Photosensitization, defined

Note 2 Photosensitivity in photosensitive polymers means that the polymers are sensitive to the irradiated light leading to some change in their properties or structure. It is different from photosensitization defined in [2], p. 307. 

Besides photoconductivity, photo-electro-motive (e.m.f.) forces were observed in copper polyacetylenides. The common results characterize the hypso-chromic shift of the photo-emf spectra compared to the photoconductivity ones. The maximum of the photoconductivity spectra coincide with the minima of the photo-emf spectra. The optical activation energies of the photosensitivity defined from the photoconductivity and photo-emf spectra are in close agreement and equal to the energy of the absorption edge. 

Resists. Resists are temporary, thin coatings appHed to the surface of the copper-clad laminate. After patterning, these films act as masks that are chemically resistant to the cleaning, plating, and etching solutions used to define the circuit traces of the PWB. Both nonphotosensitive and photosensitive types are used. 

Comparison of the Experimental and Simulation Results. The preceding discussion has shown that both the experimental anthracene fluorescence profiles and the simulated anthracene concentration profiles decrease in a manner which closely follows an exponential decay. Therefore, the most convenient way to compare the simulation results to the experimental data is to define an effective overall photosensitization rate constant, kx or k2, as described above. Adoption of this lumped-parameter effective kinetic constant allows us to conveniently and efficiently compare the experimental data to the simulation results by contrasting the rate constant obtained from the steady-state fluorescence decay with the value obtained from the simulated decrease in the anthracene concentration. 

Experimental determination of the quantum efficiency of photosensitive polymers of the sort that are used in one-component positive resist systems is a more complex experimental undertaking. Here the quantum efficiency is defined as the number of main chain scissions that occurs per photon absorbed. Guillet and coworkers at the University of Toronto have... 

The basic steps of the lithographic process are shown schematically in Figure 1. The example shown corresponds to photolithography in which the photosensitive resist or photoresist is applied as a thin film to the substrate (Si02 on Si) and subsequently exposed in an image-wise fashion through a mask. The mask contains clear and opaque features that define the circuit pattern. The areas in the photoresist that are exposed to light are made either... 

For positive lit electrodes one can register the drift of holes, and for negative ones- the drift of the electrons. The photosensitizer (for example Se) may be used for carrier photoinjection in the polymer materials if the polymer has poor photosensitivity itself. The analysis of the electrical pulse shape permits direct measurement of the effective drift mobility and photogeneration efficiency. The transit time is defined when the carriers reach the opposite electrode and the photocurrent becomes zero. The condition RC < tlr and tr > t,r should be obeyed for correct transit time measurement. Here R - the load resistance, Tr -dielectric relaxation time. Usually ttras 0, 1-100 ms, RC < 0.1 ms and rr > 1 s. Effective drift mobility may be calculated from Eq. (4). The quantum yield (photogenerated charge carriers per absorbed photon) may be obtained from the photocurrent pulse shape analysis. 

The bis(aryl)azide sensitizers must be soluble in the resin, thermally stable, and sensitive to the desired wavelength of light. A commonly used compound is 2,6-bis(4-azidobenzylidene)cyclohexanone, which absorbs at 360 nm (see structure). Conjugation extension and other structural changes can shift the absorption maximum to longer wavelengths and allow access to the other mercury lines at 405 and 436 nm. A number of bis(aryl)azides are efficient photosensitizers (21). Quantum yields, defined as the number... 

The term photosensitization is not well-defined. Mechanistically, it may comprise many different processes such as ET, H-abstraction, formation of singlet O2 and reactive free radicals. 

Comparison of Tables III and IV shows a general correlation between adsorbent color (as defined by the Munsell indices) and optical absorbance. Note that the "darkest" adsorbents (graphite WK, IL, KA, NM, EA) ashes are those on which PAH photoreactivity tends to be low, while the "lighest" adsorbents (silica, alumina, glass, TX and AR ashes) are those on which adsorbed PAHs are most photosensitive. Again, the ET ash is an exception (being a light-colored ash but one on which adsorbed PAHs are not especially susceptible to phototransformation). 

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