Fermi level alignment in molecular nanojunctions and its relation to charge transfer

Robert Stadler, Karsten Wedel Jacobsen

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Abstract

The alignment of the Fermi level of a metal electrode within the gap of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of a molecule is a key quantity in molecular electronics, which can vary the electron transparency of a single-molecule junction by orders of magnitude. We present a quantitative analysis of the relation between this level alignment (which can be estimated from charging free molecules) and charge transfer for bipyridine and biphenyl dithiolate (BPDT) molecules attached to gold leads based on density functional theory calculations. For bipyridine the charge distribution is defined by a balance between electrostatic repulsion effects and the filling of the LUMO, where the molecule loses electrons to the leads. BPDT, on the other hand, gains electrons. As a direct consequence the Fermi level of the metal is found at the energetically higher end of the gap in the transmission function for bipyridine and at its lower end for BPDT.
Original languageEnglish
JournalPhysical Review B Condensed Matter
Volume74
Issue number16
Pages (from-to)164105
ISSN0163-1829
DOIs
Publication statusPublished - 2006

Bibliographical note

Copyright 2006 American Physical Society

Keywords

  • TRANSPORT
  • CONDUCTANCE
  • BAND LINEUP
  • ELECTRONIC DEVICES

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