Nickel absorbtion

Scheme 1 Electronic states involved in the absorbtion bands in the region of the first singlet—triplet intersection for octahedral, tetragonal and trigonal complexes of nickel(II).336 Solid arrows denote spin-allowed absorbtion transitions, dotted arrows connect pairs of interacting levels. (reprinted with permission from ref. 336 1998, American Chemical Society).

Very recently, Bailey and Richards (23) have shown that a high degree of sensitivity for adsorbed species can be achieved by measuring the absorption of infrared radiation on a thin sample cooled to liquid helium temperature. The optical arrangement used in these studies is shown in Figure 10. The modulated beam produced by the interferometer is introduced into the UHV sample chamber and reflected off a thin slice of monocrystalline alumina covered on one side by a 1000 k film of nickel or copper. Radiation absorbed by the sample is detected by a doped germanium resistance thermometer. The minimum absorbed power detected by this device when operated at liquid helium temperature is 5 x 10 14 W for a 1 Hz band width. With this sensitivity absorbtivities of 10"4 could be measured. 

A thin metal layer of nickel is often used as a transparent gate of MIS photo-detectors in the infrared range. To reduce the absorbtion of photons in the gate, it is made as thin as possible. However, when the layer thickness is less than 6 nm the device yields drop off dramatically. A gate of nickel having a thickness of 6 nm absorbs from about 30 to 40 percent of the radiation. A solution to this problem is found in US-A-4654686 where a portion of the metal layer forming the gate is eliminated. 

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