Scanning chemical potential microscope: A new technique for atomic scale surface investigation

A new microscope, the scanning chemical potential microscope (SCPM), has demonstrated the measurement of thermoelectric potential variations with atomic resolution. These measurements can be attributed to atomic scale variations in the surface chemical potential gradient (∂μ/∂T). This capability was experimentally demonstrated by measuring the thermoelectric voltage produced at the tunnel junction between a tip and a heated sample with a modified scanning tunnelling microscope (STM). Registered images of STM current and thermoelectric voltage were acquired by temporally multiplexing current and voltage data from line to line, providing a direct spatial comparison of current and voltage contrast. The results on graphite and molybdenum disulfide demonstrate that the tunnelling and thermoelectric contrast is spatially different on an atomic scale. The experiments are described, and the results of some first order classical calculations are presented.