Absorber optimum thickness

Consequently, there has to be an optimum thickness for this type of device. The optimum thickness will depend on the transport properties of the semiconductor. Semiconductors with better transport properties allow us to create thicker (more highly absorbing) devices without losses. 

The optimum thickness for measuring the spectrum of any solute depends on the absorptivity of the solvent It is well known from many textbooks on instrumental analysis that the optimum pathlength of a cell should be such that the transmittance of the solvent should be about He, where e is the base of Naperian logarithms. Thus, the optimum absorbance, Aopt, of the solvent should be logioc, or 0.4... 

Thickness of the laminar layer is deterrnined both by the need to reproduce fine detail in the object and by the penetration depth of the actinic laser light into the monomer bath (21,76). There is thus a trade-off between precision of detail in the model and time required for stereohthography, ie, the number of layers that have to be written, and an optimum Light-absorbing initiator concentration in the monomer bath corresponding to the chosen layer thickness. Titanocene-based initiators, eg, bis-perfluorophenyltitanocene has been recommended for this apphcation (77). Mechanistic aspects of the photochemistry of titanocenes and mechanisms of photoinitiation have been reviewed (76). 

The use of porous formers ia the dippiag process, or porous molds prepared from plaster of Paris or uaglazed porcelaia with a surface pore size smaller than the majority of mbber particles, has been widely adopted ia the latex iadustry. With the porous porcelaia formers, the mbber particles are filtered oa the surface of the formers. The mbber latex coagulates because of its high coaceatratioa to form a film of increa sing thickness as more water is absorbed iato the ceramic. Its rate of iacrease diminishes sharply beyoad an optimum period of time, however, depending on the various characteristics of the ceramic. 

Simulated solar conversion efficiencies up to 6.8% on Ti substrates have been reported for annealed CD CdSe films in polysulphide electrolyte based on a low-ammonia-concentration-selenosulphate bath. Several successive depositions were required to build up an optimum final fihn thickness of 2.5 jim (when most of the hght was absorbed). The initial deposit was annealed to improve adherence and the final multideposited film was annealed at 550°C in air, followed by etching and zinc ion treatment. 

The optimum effect of a UV absorber in a polymer film can be calculated from the absorbancy of the UV absorber and the thickness of the film. Such calculations show that the effect of UV absorbers is small in thin films and in yarns. 

Thin solar cells are therefore much more stable than thick ones. On the other hand the initial efficiency of the thicker cells is larger because more of the solar spectrum is absorbed. The optimum design is a compromise between these two effects and the typical thickness used is about 0.5 pm. Tandem or triple cells are more efficient at absorbing over a wide spectral range because each cell is designed to cover a... 

Because most solutions absorb infrared radiation in their bulk, the design of the electrochemical cell is an important consideration in interfacial reflection experiments. The optimum configuration involves a very thin solution layer which is a few microns thick and is sandwiched between the optical window and the reflective electrode (fig. 10.8). In order to achieve maximum sensitivity, the window has a hemispherical or triangular (prism) shape. Nevertheless, most radiation is absorbed in the bulk of the solution and the effect of interfacially adsorbed molecules cannot be seen unless special steps are taken. One procedure is to polarize the light in a cyclical fashion between s- and p-polarized light. If adsorbate molecules interact with the p-polarized light, the intensity of the... 

Fig. 2.9 The function Ar(0) for Fe (14-4 keV) plotted for four values ol to show the optimum absorber thickness.

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