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Acetophenone on Si (100)
  Molecular Physics seminar

Monday 24 February 2014
from 10:00 to 11:00
at FA31
Speaker : Ondřej Krejčí (Molecular Physics Department)
Abstract : One of the main challenges of Molecular electronics is to understand and control charge transfer through a reproducible single molecule contact between electrodes. Most investigations of electron transport through molecules have been performed in “blind” junction experiments, where the molecular conformation and contact geometry cannot be probed. Therefore large gaps in our knowledge remains since in molecular electronics the atomic-scale structure of the entire junction including the leads is important for its conductance properties. Our goal is to study electrical transport through well-defined molecular junction on semiconductor surfaces. Formation of molecular junctions using organic molecules on semiconductor surfaces might lead to interesting phenomena such as negative differential resistance [1]. In this contribution, we investigate formation of molecular junction consisting of a single acetophenone molecule deposited on Si (100) surface in upright position by means of simultaneous AFM/STM measurements and DFT calculations. We used a modified UHV VT STM/AFM Omicron machine allowing simultaneous acquisition of the current and forces with atomic resolution using a tuning fork sensor [2]. At first we preformed simultaneous force spectroscopy and current spectroscopy to identify and to determine the position of the molecule. Here in addition we have an idea now how far the tip is located from the molecule and enable us to have precise control of contact formation. All this can be done only with the guide provided by DFT calculations that gives us better insight into interaction mechanism between probe and molecule. Afterwards, we record Kelvin-force spectroscopy, in which the bias voltage is swept and both frequency shift and the current through the junction are monitored as function of tiop-sample distance. In addition, we performed DFT-based simulations, which allows us to get more insight into ongoing processes along tip approach. Our approach combining AFM/STM/KPFM and theoretical simulations provides complex information about the charge states and charge transport through a single acetophenone molecule on Si(100) surface. [1] T. Rakshit et al. Nanoletters 4, 1803−1807 (2004). [2] Z. Majzik et al, Beilstein J. Of Nanotech. 3, 249 (2012). [3] A. R. Rocha et al. Phys. Rev. B 73, 085414 (2006). [4] N. Fournier et al Phys. Rev. B 84, 035435 (2011).

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