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A major area of current interest is the low temperature deposition of metallic, dielectric and semiconducting materials for electronics, including large-area flat panel displays and solar electric cells, and ultra-thin layers for next-generation ULSI circuits. Our research focuses on developing an understanding, in atomic-level detail, of the growth processes used for thin films and its relationship with microstructure and properties. To achieve this goal, we use in-situ spectroscopic techniques to analyze the deposition species, surface chemistry, chemical bonding, microstructure and electronic properties. A selection of techniques is shown on the following figure, which shows our system for metal diboride CVD processes. Current research projects are listed below.

Nanoscale Order in Amorphous Materials

Goal Analyze medium-range order using fluctuation electron microscopy in the TEM

Sponsor National Science Foundation—Division of Materials Research

Collaborators

• Dr. Murray Gibson, Argonne National Lab: inventor of fluctuation microscopy
• Prof. Paul Voyles, U. Wisconsin: fluctuation microscopy on the STEM
• Prof. David Drabold, Ohio U.: simulations of amorphous materials & properties
• Prof. Paul Goldbart, UIUC: topological theory of network solids

Using the new technique of fluctuation microscopy in the TEM, we have been able to analyze the degree of medium-range structural order in amorphous materials. For a-Si, we have shown the existence of abundant medium-range order, which has been modeled as the small grain size limit of nanocrystallinity. We are currently investigating the light-induced changes in this order and in the electronic properties of a-Si:H films. We are also extending the fluctuation microscopy technique to the study of binary materials.

Chemical Vapor Deposition of MB2 Thin Films

Goal Develop chemical vapor deposition (CVD) of MB2 thin films

Sponsor National Science Foundation—Chemistry Division

Collaborators

• Prof. Greg Girolami, UIUC Chemistry: novel precursor molecules
• Prof. Jim Eckstein, UIUC Physics: superconducting properties and devices

We are investigating the growth of metallic ceramic MB2 compounds (M = transition metal) using remote-plasma CVD methods. Girolami's group synthesizes new single-source precursors for CVD such as Zr(BH4)4 for ZrB2, Cr(B3H8)2 for CrB2, and others. We perform remote H2 plasma assisted CVD and have obtained, for the first time, thin films which are conformal in deep trenches and have outstanding structural and electronic properties. A very exciting prospect is the possible growth of s-wave, 40K superconducting MgB2 thin films for use in Josephson junctions and other devices. Girolami's group has completed the synthesis of two different precursor molecules and we have begun CVD deposition experiments.

Phase Change Chalcogenide Glasses

Goal Study amorphous (semiconducting) to crystalline (semimetallic) transformations

Sponsor UIUC campus research board

Collaborators

• Prof. Steve Bishop, UIUC Physics & ECE: expert in chalcogenides and defects

We are analyzing the optical, electronic, and transformation kinetics of phase change chalcogenide glasses, such as Ge2Sb2Te5, that have proven technological performance in rewriteable CDs but for which the basic understanding of optical and electronic properties, as well as the presence of nanometer-scale structural order in the amorphous phase, are highly incomplete. We will analyze these fundamental properties, and explore the possibility that exceedingly small volumes, < 20 nm in diameter, can be phase changed from the amorphous to crystalline states using a focused electron beam; at such length scales, quantum electronic effects are expected to occur.

Ordered Nanocrystalline Si

Goal Understand and manipulate nucleation & surface diffusion to fabricate nc-Si arrays

Sponsor National Science Foundation—Chemical &Transport Systems

Collaborators

• Prof. Ed Seebauer, UIUC ChemE: surface diffusion on Si

We had detected the existence of nm-scale medium range order in a-Si and Seebauer's group had observed the photo-enhanced migration of surface adspecies, leading to grain coarsening. We are collaborating in order to explore the possibility of producing controlled distributions of nanocrystals on the surface of amorphous silicon films. This project shares some intellectual common ground with the proposed work, but is very different in detail.