Scanning tunneling microscopy (STM) is being developed as a nanofabrication tool to extend electronic device fabrication into the sub-0.1 ;gm regime. This University Research Initiative (URI) is combining STM nanolithography with electron beam lithography, molecular beam epitaxy, dry processing, and silicon and III-V device fabrication to pursue this goal. To date, linewidths of 1 nm have been achieved on silicon surfaces using a unique ultrahigh vacuum (UHV) STM system constructed at the Beckman Institute. This capability is now being applied to fabricate devices that are controlled by quantum size effects.

An ultrahigh vacuum (UHV) scanning tunneling microscope (STM) has been constructed that is capable of operation from above room temperature down to 1.5 K. This instrument is coupled to an existing room temperature UHV-STM to enable sample and tip transfer under UHV conditions and to make use of the existing preparation facilities. This system is being used to perform atomic resolution imaging and spectroscopy experiments on adsorbed atoms, molecules, and biomolecules, as well as on semiconductor heterostructures.

The scanning tunneling microscope (STM) has been developed to image the heterointerfaces of ultrahigh vacuum (UHV) cleaved III-V compound semiconductor structures that are grown for electronic and optoelectronic device applications. Atomic resolution images of various III-V systems have provided direct views of interface roughness, alloy distribution, two-dimensional electron gas (2DEG) formation, and the penetration of the electron wavefunction into barrier layers. This information is being used as input to the crystal growth and device fabrication processes in collaboration with industrial colleagues.

Funds have been provided to construct two ultrahigh vacuum (UHV) scanning tunneling microscope (STM) systems for purposes of performing university/industry collaborative nanofabrication experiments. One of these systems has been transferred to Texas Instruments as part of this collaboration. Nanoscale selective chemistry and metallization experiments are being conducted with these systems as well as cross-sectional STM experiments on Texas Instruments heterolayer device structures.

Silicon-based heterostructures under consideration for novel device applications are being evaluated at the atomic level by means of cross-sectional scanning tunneling microscopy (STM). Cleaving techniques developed specifically for these systems enable atomic resolution experiments to be performed across the heterointerfaces. Measurements of interface roughness and changes in electronic properties that feed directly into the device design and fabrication effort at Texas Instruments are the goals of this program.

A cryogenic ultrahigh vacuum (UHV) scanning tunneling microscope (STM) is being used to study hydrogen and deuterium desorption from silicon surfaces as a function of temperature. This program augments the recent discovery by Lyding and Hess that deuterium can be used to extend CMOS transistor lifetimes by over an order of magnitude. The goal of this program is to better understand the underlying mechanisms for the isotope effect as well as to shed new light onto hot-electron degradation mechanisms in transistors.

A new ultrahigh vacuum scanning tunneling microscope (UHV STM) system has been constructed to characterize III-V heterolayer structures cleaved in situ. The goal is to provide atom-scale structural and electronic information which can be used to improve the growth, design, and performance of advanced III-V heterolayer devices. Recent results include analysis of ultrathin quantum-well photodiodes from Professor Stillman's group, interband resonant tunneling diodes from Motorola, high electron mobility transistors from Cornell University, and the first cross- sectional STM images of self-organized InAs quantum dots grown at Stanford University.

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Alan Hsu looks through a microscope to conduct an experiment on microwave modulation of a quantum-well laser while Jian Li and Professor S. L. Chuang discuss the modulation response. (Photo: Thompson-McClellan)

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Graduate students Daniel Cronin (left) and James Frame use an ultrasonic mill as part of the fabrication process for an integrated optical switch. (Photo: Thompson-McClellan)

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Members of the applied computation theory group examine new features of Mallard, a Web-based educational tool developed by the group. Clockwise from left are Professor Michael Loui, Mike Swafford, Bevan Das, Professor Donna Brown, Charles Graham, and Maiko Covington. (Photo: Thompson-McClellan)

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Members of the Sunrayce solar-powered vehicle project test the electrical circuits and mechanical structure of a prototype chassis. (Photo: Thompson-McClellan)

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A sample for a nanofabrication experiment using scanning tunneling microscopy is prepared by graduate student Sang-Yeop Lee (Photo: Thompson-McClellan)