Research opportunities on clusters and cluster-assembled materials—A Department of Energy, Council on Materials Science Panel Report

Abstract

The Panel was charged with assessing the present scientific understanding of the size-dependent physical and chemical properties of clusters, the methods of synthesis of macroscopic amounts of size-selected clusters with desired properties, and most importantly, the possibility of their controlled assembly into new materials with novel properties. The Panel was composed of both academic and industrial scientists from the physics, chemistry, and materials science communities, and met in January 1988.In materials (insulators, semiconductors, and metals) with strong chemical bonding, there is extensive spatial delocalization of valence electrons, and therefore the bulk physical properties which depend upon these electrons develop only gradually with cluster size. Recent research using supersonic-jet, gas-aggregation, colloidal, and chemical-synthetic methods indeed clearly establishes that intermediate size clusters have novel and hybrid properties, between the molecular and bulk solid-state limits. A scientific understanding of these transitions in properties has only been partially achieved, and the Panel believes that this interdisciplinary area of science is at the very heart of the basic nature of materials. In Sec. V (Future Challenges and Opportunities), a series of basic questions for future research are detailed. Each question has an obvious impact on our potential ability to create new materials.Present methods for the synthesis of useful amounts of size-selected clusters, with surface chemical properties purposefully controlled and/or modified, are almost nonexistent, and these fundamentally limit our ability to explore the assembly of clusters into potentially novel materials. While elegant spectroscopic and chemisorption studies of size-selected clusters have been carried out using molecular-beam technologies, there are no demonstrated methods for recovery and accumulation of such samples. Within the past year, the first reports of the chemical synthesis of clusters with surfaces chemically modified have been reported for limited classes of materials. Apparatus for the accumulation and consolidation of nanophase materials have been developed, and the first promising studies of their physical properties are appearing. In both the chemical and nanophase synthesis areas, clusters with a distribution of sizes and shapes are being studied. Progress on macroscopic synthetic methods for size-selected clusters of controlled surface properties is the most important immediate goal recognized by the Panel. Simultaneous improvement in physical characterization will be necessary to guide synthesis research.Assuming such progress will occur, the Panel suggests that self-assembly of clusters into new elemental polymorphs and new types of nanoscale heterogeneous materials offers an area of intriguing technological promise. The electrical and optical properties of such heterogeneous materials could be tailored in very specific ways. Such ideas are quite speculative at this time; their implementation critically depends upon controlled modification of cluster surfaces, and upon development of characterization and theoretical tools to guide experiments.The Panel concluded that a number of genuinely novel ideas had been enunciated, and that in its opinion some would surely lead to exciting new science and important new materials.

Production of Nanometer-Sized Metal Oxide Particles by Gas Phase Reaction in a Free Jet. I: Experimental System and Results

“…The powder is shaped, pressed, and sintered into dense solid materials with little void space. Advanced composite materials, with properties quite different from those which currently exist, can be obtained from particles in the nanometer-sized range (Andres et al, 1989).…”

Luminescence studies of europium doped yttrium oxide nano phosphor

“…The physical and chemical properties vary drastically with size, which clearly represents a fertile field for materials research [1][2][3]. Producing nano scale materials opens new opportunities in the creation of product with enhanced properties for applications such as electronics, optics, medicine and magnetism.…”

Preparation of nanoparticles of silver halides, superconductors and magnetic materials using water-in-oil microemulsions as nano-reactors

“…Sub-micron or nanometer sized particles are of increasing scientific and technological interest [37]. There is clear evidence that small atomic clusters (10-1000 atoms) exhibit novel and hybrid properties between the molecular and bulk solid-state limits.…”

“…The large fraction of atoms residing at the surfaces and grain boundaries of these materials also leads to materials with novel properties. Such nanoparticles are not only of basic physical interest, but have also resulted in important technological applications such as: (a) catalysis, (b) high-performance ceramic materials, (e) micro-electronic devices, and (f) high density magnetic recording [37][38][39].…”