Correlation between Contact Resistance Characteristics and Scanning Tunneling Microscopy Images for Ag-Pd Alloy with Some Example Additives

Terutaka TAMAI  

Publication
IEICE TRANSACTIONS on Electronics   Vol.E88-C   No.8   pp.1559-1565
Publication Date: 2005/08/01
Online ISSN: 
DOI: 10.1093/ietele/e88-c.8.1559
Print ISSN: 0916-8516
Type of Manuscript: Special Section PAPER (Special Section on Recent Development of Electro-Mechanical Devices--Selected Papers from International Session on Electro-Mechanical Devices 2004 (IS-EMD2004)--)
Category: Contact Phenomena
Keyword: 
STM,  contact resistance,  Ag-Pd-Cr alloy,  Ag-Pd-Mg alloy,  

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Summary: 
Scanning tunneling microscopy (STM) images indicate a change in tunnel current. The tunnel current strongly depends on the applied voltage between the specimen surface and a probe tip, and also on the work function of the specimen surface. Therefore, STM images are different from optical images. Under a certain applied voltage, the distribution of the work function on the surface is directly related to the image. In the present study, in order to understand the STM images obtained from the contact surface, example surfaces of Ag-Pd alloys with Mg and Cr additives were investigated by STM. The additives are easily oxidized, and their oxides distribute over the surface. Therefore, the effect of the additives on the STM images could be observed. For Ag-Pd-Cr, in the case of both clean and oxidized surfaces, the Cr oxides CrO and Cr2O3 formed on the surface are typical insulators, and sharp projections, such as needles, can be seen in the images which are very different from optical microscopy image. In addition, a high contact resistance was measured. On the other hand, for Ag-Pd-Mg, MgO formed on the surface was conductive, and a smooth surface was obtained, as evidenced by the STM image. Contact resistance was very low. Even if the oxides grew under heating, the same tendencies were observed. The conductivity of oxides on the surface had a great effect on the images obtained. A correlation between the contact resistance and the STM images was found.