High-resolution depth profiling of surface hydrogen by a resonant nuclear reaction

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A high-resolution depth-profiling method of hydrogen was developed at the 2C beam line of the new tandem-type Van de Graaph accelerator at the Research Center for Nuclear Science and Technology, University of Tokyo, in aimed at the investigation of hydrogen dynamics at surfaces and interfaces.The experiment was performed in a ultra-high vacuum chamber equipped with LEED and quadrupole mass spectrometer. The resonance nuclear reaction of ^1H (^<15>N,alphagamma) ^<12>C of which resonance width is 1.8KeV was applied to dydrogen detection. A ^<15>N^<2+> ion at an energy of 6.385 MeV was generated from tandem-type Van de Graaph accelerator with an energy spread of 5 keV.The gamma-ray emitted as a result of the nuclear reaction with hydrogen was detected by a Bi_4Ge_4O_<12> scintillator. The gamma-ray yield as a function of the incident energy shows the depth profile of H of the sample. Since the energy loss of a ^<15>N^<2+> ion at 6.385 MeV in Pb is 0.23 KeV/*, the depth resolution estimated from the resonance, Instrumental and Doppler widths is about 40 *. Samples we used are metal overlayr on Si (lll) 7_x7-H and Si (lll) 1_x1-H,which were prepared by exposing the Si (lll) clean surface to atomic hydrogen untill saturation at sample temperatures of 300 and 700 K,respectively, H-Au (001), and Olivine/Aqueous Solution Interface. Atomic hydrogen was produced by introducing H_2 gas through tungsten tube heated at 1800K.We demonstrated that this method is very powerful for high-resolution depth profiling of hydrogen at a surface and interfaces below the surface.