Growth of Single Crystalline 2D Materials beyond Graphene on Non-metallic Substrates.

The advent of 2D materials has ushered in the exploration of their synthesis, characterization and application. While plenty of 2D materials have been synthesized on various metallic substrates, interfacial interaction significantly affects their intrinsic electronic properties. Additionally, the complex transfer process presents further challenges.

Epitaxial Growth of 2D Binary Phosphides.

Combinations of phosphorus with main group III, IV, and V elements are theoretically predicted to generate 2D binary phosphides with extraordinary properties and promising applications. However, experimental synthesis is significantly lacking. Here, a general approach for preparing 2D binary phosphides is reported using single crystalline surfaces containing the constituent element of target 2D materials as the substrate.

High-Yield Production of Quantum Corrals in a Surface Reconstruction Pattern.

The power of surface chemistry to create atomically precise nanoarchitectures offers intriguing opportunities to advance the field of quantum technology. Strategies for building artificial electronic lattices by individually positioning atoms or molecules result in precisely tailored structures but lack structural robustness. Here, taking the advantage of strong bonding of Br atoms on noble metal surfaces, we report the production of stable quantum corrals by dehalogenation of hexabromobenzene molecules on a preheated Au(111) surface.

Vacancy-Regulated Charge Carrier Dynamics and Suppressed Nonradiative Recombination in Two-Dimensional ReX (X = S, Se).

Point defects in semiconductors usually act as nonradiative charge carrier recombination centers, which severely limit the performance of optoelectronic devices. In this work, by combining time-domain density functional theory with nonadiabatic molecular dynamics simulations, we demonstrate suppressed nonradiative charge carrier recombination and prolonged carrier lifetime in two-dimensional (2D) ReX (X = S, Se) with S/Se vacancies. In particular, a S vacancy introduces a shallow hole trap state in ReS, while a Se vacancy introduces both hole and electron trap states in ReSe.

On-Surface Synthesis toward Two-Dimensional Polymers.

Two-dimensional (2D) polymers have garnered widespread interest because of their intriguing physicochemical properties. Envisaged applications in fields including nanodevices, solid-state chemistry, physical organic chemistry, and condensed matter physics, however, demand high-quality and large-scale production. In this perspective, we first introduce exotic band structures of organic frameworks holding honeycomb, kagome, and Lieb lattices.

Phase Engineering of Epitaxial Stanene on a Surface Alloy.

Stanene is a notable two-dimensional topological insulator with a large spin-orbit-coupling-induced band gap. However, the formation of surface alloy intermediates during the epitaxial growth on noble metal substrates prevents the as-grown stanene from preserving its intrinsic electronic states. Here, we show that an intentionally prepared AuSn(111) alloy surface is a suitable inert substrate for growing stanene without the further formation of a complicated surface alloy by scanning tunneling microscopy.

Bio-Inspired Passion Fruit-like FeO@C Nanospheres Enabling High-Stability Magnetorheological Performances.

Magnetorheological (MR) fluids have been successfully utilized in versatile fields but are still limited by their relatively inferior long-term dispersion stability. Herein, bio-inspired passion fruit-like FeO@C nanospheres were fabricated via a simple hydrothermal and calcination approach to tackle the settling challenge. The unique structures provide sufficient active interfaces for the penetration of carrier mediums, leading to preferable wettability between particles and medium oils.

Reversible oxidation and reduction of gold-supported iron oxide islands at room temperature.

Monolayer iron oxides grown on metal substrates have widely been used as model systems in heterogeneous catalysis. By means of ambient-pressure scanning tunneling microscopy (AP-STM), we studied the in situ oxidation and reduction of FeO(111) grown on Au(111) by oxygen (O) and carbon monoxide (CO), respectively. Oxygen dislocation lines present on FeO islands are highly active for O dissociation.

Epitaxial Growth of Flat, Metallic Monolayer Phosphorene on Metal Oxide.

In recent years, two-dimensional (2D) group VA elemental materials have attracted considerable interest from physics/chemistry and materials science communities, with particular attention paid to honeycomb blue phosphorene. To date, phosphorene is limited to its α-phase and small sizes because it can only be produced by exfoliating black phosphorus crystals. Here, we report the direct synthesis of high-quality phosphorene on a nonmetallic copper oxide substrate by molecular beam epitaxy.

Recent Advances in Tin: From Two-Dimensional Quantum Spin Hall Insulator to Bulk Dirac Semimetal.

An atomic layer of tin in a buckled honeycomb lattice, termed stanene, is a promising large-gap two-dimensional topological insulator for realizing room-temperature quantum-spin-Hall effect and therefore has drawn tremendous interest in recent years. Because the electronic structures of Sn allotropes are sensitive to lattice strain, e.g.

Large-Scale Synthesis of Strain-Tunable Semiconducting Antimonene on Copper Oxide.

Controlled synthesis of 2D structures on nonmetallic substrate is challenging, yet an attractive approach for the integration of 2D systems into current semiconductor technologies. Herein, the direct synthesis of high-quality 2D antimony, or antimonene, on dielectric copper oxide substrate by molecular beam epitaxy is reported. Delicate scanning tunneling microscopy imaging on the evolution intermediates reveals a segregation growth process on Cu O /Cu(111), from ordered dimer chains to packed dot arrays, and finally to monolayer antimonene.

Imaging and Dynamics of Water Hexamer Confined in Nanopores.

Epitaxial two-dimensional (2D) nanostructures with regular patterns show great promise as templates for adsorbate confinement. Prospectively, employing 2D semiconductors with reduced density of states leads to a long excited-state lifetime that allows us to directly image the dynamics of the adsorbate. We show that epitaxial blue phosphorene (blueP) on Au(111) provides such a platform to trap water molecules in the periodic nanopores without formation of strong bonds.

Modulating Epitaxial Atomic Structure of Antimonene through Interface Design.

Antimonene, a new semiconductor with fundamental bandgap and desirable stability, has been experimentally realized recently. However, epitaxial growth of wafer-scale single-crystalline monolayer antimonene preserving its buckled configuration remains a daunting challenge. Here, Cu(111) and Cu(110) are chosen as the substrates to fabricate high-quality, single-crystalline antimonene via molecular beam epitaxy (MBE).

Epitaxial Growth of 6 in. Single-Crystalline Graphene on a Cu/Ni (111) Film at 750 °C via Chemical Vapor Deposition.

The future electronic application of graphene highly relies on the production of large-area high-quality single-crystal graphene. However, the growth of single-crystal graphene on different substrates via either single nucleation or seamless stitching is carried out at a temperature of 1000 °C or higher. The usage of this high temperature generates a variety of problems, including complexity of operation, higher contamination, metal evaporation, and wrinkles owing to the mismatch of thermal expansion coefficients between the substrate and graphene.

Conformational Transitions of Phase-Separated Binary Molecules Assisted by Surface Dehalogenation.

Molecular devices have become an emergent branch of nanoscience and technology beyond traditional silicon-based electronic devices. The properties of these devices are intimately related to the molecular conformation and packing. In this article, three different conformations of melamine molecules are observed on Au(111), and a transition from the lying-down to standing-up phase with long-range order is realized in melamine chains with the assistance of hexabromobenzene (HBB).

Seamless lateral graphene p-n junctions formed by selective in situ doping for high-performance photodetectors.

Lateral graphene p-n junctions are important since they constitute the core components in a variety of electronic/photonic systems. However, formation of lateral graphene p-n junctions with a controllable doping levels is still a great challenge due to the monolayer feature of graphene. Herein, by performing selective ion implantation and in situ growth by dynamic chemical vapor deposition, direct formation of seamless lateral graphene p-n junctions with spatial control and tunable doping is demonstrated.

Two-dimensional black phosphorus: its fabrication, functionalization and applications.

Phosphorus, one of the most abundant elements in the Earth (∼0.1%), has attracted much attention in the last five years since the rediscovery of two-dimensional (2D) black phosphorus (BP) in 2014. The successful scaling down of BP endows this 'old material' with new vitality, resulting from the intriguing semiconducting properties in the atomic scale limit, i.

DFT coupled with NEGF study of a promising two-dimensional channel material: black phosphorene-type GaTeCl.

A stable three-dimensional layered GaTeCl bulk counterpart is first known from experiment since 1980s. In this study, we propose a two-dimensional GaTeCl, the band structure of which has a tendency of intrinsic direct-to-indirect band gap transitions as a result of a decrease in the layer number, while the changes in the band gap value are minor. The GaTeCl monolayer possesses a wide indirect band gap of 3.

Halogen-Adatom Mediated Phase Transition of Two-Dimensional Molecular Self-Assembly on a Metal Surface.

Construction of tunable and robust two-dimensional (2D) molecular arrays with desirable lattices and functionalities over a macroscopic scale relies on spontaneous and reversible noncovalent interactions between suitable molecules as building blocks. Halogen bonding, with active tunability of direction, strength, and length, is ideal for tailoring supramolecular structures. Herein, by combining low-temperature scanning tunneling microscopy and systematic first-principles calculations, we demonstrate novel halogen bonding involving single halogen atoms and phase engineering in 2D molecular self-assembly.

Oxygen-Promoted Methane Activation on Copper.

The role of oxygen in the activation of C-H bonds in methane on clean and oxygen-precovered Cu(111) and CuO(111) surfaces was studied with combined in situ near-ambient-pressure scanning tunneling microscopy and X-ray photoelectron spectroscopy. Activation of methane at 300 K and "moderate pressures" was only observed on oxygen-precovered Cu(111) surfaces. Density functional theory calculations reveal that the lowest activation energy barrier of C-H on Cu(111) in the presence of chemisorbed oxygen is related to a two-active-site, four-centered mechanism, which stabilizes the required transition-state intermediate by dipole-dipole attraction of O-H and Cu-CH species.

Enhanced Stability and Tunable Photoluminescence in Perovskite CsPbX /ZnS Quantum Dot Heterostructure.

All-inorganic perovskite CsPbX (X = Cl, Br, I) and related materials are promising candidates for potential solar cells, light emitting diodes, and photodetectors. Here, a novel architecture made of CsPbX /ZnS quantum dot heterodimers synthesized via a facile solution-phase process is reported. Microscopic measurements show that CsPbX /ZnS heterodimer has high crystalline quality with enhanced chemical stability, as also evidenced by systematic density functional theory based first-principles calculations.

How Graphene Islands Are Unidirectionally Aligned on the Ge(110) Surface.

The unidirectional alignment of graphene islands is essential to the synthesis of wafer-scale single-crystal graphene on Ge(110) surface, but the underlying mechanism is not well-understood. Here we report that the necessary coalignment of the nucleating graphene islands on Ge(110) surface is caused by the presence of step-pattern; we show that on the preannealed Ge(110) textureless surface the graphene islands appear nonpreferentially orientated, while on the Ge(110) surfaces with natural step pattern, all graphene islands emerge coaligned. First-principles calculations and theoretical analysis reveal this different alignment behaviors originate from the strong chemical binding formed between the graphene island edges and the atomic steps on the Ge(110) surface, and the lattice matching at edge-step interface dictates the alignment of graphene islands with the armchair direction of graphene along the [-110] direction of the Ge(110) substrate.

Copper-Vapor-Assisted Rapid Synthesis of Large AB-Stacked Bilayer Graphene Domains on Cu-Ni Alloy.

The synergic effects of Cu85Ni15 and the copper vapor evaporated from copper foil enabled the fast growth of a ≈300 μm bilayer graphene in ≈10 minutes. The copper vapor reduces the growth rate of the first graphene layer while the carbon dissolved in the alloy boosts the growth of the subsequently developed second graphene layer with an AB-stacking order.

Low temperature critical growth of high quality nitrogen doped graphene on dielectrics by plasma-enhanced chemical vapor deposition.

Nitrogen doping is one of the most promising routes to modulate the electronic characteristic of graphene. Plasma-enhanced chemical vapor deposition (PECVD) enables low-temperature graphene growth. However, PECVD growth of nitrogen doped graphene (NG) usually requires metal-catalysts, and to the best of our knowledge, only amorphous carbon-nitrogen films have been produced on dielectric surfaces by metal-free PECVD.

Elementary process for CVD graphene on Cu(110): size-selective carbon clusters.

Revealing the graphene growth mechanism at the atomic-scale is of great importance for achieving high quality graphene. However, the lack of direct experimental observation and density functional theory (DFT) verification hinders a comprehensive understanding of the structure of the carbon clusters and evolution of the graphene growth on surface. Here, we report an in-situ low-temperature scanning tunneling microscopy (LT-STM) study of the elementary process of chemical vapor deposition (CVD) graphene growth via thermal decomposition of methane on Cu(110), including the formation of monodispersed carbon clusters at the initial stage, the graphene nucleation and the ripening of graphene islands to form continuous graphene film.