The development of low-temperature scanning tunneling potentiometry (II)

抄録

The surface electrical conductivity is affected by the local defect structures, such as atomic defects and steps. Since the coherence length of electrons becomes longer, quantum and non-local phenomena such as electron localization and confinement effects, in which the properties of electrons as waves become prominent, are expected at low temperature. In order to study these phenomena in nanometer scale, scanning tunneling potentiometry (STP) has been developed, which allows us to directly access the surface transport properties in real-space imaging. This microscope, which is based on scanning tunneling microscopy (STM), enables us to make an image of topograph and electrochemical potential of a sample surface simultaneously with atomic scale special resolution and uV level high potential sensitivity under the current flowing parallel to the sample surface. An STP is thus quite powerful for elucidating the mechanism of the surface conductivity and local distribution of resistance in the atomic scale. So far, however, low-temperature STP have not been performed so much on clean surfaces that hold metallic surface states, which can be fabricated by the deposition of metal elements on semiconducting substrates. In spite of expected stable performance and reduced leak current through the substrate, which makes the data analysis simple, LT-STM was hard to be operated because of technical difficulties.

In order to investigate the surface state conductivity and to capture their quantum and non-local phenomena, we have developed low-temperature (LT) ultrahigh-vacuum (UHV) STP on a step-by-step basis. Firstly, by implementing an STP circuit we developed [1,2] to an existing room-temperature(RT) UHV-STM system, and the STP observations on the Si(111)-7x7 surface at RT have been achieved [2]. At the next step, we improved the circuit and installed it to an existing LT-UHV-STM whose lowest temperature is ~4.2K and succeeded in STP measurements on the striped incommensurate (SIC) phase of Pb/Si(111) surface at T=18.4K (Fig.1). In this presentation, we'll report on the progress of the development of LT-UHV-STP.

[1] M. Hamada and Y. Hasegawa: Jpn. J. Appl. Phys. 51 (2012) 125202.

[2] M. Hamada and Y. Hasegawa: Phys. Rev. B 99, 125402 (2019).