学术讲座
题目:
(1) Single Molecule Switching and Sensing
(2) Ultrabroadband vibrational spectroscopy and dynamics at aqueous interfaces
讲座人:
Prof. Eric Borguet
Temple University, USA
时间:
4月11日（周四）上午10:00-12:00
地点:
卢嘉锡楼202报告厅
报告摘要：
报告一：Single Molecule Switching and Sensing
Charge transport through and between molecules is central to important processes in nature. Studying the conductivity of single molecules can contribute to a better understanding of charge transport, and also help develop building blocks of molecular electronics, light harvesting devices, etc. We measure the conductivity of molecules using the Scanning Tunneling Microscope break-junction (STM-BJ) method that utilizes repeatedly formed circuits where one or a few molecules are trapped between two electrodes, at least one of which has nanoscale dimensions. The statistical analysis of thousands of measurements yields the conductance of single molecules.
One particular interest is the role of the molecule-electrode contact in charge transport. In the simplest analysis this contact can present a substantial barrier to charge injection, which can have important consequences in devices such as dye sensitized semiconductor nanoparticle solar cells. We have demonstrated that carbodithioate termination of molecules can enhance conductivity by an order of magnitude. We have also shown how the sensitivity of the electrical conductivity of single molecules to external perturbations can allow for switching and sensing,as well as the use of single molecule conductance for the discovery of novel materials.Our most recent developments include controlling the orientation of the molecule in the junction so that we can measure conductance along different molecular axes, accessing elements of the anisotropy of the single molecule conductance tensor.
报告二：Ultrabroadband vibrational spectroscopy and dynamics at aqueous interfaces
Interfacial water structure is key to many chemical and physical processes. It can be probed by vibrational sum-frequency generation (vSFG) spectroscopy as well as ultrafast time-resolved vSFG. The use of ultrabroadband IR pulses enables interfacial vibrational dephasing to be probed, revealing the presence of multiple OH species as well as their relative orientations. However, a more complete microscopic understanding requires additional techniques such as molecular dynamics simulations. Our experiments show that in the absence of surface charge (pH 2), water at silica surfaces exhibits significantly slower OH stretch vibrational relaxation (~600 fs) compared to bulk water. However, at charged silica surfaces (e.g., pH 6), bulk-like fast dynamics (~200 fs) are observed at low ionic strength. This decelerates to ~600 fs with the addition of NaCl. In parallel, vSFG results demonstrated that silica interfacial water structure is most sensitive to ions at pH=6-8, correlating with the known salt and pH dependence of silica surface reactivity. Consequently, it is unclear whether the observed slowing of the vibrational dynamics is due to the reduction in the Debye length, or because of changes in the local hydrogen bonding environment caused by the electrolyte and how this might depend on the identity of the ions or the solid surface. The combination of molecular dynamics simulations with spectroscopic and time-resolved vSFG experiments on aqueous Al2O3 interfaces sheds light on the ongoing debate on the role of ions in interfacial water structure and whether behavior observed silica/water interfaces is specific to that system or can be generalized to other aqueous interfaces.
嘉宾介绍：
Eric Borguet教授主要从事单分子电子学、等离激元、非线性光学、纳米材料等研究，迄今在Nature Commun.、J. Am. Chem. Soc.、Angew. Chem. Int. Ed.、ACS Nano、J. Phys. Chem. Lett.等发表论文100余篇。论文被引4000余次，H因子44。
biwn必赢
2019年4月3日
