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TFAN UHV System Joins Laboratory Arsenal

May 14, 2009

Carnegie Mellon faculty, students and researchers — including those in the Data Storage Systems Center — have a new instrument to add to their data storage research toolbox: an ultra-high vacuum (UHV) system outfitted with a scanning probe microscope and other surface analysis tools that will aid researchers working on the Tip-Directed Field-Enhanced Nanofabrication (TFAN) project.

The TFAN UHV system, purchased from RHK Technology in Troy, Mich., can reduce atmospheric pressure to 1x10-10 torr and contains four chambers, each playing a unique role and offering different instrumentation for preparing, mapping and — possibly — patterning small surfaces. Each chamber is separated from its neighbors by a gate valve that controls contamination and keeps the pressure of each chamber intact, regardless of what happens in the other chambers.

The system's first chamber is a load lock, effectively a front door where samples can enter and exit the machine without impacting the pressure in the rest of the system. The second chamber — for surface analysis — was manufactured specifically for Carnegie Mellon by STAIB Instruments and houses X-ray photo emission spectroscopy (XPS) and Auger electron spectroscopy (AES) tools for surface analysis. Both instruments allow the user to understand the chemical composition of the surface in precise ways. These techniques are useful for both detecting contamination and ensuring proper surface preparation.

Researchers can also prepare surfaces in the UHV system's prep chamber, which contains specific tools to create a sample with a pristine surface. For example, the prep chamber holds a stage that can heat a sample to 1,250 Celsius to burn off oxides; a mass spectrometer that enables temperature-programmed desorption; an ion source used to clean a metal surface by bombarding it with Argon; and a doser that allows the operator to leak different adsorbate gases into the chamber (e.g., disilane and hydrogen).

The heart of the TFAN system lies in its scanning probe chamber and what its instrumentation could offer for the future of nanotechnology. The chamber houses a combination scanning tunneling microscope (STM) and atomic force microscope (AFM), both traditionally used to image a surface. By using the microscopes at a higher intensity, researchers hope to actually create nanoscale features on the surface. Doing so in an UHV environment means the surface will remain uncontaminated long enough for scientists to actually manipulate the surface.

Lead by principal investigator Electrical and Computer Engineering Associate Professor David Rickets, a team of cross-disciplinary experts hopes to show that tip-directed field emission may be just the technique needed to take nanofabrication to the next level. Ricketts and his team plan to use the TFAN UHV system's capabilities to expose silicon wafers to disilane, which will be adsorbed onto the silicon. They can then place the surface in the probe chamber and use the electrons from the probe tip to remove hydrogen and deposit silicon. By repeating the process numerous times, they hope to generate specific patterns on the silicon surface. This sort of purposeful patterning, which has not yet been done successfully, could open the door to a new world of nanoscale devices.

Joining Ricketts in the investigation are ECE Professor and DSSC Associate Director Jim Bain; Howard M. Wilkoff Professor and Institute for Complex Engineered Systems Director Gary Fedder; Bertucci Distinguished Professor of Materials Science and Engineering Robert Davis; Assistant Professor of Mechanical Engineering Metin Sitti; Assistant Professor of Chemical Engineering, Materials Science and Engineering and Physics Mohammad Islam; and postdoctoral researcher Joshua Smith.



Data Storage Systems Center / Pittsburgh, PA 15213-3890 / Phone: 412-268-6600 / Fax: 412-268-3497