Description
The final goal of molecular electronics is completing electronic devices by using individual molecules as the basic building blocks. To achieve such a goal, a good understanding of charge transport through individual molecule bridged into electrodes is essential. Despite continuing experimental success in building single molecular wire even single molecular devices, the widespread implementation has yet to occur, more basic research is required.The research presented in this thesis investigates three major questions. The first is a study into the effect of electrode/molecule contact and the conjugation degree of the bridged molecule in the conductance of molecular junction. Here, we have systematically determined the electrical properties of amine and thiol terminated poly(p-phenylene) molecular wires bound either between two gold electrode contacts (Au/Au) or between a gold contact and a graphene electrode (Au/graphene) using STM-I(s) method. We also compared the conductivity of 1,4-benezenedithiol and 1,4-benzene dimethanethiol with Au/Au and Au/graphene contact to explain the effect of molecular conjugation. The experimental results showed that the junction formed with Au/Au electrodes have higher conductance than those formed with Au/graphene electrodes. The measured conductance decays exponentially with an increase in the number of phenyl rings, giving a decay constant that is similar for amine and thiol terminated molecular junctions with Au/graphene system. This work reveals that poly(p-phenylene) chains are similarly coupled to either gold or graphene electrodes, independently of the anchoring group, and that the transport properties are essentially dominated by the intrinsic molecular properties.
After discussing the effect of a series of intrinsic factors, such as anchoring group, electrode materials, and molecular conjugation degree to the conductivity of (single) molecular junctions, the focus was moved to evaluate the stochastic nature of measuring the electronic properties of (single) molecular junctions, which requires to collect large data sets to obtain the full detail of a molecular system. Using the unsupervised data sorting algorithm, the multiple conductance behaviors of chain shape and phenyl based molecular junctions, which are Au/DBDT/Au, Au/TBDT/Au, Au/6MHI/Au and Au/8MOI/Au, have been observed.
With more understanding the principle in construction of (single) molecular junction, the attempts were made to a higher goal of molecular electronics, namely using a single molecule to work as an active electronic component, such as molecular switch and molecular diode, to perform a series of controllable functions. In this study, an electrochemical gating was applied to modulate the current flow through the molecular junction. Here, the conductance behavior of 6V6 has been investigated as a function of potential in an ionic liquid medium with both of Au/Au and Au/graphene contact. A clear “off-on-off” conductance switching behavior was achieved through gating of the redox state when the electrochemical potential was swept. Au/6V6/graphene junctions showed a single-molecule conductance maximum centered close to the equilibrium redox potential.
This research has shown that graphene could be used as a promising electrode material to construct stable (single) molecular junction in both ambient and ionic liquid environments. In addition, this project has shown that when performing molecular electronics measurements among the electrode material, molecule/molecule contacts, conjugation degree of bridged molecules, and the data analysis method are important. At last, the successful electrochemical gating effect indicated the true three terminal molecular electronics can could be realized based on our experimental equipment. Based on this, our group members will further explore the approach of electrostatic ‘gating’ from a third electrode to realize the practical three terminal electronic devices.
| Period | Jun 2021 → … |
|---|---|
| Degree of Recognition | International |