Silver halides, binary

The next five chapters deal with deposition of specific groups of semiconductors. In Chapter 4, II-VI Semiconductors, all the sulphides, selenides, and (what little there is on) tellurides of cadmium (most of the chapter), zinc (a substantial part), and mercury (a small part). (Oxides are left to a later chapter.) This chapter is, understandably, a large one, due mainly to the large amount of work carried out on CdS and to a lesser extent on CdSe. Chapter 5, PbS and PbSe, provides a separate forum for PbS and PbSe, which provided much of the focus for CD in earlier years. The remaining sulphides and selenides are covered in Chapter 6, Other Sulphides and Selenides. There are many of these compounds, thus, this is a correspondingly large chapter. Chapter 7, Oxides and Other Semiconductors, is devoted mainly to oxides and some hydroxides, as well as to miscellaneous semiconductors that have only been scantily studied (elemental selenium and silver halides). These previous chapters have been limited to binary semiconductors, made up of two elements (with the exception of elemental Se). Chapter 8, Ternary Semiconductors, extends this list to semiconductors composed of three elements, whether two different metals (most of the studies) or two different chalcogens. 

It has been demonstrated that the classical equihbiimn defect chemical concepts derived for binary compounds can be apphed to ternary and multinary compoimds. In the case of multicomponent materials, the space charge effects will become very important in cases in which the dimensions are no longer large compared with the thickness of the space charge layers, as in extremely thin films or in stractirral and functional ceramics with crystallites of nanometer dimensiorts. The formation of latent images in silver halide photography represents a prelude to effects of point defects in nanostractured materials, and is related to enlarged concentrations of point defects in botmdary layers. 

The Frenkel disorder is the simultaneous presence of vacancies and atoms in interstitial positions of the same element, for exattple, Va and A . This is an asymmetrical disorder one will thus have two possible Frenkel disorders for a binary sohd the disorder on the A atoms and the disorder on the B atoms. As we will see in section 2.5.2.2.2, the well and the source of the Frenkel disorder are purely local its formation does not require displacement of atoms with long distance. The defects that constitute the disorder can be ionized or not, respecting the electric neutrality. It is for the atom of smaller volume that the Frenkel disorder is most probable because it is easiest to place it in an interstitial position. We will quote, as an example, the Frenkel disorder on silver in silver halides. 

The (compositionally) simplest mineral class comprises the native elements, that is, those elements, either metals or nonmetals that occur naturally in the native state, uncombined with others. Native gold, silver, and copper, for example, are metals that naturally occur in a ductile and malleable condition, while carbon - in the form of either graphite or diamond -and sulfur are examples of nonmetallic native elements. Next in compositional complexity are the binary minerals composed of two elements a metal or nonmetallic element combined with oxygen in the oxides, with a halogen - either fluorine, chlorine bromine, or iodine - in the halides, or sulfur, in the sulfides. The oxide minerals, for example, are solids that occur either in a somewhat hard, dense, and compact form in mineral ores and in rocks, or as relatively soft, unconsolidated sediments that melt at moderate to... 

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