Photothermal techniques

The feasibility of thermic and calorimetric detection of the absorbed radiation has been mentioned in the context of grazing-incidence experiments. This is quite close to the class of photothermal techniques with which a number of different detection schemes is employed (Coufal, 1986). Out of these, photoacoustic spectroscopy (PAS) is frequently used in infrared spectroscopy (Graham et al., 1985 Urban et al., 1990 McClelland, 1992) while inspite of its potential, thermal beam deflection has not yet found as many applications as in other spectral ranges, possibly due to the lower availability of suitable lasers (Low and Morterra, 1985). 

Subsequently, it has been recognized that other IR techniques (reflection, emission and photothermal techniques) can also be applied, and that IR spectroscopy only gives partial information on the vibrational structure of most polyatomic species. In fact, selection rules apply to IR light absorption phenomena, so that only vibrational modes that are associated with changes of the molecular dipolar moment can be directly excited. 

When dealing with thermal detection, the TG method can be categorized by photothermal techniques such as the PA and TL methods [57-61]. The PA, TL, and TG methods are complementary in many senses. In PA spectroscopy, the pressure wave induced by the volume expansion (or contraction)... 

A simpler way to include the effect of water interactions entails the extraction of configurations snapshots from SDEL trajectories and to immerse each one of these structures into a box with explicit water molecules. Then MD simulations can be performed until equilibration is reached [61]. A variant of this procedure is to use constant pressure and temperature MD to extract volume and enthalpy changes during the molecular event. These properties are probed by photothermal techniques. Space and Larsen demonstrated the application of this algorithm for a small f sheet peptide [62]. 

Recently, photothermal techniques have been applied to the determination of diffusion coefficients in biopolymers [45]. However, the complete validation of this new methodology requires a knowledge of the characterisation of diffusion coefficients of plastic films used commercially, which has been achieved successfully using traditional gravimetric techniques. 

This work involved the use of photothermal techniques for determining the diffusion coefficients of O2 and CO2 of commercial LDPE. The methodology involved the monitoring of diffused gas hy a photoacoustic analysen Diffusion coefficients measured for CO2 and O2 were 2.77 x 10 cm Vs and 16.8 x 10 cm Vs, respectively. To support the gas diffusion results, thermal properties were studied using photoacoustic spectroscopy and crystallinity was determined using X-ray diffraction. Values obtained for the thermal diffusivity and specific heat capacity were 0.00165 cm and 2.33 J/cm /K, respectively, which were in good agreement with the values found in the literature for pure LDPE and thus, assured the reliability of the diffusion coefficient values. 

Development of a photothermal measuring technique for the determination of hardness profile in steel ... 

The applicability of alternative photothermal densitometric techniques, such as PAS, for characterisation of TLC plates with particular emphasis on the in-depth distribution of compounds in the sorbent, has been investigated [776], No specific applications for polymer/additive systems appear to have been reported so... 

The direct proof that H is present in certain centers in Ge came from the substitution of D for H, resulting in an isotopic energy shift in the optical transition lines. The main technique for unraveling the nature of these defects, which are so few in number, is high-resolution photothermal ionization spectroscopy, where IR photons from an FTIR spectrometer excite carriers from the ls-like ground state to bound excited states. Phonons are used to complete the transitions from the excited states to the nearest band edge. The transitions are then detected as a photocurrent. 

As for silicon, secondary ion mass spectrometry (SIMS) is the most widely used profiling analysis technique for deuterium diffusion studies in III-V compounds. Deuterium advantageously replaces hydrogen for lowering the detection limit. The investigations of donor and acceptor neutralization effects have been usually performed through electrical measurements, low temperature photoluminescence, photothermal ionization spectroscopy (PTIS) and infrared absorption spectroscopy. These spectroscopic investigations will be treated in a separated part of this chapter. 

IR photothermal beam deflection spectroscopy (PBDS) and measurements of IR spectra of solids over the range 3950-450 cm l made with an interferometer coupled with a detector which senses the photothermal effect by the deflection of a laser beam are described. PBDS is a general technique and requires no sample preparation all that is needed is to hold the sample at the IR focus. The sample must have a flat spot about 2 mm in diameter accessible to the IR and laser beams. As no sample cells per se are... 

The technique employed is IR-FT photothermal beam deflection spectroscopy (PBDS). It is an off-shoot of photoacoustic spectroscopy (PAS) [1] and is based on the "mirage detection of the photothermal effect invented by Boccara et al. [2] and shown to result in a spectroscopic technique of remarkable versatility and utility. Some applications of "mirage spectroscopy," mainly in the visible, and theoretical treatments, have been described [3 6]. The method has now been developed for use in the IR. The spectrometer and techniques are described in detail elsewhere [7], but it will be useful to give a brief outline of the principles. 

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

Other detection modes employed in capillary electromigration techniques include chemiluminescence [69-71], Raman spectroscopy [72,73], refractive index [74,75], photothermal absorbance [76,77], and radioisotope detection [78]. Some of these detection modes have found limited use due to their high specificity, which restricts the area of application and the analytes that can be detected, such as radioisotope and Raman-based detection that are specific for radionuclides and polarizable molecules, respectively. On the other hand, the limited use of more universal detection modes, such as refractive index, is either due to the complexity of coupling them to capillary electromigration techniques or to the possibility of detecting the analytes of interest with comparable sensitivity by one of the less problematic detection modes described above. 

Some recent developments in IR techniques have included IR photoacoustic and photothermal beam deflection spectroscopy. In photoacoustic spectroscopy the IR wave incident to the solid surface of the catalyst is absorbed by the sample. The radiation is converted to a... 

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