Predicting 2D silicon allotropes on SnS<Subscript>2</Subscript>

A first principles study on the stability and structural and electronic properties of two-dimensional silicon allotropes on a semiconducting layered metal-chalcogenide compound,namely SnS2,is performed.The interactions between the two-dimensional silicon layer,commonly known as silicene,and the layered SnS2 template are investigated by analyzing different configurations of silicene.The calculated thermodynamic phase diagram suggests that the most stable configuration of silicene on SnS2 belongs to a family of structures with Si atoms placed on three different planes;so-called dumbbell silicene.This particular dumbbell silicene structure preserves its atomic configuration on SnS2 even at a temperature of 500 K or as a "flake" layer (i.e.,a silicene cluster terminated by H atoms),thanks to the weak interactions between the silicene and the SnS2 layers.Remarkably,an electric field can be used to tune the band gap of the silicene layer on SnS2,eventually changing its electronic behavior from semiconducting to (semi)metallic.The stability of silicene on SnS2 is very promising for the integration of silicene onto semiconducting or insulating substrates.The tunable electronic behavior of the silicene/SnS2 van der Walls heterostructure is very important not only for its use in future nanoelectronic devices,but also as a successful approach to engineering the bang-gap of layered SnS2,paving the way for the use of this layered compound in energy harvesting applications.     

Controlled growth and photoconductive properties of hexagonal SnS2 nanoflakes with mesa-shaped atomic steps

We demonstrated the controlled growth of two-dimensional (2D) hexagonal tin disulfide (SnS2) nanoflakes with stacked monolayer atomic steps.The morphology was similar to flat-topped and step-sided mesa plateaus or step pyramids.The SnS2 nanoflakes were grown on mica substrates via an atmospheric-pressure chemical vapor deposition process using tin monosulfide and sulfur powder as precursors.Atomic force microscopy (AFM),electron microscopy,and Raman characterizations were performed to investigate the structural features,and a sequential layer-wise epitaxial growth mechanism was revealed.In addition,systematic Raman characterizations were performed on individual SnS2 nanoflakes with a wide range of thicknesses (1-100 nm),indicating that the A1g peak intensity and Raman shifts were closely related to the thickness of the SnS2 nanoflakes.Moreover,photoconductive AFM was performed on the monolayer-steppedSnS2 nanoflakes,revealing that the flat surface and the edges of the SnS2 atomic steps had different electrical conductive properties and photoconductive behaviors.This is ascribed to the dangling bonds and defects at the atomic step edges,which caused a height difference of the Schottky barriers formed at the interfaces between the PtIr-coated AFM tip and the step edges or the flat surface of the SnS2 nanoflakes.The 2D SnS2 crystals with regular monolayer atomic steps and fast photoresponsivity are promising for novel applications in photodetectors and integrated optoelectronic circuits.     

A Study of the Crystal Structure of Co<Subscript>40</Subscript>Fe<Subscript>40</Subscript>B<Subscript>20</Subscript> Epitaxial Films on a Bi<Subscript>2</Subscript>Te<Subscript>3</Subscript> Topological Insulator

Laser molecular-beam epitaxy has been used to form Co₄₀Fe₄₀B₂₀ layers on Bi₂Te₃ topological insulator substrates, and their growth conditions have been studied. The possibility of growing epitaxial ferromagnetic layers on the surface of a topological insulator is demonstrated for the first time. The CoFeB layers have a body-centered cubic crystal structure with the (111) crystal plane parallel to the (0001) plane of Bi₂Te₃. 3D mapping in the reciprocal space of high-energy electron-diffraction patterns made it possible to determine the epitaxial relationships between the film and the substrate.     

Liquid-Metal Synthesized Ultrathin SnS Layers for High-Performance Broadband Photodetectors

Atomically thin materials face an ongoing challenge of scalability, hampering practical deployment despite their fascinating properties. Tin monosulfide (SnS), a low-cost, naturally abundant layered material with a tunable bandgap, displays properties of superior carrier mobility and large absorption coefficient at atomic thicknesses, making it attractive for electronics and optoelectronics. However, the lack of successful synthesis techniques to prepare large-area and stoichiometric atomically thin SnS layers (mainly due to the strong interlayer interactions) has prevented exploration of these properties for versatile applications. Here, SnS layers are printed with thicknesses varying from a single unit cell (0.8 nm) to multiple stacked unit cells (≈1.8 nm) synthesized from metallic liquid tin, with lateral dimensions on the millimeter scale. It is reveal that these large-area SnS layers exhibit a broadband spectral response ranging from deep-ultraviolet (UV) to near-infrared (NIR) wavelengths (i.e., 280–850 nm) with fast photodetection capabilities. For single-unit-cell-thick layered SnS, the photodetectors show upto three orders of magnitude higher responsivity (927 A W⁻¹) than commercial photodetectors at a room-temperature operating wavelength of 660 nm. This study opens a new pathway to synthesize reproduceable nanosheets of large lateral sizes for broadband, high-performance photodetectors. It also provides important technological implications for scalable applications in integrated optoelectronic circuits, sensing, and biomedical imaging.     

Large‐Scale Growth and Field‐Effect Transistors Electrical Engineering of Atomic‐Layer SnS2

2D layers of metal dichalcogenides are of considerable interest for high‐performance electronic devices for their unique electronic properties and atomically thin geometry. 2D SnS₂ nanosheets with a bandgap of ≈2.6 eV have been attracting intensive attention as one potential candidate for modern electrocatalysis, electronic, and/or optoelectronic fields. However, the controllable growth of large‐size and high‐quality SnS₂ atomic layers still remains a challenge. Herein, a salt‐assisted chemical vapor deposition method is provided to synthesize atomic‐layer SnS₂ with a large crystal size up to 410 µm and good uniformity. Particularly, the as‐fabricated SnS₂ nanosheet‐based field‐effect transistors (FETs) show high mobility (2.58 cm² V^?1 s^?1) and high on/off ratio (≈10⁸), which is superior to other reported SnS₂‐based FETs. Additionally, the effects of temperature on the electrical properties are systematically investigated. It is shown that the scattering mechanism transforms from charged impurities scattering to electron–phonon scattering with the temperature. Moreover, SnS₂ can serve as an ideal material for energy storage and catalyst support. The high performance together with controllable growth of SnS₂ endow it with great potential for future applications in electrocatalysis, electronics, and optoelectronics.     

Structure of multilayer ZrO<Subscript>2</Subscript>/SrTiO<Subscript>3</Subscript>

Multilayered oxide heteroepitaxial systems, including that of a 1-nm-thick Y₂O₃-stabilised ZrO₂ (YSZ) sandwiched between layers of SrTiO₃ (STO) [1], have been a subject of much interest lately due to their significantly enhanced ionic conductivities as compared to the bulk materials. We aim to provide the foundation for understanding this increase in conductivity by considering the atomic configurations at the interfaces of such systems, specifically a ZrO₂/STO multilayer system. Possible stable lattice structures of pure ZrO₂ in the system are explored using a genetic algorithm in which the interatomic interactions are modelled by simple pair potentials. The energies of several of the more stable of these structures are then evaluated more accurately within density functional theory (DFT). We find that the fluorite ZrO₂ phase is unstable as a coherently strained epitaxial layer in the multilayer system. Instead, anatase-, columbite-, rutile-, and pyrite-like ZrO₂ epitaxies are found to be more stable, with the anatase-like epitaxy being the most stable structure over a wide range of chemical potential of the components. We also find a high energy metastable structure resembling the tetragonal fluorite structure which is predicted by DFT to be stabilised by SrO-terminated STO but not by TiO₂-terminated STO.     

Ni-doped ZnCo<Subscript>2</Subscript>O<Subscript>4</Subscript> atomic layers to boost the selectivity in solar-driven reduction of CO<Subscript>2</Subscript>

Regulating the selectivity of CO₂ photoreduction is particularly challenging. Herein, we propose ideal models of atomic layers with/without element doping to investigate the effect of doping engineering to tune the selectivity of CO₂ photoreduction. Prototypical ZnCo₂O₄ atomic layers with/without Ni-doping were first synthesized. Density functional theory calculations reveal that introducing Ni atoms creates several new energy levels and increases the density-of-states at the conduction band minimum. Synchrotron radiation photoemission spectroscopy demonstrates that the band structures are suitable for CO₂ photoreduction, while the surface photovoltage spectra demonstrate that Ni doping increases the carrier separation efficiency. In situ diffuse reflectance Fourier transform infrared spectra disclose that the CO₂^·? radical is the main intermediate, while temperature-programed desorption curves reveal that the ZnCo₂O₄ atomic layers with/without Ni doping favor the respective CO and CH₄ desorption. The Ni-doped ZnCo₂O₄ atomic layers exhibit a 3.5-time higher CO selectivity than the ZnCo₂O₄ atomic layers. This work establishes a clear correlation between elemental doping and selectivity regulation for CO₂ photoreduction, opening new possibilities for tailoring solar-driven photocatalytic behaviors.

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Analysis of morphology and microstructure of Al<Subscript>2</Subscript>O<Subscript>3</Subscript> layers

The paper presents the characterization of obtaining Al₂O₃ oxide layers on AlMg₂ aluminum alloy as a result of hard anodizing by the electrolytic method in a three-component electrolyte. The Al₂O₃ layers obtained on the AlMg₂ alloy in the three-component SBS electrolyte were subjected to detailed microstructural investigations (by means of a scanning electron microscope). By using X-ray diffraction, the phase compositions of obtained oxide layers were examined. It was found that the Al₂O₃ oxide layers obtained via hard anodizing in a three-component electrolyte are amorphous. The chemical composition of the Al₂O₃ layers is presented and compared with the results of stechiometric calculations for the Al₂O₃ layer. Surface morphologies of the obtained oxide layers are characterized and discussed in nano- and microscopic scales. The surface morphologies of the layers obtained have a significant influence on their properties, including their susceptibility to further modification (e.g., to incorporation of graphite), their wear resistance, and the capacity for sorption of lubricants.     

Nanostructured phase formation in CeO<Subscript>2</Subscript>/LaAlO<Subscript>3</Subscript> and CeO<Subscript>2</Subscript>/(Ni-W) prepared by deposition from metalorganic solutions

We have studied nanoscale structural evolution processes and phase formation in barrier cerium oxide layers grown from methacrylate solutions on lanthanum aluminate and a nickel-tungsten tape by dip coating. The layers were characterized by atomic force microscopy, scanning electron microscopy, precision electron diffraction, X-ray microanalysis, and X-ray diffraction (including texture analysis). We have investigated nanostructured morphological forms of buffer cerium oxide layers in all synthesis steps: liquid-phase, pyrolytic, and crystalline. We have established a granular character of the nanostructure and determined the type of orientation of the films: 〈111〉 texture with a 〈200〉 additional orientation. Optimal conditions for the synthesis of a barrier layer several tens of nanometers in thickness are proposed.     

Chemical Vapor Deposition of High‐Quality and Atomically Layered ReS2

Recently, anisotropic 2D materials, such as black phosphorus and rhenium disulfides (ReS₂), have attracted a lot attention because of their unique applications on electronics and optoelectronics. In this work, the direct growth of high‐quality ReS₂ atomic layers and nanoribbons has been demonstrated by using chemical vapor deposition (CVD) method. A possible growth mechanism is proposed according to the controlled experiments. The CVD ReS₂‐based filed‐effect transistors (FETs) show n‐type semiconducting behavior with a current on/off ratio of ≈10⁶ and a charge carrier mobility of ≈9.3 cm² Vs⁻¹. These results suggested that the quality of CVD grown ReS₂ is comparable to mechanically exfoliated ReS₂, which is also further supported by atomic force microscopy imaging, high‐resolution transmission electron microscopy imaging and thickness‐dependent Raman spectra. The study here indicates that CVD grown ReS₂ may pave the way for the large‐scale fabrication of ReS₂‐based high‐performance optoelectronic devices, such as anisotropic FETs and polarization detection.     

Structural and Magnetic Properties of La<Subscript>2/3</Subscript>Sr<Subscript>1/3</Subscript>MnO<Subscript>3</Subscript>/SrTiO<Subscript>3</Subscript>/CoFe<Subscript>2</Subscript> Hard-Soft Magnetic Systems

We report on the growth and magnetic properties of La_2/3Sr_1/3MnO₃/SrTiO₃/CoFe₂ hard-soft magnetic systems prepared by pulsed laser deposition on SrTiO₃(001) substrates. In situ reflection high-energy electron diffraction along the [100]SrTiO₃ substrate azimuth and atomic force microscopy measurements reveal that La_2/3Sr_1/3MnO₃ and SrTiO₃ grow both in a three dimensional mode and that the roughness of the lower and upper magnetic/non-magnetic interfaces ranges between 2 and 4 Å. Cross-section transmission electron microscopy observations show that the layers are continuous, with an homogeneous thickness, and that the interfaces are mostly sharp and correlated. The magnetization curves show a two step reversal of the magnetization, with very distinct coercive fields. A small anisotropy is observed for the CoFe₂ layer with an in plane easy magnetization axis along the [110]SrTiO₃ direction. Minor magnetization loops indicate that the coupling between the magnetic layers is negligible.     

Analysis of weakly bonded oxygen in HfO<Subscript>2</Subscript>/SiO<Subscript>2</Subscript>/Si stacks by using HRBS and ARXPS

We have used transmission electron microscopy, high-resolution Rutherford backscattering spectrometry (HRBS), and angle-resolved X-ray photoelectron spectroscopy (ARXPS) to investigate the interfacial oxidized states of hafnium oxide/silicon oxide/Si gate oxide stacks. The atomic concentrations and profiles of HRBS analysis are similar before and after annealing; however, ARXPS shows a clear difference in bond status. These results imply that weakly bonded oxygen atoms existed in the stacks alongside the suboxides. In the as-deposited layers, dioxides are found at the interfaces and suboxides in the layers whereas after annealing suboxides are found at the interfaces and dioxides are found in the layers because of redistribution of bonds during annealing. The combination of HRBS and ARXPS analyses indicated that the main oxidized states transformed from the suboxides to the dioxides with no obvious quantitative difference in the content of oxygen atoms, suggesting that reactions of the weakly bonded oxygen atoms occurred with the suboxides within the layers.     

Design of Si<Subscript>3</Subscript>N<Subscript>4</Subscript>-based ceramic laminates by the residual stresses

Ceramic laminates with strong interfaces between layers are considered a very promising material for different engineering applications because of the potential for increasing fracture toughness by designing high residual compressive and low residual tensile stresses in separate layers. In this work, Si₃N₄/Si₃N₄-TiN ceramic laminates with strong interfaces were manufactured by rolling and hot pressing techniques. The investigation of their mechanical properties has shown that the increase in apparent fracture toughness can be achieved for the Si₃N₄/Si₃N₄-20 wt.%TiN composite, while further increase of TiN content in the layers with residual tensile stresses lead to a formation of multiple cracks, and as a result, a significant decrease in the mechanical performance of the composites. Micro-Raman spectroscopy was used to measure the frequency shift across the Si₃N₄/Si₃N₄-20 wt.%TiN laminate. These preliminary Raman results can be useful for further analysis of residual stress distribution in the laminate.     

The influence of an In<Subscript>0.52</Subscript>Al<Subscript>0.48</Subscript>As transition layer design on the transport characteristics of a metamorphic high-electron-mobility transistor

We have used the atomic force microscopy and Hall effect measurements to study the influence of In_0.52Al_0.48As transition layer design on the electron mobility in the InAlAs/InGaAs/GaAs channel of a highelectron- mobility transistor (HEMT) with the metamorphic buffer. The optimum buffer layer favors suppression of the misfit dislocation threading into upper layers of the HEMT heterostructure and prevents development of the surface microrelief.     

Preparation and characterisation of nanostructural TiO<Subscript>2</Subscript>–Ga<Subscript>2</Subscript>O<Subscript>3</Subscript> binary oxides with high surface area derived form particulate sol–gel route

Nanostructured and nanoporous TiO₂–Ga₂O₃ films and powders with various Ti:Ga atomic ratios and high specific surface area (SSA) have been prepared by a new straightforward particulate sol–gel route. Titanium isopropoxide and gallium (III) nitrate hydrate were used as precursors and hydroxypropyl cellulose (HPC) was used as a polymeric fugitive agent (PFA) in order to increase the SSA. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) revealed that powders contained both rhombohedral α-Ga₂O₃ and monoclinic β-Ga₂O₃ phases, as well as anatase and rutile. It was observed that the Ga₂O₃ formed from the nitrate precursor retarded anatase-to-rutile transformation. Furthermore, transmission electron microscope (TEM) analysis also showed that Ga₂O₃ hindered the crystallisation and crystal growth of powders. SSA of powders, as measured by Brunauer–Emmett–Teller (BET) analysis, was enhanced by introducing Ga₂O₃. Ti:Ga = 50:50 (at%/at%) binary oxide annealed at 500 °C produced the smallest crystallite size (2 nm), the smallest grain size (18 nm), the highest SSA (327.8 m²/g) and the highest roughness. Ti:Ga = 25:75 (at%/at%) annealed at 800 °C showed the smallest crystallite size (2.4 nm) with 32 nm average grain size and 40.8 m²/g surface area. Ti:Ga = 75:25 (at%/at%) annealed at 800 °C had the highest SSA (57.4 m²/g) with 4.4 nm average crystallite size and 32 nm average grain size. One of the smallest crystallite size and one of the highest SSA reported in the literature is obtained, and they can be used in many applications in areas from optical electronics to gas sensors.     

Annealing temperature effect on structural and morphological properties of nano photonic LiNbO<Subscript>3</Subscript>

In this work, thermal annealing processes was depended in order to prepare (Δ) phase LiNbO₃ and the properties of nanostructure films was characterized. The sol–gel method was used to grow and deposit high purity Lithium-Niobate Nano and Micro-structure on a quartz substrate, at three different annealing temperatures. The structural, morphological, and optical properties of grown films have been investigated using X-ray diffraction, scanning electron microscopy, atomic force microscopy, optical study through Raman spectroscopy, UV–Vis and Photoluminescence. The measurements showed that the structure was crystalline in nature and the grains are regularly distributed within the film as a result of increasing the annealing temperature. This observation is typically used in optical waveguides and other optoelectronics applications.     

Effects of annealing temperature on electrochemical performance of SnSx embedded in hierarchical porous carbon with N-carbon coating by in-situ structural phase transformation as anodes for lithium ion batteries

Tuned tin chalcogenides rooted in hierarchical porous carbon(HPC)with N-carbon coating layers are prepared by thermal shock under various temperatures(denoted as HPC-SnS2-PAN-Various T).With the increase of annealing temperature,the morphology and phase structure of SnS2,as well as the cyclization degree of polyacrylonitrile(PAN),are significantly changed,which leads to the formation of rod-like SnS and ordered structure of conductive N-carbon layer.By combining HPC,N-carbon coating derived from the cyclization of PAN,with 1D SnS nanorods generated from structural phase transformation of SnS2,the optimized composite(HPC-SnS2-PAN-500)as anode for lithium ion batteries(LIBs)provides buffer space for volume changes during alloying/dealloying process,builds a highly conductive network as well as decreases irreversible capacity from solid electrolyte interphase and enhances the ion/electron transport.Attributed to the above merits from composition regulation and architecture modification by sulfur depletion and PAN cyclization,this target anode exhibits an extraordinary cycling stability with a high specific capacity of 652.5 mA h/g at 0.5 A/g after 900 cycles.It suggests that rod-like SnS embedded in HPC with cyclized PAN layers by thermal treatment approach renders a potential structural design of anode materials for LIBs.     

Oxidation kinetics of chromium in fine-particle TiO<Subscript>2</Subscript>-Cr<Subscript>2</Subscript>O<Subscript>3</Subscript> Oxides

The mass transport during the oxidation of Cr₂O₃ in mixtures of fine-particle TiO₂ and Cr₂O₃ in air has been studied at temperatures from 800 to 1000°C by magnetochemical analysis. The results indicate that the process leads to the oxidation of up to ten surface atomic layers. The mass transport is shown to be a stochastic, steplike process.     

Atomic Layers of MoO2 with Exposed High‐Energy (010) Facets for Efficient Oxygen Reduction

Although 2D nanocrystals with exposed high‐energy facets are highly desired in the field of catalysts due to their anticipant high catalytic activities, they are difficult to be gained. Here, atomic layers of metallic molybdenum dioxide (MoO₂) with primarily exposed high‐energy (010) facet are achieved via a facile carbothermic reduction approach. The resultant MoO₂ exhibits single‐crystalline, monoclinic, and ultrathin features with nearly 100% exposed (010) facet, which can significantly reduce reaction barriers toward the oxygen reduction reaction. As a consequence, the atomic layers of MoO₂ exhibit high electrocatalytic activity, excellent tolerance to methanol, and good stability for the oxygen reduction reaction in alkaline electrolyte, superior to commercial Pt/C catalysts. It is believed that such new transition metal oxide catalysts with exposed high‐energy facets have broad applications in the areas of energy storage and conversions.     

Construction of bilayer PdSe<Subscript>2</Subscript> on epitaxial graphene

Two-dimensional (2D) materials have received significant attention due to their unique physical properties and potential applications in electronics and optoelectronics. Recent studies have demonstrated that exfoliated PdSe₂, a layered transition metal dichalcogenide (TMD), exhibits ambipolar field-effect transistor (FET) behavior with notable performance and good air stability, and thus serves as an emerging candidate for 2D electronics. Here, we report the growth of bilayer PdSe₂ on a graphene-SiC(0001) substrate by molecular beam epitaxy (MBE). A bandgap of 1.15 ± 0.07 eV was revealed by scanning tunneling spectroscopy (STS). Moreover, a bandgap shift of 0.2 eV was observed in PdSe₂ layers grown on monolayer graphene as compared to those grown on bilayer graphene. The realization of nanoscale electronic junctions with atomically sharp boundaries in 2D PdSe₂ implies the possibility of tuning its electronic or optoelectronic properties. In addition, on top of the PdSe₂ bilayers, PdSe₂ nanoribbons and stacks of nanoribbons with a fixed orientation have been fabricated. The bottom-up fabrication of low-dimensional PdSe₂ structures is expected to enable substantial exploration of its potential applications.

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