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Research

Summary

In our laboratory, we use (and in some cases develop) optical spectroscopic and imaging techniques to explore elementary processes at surfaces and interfaces of technologically important electronic, photonic, organic and more recently biological heterostructures. For instance, we have been leading the implementation of infrared absorption spectroscopy to develop a detailed mechanistic understanding of semiconductor surface cleaning (both by wet and dry techniques), passivation, and chemical functionalization. In particular, we have devised sensitive, in-situ methods to probe the interaction of chemical species and the formation of thin dielectric films in a variety of environments, including liquids, ultra-high vacuum (UHV), and gaseous ambients. The work in our group has had a direct impact on:

1. Microelectronics, by identifying the surface modification after various wet chemical processes (HF etching, acid/base cleaning and etching) for several types of semiconductors (groups IV, IV-IV, III-V), by characterizing the nature of H, Cl, OH and oxide passivation of semiconductor surfaces, and by uncovering the growth mechanism of high-k dielectrics on silicon. We are currently exploring the growth by Atomic Layer Deposition (ALD) of Al₂O₃ and HfO₂ with sub nm equivalent oxide thickness (to replace SiO₂) and the best wet chemical cleaning methods for high mobility substrates (e.g. Ge, InP) to replace silicon in future CMOS devices. We are also investigating elementary processes at the surface of SiC, an important substrate for high temperature, high speed, and high voltage electronics.

2. Optoelectronics, by providing chemical information and badly needed fundamental understanding of III-V semiconductor surface passivation. After studying wet chemical etching and oxidation of InP, we are now exploring gaseous oxidation in controlled environments (e.g. UHV).

3. Organic electronics, by characterizing the chemical and structural nature of self-assembled monolayers (SAM’s) on both metal and semiconductor surfaces. We are focusing on providing chemical and structural information to understand electronic conduction in organic materials by paying special attention to contact issues (substrate/SAM interfaces and effects of depositing top metal electrodes on SAM films). We are also developing spectroscopic methods to study the dependence of electronic conduction on conformal changes within the SAM’s.

4. Nanoelectronics, by using biological approaches to patterning surfaces on the nm and sub-nm scale. For instance, the possibility to manipulate DNA scaffolding is used to meet tight nanolithography requirements of integrated nano-circuits. An important aspect of this work is the control of DNA bonding to semiconductor surfaces. To this end, we are working on the fundamentals of DNA/surface interactions.

5. Biosensors and biomedical applications, by understanding the interaction of biological macro-molecules (DNA, glucose, LDL, etc) with both organic and inorganic substrates. For instance, by studying the modulation of the electric field and charge transfer mechanisms by biological molecules, we are devising ways to implement electronic detection of biological species. The field of bio-sensors is wide open and in need of accurate surface characterization tools. Our group is therefore exploring the implementation of several tools specifically for biomedical applications, including spectroscopy and imaging. We are also exploring various means of single-wall carbon nanotube chemical functionalization to perform specific cellular functions both at the cell membrane and within the cell body.

Our group is interdisciplinary in nature, with collaborations in Physics, Chemistry, Materials Science, chemical and biomedical engineering, and even with the Medical School. We have ongoing interactions with laboratories in Belgium, France, Germany and Italy, and access to the National Synchrotron Light Source at Brookhaven Laboratory. Our goal is to develop the synergy necessary to make substantial scientific advances in surface and interfacial science, and to benefit in the process core US industries.

Awards & Honors

2006

2005