In this paper we present an experimental and theoretical study of the thermoreflectance response as a function of the probe wavelength for layered microelectronics structures. The investigated sample consists of a polycrystalline silicon conducting track grown on a SiO2-coated Si substrate. Thermoreflectance measurements were carried out in the wavelength range from 450to750nm with the track biased in modulated regime. An oscillating pattern is observed in the spectral region where the upper layer is transparent. Such oscillations are due to the interference resulting from the multiple reflections at the interfaces. Using a thermo-optical model, we show that the optical constants (n and k) of the materials, which are wavelength dependent, as well as their temperature derivatives (dn∕dT and dk∕dT), strongly influence the thermoreflectance signal. The optical thicknesses of the layers, mainly determined by the real part of the refractive indices, define the period of oscillation. On the other hand, the imaginary part of the refractive indices establishes the cutoff wavelength of the oscillations. Below this cutoff wavelength, the probe light does not penetrate the material and the upper-surface reflectance dominates the signal.
Electron spin resonance was applied on samples of Gd 5.09 Ge 2.03 Si 1.88 . The results are discussed under the scope of magnetization measurements, optical metallography, and wavelength dispersive spectroscopy. Polycrystalline arc-melted samples submitted to different heat treatments were investigated. The correlation of the electron spin resonance and magnetization results permitted a characterization of the present phases and their transitions. Two coexisting phases in the temperature range between two phase transitions have been identified and associated to distinct crystallographic phases. Additionally, the magnetic moment at high temperatures has been estimated from the measured effective g factor. A peak value of 21.5 J / kg K for the magnetocaloric effect was obtained for a sample heat treated at 1500°C for 16 h.
The possibility of using the phase shift of the photoacoustic signal of different constituents of a composite sample for resolving the spectra of the constituents, at a fixed modulation frequency, is discussed. The proposed method is experimentally tested using samples of soda-lime -silica glass doped with binary oxide mixtures.dE (x, t) E (x, t) = W(x, t)- (2) The photoacoustic signal is the result of the decay of
In this article, we review the applications of the open photoacoustic cell (OPC) technique in studies of photosynthetic activity in plant leaves. The ability to perform in vivo and in situ measurements makes this technique particularly suitable for monitoring photosynthesis of plants subjected to specific treatments. Therefore, our objective in the present article is to describe, in more detail, the principles of the OPC technique and to follow the historical path of its applications related to the study of plants and photosynthesis, including recent results.It will be shown that the technique has been used to observe spectroscopic responses to herbicide application and to soil toxicity, in the study of photosynthesis induction, gas exchange, photochemical loss, photoinhibition, photosynthesis saturation, and photosynthetic responses to changes in parameters such as temperature, atmospheric conditions, and nutrient availability. Recent results have demonstrated its usefulness in the determination of the action spectrum directly from oxygen evolution measurements.
Using a thermal lensing experimental setup the thermal properties of several vegetable oils were obtained. The samples were oils from Amazonian species and olive (the popular identifications are piqui, copaiba, buriti, and babaçu). The two lasers mismatched mode experimental configuration was used, with a He–Ne laser as the probe and an Ar+ laser as the excitation one. The time resolved spectra were measured using an automatic system, and fitting the aberrant theoretical model to the data, the characteristic relaxation time were obtained, and knowing this value, the thermal property of each oil was solved.
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