Four-terminal conductivity measurements of damascene copper (Cu) wires with various widths have been performed using platinum-coated carbon nanotube (CNT) tips in a four-tip scanning tunneling microscope. Using CNT tips enabled the probe spacing to be reduced to 70 nm, which is the shortest probe spacing in interconnect wire measurements achieved so far. The measured resistivity of Cu increased as the line width decreased and direct evidence of individual grain boundary scattering was observed when the probe spacing was varied on a scale comparable to the grain size of the Cu wires (∼200 nm).

Abstract. We performed in situ transport measurements of ultrathin Bi(111) films grown on Si(111) surface, with a four-tip scanning tunneling microscope using metal-coated carbon nanotube (CNT) tips. When the distance between the current injection tip (nonmagnetic Pt-coated CNT tip) and voltage tip (magnetic CoFe-coated CNT tip) was smaller than 1 µm, we found a violation of Green's reciprocity theorem which should hold with no spin transport. This was interpreted as a signal of the current-induced spin polarization (CISP) that occurs due to the Rashba spin-splitting surface-state bands of the Bi(111). The result was reasonably in accord with quantitative analyses based on the CISP theory of Rashba systems.

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