Virtual Fabrication of Small Ga-As/P and In-As/P Clusters with Pre-Designed Electronic Pattern Structure
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Virtual Fabrication of Small Ga-As/P and In-As/P Clusters with Pre-Designed Electronic Pattern Structure Liudmila A. Pozhar1, Alan T. Yeates2, Frank Szmulowicz3 and William C. Mitchel3 1
Western Kentucky University, Department of Chemistry, TCCW 444, 1 Big Red Way, Bowling Green, KY 42101, U.S.A. 2 Air Force Research Laboratory, Materials and Manufacturing Directorate, Polymer Materials Branch (AFRL/MLBP), 2941 Hobson Way, Wright-Patterson Air Force Base, OH 45433, U.S.A. 3 Air Force Research Laboratory, Materials and Manufacturing Directorate, Sensor Materials Branch (AFRL/MLPS), 3005 Hobson Way, Wright-Patterson Air Force Base, OH 45433, U.S.A.
ABSTRACT Quantum statistical physics methods [1] relate charge transport properties of small atomic clusters (or small quantum dots, QDs) to their equilibrium electronic energy level spectra. Thus, electronic energy level computations for such systems provide a foundation for realization of a virtual (i.e., fundamental theory- based, computational) approach [2] to synthesis of subnanoscale materials with pre-designed charge transport properties. In this publication the HarteeFock (HF) electronic energy level spectra of several pre-designed small clusters of Ga, As, In and P atoms are studied and compared to those of the corresponding clusters grown at spatially unrestricted conditions. Influence of clusters’ growth conditions on formation and structure of their valence and conduction bands is discussed.
INTRODUCTION In various studies to date [3] formation of small atomic clusters and their growth have been modeled numerically at conditions that have not involved spatial restrictions. In many cases, the stoichiometry of small clusters is chosen to be the same as that of the corresponding bulk material, and dangling bonds are tied up with hydrogen or other simple atoms that may or may not be involved in the process of actual experimental synthesis of such small atomic clusters. The structure of the clusters is obtained by a minimization of the total cluster energy using wellestablished theoretical approaches, such as the density functional theory (DFT), Hartree-Fock (HF), multi-configuration self-consistent field (MCSCF) and similar methods. The data on the cluster structure, stoichiometry and electro-optic properties so obtained are specific to clusters virtually synthesized at spatially-unconstrained conditions ( in “vacuum”), and are expected to differ from the corresponding data on clusters nucleated with the same number and types of atoms, but on surfaces or in confinement, rather than in vacuum. Nature offers many options for design of sub-nanoscale structured materials with desirable properties, including growth of atomic clusters in 3D confinement of sub-nanoscale dimension pores and voids of solid membranes (such as precisely characterized pores of several atomic diameters in width specific to alumina and silica membranes [4], etc.) or on surfaces. Nucleation and growth of the small clusters in such cases are dramatically affected by the presence of confi
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