Atomistic Insight into the Epitaxial Growth Mechanism of Single-Crystal Two-Dimensional Transition-Metal Dichalcogenides on Au(111) Substrate.

A mechanistic understanding of interactions between atomically thin two-dimensional (2D) transition-metal dichalcogenides (TMDs) and their growth substrates is important for achieving the unidirectional alignment of nuclei and seamless stitching of 2D TMD domains and thus 2D wafers. In this work, we conduct a cross-sectional scanning transmission electron microscopy (STEM) study to investigate the atomic-scale nucleation and early stage growth behaviors of chemical vapor deposited monolayer (ML-) MoS and molecular beam epitaxy ML-MoSe on a Au(111) substrate. Statistical analysis reveals the majority of as-grown domains, i.

Charge Density Modulation and the Luttinger Liquid State in MoSe Mirror Twin Boundaries.

A mirror twin-domain boundary (MTB) in monolayer MoSe represents a (quasi) one-dimensional metallic system. Its electronic properties, particularly the low-energy excitations in the so-called 4|4P-type MTB, have drawn considerable research attention. Reports of quantum well states, charge density waves, and the Tomonaga-Luttinger liquid (TLL) have all been made.

Quantum Confined Tomonaga-Luttinger Liquid in MoSe Nanowires Converted from an Epitaxial MoSe Monolayer.

Confining interacting particles in one-dimension (1D) changes the electronic behavior of the system fundamentally, which has been studied extensively in the past. Examples of 1D metallic systems include carbon nanotubes, quasi-1D organic conductors, metal chains, and domain boundary defects in monolayer thick transition-metal dichalcogenides such as MoSe. Here single and bundles of MoSe nanowires were fabricated through annealing a MoSe monolayer grown by molecular-beam epitaxy on graphene.

Multifarious Interfaces, Band Alignments, and Formation Asymmetry of WSe-MoSe Heterojunction Grown by Molecular-Beam Epitaxy.

Monolayer (ML) transition-metal dichalcogenides (TMDs) continue to attract research attention, and the heterojunctions formed by vertically stacking or laterally stitching two different TMDs, e.g., MoSe and WSe, may have many interesting electronic and optical properties and thus are at the center stage of current research.

Room-temperature ferroelectricity in MoTe down to the atomic monolayer limit.

Ferroelectrics allow for a wide range of intriguing applications. However, maintaining ferroelectricity has been hampered by intrinsic depolarization effects. Here, by combining first-principles calculations and experimental studies, we report on the discovery of robust room-temperature out-of-plane ferroelectricity which is realized in the thinnest monolayer MoTe with unexploited distorted 1T (d1T) phase.

Graphene-oxide-wrapped ZnMnO as a high performance lithium-ion battery anode.

Cation distribution between tetrahedral and octahedral sites within the ZnMnO spinel lattice, along with microstructural features, is affected greatly by the temperature of heat treatment. Inversion parameters can easily be tuned, from 5%-19%, depending on the annealing temperature. The upper limit of inversion is found for T = 400 °C as confirmed by x-ray powder diffraction and Raman spectroscopy.

Inversion Domain Boundary Induced Stacking and Bandstructure Diversity in Bilayer MoSe.

Interlayer rotation and stacking were recently demonstrated as effective strategies for tuning physical properties of various two-dimensional materials. The latter strategy was mostly realized in heterostructures with continuously varied stacking orders, which obscure the revelation of the intrinsic role of a certain stacking order in its physical properties. Here, we introduce inversion-domain-boundaries into molecular-beam-epitaxy grown MoSe homobilayers, which induce uncommon fractional lattice translations to their surrounding domains, accounting for the observed diversity of large-area and uniform stacking sequences.

Ultrathin β-tellurium layers grown on highly oriented pyrolytic graphite by molecular-beam epitaxy.

Monolayer tellurium (Te) or tellurene has been suggested by a recent theory as a new two-dimensional (2D) system with great electronic and optoelectronic promises. Here we present an experimental study of epitaxial Te deposited on highly oriented pyrolytic graphite (HOPG) by molecular-beam epitaxy. Scanning tunneling microscopy of ultrathin layers of Te reveals rectangular surface cells with the cell size consistent with the theoretically predicted β-tellurene, whereas for thicker films, the cell size is more consistent with that of the [101[combining macron]0] surface of the bulk Te crystal.

Multivalency-Driven Formation of Te-Based Monolayer Materials: A Combined First-Principles and Experimental study.

Contemporary science is witnessing a rapid expansion of the two-dimensional (2D) materials family, each member possessing intriguing emergent properties of fundamental and practical importance. Using the particle-swarm optimization method in combination with first-principles density functional theory calculations, here we predict a new category of 2D monolayers named tellurene, composed of the metalloid element Te, with stable 1T-MoS_{2}-like (α-Te), and metastable tetragonal (β-Te) and 2H-MoS_{2}-like (γ-Te) structures. The underlying formation mechanism is inherently rooted in the multivalent nature of Te, with the central-layer Te behaving more metal-like (e.

Quantum Effects and Phase Tuning in Epitaxial Hexagonal and Monoclinic MoTe Monolayers.

Monolayer (ML) transition-metal dichalcogenides exist in different phases, such as hexagonal (2H) and monoclinic (1T') structures. They show very different properties: semiconducting for 2H-MoTe and semimetallic for 1T'-MoTe. The formation energy difference between 2H- and 1T'-phase MoTe is small, so there is a high chance of tuning the structures of MoTe and thereby introducing applications of phase-change electronics.

Nanoclusters of CaSe in calcium-doped Bi2Se3 grown by molecular-beam epitaxy.

In calcium (Ca) doped Bi2Se3 films grown by molecular beam epitaxy, nanoclusters of CaSe are revealed by high-angle annular dark field imaging and energy dispersive x-ray spectroscopy analysis using a scanning transmission electron microscope. As the interface between the ordinary insulator CaSe and topological insulator, Bi2Se3, can host topological nontrivial interface state, this represents an interesting material system for further studies. We show by first principles total energy calculations that aggregation of Ca atoms in Bi2Se3 is driven by energy minimization and a preferential intercalation of Ca in the van der Waals gap between quintuple layers of Bi2Se3 induces reordering of atomic stacking and causes an increasing amount of stacking faults in film.

In situ synthesis of TiO2(B) nanotube/nanoparticle composite anode materials for lithium ion batteries.

Titania nanotubes were prepared by a simple hydrothermal route. Their electrochemical performance has been examined in detail and compared to TiO2(B) nanoparticles, TiO2 anatase and P25 titania nanoparticles. The cycling and rate performance of TiO2 nanotubes is superior to both types of nanoparticles, and it can be further improved by an in situ titanium precursor treatment, which results in the formation of TiO2 nanoparticles on/between the nanotubes.

Observation of intervalley quantum interference in epitaxial monolayer tungsten diselenide.

The extraordinary electronic structures of monolayer transition metal dichalcogenides, such as the spin-valley-coupled band edges, have sparked great interest for potential spintronic and valleytronic applications based on these two-dimensional materials. In this work, we report the experimental observation of quasi-particle interference patterns in monolayer WSe2 using low-temperature scanning tunnelling spectroscopy. We observe intervalley quantum interference involving the Q valleys in the conduction band due to spin-conserving scattering processes, while spin-flipping intervalley scattering is absent.

Line and Point Defects in MoSe2 Bilayer Studied by Scanning Tunneling Microscopy and Spectroscopy.

Bilayer (BL) MoSe2 films grown by molecular-beam epitaxy (MBE) are studied by scanning tunneling microscopy and spectroscopy (STM/S). Similar to monolayer (ML) films, networks of inversion domain boundary (DB) defects are observed both in the top and bottom layers of BL MoSe2, and often they are seen spatially correlated such that one is on top of the other. There are also isolated ones in the bottom layer without companion in the top-layer and are detected by STM/S through quantum tunneling of the defect states through the barrier of the MoSe2 ML.

Dense network of one-dimensional midgap metallic modes in monolayer MoSe2 and their spatial undulations.

We report the observation of a dense triangular network of one-dimensional (1D) metallic modes in a continuous and uniform monolayer of MoSe(2) grown by molecular-beam epitaxy. High-resolution transmission electron microscopy and scanning tunneling microscopy and spectroscopy studies show that these 1D modes are midgap states at inversion domain boundaries. Scanning tunneling microscopy and spectroscopy measurements further reveal intensity undulations of the metallic modes, presumably arising from the superlattice potentials due to the moiré pattern and the quantum confinement effect.

Crossover from 3D to 2D quantum transport in Bi2Se3/In2Se3 superlattices.

The topological insulator/normal insulator (TI/NI) superlattices (SLs) with multiple Dirac channels are predicted to offer great opportunity to design novel materials and investigate new quantum phenomena. Here, we report first transport studies on the SLs composed of TI Bi2Se3 layers sandwiched by NI In2Se3 layers artificially grown by molecular beam epitaxy (MBE). The transport properties of two kinds of SL samples show convincing evidence that the transport dimensionality changes from three-dimensional (3D) to two-dimensional (2D) when decreasing the thickness of building block Bi2Se3 layers, corresponding to the crossover from coherent TI transport to separated TI channels.

In situ synthesis of CuxO/SnOx@CNT and CuxO/SnOx@SnO₂/CNT nanocomposite anodes for lithium ion batteries by a simple chemical treatment process.

SnO2-based electrodes for lithium ion batteries (LIBs) typically exhibit high initial specific capacity but poor cycling performance. A possible strategy to improve the cycling performance is to prepare nanocomposites containing SnO2. Here we demonstrate a straightforward method to prepare composites containing SnOx and CuxO by a simple chemical treatment of the LIB electrode on copper foil.

Anisotropic topological surface states on high-index Bi2Se3 films.

A high-index topological insulator thin film, Bi2 Se3 (221), is grown on a faceted InP(001) substrate by molecular-beam epitaxy (see model in figure (a)). Angle-resolved photoemission spectroscopy measurement reveals the Dirac cone structure of the surface states on such a surface (figure (b)). The Fermi surface is elliptical (figure (c)), suggesting an anisotropy along different crystallographic directions.

Diameter control of tungsten oxide nanowires as grown by thermal evaporation.

Tungsten oxide nanowires with controllable diameter were synthesized on Si substrates by thermal evaporation of tungsten trioxide powder in a tube furnace. Depending on the temperature of the source (900-1000 °C), tungsten oxide W(18)O(49) nanowires with diameters ranging from 10 to 100 nm are obtained with high yield. The exponential dependence of the nanowire diameter on the source temperature leads to an energy of about 2.