N-15 DOPPLER SPECTROSCOPY OF H-1 ON DIAMOND

Diamond single crystals of [100], [110] and [111] orientation have been chemically treated in order to prepare monolayer (ML) coverages of H-1. Subsequently, sample surface areas of about 0.1 cm2 have been exposed to a N-15 beam of 30 nA at the resonant-reaction energy of 6.385 MeV. The resulting 4.4 MeV gamma rays have been detected by a 10 in x 10 in NaI(Tl) crystal inside a low-level system. The results can be summarized as follows: The initial H coverage of a few ML equivalent quickly desorbs under ionizing radiation, until at about 1 ML a slow desorption stage prevails. In general, the different crystal surfaces, characterized by strong topological irregularities, do not exhibit ideal ML coverage. Similarly, the corresponding Doppler widths do not show the expected dependence on crystal orientation, but are the same within experimental error.