Photothermal processing

SILAR-grown ZnO films have been tested for gas sensor applications.29 The ZnO films, doped with tin for this purpose, were grown from a mixture of dilute zinc sulfate, sodium hydroxide, and sodium tin(IV)oxide solutions. The final step, resulting in the oxide film, was treatment of the substrate and film in a nearly boiling water bath. The N02 gas sensing properties were tested for films doped with Al, Cu, Pd, and Sn, but only the film doped with tin exhibited sensitivity toward N02. The sensitivity of the ZnO Sn film was 5% /ppm after rapid photothermal processing (RPP). The best sensitivity was obtained when the tin concentration was 5-10%.29... 

Even after 25 years of research in the held of laser polymer ablation, there is still an ongoing discussion about the ablation mechanisms, for example, whether in addition to photothermal processes, photochemical reactions or even photophysical and mechanical processes are important. 

All data obtained for TP strongly suggest that photochemical reactions play an important role during UV laser ablation, but also that photothermal processes are important. This is confirmed by the presence of the thermal N2 products in the TOF curves. Photothermal processes will also always be present if the polymer decomposes exothermically during a photochemical decomposition and if the quantum yields of the photochemical reaction is not equal to one (which is most of time the case). The ablation of polymers will therefore always be a photophysical process (a mixture of photochemical and photothermal processes), where the ratio between the two mechanisms is a function of the irradiation wavelength and the polymer. In addition, photomechanical processes, such as pressure produced by trapped gaseous ablation products or shock and acoustic waves in the polymer, take place and can lead to a damage of the polymer and are most important for picosecond pulses. 

In addition, the characteristics of various materials of the semiconductor can be derived from the observed relationships. Photocurrents can also be observed because of photochemical (essentially photolytic or photothermal) processes in the solution that are close to the surface under investigation. 

Another possible mechanism is ascribe to solvent chlorobenzene i on excitation. If appreciable amount of solvent molecules are left in the film, they evaporate and result in volume increase of the film. Also ptotodissociation of chlorobenzene to Cl atom and counter radicals may involve formation of gaseous molecules. However, as mentioned above, it is confirmed directly by UV absorption spectral measurements that chlorobenzene absorption is negligible compared to PMMA. Hence, solvent role in expansion should be excluded, and we consider photothermal processes are responsible to the present expansion phenomena of PMMA. 

First we consider that the different expansion behavior at 248 nm aiul 351 nm excitation is due to the different etching mechanism discussed above. In the case of 351 nm excitation, multiphoton photochemical and photothermal processes are involved and the latter may be more important at lower fluence. The contraction behavior at 80 mJ/cm may reflect slow heat dissipation in polyimide, which behavior is actually consistent with photothermal expansion and contraction dynamics of PMMA film (21). On the other hand, toe thin surface layer is excited at 248 nm, so that heat dissipation to quartz substrate should be slower than that at 351 nm. More quantitative analysis of cooling processes by the simulation was conducted to understand the expansion and contraction dynamics. 

Photothermal decomposition of palladium acetate by scanned cw Ar+ laser irradiation produces metal features that exhibit pronounced periodic structure as a function of laser power, scan speed, substrate and beam diameter, as shown in Figures 3 and 4. The periodic structure is a function of the rate at which the film is heated by absorption of the incident laser radiation coupled with the rate at which the heat of the decomposition reaction is liberated. This coupling generates a reaction front that outruns the scanning laser until quenched by thermal losses, the process to be repeated when the laser catches up and reaches unreacted material. Clearly, such a thermal process is also affected by the thermal conductivity of the substrate, the optical absorption of the substrate in those cases where the overlying film is not fully absorbing,... 

S. E. Braslavsky, G. E. Heibel. Time-Resolved Photothermal and Photoacoustic Methods Applied to Photoinduced Processes in Solution. Chem. Rev. 1992,92,1381-1410. 

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-... 

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