Current research lines
Nanoscale order in amorphous materials
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).
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
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, halogen-free 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.
Metal diborides are refractary materials with high hardness and low electrical resistivity. These properties make them suitable candidates for applications such as hard, protective coatings or microelectronics.
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.
The electronic and structural properties of these layers must be tailored for the particular application by precisely controlling the physics and chemistry of film growth.
Our research goals are to understand the atomic-scale processes that occur at the growing film surface, optimize the plasma processes according to this knowledge, and develop devices with improved performance.
Phase Change Chalcogenide Glasses
Collaborators: Prof. Steve Bishop, UIUC Physics and 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, less than 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
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.
Thermal CVD of metallic thin films
In the last years Ruthenium is being considered a good candidate for conductive layers in microelectronics and memory storing devices.
In our group we study the growth and properties of Ru thin films grown by CVD. Ru thin films with low electrical resistivities have been obtained, and our research focuses in understanding the chemistry of the growth process and the relationship between microstructure, texturing and electrical properties of the material.