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Two-probe STM/STS experiments performed on atomic wires and single molecules supported on Ge(001) surface

AuthorsKolmer, Marek; Brandimarte, Pedro; Zajac, Lukasz; Godlewski, Szymon; Kawai, Hiroyo; Frederiksen, Thomas; Engelund, Mads; García-Lekue, Aran; Lorente, Nicolás ; Lis, Jakub; Echavarren, Antonio M.; Joachim, Christian; Sánchez-Portal, Daniel ; Szymonski, Marek
Issue Date2018
CitationEuropean Symposium on Surface Science (2018)
AbstractDue to unprecedented precision reaching sub-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 and spectroscopy (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 a planar geometry. It is realized by a novel two-probe STS (TP-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 both of the probes, we extract corresponding dI1/dV1 (single-probe, vertical) and dI2/dV1 (two-probe, planar) STS signals. In this case of Ge(001) we show that the detection of TPSTS signal is related to quasi-ballistic hot-electron transport through one-dimensional π* states of Ge dimer-row wires located within bulk bang gap of the surface. Our two-probe experimental results are corroborated by first-principles calculations combining the nonequilibrium Green's function (NEGF) formalism with density function theory (DFT) in a fourterminal setup. Finally, we present a non-local switching of single trinaphthylene molecule adsorbed on Ge(001) surface. The switching is induced by hot electrons injection into discussed π* states of Ge dimer-rows. Here by taking the advantage of two-probe STM configuration we observe “in-situ” non-local molecule switching using one of the probes as a source of hot electrons injected into surface states and the other as a detector of a molecule motion.
DescriptionResumen del trabajo presentado al Symposium on Surface Science (3S), celebrado en St. Christoph am Arlberg (Austria) del 25 de febrero al 10 de marzo de 2018.
Appears in Collections:(CFM) Comunicaciones congresos
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