Design and Construction of a Scanning Tunneling Microscope for Atomic Scale Imaging of Surfaces in Ultra-High Vacuum

Abstract

The goal of this research project was to design and build a scanning tunneling microscope to be used in the ultra-high vacuum based surface analysis system in the Surface Science Laboratory at Texas State University-San Marcos. The instrument that was constructed is designed to produce atomic-scale images on single crystal samples and to allow transfer of samples to the horizontal manipulator of the system for surface preparation and high-resolution electron energy loss spectroscopy measurements. The outer layer of atoms of most materials either relax or reconstruct, which often results in a change in the electronic, magnetic, and/or chemical properties. Therefore, it is important to be able to characterize the geometric structure of the surface of a material if one is to understand the effect of surface interactions. The main body of the scanning tunneling microscope is constructed from Macor, which is a machinable ceramic. Macor is ultra-high vacuum compatible and has a high strength to weight ratio, low thermal expansion coefficient, and low thermal conductivity, which are all properties desirable for atomic scale imaging. The instrument is mounted on springs with a 13" extension length, which gives it a resonant frequency of less than 1 Hz for vibration isolation. The tube scanner is mounted to an ultra-high vacuum compatible inchworm for coarse and fine approach of the tip to the sample surface. Custom designed analog electronics and software are used to control the instrument.