Photothermal spectroscopies

S. Bialkowski, Photothermal Spectroscopy Methodsfor ChemicalAnalysis,]ohxi Wiley Sons, Inc., New York, 1996. 

Photothermal Spectroscopy Methods for Chemical Analysis. By Stephen E. Bialkowski Element Speclatlon in Bioinorganic Chemistry. Edited by Sergio Caroli Laser-Enhanced Ionization Spectrometry. Edited by John C. Travis and Gregory C. Turk Fluorescence Imaging Spectroscopy and Microscopy. Edited by Xue Feng Wang and Brian Herman... 

Photothermal Spectroscopy Methods for Chemical Analysis. By Stephen E. Bialkowski Element Speciation in Bioinorganic Chemistry. Edited by Sergio Carol ... 

Table I consists of a compilation of r /4> ratios as a function of X. Our results and those presented for p-GaP and n-ZnO are in rough agreement with this simple model (8,9,30,31,32). Construction of a more refined model awaits incorporation of other data (nonexponential lifetimes, electroabsorption, carrier properties, intensity effects, quantitative evaluation of 4>nr by photothermal spectroscopy, e.g.) and examination of other systems.

Thermal lens microscopy (TLM) is a type of photothermal spectroscopy. TLM depends on the coaxial focusing of the excitation and probe laser beams (see Figure 7.20). Which is achieved using the chromatic aberration of a microscopic objective lens [731]. The excitation beam can be provided by a YAG laser (532 nm) [846,1021] or an Ar ion laser (514.5 nm [846] or 488 nm [732]).The probe beam can be provided by a He-Ne laser (632.8 nm) [846,1021], After optical excitation of the analyte molecules, radiationless relaxation of the analytes occurs,... 

Give two reasons why colloidal gold is suitable as a labeling material in immunoassay using laser-induced photothermal spectroscopy. [1021] (2 marks)... 

We have developed a novel ultrasensitive detection method, thermal lens microscopy (TLM), for nonfluorescent species [13]. TLM is photothermal spectroscopy under an optical microscope. Our thermal lens microscope (TLM) has a dual-beam configuration excitation and probe beams [13]. The wavelength of the excitation beam is selected to coincide with an absorption band of the target molecule and that of the probe beam is chosen to be where the sample solution (both solvent and solute) has no absorption. For example, in determination of methyl red dye in water, cyclohexane, and n-octanol, a 514-nm emission line of an argon-ion laser and a 633-nm emission line of a helium-neon laser were used as excitation and probe beams, respectively [21], Figure 4 shows the configuration and principle of TLM [13]. The excitation beam was modulated at 1 kHz by an optical chopper. After the beam diameters were expanded, the excitation and probe beams were made coaxial by a dichroic mirror just before they were introduced into an objective lens whose magnification and numerical aper-... 

Good summaries of accepted experimental techniques can be found in the references that are cited for individual radionuclides in the sections below. Nitsche (1991) provides a useful general summary of the principles and techniques of solubility studies. A large number of techniques have been used to characterize the aqueous speciation of radionuclides. These include poten-tiometric, optical absorbance, and vibrational spectroscopy. Silva and Nitsche (1995) summarize the use of conventional optical absorption and laser-based photothermal spectroscopy for detection and characterization of solution species and provide an extensive citation list. A recent review of the uses of Raman and infrared spectroscopy to distinguish various uranyl hydroxy complexes is given by Runde et al. (2002b). 

Optical techniques like photoluminescence (10) and infrared photothermal spectroscopy (11.) work well for the characterization of shallow level impurities, while electrical techniques work well for deep level impurities. There are a number of methods that have been used for electrical characterization. I will only discuss deep level transient spectroscopy (DLTS), however, because it has become the most popular and gives a fairly complete characterization. 

Reactions of Halo Compounds. - Calculations have been carried out to investigate the decomposition paths for methyl fluoride and methyl chloride. Methyl chloride undergoes photodissociation on irradiation at 157.6 nm. Photodissociation of methyl iodide at 266 nm has been studied. The methyl radical recombination has been followed by time-resolved photothermal spectroscopy. Methyl iodide also undergoes photochemical decomposition on a GaAs(llO) surface. " Photolysis of methyl iodide at 236 nm in the gas phase brings about liberation of iodine atoms with a quantum yield of 0.69. ... 

Karas et al. and others 256-261 published several papers which deal with the use of luminescence from Te-doped CdS photoelectrodes to probe excited-state deactivation processes in photoelectrochemical cells, and Fujishima et have applied photothermal spectroscopy to the simultaneous determination of quantum efficiency and energy efficiency of CdS and TiOj photoelectrodes. As more sophisticated models are developed to describe interfacial photoelectrochemistry, measurements of this kind will be needed to separate the different routes for the deactivation of excited charge carriers. 

Experimentally, these principles emphasize dynamic measurements that make possible the separation of the dissipative and the conservative components of energy Incident upon the system. Dynamic mechanical analysis has been an Important area of research for over 40 years. Computer-controlled experimentation now makes It possible to apply analogous techniques to the measurement of many other thermodynamic stresses. One example currently under Investigation, dynamic photothermal spectroscopy. Is expected to provide a new approach to predicting the long-term effects of ultraviolet radiation on materials [39]. 

Fig. 5.30. Probe beam deflection setup for photothermal spectroscopy [129]...

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