for 1 min. Multiple spin coatings were applied to achieve various thin film thickness.
  • the BaTiO 3 nanocrystal thin films were prepared by adding several drops of the solution on substrates followed by drying at room temperature.
  • the thin films composed of oleic acid-coated BaTiO 3 were subject to heating treatment at 40O 0 C to remove the organic coating and solidify the films, if necessary.
  • the thin films prepared from uncoated BaTiO 3 nanocrystals (ethanol suspension) were baked at 60 0 C for 12 h to remove the solvent residual and to become stabilized.

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Abstract

L'invention concerne des formes nanocristallines d'oxydes de métaux, comprenant des oxydes de métaux binaires, des oxydes de métaux de type pérovskite et des oxydes de métaux complexes, y compris les oxydes de métaux dopés. Des procédés de préparation des nanocristaux sont également proposés. Les nanocristaux, comprenant des nanocristaux d'oxyde de métal non coiffés et non revêtus, peuvent être dispersés dans un liquide pour former des dispersions qui sont stables et ne précipitent pas sur une période allant de plusieurs heures à plusieurs mois. Des procédés de préparation des dispersions, et des procédés d'utilisation des dispersions dans la formation de films sont également proposés. Les films peuvent comprendre une matrice organique, inorganique ou organique/inorganique mixte. Les films peuvent être sensiblement dépourvus de toute matière organique. Les films peuvent être utilisés comme revêtements, ou peuvent être utilisés comme couches diélectriques dans une variété d'applications électroniques, par exemple comme matériau diélectrique pour un ultracondensateur, qui peut comprendre un matériau mésoporeux.
PCT/US2008/003878 2007-03-26 2008-03-25 Nanocristaux d'oxyde métallique : préparation et utilisations WO2008118422A1 (fr)

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US10975251B2 (en) 2018-12-21 2021-04-13 Iowa State University Research Foundation, Inc. UV-absorbing coating including zinc oxide nanoparticles
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EP4029064A4 (fr) * 2019-09-12 2023-07-26 The Research Foundation for The State University of New York Photomultiplicateur au sélénium amorphe à gain élevé
WO2021104087A1 (fr) * 2019-11-28 2021-06-03 深圳先进技术研究院 Nanoparticules d'oxyde métallique, procédé de préparation associé et application associée
CN111171814A (zh) * 2020-01-08 2020-05-19 上海大学 钙钛矿纳米棒的合成方法
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CN112599420A (zh) * 2020-12-28 2021-04-02 绵阳惠科光电科技有限公司 一种铟镓锌氧基多层结构薄膜晶体管的制备方法
CN113248247A (zh) * 2021-06-23 2021-08-13 上海大学 一种三元压电陶瓷及其制备方法和应用
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