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Friday, 09 January 2015

A step further in the application of the Raman thermometry

Two-Laser Raman Thermometry is a new contactless technique to study the properties of a material at a nanoscale with higher precision. The two-laser approach has been developed by the researchers of ICN2 Phononic and Photonic Nanostructures Group.

The Institut Catala de Nanociencia i Nanotecnologia (ICN2) group at the head of this investigation is the Phononic and Photonic Nanostructures Group (P2N) led by ICREA Research Prof. Clivia Sotomayor. Dr. Emigdio Chavez, member of the P2N Group, presented recent results of the Group at a Winter School Seminar about Advanced Thermal Metrologies held in December 2014 in Fréjus, France. The present article is based in two papers in APL Materials and Review of Scientific Instruments, with Dr. Emigdio Chavez among the first authors.

Raman Effect takes place when light impacts over an atom layer and excites the material. It absorbs the energy and re-emits a photon. If the re-emitted photon has the same energy as the incident one the process is called Rayleigh or elastic scattering. On the contrary, if the photon has different energy its name is Stokes or anti-Stokes scattering. Consequently, in the last two cases, the photons emitted from the studied sample have a different frequency than the incident ones. Raman scattering is related to this behaviour. Usually, this phenomenon is strongly related to vibration, rotation or electronic effects. In the same way, vibration is related with parameters as symmetry, strain or temperature that affect the results of the photon scattering.

In the particular case of Raman thermometry, the mentioned relation with temperature is used to study additional characteristics of the sample. Specifically it serves to visualize the type of heat transport that takes place when increasing the temperature of the material. The ICN2 P2N group has developed a new way to measure these characteristics related with temperature. The new device is called Two-Laser Raman Thermometry and it reduces the risk of deviation of the measurements respect traditional Raman thermometry using just one laser. The studied samples have been provided by our collaborators from Technical Research Centre of Finland, VTT, Dr Andrey Shchepetov, Dr Mika Prunnila and Prof. Dr Jouni Ahopelto.

The new technique places the sample between two lasers. The first of them is a static violet laser and its function is to heat the material. The second one can move over the heated sample measuring the spatial distribution of the local temperature through the temperature dependent redshift of a Raman model. It is important to mention that working at a nanoscale implies measurement instruments of a similar size, which represents big challenges for the fabrication processes. The use of a contactless lecture solves this problem because there is no physical interaction with the sample and it does not suffer any damage.

 

Article Reference

 

E. Chavez-Angel, J. S. Reparaz, J. Gomis-Bresco, M. R. Wagner, J. Cuffe, B. Graczykowski, A. Shchepetov, H. Jiang, M. Prunnila, J. Ahopelto, F. Alzina, and C. M. Sotomayor Torres. Reduction of the thermal conductivity in free-standing silicon nano-membranes investigated by non-invasive Raman thermometry. APL Materials 2, 012113 (2014); doi: 10.1063/1.4861796

http://scitation.aip.org/content/aip/journal/aplmater/2/1/10.1063/1.4861796

 

J. S. Reparaz, E. Chavez-Angel, M. R. Wagner, B. Graczykowski, J. Gomis-Bresco, F. Alzina, and C. M. Sotomayor Torres. A novel contactless technique for thermal field mapping and thermal conductivity determination: Two-Laser Raman Thermometry. Review of Scientific Instruments 85, 034901 (2014); doi: 10.1063/1.4867166

http://scitation.aip.org/content/aip/journal/rsi/85/3/10.1063/1.4867166