Graduate Student Seminar Scheduled for November 3rd

The Fall 2010 Beckman Institute Graduate Student Seminar Series continues on Wednesday, November 3rd. The seminar will feature two short talks from students Rohith Reddy, and Angel R. Aquino. The seminar will be held in Beckman Institute Room 1005 and a pizza lunch will be served to those attending the talks.

Fourier Transform Infrared (FT-IR) Spectroscopic Imaging of Human Tissue Specimens
Rohith Reddy
Bioimaging Science and Technology

Fourier transform infrared (FT-IR) spectroscopic imaging is an emerging technique that provides both chemically and spatially resolved information that can be used, for example, to perform automated histological recognition in tissues. The uses of Bayesian and genetic-algorithm-based classifiers have been shown to be effective in histological recognition in tissues, yielding an accuracy of 94% to 99%. However, clinical translation of these results requires that the classifiers be robust to factors such as tissue sample preparation and systematic bias introduced by handling of tissues. We examine the dependence of classification accuracy on such factors by using independently procured and processed datasets for analysis and validation. We also present data visualization techniques that format would help both experts and non-experts visualize complex relationships in data. The spatial heterogeneity of samples results in distortions in the collected data (spectra). We present models based on rigorous electromagnetic wave theory quantifying these distortions. An understanding of these spectral distortions is especially important in performing automated data analysis. We explore methods of extracting underlying information from distorted spectra. In particular, we show that choosing appropriate metrics and classification algorithms in human tissue histopathology can help overcome consequences of these distortions.

Cathodoluminescence of CuxAg1-xInSe2 thin films for solar cells
Angel R. Aquino

Department of Materials Science and Engineering,
University of Illinois at Urbana-Champaign

imageCathodoluminescence of CuAgInSe2 thin films

I-III-VI2 chalcopyrite semiconductors are among the most studied materials for solar cell absorber layers.  The bandgaps of the I-III-VI2 system (I-Cu,Ag; III-Ga,In; VI-S,Se) cover almost the entire solar spectrum (1.07 eV – 2.73 eV), making it an ideal system for multijunction solar cells.  Their performance is also enhanced by the presence of grain boundaries, making it possible to deposit these films using relatively inexpensive techniques.  Among these, AgInSe2 has gained a lot of attention because of its higher bandgap (1.24 eV), which is better matched to the solar radiation received on earth, and its high absorption coefficient.  Here we present results of the first cryogenic cathodoluminescence experiments with spectral imaging on CuxAg1-xInSe2 (CAIS) thin films.  The purpose of this work was to study the emission spectrum of grains and grain boundaries in CAIS as a function of alloy composition in order to identify any differences in grain boundary behavior.  Our current work suggests that AgInSe2 should yield more uniform device performance compared to CuInSe2.  We will discuss the implications that these findings have on the fabrication of solar cells.