Two-dimensional (2D) layered materials hosting dislocations have attracted considerable research attention in recent years. In particular, screw dislocations can result in a spiral topology and an interlayer twist in the layered materials, significantly impacting the stacking order and symmetry of the layers. Moreover, the dislocations with large strain and heavily distorted atomic registry can result in a local modification of the structures around the dislocation. The dislocations thus provide a useful route to engineering optical, electrical, thermal, mechanical and catalytic properties of the 2D layered materials, which show great potential to bring new functionalities. This article presents a comprehensive review of the experimental and theoretical progress on the growth and properties of the dislocated 2D layered materials. It also offers an outlook on the future works in this promising research field.
Based on first-principles calculations, we propose that a layered electride Mg2O can serve as an effective substrate, in place of metal substrate, to grow honeycomb borophene (h-borophene). We first confirm the thermodynamic stability of h-B@Mg2O heterostructure by energetics analysis and dynamic stability by absence of imaginary frequency in phonon spectra. Then, kinetically, we identify the atomistic pathways for a preferred 2D growth mode over 3D growth, and reveal a growth transition from 2D compact islands to h-borophene at ~13-atom cluster size, indicating the feasibility of epitaxial gr…
Layered transition metal dichalcogenides: promising near-lattice-matched substrates for GaN growth
大多数III族氮化物半导体生长在非晶格匹配的衬底上，如蓝宝石或硅，这是由于获得原生GAN衬底的极端困难。我们发现，几个层状过渡金属二硫属化物是密切晶格匹配的GAN和报告的GAN的生长范围内的这种层状材料。我们报告的GAN的生长的详细研究的机械剥离片WS $_2$和MoS $_2$的金属有机气相外延。结构和光学特性表明，无应变，单晶岛的GaN上获得的硫属化物薄片。我们从这些层获得了强的近带边发射，并分析了它们的温度依赖的光致发光特性。我们还报告了在CVD MoS $_2$上大面积外延生长GAN的概念验证演示。我们的研究结果表明，过渡金属二硫属化物可以作为一种新的近晶格匹配的氮化物生长衬底。
A model for the formation of carbon nanotubes (CNTs) and layered graphene in an arc discharge method is developed on the basis of observed erosion of graphite anode under various experimental conditions and analyses of the morphology of the eroded anode-surface, concerned cathode deposits and their constituents. It is predicted that, cold thermal shock, triggered by the rapid movement of the anode-spot, leads to crack microbranching at some selected locations on the anode-surface. These crack-microbranches cleave and fragment the basal planes of pairs of adjacent crystallites into curved graph…
Transition metal dichalcogenide (TMD) monolayers and heterostructures have emerged as a compelling class of materials with transformative new science that may be harnessed for novel device technologies. These materials are commonly fabricated by exfoliation of flakes from bulk crystals, but wafer-scale epitaxy of single crystal films is required to advance the field. This article reviews the fundamental aspects of epitaxial growth of van der Waals bonded crystals specific to TMD films. The structural and electronic properties of TMD crystals are initially described along with sources and metho…
Layered bismuthides of the family ATM2Bi2 are showing very interesting structural and physical properties. Here, we report crystal growth and characterization of new ternary layered bismuthides: RbCd2Bi2, RbZn2Bi2 and KZn2Bi2. Single crystals were grown by self-flux technique. As grown crystals were characterized by combination of powder X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy and single crystal X-ray diffraction. All novel compounds crystallize in layered ThCr2Si2 structure type with plate-like morphology with weak bonding between layers. Signific…
In this paper, we propose a multi-layered hyperelastic plate theory of growth within the framework of nonlinear elasticity. First, the 3D governing system for a general multi-layered hyperelastic plate is established, which incorporates the growth effect, and the material and geometrical parameters of the different layers. Then, a series expansion-truncation approach is adopted to eliminate the thickness variables in the 3D governing system. An elaborate calculation scheme is applied to derive the iteration relations of the coefficient functions in the series expansions. Through some further m…
Mn as surfactant for the self-assembling of Al$_x$Ga$_{1-x}$N/GaN layered heterostructures
GAN和Al $_x$ Ga $_{1-x}$ N/GAN异质结构在Mn存在下通过金属有机气相外延生长的结构分析揭示了Mn如何影响生长过程，特别是Al的掺入、表面的形态以及GAN上的Al $_x$ Ga $_{1-x}$ N的塑性弛豫。此外，Mn的掺杂促进了层状Al $_x$ Ga $_{1-x}$ N/GAN超晶格异质结构的形成，为控制晶体生长过程中三元合金的偏析和促进功能层状结构的自组装开辟了广阔的前景。
A graphyne (GY) family composed of the triple (sp) and double (sp2) bonds-hybridized carbon atoms is a promising allotrope of carbon for the development of nanoscale electronic devices. Unlike graphene, the GY family containing carbon sp bonds remains an unsolved problem in efficient two-dimensional (2D) growth due to monomer instability and side reactions. Herein, we synthesize GY into a single 2D layer by chemical vapor deposition (CVD) at low temperatures preventing unexpected reactions, using 1,3,5-tribromo-2,4,6-triethynylbenzene (TBTEB). The CVD-grown GY via a surface-confined coupling b…
We report here a discovery of electrically driven insulator to metal transition (IMT) and concomitant isostructural volume expansion in the layered cobaltates which otherwise do not exhibit temperature dependent IMT. These findings are demonstrated at macroscopic, microscopic and atomic scales. With application of voltage growth of metallic regions have been observed in the 2D layered La2-xSrxCoO4. Growth of metallic regions is associated with volume increase (strain as high as 0.3%). Non thermal IMT and electro-strain are proposed to be caused by electro-proliferation of the Co3+ high spin st…
Nanoscale layered ferromagnets have demonstrated fascinating two-dimensional magnetism down to atomic layers, providing a peculiar playground of spin orders for investigating fundamental physics and spintronic applications. However, strategy for growing films with designed magnetic properties is not well established yet. Herein, we present a versatile method to control the Curie temperature (T_{C}) and magnetic anisotropy during growth of ultrathin Cr_{2}Te_{3} films. We demonstrate increase of the TC from 165 K to 310 K in sync with magnetic anisotropy switching from an out-of-plane orientati…
Pnictogens have multiple allotropic forms resulting from their ns2 np3 valence electronic configuration, making them the only elemental materials to crystallize in layered van der Waals (vdW) and quasi-vdW structures throughout the group. Light group VA elements are found in the layered orthorhombic A17 phase such as black phosphorus, and can transition to the layered rhombohedral A7 phase at high pressure. On the other hand, bulk heavier elements are only stable in the A7 phase. Herein, we demonstrate that these two phases not only co-exist during the vdW growth of antimony on weakly interact…
The application of new materials in nanotechnology opens new perspectives and enables ground-breaking innovations. Two-dimensional van der Waals materials and more specific, 2D chalcogenides are a promising class of new materials awaiting their usage in the semiconductor industry. However, the integration of van der Waals materials relying on industry-compatible manufacturing processes is still a major challenge. This is currently restricting the application of these new materials to the research laboratories environment only. The large-area and single-crystalline growth of van der Waals mater…
The Pd, and Pt based ABO2 delafossites are a unique class of layered, triangular oxides with 2D electronic structure and a large conductivity that rivals the noble metals. Here, we report successful growth of the metallic delafossite PdCoO2 by molecular beam epitaxy (MBE). The key challenge is controlling the oxidation of Pd in the MBE environment where phase-segregation is driven by the reduction of PdCoO2 to cobalt oxide and metallic palladium. This is overcome by combining low temperature (300 °C) atomic layer-by-layer MBE growth in the presence of reactive atomic oxygen with a post-growth …
The subtle balance of electronic correlations, crystal field splitting and spin--orbit coupling in layered Ir$^{4+}$ oxides can give rise to novel electronic and magnetic phases. Experimental progress in this field relies on the synthesis of epitaxial films of these oxides. However, the growth of layered iridates with excellent structural quality is a great experimental challenge. Here we selectively grow high quality single--phase films of Sr$_2$IrO$_4$, Sr$_3$Ir$_2$O$_7$, and SrIrO$_3$ on various substrates from a single Sr$_3$Ir$_2$O$_7$ target by tuning background oxygen pressure and epita…
The growth of single crystals of MoS2 and WS2 by materials transport through a liquid salt flux made from a low melting mixture of NaCl and CsCl is described. The crystals are characterized by single crystal X-ray diffraction, which reveals that they are 2H-MoS2 with a small percentage (about 3%) of 3R intergrowths. The 2H-WS2 crystals display less than 1% of 3R intergrowths. Photoluminescence spectra of exfoliated monolayers suggest that MoS2 grown by this method has superior crystallinity in comparison to commercially-available MoS2 crystals.
Transition metal dichalcogenides (TMDs) are van der Waals layered materials with sizable and tunable bandgaps, offering promising platforms for two-dimensional electronics and optoelectronics. To this end, the bottleneck is how to acquire high-quality single crystals in a facile and efficient manner. As one of the most widely employed method of single-crystal growth, conventional chemical vapor transport (CVT) generally encountered problems including the excess nucleation that leads to small crystal clusters and slow growth rate. To address these issues, a seed crystal is introduced to suppres…
Two-dimensional (2D) magnets with intrinsic ferromagnetic/antiferromagnetic (FM/AFM) ordering are highly desirable for future spintronics devices. However, the synthesis of 2D magnetic crystals, especially the direct growth on SiO2/Si substrate, is just in its infancy. Here, we report a chemical vapor deposition (CVD)-based rational growth approach for the synthesis of ultrathin FeTe crystals with controlled structural and magnetic phases. By precisely optimizing the growth temperature (Tgrowth), FeTe nanoplates with either layered tetragonal or non-layered hexagonal phase can be controlled wi…
Inversion symmetry breaking is a ubiquitous concept in condensed-matter science. On the one hand, it is a prerequisite for many technologically relevant effects such as piezoelectricity, photovoltaic and nonlinear optical properties and spin-transport phenomena. On the other hand, it may determine abstract properties such as the electronic topology in quantum materials. Therefore, the creation of materials where inversion symmetry can be turned on or off by design may be the ultimate route towards controlling parity-related phenomena and functionalities. Here, we engineer the symmetry of ultra…
Single crystals of the metallic Ruddlesden-Popper trilayer nickelates R$_4$Ni$_3$O$_{10}$ (R=La, Pr) were successfully grown using an optical-image floating zone furnace under oxygen pressure (pO$_2$) of 20 bar for La$_4$Ni$_3$O$_{10}$ and 140 bar for Pr$_4$Ni$_3$O$_{10}$. A combination of synchrotron and laboratory x-ray single crystal diffraction, high-resolution synchrotron x-ray powder diffraction and measurements of physical properties revealed that R$_4$Ni$_3$O$_{10}$ (R=La, Pr) crystallizes in the monoclinic $P$2$_1$/$a$ (Z=2) space group at room temperature, and that a metastable ortho…
The van der Waals material CeOI is predicted to be a layered antiferromagnetic Mott insulator by DFT+U calculation. We successfully grow the CeOI films down to monolayer on graphene/6H-SiC(0001) substrate by using molecular beam epitaxy. Films are studied by {\it in-situ} scanning tunneling microscopy and spectroscopy, which shows a band gap of 4.4 eV. A metallic phase with composition unidentified also exists. This rare earth oxyhalide adds a new member to the two-dimensional magnetic materials.
With the miniaturization and integration of nanoelectronic devices, efficient heat removal becomes a key factor affecting the reliable operation of the nanoelectronic device. With the high intrinsic thermal conductivity, good mechanical flexibility, and precisely controlled growth, two-dimensional (2D) materials are widely accepted as ideal candidates for thermal management materials. In this work, by solving the phonon Boltzmann transport equation (BTE) based on first-principles calculations, we comprehensively investigated the thermal conductivity of novel 2D layered MSi$_2$N$_4$ (M = Mo, W)…
Reducing the lateral scale of two-dimensional (2D) materials to one-dimensional (1D) has attracted substantial research interest not only to achieve competitive electronic device applications but also for the exploration of fundamental physical properties. Controllable synthesis of high-quality 1D nanoribbons (NRs) is thus highly desirable and essential for the further study. Traditional exploration of the optimal synthesis conditions of novel materials is based on the trial-and-error approach, which is time consuming, costly and laborious. Recently, machine learning (ML) has demonstrated prom…
Layered nanolaminate ternary carbides, nitrides and carbonitrides with general formula Mn+1AXn or MAX (n = 1, 2, or 3, M is an early transition metal, A is mostly group 13 or 14 element, and X is C and/or N) has revolutionized the world of nanomaterials, due to the coexistence of both ceramic and metallic nature, giving rise to exceptional mechanical, thermal, electrical, chemical properties and wide range of applications. Although several solid-state bulk synthesis methods have been developed to produce a variety of MAX phases, however, for certain applications, the growth of MAX phases, espe…
Atom-layered hexagonal boron nitride (hBN), with excellent stability, flat surface and large bandgap, has been reported to be the best 2D insulator to open up the great possibilities for exciting potential applications in electronics, optoelectronics and photovoltaics. The ability to grow high-quality large single crystals of hBN is at the heart for those applications, but the size of single-crystal 2D BN is less than a millimetre till now. Here, we report the first epitaxial growth of a 10*10 cm2 single-crystal hBN monolayer on a low symmetry Cu(110) "vicinal surface". The growth kinetics, un…
Developing techniques for high-quality synthesis of mono and few-layered 2D materials with lowered complexity and cost continues to remain an important goal, both for accelerating fundamental research and for applications development. We present the simplest conceivable technique to synthesize micrometer-scale single-crystal triangular monolayers of MoS2, i.e. by direct heating of bulk MoS2 powder onto proximally-placed substrates. Room-temperature excitonic linewidth values of our samples are narrower and more uniform than those of 2D-MoS2 obtained by most other techniques reported in literat…
We report the crystal growth and structural and electronic properties of superconducting, van der Waals layered PtTe. Easily cleavable crystals with a plate-like morphology consistent with the layered structure were grown from a platinum rich flux. A consistent determination of $T_c = 0.57$ K is made from the onset of diamagnetism, the zero of resistivity, and the midpoint of the heat capacity jump. The observed behavior is consistent with type-II superconductivity, with upper critical field at $T=0$ estimated using the Werthamer-Helfand-Hohenberg theory to be 143 and 65 Oe for fields out of a…
Layered van der Waals (vdW) materials grown by physical vapor deposition techniques are generally assumed to have a weak interaction with the substrate during growth. This leads to films with relatively small domains that are usually triangular and a terraced morphology. In this paper, we demonstrate that Bi2Se3, a prototypical vdW material, will form a nano-column morphology when grown on GaAs(001) substrates. This morphology is explained by a relatively strong film/substrate interaction, long adatom diffusion lengths, and a high reactive selenium flux. This discovery paves the way toward gro…
One-dimensional (1D) nanostructures - nanowires (NWs) - exhibit promising properties for integration in different types of functional devices. Their properties can be enhanced even further or tuned for a specific application by combining different promising materials, such as layered van der Waals materials and conventional semiconductors, into 1D-1D core-shell heterostructures. In this work, we demonstrated growth of GaN-MoS2 and GaN-WS2 core-shell NWs via two different methods: (1) two-step process of sputter-deposition of a sacrificial transition metal oxide coating on GaN NWs followed by s…
Heterostructures of two-dimensional (2D) layered materials with selective compositions play an important role in creating novel functionalities. Effective interface coupling between 2D ferromagnet and electronic materials would enable the generation of exotic physical phenomena caused by intrinsic symmetry breaking and proximity effect at interfaces. Here, epitaxial growth of bilayer Bi(110) on 2D ferromagnetic Fe3GeTe2 (FGT) with large magnetic anisotropy has been reported. Bilayer Bi(110) islands are found to extend along fixed lattice directions of FGT. The six preferred orientations could …
Two-dimensional (2D) layered materials are ideal for micro- and nanoelectromechanical systems (MEMS/NEMS) due to their ultimate thinness. Platinum diselenide (PtSe$_{2}$), an exciting and unexplored 2D transition metal dichalcogenides (TMD) material, is particularly interesting because its scalable and low temperature growth process is compatible with silicon technology. Here, we explore the potential of thin PtSe$_{2}$ films as electromechanical piezoresistive sensors. All experiments have been conducted with semimetallic PtSe$_{2}$ films grown by thermally assisted conversion of Pt at a CMOS…
The emergence of two-dimensional (2D) materials launched a fascinating frontier of flatland electronics. Most crystalline atomic layer materials are based on layered van der Waals materials with weak interlayer bonding, which naturally leads to thermodynamically stable monolayers. We report the synthesis of a 2D insulator comprised of a single atomic sheet of honeycomb structure BeO (h-BeO), although its bulk counterpart has a wurtzite structure. The h-BeO is grown by molecular beam epitaxy (MBE) on Ag(111) thin films that are conveniently grown on Si(111) wafers. Using scanning tunneling micr…
Visualization of Defect Electronic States in Layered Semiconductor CrSBr
University of Ottawa（渥太华大学）；Radboud University（拉德堡德大学）；Argonne National Laboratory（阿贡国家实验室）；University of Chemistry and Technology Prague（布拉格化工大学）；Bielefeld University（比勒费尔德大学）；Center for Nanoscale Materials, Argonne National Laboratory（阿贡国家实验室纳米材料中心）；University of Illinois（伊利诺伊大学）
研究利用扫描隧道显微镜/光谱探索块状 CrSBr 中两个突出缺陷的结构和电子特征，通过与模拟图像比较，推断常见缺陷为 b 轴对齐的双硫空位，推进了对 CrSBr 本征缺陷塑造电子结构作用的理解。
Due to their physical properties and potential applications in energy conversion and storage, transition metal dichalcogenides (TMDs) have garnered substantial interest in recent years. Amongst this class of materials, TMDs based on molybdenum, tungsten, sulfur and selenium are particularly attractive due to their semiconducting properties and the availability of bottom-up synthesis techniques. Here we report a method which yields high quality crystals of transition metal diselenide and ditelluride compounds (PtTe2, PdTe2, NiTe2, TaTe2, TiTe2, RuTe2, PtSe2, PdSe2, NbSe2, TiSe2, VSe2, ReSe2) fr…
The quest to improve transparent conductors balances two key goals: increasing electrical conductivity and increasing optical transparency. To improve both simultaneously is hindered by the physical limitation that good metals with high electrical conductivity have large carrier densities that push the plasma edge into the ultra-violet range. Transparent conductors are compromises between electrical conductivity, requiring mobile electrons, and optical transparency based on immobile charges to avoid screening of visible light. Technological solutions reflect this trade-off, achieving the desir…
Quantum confinement was found to play a critical role in the formation of Au(111) islands grown on the surface of MoS2. These confinement effects are fully three dimensional, with a strong correlation to the relatively large Fermi wavelength associated with the Au(111) planes. The confinement effects result in preferred heights with a periodicity of nearly 2 nm and persist to much higher temperatures than are typically seen in electronic growth mode systems. These findings indicate the potential to explore electronic growth modes in a new class of systems based on metal - layered semiconductor…
Monolayer NaCrX2 (X=Te,Se,S) were theoretically proposed to be two-dimensional intrinsic ferromagnetic semiconductors while their physical properties have not been thoroughly investigated in bulk single crystals. We report the single-crystal growth, structural, magnetic and electronic transport properties of NaCr(Te1-xSex)2 (0 6 x 6 1) and NaCrS2. For NaCr(Te1-xSex)2, the strong perpendicular magnetic anisotropy of NaCrTe2 can be gradually tuned to be a nearly isotropic one by Se-doping. Meanwhile, a systematic change in the conductivity with increasing x is observed, displaying a doping-induc…
Starting from graphene, 2D layered materials family has been recently set up more than 100 different materials with variety of different class of materials such as semiconductors, metals, semimetals, superconductors. Among these materials, 2D semiconductors have found especial importance in the state of the art device applications compared to that of the current conventional devices such as (which material based for example Si based) field effect transistors (FETs) and photodetectors during the last two decades. This high potential in solid state devices is mostly revealed by the transition me…
