Synchrotron x-ray-diffraction study of the structure and growth of Xe films adsorbed on the Ag(111) surface

Abstract

Synchrotron x-ray scattering has been used to investigate the structure and growth of perhaps the simplest of all films: xenon physisorbed on the Ag͑111͒ surface. High-resolution x-ray scans of the in-plane structure and lower-resolution scans ͑specular and nonspecular͒ of the out-of-plane order were performed. The Xe films were prepared under both quasiequilibrium and kinetic growth conditions, and have fewer structural defects than those investigated previously by others on graphite substrates. Under quasiequilibrium conditions, the bulk Xe-Xe spacing is reached at monolayer completion, and the monolayer and bilayer lattice constants at coexistence are inferred equal to within 0.005 Å, consistent with theoretical calculations. The Xe/vacuum interface profile for a complete monolayer and bilayer grown at quasiequilibrium is found to be sharper than for kinetically grown films. At coverages above two layers, diffraction scans along the Xe(01l) rod for quasiequilibrated films are consistent with the presence of two domains having predominantly an ABC stacking sequence and rotated 60°with respect to each other about the surface normal. Annealing of these films alters neither the population of the two domains nor the fraction of ABA stacking faults. The thickest film grown under quasiequilibrium conditions exceeds 220 Å ͑resolution limited͒. Under kinetic growth conditions, x-ray intensity oscillations at the Xe anti-Bragg position of the specular rod are observed as a function of time, indicating nearly layer-by-layer growth. Up to four complete oscillations corresponding to a film of eight layers have been observed before the intensity is damped out; the number of oscillations is found to depend on the substrate temperature, the growth rate, and the quality of the Ag͑111͒ substrate. The specular reflectivity from kinetically grown films at nominal coverages of three and four layers has been analyzed using a Gaussian model which gives a film thickness standard deviation of 0.5 and 1.0 layers, respectively. Diffraction scans along the Xe(01l) rod of these films indicate a larger fraction of ABA stacking faults than found for thicker films. These results demonstrate the difficulty of kinetically growing Xe films thicker than two layers which have an ideal slab geometry. ͓S0163-1829͑99͒03723-6͔

Evolution of Topological Order in Xe Films on a Quasicrystal Surface

“…Their origin appears to be dislocations in the layers, which are most prevalent at the highest temperatures studied, as expected for entropic reasons. This is consistent with x-ray diffraction studies of the growth of Xe on Ag(111), where stacking faults were observed for Xe growth under various growth conditions [24,25], although the overall structure observed was fcc(111). Such a stacking fault is evident in Figure 5, which shows a superposition of Xe layers 2 and 4 at point e in Figure 2.…”

Many-body dispersion effects in the binding of adsorbates on metal surfaces

“…The adsorption height of Xe on Ag(111) has been studied experimentally using low-energy electron diffraction (LEED) 69 and synchrotron x-ray scattering 70 , both assuming bulk truncation of the metal surface. Adsorption energetics have been studied using temperatureprogrammed desorption (TPD) 71,72 and data from inelastic helium scattering 73 .…”

“…Table I shows the optimal adsorption distance and energy using PBE and HSE as underlying exchangecorrelation functionals whereas Figure 1 depicts the binding curve with the HSE+vdW surf and HSE+MBD methods. The adsorption height of Xe on Ag(111) has been studied experimentally using low-energy electron diffraction (LEED) 69 and synchrotron x-ray scattering 70 , both assuming bulk truncation of the metal surface. Adsorption energetics have been studied using temperatureprogrammed desorption (TPD) 71,72 and data from inelastic helium scattering 73 .…”

Late growth stages and post-growth diffusion in organic epitaxy: PTCDA on Ag(111)

“…In the case of layer-by layer growth, characteristic intensity oscillations with the minimum intensity I min = 1 + A + B and the maximum intensity I max = 1 are observed as a function of the deposition time [15,19,20,21] (see Fig. 2).…”