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Energy Dispersive Raman Spectroscopy (with a little help from friends!)

Mario Hofmann discusses his time as Millie's graduate student (2005-2011).

Published onApr 13, 2018
Energy Dispersive Raman Spectroscopy (with a little help from friends!)

Mario Hofmann
Millie’s student 2005-2011, now Nat’l Technical Univ, Taiwan

Energy dispersive Raman…

  • 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

…is hard…

  • 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

Photo courtesy of the Dresselhaus Family

…but Millie helped.

  • Millie heard that our project was not progressing and helped us approach collaborators

  • she put together a proposal and helped with finances

A trip to UFMG…

  • 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.

Paulo Araujo (Prof., Alabama), Leandro Malard (Prof., UFMG), Leonardo Campos (Prof., UFMG), Mario Hofmann (Prof., NTU), Marcos Pimenta (Prof., UFMG) Ya-Ping Hsieh (Prof., Academia Sinica), Cristiano Fantini (Prof., UFMG), Luciano Moura (Prof., UFV), Pedro Pesce.

…leads to discoveries…

  • 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.

…and new ideas!

• 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.

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