Photogenerated

Figure Bl.16.20. FTEPR spectra of photogenerated DQ m TXlOO solution for delay times between laser excitation of ZnTPPS and microwave pulse ranging from 20 ns to 11 ps. The central hyperfme line (M= 0) is at s - 4.5 MHz. Reprinted from [63].

Houle F A 1989 Photochemical etching of silicon the Influence of photogenerated charge carriers Phys. Rev. B 39 10 120-32... 

S. Zilberg and Y. Haas, The photochemistry of 1,4-cyclohexadiene in solution and in the gas phase Conical intersections and the origin of the helicopter-type motion of H2 photogenerated in Che isolated molecule, PCCP 4, 34 (2002). 

In the following sections the properties of photogenerators of strong Bronsted acids and their use in microlithography are summarized. 

The chemical pathways leading to acid generation for both direct irradiation and photosensitization (both electron transfer and triplet mechanisms) are complex and at present not fully characterized. Radicals, cations, and radical cations aH have been proposed as reactive intermediates, with the latter two species beHeved to be sources of the photogenerated acid (Fig. 20) (53). In the case of electron-transfer photosensitization, aromatic radical cations (generated from the photosensitizer) are beHeved to be a proton source as weU (54). 

Pos twe-Tone Photoresists. The ester, carbonate, and ketal acidolysis reactions which form the basis of most positive tone CA resists are thought to proceed under specific acid catalysis (62). In this mechanism, illustrated in Figure 22 for the hydrolysis of tert-huty acetate (type A l) (63), the first step involves a rapid equihbrium where the proton is transferred between the photogenerated acid and the acid-labile protecting group ... 

Fig. 11. Cutaway view of a CCD shift register where the ( ) represent gate electrodes. Voltage pulses appHed to the phase gates move photogenerated charge in the charge-transfer direction. The channel stops confine the charge during integration and transfer. See text.

Under both short-circuit and open-circuit conditions, a solar cell produces no electric power, the power is consumed internally in the cell and is dissipated as heat. When a resistive load is connected to a cell in sunlight, a photogenerated voltage, F, is induced across the load and a current flows through it. The existence of requites that the flow of majority carriers be reduced from that in the open-circuit condition there must be a higher battier potential than in the open-circuit case (Fig. 2d). This higher barrier potential (V6 — ) indicates a smaller reduction from Since the photogenerated... 

The photogenerated current is in the same direction as /, but is always less than because the battier potential under load conditions is always less than F, which results in a larger flow of majority carriers than that in a short-circuited cell. Thus, when a solar cell is under load, the current and voltage are always less than and lU, respectively this condition is the curve-factor loss. Depending on the characteristics of the particularp—n junction and on the cell operating conditions, there is an optimal load resistance that maximizes the power output of the cell, ie, the product of its current and voltage. 

Amorphous Silicon. Amorphous alloys made of thin films of hydrogenated siUcon (a-Si H) are an alternative to crystalline siUcon devices. Amorphous siUcon ahoy devices have demonstrated smah-area laboratory device efficiencies above 13%, but a-Si H materials exhibit an inherent dynamic effect cahed the Staebler-Wronski effect in which electron—hole recombination, via photogeneration or junction currents, creates electricahy active defects that reduce the light-to-electricity efficiency of a-Si H devices. Quasi-steady-state efficiencies are typicahy reached outdoors after a few weeks of exposure as photoinduced defect generation is balanced by thermally activated defect annihilation. Commercial single-junction devices have initial efficiencies of ca 7.5%, photoinduced losses of ca 20 rel %, and stabilized efficiencies of ca 6%. These stabilized efficiencies are approximately half those of commercial crystalline shicon PV modules. In the future, initial module efficiencies up to 12.5% and photoinduced losses of ca 10 rel % are projected, suggesting stabilized module aperture-area efficiencies above 11%. 

The Fuji CopiArt monochrome proofing system is based on the photogeneration of color from leuco dyes or diazo-coupling (35). CopiArt includes both positive and negative working systems (Fig. 6). For the positive working system, a diazo compound (6) reacts with a coupler (7) as shown. 

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