[MOS] October 7, 2008

[Zina Queen]

Seminar on
Modern Optics and Spectroscopy


Fluorescence Spectra of Single-Walled Carbon Nanotubes:   From 
Discovery to Applications

Bruce Weisman, Rice University,

Tuesday , October 7, 2008

12:00 - 1:00 p.m.



Single-walled carbon nanotubes (SWCNTs) are artificial nanostructures 
composed of carbon atoms covalently bonded into cylindrical tubular 
frameworks with large aspect ratios. They display a range of 
remarkable mechanical, thermal, electronic, and optical properties 
that have attracted intense interest among basic and applied 
researchers. SWCNTs exist in a variety of well defined structures 
differing in diameter and chiral angle. Most of these forms are 
semiconducting, with band gaps that depend on nanotube physical 
structure. A seminal event in SWCNT research was the discovery and 
structural assignment of near-infrared photoluminescence 
(fluorescence) spectra of disaggregated semiconducting nanotubes. 
This spectral assignment process and several subsequent applications 
will be reviewed.  In one application, near-IR fluorescence 
microscopy is used to investigate the photophysical properties of 
individual SWCNTs. Calibrated photometric measurements on selected 
nanotubes provide absolute intrinsic values of fluorescence action 
cross-sections as a function of (n,m) structure. To quantify the 
extrinsic variations in these values, fluorimetric brightness has 
been measured for more than 400 (10,2) nanotubes whose lengths were 
individually deduced from translational diffusion constants 
determined by trajectory analysis. Individual nanotubes were also 
observed in fluorescence microscopy while they were exposed to 
chemical reactants that quench the emission. Stepwise changes in 
emission intensity were clearly observed and identified as 
single-molecule reaction events. Analysis of the step heights reveals 
that each sidewall reactive event quenches excitons in a ~100 nm 
region of the nanotube surrounding the reaction site. Another 
application area involves the development of near-IR fluorimetry into 
a rapid, sensitive, and automated method for quantitative (n,m)-level 
analysis of bulk SWCNT samples. Near-IR fluorescence is also proving 
useful in developing SWCNT biomedical applications. In the first 
observation of nanotubes inside a living organism, SWCNTs have been 
imaged inside fruit fly larvae that had been fed nanotubes in their 
food. Individual nanotubes could be imaged and structurally 
identified inside dissected tissue specimens.



Grier Room, MIT Bldg 34-401
Refreshments served after the lecture
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