Coating processes – Particles – flakes – or granules coated or encapsulated – Inorganic base
Reexamination Certificate
2000-12-08
2003-06-10
Le, H. Thi (Department: 1773)
Coating processes
Particles, flakes, or granules coated or encapsulated
Inorganic base
C075S010620, C075S343000, C075S362000, C075S370000, C427S314000, C516S033000, C516S922000
Reexamination Certificate
active
06576291
ABSTRACT:
TECHNICAL FIELD
The invention relates to methods of manufacturing a nanocrystallite.
BACKGROUND
Nanocrystallites having small diameters can have properties intermediate between molecular and bulk forms of matter. For example, nanocrystallites based on semiconductor materials having small diameters can exhibit quantum confinement of both the electron and hole in all three dimensions, which leads to an increase in the effective band gap of the material with decreasing crystallite size. Consequently, both the optical absorption and emission of nanocrystallites shift to the blue (i.e., to higher energies) as the size of the crystallites decreases.
Methods of preparing monodisperse semiconductor nanocrystallites include pyrolysis of organometallic reagents, such as dimethyl cadmium, injected into a hot, coordinating solvent. This permits discrete nucleation and results in the controlled growth of macroscopic quantities of nanocrystallites. Organometallic reagents can be expensive, dangerous and difficult to handle.
SUMMARY
The invention features methods of manufacturing a nanocrystallite. The nanocrystallite has a diameter of less than 150 Å. The nanocrystallite can be a member of a population of nanocrystallites having a narrow size distribution. The nanocrystallite can be a sphere, rod, disk, or other shape. The nanocrystallite can include a core of a semiconductor material. The core can have an overcoating on a surface of the core. The overcoating can be a semiconductor material having a composition different from the composition of the core. Semiconducting nanocrystallites can photoluminesce and can have high emission quantum efficiencies. The method forms the nanocrystallite from an M-containing salt. The nanocrystallite can include a core having the formula MX, where M is cadmium, zinc, magnesium, mercury, aluminum, gallium, indium, thallium, or mixtures thereof, and X is oxygen, sulfur, selenium, tellurium, nitrogen, phosphorus, arsenic, antimony, or mixtures thereof. The M-containing salt can be the source of M in the nanocrystallite. An X-containing compound can be the source of the X in the nanocrystallite.
The M-containing salt can be a safe, inexpensive starting material for manufacturing a nanocrystallite relative to typical organometallic reagents which can be air sensitive, pyrophoric, or volatile. The M-containing salt is not air sensitive, is not pyrophoric, and is not volatile relative to organometallic reagents.
In one aspect, the invention features a method of manufacturing a nanocrystallite. The method includes contacting a metal, M, or an M-containing salt, and a reducing agent to form an M-containing precursor, M being Cd, Zn, Mg, Hg, Al, Ga, In or Tl. The M-containing precursor is contacted with an X donor, X being O, S, Se, Te, N, P, As, or Sb. The mixture is then heated in the presence of an amine to form the nanocrystallite. In certain embodiments, heating can take place in the presence of a coordinating solvent.
In another aspect, the invention features a method of manufacturing a nanocrystallite including contacting a metal, M, or an M-containing salt, and a reducing agent to form an M-containing precursor, contacting the M-containing precursor with an X donor, and heating the mixture to form the nanocrystallite. In certain embodiments, heating can take place in the presence of a coordinating solvent.
In another aspect, the invention features a method of manufacturing a nanocrystallite including contacting a metal, M, or an M-containing salt, an amine, and an X donor, and heating the mixture to form the nanocrystallite.
In yet another aspect, the invention features a method of overcoating a core nanocrystallite. The method includes contacting a core nanocrystallite population with an M-containing salt, an X donor, and an amine, and forming an overcoating having the formula MX on a surface of the core. In certain embodiments, a coordinating solvent can be present.
The amine can be a primary amine, for example, a C
8
-C
20
alkyl amine. The reducing agent can be a mild reducing agent capable of reducing the M of the M-containing salt. Suitable reducing agents include a 1,2-diol or an aldehyde. The 1,2-diol can be a C
6
-C
20
alkyl diol. The aldehyde can be a C
6
-C
20
aldehyde.
The M-containing salt can include a halide, carboxylate, carbonate, hydroxide, or diketonate. The X donor can include a phosphine chalcogenide, a bis(silyl) chalcogenide, dioxygen, an ammonium salt, or a tris(silyl) pnictide.
The nanocrystallite can photoluminesce with a quantum efficiency of at least 10%, preferably at least 20%, and more preferably at least 40%. The nanocrystallite can have a particle size (e.g., average diameter when the nanocrystallite is spheroidal) in the range of about 20 Å to about 125 Å. The nanocrystallite can be a member of a substantially monodisperse core population. The population can emit light in a spectral range of no greater than about 75 nm at full width at half max (FWHM), preferably 60 nm FWHM, more preferably 40 nm FWHM, and most preferably 30 nm FWHM. The population can exhibit less than a 15% rms deviation in diameter of the nanocrystallites, preferably less than 10%, more preferably less than 5%.
The method can include monitoring the size distribution of a population including of the nanocrystallite, lowering the temperature of the mixture in response to a spreading of the size distribution, or increasing the temperature of the mixture in response to when monitoring indicates growth appears to stop. The method can also include exposing the nanocrystallite to a compound having affinity for a surface of the nanocrystallite.
The method can include forming an overcoating of a semiconductor material on a surface of the nanocrystallite. The semiconductor material can be a group II-VI, III-V or IV semiconductor, such as, for example, ZnO, ZnS, ZnSe, ZnTe, CdO, CdS, CdSe, CdTe, MgO, MgS, MgSe, MgTe, HgO, HgS, HgSe, HgTe, AlN, AlP, AlAs, AlSb, GaN, GaP, GaAs, GaSb, InN, InP, InAs, InSb, TlN, TlP, TlAs, TlSb, or mixtures thereof.
The details of one or more embodiments of the invention are set forth in the description below. Other features, objects, and advantages of the invention will be apparent from the description and from the claims.
DETAILED DESCRIPTION
The method of manufacturing a nanocrystallite is a colloidal growth process. Colloidal growth occurs by rapidly injecting an M-containing salt and an X donor into a hot coordinating solvent including an amine. The injection produces a nucleus that can be grown in a controlled manner to form a nanocrystallite. The reaction mixture can be gently heated to grow and anneal the nanocrystallite. Both the average size and the size distribution of the nanocrystallites in a sample are dependent on the growth temperature. The growth temperature necessary to maintain steady growth increases with increasing average crystal size. The nanocrystallite is a member of a population of nanocrystallites. As a result of the discrete nucleation and controlled growth, the population of nanocrystallites obtained has a narrow, monodisperse distribution of diameters. The monodisperse distribution of diameters can also be referred to as a size. The process of controlled growth and annealing of the nanocrystallites in the coordinating solvent that follows nucleation can also result in uniform surface derivatization and regular core structures. As the size distribution sharpens, the temperature can be raised to maintain steady growth. By adding more M-containing salt or X donor, the growth period can be shortened.
The M-containing salt is a non-organometallic compound, e.g., a compound free of metal-carbon bonds. M is cadmium, zinc, magnesium, mercury, aluminum, gallium, indium or thallium. The M-containing salt can be a metal halide, metal carboxylate, metal carbonate, metal hydroxide, or metal diketonate, such as a metal acetylacetonate. The M-containing salt is less expensive and safer to use than organometallic compounds, such as metal alkyls. For example, the M-containing salts are stable in air, wh
Bawendi Moungi
Stott Nathan E.
Fish & Richardson P.C.
Massachusetts Institute of Technology
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