Professor Kuan

Electron microscopy, since its invention in the late 1920s has been a most powerful and versatile tool for investigating the structur of materials. For the study of interfaces, boundaries, and various point, line, or planar defects, electron microscopy offers unique advantages over other techniques because individual defects and their interactions can be observed directly. With the advent of new lens designs and field-emitter technology, it is now possible to resolve spatial features as small as 0.2 nm and to study a sample area as small as 1 nm with high beam intensity. These advantages are critical when the chemical nature of point or line defects or the composition of small precipitates is being investigated.

The major theme of this research program is to study the microstructure of a wide variety of materials, including metals, semiconductors, superconductors, ceramics, and polymers. The defect structures which strongly affect a material's electrical, optical, mechanical, and other properties are of particular interest. The atomic scale imaging, electron diffraction, and nm-area chemical analysis is being used to explore the atomic and chemical nature of these defects. The microstructure revealed under a transmission electron microscope at magnifications up to more than a million times often provides important clues which help us understand how different processes change materials' properties.

The scanning electron microscope is most useful in studies of materials' surface morphology and the cross-sections of multilayer structures. The scanning electron microscope can also be used to write nanometer patterns in a resist layer. This e-beam lithography technique can be used in conjunction with plasma etching and thin film deposition processes to build nanostructures for Si or III-V quantum device studies and/or for developing various sub-quarter-micron processing technology.

Much of the microstructure and lithography research is done in the newly established Electron Microscope Laboratory, which houses a 200 kV state-of-the-art transmission electron microscope equipped with a field emission gun, a parallel electron energy loss spectrometer, and an energy dispersive x-ray spectrometer. This laboratory also has a 40 kV scanning electron microscope, a second 200 kV high-resolution transmission electron microscope with a LaB6 emitter, and a sample preparation facility.