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Two-probe scanning tunneling spectroscopy: determination of transconductance in planar atomic structures

AuthorsKolmer, Marek; Brandimarte, Pedro; Zuzak, Rafał; Godlewski, Szymon; Kawai, Hiroyo; Frederiksen, Thomas; Engelund, Mads; García-Lekue, Aran; Lis, Jakub; Joachim, Christian; Sánchez-Portal, Daniel ; Szymonski, Marek
Issue Date2018
CitationInternational Conference on Nanoscience + Technology (2018)
AbstractDue to unprecedented precision reaching picometers scanning probe microscopy (SPM) methods are currently the most popular and reliable tools for local characterization of atomic and single-molecule systems supported on surfaces of solids. However, direct determination of many functional properties, including especially electronic transport in prototypical planar atomic-scale devices, lies beyond the single-probe SPM approach. Recent technical advances provide multi-probe SPM instruments, which are able to operate on the same surface simultaneously with stability comparable to best cryogenic single-probe SPMs. In this work, we describe the full methodology behind atomically defined two-probe scanning tunneling microscopy/spectroscopy (2P-STM/STS) experiments performed on model systems on the germanium (001) surface. Firstly, we discuss our methodology for fine relative positioning of two STM probes on Ge(001) and Ge(001):H surfaces with exact atomic precision and lateral probe to probe distances below 50 nm. That technical results opens possibility of direct testing of on-surface electron transport in atomic-scale systems. Here, it is realized by a novel 2P-STS methodology, in which both STM tips are kept in tunneling conditions above a grounded sample. By applying a small AC component to a varied DC bias voltage on one of the probes and by demodulation of resulting current signals on the second probe, we extract corresponding transconductance dI2/dV1 2P-STS signal. In the case of the Ge(001) surface we show that the detection of transconductance is related to coherent hot-electron transport through quasi one-dimensional π* states of Ge dimer-rows located within bulk bang gap of the surface. Our two-probe experimental results are corroborated by first-principles calculations combining the non-equilibrium Green’s function (NEGF) formalism with density function theory (DFT) in a four-terminal setup.
DescriptionResumen del trabajo presentado a la International Conference on Nanoscience + Technology (ICN+T), celebrada en Brno (Czech Republic) del 22 al 27 de julio de 2018.
Appears in Collections:(CFM) Comunicaciones congresos
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