NSF-EC Activity: Nanometer Scale Induced Structure Between Amorphous Layers and Crystalline Materials

Massachusetts Institute Of Technology, Cambridge MA

Investigators

Abstract

This combined experimental and computational effort investigates novel properties of stable intergranular films. Stable films have nanoscale structures and compositions which would not be stable as a bulk phase and, therefore, can have physical properties that are not found in bulk phases. For instance, the dielectric constant and the observed atomic structure of the intergranular films cannot be extrapolated from bulk behavior. Furthermore, some physical attributes that are normally tailored by engineering processes, such as film width, become equilibrium quantities that are naturally uniform and highly tunable with composition. Their stability is assumed to be associated with remnant order induced into their molecular structure from the crystalline materials proximate to them; we seek to characterize experimentally these films in silicate and titanate systems and find theoretical and computational models to categorize their behavior. The thin films will be processed with controlled composition and characterized by combined experimental techniques (EXAFS, EXELFS, ELNES, VEELS and VUV spectroscopies, and HREM). Models will be developed and correlated with experiments by combined ab-initio, density functional theory, OLCAO, molecular dynamics, and interface thermodynamics. %%% The production of new technological devices often depends on the development of a novel material or a new way to process materials that generate novel properties. With ever smaller devices, there is an increased demand on precise material properties---as well as an increased technological reward. In some materials, such as the silicates and titanates we investigate, the properties of materials undergo acute changes as the size of the material system (i.e. the materials and their architecture within a device) shrinks. These changes can have profound effects on our ability to enhance and control properties. For instance, the electronic properties of very thin films may be modified for particular devices and our ability to engineer them may be enhanced due to the physical effects of their small size. We will attempt to characterize and understand these effects with an integrated experimental, theoretical, and computational approach. We expect that our results may used directly to enhance the properties of existing electronic devices and that our research may illuminate specific material properties that result in the production of new technologies. This proposal was submitted in response to the solicitation "Proposals for Cooperative Activities in Materials Sciences between the National Science Foundation and the European Commission: NSF (00-18)".