Photothermal deflection

Figure 7. Schematic diagram of a photothermal deflection spectroscopy (PDS) apparatus for infrared- spectral measurements of surfaces at high temperatures and high pressures constructed at Utah by L.B. Lloyd.

Stage I Parallel and quasi-parallel analytical techniques IR thermography Photoacoustic analysis Photothermal deflection... 

Figure 6.18 The room temperature absorption and emission spectra of Yb + ions (1 %) in ZBLANP (top). The amplitude of the photothermal-deflection waveforms as a function of the pump wavelength (bottom) (reproduced with permission from Epstein et al., 1995).

U. Zammit, Photothermal Deflection Spectroscopy Characterization of lon-lmplanted and Annealed Silicon Films... 

Combinatorial methods were also applied in the discovery of new catalysts for the low-temperature oxidation213 and oxidative dehydrogenation of propane.214 A 144-member catalyst library was screened by photothermal deflection spectroscopy and mass spectrometry to find the most active compositions of V-Al-Nb and Cr-Al-Nb oxides for the oxidative dehydrogenation of ethane.215 The ternary combination V(45)-Sn(45)-Mo(10)-O selected by laser-induced fluorescence imaging gave much higher yield than did V205 in the selective oxidation of naphthalene to naphthoquinone.216... 

Fig. 3.14 Plots of (a) ethylene and (b) C02 production (ppm) as measured by photothermal deflection spectroscopy and mass spectrometry for the NiTaNb oxide library.

Oxidative dehydrogenation (ODH) is an important process for converting ethane or propane into more valuable ethylene or propylene. Ethylene has a specific IR absorption band around 950 cm4, which has been utilized by two research groups, using IR-based gas sensors, in the HTS of ethane ODH. Cong et al. at Symyx have used photothermal deflection [12, 13] and Johann et al. at the Max Planck Institute used a PAS sensor [24]. Johann et al. reported that position-sensi-... 

Another type of IR gas-sensor has been reported by Cong et al. for the HTS of ethane ODH [12, 13]. They used a photothermal deflection (PTD) detector with a mass spectrometer because an electron-impact mass spectrometer cannot detect C2H4 concentrations at the ppm level in the presence of high concentrations of... 

Figure 3.35 Ethylene produced by oxidative dehydrogenation of ethane over Mo-V-Nb and Ni-Ce-Ta oxide catalyst libraries. The detection of ethylene was performed in a scanning mass spectrometer using a photothermal deflection method. Inactive Mo-V-Nb oxide catalyst (a) active Ni-Ce-Ta oxide library (b) [7] (by courtesy of Kluwer Academic Publishers).

Direct measurements of the change in the number of states caused by doping with oxygen have only been made by a few groups. Of particular interest are electronic states that are in the band gap, but whose concentrations are too small to be observed using conventional optical transmission measurements. Photothermal deflection spectroscopy (PDS) is capable of revealing sub-gap states and has been used extensively on amorphous inorganic semiconductors [52]. PDS has been... 

P PAE PD PDS PEC PL PLE PMBE PPC PPPW PR PV PWP PWPP pi-MODFET precipitate power added efficiency photodetector photothermal deflection spectroscopy photoelectrochemical photoluminescence photoluminescence excitation spectroscopy plasma-assisted molecular beam epitaxy persistent photoconductivity pseudo-potential plane-wave photoreflectance photovoltage plane-wave pseudo-potential plane-wave pseudo-potential piezoelectric modulation doped field effect transistor... 

Figure 7 Electrochemical photothermal deflection spectroscopy experiment (0.5 mol dm-3 Na2S04 pH = 10.5, 20 mV s 1), illustrating the detection of the onset of dissolution of nuclear fuel (U02) (A) voltammetric response for scans to various anodic potential limits (B) and (C) probe beam deflection for each scan. The deflection of the probe beam is proportional to the dissolved uranium concentration, and deflection of the probe beam towards the electrode surface is an indication that dissolution is occurring (Reprinted from Ref. 2 with permission from Elsevier Science S.A.)...

Direct mirage effect — A deflection signal usually associated with photothermal experiments in which the deflected probe light beam passes on the same side of the photoilluminated -> interface [i]. See also - photothermal deflection spectroscopy. 

The term mirage effect has been indistinctly assigned to studies performed by - photothermal deflection spectroscopy (PDS) and - probe beam deflection (PBD). However, PDS is based on the analysis of the first term of the last equation, whilst in PBD, essentially the second term is evaluated. 

Photothermal deflection spectroscopy — Photothermal deflection is a photothermal spectroscopic technique used to detect the changes in the refractive index of the fluid above an illuminated sample by the deflection of a laser beam. There are two sources from which the thermal deflection effect might appear. One of them is produced by a gradient in the refractive index after a thermal excitation where the density also varies with temperature, in the so-called mirage effect. And the other one is produced by the topographical deformation of the surface over which the laser beam is reflected. This effect is known as photothermo-elastic effect or surface photothermal deflection [i]. 

Surface photothermal deflection - photothermal deflection spectroscopy... 

Figure 16 Photothermal deflection spectrum of a NH3 -compensated trans-VA. Dots and dashed line show the absorption edge recorded on two films, 4 p.m and 0.1 xm, respectively. Dotted line shows the residual absorption of an uncompensated sample. Solid line sketches the expected neutral soliton absorption in the absence of electron correlation. (From Ref. 130.)...

Where R is the reflectivity and d is the thickness. Very accurate values of R and T are needed when the absorptance, (id, is small. The technique of photothermal deflection spectroscopy (PDS) overcomes this problem by measuring the heat absorbed in the film, which is proportional to ad when ad 1. A laser beam passing just above the surface is deflected by the thermal change in refractive index of a liquid in which the sample is immersed. Another sensitive measurement of ad is from the speetral dependence of the photoconductivity. The constant photocurrent method (CPM) uses a background illumination to ensure that the recombination lifetime does not depend on the photon energy and intensity of the illumination. Both techniques are capable of measuring ad down to values of about 10 and provide a very sensitive measure of the absorption coefficient of thin films. 

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