Relentless downscaling of conventional electronic devices demands continuous improvement in characterization of microscopic surface electronic properties. Moreover, in the pursuit of more exploratory device concepts such as atomic-scale logic gates [1] and memories [2] composed of dangling bonds on hydrogen-terminated Si surfaces there is great need for characterization of extremely small one- and two-dimensional structures. To assess the electrical conduction properties lateral to the surface two-probe (2P-) and four-probe (4P-) scanning tunneling microscope (STM) has been developed [3]. The measurement of conductance with 4P-STM is generally preferred over 2P-STM as it can eliminate the uncertainty in the probe-to-surface contact resistance. However, if we can solve the issue of the high resistive contact resistance with 2P configuration, we would be able to measure surface conduction with the minimum number of independently movable probes, reducing arduous tasks in this field. In this seminar, we will discuss the refinement of 2P-STM for surface conduction measurements by Ohmic contact between probe and surface [4]. We also utilized STM lithography to create electronically isolated regions from the otherwise surface area, finding that we can measure their conduction properties correctly by the Ohmic 2P-STM. Since the probe-to-probe distance can be reduced down to 30 nm, the present method will be useful in a wide range of fields of material sciences.

References:
[1] T. Huff et al., Nat. Electron. 1 (2018) 636.
[2] R. Achal et al., Nat. Commun. 9 (2018) 1.
[3] B. Voigtländer et al., Rev. Sci. Instrum. 89 (2018) 101101.
[4] J. Onoda et al., ACS Nano (2021) in press; DOI: 10.1021/acsnano.1c05777.

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