Winston A. Saunders

Nanometer‐scale GaAs clusters from organometallic precursors

We report the synthesis of crystalline nanometer-scale GaAs clusters by homogeneous vapor-phase nucleation from organometallic precursors. Cluster synthesis is performed in a hot wall organometallic vapor-phase epitaxy reactor at atmospheric pressure. High resolution transmission electron microscopy studies reveal that the aerosol produced is composed of highly faceted single crystal GaAs particles in the 10–20 nm range. The influence of growth temperature and reactant concentration on cluster morphology is discussed.

Vapor phase synthesis of crystalline nanometer‐scale GaAs clusters

We report the synthesis of crystalline nanometer‐scale GaAs clusters in the 5–10 nm size regime. The clusters are formed by the homogeneous nucleation of a nonequilibrium vapor created by the explosive vaporization of a bulk GaAs sample in an inert atmosphere. High resolution electron microscopy and diffraction show that the clusters have zincblende crystal structure and are faceted. Optical measurements on the particles are suggestive of quantum confinement effects.

Synthesis of luminescent silicon clusters by spark ablation

The synthesis of luminescent nanometer-scale Si clusters by spark ablation from a crystalline Si substrate is described. The cluster source, described in the text, generates clusters in a flowing Ar stream at atmospheric pressure. Electron microscopy reveals that the clusters have diameters in the 2-4 nm size range. The luminescence spectra of the clusters, similar to that of porous Si, are presented.

Electrostatic propulsion using C60 molecules

Buckminsterfullerene, a newly discovered allotrope of Thus, a gap in propulsion capability exists for missions carbon (C6 0 ), has demonstrated properties that make it an with a requirement for low-to-moderate specific impulse, ideal candidate as a propellant for electrostatic propulsion. yet at higher propulsion system efficiency than is provided Here, we present a discussion of the potential benefits C60 by state-of-the-art xenon ion engines or arcjets. ion propulsion may provide over conventional ion propulsion and previously suggested methods of cluster 0 8 ion propulsion. These benefits include improved propulsion system power efficiency, especiallylin the

Lower-dimensional quantum structures by selective growth and gas-phase nucleation

There is increasing interest in the potential application of quantum dots and quantum wires to various solid state devices. In this article, the physics of lower-dimensional quantum structures will be reviewed with emphasis on applications. In addition, two fabrication approaches under investigation at Caltech will be discussed. The first is based on selective nucleation of III–V semiconductors on a patterned host substrate and the second is gas-phase nucleation of III–V clusters. Recent results on formation of nanocrystal GaAs and silicon clusters in the gas phase are presented.

Resonance‐enhanced spontaneous emission from quantum dots

Enhanced and inhibited spontaneous emission from a pointlike quantum dot embedded in a finite dielectric sphere are treated classically. Numerical results given for a GaAs quantum dot embedded in an Al0.4Ga0.6As sphere show the spontaneous emission rate is decreased by a factor of 80 when the radius of the sphere is small compared to the wavelength of emitted light. When the radius of the sphere is comparable to the wavelength, the spontaneous emission rate depends strongly on the radius. Sharp resonances, related to Mie resonances, with enhancements up to a factor of 100, are found in some cases.

Si-Cluster Luminescence

We report on a technique for generating Si-clusters in the nanometersize regime. The cluster source is capable of generating micron-thick cluster films in a few minutes. The cluster films luminesce in thevisible and infrared. Source construction is discussed. Electron micrographs of the clusters are shown. Luminescence and optical absorption spectra for the clusters are presented.

The role of Ga-droplet formation in nanometer-scale GaAs cluster synthesis from organometallic precursors

Recently we demonstrated the formation of crystalline nanometer scale GaAs clusters from organometallic precursors using an aerosol process derived from organometallic vapor phase epitaxy (OMVPE) [P. C. Sercelet al., Appl Phys. Lett.61, 696 (1992)]. Here, we explore the influence of precracking the Ga precursor (trimethyl-gallium), forming nanometer scale Ga droplets, prior to introduction of AsH3 to the reaction. We find the GaAs clusters so formed have an entirely different morphology than do those formed when the reactants are pre-mixed prior to reaction. This data supports our earlier contention that homogeneous nucleation is the dominant reaction mechanism for the formation of the clusters.

Crystalline Nanometer-Scale III–V Clusters

We report the synthesis of crystalline nanometer-scale III–V clusters in the 5 to 50 nm size regime. The clusters are formed by homogeneous nucleation of a non-equilibrium vapor created by the explosive vaporization of a bulk sample in an inert atmosphere via a high voltage electrical discharge. Transmission electron micrographs and diffraction patterns for GaAs, InAs, and InP are presented.