The effect of three-body interactions on thermal desorption spectra

Thermal desorption spectra are calculated for a one-dimensional chain and for a two-dimensional square lattice using the transfer-matrix technique and Monte Carlo simulations. Lateral interactions of adsorbed particles cause a splitting of spectra. The repulsive three-body interactions are shown to lead to an inequality of the integral intensities of the thermal desorption peaks.     

On the reaction order in thermal desorption spectroscopy

Experimental results are presented about stability of electron beams from electron field emission. Differently oriented monocrystalline tips were tested in different environmental conditions: vacuum quality, current density and temperature. It is concluded that [111] oriented tips must be preferred either in cold emission or in 1200 K emission from a built-up tip.     

The effect of sample readsorption on thermal desorption experiments

The influence of sample readsorption on the desorption transients measured in thermal desorption experiments is discussed. In particular, shifts in the temperature of the maximum of the rate of change of the number of sorbed atoms for first and second order desorption transients are calculated in the approximation of small (βτ/ΔW where β is the sweep rate, τ the vacuum time constant and ΔW the width (K) of the desorption transient. Evidence of significant distortion when sample readsorption is moderate is given from numerical solutions of the appropriate equation. A framework is proposed in which activation energies for desorption can be calculated in the presence of non-negligible sample readsorption.     

Intercalation of potassium in graphite studied by thermal desorption spectroscopy

Thermal desorption spectra obtained after multilayer potassium depositions on graphite at T_s = 160 K reveal information about the formation and decomposition of potassium/graphite intercalation structures. Up to six desorption peaks were observed, of which three could be attributed to decomposition of three different intercalation-like surface structures. These structures are formed as the deposited potassium diffuses into the graphite substrate during the recording of the thermal desorption spectra. At submonolayer coverages, potassium desorbs in a sharp peak around 500 K, attributed to decomposition of a single intercalated potassium layer positioned between the two uppermost graphite layers.     

The chemisorption of chlorine on zirconium: Neutral and negative ion thermal desorption spectroscopy

Chloride growth on zirconium is investigated by means of the novel thermal desorption spectroscopy of both neutral and negatively ionized products, and interpreted in terms of a single ionic adsorption model. The monohalide desorption energy decreases from a low-coverage value of 320 kJ to 255 kJ mol⁻¹ at the monolayer level, at which point trihalide growth continues indefinitely, indicative of a corrosion layer. In contrast, the desorption energy for the chloride ion remains essentially independent of coverage, at 293 kJ mol⁻¹     

Combination of temperature-programmed thermal desorption and laser-induced thermal desorption

The combination of temperature-programmed thermal desorption with heating rates of the order of 1 K s^–1 and laser-induced thermal desorption with of the order of 10¹⁰ K s^–1 has proved to be a suitable method to determine both the frequency factor v and the activation energy E _d of desorption. The systems Ni(110)/N₂ and Ni(110)/CO serve as examples.     

Multi-site kinetic Monte Carlo simulations of thermal desorption spectroscopy data

Presented is a kinetic Monte Carlo simulation (KMCS) algorithm for simulating experimental thermal desorption spectroscopy (TDS) data. The KMCS is based on the Master equation approach and applies a first-passage-time analysis, i.e., the time dependence of the kinetics is matched correctly. The KMCS–TDS scheme used here includes multiple kinetically distinct adsorption sites and the effect of lateral interactions as required for fitting experimental data. After the results of extensive tests of the algorithm by means of synthetic data are discussed, experimental TDS curves are reproduced by the KMCS. Two applications are demonstrated: iso-butane adsorption on ZnO(0 0 0 1)–Zn and n-pentane adsorption on carbon nanotubes.     

Study of reactive film heterostructures with several interfaces using the thermal desorption spectroscopy

The thermal desorption spectroscopy is used to study the interaction of the chemisorbed oxygen and carbon monoxide molecules with the nanometer-thick ytterbium films that are formed on the surfaces of silicon substrates at room temperature. In accordance with the results at a temperature of 300 K, the O₂ and CO molecules are chemisorbed on the surface of a metal film and do not exhibit dissociation to atoms under such conditions. The molecular dissociation is observed at higher temperatures. The liberated oxygen is involved in reactions with ytterbium and silicon that lead to the formation of complicated silicates, which dissociate at even higher temperatures.     

Image theory of lateral interactions applied to desorption rate of Xe from W and Ag

The image theory of lateral interactions between rare gas atoms given by Mahanty and March [J. Phys. C9 (1976) 2905] is shown to be consistent with the mean features of desorption rate measurements for Xe on W(111) and W(110). Some results are also presented for both Xe and Ar on Ag(111).     

Electron-stimulated defect formation in single-walled carbon nanotubes studied by hydrogen thermal desorption spectroscopy

Defects in single-walled carbon nanotubes introduced by low-energy electron irradiation at 8 K were sensitively detected by cryogenic thermal desorption of hydrogen molecules H₂ in the temperature range of 10-40 K. The thermal desorption spectrum was found to change significantly with sample annealing at temperatures as low as 40-70 K. Experimental results suggest that the H₂ physisorption sites responsible for the ‘defect’ peak at 28 K are interstitial channel space between nanotubes closely packed in bundles which becomes more easily accessible on damage. It is also suggested that the disordering provides groove sites for H₂ physisorption with smaller binding energy causing the damage-induced spectral component around 16 K, slightly lower than the desorption peak at 20 K that is observed in undamaged samples. The spectral change at 40-70 K could be interpreted by migration of adatoms at the low temperatures.     

Sticking of rare gases: the effect of lateral interactions

A theory of sticking, based on the kinetic lattice gas that accounts for intrinsic and extrinsic precursors and incorporates the effects of lateral interactions, is used to develop a model for the sticking of rare gases on metals and to derive analytically the model of Zeppenfeld et al. [Surf. Sci. 318 (1994) L1187] that explains their data as due to the formation and coalescence of condensed islands in the adsorbate.     

Correlation between thermal desorption spectroscopy and optical second harmonic generation for monitoring surface coverages

Optical second harmonic generation was used to monitor CO coverages on Cu(100) and Ni(111) in an ultrahigh vacuum chamber. In both cases, the adsorption kinetics were found to obey the simple Langmuir model. In monitoring CO coverages remained on Cu(100) and Ni(111) during a thermal desorption process, optical second harmonic generation correlates well with thermal desorption spectroscopy.     

Chemisorption of halogens on silver a critical comparison of results from photqemission and thermal desorption spectroscopy

Conflicting thermal desorption (TDS) results from submonolayer coverages of atomic Cl, Br or I on Ag(100), Ag(110) or Ag(111) stimulated us to check for the possible influence of different sample preparation procedures. We present experimental evidence, that a combined approach using TDS and angle-resolved ultraviolet photoemission may help to distinguish between better and worse surface preparation. We present detailed new results for the Cl/Ag(110) system. From our observations we conclude that all three halogens listed above give one and only one TDS peak in the submonolayer regime and show very similar adsorption/desorption-characteristics. This fact removes the apparent contradictions reported in the literature and demonstrates that the halogen-Ag bond is not very sensitive to the surface crystallography.     

钨中氢同位素热脱附实验的速率理论模拟研究

本文采用基于速率理论的模拟方法研究钨材料中氢同位素氘的热脱附谱. 热脱附数据来源于520 K下受等离子体辐照的多晶钨, 入射离子能量为40 eV, 剂量为1× 10²⁶ D/m². 通过调节速率理论中的俘获能、俘获率等参数, 最终获得与实验相符合的热脱附拟合谱. 拟合结果表明, 钨中俘获的氘存在于三种俘获态, 俘获能分别为1.14 eV, 1.40 eV和1.70 eV, 相应脱附温度峰值为500 K, 600 K和730 K. 这三个俘获能分别应对应于第一原理计算得到的空位俘获第3–5个氢原子的俘获能(含零点振动能修正)、空位俘获第1–2个氢原子的俘获能, 空位团簇对氢原子的俘获能. 模拟结果表明, 在本辐照实验条件下, 钨中空位及空位团簇是氘在钨中的主要俘获态.     

Thermal desorption spectra of chemisorbed atoms and molecules with lateral interactions and finite mobility: Nondissociatively adsorbed molecules

A model of thermal flash desorption of interacting chemisorbed atoms and molecules from a crystal surface is developed. The possibility of adatom diffusion along the surface is taken into account, but thermal equilibrium of the adatom system during the desorption process is not assumed. The whole range of adsorbate mobilities, including absolutely immobile species as well as adsorbates in thermal equilibrium, is investigated. The result is obtained in the form of a chain of differential equations for correlation functions of occupation numbers which is solved in various approximations. The numerical results differ from the results of previous calculations and are in better agreement with the experiments. The experimental thermal desorption spectrum of CO on W(210) is satisfactorily reproduced.     

Fractional and zero order desorption kinetics of adsorbed monolayers: The role of attractive lateral interactions in the Hg/W(100) system

We demonstrate that fractional and zero order desorption kinetics can result from a first order desorption mechanism with an activation energy which is a function of coverage. The changing activation energy is calculated by applying the quasi-chemical approximation to attractive lateral pairwise interactions between adsorbate species. The procedure is shown to give good agreement with the zero order kinetics found for the Hg/W(100) system using the same parameters as those employed to describe the equilibrium adsorption behaviour of the same system.