Добірка наукової літератури з теми "MID-IR photothermal beam deflection"

Photothermal beam-deflection (mirage effect) detection in the mid-infrared with a commercial scanning Fourier-transform infrared spectrometer has been used to characterize various solid–liquid interface and surface-bound species. The inherently unfavorable ambient noise level and relatively high Fourier (photothermal modulation) frequencies associated with commercial scanning instrumentation are compensated by the thermal and refractive properties of the liquid beam-deflection medium, which enhance the signal. Preliminary results described illustrate the potential of the technique for infrared (IR) studies of electrochemistry, catalysis, corrosion, and other surface modifications, as well as for polarized IR single-crystal spectra.

FT-IR photothermal beam deflection (PBD) spectra were recorded of solids submerged in liquid CCl4 and in C2Cl4. Some PBD effects are described. Submerging the sample leads to PBD signals 40 times larger than those found with the sample in air, but the signal-to-noise ratio of FT-IR/PBD spectra is only increased by a factor of ten. Certain aspects of the technique and its utility are discussed.

Infrared spectra of several different black inks on paper were obtained by FT-IR photothermal beam deflection spectroscopy (PBDS). Even though the manuscript samples contained about 0.1–0.5 μg of ink solid, spectra of sufficient quality were obtained to enable us to tell which inks contain carbon and to permit some differentiation between similar black inks to be made. However, the identification of an unknown ink is not feasible at present. Spectra of the ink printed on two stamps, and of the black print of a dollar bill, were also recorded. IR/PBDS studies of manuscript and print are totally nondestructive, and may prove to be useful in the fields of forensics and art history.

Infrared (IR) photothermal beam deflection spectroscopy (PBDS) is briefly described and some of its applications to studies of carbons and highly scattering materials are reviewed. PBDS is especially useful for the study of materials which absorb IR radiation very strongly or act as strong IR scatterers, so that conventional IR techniques fail. Application of PBDS to study the thermal degradation of a phenol-formaldehyde resin, the reaction of NH3 and H2O with the surfaces of intermediate-temperature chars, the effect of Fe3+ on the charring of cellulose, the dehydration of titanyl sulphate, and TiO2 pigments, are described.

Detection of species at the solid/liquid interface using infrared spectroscopy is severely limited by the opacity of most liquids to the infrared beam. In this work we use a variant of the photothermal beam deflection (“mirage effect”) method to avoid this problem. With this variant of the method (the “reverse mirage effect”), the IR beam passes through a transparent solid first, and then is absorbed by a liquid medium or by chromophoric species at the solid/liquid interface. The probe laser beam grazes the nonilluminated (back) surface of the solid and is deflected by the thermal gradient in the liquid. Results are presented that were obtained with the use of the reverse mirage technique with single-crystal silicon as the transparent solid and the use of pure acetonitrile as the absorbing sample and beam deflection medium. Studies of the position of the laser probe beam center with respect to the Si/CH3CN interface reveal interesting qualities about photothermal detection within the absorbing medium. The resulting spectra are analyzed in terms of the Rosencwaig-Gersho model.

FT-IR photoacoustic (PA) and also photothermal beam deflection (PBD) spectra were recorded with the same particulate samples (graphite, charcoal, aspirin, and silica) under the same conditions in order to compare the quality of the spectra obtainable with the two techniques. A PA cell fitted with windows for the PBD laser probe beam was used, and PA and PBD spectra of each sample were recorded at 8 cm−1 resolution at each of the four different interferometer scan velocities. Although the overall aspects of FT-IR/PA and FT-IR/PBD spectra are the same, the signal-to-noise ratios of PA spectra are appreciably better than those of PBD spectra because PBD detection is more prone to disturbance by vibration than is PA detection. Absorption bands appear at the same wavenumbers in PA and PBD spectra. However, the relative intensities of bands of PBD spectra depend on the absorptive properties of the powdered solids; with weak absorbers, some bands may not be detected at all. PAS can be used with all powders. PBDS is of little or no use for the examination of weakly absorbing powders unless they scatter IR radiation extensively.

Une gestion thermique efficace est souvent considérée comme une étape clé vers un système technologique réussi. L'élimination rapide de l'excès de chaleur, des systèmes électroniques exposés à des températures extrêmes, améliore la fiabilité et empêche la défaillance prématurée de ces systèmes. De nos jours, les approches habituelles, pour évacuer la chaleur et maintenir le système à une température souhaitée, consistent à utiliser un dissipateur thermique à semi-conducteur ou un système complexe de contrôle de vitesse de ventilateur qui repose sur une mesure continue de la température. Cependant, l'optimisation d'un dissipateur thermique à semi-conducteur très efficace nécessite le contrôle de diverses propriétés intrinsèques et extrinsèques à différentes échelles, car le flux thermique macroscopique et le transport de chaleur dépendent des propriétés vibrationnelles microscopiques. En outre, l'utilisation généralisée de dissipateurs thermiques à semi-conducteurs hautement efficaces nécessite la capacité de les métalliser et de former des structures multicouches. En raison de ses vitesses de groupe de phonons élevées, le nitrure d'aluminium (AlN) semble être l'un des meilleurs candidats pour la fabrication de dissipateurs thermiques à semi-conducteurs efficaces. Dans cette thèse, nous avons comme objectif de développer une nouvelle technologie d’un substrat à base de la structure Métal/AlN/Métal à haute diffusivité thermique pour des applications à haute température (>300°C). Cette thèse vise à développer des technologies d'électronique de puissance hautement efficaces, intégrées et fiables fonctionnant à haute température pour l'automobile, l'aéronautique et l'énergie. Dans un premier temps, nous avons élaboré des films minces de molybdène pour métalliser le nitrure d'aluminium et synthétiser nos nouveaux substrats de dissipateur thermique pour les modules de puissance. Ensuite, nous avons optimisé les dispositifs établis en étudiant leurs propriétés physico-chimiques et en mettant l'accent sur leurs performances thermiques. Enfin, nous avons étudié les performances des échantillons en utilisant une imagerie souterraine et tout en augmentant la température afin de surveiller la formation de défauts. La caractérisation thermique et l'imagerie souterraine des échantillons ont été effectuées à l'aide de notre nouvelle configuration de déviation de faisceau photo-thermique, dans laquelle nous installons un laser IR pour chauffer les échantillons et qui génère des bosses thermiques qui sont mesurées par des faisceaux de sonde déviant à différents endroits de l'échantillon
Efficient thermal management is often considered a key step towards a successful technological system. The fast removal of excess heat from electronic systems exposed to temperature extremes improves the reliability and prevents the premature failure of these systems. Nowadays, the usual approaches to evacuate heat and maintain the system at the desired temperature consist in using a semiconductor heat sink or a complex fan speed control system that relies on continuous temperature measurement. However, the optimization of a highly efficient semiconductor heat sink requires the control of diverse intrinsic and extrinsic properties at different scales because the macroscopic thermal flow and heat transport depend on microscopic vibrational properties. Besides, widespread use of highly efficient semiconductor heat sinks requires the ability to metalize them and form multilayer structures. Due to its high phonon group velocities, Aluminium Nitride (AlN) appears to be one of the best candidates for the manufacturing of efficient semiconductor heat sinks. In this PhD. thesis work, we intend to develop a new substrate technology Metal/AlN/Metal structures with high thermal diffusivity for integrated power systems for high-temperature applications (>300°C). This PhD. Aims at developing highly efficient, integrated and reliable power electronics technologies operating at high temperatures for automotive, aeronautic, and energy applications

In this letter, based on the beam theory and the thermal analysis of a bi-material cantilever, we demonstrate that the effective thermal conductance of the cantilever and the temperature at the tip of the cantilever can be determined by measuring the bending of the cantilever in response to two different thermal inputs: power absorbed at the tip and ambient temperature. The bi-material cantilevers were first introduced as a calorimeter to measure the heat generated in chemical reactions. [1] The same device was demonstrated to be sensitive enough to measure power as small as 100 pW or energy of 150 fJ in photothermal measurements. [2] They were also used as IR detectors [3, 4, 5] or as scanning thermal imaging probes. [6] Although the bi-material cantilevers are often used as temperature or heat flux sensors based on the beam bending due to the unequal thermal expansion of the two materials, the exact temperature at the tip of the cantilever is usually unknown. Directly measuring the temperature is difficult due to the small geometry of the cantilever structure. To find out the temperature of the cantilever, one should obtain the thermal conductance of the cantilever. However, since the thermal properties of two layers of the cantilever are dependent on their thickness, one cannot rely on theoretical calculation. In this letter, we develop a technique to determine the thermal conductance of the cantilever by measuring the bending of the cantilever in response to the variations of the absorbed power at the tip and the ambient temperature. A triangular silicon nitride cantilever coated with 70 nm gold film is used in the current experiment. As shown in Fig.1 (a), a semiconductor laser beam is focused on the tip of the cantilever and reflected onto a position sensing detector (PSD). The deflection of the reflected laser beam spot on the PSD is used as a measure of the deflection of the cantilever. A part of the laser power is absorbed by the cantilever and thus creates a temperature rise at the end of the cantilever. The output of the PSD is converted into an X or Y signal corresponding to the position of the laser spot on the PSD and a sum signal proportional to the incident laser power.