Tungsten 2 structure

It is possible that a small amount of oxygen is necessary to stabilize the -tungsten structure (see, e.g. Moss Woodward, 1959). A consideration of the effect of this oxygen might lead to a small revision in the values of the single-bond radii and amounts of d character. 

Table 9.8. Intermetallic phases with the SnNb3 (or (3-tungsten) structure.

This section describes the structural chemistry of 14 molecular structures, 3 of chromium, 8 of molybdenum, and 3 of tungsten. The only binary xanthate structures are those of chromium, all other structures are at least ternary in nature. For the chromium and tungsten structures, conventional monodent-ate and bidentate coordination modes of the xanthate ligand are found. By contrast, a rich, diverse, and fascinating coordination range is observed for the... 

Synthesis of [2,3-bis(methoxycarbonyl)-5,6-dimethyl-7-phenyl-7-phospha-norbornadiene](pentacarbonyl)tungsten (Structure 5 Scheme 1), the starting compound for the generation of (phenylphosphinidene)(pentacarbonyl)tungsten (Structure 6,... 

On a typical product wafer, the tungsten density is usually low, that is, about 20% or less. The remaining surface is covered mainly by oxide or other dielectric materials. This leaves four times more chances to have the scratch on the oxide or dielectric material than on tungsten. Furthermore, the tungsten structures are usually very small and a scratch is typically less visible. On a very small structure, a scratch on the W will look more like a pit. In addition, W is one of the hardest metals that is more difficult to scratch than other softer materials such as copper or aluminum. For all these reasons, after W CMP, it is more likely to see scratches on the dielectric materials than on the W structures (Fig. 17.18). 

FIG. 29.4. (a) The p-tungsten structure. As regards environment the atoms are of two types. The twelve equidistant neighbours of an atom of the first type (shaded circles) and the six nearest neighbours of an atom of the second type (open circles) are shown, (b) The arrangement of the four nearest neighbours of an atom in metallic uranium (a form). 

Figure 1.8 The cubic unit cell of the A2, tungsten, structure...

Most pure metals adopt one of three crystal structures, Al, copper structure, (cubic close-packed), A2, tungsten structure, (body-centred cubic) or A3, magnesium structure, (hexagonal close-packed), (Chapter 1). If it is assumed that the structures of metals are made up of touching spherical atoms, (the model described in the previous section), it is quite easy, knowing the structure type and the size of the unit cell, to work out their radii, which are called metallic radii. The relationships between the lattice parameters, a, for cubic crystals, a, c, for hexagonal crystals, and the radius of the component atoms, r, for the three common metallic structures, are given below. 

For the body-centred cubic [A2, tungsten structure] the atoms are in contact along a cube body diagonal. The body diagonal of the unit cell is thus equal to 4 r. This is also equal to 3dm, i.e. 3 a/y/3, so that... 

Fig. 5.1 Spin resolved intensities of Co/W(110) after excitation with Ne I radiation hv = 16.85 eV). Filled upward triangle denote majority and filled downward triangle minraity electrons. The tungsten structure at a binding energy of 2.9 eV shows significantly different peak areas in both spin channels (light and dark gray shaded) indicating a spin dependence of the particular attenuation lengths...

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