Charge transport of alkanethiol self-assembled monolayers on Au(111)

Foundry Users: Prof. Jaume Veciana i Miró, Dr. Imma Ratera, Institut Català de Nanotecnologia

The use of molecules as building blocks of electronic devices is potentially promising for technological applications such as organic light emitting diodes (OLEDs), solar cells, and single molecule devices. Alkane chains, a well-characterized system ideal for fundamental studies, are known to have large electronic gap between frontier states, and electron transport has been shown to occur via a tunneling mechanism . When such molecules are placed between electrodes the junction resistance changes exponentially with electrode separation. In most experiments, the electrode separation is varied through the use of alkyl chains of different lengths. However, for fixed length, the manner in which the conductance varies with tilt angle is largely unexplored. Using AFM, an applied load on the nanocontact can be used to vary the tilt angle of the molecules, permitting the study of resistance and electron transfer as a function of molecular deformation and angle.

In close collaboration with Foundry users Prof. Jaume Veciana i Miró and Dr. Imma Ratera at Institut Català de Nanotecnologia (ICN), and with experimentalists in the Imaging and Manipulation Facility, the electronic transport and electromechnical properties of alkanethoil self-assembled monolayers is being calculated and compared with atomic-force microscopy (AFM) measurements. Through detailed calculations in progress, we will be able to distinguish contributions to the conductance from through-bond and through-space tunneling, and explore the sensitivity of the conductance to changes in S-Au bonding that occur with molecular tilting.