Tip-enhanced THz Raman spectroscopy for local temperature determination at the nanoscale
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Local temperature of a nanoscale volume is precisely determined by tip-enhanced terahertz Raman spectroscopy in the low temperature range of several tens of degrees. Heat generated by the tip-enhanced electric field is directly transferred to single-walled carbon nanotubes by heat conduction and radiation at the nanoscale. This heating modulates the intensity ratio of anti-Stokes/Stokes Raman scattering of the radial breathing mode of the carbon nanotube based on the Boltzmann distribution at elevated temperatures. Owing to the low-energy feature of the radial breathing mode, the local temperature of the probing volume has been successfully extracted with high sensitivity. The dependence of the temperature rise underneath the tip apex on the incident power coincides with the analytical results calculated by finite element method based on the tip enhancement effect and the consequent steady-state temperature via Joule heat generation. The results show that the local temperature at the nanoscale can be controlled in the low temperature range simply by the incident laser power while exhibiting a sufficiently high tip enhancement effect as an analytical tool for thermally sensitive materials (e.g., proteins, DNA).
KeywordsIR spectroscopy/Raman spectroscopy Nanoparticles/nanotechnology Bioanalytical methods Laser spectroscopy Thermal methods
We gratefully acknowledge the financial support by the “Grant-in-Aid for Young Scientists A” No. 24686009 (N.H.) from the Ministry of Education, Culture, Sports, Science and Technology of Japan and the ‘Program for Junior Scientists – International Program Associate’ (M.V.B.) from The Institute of Physical and Chemical Research (RIKEN).
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