Photothermal Deflection Spectroscopy PDS

Fundamentals. Absorption of electromagnetic radiation illuminating an electrode surface, particularly the surface layer, or by adsorbates on the electrode surface, can result in thermal effects. These can be detected by various means, as described 

The closely related photoacoustic method (wherein no wavelength dependency is taken 

The availability of tunable infrared diodes limits the accessible spectral range in the study by Deng et al. [330], data for the range 600-1000 cm could be obtained. LiOH was identified as the dominant species in the lithium/solid polymer electrolyte interphase. 

---

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.

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... 

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. 

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. 

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

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. 

Variants of these techniques are the Photothermal Deflection Spectroscopy (PDS or Mirage effect) and Photothermal Displacement Spectroscopy (102). These techniques are based on deflection of a light beam due to refractive index gradients either In a fluid (or air) in contact with a light absorbing solid or in the solid itself. If the fluid is inert the technique can be used to measure absorption spectra of solid materials and transport properties. A version of these techniques was applied to electrochemical and photoelectrochemical systems (103). The authors describe the experimental conditions needed to separate the contributions from the temperature and concentration gradients. Once this is done the results can be correlated with the kinetics and mechanism of the electrochemical reactions. 

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 5 Calibration curves for the dinitrophenol herbicide DNOC in aqueous solution when using different techniques (A) PDS Photothermal deflection spectroscopy, (B) TL thermal leasing, (C) PIS Photothermal Interferometric spectroscopy, (D) PAS a photoacoustic spectroscopy, (E) a conventional spectrophotometer Cary 2400. Reproduced with permission of SPIE from Faubel W (1997) Detection of pollutants in liquids and gases. In Mandelis A and Hess P (eds) Life and Earth Sciences. Progress in Photothermal and Photoacoustic Science and Technology, Vol III, Chapter 8. Bellingham SPIE.

Infrared Photothermal Beam Deflection Spectroscopy Infrared photothermal beam deflection spectroscopy (IR-PDS) is better than PAS because it does not have a microphone near the sample. It involves two light sources. One is an interferometer that produces modulated radiations to illuminate the sample, and the other is a laser source that is placed so that its beam grazes the surface of the carbon sample. The absorption of the incident-modulated radiation beam by the sample produces heat, causing thermal gradients that deflect the laser beam. The deflected laser beam is detected by the detector, and the signal reproduced is a measure of the photothermal effect induced on the sample surface. The resulting... 

The other difficulty in the IR studies of carbons using halide pellets is the exposure of the carbon material to atmospheric gases and vapors that tend to vitriate the results. The development of elaborate techniques for obtaining carbonaceous films and preparation of charcoals by carbonization under vacuum conditions broadened the scope of applications of IR spectroscopy to the study of carbons and their surface groups. Furthermore, the sensitivity of IR measurements has been largely enhanced by using Fourier-Transform (FT), Photoacoustic (PAS), and Photothermal Beam Deflection (PDS) IR spectroscopy. 

---