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-energy electron diffraction (LEED). To prepare a surface covered by atomic nitrogen we have used ionization-gauge assisted adsorption. A saturation coverage of theta(N)=0.6 is achieved of which about 30% is in the subsurface region. At saturation coverage a [GRAPHICS] LEED pattern is observed. The nu(parallel to)(Ru-N) mode at 41 meV and the Y-perpendicular to(Ru-N) mode at 60 meV are identified. Upon exposing the nitrogen covered surface to hydrogen at 300 K we have observed the formation 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 vibrational 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 at 740 K (from subsurface N), N-beta shifting from 690 to 640 K with increasing coverage, and N-gamma at 550 K. The activation energy for desorption via the N-beta state is 120+/-10 kJ/mol. The TD spectra of mass two showed three desorption states at 450, 550, and 650 K due to the decomposition of NHx. (C) 1997 American Institute of Physics.