Two-dimensional Nanoplates Research Articles

Enhancing the Photoelectrochemical Activity of CuO/ZnO Junction Photocathodes for Water Splitting.

To facilitate fast transfer of photogenerated electrons and surface stability, the CuO photocathode needs to be coupled with another heterojunction material. Here, we propose CuO/ZnO heterojunctions as photocathodes for photoelectrochemical (PEC) water splitting. First, CuO was grown on a Cu substrate, either in the form of a foil or mesh gauge, via anodization followed by postheating treatment. Subsequently, ZnO was electrodeposited on the grown CuO. The grown CuO film was composed of two-dimensional nanoplates aligned vertically against the substrate. The film morphology changed to flower-like or nearly spherical when ZnO was deposited by electrodeposition. Based on its open-circuit potential (OCP), overpotential and current density, CuO/ZnO grown on the Cu mesh exhibited better PEC performance than its counterpart grown on the Cu foil. When the mesh substrate was used, the surface area of the grown nanostructures was high and reached approximately 102.42 m2 g-1. The OCP of the CuO/ZnO mesh reached a low value of approximately -137 mV; this value quantitatively indicated that its PEC activity was more favorable for the hydrogen evolution reaction (HER). Moreover, the overpotential at the benchmark current density of 10 mA cm-2 for the Cu mesh was 379 mV, and this value was lower than those of the other photocathode materials.

Construction of polyaniline/MXene/graphene oxide ternary nanohybrid for sequestration and reduction of hypertoxic Cr(VI) in water

The anionic heavy metal contaminant chromium (Cr) is highly mobile, oxidizing, and carcinogenic, predisposing it to a range of biological health and environmental issue. Herein, polyaniline/MXene/graphene oxide ternary nanohybrid (PMG) with multiple types of functional groups and high efficiency of electron transfer capacity was synthesized by electrostatic self-assembly of polyaniline (PANI)-assisted MXene and graphene oxide (GO) two-dimensional nanoplates for the adsorption of hazardous Cr(VI). The charge transfer process promoted the polymerization of aniline on the surface of MXene, and the generation of PANI induced MXene and GO to intercalate with each other and ultimately ameliorated the over-negative potential of the MXene and GO composites. The adsorbent PMG exhibited the optimum adsorption effectiveness of 156.2 mg/g for Cr(VI) at pH = 2 and a sample dosage of 1 g/L. Isotherm and kinetic exploration experiments, combined with the findings of zeta potential, XPS, and first-principles calculations, indicated that approximately 89.3% of Cr(VI) was transformed into Cr(III) and anchored by PMG, revealing the adsorption mechanism to be probably a multilayered chemisorption involving redox reactions, electrostatic interactions, and complexation. The anti-interference experiments and cycling tests further confirmed the prominent application potential of PMG. This study provides feasible insights for remediating water contaminated with hexavalent chromium.

Size effect on vibration properties of axially moving nanoplates under different boundary conditions

The nonlocal strain gradient theory is employed to investigate the transverse free vibration characteristics of two-dimensional nano-plates with axial velocities. A generalized Hamiltonian principle has been used to establish the vibration governing equations for the system as well as the corresponding boundary conditions. By applying complex modal analysis to three boundary conditions, the plate’s natural frequency is determined, including four-end simply supported, four-end clamped, and opposite-edge simply supported and clamped, and comparing the effect of the size parameters on the natural frequency in relation to the boundary conditions; based on different theories, the effects of changing boundary conditions on natural frequencies are systematically compared. In the numerical study, it is demonstrated that the size effect significantly influences only the self-oscillation frequency at the nanoscale, whereas the nonlocal parameter as well as the material characteristic parameter have “softening” and “hardening” effects on the equivalent stiffness of the nanoplates, respectively, which are directly related to their natural frequencies. Compared to simple supports, clamped boundary conditions are more significantly affected by size parameters. In addition, higher order frequencies exhibit greater sensitivity and are susceptible to changes in boundary conditions and size parameters.

Fabricating oxygen vacancy-rich Li3VO4 nanoplates to improve electrochemical performance

Li3VO4 is one of the most potential anode materials for high-performance lithium ions batteries due to its suitable voltage platform and considerable theoretical capacity. Nevertheless, unsatisfactory electronic conductivity is hindering its further practical application. In this study, we report the synthesis of oxygen vacancy-rich Li3VO4 nanoplates via adjusting surface tension of reaction solution in the hydrothermal process. Decreasing the surface tension of reaction solution leads to a morphology change of Li3VO4 from large block to nanoplate and then nanoparticles gradually, accompanied by the generation of oxygen vacancies. The optimal Li3VO4 sample, consisting of two-dimensional nanoplates rich in oxygen vacancies, delivers a discharge specific capacity of 458 mAh g−1 at 0.1 A g−1 after 100 cycles. Even at a high current density of 1 A g−1, its capacity still reaches 235 mAh g−1 after 300 cycles, exhibiting outstanding cycling stability. The rich oxygen vacancies and two-dimensional nanoplate morphology synergistically accelerate lithium ions conduction and enhance the electrochemical performance of Li3VO4. The strategy reported in this paper can be readily extended to a variety of alkali metal vanadium oxides, possibly expanding the exploration of other metal oxides in the two dimensions.

Different shape-controlled synthesis and catalytic property studies on bismuth nanomaterials

Bi with four different morphologies (zero-dimensional (0D) nanoparticles, one-dimensional (1D) nanowires, two-dimensional (2D) nanoplates, and three-dimensional (3D) shuttle like structures) was successfully synthesized by changing the synthetic conditions. The Bi nanostructures were characterized in terms of structure, morphology, surface characteristics, optical properties and catalytic activity using X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FT-IR), Brunauer-Emmett-Teller (BET), photoluminescence (PL), UV–vis absorption spectroscopy (UV–Vis) and total organic carbon (TOC) analyzer techniques, respectively. The PL spectra is shown that the reduction of the size of Bi nanomaterials can reduce the recombination rate of photoelectrons and holes, which leads to the effective separation of photocharge carriers and the lowest photoelectron and hole recombination rates. The band gap values of Bi nanoparticles, nanowires, nanoplates and shuttle like structures are 2.71 eV, 2.76 eV, 2.92 eV and 3.22 eV respectively, favouring the harvesting of visible-light. The experimental results of the degradation performance of Bi with different morphologies exhibited that 99.9%, 97.9%, 96.2% and 74.4% degradations of the Rhodamine B (Rh B) was observed for Bi nanoparticles, nanowires, nanoplates and shuttle like structures, respectively. During the degradation of RhB, with the prolongation of treatment time to 90 min, the highest removal rates of chemical oxygen demand (COD) and TOC was 73.5% and 68.4%, respectively. According to TOC analysis, more than 68% of the carbon in the dyes will produce CO2 products. The removal efficiency is attributed to the production of ·O2−, ·OH and h+ and their mineralization to RhB. At the same time, the achieved results also reveal that Bi2O3 and BiOCl was found in Bi surfaces before and after catalytic degradation, which was confirmed by XPS and FTIR technology. In addition, Bi with the same morphology performed different catalytic activities in Rh B solution with different pH values. It was found that the degradation efficiency increased evidently when the pH value decreased. The mechanism of Bi photocatalytic activity was proposed based on the results of product analysis, radical capture and XPS analysis.

Phase Engineering of Intermetallic PtBi2 Nanoplates for Formic Acid Electrochemical Oxidation.

Phase engineering of Pt-based intermetallic catalysts has been demonstrated as a promising strategy to optimize catalytic properties for a direct formic acid fuel cell. Pt-Bi intermetallic catalysts are attracting increasing interest due to their high catalytic activity, especially for inhibiting CO poisoning. However, the phase transformation and synthesis of intermetallic compounds usually occurring at high temperatures leads to a lack of control of the size and composition. Here, we report the synthesis of intermetallic β-PtBi2 and γ-PtBi2 two-dimensional nanoplates with controlled sizes and compositions under mild conditions. The different phases of intermetallic PtBi2 can significantly affect the catalytic performance of the formic acid oxidation reaction (FAOR). The obtained β-PtBi2 nanoplates exhibit an excellent mass activity of 1.1 ± 0.01 A mgPt-1 for the FAOR, which is 30-fold higher than that of commercial Pt/C catalysts. Moreover, intermetallic PtBi2 demonstrates high tolerance to CO poisoning, as confirmed by in situ infrared absorption spectroscopy.

High Thermoelectric Performance in 2D Sb2Te3 and Bi2Te3 Nanoplate Composites Enabled by Energy Carrier Filtering and Low Thermal Conductivity.

Thermoelectrics are an important class of materials with great potential in alternative energy applications. In this study, two-dimensional (2D) nanoplates of the layered chalcogenides, Sb2Te3 and Bi2Te3, are synthesized and composites of the two are investigated for their thermoelectric properties. The two materials, Sb2Te3 and Bi2Te3, were synthesized as hexagonal, 2D nanoplates via a colloidal polyol route. The as-synthesized Sb2Te3 and Bi2Te3 vary drastically from one another in their lateral and vertical dimensions as revealed by scanning electron microscopy and atomic force microscopy. The single crystalline nanoplate nature is deduced by high-resolution transmission electron microscopy and selected area electron diffraction. Nanoplates have well-defined hexagonal facets as seen in the scanning and transmission electron microscopy images. The nanoplates were consolidated as an anisotropic nanostructured pellet via spark plasma sintering. Preferred orientation observed in the powder X-ray diffraction pattern and scanning electron microscopy images of the fractured pellets confirm the anisotropic structure of the nanoplates. Thermoelectric properties in the parallel and perpendicular directions were measured, revealing strong anisotropy with a significant reduction to thermal conductivity in the perpendicular direction due to increased phonon scattering at nanoplate interfaces. All compositions, except that of the 25% Bi2Te3 nanoplate composite, behave as degenerate semiconductors with increasing electrical resistivity as the temperature increases. The Seebeck coefficient is also increased dramatically in the nanocomposites, the highest reaching 210 μV/K for 15% Bi2Te3. The increase in Seebeck is attributed to energy carrier filtering at the nanoplate interfaces. Overall, these enhanced thermoelectric properties lead to a drastic increase in the thermoelectric performance in the perpendicular direction, with zT ∼ 1.26, for the 15% Bi2Te3 nanoplate composite at 450 K.

Shape Evolution of Two-Dimensional Au Hexagonal Nanoplates into Pseudo Three-Dimensional Oblate Spheroids

Herein, we report a seed-mediated synthetic method for pseudo three-dimensional oblate spheroids with structural complexity where concave and convex nanofeatures are formed simultaneously through manipulation of the growth directions. By exploiting hexagonal Au nanoplates as a seed material that consists of two Au(111)-faceted basal planes and side-by-side alternating arrangement of six Au(111) and six Au(100) side facets, we identified three growth patterns via a combination of kinetic and thermodynamic controls, leading to concomitant formation of concavity and convexity of the crystal facets. We denote the respective ellipsoidal nanoplates as convex or concave oblate spheroids. Various types of six-fold oblate spheroids were synthesized with high homogeneity in size, shape, and yield, and their optical responses in the ensemble were investigated. Given the many types of complex seed nanocrystals available, the suggested synthetic scheme using two-dimensional nanoplates as a seed will pave the way for the design of highly complex and sophisticated nanoparticles, especially where surface curvature is the main interest.

Nonlocal Strain Gradient Theory for the Bending of Functionally Graded Porous Nanoplates.

Many investigators have become interested in nanostructures due to their outstanding mechanical, chemical, and electrical properties. Two-dimensional nanoplates with higher mechanical properties compared with traditional structural applications are a common structure of nanosystems. Nanoplates have a wide range of uses in various sectors due to their unique properties. This paper focused on the static analysis of functionally graded (FG) nanoplates with porosities. The nonlocal strain gradient theory is combined with four-variable shear deformation theory to model the nanoplate. The proposed model captures both nonlocal and strain gradient impacts on FG nanoplate structures by incorporating the nonlocal and strain gradient factors into the FG plate's elastic constants. Two different templates of porosity distributions are taken into account. The FG porous nanoplate solutions are compared with previously published ones. The impact of nonlocal and strain gradient parameters, side-to-thickness ratio, aspect ratio, and porosity parameter, are analyzed in detail numerically. This paper presents benchmark solutions for the bending analysis of FG porous nanoplates. Moreover, the current combination of the nonlocal strain gradient theory and the four-variable shear deformation theory can be adapted for various nanostructured materials such as anisotropic, laminated composites, FG carbon nanotube reinforced composites, and so on.

Spinel-structured CuCo2O4 with a mixed 1D/2D morphology for asymmetric supercapacitor and oxygen evolution electrocatalyst applications

Transition metal oxides with multifunctional properties have attracted attention for use in various electro-catalytic applications, but their weak electroactive centers have severely limited their commercialization. In the present study, we describe an efficient bifunctional material whose structural morphology makes it both an effective oxygen evolution reaction (OER) electrocatalyst and a reliable power source for supercapacitor (SC) electrodes. We successfully fabricated spinel-structured CuCo2O4 consisting of a mix of one-dimensional (1D) nanorods and two-dimensional (2D) nanoplates using precipitation followed by hydrothermal treatment and calcination. For comparison purposes, CuO nanoplates and Co3O4 nanorods were synthesized individually, and their multifunctional features were examined. The synthesized mixed-morphology CuCo2O4 delivered an excellent electrochemical performance for SC and OER electrocatalyst applications. The mixed-morphology CuCo2O4 produced a specific capacity of 561 C g−1 (1122 F g−1) at 1 A g−1 and exhibited a superior rate capability and excellent stability, with 92% retention of capacity after 5000 cycles at 30 A g−1 in a three-electrode cell. In addition, a fabricated asymmetric supercapacitor device (CuCo2O4//activated carbon) delivered an energy density of 47.6 W h kg−1 and a power density of 1280 W kg−1, with outstanding long-term cyclic stability. Furthermore, the prepared CuCo2O4 had a low Tafel slope, a high electrochemical surface area, and excellent long-term durability. Therefore, mixed-morphology CuCo2O4 holds significant promise for use in SC and OER catalyst applications. Moreover, this study offers a useful method for preparing multifunctional materials.

Aggregative stability of colloidal 3D and 2D silver nanoparticles, stabilised by 11-mercaptoundecanoic acid, in the presence of singly charged cations

We studied the aggregative stability of colloidal silver quasi-spherical nanoparticles and two-dimensional nanoplates, stabilised by 11-mercaptoundecanoic acid, in the presence of phosphate buffers containing different singly charged cations (Li+ , Na+ , K+ , Cs+) and tris-HCl at pH 8.0 and concentration 0.02 mol/L which mimics the carbodiimide conjugation conditions of nanoparticles with biomolecules. Aggregation of silver nanoplates occurs in the presence of Na-phosphate buffer whereas at the same conditions the quasi-spherical nanoparticles retain colloidal stability. The difference in colloidal stability between 3D and 2D silver nanoparticles is due to the increase of the apparent acid dissociation constant on the nanoplates’ basal faces and the subsequent increase in specific bridging interactions nanoparticle – cation – nanoparticle which can be eliminated by introducing of non-ionic spacer (11-mercapto-1-undecanol) in the ligand layer. Silver nanoplates with mixed ligand layer have increased colloidal stability across the pH.

Role of the Spatial Distribution of Gas Flow for Tuning the Vertical/Planar Growth of Nonlayered Two-Dimensional Nanoplates

Role of the Spatial Distribution of Gas Flow for Tuning the Vertical/Planar Growth of Nonlayered Two-Dimensional Nanoplates

Synthesis of single atom cobalt dispersed on 2D carbon nanoplate and degradation of acetaminophen by peroxymonosulfate activation

Single Co atoms dispersed on 2D carbon nanoplate catalyst (SA-Co CNP) was synthesized successfully by a facile one-step method. Its morphology and structure were characterized by SEM, TEM, HAADF-STEM, XRD and XPS. Results showed that SA-Co CNP exbibit uniform two-dimensional nanoplate structure with several micrometers. Co was single atomic dispersed in carbon skeleton with the form of CoN4 coordination. The kinetic constant of acetaminophen (APAP) degradation with 0.1% SA-Co CNP/PMS was 6.99 times and 1.24 times as great as that of conventional CoOx-CNP/PMS and Co2+/PMS process, respectively. APAP could be efficiently degraded in a wide pH range of 3 to 9. The presence of Cl− could enhance the removal of APAP, while HCO3–, HPO4− and humic acid inhibit APAP degradation. The results of cyclic test demonstrated that 0.1% SA-Co CNP owns excellent catalytic ability and stability for PMS activation in a wide pH range of 3–9. Additionally, the reaction mechanism for APAP degradation by 0.1% SA-Co CNP/PMS was explored using ESR and trapping experiments. 1O2 was proved to be the predominant ROS. Hydroquinone was detected as the intermediate by LC-MS technique and a possible pathway for APAP removal was proposed. Finally, the degradation of APAP in real water matrix were investigated. The results showed that 0.1% SA-Co CNP/PMS not only possessed good performance for APAP degradation in tap water and surface water, but also could improve the biodegradability for secondary biochemical effluent.

High-active nanoplates of nitrogen-doped carbon@Mo2C as efficient catalysts in water splitting

Carbon doped metallic compounds have attracted a great deal of interest due to their new synergistic properties and enhanced catalytic performance from the doped-element induced defects. In this paper, polyaniline (PANI) is used as the carbon source to dope molybdenum carbide, which is annealed at 1000 °C to be nitrogen-doped carbon coupled with Mo2C (NC@Mo2C). Through the XRD, SEM and TEM methods the prepared NC@Mo2C composite is thoroughly characterized. The NC@Mo2C composite illustrates two-dimensional nanoplate morphology, and shows low overpotential in hydrogen evolution reaction (HER, 0.04 V) and oxygen evolution reaction (OER, 0.13 V) in 1 M KOH solution. Tafel slopes of NC@Mo2C for HER and OER are 100 mV decade−1 and 99 mV decade−1, respectively, rather lower than pure Mo2C (HER: 130 mV decade−1 and OER: 126 mV decade−1). The Raman and XPS results show that it is the structural defects of Mo2C derived from NC doping that activate the reaction. Meanwhile, the NC doping and resulted defects enhance the conductivity of Mo2C, as well as endow NC@Mo2C nanoplates high electrochemical active surface area, facilitating the ion transfer, water absorption and gas desorption. The results of our work open up a new chance to design efficient non-noble metal-based catalysts for water electrolysis.

Hybrid 3D Nanostructure-Based Hole Transport Layer for Highly Efficient Inverted Perovskite Solar Cells.

In this study, we demonstrate a new hybrid three-dimensional (3D) nanostructure system as an efficient hole transport layer (HTL) by a facile design of a low-temperature solution process. It is realized by integrating high-conductive chromium-doped CuGaO2 nanoplates synthesized with choline chloride (denoted as Cr/CuGaO2-CC) into ultrasmall NiOx nanoparticles. First, we propose to incorporate a Cr-doped strategy under hydrothermal synthesis conditions together with controllable intermediates and surfactants' assistance to synthesize fine-sized Cr/CuGaO2-CC nanoplates. Subsequently, these two-dimensional (2D) nanoplates serve as the expressway for improving hole transportation/extraction properties. Meanwhile, the ultrasmall-sized NiOx nanoparticles are employed to modify the surface for achieving unique surface properties. The HTL formed from the designed hybrid 3D-nanostructured system exhibits the advantages of smooth and full-covered surface, remarkable charge collection efficiency, energy level alignment between the electrode and perovskite layer, and the promotion of perovskite crystal growth. Consequently, nearly 20% of power conversion efficiency with negligible hysteresis is achieved in inverted perovskite solar cells (PSCs). This work not only demonstrates the potential applications of a 3D-nanostructured Cr/CuGaO2-CC/NiOx hybrid HTL in PSCs but also provides a fundamental insight into the design of hybrid material systems by manipulating electric behavior and morphology structure for achieving high-performance photovoltaic devices.

Highly efficient photoluminescence of 2D perovskites enabled by dimensional increasing

Herein, we proposed a dimension-increasing regulation strategy to realize the dimensionality engineering of perovskite from two-dimensional (2D) nanoplates (NPs) to quasi-two-dimensional (Q-2D) nanocrystals (NCs), and successfully prepared 2D (PEA)2PbBr4 NPs (PEA (phenylethylammonium) = C8H9NH3), Q-2D (PEA)2CsPb2Br7 (1) and (PEA)2Cs2Pb3Br10 (2) NCs. The photoluminescence dynamics changes from 2D (PEA)2PbBr4 NPs to Q-2D (1), (2) NCs by performing the time-resolved nanosecond transient absorption (NTAS) measurement for our perovskites. Compared with 2D (PEA)2PbBr4 NPs, we discovered for the first time that the electronic spectral redshift is intrinsic property of Q-2D NCs, which is caused by excitons transition to higher dimensionality. And the photoluminescence quantum yields (PLQYs) of Q-2D (1), (2) NCs is effectively increased from 8.780% to 14.72%, 21.80%, respectively. This directly verifies that Q-2D (1) and (2) NCs have enhanced their interlayer energy transfer capabilities. Moreover, the photoluminescence mechanism of these perovskites is investigated by the NTAS and the time-resolved photoluminescence (TR-PL) spectroscopy. The photophysical process of Q-2D samples exhibits a highly efficient and single photoluminescence pathway. The photoluminescence comes from the radiation recombination of free excitons. The Q-2D samples also have excellent photostability and decay lifetime stability. Our findings advance the research of improving 2D perovskites photoluminescence, and highlight potential of Q-2D NCs for optoelectronic applications.

Ethylene glycol assisted three-dimensional floral evolution of BiFeO3-based nanostructures with effective magneto-electric response.

Controlled growth of nanostructures plays a vital role in tuning the physical and chemical properties of functional materials for advanced energy and memory storage devices. Herein, we synthesized hierarchical micro-sized flowers, built by the self-assembly of highly crystalline, two-dimensional nanoplates of Co- and Ni-doped BiFeO3, using a simple ethylene glycol-mediated solvothermal method. Pure BiFeO3 attained scattered one-dimensional nanorods-type morphology having diameter nearly 60 nm. Co-doping of Co and Ni at Fe-site in BiFeO3 does not destabilize the morphology; rather it generates three-dimensional floral patterns of self-assembled nanoplates. Unsaturated polarization loops obtained for BiFeO3 confirmed the leakage behaviour of these rhombohedrally distorted cubic perovskites. These loops were then used to determine the energy density of the BiFeO3 perovskites. Enhanced ferromagnetic behaviour with high coercivity and remanence was observed for these nanoplates. A detailed discussion about the origin of ferromagnetic behaviour based on Goodenough–Kanamori's rule is also a part of this paper. Impedance spectroscopy revealed a true Warburg capacitive behaviour of the synthesized nanoplates. High magneto-electric (ME) coefficient of 27 mV cm−1 Oe−1 at a bias field of −0.2 Oe was observed which confirmed the existence of ME coupling in these nanoplates.

Structural effects of dimensional nano-fillers on the properties of Sapium sebiferum oil-based polyurethane matrix: Experiments and molecular dynamics simulation

A study is presented on the experimental methods to synthesize bio-based polymer nano-composites with unique hierarchical microstructures having enhanced thermal stability and the mechanical properties. The solution-processable polymer nano-composites were prepared from Sapium sebiferum oil (SSO) bio-based polyurethane (BPU) and nano-materials with varied dimensional morphologies, including two-dimensional (2D) nanoplates, one-dimensional (1D) tubular structures, and zero-dimensional (0D) particles. The structures and properties of the nano-materials and their BPU nano-composites were characterized. The results showed that the nano-materials were evenly dispersed in the BPU matrix, and the thermal stability and the mechanical properties of the synthetic nano-composites were noticeably improved. The effect was pronounced with 0D aminated silicon dioxide nano-particles (SiO2) , and 1D carboxylic acid functionalized multi-walled carbon nanotubes (MWCNTs-COOH), suggesting that structural dimensions of nano-materials have a marked effect on advanced properties of nano-composites. Furthermore, the structural specificity of nano-materials on the improvement of the nano-composite properties was validated by molecular dynamic (MD) simulations. MD simulations provided insight into the molecular interaction between nano-materials and the BPU matrix.

Growth mechanism for vertically oriented layered In2Se3 nanoplates

Vertically oriented layered $\mathrm{I}{\mathrm{n}}_{2}\mathrm{S}{\mathrm{e}}_{3}$ nanoplates have been grown by chemical vapor deposition. It is demonstrated that the growth is subject to the species of substrates because the morphologies of nanoplates grown on mica and $\mathrm{Si}{\mathrm{O}}_{2}/\mathrm{Si}$ substrates are quite different. We obtained vertical $\mathrm{I}{\mathrm{n}}_{2}\mathrm{S}{\mathrm{e}}_{3}$ nanosheets on $\mathrm{Si}{\mathrm{O}}_{2}/\mathrm{Si}$ and sapphire substrates with surface dangling bonds, while we obtained horizontal $\mathrm{I}{\mathrm{n}}_{2}\mathrm{S}{\mathrm{e}}_{3}$ nanosheets on mica without surface dangling bonds. A continuum model based on surface diffusion and a moving boundary is developed to describe the intermediate states of the steps and the edge. The dangling-bond-assisted heterogeneous nucleation mechanism is proposed to describe the growth of vertical $\mathrm{I}{\mathrm{n}}_{2}\mathrm{S}{\mathrm{e}}_{3}$ nanoplates: difficult diffusion of $\mathrm{I}{\mathrm{n}}_{2}\mathrm{S}{\mathrm{e}}_{3}$ adatoms on dangling-bonded substrate surface due to large interface energy between $\mathrm{I}{\mathrm{n}}_{2}\mathrm{S}{\mathrm{e}}_{3}$ adatoms and $\mathrm{Si}{\mathrm{O}}_{2}/\mathrm{Si}$ (and sapphire) substrates results in $\mathrm{I}{\mathrm{n}}_{2}\mathrm{S}{\mathrm{e}}_{3}$ seeds growing perpendicularly to the substrate; then vertical nanoplates inherit the growth direction of $\mathrm{I}{\mathrm{n}}_{2}\mathrm{S}{\mathrm{e}}_{3}$ seeds. This work paves the way for the growth of monodisperse vertical two-dimensional nanoplates on $\mathrm{Si}{\mathrm{O}}_{2}/\mathrm{Si}$ substrates, and it expands their utilizations from conventional lateral structured devices to nonplanar vertical electronic and optoelectronic devices.

Space-confined and substrate-directed synthesis of transition-metal dichalcogenide nanostructures with tunable dimensionality

Atomically thin transition-metal dichalcogenide (TMDC) nanostructures are predicted to exhibit novel physical properties that make them attractive candidates for the fabrication of electronic and optoelectronic devices. However, TMDCs tend to grow in the form of two-dimensional nanoplates (NPs) rather than one-dimensional nanoribbons (NRs) due to their native layered structure. Herein, we have developed a space-confined and substrate-directed chemical vapor deposition strategy for the controllable synthesis of WS2, WSe2, MoSe2, MoS2, WS2(1−x)Se2x NPs and NRs. TMDC NRs with lengths ranging from several micrometers to 100 μm have been obtained and the widths of TMDC NRs can be effectively tuned. Moreover, we found that TMDC NRs show different growth behaviors on van der Waals (vdW) and non-vdW substrates. The micro-nano structures, optical and electronic properties of synthesized TMDC NRs have been systematically investigated. This approach provides a general strategy for controllable synthesis of TMDC NRs, which makes these materials easily accessible as functional building blocks for novel optoelectronic devices.