WEDNESDAY 10:00
INFLUENCE OF SURFACE COVERAGE ON THE FORMATION OF 4,4’-BIPYRIDINIUM (VIOLOGEN) SINGLE MOLECULAR JUNCTIONS
Henrry M. Osorio, Santiago Martín, David C. Milan, Alejandro González-Orive, Josef B. G. Gluyas, Simon J. Higgins, Paul J. Low, Richard J. Nichols, and Pilar Cea.
ABSTRACT
Molecular electronics is an emergent technology in which organic, inorganic or organometallic molecules are connected between two (or three) electrodes, and their electrical properties are harnessed to perform some useful function that can translate to enhanced or novel performance in an electronic device. The study of single molecule junctions has greatly contributed to the understanding the influence of different parameters (backbone structure, solvent environment, electrode material, nature of the electrode-molecule contact, etc.) on charge transport phenomena at the molecular scale. In turn, studies of larger area metal–molecular monolayer–metal junctions (in which molecular components are assembled into a well-defined, high surface coverage and usually well-characterized monolayer film within the junction) play a further crucial role in understanding the effect of intermolecular interactions, such as van der Waals interactions and polarization effects, on the electronic transport properties of the molecular film.
Both single molecule and molecular film experiments are relevant for molecular electronics experiments; however, it is not yet clear how, or if, the changes in molecular geometry and orientation that can be expected to occur upon increasing surface coverage of molecular components from truly isolated single molecules to more densely packed and ordered films can influence the electrical response of a junction. In this context, a comparative study of molecules within both single molecule junctions and well-ordered films offers additional challenges and avenues for exploration that have not been explored to date. In this contribution, single-molecule junctions of the viologen derivative, N,N’-di(4-(trimethylsilylethynyl)benzy)-4,4’-bipyridinium, 12+, have been formed from both dilute solution, leading to low surface coverage, and well-ordered and tightly-packed LB films. The electrical properties from the single molecule junctions of 12+ on the surface and well-ordered films reveal two distinct conductance values. Experiments reveal that these different conductance values can be attributed to different molecular configurations and contacts within the junction (Figure 1). Both types of molecular contact are observed from for junctions formed from the isolated molecules, but in the case of the LB film-based junctions, only the more compact, viologen (V2+)-contacted junction has been observed.