The light-sensitive elements of conventional photographic materials are crystallites principally of the bromide or chloride salts of silver. Certain chemical modifications employing sulphur and gold compounds are used to maximize the response, and organic dyes are adsorbed to provide sensitivity throughout the visible spectrum. Absorption of a few photons results in the reductive formation of one or more clusters of silver or gold atoms on the surface. These clusters act as catalysts to promote further reduction of the host crystallites during photographic development. The success of the system depends upon the particular physical properties of the silver halides, such as their bonding and electron structure, the dielectric properties, the point defect structure, and the electronic transport characteristics. These are all reviewed, and the ways in which they interact to lead to the favourable photodecomposition are followed in some detail. A nucleation-and-growth mechanism operates to provide sev...

The silver halide photographic process

Firstly the basic theoretical methods of calculating the dielectric properties of heterogeneous mixtures are discussed. These are the mean field and effective medium theories and integral methods. Formulae are presented for systems containing parallel oriented ellipsoids and for randomly oriented ellipsoidal systems. Theoretical formulae are divided into two sub-groups: symmetric equations for statistical mixtures and asymmetric equations for matrix-inclusion type composites. In the former case only the relative amount of the components is important, in the second case phase inversion results in a change of the dielectric properties. Formulae are compared numerically using spherical and spheroidal systems with sharply different components (permittivity ratio is 1 ∶ 100). In the case of asymmetric formulae the effect of phase inversion is studied as well. Percolation behaviour predicted by the equations is demonstrated and discussed. Functional shapes are compared in relation to the theoretical differences. Finally, experimental data are compared with the theoretical results, advantages and drawbacks of the various formulae are discussed. For spherical systems the simplest mean field formula yields somewhat worse values than effective medium or integral equations. The Looyenga equation does not work very well if the permittivity difference is high. For nonspherical systems the fit is better in general, even the simplest formula works satisfactorily. The shape independence predicted by the Looyenga theory for randomly oriented ellipsoids is in conflict with experimental data.

Comparison of electrical mixture rules for composites

The role of Ag+‐interstitial and Ag+‐vacancy transport across silver halide surfaces is important for both ionically blocking and nonblocking interfaces. One technique to evaluate the nature of a blocking silver halide surface is to measure the alternating‐current dielectric loss of silver halide microcrystals in contact with an insulating dry‐gelatin phase. From the results of these measurements, the availability of the potential‐determining Ag+ interstitial was determined as a function of silver halide type, crystal size and morphology, and the addition of divalent cations within the silver halide phase and adsorbed at the surface. The results on small crystals (0.2 μm) and, analogously, for very thin films, where the Debye length is comparable to the linear thickness, indicated that the Ag+‐interstitial concentration is a critical function of the surface properties of the silver halide. Consequently, the transport of ionic carriers across the silver halide is not only dependent on bulk solid‐state prop...

Dielectric‐loss measurements of interfacial polarization at silver halide–insulator interfaces

Ionic conductivity of small-grain polycrystals of silver iodide

Chemical Sensitization, Spectral Sensitization, and Latent Image Formation in Silver Halide Photography

Dielectric measurements effected on silver bromide emulsions in the frequency range 102−107 Hz show a maximum in the absorption curve. This dielectric absorption is interpreted as a consequence of the conductivity of the interstitials in the AgBr crystals. According to this interpretation, the influence of the morphology and size of the AgBr grains, and of the addition of stabilizing agent on the conductivity of the AgBr grains can be detected in a simple manner. A continuous transition from surface conductivity towards bulk conductivity of the AgBr grain is observed.

Maxwell‐Wagner Effect in Silver Bromide Emulsions

The recent findings of Park, Lindholm, and Neugroschel [J. Appl. Phys. 62, 948 (1987)] regarding the depletion capacitance of p‐n junctions of the symmetrical‐step type and of the linearly graded type under high‐forward voltage are compared to the results of an earlier analysis of the same subject. The difference in the method of solution and the role of a characteristic length in linearly graded junctions is briefly discussed.

J. J. H. van den Biesen

Papers

Maxwell‐Wagner Effect in Silver Bromide Emulsions

Comments on ``An analytical study of the p-n junction space-charge region under high forward voltage'' [J. Appl. Phys. 62, 948 (1987)]