Co interaction on ZnO(000–1) investigated by scanning tunneling microscopy

The interaction of Co thin films on atomically flat ZnO(000–1) has been investigated by low energy electron diffraction (LEED), scanning tunneling microscopy (STM) and Auger electron spectroscopy (AES). A high density of islands nucleates at the earliest stages of the growth and a subsequent Wolmer–Weber growth of these islands is observed. Upon annealing at 600 °C, an atomically flat surface (Zn,Co)O(000–1) is restored due to the diffusion of the Co into the semiconductor. PACS 68.37.Ef; 68.49.Uv; 68.47.Fg; 68.47.Gh; 68.55.Ac     

Annealing effect on InAs islands on GaAs(0 0 1) substrates studied by scanning tunneling microscopy

Post-annealing effects on InAs islands grown on GaAs(0 0 1) surfaces have been investigated by scanning tunneling microscopy (STM) connected to molecular beam epitaxy (MBE). It is found that for islands grown by 1.6 ML InAs deposition at 450 °C, post-annealing at 450 °C in an As₄ atmosphere causes dissolving of the InAs islands. In contrast, for larger islands obtained by 2.0 ML InAs deposition at 450 °C, the post-annealing leads to coarsening of the islands. The result can be explained in terms of a critical nucleus in heterogeneous nucleation.     

Electronic structure of MgO-supported Au clusters: quantum dots probed by scanning tunneling microscopy

We investigate via density functional theory (DFT) the appearance of small MgO-supported gold clusters with 8 to 20 atoms in a scanning tunneling microscope (STM) experiment. Comparison of simulations of ultrathin films on a metal support with a bulk MgO leads to similar results for the cluster properties relevant for STM. Simulated STM pictures show the delocalized states of the cluster rather than the atomic structure. This finding is due to the presence of s- derived delocalized states of the cluster near the Fermi energy. The properties of theses states can be understood from a jellium model for monovalent gold.     

Formation and atomic structure of GaSb nanostructures in GaAs studied by cross-sectional scanning tunneling microscopy

GaSb nanostructures in GaAs, grown by metalorganic chemical vapor deposition, were studied with cross-sectional scanning tunneling microscopy. Three different samples were examined, containing a thin quantum well, a quantum well near the critical thickness for dot formation, and finally self-organized quantum dots with base lengths of 5–8 nm and heights of about 2 nm. The dots are intermixed with a GaSb content between 60% and 100%. Also small 3D and 2D islands were observed, possibly representing quantum dots in an early growth stage and quantum dot precursors. All GaSb layers exhibit gaps, which are indications of an island-like growth mode during epitaxy.     

Oxygen induced surface structure of Mo(1 1 0) studied by scanning tunneling microscopy

The oxygen induced surface structures formed on Mo(1 1 0) by oxygen exposure at 1300 K in UHV has been studied by scanning tunneling microscopy (STM). Two kinds of oxygen-adsorbed surface structures are observed. One consists of one-dimensional rows running along or directions at substrate molybdenum lattices, and another shows more complex structure including discrete arrangement of large protrusions and zig-zag alignments of small protrusions. This complex structure is probably a further oxygen-adsorbed structure than the well-known p(2 × 2) structure of 0.3 ML coverage. On the basis of STM image, an atomic model is proposed, where adsorbed oxygen atoms occupy both long-bridge and the quasi-threefold sites of molybdenum lattice (0.4 ML coverage). This structure is presumed to be a transient state during site-conversion with increase of oxygen exposure.     

Atomic structure of the non‐polar GaN($ \bar 2 $110) surface by cross‐sectional scanning tunneling microscopy

The ( 110) plane of gallium nitride, exposed by cleaving a GaN single crystal under ultra‐high vacuum conditions, has been atomically resolved for the first time, using cross‐sectional scanning tunneling microscopy. The spatial period length supports a (1 × 1) unit mesh size, i.e., the absence of a reconstruction. The contrast observed in the experimental data is well explained by the atomic arrangement expected for a truncated‐bulk structure. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Low temperature InSb(0 0 1) surface structure studied by scanning tunneling microscopy

InSb(0 0 1) surface prepared by ion sputtering and thermal annealing has been studied in the temperature range from 77 K up to 300 K using scanning tunneling microscopy (STM). At 300 K the surface is c(8 × 2) reconstructed as indicated by low energy electron diffraction and STM images, and its structure appears to be consistent with the “ζ-model” recently proposed for this surface. Upon lowering of the temperature below 180 K a new phase appears on the surface. This phase is characterized by the surface structure period doubling along [1 1 0], lowering the surface symmetry from c2mm to p2, and appearance of structural domains. Possible origins of the new phase are discussed.     

Growth of Cr on Ir(1 1 1) studied by scanning tunneling microscopy

We have studied the room-temperature growth of Cr on Ir(1 1 1) by scanning tunneling microscopy. Even in the low-coverage regime, up to a total coverage of 2 monolayers (ML), Cr does not grow in the layer-by-layer mode. Instead, we observe islands with local coverages Θ between 1 ML and 5 ML. While the 1st layer growth is pseudomorphic, sporadic defect lines are observed in the 2nd layer. For Θ ? 3 ML periodic one-dimensional dislocation lines appear indicating the onset of strain relief. Scanning tunneling spectroscopy reveals that islands with Θ = 1 ML exist in two modifications. Though their tunneling spectra are qualitatively rather similar, direct comparison shows that the main peak is shifted by about 15 mV, resulting in peak positions of −0.255 V and −0.270 V. We interpret these two modifications as regular fcc Cr and Cr which exhibits a faulted hcp stacking on Ir(1 1 1), respectively. The assignment of fcc to areas directly attached to substrate steps together with the evolution of the ratio of the different ML-areas with coverage leads to the conclusion that hcp is the more favorable stacking.     

Ordered thin films of alkyloxy-substituted benzaldehydes on a graphite surface studied by scanning tunneling microscopy

The molecular assembly of three different trialkyloxy-substituted benzaldehydes on graphite has been studied using scanning tunneling microscopy (STM). It is found that these benzaldehydes, which do not have intermolecular hydrogen bonding, could form a lamella arrangement in which the headgroups are aligned side by side. The effect due to the alkyl chain length on the lamella structure is also presented. Received: 21 January 2002 / Accepted: 22 March 2002 / Published online: 10 September 2002 RID="*" ID="*"Corresponding author. Fax: +86-10/6255-7908     

Self-limiting growth of Pt nanoparticles from MeCpPtMe3 adsorbed on TiO2110 studied by scanning tunneling microscopy

The growth of Pt nanoparticles from the metal-organic precursor [MeCpPtMe3: (methylcyclopentadienyl) trimethyl platinum] on TiO2(110) was studied by scanning tunneling microscopy. 2D-like Pt particles on the surface were formed in a self-limiting growth mode. The inner structure of the particles was resolved as unique tetramerlike bright spots. A mechanism for the self-limiting growth of Pt particles is proposed.     

The decomposition of ammonia on an oxygen-precovered Ni(110) surface studied by scanning tunneling microscopy

The decomposition of ammonia on a Ni(110) surface with preadsorbed oxygen has been investigated in ultra-high vacuum at room temperature using scanning tunneling microscopy (STM). We propose a reaction model in which the high reactivity observed at low O coverage is ascribed to a direct interaction between the NH₃ molecules and the terminating atoms of the short, mobile -Ni-O- added rows which are observed on the surface under these conditions. This model is consistent with the observation that the surface becomes inert at high O coverage. We believe that the present reaction model can also explain results from some other experiments in which preadsorbed oxygen has been found to act as a promoter for dissociation of H-containing species, such as for NH₃ on Cu(110) and H₂O on Ni(110).     

Edge states of epitaxially grown graphene on 4H-SiC(0001) studied by scanning tunneling microscopy

The edge properties of single layer graphene epitaxially grown on partially graphitized 4H-SiC(0001) surface have been investigated with scanning tunneling microscopy (STM). We directly observed the atomic-structure dependency of the super structures in the vicinity of armchair and zigzag edges due to the different kinds of symmetry-breaking at those two edges.     

Interaction of Ag and O on W(1 1 0) studied by scanning tunneling microscopy

The structural changes of Ag films on W(1 1 0) upon coadsorption of oxygen have been studied by scanning tunneling microscopy. The exposure of one monolayer Ag to oxygen leads to a phase separation into an Ag bilayer and patches of O-covered W(1 1 0). The effective Ag island thickness increases linearly with oxygen exposure. For Ag submonolayer-islands the onset of the bilayer formation is delayed, the induction period increases with the available free W area. We conclude that the steps of the transport process are (1) dissociation of oxygen on W and on the Ag islands, (2) site exchange of atomic oxygen with Ag atoms predominantly at the island edges - while on W(1 1 0) the oxygen is immobile, (3) diffusion of the displaced Ag atoms to the island edges where they are incorporated into the monolayer and (4) initiation of Ag bilayer formation, once the W(1 1 0) is saturated with O. This indicates an unexpected activity of the Ag monolayer on W(1 1 0) towards oxygen dissociation. In case of a reversed deposition sequence, where submonolayer quantities of Ag are adsorbed on an oxygen-precovered W(1 1 0) surface, growth of Ag clusters is observed. The distribution of cluster size and cluster height depends critically on the spatial order within the predeposited oxygen overlayer - it is obvious that the oxygen overlayer on the W surface acts as a structured template for preferential Ag nucleation.