Guest Speaker Talk: Designing, Measuring and Controlling Molecular- and Supramolecular-Scale Properties for Molecular Devices
Guest speaker: Professor Paul Weiss, UCLA
Monday, January 26, 2009
We welcome PKU/UCLA JRI's guest speaker, Professor Paul Weiss from UCLA to give us a talk on Designing, Measuring and Controlling Molecular.
Professor Lian-Mao Peng, director of Key Laboratory for the Physics and Chemistry of Nanodevices and his research group, Professor Yan Li from College of Chemistry and Molecular Engineering listend to the lecture and had discussion afterwards.
We use molecular design, tailored syntheses, intermolecular interactions, and selective chemistry to direct molecules into desired positions to create nanostructures, to connect functional molecules to the outside world, and to serve as test structures for measurements of single or bundled molecules. Interactions within and between molecules can be designed, directed, measured, understood, and exploited at unprecedented scales. We examine how these interactions influence the chemistry, dynamics, structure, electronic function, and other properties. Such interactions can be used to advantage to form precise molecular assemblies, nanostructures, and patterns, and to control and to stabilize function. These nanostructures can be taken all the way down to atomic-scale precision or can be used at larger scales. We select and tailor molecules to choose the intermolecular interaction strengths and the structures formed within the film. We selectively test hypothesized mechanisms for electronic switching and driven motion by varying molecular design, chemical environment, and measurement conditions to enable or to disable functions and control of these molecules using predictive and testable means. Critical to understanding these variations has been developing the means to make tens to hundreds of thousands of independent single-molecule measurements in order to develop sufficiently significant statistical distributions, comparable to those found in ensemble-averaging measurements, while retaining the heterogeneity of the measurements. We quantitatively compare the conductances of molecule-substrate junctions. We find that the contacts and substrate play critical roles in switching. Switching of rigid, conjugated molecules is due to changes in the molecule-substrate bonds, which involves motion of the molecules and of substrate atoms. We are able to measure the coupling of the electrons of the molecules and substrate by measuring the polarizabilities of the connected functional molecules in high and low conductance states. These polarizabilities are compared to those of other families of molecules and to detailed calculations.