Motivation:
The energy dissipation of conduction electrons at phonons, atomic steps, grain boundaries etc. contribute to the total resistivity. To get access to these effects scanning tunneling potentiometry [1] was performed on a Si(111)-(√3x√3)-Ag surface superstructure. Due to the boundary condition of the silver layer two dimensional electronic properties may be analysed [2, 3].
Experimental:
Our setup consists of an optimized Omicron-Nanoprobe equipped with three independent STM-units. Two STM-tips were used to contact the silver reconstruction applying a constant lateral current through the Ag adlayer. The third tip simultaneously maps the topography as well as the local potential. By reversing the polarity of the applied current during the measurement the consistency of the data could be checked.
Results:
The STM and simultaneously recorded potential images show a correlation between the topography of the sample and the potential signal. Since the Ag layer directly grows on the silicon terraces each Si step is correlated to a step of the Ag layer. If the current is applied orthogonal to the step edges at each step edge at voltage drop occurs. Hence, the resistivity of a monoatomic step can be determined to about 1x10-13Ωm2. On top of the Ag terraces no significant potential decay is visible. Hence, the potential signal reveals a stepwise characteristic related to the topographic surface steps. Within the resolution limit of the experiment no oscillatory behaviour of the potential can be seen in the vicinity of the step edges. If the current is applied parallel to the steps, voltage drops at grain boundaries of the silver adlayer become visible.
References:
[1] Muralt, P., Pohl, D.W., Appl. Phys.Lett. 48, 5146 (1986)
[2] Hasegawa, S., et al., Jpn. J. Appl. Phys. 39, 3815 (2000)
[3] Matsuda, I. et al. Phys. Rev. Lett- 93, 236801 (2004)
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