Conditions inducing reliable transient gratings of a LaCoO 3 thin film using transient grating technique
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First, a grating decay rate and a thermal diffusion rate of the transient gratings are determined out of the energy-time trace observed by using a transient grating technique with 266-nm laser pulse inducing transient gratings in a LaCoO3 thin film. Second, the grating models aimed at studying two different thermal diffusion phenomena in contrast with the previous paper are described. The difference between both phenomena is attributable to the volume of photon scattering to characterize induced transient gratings. It is concluded that a reliable energy-time trace is observed when the transient gratings with a thickness smaller than a film are induced on the very surface of a thin film sample.
The transient grating techniques1–3 in solid-state physics, based on observations and theories of grating decay rate of induced transient gratings in the thin film, represent the most promising nanometer-scale observation method from the standpoint of being able to evaluate the thermal diffusivities of the submicrometer-scale materials such as a superconductor thin film4 and a thermoelectric thin film.5,6 The grating decay rate is provided by assessing an energy-time trace [a J(t)-t trace], which is an observed response of the decay behavior of the transient gratings. We are directly supposed to replace the grating decay rate by the thermal diffusion rate, which is defined as a linear equation of the inverse squared grating spacing, and simultaneously the thermal diffusivity is given as a slope of the linear equation.1,2 As a result of assessments with numerous data points of the thermal diffusion rates, a reliable thermal diffusivity should be determined for a thin film sample.3 But, first there is a great lack of the observed data, that is, the J(t)-t trace for a translucent thin film such as a covered LaCoO3 thin film upon a SrTiO3(100) substrate.5 Second, a large deviation5 of the thermal diffusion rates, that is, the grating decay rate, assessed out of the J(t)-t trace, from the notable feature of a grating spacing dependence that the thermal diffusion rate is expressed as a linear equation of the inverse squared grating spacing is, as yet, unexplained. The objective of the current investigation is the exploration of a more suitable condition inducing the transient gratings for observing a reliable J(t)-t trace in a translucent LaCoO3 thin film. DOI: 10.1557/JMR.2004.0422 J. Mater. Res., Vol. 19, No. 11, Nov 2004
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Here, we extended application of a shorter wavelength (266 nm) inducing than that (800 nm) of the previous laser pulse inducing,5 and took up semiconducting LaCoO3 thin film as a sample. LaCoO3 is a typical perovskite oxide of the type ABO3, where B is a transition-metal ion occupying octahedral sites. This compound has been generally used in connection with the studies of the spin-state transition7,8 and the oxidation catalyst.9 The creative preparation of sample of a translucent LaCoO3 thin film, covered with a 150-nm film thickness upon a SrTiO3(100) s
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