Single Molecular Conductance With Different Anchoring Group With NON-AU Electrodes

Molecular electronics was proposed to replace the traditional silicon-based semiconductor electronics, and has been attached much attention. Metal-molecular-metal junctions exhibit novel quantum transport properties, such as negative differential resistance, transistor field effect, storage, switch and so on. This may expected to be applied to the nano-electronics and molecular electronic devices. Conductance measurement of the single molecular junction is one of the most important aspects in molecular electronics. There are several factors which can affect the conductance of single-molecular junctions, such as the intrinsic properties of the molecule, the contact geometries and energy-level alignment of single molecular junctions, the surrounding environment, the kinds of metals and the electrochemical potential. The traditional scanning tunneling microscope-break junction (STM-BJ) is one of the most successful methods in construction of single molecular junctions, however, it also has its limitations in measurement the conductance of single molecular junctions with non-Au electrodes. Here, we use the electrochemical jump-to-contact scanning tunneling microscope break junction approach (ECSTM-BJ) to study several molecules with kinds of anchoring groups. The main works are as follows:1、The single molecular conductance of dipyridines (BPY) with conjugated ethane (BPY-EE) and nonconjugated ethane (BPY-EA) binding to A、Cu and Ag electrodes is systematically studied by using the ECSTM-BJ. All three moleculars have three sets of conductance values and show the order of BPY> BPY-EE> BPY-EA, and Au> Ag> Cu, this may attributed to the different electronic coupling efficiencies between the molecules and the electrodes. Furthermore, we found that the conductance values of pyridyl-based molecules in acidic and neutral solutions are almost the same, which may show that the protonated pyridyl group contacting to the electrode through the deprotonated form.2、The conductance of azo pyridine and pyrazine were measured by using STM-BJ and ECSTM-BJ respectively. The two molecules both show three sets of conductance values, and the conductance of pyrazine is complicated, further experiments and theoretical calculation are needed.3、The single molecular conductance of4-aninobenzonitrile,1,4-dicyanobenzene and4,4’-biphenyldicarbonitrile binding to Cu and Ag electrodes were studied by using ECSTM-BJ. Three molecules all have three sets of conductance values and show the order of1,4-dicyanobenzene>4-aninobenzonitrile>4,4’-biphenyldicarbonitrile. We have found the negative impact of the contact-asymmetry on conductance, which is the same as literature’s results by experiments and theoretical calculation.