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.

Ag(40 wt%)-Pd(60 wt%) alloy has been widely applied to contact materials installed in various electromechanical devices. However, in application to the down sized relays, failure due to contact resistance is caused easily by both growth of oxide film on the contact surface and low contact force. To solve the increase in contact resistance, an overlay of thin Au or thin Au-Ag (8-10 wt%) has been used on the alloy. Despite this, cleanliness and low hardness of these overlays cause adhesion, or sticking, at contact interface. Increase in contact resistance and sticking are contrary to each other. In order to eliminate these contrary properties, the author studied improving the Ag-Pd alloy with a dopant. Low level of contact resistance for both static and dynamic contacts of Ag-Pd with Mg doping was found even if the contact surface was covered with an oxide contaminant film. This paper presents the excellent contact resistance and adhesion behaviors of Ag-Pd-Mg alloy and their mechanisms, and also presents in the later part, surface contamination behaviors for organic gases.