A tungsten ribbon and a grounded sample form two electrodes of a vibrating capacitor connected to a sensitive radio frequency capacitance bridge and to a source of dc and ac bias. The ac bias frequency is tuned to the fundamental resonance of the ribbon (f?2.5 kHz, Q≳500) and the work function difference between the ribbon and the sample is determined from the dc bias for which the ribbon capacitance variation at the ac driving frequency vanishes. Work function differences at different positions on a flat sample can be measured to millivolt precision. An example of the change in work function of evaporated Ag–Au alloys with oxygen exposure is given.
REFERENCES
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J. C. Riviere, in Solid State Surface Science, edited by Mino Green (Marcel Dekker, New York, 1969), Vol. 1, p. 179.
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The ribbon tensions used were such that the stiffness was relatively unimportant for the fundamental vibration mode As this mode will have no twisting motion along the ribbon, the formalism for a damped string with no stiffness should provide a good first approximation to the ribbon response. See, for example, P. M. Morse, Vibration and Sound (McGraw‐Hill, New York, 1936), p. 98.
10.
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Reference 7, p. 370.
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Brookdeal Electronics, model 850 or equivalent.
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Brookdeal Electronics, model 464 or equivalent.
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Hewlett‐Packard, model 200 CD or equivalent.
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© 1976 American Institute of Physics.
1976
American Institute of Physics
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