Building Bilayer MoS with Versatile Morphologies via Etching-And-Growth Coexisting Method.

The etch-engineering is a feasible avenue to tailor the layer number and morphology of 2D layered materials during the chemical vapor deposition (CVD) growth. However, less reports strengthen the etch-engineering used in the fabrication of high-quality transition metal dichalcogenide (TMD) materials with tunable layers and desirable morphologies to improve their prominent performance in electronic and optoelectronic devices. Here, an etching-and-growth coexistence method is reported to directly synthesize high-quality, high-symmetric MoS bilayers with versatile morphologies via CVD.

Isotropic Quantum Griffiths Singularity in Nd_{0.8}Sr_{0.2}NiO_{2} Infinite-Layer Superconducting Thin Films.

This work reports on the emergence of quantum Griffiths singularity (QGS) associated with the magnetic field induced superconductor-metal transition (SMT) in unconventional Nd_{0.8}Sr_{0.2}NiO_{2} infinite layer superconducting thin films.

Homo-Site Nucleation Growth of Twisted Bilayer MoS with Commensurate Angles.

Moiré superlattices, composed of two layers of transition metal dichalcogenides with a relative twist angle, provide a novel platform for exploring the correlated electronic phases and excitonic physics. Here, a gas-flow perturbation chemical vapor deposition (CVD) approach is demonstrated to directly grow MoS bilayer with versatile twist angles. It is found that the formation of twisted bilayer MoS homostructures sensitively depends on the gas-flow perturbation modes, correspondingly featuring the nucleation sites of the second layer at the same (homo-site) as or at the different (hetero-site) from that of the first layer.

Kondo scattering in underdoped NdSrNiO infinite-layer superconducting thin films.

The recent discovery of superconductivity in infinite-layer nickelates generates tremendous research endeavors, but the ground state of their parent compounds is still under debate. Here, we report experimental evidence for the dominant role of Kondo scattering in the underdoped NdSrNiO thin films. A resistivity minimum associated with logarithmic temperature dependence in both longitudinal and Hall resistivities are observed in the underdoped NdSrNiO samples before the superconducting transition.

A natural indirect-to-direct band gap transition in artificially fabricated MoS and MoSe flowers.

Twisted bilayer (tB) transition metal dichalcogenide (TMD) structures formed from two pieces of a periodic pattern overlaid with a relative twist manifest novel electronic and optical properties and correlated electronic phenomena. Here, twisted flower-like MoS and MoSe bilayers were artificially fabricated by the chemical vapor deposition (CVD) method. Photoluminescence (PL) studies demonstrated that an energy band structural transition from the indirect gap to the direct gap happened in the region away from the flower center in tB MoS (MoSe) flower patterns, accompanied by an enhanced PL intensity.

Low-Temperature Synthesis of Boron Nitride as a Large-Scale Passivation and Protection Layer for Two-Dimensional Materials and High-Performance Devices.

Two-dimensional materials (2DMs) with extraordinary electronic and optical properties have attracted great interest in optoelectronic applications. Due to their atomically thin feature, 2DM-based devices are generally sensitive to oxygen and moisture in ambient air, and thus, practical application of durable 2DM-based devices remains challenging. Here, we report a novel strategy to directly synthesize amorphous BN film on various 2DMs and field-effect transistor (FET) devices at low temperatures by conventional chemical vapor deposition.

Ionic Current Fluctuation and Orientation of Tetrahedral DNA Nanostructures in a Solid-State Nanopore.

Understanding the dynamic behavior of a nanostructure translocating through a nanopore is important for various applications. In this paper, the characteristics in ion current traces of tetrahedral DNA nanostructures (TDN) translocating through a solid-state nanopore are examined, by combined experimental and theoretical simulations. The results of finite element analysis reveal the correlation between orientation of TDN and the conductance blockade.

Enhanced Valley Polarization of Bilayer MoSe with Variable Stacking Order and Interlayer Coupling.

In two-dimensional transitional metal dichalcogenides, tuning the spin-valley-layer coupling via changing layer numbers and stacking orders remains desirable for their application in valleytronics. Herein, six-point star-like MoSe nanoflakes simultaneously containing different atom registration regions from monolayer to bilayer with 2H and 3R stacking order were fabricated, and the valley polarizations were comparably investigated by circular polarized photoluminescent spectroscopy. The degree of valley polarization was detected to be about 12.

Robust atomic-structure of the 6 × 2 reconstruction surface of Ge(110) protected by the electronically transparent graphene monolayer.

Wafer-scale growth of the unidirectional graphene monolayer on Ge surfaces has rejuvenated the intense study of the surfaces and interfaces of semiconductors underneath graphene. Recently, it was reported that the Ge atoms in the Ge(110) surface beneath a graphene monolayer underwent a rearrangement and formed an ordered (6 × 2) reconstruction. However, a plausible atomic model related to this (6 × 2) reconstruction is still lacking.

Large linear magnetoresistance caused by disorder in WTethin film.

Weyl semimetal WTehas attracted considerable attention owing to its extremely large, unsaturated and quadratic magnetoresistance. Here, we study the magnetotransport properties of WTethin film, which shows an unsaturated and linear magnetoresistance of up to ∼1650%. A more complex and accurate method, known as the maximum entropy mobility spectrum, is used to analyze the mobility and density of carriers.

Enhancement of Rashba spin-orbit coupling by electron confinement at the LaAlO/SrTiO interface.

Electrical transport property is closely related to the dimensionality of carriers' distribution. In this work, we succeed in tuning the carriers' distribution and the Rashba spin-orbit coupling at LaAlO/SrTiO interface by varying the oxygen pressure (c-P ) adopted in crystalline LaAlO growth. Measurements of the in-plane anisotropic magnetoresistance and the conducting-layer thickness indicate that the carriers' distribution changes from three to two dimensions with c-P increasing, i.

Mo Concentration Controls the Morphological Transitions from Dendritic to Semicompact, and to Compact Growth of Monolayer Crystalline MoS on Various Substrates.

The domain morphology in the growth of transition-metal dichalcogenides (TMDCs) is mostly triangular but rarely dendritic. Here, we report a robust chemical vapor deposition method to fabricate atomic-thin 2H-phase MoS dendrites on several single-crystalline substrates with different lattice structures, such as rutile-TiO(001), SrTiO(001), and sapphire(0001). It is found that by tuning the concentration of Mo adatoms, the morphology of MoS domains on these substrates evolves from tridentate dendrites at a low Mo concentration to semicompact fractal domains at an intermediate Mo concentration, and to a compact triangular shape at a high Mo concentration.

Planar Hall effect induced by anisotropic orbital magnetoresistance in type-II Dirac semimetal PdTe.

We measure planar Hall effect (PHE) and longitudinal anisotropic magnetoresistance (AMR) with a magnetic field rotating in the a-b plane in the type-II Dirac semimetal PdTe. The measured PHE and AMR curves can be fitted by the theoretical equations; however, a detailed analysis of the extracted data demonstrates that the parameter related to PHE and AMR has no relationship with the chiral anomaly due to the absence of negative longitudinal magnetoresistance (MR) when the electric and magnetic fields are parallel to each other. Meanwhile, we prove that the origin of PHE in PdTe is the anisotropic orbital MR.

Translocation of tetrahedral DNA nanostructures through a solid-state nanopore.

Tetrahedral DNA nanostructures (TDNs) are programmable DNA nanostructures that have great potential in bio-sensing, cell imaging and therapeutic applications. In this study, we investigate the translocation behavior of individual TDNs through solid-state nanopores. Pronounced translocation signals for TDNs are observed that are sensitive to the size of the nanostructures.

Interaction between in-gap states and carriers at the conductive interface between perovskite oxides.

The 2D electron systems of SrTiO/NdGaO (STO/NGO) and amorphous-LaAlO/SrTiO/NdGaO (a-LAO/STO/NGO) heterojunctions were explored. An obvious interaction between in-gap states (IGSs) and carriers was found. The IGSs can trap a large number of carriers and enhance carrier scattering.

Formation of Two-dimensional Electron Gas at Amorphous/Crystalline Oxide Interfaces.

Experimentally, we found the percentage of low valence cations, the ionization energy of cations in film, and the band gap of substrates to be decisive for the formation of two-dimensional electron gas at the interface of amorphous/crystalline oxide (a-2DEG). Considering these findings, we inferred that the charge transfer from the film to the interface should be the main mechanism of a-2DEG formation. This charge transfer is induced by oxygen defects in film and can be eliminated by the electron-absorbing process of cations in the film.

Building chessboard-like supramolecular structures on Au(111) surfaces.

We investigate an anthracene derivative, 3(5)-(9-anthryl) pyrazole (ANP), self-assembled on the Au(111) surface by means of scanning tunneling microscopy (STM) and density functional theory (DFT) calculations. A chessboard-like network structure composed of ANP molecules is found, covering the whole Au(111) substrate. Our STM results and DFT calculations reveal that the formation of chessboard-like networks originates from a basic unit cell, a tetramer structure, which is formed by four ANP molecules connected through C-H…N hydrogen bonds.

Liquid-assisted tip manipulation: fabrication of twisted bilayer graphene superlattices on HOPG.

We use the tip of a scanning tunneling microscope (STM) to manipulate single weakly bound nanometer-sized sheets on a highly oriented pyrolytic graphite (HOPG) surface through artificially increasing the tip and sample interaction by pretreatment of the surface using a liquid thiol molecule. By this means it is possible to tear apart a graphite sheet against a step and fold this part onto the HOPG surface and thus generate graphene superlattices with hexagonal symmetry. The tip and sample surface interactions, including the van der Waals force, electrostatic force and capillary attraction force originating from the Laplace pressure due to the formation of a highly curved fluid meniscus connecting the tip and sample, are discussed quantitatively to understand the formation mechanism of a graphene superlattice induced by the STM tip.

Strain and curvature induced evolution of electronic band structures in twisted graphene bilayer.

It is well established that strain and geometry could affect the band structure of graphene monolayer dramatically. Here we study the evolution of local electronic properties of a twisted graphene bilayer induced by a strain and a high curvature, which are found to strongly affect the local band structures of the twisted graphene bilayer. The energy difference of the two low-energy van Hove singularities decreases with increasing lattice deformation and the states condensed into well-defined pseudo-Landau levels, which mimic the quantization of massive chiral fermions in a magnetic field of about 100 T, along a graphene wrinkle.

Angle-dependent van Hove singularities in a slightly twisted graphene bilayer.

Recent studies show that two low-energy van Hove singularities (VHSs) seen as two pronounced peaks in the density of states could be induced in a twisted graphene bilayer. Here, we report angle-dependent VHSs of a slightly twisted graphene bilayer studied by scanning tunneling microscopy and spectroscopy. We show that energy difference of the two VHSs follows ΔE(vhs)∼ℏν(F)ΔK between 1.

Scanning tunnelling microscope studies of angstrom-scale Co3O4 nanowires.

We report the bottom-up assembly of an atomic-scale building block, which consists of four Co(3+) cations, two Co(2+) cations, and eight O(2-) anions, for generating one-dimensional Co(3)O(4) nanostructures with diameters ranging from 0.5 to 3 nm. Controlled experiments were carried out and the growth mechanism of the Co(3)O(4) nanowires was investigated.

Self-assembled monolayers of CH3COS- terminated surfactant-encapsulated polyoxometalate complexes.

Self-assembled monolayers (SAMs) on gold surfaces based on three kinds of acetylthio-surfactant-encapsulated polyoxometalate clusters (thio-SECs) terminated with multiple CH(3)COS- groups, (NC(26)H(55)S(CO)CH(3))(6)H(2)[Co(H(2)O)CoW(11)O(39)], (NC(26)H(55)S(CO)CH(3))(13)H(3)[Co(4)(H(2)O)(2)(P(2)W(15)O(56))(2)], and (NC(26)H(55)S(CO)CH(3))(13)[Fe(4)(H(2)O)(2)(P(2)W(15)O(56))(2)]Br, have been prepared, which is representative of a general methodology to fabricate polyoxometalate-based SAMs. Thio-SECs self-assembled into monolayers on gold surfaces through the hydrolysis of CH(3)COS- groups and the subsequent formation of S-Au bonds, which was confirmed by grazing angle infrared spectroscopy, X-ray photoelectron spectroscopy, and ellipsometric and scanning tunneling microscopy (STM) measurements. Furthermore, the SAMs of the thio-SECs possess closely packed structures, and the local short-range order is clearly observed in the magnified STM image.

Self-assembled monolayers of aromatic thiols stabilized by parallel-displaced pi-pi stacking interactions.

Parallel-displaced pi-pi stacking interactions have been known to be the dominant force in stabilizing the double helical structure of DNA and the tertiary structure of proteins. However, little is known about their roles in self-assembled monolayers of other large pi molecules such as aromatic thiols. Here we report on a systematic study of the self-assembled monolayers of four kinds of anthracene-based thiols, 9-mercaptoanthracene (MA), (4-mercaptophenyl) (9-anthryl) acetylene (MPAA), (4-mercaptophenyl) (10-nitro-9-anthryl) acetylene (MPNAA), and (4-mercaptophenyl) (10-carboxyl-9-anthryl) acetylene (MPCAA) on Au(111), in which a spacer and different functional groups (NO2 and COOH) are intentionally designed to introduce and thus allow the investigation of various intermolecular interactions, in addition to pi-pi interactions in the base molecules.

Borderline magic clustering: the fabrication of tetravalent Pb cluster arrays on Si(111)-(7x7) surfaces.

Well-ordered arrays of identical Pb clusters have been fabricated on a Si(111)-(7x7) substrate by the temperature-mediated surface clustering method. Interestingly, these clusters can easily transform into other forms when the growth temperature deviates slightly from the optimal values. In accord with experiments, first-principle total-energy calculations reveal several cluster structures centered on a mixed cluster model involving surface Pb and Si exchange.