Local density of states effects at the metal-molecule interfaces in a molecular device

Abstract

Clarifying the nature of interactions between metal electrodes and organic molecules still represent one of the challenging problems in molecular electronics that needs to be solved in order to optimize electron transport through a molecular device. For this purpose, electronic properties at metal-molecule interfaces were studied by combining experimental and theoretical methods. Applying a novel electrochemical approach, strictly two-dimensional Pd islands were prepared on top of 4-mercaptopyridine self-assembled monolayers (4MP-SAMs) which, in turn, were deposited on (111)-oriented Au single crystals. Electron spectroscopy together with density functional theory calculations revealed strong interactions between the molecules and the islands due to Pd-N bonds, resulting in a drastically reduced density of states (DOS) at the Fermi level EF for a nearly closed Pd monolayer, and even non-metallic properties for nanometre-sized islands. Similarly, a significantly reduced DOS at EF was observed for the topmost Au layer at the Au-SAM interface due to Au-S interactions, suggesting that these effects are rather general.

Chemical Interactions at Metal/Molecule Interfaces in Molecular Junctions—A Pathway Towards Molecular Recognition

“…In situ STM has also been employed to characterize the structure of the electrodeposited Pd on the 4-ATP adlayer, as shown in Figure 2c. Like in former studies on Pd overlayers on top of 4-mercaptopyridine SAMs, [7,8,13,14] monoatomic height islands are seen in line-scans (not shown here), which finally can be assigned to Pd islands on top of the 4-ATP adlayer (see below). However, unlike in former studies where the maximum coverage for one single complexation step was about 30%, we now observe a coverage twice as large, namely 60% of a full monolayer.…”

Progress with Molecular Electronic Junctions: Meeting Experimental Challenges in Design and Fabrication

“…[81] In addition, examination of molecules on conductors with photoelectron spectroscopy has shown that the orbital energies and tunneling barrier derived from them can be significantly modified by broadening and electronic coupling with the contacts. [7,116] An elegant application of a mesoscale cpAFM experiment appeared recently, for the case of conjugated molecules of variable length. [82] A layer by layer synthesis produced oligophenyleneimine (OPI) molecules of various lengths bonded to Au through a thiolate linkage (Fig.…”

Electrodeposition of gold templated by patterned thiol monolayers

“…The principle has been demonstrated for uniform thiol SAMs featuring tail groups which coordinate metal ions [74][75][76][77][78][79]. Upon reduction of the ions the metal forms 2D or 3D clusters on top of the SAM.…”

“…Furthermore, if the ions are discharged at the outer surface of the SAM which is accomplished by coordinating the ions to the terminal group of the SAM, the neutral metal species do not penetrate but diffuse at the SAM/electrolyte interface to form 2D islands and 3D clusters on top of the SAM [74][75][76][77][78][79].…”