Low-Energy Electron-Diffraction Study of the Clean (100), (111), and (110) Faces of Platinum

Abstract

The structures of the (111), (100), and (110) crystal faces of platinum were studied as a function of temperature in the range 300°—1769°C (melting point). The (111) and (100) substrates are stable while the (110) face shows faceting above 600°C. Several surface structures were found to exist on the stable platinum substrates. These have well-defined temperature ranges of stability. There are two types of surface structures, ordered and disordered. Both types appear to be the property of the clean platinum substrates. The ordered structures appear during annealing, after ion bombardment at lower temperatures (<900°C). They exhibit long-range order and their stability ranges overlap on a given substrate. These structures are believed to be due to ordered arrays of vacancies in the substrate plane which, under proper conditions, show remarkable stability. A high, nonequilibrium concentration of defects at the surface may be necessary to induce their formation. The disordered surface structures appear at high temperatures, above the stability range of most of the ordered structures. They are characterized by ringlike diffraction features which develop gradually as a function of increased heating time or temperature. The formation of these structures is irreversible and they can only be removed by ion bombardment. Near the melting point, the ring patterns remain the only diffraction features of the presumably greatly disordered surfaces. The ratio of lattice parameters assigned to the diffraction rings on each substrate indicate that they can be due to domains of (111) surface structures. These hexagonal structures appear on all of the platinum surfaces, are freely rotated in the substrate plane, and show an ∼11% contraction with respect to the inter-planar spacing in the ordered (111) face. The disordered close-packed-hexagonal structure seems to be the stable high-temperature surface phase of platinum.

Kinetics of crystallite sintering during heat treatment of supported metal catalysts

“…Lyon and Somorjai ( 1967), using low energy electron diffraction to study structures of the clean (loo), ( l l l ) , and (110) faces of platinum crystals as a function of temperature up to 1769"C, observed, for temperature higher than about 750°C, some more or less disordered surface structures (perhaps a kind of liquid-like structure due to a surface premelting phenomenon). These disordered structures remain the only ones evidenced by low energy diffraction near the melting point.…”

Defects of graphene on Ir(111): Rotational domains and ridges

“…3 Typical templates include Ni(111), [4][5][6][7] Ru(0001), [8][9][10][11][12][13][14][15][16][17] Ir(111) [18][19][20][21][22][23][24] and Pt(111). [25][26][27][28][29][30][31] The latter three surfaces are not well lattice-matched to graphene. Because of this mismatch and the strong C-C bonding within the graphene sheet, the metal lattice and the graphene lattice form moiré structures.…”

Sputtering Experiments with 1- to 5-keV Ar+ Ions. III. Monocrystal Targets of the Hexagonal Metals Mg, Zn, Zr, and Cd

“…36 The behavior exhibited by our Zn and Cd (1120) crystals seems to be different from that of either Ge or Mo. Unusual surface structures, produced on crystals of Ag, Pt, and Au by ion bombardment and annealing, have recently been described by Somorjai et al 37 Because of their much lower melting points, similar changes might be induced in Zn and Cd without heating them above room temperature. LEED studies of these surfaces appear to be required for the further pursuit of this topic.…”