Amorphous conduction electrons

In this chapter we present a survey of our current understanding of interrelations between the electronic and ionic structure in late-transition-polyvalent-element metallic glasses. Evidence of a strong influence of conduction electrons on the ionic structure, and vice versa, of the ionic structure on the conduction electrons, is presented. We discuss as well the consequences to phase stability, the electronic density of states, dynamic properties, electronic transport, and magnetism. A scaling behaviour of many properties versus Z, the mean electron number per atom, is the most characteristic feature of these alloys. Crystalline alloys which are also strongly dominated by the conduction electrons are often called electron phases or Hume-Rothery phases. The amorphous alloys under consideration are consequently described as an Electron Phase or Hume-Rothery Phase with Amorphous Structure. Similar theoretical concepts as applied to crystalline Hume-Rothery alloys are used for the present amorphous samples. 

Fig. 5. Fluctuating band edges of amorphous semiconductors arising from compositional or structural inhomogeneities. A typical eigenstate near the conduction band edge is shown transport of conduction electrons involves tunneling between neighboring minima or thermal activation.

The lowering in symmetry is also the reasop for the much lower relaxation rate observed in amorphous DyosAgoj. It stems from the fact that in the isolated I 15/2) state the possibilities of conduction electron relaxation or dipole-dipole relaxation are absent. Enhancement of the relaxation rate can only take place when... 

Amorphous samples were prepared via the glow discharge of silane, and the kinetics of H exo-diffusion were studied by using conductivity, electron paramagnetic resonance, nuclear activation, and infra-red absorption methods. The results revealed the existence of two main stages of exo-diffusion. Below 500C, H evolution was controlled by a diffusion process which could be described by ... 

Uhlmann [118] conducted electron microscopy studies of thin amorphous films and observed what he termed a typical pepper and salt texture, characteristic of textures seen near the resolution limit in the electron microscope. For comparison Uhlmann and coworkers [118, 1221 obtained small angle x-ray scattering (SAXS) data that are not consistent with a nodular texture in glassy polymers. The SAXS intensity measurements of glassy polymers such as PC, PMMA, PET, PVC and PS do not support such a domain structure. SAXS is a more suitable technique than TEM for detecting order, as a larger sample volume is statistically sampled. 

The short-range order in a material is important in determining optoelectronic properties. For instance, x-ray and electron diffraction experiments performed on amorphous siHcon (i -Si) and germanium (a-Ge) have revealed that the nearest neighbor environments are approximately the same as those found in their crystalline counterparts (6) photoemission experiments performed on i -Si show that the DOS in valence and conduction bands are virtually identical to the corresponding crystal with the exception that the singularities (associated with periodicity) present in the latter are smeared out in the former. 

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