Electric Behaviors of Metal String Complexes and Metal-String Modified Gold Clusters: Fabrication of Single-Molecule Transistors by Electromigration
Date Issued
2010
Date
2010
Author(s)
Kuo, Chun-Ting
Abstract
The goals of this research focus on the understanding of the dielectric constant and the single-molecule conductance of EMACs (extended metal-atom chains). Firstly, the dielectric constant of EMACs will be explored by the measurements of DPV (differential pulse voltammetry) for Au MPCs (monolayer-protected gold cluster) exhibiting quantized double-layer charging (QDL) which is dictated by both the core size and the dielectric constant of capping ligands. EMACs is place-exchanged with triphenylphosphine-modified Au MPCs, [Au101(PPh3)21Cl5], and DPV gives the capacitance of EMAC-capped MPCs and hence the dielectric constant of EMACs. However, the diameters of Au MPCs become polydisperse during exchange reactions, making the estimated dielectric constant unreliable. To keep unchanged the size of Au MPCs during exchange reactions, systematically examined factors are the concentration, chain length, and a range of headgroups of incoming ligands. The results suggest that the size evolution of Au MPCs is determined by the strength of headgroup–Au adsorption.
For the exploration of single-molecule conductance, we fabricate single-molecule transistors by e-beam lithography and electromigration. The energy alignment between the electronic level of EMACs and Fermi level of electrodes can be achieved via the gate voltage. Preliminary results for [Ni3(dpa)4(NCS)2] show transistor-like behaviors. A color scale plot of conductance as a function of the bias voltage (VSD) and the gate voltage (VG) was obtained to help us to realize the molecular orbital levels. This technology can be utilized to investigate the electric properties for EMACs with metal centers such as Co, Cr, and Ru. This information will provide a comprehensive understanding concerning the correlation between the electronic structure of a molecule and its conductance.
Subjects
Au MPCs
QDL
SMT
EMACs
Type
thesis
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