Photothermal deflection spectroscopy

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.

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.

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... 

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. 

While the MIPs used in this work were inherently stable for at least 1 year, the silver films were prone to atmospheric degradation. Indeed, it was found that the application of the MIPs to the film protected it to some extent, but even when stored in vacuo these substrates were only stable for 5 days. The use of gold substrates is reportedly under investigation. Finally, it must be noted that the equipment used in this work was not a simple off-the-shelf commercial SPR system. These custom-made systems employed either highly sensitive photothermal deflection spectroscopy or a photodiode array to detect the changes in resonance... 

FIGURE 8.5. Absorption spectrum of a ladder-type PIPP as determined by conventional UV/vis transmission spectroscopy (dashed line) and photothermal deflection spectroscopy (PIDS, solid line) the dotted line shows the intensity of the PIDS pump beam. (Reproduced from Ref. 160.)... 

Bohnert B, Faubel W, Ache HJ. 1992. Comparison of collinear and transverse photothermal deflection spectroscopy for trace analysis of pesticides in water. Fresenius J Anal Chem 343 513-517. 

Goris L., Haenen K., Nesladek M., Wagner P., Vanderzande D., de Schepper L., d Haen J., Lutsen L. and Manca J. V. (2005), Absorption phenomena in organic thin films for solar cell applications investigated by photothermal deflection spectroscopy , /. Mat. Sci. 40, 1413-1418. 

Royce B. S. H., Sanchez-Sinencio F., Goldstein R. and Mnratore R. (1982), Studies of photocorrosion at the ZnSe-electrolyte interface by photothermal deflection spectroscopy , J. Electrochem. Soc. 129, 2393-2395. 

One way of measuring true absorption is to employ photothermal deflection spectroscopy (see Fig. 9-1). In this case the absorbed light, leading to a slight heating up of the sample, is detected by the temperature-dependent deflection of a laser beam passing close by the sample. The obvious advantage of this method is that it really measures the absorption coefficient (a). 

Figure 9-13. Absorption spectrum of mLPPP, determined using photothermal deflection spectroscopy (PDS) - from Ref. [143].

The photoacoustic sample cell/detector assemblies are inside a controlled atmosphere glove box. This glove box has two functions, firstly to allow experiments to be carried out in the anaerobic conditions expected in deep repositories, and secondly to act as containment for the radioactive materials. The nitrogen atmosphere glove box has been fitted with sufficient windows to allow ready adaptation of the LPAS system to carry out other photothermally-based spectroscopy techniques, namely thermal lensing spectroscopy and photothermal deflection spectroscopy. 

Measurements of the deflection of a light beam caused by local heating at the solid/solution interface as a function of the wavelength of light illuminating this interface are an alternative possibility the resulting method is called photothermal deflection spectroscopy (PDS) [127, 128]. The experimental setup as depicted in Fig. 5.30 closely resembles the arrangement for probe beam deflection studies treated in Sect. 5.1.9. 

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