Electron Microscope Studies of Materials

Professors Kuan and Lanford

Electron microscopy, since its invention in the late 1920s has been a most powerful and versatile tool for investigating the structure 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.

Ion Beam Characterization and Modification of Material

Professor Lanford

The 4MV ion beam accelerator located on the Albany campus offers unique capabilities for materials physics. Current materials research topics include: 1) clean surfaces, interfaces, and surface-sensitive properties of materials; 2) defects in solids; 3) hydrogen in solids. 

Much of this research is interdisciplinary, ranging from fundamental physics, to new technologies (particularly microelectronics), to applications in art history and archaeology. Recent basic physics work has discovered that (upon annealing in some metal/metal thin film structures) there can be elemental transport in patterns that challenge our understanding of the mechanisms driving atom transport in solids. In the technology area, recent work has enhanced our knowledge of how ion implantation can be used to inhibit the corrosion of copper and how this knowledge can be utilized in designing a microelectronic manufacturing processes in which copper is used as a principal conductor. In the area of art history and archaeology, work has included studies of how trace element content can be used to determine the geologic sources of materials used by prehistoric peoples to manufacture pottery and obsidian artifacts. Other work has concentrated on understanding how glasses react with atmospheric water and how this knowledge can be used to improve the accuracy of obsidian hydration dating and to better conserve historic stained glass in cathedral windows. 

The ion beam facility has four accelerators devoted to different aspects of materials physics. The largest is a computer-controlled 4.5 MV Dynamitron which can accelerate electrons, protons and heavier ions. This machine has specialized experimental end-stations, including an ultrahigh vacuum chamber, goniometers for channeling measurements, and a focused ion beam microprobe with a spatial resolution of 1-2 microns. The smaller accelerators are a 1 MV tandem, and 400 KV and 150 KV ion implanters. Two highly skilled engineers, lots of electronics and computers, and an extensive software library make these accelerators specially productive.

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