Spatial variation of geometry, binding, and electronic properties in the moiré superstructure of MoS2 on Au(111)

Abstract The lattice mismatch between a monolayer of MoS2 and its Au(111) substrate induces a moiré superstructure. The local variation of the registry between sulfur and gold atoms at the interface leads to a periodic pattern of strongly and weakly interacting regions. In consequence, also the electronic bands show a spatial variation. We use scanning tunneling microscopy and spectroscopy (STM/STS), x-ray photoelectron spectroscopy (XPS) and x-ray standing wave (XSW) for a determination of the geometric and electronic structure. The experimental results are corroborated by density functional theory (DFT). We obtain the geometric structure of the supercell with high precision, identify the fraction of interfacial atoms that are strongly interacting with the substrate, and analyze the variation of the electronic structure in dependence of the location within the moiré unit cell and the nature of the band.

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On the Structure of Ultrathin FeO Films on Ag(111)

Nanomaterials ◽

10.3390/nano8100828 ◽

2018 ◽

Vol 8 (10) ◽

pp. 828 ◽

Cited By ~ 1

Author(s):

Mikołaj Lewandowski ◽

Tomasz Pabisiak ◽

Natalia Michalak ◽

Zygmunt Miłosz ◽

Višnja Babačić ◽

...

Keyword(s):

Transition Metal ◽

Photoelectron Spectroscopy ◽

Density Functional ◽

Lattice Mismatch ◽

Transition Metal Dichalcogenides ◽

Chemical Properties ◽

Scanning Tunneling ◽

Tunneling Microscopy ◽

Free Standing ◽

Preparation Conditions

Ultrathin transition metal oxide films exhibit unique physical and chemical properties not observed for the corresponding bulk oxides. These properties, originating mainly from the limited thickness and the interaction with the support, make those films similar to other supported 2D materials with bulk counterparts, such as transition metal dichalcogenides. Ultrathin iron oxide (FeO) films, for example, were shown to exhibit unique electronic, catalytic and magnetic properties that depend on the type of the used support. Ag(111) has always been considered a promising substrate for FeO growth, as it has the same surface symmetry, only ~5% lattice mismatch, is considered to be weakly-interacting and relatively resistant to oxidation. The reports on the growth and structure of ultrathin FeO films on Ag(111) are scarce and often contradictory to each other. We attempted to shed more light on this system by growing the films using different preparation procedures and studying their structure using scanning tunneling microscopy (STM), low energy electron diffraction (LEED) and X-ray photoelectron spectroscopy (XPS). We observed the formation of a previously unreported Moiré superstructure with 45 Å periodicity, as well as other reconstructed and reconstruction-free surface species. The experimental results obtained by us and other groups indicate that the structure of FeO films on this particular support critically depends on the films’ preparation conditions. We also performed density functional theory (DFT) calculations on the structure and properties of a conceptual reconstruction-free FeO film on Ag(111). The results indicate that such a film, if successfully grown, should exhibit tunable thickness-dependent properties, being substrate-influenced in the monolayer regime and free-standing-FeO-like when in the bilayer form.

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Nanodomain structure of single crystalline nickel oxide

Scientific Reports ◽

10.1038/s41598-021-82070-1 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

B. Walls ◽

A. A. Mazilkin ◽

B. O. Mukhamedov ◽

A. Ionov ◽

I. A. Smirnova ◽

...

Keyword(s):

Nickel Oxide ◽

Domain Structure ◽

Point Defects ◽

Photoelectron Spectroscopy ◽

Density Functional ◽

Gas Sensing ◽

Density Functional Theory Calculations ◽

Scanning Tunneling ◽

Tunneling Microscopy ◽

X Ray

AbstractIn this work we present a comprehensive study of the domain structure of a nickel oxide single crystal grown by floating zone melting and suggest a correlation between point defects and the observed domain structure. The properties and structure of domains dictate the dynamics of resistive switching, water splitting and gas sensing, to name but a few. Investigating the correlation between point defects and domain structure can provide a deeper understanding of their formation and structure, which potentially allows one to tailor domain structure and the dynamics of the aforementioned applications. A range of inhomogeneities are observed by diffraction and microscopy techniques. X-ray and low-energy electron diffraction reveal domains on the submicron- and nanometer-scales, respectively. In turn, these domains are visualised by atomic force and scanning tunneling microscopy (STM), respectively. A comprehensive transmission electron microscopy (TEM) study reveals inhomogeneities ranging from domains of varying size, misorientation of domains, variation of the lattice constant and bending of lattice planes. X-ray photoelectron spectroscopy and electron energy-loss spectroscopy indicate the crystal is Ni deficient. Density functional theory calculations—considering the spatial and electronic disturbance induced by the favourable nickel vacancy—reveal a nanoscale distortion comparable to STM and TEM observations. The different inhomogeneities are understood in terms of the structural relaxation induced by ordering of nickel vacancies, which is predicted to be favourable.

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LOCAL ELECTRONIC STATES ON TWO-DIMENSIONAL NANOSCALE ISLAND OF Si AND Ge FABRICATED ON Si(111) 7 × 7 SUBSTRATE

International Journal of Nanoscience ◽

10.1142/s0219581x09006444 ◽

2009 ◽

Vol 08 (06) ◽

pp. 595-603

Author(s):

YUKICHI SHIGETA ◽

RYOTA NEGISHI ◽

MASAHIKO SUZUKI

Keyword(s):

Electronic Structure ◽

Photoelectron Spectroscopy ◽

Density Functional ◽

Great Influence ◽

Energy Difference ◽

Scanning Tunneling Spectroscopy ◽

Local Deformation ◽

Scanning Tunneling ◽

Two Dimensional ◽

Tunneling Microscopy

Nanoscale islands on semiconductor are a strong candidate as building block in nanodevices. In the nanoisland, some local deformation is induced by the surface tension, which has a great influence on the electronic property of the nanoislands. To study the electronic structure of two-dimensional (2D) nanoislands of Si and Ge on the Si(111) 7 × 7 surface, we formed nanoislands of the same size and measured with angle resolved ultraviolet photoelectron spectroscopy (ARUPS), scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS). We found that the nanoisland shows a characteristic fine structure due to some strain. We also calculated a relation between the strain and electronic state based on the density-functional theory. In the calculation, the dangling-bond state at the strained adatom on the nanoisland (SR state) shifts to lower energy, which has liner dependence with the height of the adatoms. The ARUPS spectrum and the STS show characteristic peaks corresponding to the SR state, whose energy depends on the deformation of the adatom. The height of the adatom on the nanoisland estimated from the energy difference is consistent with a result of the STM measurement. The strain of adatoms can be estimated from the electronic structure.

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