Coadsorption of water and lithium on the Ru(001) surface

A549 desorption of surface species. The desorbed molecules produce a pressure rise in the vacuum system that is proportional to the coverage and is detected with a quadrupole mass spectrometer. For surface temperatures between 160 and 280 K, SO for D 2 increases by - 50% and for H 2 by - 70%. Low-coverage sticking coefficients So for both NO and CO are found to be independent of surface temperature in the range 160 to 430 K and indicate adsorption through a precursor state. Isosteric heats of adsorption of NO and CO decline as the coverage increases from initial values of 26 +_2 and 32 + 2 kcal/mol to 12 + 2 and 16 + 2 kcal/mol, respectively. By combining the equilibrium and adsorption data, pre-exponential factors for desorption have been determined as a function of coverage. Laser-induced surface damage does not appear to be significant in these results. However, repeated desorption without high temperature annealing causes a drop in SO for NO and CO by 30% and a rise in SO for D 2 by a factor of five. Measurements made with LITD agree well with available literature values obtained by other methods. However, LITD has several important advantages, especially the capability for the repeated measurement of surface coverages of a wide variety of adsorbates at high repetition rates in the presence of background pressures up to 10 -4 Torr.

157

Surface Science 176 (1986) 157-164 North-Holland, Amsterdam WATER ADSORPTION

ON Pt(U0)

Jean FUSY and Robert DUCROS

CNRS, Laboratoire Maurice Letort associb ~ l'Universitb de Nancy 1, B.P. 104, 54600 Villers-les-Nancy, France Received 10 February 1986; accepted for publication 9 May 1986 Water adsorption on Pt(ll0) has been electron stimulated desorption ion angular troscopy (TDS), and work function (A~) molecularly adsorbed. The first fractions are to build up.

studied by electron stimulated desorption (ESD), distribution (ESDIAD), thermal desorption specmeasurements. Between 100 and 200 K water is adsorbed as small clusters before an ice layer starts

Surface Science 176 (1986) 165-182 North-Holland, Amsterdam COADSORPTION O N T H E Ru(001)

165

OF WATER AND LITHIUM SURFACE

S. S E M A N C I K

Chemical Process Metrology Division, National Bureau of Standards, Gaithersbur~ MD 20899, USA D.L. DOERING

Department of Physics, University of Florida, Gainesville, FL 32611, USA and

A550 T.E. M A D E Y

Surface Science Division, National Bureau of Standards, Gaithersbur~ MD 20899, USA Received 4 May 1986; accepted for publication 15 May 1986 The interactions between water and lithium have been studied on the surface of a Ru(001) crystal using thermal desorption spectroscopy, electron stimulated desorption ion angular distributions (ESDIAD), Auger spectroscopy and LEED. The presence of Li was found to influence strongly the H + ESD yield and the ESDIAD patterns from adsorbed water even at Li coverages of 0.02 monolayer; changes in the thermal desorption states for water were also observed at low Li coverages. For coadsorbed Li coverages above 0.05, ESDIAD measurements provided clear evidence of water decomposition, even at surface temperatures near 80 K; evidence for dissociation was also obtained from thermal desorption and Auger measurements. The present results are compared and contrasted to those reported previously for the H20/Na/Ru(001 ) system.

Surface Science 176 (1986) 183-192 North-Holland, Amsterdam REACTION

MECHANISMS

OF SEMICONDUCTORS: UV-STIMULATED R.B. J A C K M A N ,

183 FOR THE PHOTON-ENHANCED AN INVESTIGATION

INTERACTION

ETCHING

OF THE

OF CHLORINE

WITH Si(100)

H . E B E R T a n d J.S. F O O R D

Department of Chemistry, The University, Southampton, S09 5NH, UK Received 2 January 1986; accepted for publication 3 June 1986 The interaction of chlorine with Si(100) has been studied, both in the absence and presence of UV radiation. In the dark, two adsorption states (a,/3) are populated sequentially with high sticking probability. The a state exhibits an approximate activation energy to desorption of 115 kJ mol 1 and evolves as SIC14; the corresponding value for the /3 state is 235 kJ mo1-1 and desorption takes place predominately as a mixture of SiC14 and SiC12. Analysis also indicates that spontaneous evolution of SiC14 occurs simultaneous to adsorption into the a and /3 states. The effects of UV radiation are such as to induce surface interconversion of strongly adsorbed forms into more weakly bound species. This should lead to increased desorption rates and identifies a possible mechanism for photo-enhanced etching.

Surface Science 176 (1986) 193-218 North-Holland, Amsterdam A SIMPLE RATE EQUATION USEFUL FOR ADSORPTION ANALYSES OF THERMAL DESORPTION SPECTRA

193 SYSTEMS:

Kiyoshi NAGAI

Research Institute for Catalysis, Hokkaido University, Sapporo 060, Japan Received 30 August 1985; accepted for publication 20 May 1986 Using the lattice gas model, a simple rate equation is derived by stressing upon the many body aspect among adsorbates within the absolute reaction rate theory. The rate equation incorporates two more excess modification factors - interaction among reactants and the excluded volume effect - than the conventional Polanyi-Wigner or Arrhenius equation. From the thermodynamic