Periodic Trends in Adsorption and Activation Energies for Heterometallic Diffusion on (100) Transition Metal Surfaces Handan Yildirim, Subramanian K.R.S. Sankaranarayanan,* and Jeffrey P. Greeley* Center for Nanoscale Materials, Argonne National Laboratory, Argonne, Illinois 60439, United States * S Supporting Information ABSTRACT: A first-principles analysis of trends in metal-on-metal hopping diffusion for 64 admetal/substrate systems is presented. Focusing on the (100) facets of various transition metal substrates, we demonstrate that the calculated hopping diffusion barriers may be interpreted in terms of the cohesive energies of the admetals and substrates, as well as the lattice constants of the substrates. We further show that general linear relationships exist between the diffusion barriers and the corresponding adsorption energies on each transition metal substrate. The slopes in these Brønsted-Evans- Polanyi relationships are related to the degree of resemblance between the initial states and the transition states for hopping diffusion, and the slopes are found to depend sensitively on the nature of the transition metal substrate. Substrates with higher cohesive energies and smaller lattice constants generally exhibit smaller slopes and, therefore, a closer correspondence between the transition states and the initial states. These relationships, in addition to providing fundamental insights into trends in diffusion across different transition metal surfaces, give a powerful and convenient means of predicting diffusional kinetics from purely thermodynamic quantities. The results may ultimately provide a useful input to kinetic Monte Carlo (kMC)-type simulations, enabling efficient and accurate studies of heteroepitaxial metal-on-metal growth. I. INTRODUCTION Metal-on-metal surface diffusion is central to both the basic physics of crystal and thin film growth and to a variety of technologically important fields, including catalysis, micro- electronics, and corrosion. In spite of these diverse and significant applications, however, fundamental knowledge of the kinetics and dynamics of diffusing metal adspecies is far from complete, and nearly all atomistic studies of these phenomena have focused on the diffusion of specific metals across specific substrates. 1-6 While such studies, involving both experimen- tal 7,8 and computational techniques, have identified many important principles of surface diffusive processes, a more general understanding of atomic-scale trends in surface diffusion across different admetals and substrates is lacking. The development of such a generalized understanding, in turn, could be of significant benefit in controlling the structure of alloys during growth or dealloying processes and in designing bimetallic materials for desired applications. Theoretical surface science studies have emerged in recent years as a powerful tool to elucidate the kinetics, dynamics, and atomistic details of the mechanisms governing surface processes. Such studies, based primarily on periodic Density Functional Theory (DFT) calculations, have found extensive uses in a variety of applications. 9-15 These calculations have been shown, for example, to be useful for obtaining linear energy scaling relationships for a variety of molecular adsorbates on transition metal surfaces. 16 Additional linear relationships are of the Brønsted-Evans-Polanyi (BEP) type, 17-19 which describes the correlations between the kinetics of elementary surface processes and the corresponding thermodynamics. 20,21 For complex catalytic reactions, these relationships have permitted the description of fundamental reactivity trends across diverse catalyst surfaces using just a few independent parameters, or descriptors. 22-27 To a significantly lesser extent, simplified forms of these general classes of linear correlations have been used to describe metal adatom diffusion on transition metal substrates. 28-31 In particular, adatom diffusion on corrugated surfaces such as (100) has often been studied, 28-31 and some correlations between the adsorbate binding strengths and the bulk bond energies have been suggested for self-diffusion processes 32 wherein the admetal and the substrate have the same elemental identity (these systems are also referred to with the term “homodiffusion” in the remainder of this article). A linear relation between the hopping barriers over step edges and the (111) terrace adsorption energies has also been reported for a few heterodiffusive processes, wherein the elemental identities of the admetal and substrate are different. 33 Similarly, a relatively recent first- principles study, using related ideas, has reported that BEP-type correlations exist for the diffusion of several atomic and molecular adsorbates (C, N, NO) on close-packed transition metal surfaces. 34 In spite of the advances described above, there are relatively few general principles that have been identified for describing atomistic details of heterodiffusion of metal adatoms on metal Received: September 7, 2012 Published: September 29, 2012 Article pubs.acs.org/JPCC © 2012 American Chemical Society 22469 dx.doi.org/10.1021/jp3089275 | J. Phys. Chem. C 2012, 116, 22469-22475