Nanometer Scale Induced Structure Between Amorphous Layers and Crystalline Materials

Executive Summary

Nanometer Scale Induced Structure

Between

Amorphous Layers and Crystalline Materials

This work was supported by NSF Award DMR-0010062 in cooperation with EU Commission Contract G5RD-CT-2001-00586

     A complementary ensemble of capable EU and US groups present an integrated experimental and computational proposal to investigate the extraordinary properties of stable intergranular films. These films can have nanoscale structures and compositions that would not be stable as a bulk phase, and therefore can have physical properties that are not found in bulk phases. Furthermore, some physical attributes, such as film width, that are normally tailored by engineering processes, become an equilibrium quantity that are naturally uniform and highly tunable with composition. Because of nanometer length scales of these films and their unexpected physical properties (e.g., the dielectric properties of thin intergranular films cannot be extrapolated from known bulk values), development and integration into devices is expected to yield beneficial consequences.

     The existence of disordered stable interfacial and surficial films has been established experimentally in disparate material systems. The general behavior of the stabilized films is demonstrably dependent on their composition. Their stability is assumed to be associated with remnant order induced into their molecular structure from the crystalline materials proximate to them. Phenomenological theories can account for their stability; no general theory accounts for combined effects of crystallographic and imposed constraints, molecular structure, and composition. A satisfactory description of these interfaces has not been attained, not has sufficient data been collected to categorize their behavior thoroughly.

     Anticipated benefits towards the foundation for the understanding and subsequent engineering of intergranular and surficial thin films are to be achieved with a collective approach of experimentation, theory and modeling, and subsequent experimental verification on selected specific material subsystems (silicate and titanate based systems) that may be extrapolated to general systems in which analogous films have been observed. The associated research groups from Europe and the US span the experimental and computational length and time scales that will be required for a successful complete understanding. Many of the principals have been active leaders in the initial exploration of stable thin film properties.

     Spatially varying atomic ordering and composition, bonding and electronic structure, transport properties, dispersion and steric forces, bulk and gradient thermodynamic properties will be studied by combined techniques of EXAFS, EXELFS, ELNES, VEELS and VUV spectroscopies and HREM and computational microscopy on prepared controlled reference-standard materials. Models will be developed and correlated with experiments by combined ab-initio, density functional theory, OLCAO, molecular dynamics, and diffuse interface thermodynamics.