We are interested in the electronic properties of organic and organometallic molecules, usually crystallized into self-assembled monolayers (SAMs). The simplest SAMs comprise alkanethiolates; more complex versions have a substituted end group at the non-binding end of the molecules. The electronic properties of a SAM are dependent on the metal substrate on which the SAM forms (Au, Ag, Cu, Pd, Pt, Hg), the head group that binds to the metal (commonly a thiolate), the chemical structure of the chain (alkane, aromatic), and the substituted end group (-COOH, -OH, -CN, etc).

We study SAMs using a two-terminal junction, where one electrode is a mercury drop covered with a standard SAM (usually C12 alkanethiolate) and the other is a sample metal covered with one of a series of SAMs of interest (Figure 1). By using a series of related molecules, we can determine the ease of tunneling across a certain type of molecule (Figure 2). We are interested in understanding the features that will cause a molecule have an unusual current response, such as rectification or negative differential resistance, with the goal of being able to design systems with interesting electronic responses.

Related techniques in the field of organic electronics examine single molecules or molecules in self-assembled monolayers (SAMs) using break junctions, nanopores, conducting atomic force microscopy (cAFM), scanning tunneling microscopy (STM), and three-terminal junctions. The components of the systems vary widely, but there is widespread agreement on the ease of tunneling through a few key types of molecules. The understanding of these relatively simple systems paves the way for the field to broaden into more exploratory and novel systems. The mercury drop junction is an ideal tool for exploratory work due to its ease of use and quick sample preparation time.

Figure 1

Figure 2