ADSORPTION DYNAMICS OFCO2ON HYDROGEN PRECOVEREDZn-ZnO(0001): A MOLECULAR BEAM STUDY

2004 ◽  
Vol 11 (06) ◽  
pp. 521-529 ◽  
Author(s):  
J. WANG ◽  
U. BURGHAUS
Keyword(s):  
Monte Carlo ◽  
Binding Energy ◽  
Thermal Desorption ◽  
Impact Energy ◽  
Atomic Hydrogen ◽  
Molecular Beam ◽  
Thermal Desorption Spectroscopy ◽  
Adsorption Dynamics ◽  
Site Blocking ◽  
The Impact

Presented are initial, S0, and coverage, Θ, dependent, S(Θ), adsorption probability measurements, respectively, of CO2adsorption on a hydrogen precovered, polar, Zn -terminated surface of ZnO , parametric in the impact energy, Ei, and atomic hydrogen precoverage, ΘH. Furthermore, CO2Thermal Desorption Spectroscopy has been used to estimate ΘHas well as the binding energy of CO2on H / Zn - ZnO . The S(Θ) curves are below Ei=0.56 eV , consistent with precursor-mediated adsorption (S~ const ), and above that impact energy with adsorbate-assisted adsorption (S increases with Θ). Although a decrease in the CO2binding energy from 32.5 to 28.8 kJ/mol with ΘHis present, S(Θ, ΘH) curves are consistent with a physical site blocking, as demonstrated by Monte Carlo Simulations.

Modification of InN Properties by Interactions with Hydrogen and Nitrogen

2005 ◽  
Vol 892 ◽  
Author(s):  
Maria Losurdo ◽  
Maria Michela Giangregorio ◽  
Giovanni Bruno ◽  
Tong-Ho Kim ◽  
Pae Wu ◽  
...  
Keyword(s):  
Atomic Hydrogen ◽  
Molecular Beam ◽  
Morphological Changes ◽  
Epitaxial Films ◽  
Intensity Increase ◽  
Force Microscopy ◽  
Atomic Force ◽  
Peak Energy ◽  
Hall Effect Measurements ◽  
The Impact

AbstractThe interaction of InN epitaxial films grown by r.f. plasma assisted molecular beam epitaxy with atomic hydrogen and nitrogen, produced by remote r.f. H2 and N2 plasmas, is investigated. InN strongly reacts with both atomic hydrogen and nitrogen yielding depletion of nitrogen and concurrent formation of In clusters. The impact of hydrogen treatments on the optical properties of InN is assessed using photoluminescence (PL). It is found that hydrogen suppresses the intense PL band peaked at approximately 0.7eV for the as-grown InN epitaxial layers, and results in the appearance of a new PL band whose peak energy and intensity increase with H-dose. The effect of exposure to atomic hydrogen and nitrogen on electrical properties of InN is investigated using Hall effect measurements. Atomic force microscopy is also used for studying the morphological changes of InN upon interaction with atomic hydrogen and nitrogen.

On the Methodology of Thermal Desorption Spectroscopy to Evaluate Hydrogen Embrittlement

2012 ◽  
Vol 706-709 ◽  
pp. 2354-2359 ◽  
Author(s):  
Diana Pérez Escobar ◽  
Kim Verbeken ◽  
Lode Duprez ◽  
Marc Verhaege
Keyword(s):  
Hydrogen Embrittlement ◽  
Thermal Desorption ◽  
Surface Preparation ◽  
Thermal Desorption Spectroscopy ◽  
Sample Surface ◽  
Hydrogen Desorption ◽  
Sample Geometry ◽  
Metal Interactions ◽  
Charging Time ◽  
The Impact

Thermal desorption spectroscopy (TDS) is a very important tool in hydrogen embrittlement (HE) related research and has been applied on many different materials over the last decades in order to improve knowledge on the HE phenomenon. TDS provides the opportunity to distinguish between different types of hydrogen traps based on the analysis of a spectrum with different peak temperatures each corresponding to hydrogen desorption from a specific trap. These peak temperatures, and consequently the different traps in a material, arise from the various microstructural characteristics of the material. However, TDS results are also influenced by many other parameters, such as the sample surface preparation, the electrolytes used for hydrogen charging, sample geometry, charging time, current density, charging temperature. Even though the use of thermal desorption to evaluate hydrogen-metal interactions has increased over the past years, a careful evaluation of the effect of these other parameters was not yet performed. In this work, the impact of some of the above mentioned parameters was studied. It was demonstrated that the sample geometry, the surface roughness, and the initial total pressure of the TDS chamber influenced significantly the obtained TDS spectrum.

scholarly journals Kinetics of Molecular Beam Epitaxy: Effect of Ion-Induced Sputtering

1990 ◽  
Vol 202 ◽  
Author(s):  
Peter M. Richards
Keyword(s):  
Monte Carlo ◽  
Steady State ◽  
Binding Energy ◽  
Molecular Beam Epitaxy ◽  
Monte Carlo Simulations ◽  
Molecular Beam ◽  
Ion Beam ◽  
Kinetics Of

ABSTRACTSteady state roughness of surfaces growing by molecular beam epitaxy is investigated by Monte Carlo simulations under conditions where an ion beam is also present which sputters adatoms off the surface. If the sputtering is random, it only increases the roughness. But if the sputtering probability is strongly dependent on the binding energy of an adatom within a cluster or island, the ions can have a smoothening effect. Physical arguments are given in support of the results.

scholarly journals A kinetic Monte Carlo approach to diffusion-controlled thermal desorption spectroscopy

2017 ◽  
Vol 375 (2098) ◽  
pp. 20160404 ◽  
Author(s):  
T. Schablitzki ◽  
J. Rogal ◽  
R. Drautz
Keyword(s):  
Monte Carlo ◽  
Markov Chains ◽  
Thermal Desorption ◽  
Kinetic Monte Carlo ◽  
Thermal Desorption Spectroscopy ◽  
Structural Features ◽  
Coarse Grained ◽  
Analytic Approximation ◽  
Absorbing Markov Chains ◽  
Constant Heating

Atomistic simulations of thermal desorption spectra for effusion from bulk materials to characterize binding or trapping sites are a challenging task as large system sizes as well as extended time scales are required. Here, we introduce an approach where we combine kinetic Monte Carlo with an analytic approximation of the superbasins within the framework of absorbing Markov chains. We apply our approach to the effusion of hydrogen from BCC iron, where the diffusion within bulk grains is coarse grained using absorbing Markov chains, which provide an exact solution of the dynamics within a superbasin. Our analytic approximation to the superbasin is transferable with respect to grain size and elliptical shapes and can be applied in simulations with constant temperature as well as constant heating rate. The resulting thermal desorption spectra are in close agreement with direct kinetic Monte Carlo simulations, but the calculations are computationally much more efficient. Our approach is thus applicable to much larger system sizes and provides a first step towards an atomistic understanding of the influence of structural features on the position and shape of peaks in thermal desorption spectra. This article is part of the themed issue ‘The challenges of hydrogen and metals’.

Interactions among 18O2, C2H4, and NO on the surface of stepped Pt(332)

2008 ◽  
Vol 86 (1) ◽  
pp. 39-49 ◽  
Author(s):  
Yuhai Hu ◽  
Keith Griffiths
Keyword(s):  
Thermal Desorption ◽  
Annealing Temperature ◽  
Catalytic Reduction ◽  
Thermal Desorption Spectroscopy ◽  
Blocking Effect ◽  
No Adsorption ◽  
Infrared Reflection Absorption Spectroscopy ◽  
Infrared Reflection ◽  
Site Blocking

The influence of co-adsorbed 18O2 (18O) on NO/C2H4 reactions on the surface of stepped Pt(332) has been investigated using Fourier transform infrared reflection–absorption spectroscopy (FTIR-RAS) and thermal desorption spectroscopy (TDS). The presence of 18O2 (18O) results in changes in C2H4 dissociation behavior, with formation of ethylidyne taking place at surface temperature much higher than that in the absence of 18O2 (18O). Pre-annealing 18O2/C2H4 co-adlayers to 250 and 300 K does not lead to significantly different IR spectra, but a variety of spectra are observed when the 250 K and 300 K 18O/C2H4 co-adlayers are further exposed to 0.8 L NO at 90 K, depending on the 18O2 pre-exposure. NO adsorption in bridge sites, both on steps and on terraces is more significantly suppressed for the co-adlayers in which 18O2/C2H4 is pre-annealed to 250 K. This site-blocking effect is enhanced with increasing 18O2 exposure. However, no new surface species, which are intermediates for N2 production, are detected. Thermal desorption spectra indicate that various species are produced, but only N2 and H2 desorption have intensities that can be reliably analyzed (that is to be able to quantitatively elucidate how the yields of these two species vary with change in the ratios of NO to C2H4 and 18O2). Desorption of both N2 and H2 is more strongly dependent on 18O2 exposure than on the temperature to which 18O2/C2H4 adlayers are pre-annealed. The presence of 18O2, irrespective of the dosing sequence, suppresses N2 desorption, but this effect is much weaker when 18O2 is post-dosed. For the case with 18O2 pre-dosed, irrespective of the annealing temperature (250 K or 300 K), N2 desorption is greatly suppressed at an 18O2 exposure of 0.2 L, but thereafter remains almost unchanged with increasing 18O2 exposure from 0.4 to 1.6 L. This feature of N2 desorption is explained by the restoration of the adsorption of NO onto steps and the subsequent NO dissociation on these sites. In contrast, H2 desorption decreases continuously and disappears at 0.8 L 18O2 and higher. It is concluded that the presence of 18O2 in the reaction of NO with C2H4 on the surface of Pt(332) does not play any role of activating the surface reactants.Key words: NO, platinum, C2H4, deNOx, hydrocarbon, selective catalytic reduction.

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