First-Principles Theory of Surface Thermodynamics and Kinetics

Abstract

Understanding the complex behavior of particles at surfaces requires detailed knowledge of both macroscopic and microscopic processes that take place; also certain phenomena depend critically on temperature and gas pressure. To link these processes we combine state-of-the-art microscopic, and macroscopic phenomenological, theories. We apply our theory to the O͞Ru(0001) system and calculate thermal desorption spectra, heat of adsorption, and the surface phase diagram. The agreement with experiment provides validity for our approach which thus identifies the way for a predictive simulation of surface thermodynamics and kinetics. PACS numbers: 68.45.Da, 82.65.Dp, 82.65.My The study of the physical and chemical processes that take place at gas-surface interfaces have long been an area of intense research. This interest is both fundamental as well as driven by the possible discovery of important technological applications, e.g., in the field of heterogeneous catalysis, corrosion, etc. [1,2]. With respect to the field of the theory of adsorption of gases on solid surfaces, advancement in recent years has developed in two distinct, albeit complimentary, directions: (i) electronic structure calculations, at best done by density-functional theory (DFT), to determine the geometries, energetics, and vibrational properties of adsorbate covered surfaces, and (ii) phenomenological models, both for the thermodynamics and the kinetics [3] of the adsorbate. If one can assume that the geometry of the solid surface does not change dramatically and that adsorption occurs at well defined sites, one frequently employs a lattice gas model. A number of parameters enter this type of model, such as the binding energies and vibrational frequencies of a single adparticle in the various adsorption sites, and their mutual lateral interactions with adparticles in close-by sites. Traditionally, these parameters are adjusted in the theory in order to fit a variety of experimental data such as phase diagrams, heats of adsorption, infrared spectra, and thermal desorption data, etc. Such an approach, while useful, is clearly not necessarily predictive in nature, nor the parameters unique, and may not capture the physics of the microscopic processes that are behind the "best-fit" adjusted "effective" parameters.In this Letter, with the aim to improve upon this approach, we combine state-of-the-art procedures of (i) microscopic theories, i.e., DFT electronic structure calculations and (ii) macroscopic phenomenological approaches, i.e., lattice gas and rate equations, and Monte Carlo schemes. On doing this, we present a consistent first-principles-based approach for calculation of the thermodynamic and kinetic properties of an adsorbate, such as heats of adsorption, temperature programmed desorption (TPD) spectra, and the surface phase diagram. We have chosen the system of oxygen at Ru(0001) for which detailed structural [4-9], thermodynamic [10], and kinetic data [11,12] exist. We will show that, with the present approach, a realistic description...

Catalysis and corrosion: the theoretical surface-science context

“…In what follows, we give an example of this approach for the system of oxygen at Ru(0 0 0 1) where the temperature-programmed desorption of O 2 is calculated in the coverage regime from low coverage to a full monolayer [36]. Temperatureprogrammed desorption is one of the most widely used experimental techniques for studying the binding energies of adsorbed species.…”

“…The presence of such phases can be predicted by calculation of the isosteric heat of adsorption (the energy which an O 2 molecule gains by dissociatively adsorbing on the surface) as a function of coverage, which was also presented in Ref. [36]. From the calculated isosteric heat of adsorption, stable structures of O on Ru(0 0 0 1) were identified for coverages 1/4, 1/2, 3/4, and 1 ML which correspond to each of the ordered phases that form in nature, namely, ð2 Â 2Þ-O, ð2 Â 1Þ-O, ð2 Â 2Þ-3O, and ð1 Â 1Þ-O [36].…”

“…The prefactor to the exponential involves a sticking probability (as will be discussed in Section 3.3). The lattice-gas Hamiltonian constructed in this study [36] used two-body interactions up to third neighbor distances and three types of three-body (trio) interactions. Also two types of adsorption sites were included, namely, the hcp-and fcc-hollow site, and also interactions between the O atoms in these two types of hollow sites were included up to third neighbor distances.…”

Nanometer and Subnanometer Thin Oxide Films at Surfaces of Late Transition Metals

“…Particularly the sharp drop after reaching a coverage of about 0.5 ML at Ru(0001) and Rh(111) leads to an apparent uptake saturation, when employing low gas exposures as typical for many early ultra-high vacuum (UHV) surface science studies. 12,13,14 DFT calculations predicted, however, that much higher coverages should still be possible 15,16,17 , and Fig. 2 shows such data for some selected adsorbate configurations spanning the whole coverage range up to 1 ML 18 .…”

Substrate-Mediated Interaction on Ag(111) Surfaces from First Principles

“…We can express ∆E in terms of these interactions using the lattice-gas Hamiltonian approach (see, e.g. [24]), which yields…”