About the Nature and the Role of the Sensitivity Speck Formed during Gold Ripening

After a critical survey of recent literature about the present state of the mechanism of gold sensitization, there are presented new experimental results obtained by tracer techniques using 1,8Au, which lead us to believe that during a gold + sulphur ripening in addition to gold sulphide or silver gold sulphide metallic gold specks are formed. These specks are to be considered as real sensitivity specks.

It seems likely that the function of gold in latent image formation is more related to better catalytic properties and better stability of the latent silver specks than to an increasing efficiency of the electron trapping at the grain surface.     

Solid State Properties and Photographic Activity of Crystalline Ag2S- and (Ag,AU)2S-Specks at the Surface of Silver Halide Crystals

In the present paper a model is proposed according to which the photographic activity of silver sulphide specks is explained on behalfof the solid state properties of crystalline cubic silver sulphide, Epitaxial deposit ion of the laller is cia imed to occur at least partly at the (III) faces of AgBr during chemical sensitization, The disorder of the cation sublallice in cubic silver sulphide is con idered to be the physical base of highly efficient electron trapping, whereas the high electronic conductivity is rcsponsible for its catalytic activity towards developmcnt (fog). Excess silvcr in non stoichiometric cubic silver sulphide plays a very important role in its photographic behaviour inclUding development kinetics, The model provides a coherent explanation of a great number of experimental facts including the effects introduced by gold ions during sulphur sensitization.     

A Computer Simulation of Latent Image Formation in Photographic Emulsion by a Monte Carlo Method

A digital computer analysis has been made of photon absorption, chemical sensitization and latent image distribution in a silver halide photographic emulsion, using the Bayer Hamilton model but with a different approach in treating the positive holes.

In discussing the effect of sulphur sensitization it has been assumed that silver sulphide molecules can play a dual role in latent image formation, undergoing partial thermal dissociation to increase both the number of electron traps by providing more interstitial silver ions and that of positive hole traps by forming AgS^-. The increased interstitial silver ion concentration has also been supposed to lead to an increase in the stability of single silver atoms. As to gold sensitization, it has been assumed that the main effect of gold is to enhance the developahility of latent image centres.

Parameter values for simulation under various conditions of chemical sensitization have been calculated, based upon the above assumptions. The results have, as expected, reproduced in many respects those shown by experiments. Finally, a relation between the concentration of interstitial silver ions and the sulphur content in the emulsion grain has been derived.     

The Cluster Mechanism in Sulphur Sensitization

. The production of silver sulphide on two cubic silver halide emulsions has been followed using sodium thiosulphate sensitizer with the outer sulphur atom labelled ³⁵S. It is found that the position of sensitizer adsorption on the silver halide grain has an effect upon its rate of breakdown to yield silver sulphide. The concentration of sensitizer added to the emulsion affects the photographic response. At optimum sensitivity the quantity of silver sulphide present depends upon the initial sensitizer level, the silver sulphide becoming less efficient with increasing sensitizer. Clusters of silver sulphide are probably produced as a result of preferential adsorption of sensitizer by silver sulphide.     

Thiosulphate Reactions at the Surface of Developed Silver

The detection of silver sulphide in processed photographic images has been attributed to the silver adsorbing a monomolecular layer of thiosulphate ions, which react to form silver sulphide when the silver image is bleached in acid dichromate solution. By studying adsorption with thiosulphate having the inner sulphur atom labelled, it has now been shown that most of the thiosulphate ions believed to be adsorbed by the silver image had already suffered rupture at the sulphur-sulphur bond, even before the bleaching step. Treatment of the silver image with a cyanide solution was relatively ineffective in removing the adsorbed sulphur, and it is thus doubtful whether it can be considered to be present in the form of silver sulphide.     

Sulphur Sensitization: The Effect of Sensitizer Concentration on the Constitution of Fog and Sensitivity Centres

Coatings prepared from emulsions sensitized with a range of quantities of thiourea have been treated with dilute solutions of chromic acid and gold thiocyanate prior to exposure and development. The effect of the oxidizing agent and gold treatment on the fog centres depends on the condition of sulphur sensitization. The results can be explained if fog centres consist of both silver and silver sulphide. The relative proportions of these two components are related to the quantity of sulphur sensitizer added to the emulsion.     

Industrial Radiology,Past, Present and Future

A new model for sulphur sensitization has been developed. It is based on the surface double layer which has previously been shown to occur in silver halides. The charge present in this double layer causes the energy bands to bend downward or upward according to whether silver sulphide is present on the crystal surface or not. Where silver sulphide is not in contact with the surface the bands bend upward, thus impeding the motion of photo-electrons towards the surface. Conversely in points where silver sulphide is adsorbed onto the Srystal surface, the bands bend downwards, thus yielding an attracting force driving the photoelectron towards the silver sulphide speck. The bending of the bands may have the additional effect of increasing the lifetime of electrons in traps which are near to a silver sulphide Speck, thus holding the trapped electron for a long enough time as to allow the “ionic step” to take place. Our experimental results as well as others reported in the literature are explained with this model.     

Electrokinetic Mea urements on Silver,Silver Bromide and Silver Sulphide

The zeta-potentials af silver. silver bramide and silver sulphide have been determined by streaming potential and microelectrophoresis measurements. It is shown that the zela-potential af SIlver bromIde depends on crystal size and can be altered by photolysis. The charge on colloidal silver and silver sulphide is negative at pAg values above 5 O. The effect of adsorbed gelatin an the zeta-potential of the three substances has been examined and the results are discussed in relation to theories of photographic development.     

Adsorption of Photographic Sulphur Sensitizers to Silver Bromide and Silver Sulphide

Heats of adsorption of thiosulphate, thiosulphatoargentate and p-toluenethiosulphonate to silver bromide, silver bromo"dide, silver chloride and silver sulphide were measured using a slow microcalorimeter. The results did not confirm previous evidence for the cluster mechanism for silver sulphide formation during sulphur sensitization. The possibility of this model was discussed. Heats of adsorption of silver and sulphide ions were also measured.     

The Role of Thiosulphate in the Formation of Sulphide Stains during Bleaching

Image-wise silver sulphide stains were produced on pure, silver bromide emulsions during reversal processing with a dichromate bleach when the first developer contained a small quantity of sodium thiosulphate. The role of the thiosulphate in promoting the stain was investigated. The thiosulphate was found to be strongly adsorbed to the negative-image silver and could not be removed even by strong alkaline hydrogen peroxide. The adsorbed thiosulphate was decomposed in the bleach bath and silver sulphide was formed. Sulphite ion would inhibit the stain only in the presence of silver bromide. Iodide ion acted as a stain inhibitor with or without residual silver bromide and probably competed with thiosulphate in the adsorbed layer.     

Book Review

By tracer methods it was demonstrated that thiosulphate is most tenaciously adsorbed to developed silver or silver foil. A limiting amount was held by any surface: one thiosulphate ion being estimated for every three silver atoms in the surface. On bleaching developed silver with acid dichromate, no decrease in radioactivity occurred, demonstrating quantitative formation of silver sulphide from adsorbed thiosulphate. On the basis of these observations, the silver sulphide content of bleached photographic images can be used to estimate the specific surface of the silver. Reasonable estimates were obtained of the particle size of a Carey-Lea silver sol. In agreement with earlier X-ray determinations, the mean filament diameters of developed silver from a series of emulsions did not increase much with increased undeveloped grain size.     

Exposure Addition Effects and Their Terminology

Studies of the increases in overall sensitivity, in red light sensitivity, and in silver sulphide during sulphur sensitization of a photographic emulsion have been carried out. They suggest that there are two quite distinct mechanisms by which the silver sulphide can give rise to increase of light sensitivity.     

Structural and electrical conductivity studies on nanocrystalline undoped and silver doped zinc sulphide

Zinc sulphide (ZnS) and silver doped zinc sulphide nanocrystallites (ZnS:Ag) of average size 4 and 8 nm, respectively, have been synthesized by chemical precipitation technique. The structural and morphological studies using X-ray and high resolution transmission electron microscopy (HRTEM) measurements have confirmed hexagonal structure for the samples. Using the impedance spectroscopy method, the effect of grain interior and electrode–sample interface effect on their conductivity have been studied at various temperatures. In high temperature region, the electrode–sample interface effect is found to be larger than that of the grain interior region. Further, the results of the activation energies of the charge carriers in both the regions are determined and analyzed. The conduction mechanism of silver doped zinc sulphide nanocrystallites has been studied at various temperatures and the results are reported.     

Aqueous synthesis of Zn-based ternary core/shell quantum dots with excellent stability and biocompatibility against different cell lines

Journal of Materials Science - Ternary quantum dots (QDs) such as zinc indium sulphide (ZIS), copper indium sulphide (CIS) and silver indium sulphide (AIS) have received great attention. Among...     

The Adsorption of Thiosulphate Ions to Emulsion Grains,and the Role of these Adsorption Ions in Silver Sulphide Formation

The adsorption of thiosulphate to the grains of a silver halide emulsion has been studied with the aid of radioactive thiosulphate. The adsorption has been shown to follow a Langmuir isotherm. The amount of thiosulphate adsorbed falls with increasing emulsion pAg, but is not greatly affected by emulsion pH or temperature. In the digestion process, adsorption is necessary before silver sulphide formation can take place, and this breakdown reaction is a first order one with respect to the amount of thiosulphate adsorbed.     

Analytical Evidence Bearing on the Halogen Acceptor Theories of Sulphur Sensitization

It is shown analytically that when a sulphur-sensitized emulsion is exposed, silver sulphide is destroyed by the halogen produced during the exposure. The amount destroyed is dependent upon the time of exposure. If, however, other halogen acceptors are present during the exposure, they will preferentially accept the halogen. As these halogen acceptors have no effect on the sensitivity of either the sensitized or the unsensitized emulsion, it is concluded that the analytical evidence is not compatible with theories of sulphur sensitization in which the primary function of the silver sulphide is considered to be one of halogen acceptance.     

The Eleventh Renwick Memorial Lecture: The Nature Of Photographic Sensitivity

This paper reviews the work on photographic sensitivity which has been carried out by the author and his colleagues, and presents the conclusions which have been drawn from it. The earlier concept of the sensitivity speck has been replaced by that of the sensitivity centre. The sensitivity speck was assumed to consist of silver or of silver sulphide and to have the function of concentrating silver atoms: the sensitivity centre is a region of enhanced reactivity associated with a crystal imperfection. The conclusion is now that the principal function of the silver sulphide is to trap positive holes and thus to prevent the regression of latent image specks. The theory of dye sensitization has been extended and a number of new features introduced. According to present ideas, the latent image is formed in two stages. In the primary stage, electrons and positive holes are liberated and the positive holes are trapped with the production of interstitial silver ions. In the secondary stage these combine with the conduction electrons to form first latent pre-image specks, then latent sub-image specks, and finally stable latent image specks. A discussion of reciprocity failure is given. The new approach to the theory of photographic sensitivity, in which the role of kink sites Is emphasized throughout, leads to the enunciation of four basic principles which must be satisfied by any theory of the formation of the latent image. Of these, only the Gurney-Mott principle has previously been recognized.     

Surface-enhanced Raman scattering dendritic substrates fabricated by deposition of gold and silver on silicon

This paper reports a study on the preparation of gold nanoparticles and silver dendrites on silicon substrates by immersion plating. Firstly, gold was deposited onto silicon wafer from HF aqueous solution containing HAuCl4. Then, the silicon wafer deposited gold was dipped into HF aqueous solution of AgNO3 to form silver coating gold film. Scanning electron microscopy reveals a uniform gold film consisted of gold nanoparticles and rough silver coating gold film containing uniform dendritic structures on silicon surface. By SERS (surface-enhanced Raman scattering) measurements, the fabricated gold and silver coating gold substrates activity toward SERS is assessed. The SERS spectra of crystal violet on the fabricated substrates reflect the different SERS activities on gold nanoparticles film and silver coating gold dendrites film. Compared with pure gold film on silicon, the film of silver coating gold dendrites film significantly increased the SERS intensity. As the fabrication process is very simple, cost-effective and reproducible, and the fabricated silver coating gold substrate is of excellent enhancement ability, spatial uniformity and good stability.     

中国古代金银器物设计的发展历史

从原始社会末期至魏晋南北朝,金银主要是作为饰品和货币,少有用来制作器皿。进入隋唐以后,西方金银器物的大量输入,使得金银被广泛制作成器物,金银器物设计得到高度发展。宋代开始,金银器物世俗化、商品化的现象十分突出,因而在设计上表现出轻巧玲珑、典雅秀丽等风格特点。元明清时期,在金银器的制作方面,官府有专门的作坊,民间也出现了一些＂治金＂＂治银＂的名家高手,金银器物的设计与制作相当繁荣。梳理中国古代金银器物的发展演变过程,不难发现,中国古代金银器物的发展是逐步从小件饰品向器皿演变的,中国古代金银器物设计艺术在本土文化艺术的影响下产生并发展,同时在吸收域外设计艺术的情况下形成了别具一格的艺术特色。     

Ultrasonic Alloying of Preformed Gold and Silver Nanoparticles

Alloyed gold/silver nanoparticles with a core/shell structure are produced from preformed gold and silver nanoparticles during ultrasonic treatment at different intensities in water and in the presence of surface‐active species. Preformed gold nanoparticles with an average diameter of 15 ± 5 nm are prepared by the citrate reduction of chloroauric acid in water, and silver nanoparticles (38 ± 7 nm) are formed after reduction of silver nitrate by sodium borohydride. Bare binary gold/silver nanoparticles with a core/shell structure are formed in aqueous solution after 1 h of sonication at high ultrasonic intensity. Cationic‐surfactant‐coated preformed gold and silver nanoparticles become gold/silver‐alloy nanoparticles after 3 h of sonication in water at 55 W cm^?2, whereas only fusion of isolated gold and silver nanoparticles is observed after ultrasonic treatment in the presence of an anionic surfactant. As the X‐ray diffraction profile of alloyed gold/silver nanoparticles reveals split, shifted, and disappeared peaks, the face‐centered‐cubic crystalline structure of the binary nanoparticles is defect‐enriched by temperatures that can be as high as several thousand Kelvin inside the cavitation bubbles during ultrasonic treatment.