Mario Hofmann discusses his time as Millie's graduate student (2005-2011).
Millie’s student 2005-2011, now Nat’l Technical Univ, Taiwan
Raman intensity increases dramatically if excitation energy matches band structure
“resonance windows” can reveal details about electronic structure and phonon interactions
energy dispersion is a fingerprint for each nanotube and can be applied in nanotube metrology
to obtain information on resonance windows, Raman spectra at many different laser excitation wavelengths have to be collected
laser has to be tuned to each wavelength and its intensity optimized
organic dyes are used as excitation sources
dirty, tedious, and complicated process
Millie heard that our project was not progressing and helped us approach collaborators
she put together a proposal and helped with finances
3 of Millie’s students got to travel to Belo Horizonte, Brazil, and overall spent 2 months at UFMG in Prof. Marcos Pimenta’s lab
during that time we used the colortunable Raman system for energy dispersive Raman investigation of individual nanotubes
the UFMG team changed the dye 6 times for us
we learned a lot about the operation and optimization of the dye laser (it’s all in the dye circulation system)
it’s still messy and tedious
But the nice company helped in forgetting the countless hours staring at the spectrograph.
our results were the first systematic study of the resonance windows of individual nanotubes
we observed that the RBM window was surprisingly narrow
Also, there seemed to be a clear difference between metallic and semiconducting nanotube families.
The G-band resonance window remained incomplete.
• we learned that the dye circulation system was the bottleneck for efficient operation
• so we updated our system to have 3 separate dye circulators that could be switched quickly
• it just took 3 pumps and a few connectors from a plumbing store
Following generations of MIT students had access to more laser lines and dye types for important studies on double and triple-wall nanotubes.