[MOS] April 22, 2008

[Zina Queen]

Seminar on
Modern Optics and Spectroscopy


Martin Gruebele,
University of Illinois Urbana-Champaign

STM-assisted single molecule absorption spectroscopy

APRIL 22, 2008

12:00 - 1:00 p.m.
Grier Room 34-401


Scanning tunneling microscopy provides exquisite spatial resolution, 
but only moderate energy resolution via current-voltage derivative 
curves.  Absorption spectroscopy can resolve individual molecular 
energy levels, but usually provides no spatial information.  We 
combined the two techniques by using an STM tip to detect the 
electron density change when a molecular absorption line is 
resonantly excited by a laser.  There are plenty of technical 
difficulties, beginning with laser heating effects, and I show how 
they can be overcome by combining laser frequency modulation, rear 
illumination, tip field enhancement, and lock-in detection of the STM 
current signal.  The results is a technique that simultaneously 
returns topographic images and absorption spectra with sub-molecular 
resolution.  The ability to tell where a macromolecule actually 
absorbs can be usefully applied, for example to detecting defects in 
the molecule invisible in ordinary STM scans.  Future applications to 
energy transfer from one quantum dot to another will also be 
discussed, along with ultrathin gold surfaces needed to satisfy the 
requirements of both STM and absorption spectroscopy.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://mailman.mit.edu/pipermail/mos/attachments/20080418/405e8b2c/attachment.htm