1,721,149 research outputs found
ON THE DISSOCIATION OF O-2 ON ALKALI-METALS
No full textThe reaction of O-2 With Li and Cs films is accompanied by the emission of electrons. The variations of the initial yields with the velocity of the impinging molecules is exploited to access the dynamics of the adsorption process. The data are analysed in terms of a model where chemisorption proceeds via an intermediate O-2(2-) species. This O-2(2-) state readily dissociates while the de-excitation of the resulting O- into O2- may cause electron emission. From a comparison with experimentally observed electron yields the reaction time and velocity uptake of the products is accessed
Disordering of the Ge(001) surface studied by He atom scattering
No full textThe Ge(001) surface is known to undergo phase transitions from c(4 x 2) to (2 x 1) at low temperature and from (2 x 1) to (I x 1) at high temperature. In the former case the phase transition is shown to occur at 240 K and to fall into the 2D Ising universality class. The high temperature phase transition takes place above 900 K and is characterized by (2 x 1) domain wall proliferation, thus indicating an order-disorder character. We have also observed an increase in the density of steps, but these are shown to be only partially involved in the disordering of the (2 x 1) phase
Comment on "local methylthiolate adsorption geometry on au(111) from photoemission core-level shifts"
No full textThe photoemission from the alkanethiol=
Auð111Þ SAMs is strongly affected by initial and final state
effects, which prevent the determination of the distinct
atomic populations from a simple CLS spectroscopical
analysis
Deuterium scattering from Rh(110) surface
No full textThermal energy deuterium beam scattering (TEDS) from Rh(110) surface is reported and compared to helium atom scattering (HAS). Unlike for He, we find quite strong D-2 off-specular diffraction. The D-2 diffraction intensities are fairly isotropic along the [001] and [1 (1) over bar 0], reflecting the presence of a finite dissociation barrier in the potential energy surface (PES) rather than the anisotropic corrugation of the relevant Rh(110) surface electron density. Inelastic D-2 scattering with strong J=0-->2 kinetic-to-rotational energy conversion is also presented and discussed
Disorder-order evolution of InSb(110) studied by He scattering
No full textThe evolution of surface defects created by low energy ion bombardment on InSb(110) is studied by He beam scattering experiments. At surface temperatures above 500 K the ion erosion is found to proceed layer-by-layer without changing the stoichiometric composition of the surface. This indicates that the nucleation of surface islands driven by vacancy diffusion is faster than the ion erosion. After different doses of Ar+ ion bombardment, the surface is left in a non-equilibrium state whose time evolution is monitored by measuring the profiles of the He diffraction peaks. It is seen that the coalescence of islands proceeds with anisotropic island size distributions
Surface burgers vectors and surface defects
No full textAlthough extended surface defects are often described as dislocations, they are less commonly associated with Burgers vectors. The concept of linear surface dislocations and their associated surface Burgers vectors is defined and discussed in an introductory way and the main properties are summarised. The definition of the Burgers vector differs from that used in the bulk, as a closed path integral is not used. The Burgers vector is a quantity which is conserved, modulo a surface unit vector, and which adds vectorially; and a surface dislocation must form either a closed loop on a surface, or else begin and terminate at a bulk dislocation. The utility of this approach is illustrated by considering a number of applications in real space, in particular imaging with topographic or diffraction contrast, where the concept allows a general means of classifying defects. In diffraction, the surface Burgers vector provides a convenient way of quantifying the effect of defects on peak profiles
O- escape during the oxidation of cesium
No full textExposure of Cs surfaces to O2 causes ejection of O- ions with low yields (∼10-8 per incident O2 molecule) during the first stages of dissociative chemisorption (followed by exoelectron emission at higher exposures), although the work function of the surface exceeds the electron affinity of O and the energetics of the overall reaction is almost zero. A mechanism is proposed whereafter the release of O- is a consequence of strong repulsion in O22- species intermediately formed in front of the surface
Phase diagram of pentacene growth on Au(110)"
No full textWe studied the growth of pentacene (C22H14) on the Au(110) surface by means of He atom scattering and Synchrotron X-ray photoemission. We found that two-dimensional commensurate growth only occurs in the monolayer range for a substrate temperature, T-s, higher than similar to 370 K. Larger amounts of deposited molecules forms three-dimensional uncorrelated clusters on the wetting layer. The desorption of second layer molecules occurs at T-s >= 420 K. The highest coverage ordered phase displays a (6 x 8) symmetry and corresponds to the saturation coverage at T, = 420 K. The (3 x 6) symmetry phase, recently reported for a multilayer planar film [Ph. Guaino, et al. Appl. Phys. Lett. 2004, 85, 2777], is only found at a coverage slightly lower than the (6 x 8) one. The (3 x 6) phase corresponds to the saturation coverage of the first layer at T-s = 470 K
Exoelectron emission during the oxidation of Na films
No full textOxidation of Na films is accompanied by a low yield of electron emission which is, however, confined to the later stages of reaction in which transformation of peroxide (Na2O2) into Superoxide (NaO2) species at the surface takes place. By probing the electronic properties of the outermost layer by means of metastable deexcitation spectroscopy (MDS) and by recording the energy distribution of the emitted exoelectrons the mechanism of this process was found to be analogous to that established previously for the oxidation of Cs films and as proposed earlier theoretically. It involves decay of a hole state derived from the affinity level of the impinging O2 molecule in front of the surface via an Auger transition which, on the other hand, may efficiently be quenched by resonance ionisation from metallic electrons near the Fermi level. Experiments with Na submonolayers adsorbed on a Ru(0001) substrate reveal that for coverages < 0.6 ML the latter effect dominates so strongly that exoelectron emission is no longer observed
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