A van der Waals Heterostructure with an Electronically Textured Moiré Pattern: PtSe/PtTe.

The interlayer interaction in Pt-dichalcogenides strongly affects their electronic structures. The modulations of the interlayer atom-coordination in vertical heterostructures based on these materials are expected to laterally modify these interlayer interactions and thus provide an opportunity to texture the electronic structure. To determine the effects of local variation of the interlayer atom coordination on the electronic structure of PtSe, van der Waals heterostructures of PtSe and PtTe have been synthesized by molecular beam epitaxy.

Catalytic Activity of Defect-Engineered Transition Me tal Dichalcogenides Mapped with Atomic-Scale Precision by Electrochemical Scanning Tunneling Microscopy.

Unraveling structure-activity relationships is a key objective of catalysis. Unfortunately, the intrinsic complexity and structural heterogeneity of materials stand in the way of this goal, mainly because the activity measurements are area-averaged and therefore contain information coming from different surface sites. This limitation can be surpassed by the analysis of the noise in the current of electrochemical scanning tunneling microscopy (EC-STM).

Formation of In-Plane Semiconductor-Metal Contacts in 2D Platinum Telluride by Converting PtTe to PtTe.

Monolayer PtTe is a narrow gap semiconductor while PtTe is a metal. Here we show that the former can be transformed into the latter by reaction with vapor-deposited Pt atoms. The transformation occurs by nucleating the PtTe phase within PtTe islands, so that a metal-semiconductor junction is formed.

Water dissociation and association on mirror twin boundaries in two-dimensional MoSe: insights from density functional theory calculations.

The adsorption and dissociation of water molecules on two-dimensional transition metal dichalcogenides (TMDs) is expected to be dominated by point defects, such as vacancies, and edges. At the same time, the role of grain boundaries, and particularly, mirror twinboundaries (MTBs), whose concentration in TMDs can be quite high, is not fully understood. Using density functional theory calculations, we investigate the interaction of water, hydroxyl groups, as well as oxygen and hydrogen molecules with MoSe monolayers when MTBs of various types are present.

Controlling Stoichiometry in Ultrathin van der Waals Films: PtTe, PtTe, PtTe, and PtTe.

The platinum-tellurium phase diagram exhibits various (meta)stable van der Waals (vdW) materials that can be constructed by stacking PtTe and PtTe layers. Monophase PtTe, being the thermodynamically most stable compound, can readily be grown as thin films. Obtaining the other phases (PtTe, PtTe, PtTe), especially in their ultimate thin form, is significantly more challenging.

Correction: Mirror twin boundaries in MoSe monolayers as one dimensional nanotemplates for selective water adsorption.

Correction for 'Mirror twin boundaries in MoSe2 monolayers as one dimensional nanotemplates for selective water adsorption' by Jingfeng Li et al., Nanoscale, 2021, 13, 1038-1047, DOI: 10.1039/D0NR08345C.

Mirror twin boundaries in MoSe monolayers as one dimensional nanotemplates for selective water adsorption.

Water adsorption on transition metal dichalcogenides and other 2D materials is generally governed by weak van der Waals interactions. This results in a hydrophobic character of the basal planes, and defects may play a significant role in water adsorption and water cluster nucleation. However, there is a lack of detailed experimental investigations on water adsorption on defective 2D materials.

Molecular Beam Epitaxy of Transition Metal (Ti-, V-, and Cr-) Tellurides: From Monolayer Ditellurides to Multilayer Self-Intercalation Compounds.

Material growth by van der Waals epitaxy has the potential to isolate monolayer (ML) materials and synthesize ultrathin films not easily prepared by exfoliation or other growth methods. Here, the synthesis of the early transition metal (Ti, V, and Cr) tellurides by molecular beam epitaxy (MBE) in the mono- to few-layer regime is investigated. The layered ditellurides of these materials are known for their intriguing quantum- and layer dependent- properties.

A magnetic sensor using a 2D van der Waals ferromagnetic material.

Two-dimensional (2D) van der Waals ferromagnetic materials are emerging as promising candidates for applications in ultra-compact spintronic nanodevices, nanosensors, and information storage. Our recent discovery of the strong room temperature ferromagnetism in single layers of VSe grown on graphite or MoS substrate has opened new opportunities to explore these ultrathin magnets for such applications. In this paper, we present a new type of magnetic sensor that utilizes the single layer VSe film as a highly sensitive magnetic core.

Monolayer Modification of VTe and Its Charge Density Wave.

Interlayer interactions in layered transition metal dichalcogenides are known to be important for describing their electronic properties. Here, we demonstrate that the absence of interlayer coupling in monolayer VTe also causes their structural modification from a distorted 1T' structure in bulk and multilayer samples to a hexagonal 1T structure in the monolayer. X-ray photoemission spectroscopy indicates that this structural transition is associated with electron transfer from the vanadium d bands to the tellurium atoms for the monolayer.

Which Transition Metal Atoms Can Be Embedded into Two-Dimensional Molybdenum Dichalcogenides and Add Magnetism?

As compared to bulk solids, large surface-to-volume ratio of two-dimensional (2D) materials may open new opportunities for postsynthesis introduction of impurities into these systems by, for example, vapor deposition. However, it does not work for graphene or h-BN, as the dopant atoms prefer clustering on the surface of the material instead of getting integrated into the atomic network. Using extensive first-principles calculations, we show that counterintuitively most transition metal (TM) atoms can be embedded into the atomic network of the pristine molybdenum dichalcogenides (MoDCs) upon atom deposition at moderate temperatures either as interstitials or substitutional impurities, especially in MoTe, which has the largest spacing between the host atoms.

Mirror twin grain boundaries in molybdenum dichalcogenides.

Mirror twin grain boundaries (MTBs) exist at the interface between two grains of 60° rotated hexagonal transition metal dichalcogenides (TMDC). These grain boundaries form a regular atomic structure that extends in one dimension and thus may be described as a one-dimensional (1D) lattice embedded in the 2D TMDC. In this review, the different atomic structures and compositions of these MTBs are discussed.

Post-Synthesis Modifications of Two-Dimensional MoSe or MoTe by Incorporation of Excess Metal Atoms into the Crystal Structure.

Phase engineering has extensively been used to achieve metallization of two-dimensional (2D) semiconducting materials, as it should boost their catalytic properties or improve electrical contacts. In contrast, here we demonstrate compositional phase change by incorporation of excess metals into the crystal structure. We demonstrate post-synthesis restructuring of the semiconducting MoTe or MoSe host material by unexpected easy incorporation of excess Mo into their crystal planes, which causes local metallization.

A first-principles study of stability of surface confined mixed metal oxides with corundum structure (FeO, CrO, VO).

Surface-confined mixed metal oxides can have different chemical properties compared to their host metal oxide support. For this reason, mixed transition metal oxides can offer tunable redox properties. Herein, we use density functional theory to predict the stability of the (0001) surface termination for mixed metal oxides consisting of FeO, CrO and VO.

Strong room-temperature ferromagnetism in VSe monolayers on van der Waals substrates.

Reduced dimensionality and interlayer coupling in van der Waals materials gives rise to fundamentally different electronic , optical and many-body quantum properties in monolayers compared with the bulk. This layer-dependence permits the discovery of novel material properties in the monolayer regime. Ferromagnetic order in two-dimensional materials is a coveted property that would allow fundamental studies of spin behaviour in low dimensions and enable new spintronics applications.

Comparison of surface structures of corundum CrO(0 0 0 1) and VO(0 0 0 1) ultrathin films by x-ray photoelectron diffraction.

Thin CrO(0 0 0 1) layers are formed by oxidation of a Cr(1 1 0) single crystal. This surface is further modified by growing an epitaxial ultrathin VO(0 0 0 1) film by reactive vapor deposition. Synchrotron based soft-x-ray photoemission spectroscopy and x-ray photoelectron diffraction are used to characterize the surface layers of these two corundum-structured oxides.

Metallic Twin Grain Boundaries Embedded in MoSe Monolayers Grown by Molecular Beam Epitaxy.

Twin grain boundaries in MoSe are metallic and undergo a metal to insulator Peierls transition at low temperature. Growth of MoSe by molecular beam epitaxy results in the spontaneous formation of a high density of these twin grain boundaries, likely as a mechanism to incorporate Se deficiency in the film. Using scanning tunneling microscopy, we study the grain boundary network that is formed in homoepitaxially grown MoSe and for MoSe grown heteroepitaxially on MoS and HOPG substrates.

Angle resolved photoemission spectroscopy reveals spin charge separation in metallic MoSe grain boundary.

Material line defects are one-dimensional structures but the search and proof of electron behaviour consistent with the reduced dimension of such defects has been so far unsuccessful. Here we show using angle resolved photoemission spectroscopy that twin-grain boundaries in the layered semiconductor MoSe exhibit parabolic metallic bands. The one-dimensional nature is evident from a charge density wave transition, whose periodicity is given by k/π, consistent with scanning tunnelling microscopy and angle resolved photoemission measurements.

Fusing tetrapyrroles to graphene edges by surface-assisted covalent coupling.

Surface-assisted covalent linking of precursor molecules enables the fabrication of low-dimensional nanostructures, which include graphene nanoribbons. One approach to building functional multicomponent systems involves the lateral anchoring of organic heteromolecules to graphene. Here we demonstrate the dehydrogenative coupling of single porphines to graphene edges on the same metal substrate as used for graphene synthesis.

Ordered Fe(II)Ti(IV)O3 Mixed Monolayer Oxide on Rutile TiO2(011).

Oxide monolayers supported or intermixed with an oxide support are potential nanocatalysts whose properties are determined by the interplay with the support. For fundamental studies of monolayer oxides on metal oxide supports, well-defined systems are needed, but so far, the synthesis of monolayer oxides with long-range order on single-crystal oxide surfaces is rare. Here, we show by a combination of scanning tunneling microscopy, photoemission spectroscopy, and density functional theory (DFT)-based computational analysis that the rutile TiO2(011) surface supports the formation of an ordered mixed FeTiO3 monolayer.

Growth from behind: Intercalation-growth of two-dimensional FeO moiré structure underneath of metal-supported graphene.

Growth of graphene by chemical vapor deposition on metal supports has become a promising approach for the large-scale synthesis of high quality graphene. Decoupling of the graphene from the metal has been achieved by either mechanical transfer or intercalation of elements/molecules in between the metal and graphene. Here we show that metal stabilized two-dimensional (2D)-oxide monolayers can be grown in between graphene and the metal substrate thus forming 2D-heterostructures that enable tuning of the materials properties of graphene.

Direct observation of interlayer hybridization and Dirac relativistic carriers in graphene/MoS₂ van der Waals heterostructures.

Artificial heterostructures assembled from van der Waals materials promise to combine materials without the traditional restrictions in heterostructure-growth such as lattice matching conditions and atom interdiffusion. Simple stacking of van der Waals materials with diverse properties would thus enable the fabrication of novel materials or device structures with atomically precise interfaces. Because covalent bonding in these layered materials is limited to molecular planes and the interaction between planes are very weak, only small changes in the electronic structure are expected by stacking these materials on top of each other.