VIBRATIONS, COVERAGE, AND LATERAL ORDER OF ATOMIC NITROGEN AND FORMATION OF NH3 ON RU(10(1)OVER-BAR0)

The dissociative chemisorption of nitrogen on the Ru(10 (1) over bar 0 ) surface has been studied using high-resolution electron energy loss spectroscopy (HREELS), thermal desorption spectroscopy (TDS) and low-e nergy electron diffraction (LEED). To prepare a surface covered by ato mic nitrogen we have used ionization-gauge assisted adsorption. A satu ration coverage of theta(N)=0.6 is achieved of which about 30% is in t he subsurface region. At saturation coverage a [GRAPHICS] LEED pattern is observed. The nu(parallel to)(Ru-N) mode at 41 meV and the Y-perpe ndicular to(Ru-N) mode at 60 meV are identified. Upon exposing the nit rogen covered surface to hydrogen at 300 K we have observed the format ion of NH3 which is characterized by its symmetric bending mode delta( s)(NH3) at 149 meV. At 400 K, NH3 could not be detected. The reaction intermediate NH is stable up to 450 K and has been identified by its v ibrational losses nu(Ru-NH) at 86 meV, and nu(N-H) at 408 meV. The TD spectra of mass 14 show three desorption states of nitrogen, N-alpha a t 740 K (from subsurface N), N-beta shifting from 690 to 640 K with in creasing coverage, and N-gamma at 550 K. The activation energy for des orption via the N-beta state is 120+/-10 kJ/mol. The TD spectra of mas s two showed three desorption states at 450, 550, and 650 K due to the decomposition of NHx. (C) 1997 American Institute of Physics.