Doctoral Dissertations

Date of Award

8-1995

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Physics

Major Professor

Tom Callcott

Committee Members

Ed Arakawa, Tom Ferrell, Bruce Warmack

Abstract

Photon scanning tunneling microscopy in the ultraviolet and soft x-ray regions is investigated. In the ultraviolet region a photon scanning tunneling microscope (PSTM) has been created by slightly modifying the visible PSTM. Improvements in resolution with decreasing wavelength are shown in images obtained with constant probe size.. Comparisons between signals in the visible and ultraviolet region are discussed, and probe geometries beneficial to increasing signal-to-background and signal-to-noise ratios are introduced. The ultraviolet PSTM expands the capability of the PSTM by improving resolution and making a larger photon spectrum available for spectroscopic and experimental applications.

In the soft x-ray region a PSTM has been constructed, and experiments have been performed to investigate the feasibility of creating a soft x-ray PSTM capable of imaging with subwavelength resolution. Special PSTM components were developed for the soft x-ray region. A freestanding thin-film grating provides a method of creating total internal reflection at the L23-shell absorption edge of aluminum, and phosphor-coated fiber optic probes permit submicron area detection of soft x-rays. With synchrotron radiation a periodic soft x-ray evanescent field was created on the surface of the thin-film grating and mapped with the soft x-ray probe. The demonstration of total internal reflection in the thin-film grating and frustrated total internal reflection to the soft x-ray probe provides a basis for further research in the soft x-ray region.

The spectroscopic potential of the PSTM increases as the PSTM operates over a wider photon range. Elemental spectroscopy with the scanning electron microscope (SEM) has been investigated for comparison with and consideration of spectroscopy with the PSTM. The elemental spectroscopic range of the SEM has been extended by observing soft x-ray emission from light elements. During normal SEM operation the concentration of light elements is spatially mapped by monitoring the emission of characteristic soft x rays with a grazing-incidence spectrometer. Experimental soft x-ray yields for the light elements are given and compared with theoretical calculations.

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