Room Temperature Gold-Vacuum-Gold Tunneling Experiments

Abstract

Preface Number 4An experiment has been completed which demonstrated quantum mechanical tunneling of electrons between two gold electrodes separated in vacuum. The tunneling current between the gold electrodes has been measured, for fixed voltages of 0.1 and 0.01 volts, as the electrode spacing was varied from a distance of approximately 2.0 nm down to a point where the electrodes touched. Current changes of over five orders of magnitude were found for electrode spacing changes of approximately 1.2 nm. For the first time, these data enable one to deduce the work function of the electrodes in a tunneling experiment from experimental parameters independent of the tunneling device. Also obtained were current-voltage characteristics for fixed electrode spacings in the direct tunneling region where electrode spacings were less than 2.0 nm. An analysis is given which attempts to deduce an absolute electrode spacing and tunneling area from the nonlinear properties of the I-V data and the curJuly-August 1986 rent versus spacing data. The analysis suggests that van der Waals and electrostatic forces playa major role in determining the I-V characteristics and that the tunneling area may be as small as 10-16 m 2 • Along with a review of the theory of work functions and quantum mechanical tunneling, numerical calculations of the tunneling current based on the free-electron model of the electrodes and the barrier, an image-potential reduced barrier, and a WKB approximation for the tunneling probability have been performed and compared with Simmons' theory and with the experimental results.Key words: metal-vacuum-metal tunneling; point-contact diode; scanning tunneling microscopy; temperature control; tunneling theory; vacuum tunneling; vibration isolation; work function Accepted: April 24, 1986 The following paper is a reproduction of the author's dissertation which was completed and submitted to North Texas State University in August 1978. A majority of the experimental work was performed at the National Bureau of Standards. Results from the experiments were first reported at the Spring 1978 APS meeting and later at a National Science Foundation Workshop on Opportunities for Microstructures Science, Engineering, and Technology held in Airlie, VA, November 19-22, 1978. While a complete description of the experiments and results is available as a publication from University Microfilms, pUblication in the more accessible form represented here has been prompted by requests from colleagues and by the significant number of recent references to the work. In accordance with the requests, the Board of Editors of the Journal of Research has agreed to publish the document unchanged except for the adAbout the Author: E. Clayton Teague is with the Center for Manufacturing Engineering in the NBS National Engineering Laboratory. dition of footnotes to identify recent work to which it is closely related. Renewed interest in these experiments has primarily resulted from the success and current widespread use of the scanning tunneling mic...

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