Island morphology and adatom self-diffusion on Pt(111)

Abstract

The results of a density-functional-theory study of the formation energies of (100)- and (111)-faceted steps on the Pt(111) surface, as well as of the barrier for diffusion of an adatom on the flat surface, are presented. The step formation energies are found to be in a ratio of 0.88 in favour of the (111)-faceted step, in excellent agreement with experiment; the equilibrium shape of islands should therefore clearly be non-hexagonal. The origin of the difference between the two steps is discussed in terms of the release of stress at the surface through relaxation. For the diffusion barrier, we also find relaxation to be important, leading to a 20% decrease of its energy. The value we obtain, 0.33 eV, however remains higher than available experimental data; possible reasons for this discrepancy are discussed. We find the ratio of step formation energies and the diffusion barrier to be the same whether using the local-density approximation or the generalized-gradient approximation for the exchange-and-correlation energy.Comment: Submitted to Physical Review B; 11 postscript pages including 4 figures; this and related publications available from web sites at http://www.centrcn.umontreal.ca/~lewis and http://www.fhi-berlin.mpg.de/th/th.htm

Determination of Step Free Energies from Island Shape Fluctuations on Metal Surfaces

“…A prominent example of studies of this type is the work of Michely et al who determined a ratio of 0.87 6 0.02 for the step energies of so-called type B and type A steps on Pt(111), i.e., the (111)-and (100)-microfaceted close-packed steps [2]. This experimental result has been a challenge for advanced ab initio energy calculations [3], and could be reproduced only recently by calculations of Boisvert et al [4]. Experiments suited to reliably determine the absolute value of the step free energy on metal surfaces, however, are hardly available [5].…”

Ab initio pseudopotentials for electronic structure calculations of poly-atomic systems using density-functional theory

“…Questions addressed with pseudopotentials provided by this code, or its earlier version, range from phase transitions [10,11], defects in semiconductors [12][13][14], the structure of and diffusion on surfaces of semiconductors [15][16][17], simple metals [18], and transition metals [19][20][21], up to surface reactions [22,23], including molecules [24,25] of first-row species.…”

“…This procedure is analogous to (17) - (20) for bound states. The corresponding pseudopotential component results from (21), and merges into the all-electron potential for r > r match l . The value of ǫ l should be chosen in the energy range where the valence states are expected to form bands or molecular orbitals, as a default, the program psgen employs the highest eigenvalue of the occupied states, e.g., for Al to ǫ l=2 = ǫ 3p .…”

“…Part 1 (program psgen) serves to generate the pseudopotentials using the schemes by Hamann [33] or by Troullier and Martins [34]. This combination provides efficient pseudopotentials for "canonical" applications like group IV and III-V semiconductors [9,10,[15][16][17]22,23], as well as for systems where first-row, transition or noble metal elements are present [11,[19][20][21]24,25], or where "semicore" d-states must be treated as valence states, like in GaN [41] or InN [14]. In such cases the strongly localized 2p and 3, 4, 5d valence states are readily handled with the Troullier-Martins scheme.…”

Migration of point defects at charged Cu, Ag, and Au (100) surfaces

“…As a part of a detailed study of surface transport Stumpf and Scheffler presented ab initio results of the formation and activation energies and electrical dipole moments of adatoms, vacancies and dimers at various Al surfaces, 13 Yu and Scheffler reported formation and activation energies of adatoms and dimers on Ag͑100͒, 14 and Polatoglou et al calculated vacancy formation energies at the ͑111͒ surfaces of Al, Cu, Ag, and Rh. 15 Boisvert et al calculated adatom activation energies for the ͑100͒ and ͑111͒ surfaces of Ag, Au, and Ir surfaces, 16 for the Pt͑100͒ surface, 17 as well as adatom and vacancy activation energies for the Cu͑100͒ surface. 18 Using the Car-Parrinello method Lee et al obtained the activation energies of adatoms and dimers at the Cu ͑100͒ surface.…”