Vapour deposition

For direct neutron imaging both IP-ND with inherently present neutron converter material (Gd oxide) or common IP in combination with Gd metal or vapour deposited... 

Thin oxide films may be prepared by substrate oxidation or by vapour deposition onto a suitable substrate. An example of the fomrer method is the preparation of silicon oxide thin-films by oxidation of a silicon wafer. In general, however, the thickness and stoichiometry of a film prepared by this method are difficult to control. 

Model catalysts such as An/Ti02(l 10) have been prepared by metal vapour deposition [42]. Figure A3.10.14... 

Figure A3.10.14 STM image of 0.25 ML Aii vapour-deposited onto Ti02(l 10). Atomie resolution of the substrate is visible as parallel rows. The Au elusters are seen to nueleate preferentially at step edges.

In practical applications, gas-surface etching reactions are carried out in plasma reactors over the approximate pressure range 10 -1 Torr, and deposition reactions are carried out by molecular beam epitaxy (MBE) in ultrahigh vacuum (UHV below 10 Torr) or by chemical vapour deposition (CVD) in the approximate range 10 -10 Torr. These applied processes can be quite complex, and key individual reaction rate constants are needed as input for modelling and simulation studies—and ultimately for optimization—of the overall processes. 

Molecular dissociation and chain reactions in chemical vapour deposition... 

Another trend which can be anticipated from electronegativity data, is drat the bromides will be more easily decomposed thermally than the chlorides, and the iodides more readily than the bromides. A typical comparison is between the compounds of titanium and those of hafnium, which play a significant role in vapour deposition. 

A situation which is frequently encountered in tire production of microelectronic devices is when vapour deposition must be made into a re-entrant cavity in an otherwise planar surface. Clearly, the gas velocity of the major transporting gas must be reduced in the gas phase entering the cavity, and transport down tire cavity will be mainly by diffusion. If the mainstream gas velocity is high, there exists the possibility of turbulent flow at tire mouth of tire cavity, but since this is rare in vapour deposition processes, the assumption that the gas widrin dre cavity is stagnant is a good approximation. The appropriate solution of dre diffusion equation for the steady-state transport of material tlrrough the stagnant layer in dre cavity is... 

Chemical vapour deposition Example. The preparation of films of titanium dioxide. 

A unique application of the solid oxygen electrolytes is in dre preparation of mixed oxides from metal vapour deposits. For example, the ceramic superconductors described below, have been prepared from mixtures of the metal vapours in the appropriate proporhons which are deposited on the surface of a solid electrolyte. Oxygen is pumped tluough the electrolyte by the application of a polarizing potential across the electrolyte to provide the oxidant for the metallic layer which is formed. 

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