Survey of Solid-State Physics

Semiconductors are the base materials of most modern chemical sensors. This appendix surveys the fundamental properties of semiconductors both in isolation and in combination with other materials. 

The magnitude of Eg classifies the materials on the basis of their ability to conduct electricity. For Eg kT the material is a good conductor and the Ev and Ec overlap. Insulators, on the other hand, have a large value of Eg, typically in excess of 5 eV. Packets of coherent acoustic energy called phonons move through the crystal lattice and cause dissociation of electrons from the valence band to the conduction band leaving behind holes. In an intrinsic semiconductor, the concentration of electrons n (or holes p) is given by 

Here Nc and Nv are the effective densities of occupied energy states in the conduction and valence band, respectively. The Fermi level Ep represents the average energy position of electron in the material (Fig. C.2). It is defined as 

In intrinsic semiconductors Av Ac, therefore EF lies approximately in the middle of the bandgap. For the intrinsic semiconductor, the concentration of holes and electrons is equal because they are generated by the same process. Therefore 

The analogy between self-dissociation of water to H+ and OH- is obvious. Addition of an impurity (or dopant) is analogous to the addition of a weak base or a weak acid to water. The same condition of electroneutrality must apply. 

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This book covers the important topics of quantum physics, chemistry, simulation, and modehng in soHd state theory, an application of electronic and atomic properties to service performance of materials. The book is not an exhaustive survey of the applications. Other authors would have chosen different topics. Nevertheless, 1 hope that the book will introduce the reader into this vast area of solid-state physics and chemistry and its applications. 

D. R. Hartree, Reports on Progress in Physics 11, 113 (1948) this survey is brought up to date in D. R. Hartree, The Calculation of Atomic Structures Wiley and Sons, New York, and Chapman and Hall, London, 1957. See also R. S. Knox, Bibliography of Atomic Wave Functions/ in Solid State Physics (Seitz and Turnbull, eds.), Academic Press, New York, 1957, Yol. 4, p. 413. 

Two German physical chemists, W. Sehottky and C. Wagner, founded this branch of materials seience. The story is very clearly set out in a biographical memoir of Carl Wagner (1901 1977) by another pioneer solid-state chemist, Hermann Schmalzried (1991), and also in Wagner s own survey of point defects and their interaction (Wagner 1977) - his last publieation. Sehottky we have already briefly met in connection with the Pohl school s study of colour centres... 

As the active substance in a solid solution is in an amorphous state and therefore in a more energetic form, and as its surface area is much greater both in solid solutions and in solid dispersions, the question of its physical and chemical stability arises. The main criterion for physical stability is the extent of recrystallization, which can reduce the bioavailability of the active substance. Surprisingly, a survey of publications in which recrystallization and chemical stability have been investigated reveals only relatively few cases of instability. Table 80 contains a list of publications with stability data for solid solutions of drugs in povidone with a... 

In this chapter, stable polyyne-type compounds and materials are surveyed with regard to their synthesis, properties, and possible applications. They are classified into end-capped polyynes with or without metals and alternating co-polymers having a polyyne unit with or without metals. In order to determine the possible application of polyynes, the detailed chemical and physical properties in solution, and in the liquid, and solid states, must be known. 

A survey of some of the now considerable physical evidence in support of bonding schemes offered for interstitial stabilization of clusters is presented here. This evidence derives from optical, NMR, and Mossbauer spectroscopy, and measurements of magnetic and electrochemical properties. The gathering of much of this evidence has been made possible by successful efforts to excise centered hexazirconium clusters from solid state precursors and to study them as discrete complexes, [(ZrgZjXnLg]"" (Figure 1), both in solution and as discrete species in salts. 

The enormous development of the subject within the last decade is evidenced by the overwhelming number of research papers published, the creation of a number of specialized professional societies and congresses and the appearance of several new journals. Thermal analysis of polymers is too broad in scope to be covered in a single survey. In this report the subject matter is essentially restricted to the problems of the solid state characterization of polymers by thermal techniques, a topic which occupies a central position in Polymer physics. Still, the topic is far too interdisciplinary in nature to lend itself to a coherent line of presentation. Thus the material selected for discussion had to be separated into three individual parts ... 

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