Making particles of uniform size

Details Making particles of uniform size Making particles of uniform size

1996-06-18

1999-05-25

Ryan, Patrick

Specialized metallurgical processes, compositions for use therei

Processes

Producing or purifying free metal powder or producing or...

75343, 257 17, B22F 926

Patent

active

059066709

DESCRIPTION:

BRIEF SUMMARY
FIELD OF INVENTION

This invention relates to a method of making particles of uniform size. These are preferably semiconductor particle of nanometer dimensions, known generally as quantum sized particles, or more particularly as zero dimensional crystallites or quantum dots.


BACKGROUND AND SUMMARY OF THE INVENTION

Quantum dots are defined as small particles whose linear dimension in all three directions is less than the de Broglie wavelength of the electrons or holes. Such particles have a greatly modified electronic structure from the corresponding bulk semiconductor material and, in particular, the density of states becomes more like that for molecules. The applications for quantum dots are generally in the field of optoelectronics, and includes such things as light switches and light emitters. A paper describing quantum dots and some of their properties has been published in Angewandte Chemie International Edition (English) 1993, 32, at pages 41-53: "semiconductor q-particles: chemistry in the transition region between solid state and molecules" by Horst Weller.
For the successful exploitation of quantum dots, it is important that all or most of the particles are of the same physical size and shape. With improved consistency of particle size and shape the materials made from such particles have well defined excitonic features which in turn improves the responsiveness and efficiency of optoelectronic devices utilising such materials. A number of methods of achieving this has been tried and most are centred on the production of colloids or inverse micelles or on "smokes". Size control or size selection remains a problem and is the subject of a great deal of research effort. This invention offers a new approach to this problem which may be capable of giving up to about an order of magnitude better size control.
In one aspect, the invention provides a method of making particles of substantially uniform size of a metal or metal compound, which method comprises providing a solution in an evaporable solvent of the metal in chemically combined form, forming the solution into droplets of substantially uniform size, contacting the droplets with a gas-phase reagent so as to form the metal or metal compound, and removing the evaporable solvent from the droplets.


BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is schematic diagram of a spray nozzle assembly which may be used in accordance with the present invention to generate the desired droplet size;
FIG. 1a is detailed cross-sectional view of the capillary nozzle member employed in the assembly depicted in FIG. 1;
FIG. 2 shows an absorption spectrum of material made by the present invention (Line A) compared to absorption spectra of material made by a previously known colloid method (Line B) and macrocrystalline cadmium sulfide of approximately 515 nm (Line C);
FIG. 3 is an absorption spectrum of material made in accordance with Example 2 below; and incorporating wave guide geometry.
The method starts with a solution in an evaporable solvent of the chosen metal in chemically combined form. The evaporable solvent is volatile in the sense that the solvent is evaporable under the reaction conditions used and may be water or an organic solvent whose nature is not important. Although other chemically combined forms are possible, the metal is typically present in the form of a salt, preferably a salt with a volatile anion such as nitrate, chloride, fluoride or acetate.
A wide variety of metals may be used, most usually transition metals and metals from Groups II, III, and IV of the Periodic Table. Thus Group II metals such as zinc or cadmium can be used with hydrogen sulphide or hydrogen selenide to make II-VI semiconductors. Mixtures of metals from Groups II and IV, such as Cd/Hg or Pb/Sn, can be used again for example with hydrogen sulphide or hydrogen selenide to make II-IV-VI semiconductors. Also, group III metals such as aluminium, gallium or indium can be used to make III-V semiconductors. Other compounds which may be made using this method are, for example IV-VI

REFERENCES:
patent: 4331707 (1982-05-01), Muruska et al.
patent: 5260957 (1993-11-01), Hakimi et al.
(Abstract) Proc. Spie--Int. Soc. Opt. Eng. 1758, 1992.

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