Growth of Single- and Bilayer ZnO on Au(111) and Interaction with Copper

Abstract

The stoichiometric single-and bilayer ZnO(0001) have been prepared by reactive deposition of Zn on Au(111) and studied in detail with X-ray photoelectron spectroscopy, scanning tunneling microscopy, and density functional theory calculations. Both single-and bilayer ZnO(0001) adopt a planar, graphite-like structure similar to freestanding ZnO(0001) due to the weak van der Waals interactions dominating their adhesion with the Au(111) substrate. At higher temperature, the single-layer ZnO(0001) converts gradually to bilayer ZnO(0001) due to the twice stronger interaction between two ZnO layers than the interfacial adhesion of ZnO with Au substrate. It is found that Cu atoms on the surface of bilayer ZnO(0001) are mobile with a diffusion barrier of 0.31 eV and likely to agglomerate and form nanosized particles at low coverages; while Cu atoms tend to penetrate a single layer of ZnO(0001) with a barrier of 0.10 eV, resulting in a Cu free surface.

Influence of hydrogen on the structure and stability of ultra-thin ZnO on metal substrates

“…Table I. The agreement with experimental values for sub-monolayer ZnO islands is good (Ag, 35,36 Pd, 37 Pt, 38 Au, 39 Cu (brass), 40 and Ru (0001) 41 ). The coincidence structures for which the ZnO in-plane lattice parameter is closest to that of the free-standing structure gives the lowest formation energy.…”

Graphene-Like ZnO: A Mini Review

“…Examples include Pd(111) [17], Pt(111) [18,19], Au(111) [20], Ag(111) [4,21,22], Cu(111) [22] and Brass(111) [23]. Prior to deposition, the surfaces of the metal substrates were cleaned by mechanical polishing [4] and by cycles of Ar + ion sputtering followed by annealing in UHV, at 1000 K for Pd [17], 750 K for Ag [4], 670 K [21] or 700 K for Au [20], and 1200 K for Pt [19]. In some cases [17][18][19]22], an annealing step was carried out in the presence of O 2 at high temperature (700-800 K) to remove residual carbon.…”

“…g-ZnO layers can be obtained by first depositing pure Zn at room temperature on to a clean metal substrate by heating a Zn rod using a Knudsen cell [17,21]; in other cases, pulsed laser deposition [4], an electron beam-assisted evaporator [20] or applied current through a thoriated tungsten wire wrapped around the Zn rod can be used [18,19,22]. When oxygen is injected, it is done so at relatively high pressures ranging from~10 −8 and~10 −5 mbar either during or after Zn deposition at room temperature, followed by an annealing step in UHV (the annealing temperature depends on the metal substrate and typically varies between 550 K and 680 K).…”

“…Figure 3a shows typical room-temperature STM images of g-ZnO grown over Au(111) [20]. Panel (i) clearly shows the hexagonal Moiré pattern of ZnO over Au(111) as seen on both low-ZnO (where the height of the flake is measured in STM to be~3.5 Å) and high-ZnO (where the height of the flake is~5.5 Å from the Au plane) crystals.…”

Reactivity of Ultra-Thin ZnO Films Supported by Ag(111) and Cu(111): A Comparison to ZnO/Pt(111)

“…However, our studies of FeO(111) [10] and ZnO(0001) [13] films on Pt(111) showed that such a monolayer structure is unstable under realistic pressure conditions. Moreover, other DFT studies of ZnO(0001) films on noble metals (Pd(111) [35], Cu(111) [36], and Au(111) [37]) and experimental data available for ZnO/Ag(111) [21] revealed substantial interlayer relaxations such that ultrathin ZnO films resemble the co-planar sheets in the boron nitride (or graphite) structure, and they are only weakly bound to a metal support, in contrast to the models used by Sun et al [34].…”