Abstract
A novel transient thermal characterization technology is developed based on the principles of transient optical heating and Raman probing: time-domain differential Raman. It employs a square-wave modulated laser of varying duty cycle to realize controlled heating and transient thermal probing. Very well defined extension of the heating time in each measurement changes the temperature evolution profile and the probed temperature field at μs resolution. Using this new technique, the transient thermal response of a tipless Si cantilever is investigated along the length direction. A physical model is developed to reconstruct the Raman spectrum considering the temperature evolution, while taking into account the temperature dependence of the Raman emission. By fitting the variation of the normalized Raman peak intensity, wavenumber, and peak area against the heating time, the thermal diffusivity is determined as 9.17 × 10(-5), 8.14 × 10(-5), and 9.51 × 10(-5) m(2)/s. These results agree well with the reference value of 8.66 × 10(-5) m(2)/s considering the 10% fitting uncertainty. The time-domain differential Raman provides a novel way to introduce transient thermal excitation of materials, probe the thermal response, and measure the thermal diffusivity, all with high accuracy.
Highlights
Raman scattering is applicable for structural characterization of molecular configuration and conformation in chemistry, but is suitable for measuring physical characteristics of materials, such as temperature and stress
The peak intensity, wavenumber (Raman shift) and linewidth of the Raman signal are tightly related to phonon emission, frequency and lifetime [1, 2]
Raman thermometry has unprecedented selective temperature measurement capacity and a very high spatial resolution, normal Raman technology is not able to probe transient temperature variations to achieve the same capacity of the transient electro-thermal (TET) technique
Summary
Raman scattering is applicable for structural characterization of molecular configuration and conformation in chemistry, but is suitable for measuring physical characteristics of materials, such as temperature and stress. To precisely determine the temperature in the previously mentioned investigations of interface energy coupling, additional calibration was needed to build the relation between peak position, linewidth, intensity and temperature. We will develop a new Raman technology to probe the temperature evolution of a sample under well-defined heating, and to determine the sample’s thermal diffusivity. Raman thermometry has unprecedented selective temperature measurement capacity and a very high spatial resolution, normal Raman technology is not able to probe transient temperature variations to achieve the same capacity of the TET technique. A brand-new and compelling transient thermal probing and characterization technology is developed based on Raman thermometry and our TET concept: time-domain differential Raman (TD Raman) This new technique overcomes the drawbacks of other techniques listed above and is able to accurately measure the thermal diffusivity of materials. Physical and mathematical models are developed to relate the measured Raman spectrum to the temperature evolution of the sample, and use this information to determine the sample’s thermal diffusivity
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