Hydrogen embedded in Ni: Production by incident atomic hydrogen and detection by high-resolution electron energy loss

The vibrational modes of hydrogen embedded in a Ni crystal are shown to be detectable by high-resolution electron-energy-loss spectroscopy and to be unambiguously distinguishable from the vibrational modes of adsorbed hydrogen on the basis of the dependence of the inelastic electron intensity on electron impact energy. The embedded hydrogen has a vibrational frequency of 800--850 cm^-1 and is observed to recombine and desorb as H₂ between 180 and 220 K. The absorption of hydrogen into Ni(111) is achieved under UHV conditions by exposure to atomic hydrogen. As much as an equivalent of 8 monolayers has been absorbed.