Tungsten implantation

The oxidation rate of niobium in air from 800°C to above 1000°C can be decreased by alloying e.g. with hafnium, zirconium, tungsten, molybdenum, titanium or tantalum . However, the preferred fabricable alloys still require further protection by coating . Ion implantation improves thermal oxidation resistance of niobium in oxygen below 500°C . 

Applications Ion implantation is widely employed to improve the life of tools. Thus press tools, dies and gear cutters can be treated to increase their durability by three times or more. Nitrogen-implanted tungsten carbide drawing dies for copper and iron wire can be improved up to fivefold. By implanting chromium, aluminium or silicon a considerable increase in the corrosion resistance of steel can be obtained. Implantation of chromium into aircraft bearing alloys has improved their durability in marine environments . 

Compared to the corresponding carbides the heats of oxygen chemisorption on metals are higher. For example, on metallic tungsten the heat of adsorption is 812 kJ/mole 02, while on metallic chromium it is 730 kJ/ mole 02n. These values are significantly higher that those of the carbides of the same metals (Table 16.2). Thus, carbon atoms, when implanted in the metal lattice, reduce the adsorption affinity of the metal atoms towards oxygen. 

Peuster M, Pink C, Wohlsein P, et al. (2003) Degradation of tungsten coils implanted into the subclavian artery of New Zealand white rahhits is not associated with local or systemic toxicity. Biomaterials 24 393-399. 

Figure 8.2. Selective tungsten using silicon implantation, a) Mo is used as an implant mask, b) after removal of the Mo mask, c) after selective tungsten deposition.

A good correlation was found between the linewidth of the Mo mask and the tungsten line width. A disadvantage of this technique is that a high dose is needed before tungsten growth starts to occur. With an implant current of 100 /jlA and a dose of 5E16 at/cm2, a 6" wafer needs about 250 minutes of implantation time ... 

A consistent model of the action of fluorine on gate oxide was proposed by Wright and Saraswat243. In this study the fluorine was introduced in the poly-Si by means of ion implantation. This approach allows various fluorine levels to be studied and eliminates complications from other elements like tungsten or hydrogen or stress induced effects. To... 

Use the tungsten needle to gently separate the neural plate from the paraxial mesoderm Roll off or push away the neural plate as it comes loose (Note 6). Rinse the operated area with saline-PS from the 1-mL syringe to wash off the Dispase. The aim of this procedure is to make a pocket beneath the lateral part of the neural plate to house the notochord implant in close apposition with the basal surface of the neuroepithelium. Therefore, do not fully separate the neural plate and the paraxial mesoderm, as the graft will then settle down too deeply next to the host notochord. Cut donor notochords into pieces of about 5(X)-l,000 jm, transfer one piece in as little volume as possible to a serum-coated 20-pL pipet tip. 

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