Correlation of adhesion force and electrical conductivity in Magnéli-type vanadium oxides and highly oriented pyrolytic graphite

A correlation of adhesion force and electrical conductivity is established for a vanadium oxide and highly oriented pyrolytic graphite (HOPG). Adhesion forces were determined by analysis of pull-off forces obtained from force–distance curves with atomic force microscopy in ultrahigh vacuum, on clean surfaces and with defined contact conditions. The investigated samples include (i) different stoichiometries of Magnéli-type vanadium oxides (V3O5, V4O7, V6O11, and V7O13), which undergo metal-insulator-transitions as a function of temperature, (ii) the (0001) basal plane and the (10–10) prism plane of highly oriented pyrolytic graphite (HOPG), which differ in their respective perpendicular-plane electrical conductivities by several orders of magnitude, and (iii) the (100) surfaces of pure metal single crystals, i.e., silver (Ag), copper (Cu), iron (Fe) and gold (Au). It is shown, that the vanadium oxides as well as the graphite exhibit significantly lower adhesion forces in their electrical conductive state than in their non-electrical conductive state. The values obtained for the electrical conductive states are quantitatively confirmed by the measurements on the single crystal metals.