Optical and Tunneling Microscopy and Spectroscopy at the Ultimate Spatial Limit

Combing photon with STM: My main research topic is to study both optical and electron tunneling spectroscopic properties of single molecules at the spatial limit by combining optical methods with scanning tunneling microscope (STM). With this combination, both laser irradiation and photon detection are  executable in this configuration. 

STM induced photon emission:  In my experiments, the spatial resolution of STM-luminescence signal is far below diffraction limit and down to sub-Ångstrom level. With this resolution, individual vibronic transitions were imaged in real space and even quantum phenomenon associated with the radiative transition between electronic states was directly visualized.

Molecular motion and tunneling spectroscopy: I also studied the single bond rotation and flipping motion of small pro-chiral molecules on surfaces.  In addition, tunneling spectroscopies of various molecules are routinely carried out to characterize the electronic properties at single molecule level.

Construction of sub-Kelvin STM (Apr/2003-Oct/2005): This was my "training project" when I first joined the group. Please click here to see what I have done. I learned how to do machining work,  electronics and instrument interface during this period. Thanks for Xi and Ungdon so that I became what I have never imagined about myself before. 

In the two years of graduate research, I worked with Dr. Juen-Kai Wang in the area of ultrafast dynamics and devoted all my time to work on the thesis "Photophysics and Photochemistry of Distyrylbenzene - Iosmerization Dynamics". This DSB molecule is interesting not only because its high luminescence efficiency but also acting as an extension of photoisomerization of stilbene. The final target of this study is to measure isomerization rate of DSB isomers.  From synthesis, separation, spectroscopy work (including absorption, fluorescence, IR, Raman, lifetime and quantum yield), kinetics and femtosecond pump-probe measurements, each step challenged my experimental skill and patience.

     Undergraduate Research (1997-1999)

 In my junior and senior year, I joined Dr. Juen-Kai Wang‘s research plan: "vibrational Spectroscopy of Hydrogenated Semiconductor Surfaces".  In addition to the surface Raman spectroscopy method, collection of extremely weak signal, complex data fitting and analysis also benefited me a lot in latter research.