Metal—hydrogen vibrations and surface vibrational states

1 Metal-hydrogen vibrations and surface vibrational states 

Surface vibrational states of nickel particles have been investigated by comparing the INS spectra of nickel particles of different sizes [2] macroparticles (polycrystalline granules 6—8 mm diameter) and 

The spectrum of the adsorbed layer (water, arising from exposure of both samples of nickel particles to the atmosphere) was obtained by 

The vibrational density of states was calculated for nickel slabs up to 50 layers thick [8], For the first and second layers, the vibrational density of states was different from that of the bulk reflecting their surface configuration. The calculated surface modes for the various surface planes were compared with experiment. The best agreement was for the (111) surface, see Fig. 7.4, evidence for predominant (111) faceting of the micro particles. Although by today s standards the spectra and the fits are poor, the work is of interest as an example of the use of INS in surface characterisation. 

A more recent (2000) INS study of the vibrational density of states of nanocrystalline iron and nickel gave results consistent with the earlier work but with better quality spectra [9]. In comparison with reference coarse-grained specimens the nanocrystalline specimens exhibited a modest increase in the population of low-frequency modes, related to the 

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