Showing papers on "Chemical vapor deposition published in 2019"

MOCVD homoepitaxy of Si-doped (010) β-Ga2O3 thin films with superior transport properties

Abstract: Record-high electron mobilities were achieved for silicon-doped (010) β-Ga2O3 homoepitaxial films grown via metalorganic chemical vapor deposition (MOCVD). Key growth parameters were investigated to reduce the background doping and compensation concentration. Controllable n-type Si doping was achieved as low as low-1016 cm−3. Record carrier mobilities of 184 cm2/V s at room temperature and 4984 cm2/V s at low temperature (45 K) were measured for β-Ga2O3 thin films with room-temperature doping concentrations of 2.5 × 1016 and 2.75 × 1016 cm−3, respectively. Analysis of temperature-dependent Hall mobility and carrier concentration data revealed a low compensation concentration of 9.4 × 1014 cm−3. Using the two-donor model, Si on the tetrahedrally coordinated Ga(I) site represented the primary shallow donor state, and the secondary donor state was found to possess an activation energy of 120 meV. The demonstration of high-purity and high-quality β-Ga2O3 thin films with uniform and smooth surface morphology via MOCVD will harness its advantages as an ultrawide-bandgap semiconductor for power electronic and short-wavelength optoelectronic device applications.

MOCVD grown epitaxial β-Ga2O3 thin film with an electron mobility of 176 cm2/V s at room temperature

Abstract: In this work, we report record electron mobility values in unintentionally doped β-Ga2O3 films grown by metal-organic chemical vapor deposition. Using degenerately Sn-doped regrown n+ β-Ga2O3 contact layers, we were able to maintain Ohmic contact to the β-Ga2O3 films down to 40 K, allowing for reliable temperature-dependent Hall measurement. An electron mobility of 176 cm2/V s and 3481 cm2/V s were measured at room temperature and 54 K, respectively. The room and low temperature mobilities are both among the highest reported values in a bulk β-Ga2O3 film. A low net background charge concentration of 7.4 × 1015 cm−3 was confirmed by both temperature dependent Hall measurement and capacitance-voltage measurement. The feasibility of achieving low background impurity concentration and high electron mobility paves the road for the demonstration of high performance power electronics with high breakdown voltages and low on-resistances.

Room temperature toluene gas sensor based on TiO2 nanoparticles decorated 3D graphene-carbon nanotube nanostructures

Abstract: This work presents a highly sensitive room-temperature gas sensor based on 3D titanium dioxide/graphene-carbon nanotube (3D TiO2/G-CNT) fabricated by chemical vapor deposition and sparking methods. Characterizations by scanning electron microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy and Transmission electron microscopy confirmed the formation of 3D graphene-carbon nanotube nanostructures decorated with TiO2 nanoparticles. The toluene detection performances of 3D TiO2/G-CNT structures with varying Ti sparking times were investigated in comparison with 3D G-CNT, TiO2-CNT, graphene and CNTs at room temperature. From result, the optimal sparking time of 60 s led to an optimal sensor response of 42%–500 ppm at room temperature. In addition, the optimal 3D TiO2/G-CNT exhibited substantially higher toluene response, sensitivity and selectivity than 3D G-CNT, TiO2-CNT, graphene and CNTs over a low concentration range of 50–500 ppm. The toluene-sensing mechanisms of 3D titanium dioxide/graphene-carbon nanotube nanostructures were proposed based on the formation of Schottky metal-semiconductor junctions between metallic 3D graphene-carbon nanotube structures and n-type semiconducting titanium dioxide nanoparticles due to the adsorption of toluene molecules via low-temperature reducing reactions or direct charge transfer process.

High-Mobility, Wet-Transferred Graphene Grown by Chemical Vapor Deposition.

Abstract: We report high room-temperature mobility in single-layer graphene grown by chemical vapor deposition (CVD) after wet transfer on SiO2 and hexagonal boron nitride (hBN) encapsulation. By removing contaminations, trapped at the interfaces between single-crystal graphene and hBN, we achieve mobilities up to ∼70000 cm2 V-1 s-1 at room temperature and ∼120 000 cm2 V-1 s-1 at 9K. These are more than twice those of previous wet-transferred graphene and comparable to samples prepared by dry transfer. We also investigate the combined approach of thermal annealing and encapsulation in polycrystalline graphene, achieving room-temperature mobilities of ∼30 000 cm2 V-1 s-1. These results show that, with appropriate encapsulation and cleaning, room-temperature mobilities well above 10 000 cm2 V-1 s-1 can be obtained in samples grown by CVD and transferred using a conventional, easily scalable PMMA-based wet approach.

Multilayer-graphene-stabilized lithium deposition for anode-Free lithium-metal batteries.

Abstract: The will to circumvent capacity fading, Li dendrite formation, and low coulombic efficiency in anode-free Li-metal batteries (AFLMBs) requires a radical change in the science underpinning new materials discovery, battery design, and understanding electrode interfaces. Herein, a Cu current collector formed with ultrathin multilayer graphene grown via chemical vapor deposition (CVD) was used as an artificial layer to stabilize the electrode interface and sandwich-deposited Li with Cu. A multilayer graphene film's superior strength, chemical stability, and flexibility make it an excellent choice to modify a Cu electrode. Fabricating an anode bigger than the cathode improved the alignment of the electrodes during assembly, minimizing interfacial stress. Here, 19 mm electrodes when paired with a commercial LiFePO4 cathode (mass loading: ∼12 mg cm−2) delivered the first-cycle discharge capacities of 147 and 151 mA h g−1 for bare and multilayer-graphene-protected electrodes, respectively, which could alleviate the big hurdle (initial capacity loss) in anode-free batteries. After 100 round-trip cycles, bare Cu and multilayer-graphene-protected electrodes retained ∼46 and ∼61% of their initial capacities, respectively, in an ether-based electrolyte at the rate of 0.1 C.

MOCVD epitaxy of β-(AlxGa1−x)2O3 thin films on (010) Ga2O3 substrates and N-type doping

Abstract: (010) β-(AlxGa1−x)2O3 thin films were grown on (010) β-Ga2O3 substrates via metalorganic chemical vapor deposition with up to 40% Al incorporation by systematic tuning of the Trimethylaluminum (TMAl)/triethylgallium molar flow rate ratio and growth temperature. High crystalline quality with pure β-phase (AlxGa1−x)2O3 was achieved for films with Al composition x < 27%, while a higher Al composition induced phase segregation which was observed via X-ray diffraction spectra. Al incorporation was highly dependent on the growth temperature, chamber pressure, oxygen partial pressure, and TMAl molar flow rate. Atomic resolution scanning transmission electron microscopy (STEM) imaging demonstrated a high crystalline quality β-(Al0.15Ga0.85)2O3 film with an epitaxial interface. High resolution STEM imaging of (AlxGa1−x)2O3/Ga2O3 superlattice (SL) structures revealed superior crystalline quality for the 23% Al composition. When the Al composition reaches 40%, the SL structure maintained the β-phase, but the interfaces became rough with inhomogeneous Al distribution. N-type doping using Si in β-(AlxGa1−x)2O3 films with the Al composition up to 33.4% was demonstrated.

Liquid‐Alloy‐Assisted Growth of 2D Ternary Ga2In4S9 toward High‐Performance UV Photodetection

Abstract: 2D ternary systems provide another degree of freedom of tuning physical properties through stoichiometry variation. However, the controllable growth of 2D ternary materials remains a huge challenge that hinders their practical applications. Here, for the first time, by using a gallium/indium liquid alloy as the precursor, the synthesis of high-quality 2D ternary Ga2 In4 S9 flakes of only a few atomic layers thick (≈2.4 nm for the thinnest samples) through chemical vapor deposition is realized. Their UV-light-sensing applications are explored systematically. Photodetectors based on the Ga2 In4 S9 flakes display outstanding UV detection ability (R λ = 111.9 A W-1 , external quantum efficiency = 3.85 × 104 %, and D* = 2.25 × 1011 Jones@360 nm) with a fast response speed (τring ≈ 40 ms and τdecay ≈ 50 ms). In addition, Ga2 In4 S9 -based phototransistors exhibit a responsivity of ≈104 A W-1 @360 nm above the critical back-gate bias of ≈0 V. The use of the liquid alloy for synthesizing ultrathin 2D Ga2 In4 S9 nanostructures may offer great opportunities for designing novel 2D optoelectronic materials to achieve optimal device performance.

Wafer-scale MOCVD growth of monolayer MoS2 on sapphire and SiO2

Abstract: High-quality and large-scale growth of monolayer molybdenum disulfide (MoS2) has caught intensive attention because of its potential in many applications due to unique electronic properties. Here, we report the wafer-scale growth of high-quality monolayer MoS2 on singlecrystalline sapphire and also on SiO2 substrates by a facile metal-organic chemical vapor deposition (MOCVD) method. Prior to growth, an aqueous solution of sodium molybdate (Na2MoO4) is spun onto the substrates as the molybdenum precursor and diethyl sulfide ((C2H5)2S) is used as the sulfur precursor during the growth. The grown MoS2 films exhibit crystallinity, good electrical performance (electron mobility of 22 cm2·V-1·s-1) and structural continuity maintained over the entire wafer. The sapphire substrates are reusable for subsequent growth. The same method is applied for the synthesis of tungsten disulfide (WS2). Our work provides a facile, reproducible and cost-efficient method for the scalable fabrication of high-quality monolayer MoS2 for versatile applications, such as electronic and optoelectronic devices as well as the membranes for desalination and power generation.

Hybrid chemical vapor deposition enables scalable and stable Cs-FA mixed cation perovskite solar modules with a designated area of 91.8 cm2 approaching 10% efficiency

Abstract: The development of scalable deposition methods for stable perovskite layers is a prerequisite for the development and future commercialization of perovskite solar modules. However, there are two major challenges, i.e., scalability and stability. In sharp contrast to a previous report, here we develop a fully vapor based scalable hybrid chemical vapor deposition (HCVD) process for depositing Cs-formamidinium (FA) mixed cation perovskite films, which alleviates the problem encountered when using conventional solution coating of mainly methylammonium lead iodide (MAPbI3). Using our HCVD method, we fabricate perovskite films of Cs0.1FA0.9PbI2.9Br0.1 with enhanced thermal and phase stabilities, by the intimate incorporation of Cs into FA based perovskite films. In addition, the SnO2 electron transport layer (ETL) (prepared by sputter deposition) is found to be damaged during the HCVD process. In combination with precise interface engineering of the SnO2 ETL, we demonstrate relatively large area solar modules with efficiency approaching 10% and with a designated area of 91.8 cm2 fabricated on 10 cm × 10 cm substrates (14 cells in series). On the basis of our preliminary operational stability tests on encapsulated perovskite solar modules, we extrapolated that the T80 lifetime is approximately 500 h (under the light illumination of 1 sun and 25 °C).

Chemical Vapor Deposition Growth of High Crystallinity Sb2Se3 Nanowire with Strong Anisotropy for Near-Infrared Photodetectors

Abstract: Low-dimensional semiconductors have attracted considerable attention due to their unique structures and remarkable properties, which makes them promising materials for a wide range of applications related to electronics and optoelectronics. Herein, the preparation of 1D Sb2 Se3 nanowires (NWs) with high crystal quality via chemical vapor deposition growth is reported. The obtained Sb2 Se3 NWs have triangular prism morphology with aspect ratio range from 2 to 200, and three primary lattice orientations can be achieved on the sixfold symmetry mica substrate. Angle-resolved polarized Raman spectroscopy measurement reveals strong anisotropic properties of the Sb2 Se3 NWs, which is also developed to identify its crystal orientation. Furthermore, photodetectors based on Sb2 Se3 NW exhibit a wide spectral photoresponse range from visible to NIR (400-900 nm). Owing to the high crystallinity of Sb2 Se3 NW, the photodetector acquires a photocurrent on/off ratio of about 405, a responsivity of 5100 mA W-1 , and fast rise and fall times of about 32 and 5 ms, respectively. Additionally, owing to the anisotropic structure of Sb2 Se3 NW, the device exhibits polarization-dependent photoresponse. The high crystallinity and superior anisotropy of Sb2 Se3 NW, combined with controllable preparation endows it with great potential for constructing multifunctional optoelectronic devices.

High-mobility, wet-transferred graphene grown by chemical vapor deposition

Abstract: We report high room-temperature mobility in single layer graphene grown by Chemical Vapor Deposition (CVD) after wet transfer on SiO$_2$ and hexagonal boron nitride (hBN) encapsulation. By removing contaminations trapped at the interfaces between single-crystal graphene and hBN, we achieve mobilities up to$\sim70000cm^2 V^{-1} s^{-1}$ at room temperature and$\sim120000cm^2 V^{-1} s^{-1}$ at 9K. These are over twice those of previous wet transferred graphene and comparable to samples prepared by dry transfer. We also investigate the combined approach of thermal annealing and encapsulation in polycrystalline graphene, achieving room temperature mobilities$\sim30000 cm^2 V^{-1} s^{-1}$. These results show that, with appropriate encapsulation and cleaning, room temperature mobilities well above $10000cm^2 V^{-1} s^{-1}$ can be obtained in samples grown by CVD and transferred using a conventional, easily scalable PMMA-based wet approach.

Chemical Vapor Deposition Grown Large-Scale Atomically Thin Platinum Diselenide with Semimetal-Semiconductor Transition.

Abstract: Among two-dimensional (2D) transition-metal dichalcogenides (TMDCs), platinum diselenide (PtSe2) stands in a distinct place due to its fancy transition from type-II Dirac semimetal to semiconductor with a thickness variation from bulk to monolayer (1 ML) and the related versatile applications especially in mid-infrared detectors. However, achieving atomically thin PtSe2 is still a challenging issue. Herein, we have designed a facile chemical vapor deposition (CVD) method to achieve the synthesis of atomically thin 1T-PtSe2 on an electrode material of Au foil. Thanks to the high crystalline quality, we have confirmed the complete transition from semimetal to semiconductor from trilayer (3 ML) to 1 ML 1T-PtSe2. More importantly, we have found that such atomically thin 1T-PtSe2 can serve as perfect electrocatalysts, featured with a record high hydrogen evolution reaction (HER) efficiency (comparable to traditional Pt catalyst). Our work is helpful toward the large-scale synthesis, exotic physical property exploration, and intriguing application development of atomically thin TMDCs.

Accessing high optical quality of MoS2 monolayers grown by chemical vapor deposition

Abstract: Chemical vapor deposition (CVD) allows growing transition metal dichalcogenides (TMDs) over large surface areas on inexpensive substrates. In this work, we correlate the structural quality of CVD grown MoS$_2$ monolayers (MLs) on SiO$_2$/Si wafers studied by high-resolution transmission electron microscopy (HRTEM) with high optical quality revealed in optical emission and absorption from cryogenic to ambient temperatures. We determine a defect concentration of the order of 10$^{13}$ cm$^{-2}$ for our samples with HRTEM. To have access to the intrinsic optical quality of the MLs, we remove the MLs from the SiO$_2$ growth substrate and encapsulate them in hBN flakes with low defect density, to reduce the detrimental impact of dielectric disorder. We show optical transition linewidth of 5 meV at low temperature (T=4 K) for the free excitons in emission and absorption. This is comparable to the best ML samples obtained by mechanical exfoliation of bulk material. The CVD grown MoS$_2$ ML photoluminescence is dominated by free excitons and not defects even at low temperature. High optical quality of the samples is further confirmed by the observation of excited exciton states of the Rydberg series. We optically generate valley coherence and valley polarization in our CVD grown MoS$_2$ layers, showing the possibility for studying spin and valley physics in CVD samples of large surface area.

Adlayer-Free Large-Area Single Crystal Graphene Grown on a Cu(111) Foil.

Abstract: To date, thousands of publications have reported chemical vapor deposition growth of "single layer" graphene, but none of them has described truly single layer graphene over large area because a fraction of the area has adlayers. It is found that the amount of subsurface carbon (leading to additional nuclei) in Cu foils directly correlates with the extent of adlayer growth. Annealing in hydrogen gas atmosphere depletes the subsurface carbon in the Cu foil. Adlayer-free single crystal and polycrystalline single layer graphene films are grown on Cu(111) and polycrystalline Cu foils containing no subsurface carbon, respectively. This single crystal graphene contains parallel, centimeter-long ≈100 nm wide "folds," separated by 20 to 50 µm, while folds (and wrinkles) are distributed quasi-randomly in the polycrystalline graphene film. High-performance field-effect transistors are readily fabricated in the large regions between adjacent parallel folds in the adlayer-free single crystal graphene film.

Synthetic WSe2 monolayers with high photoluminescence quantum yield

Abstract: In recent years, there have been tremendous advancements in the growth of monolayer transition metal dichalcogenides (TMDCs) by chemical vapor deposition (CVD). However, obtaining high photoluminescence quantum yield (PL QY), which is the key figure of merit for optoelectronics, is still challenging in the grown monolayers. Specifically, the as-grown monolayers often exhibit lower PL QY than their mechanically exfoliated counterparts. In this work, we demonstrate synthetic tungsten diselenide (WSe2) monolayers with PL QY exceeding that of exfoliated crystals by over an order of magnitude. PL QY of ~60% is obtained in monolayer films grown by CVD, which is the highest reported value to date for WSe2 prepared by any technique. The high optoelectronic quality is enabled by the combination of optimizing growth conditions via tuning the halide promoter ratio, and introducing a simple substrate decoupling method via solvent evaporation, which also mechanically relaxes the grown films. The achievement of scalable WSe2 with high PL QY could potentially enable the emergence of technologically relevant devices at the atomically thin limit.

Effect of graphene substrate type on formation of Bi2Se3 nanoplates.

Abstract: Knowledge of nucleation and further growth of Bi2Se3 nanoplates on different substrates is crucial for obtaining ultrathin nanostructures and films of this material by physical vapour deposition technique. In this work, Bi2Se3 nanoplates were deposited under the same experimental conditions on different types of graphene substrates (as-transferred and post-annealed chemical vapour deposition grown monolayer graphene, monolayer graphene grown on silicon carbide substrate). Dimensions of the nanoplates deposited on graphene substrates were compared with the dimensions of the nanoplates deposited on mechanically exfoliated mica and highly ordered pyrolytic graphite flakes used as reference substrates. The influence of different graphene substrates on nucleation and further lateral and vertical growth of the Bi2Se3 nanoplates is analysed. Possibility to obtain ultrathin Bi2Se3 thin films on these substrates is evaluated. Between the substrates considered in this work, graphene grown on silicon carbide is found to be the most promising substrate for obtaining of 1–5 nm thick Bi2Se3 films.

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

Abstract: The future electronic application of graphene highly relies on the production of large-area high-quality single-crystal graphene. However, the growth of single-crystal graphene on different substrates via either single nucleation or seamless stitching is carried out at a temperature of 1000 °C or higher. The usage of this high temperature generates a variety of problems, including complexity of operation, higher contamination, metal evaporation, and wrinkles owing to the mismatch of thermal expansion coefficients between the substrate and graphene. Here, a new approach for the fabrication of ultraflat single-crystal graphene using Cu/Ni (111)/sapphire wafers at lower temperature is reported. It is found that the temperature of epitaxial growth of graphene using Cu/Ni (111) can be reduced to 750 °C, much lower than that of earlier reports on catalytic surfaces. Devices made of graphene grown at 750 °C have a carrier mobility up to ≈9700 cm2 V-1 s-1 at room temperature. This work shines light on a way toward a much lower temperature growth of high-quality graphene in single crystallinity, which could benefit future electronic applications.

Horizontal-to-Vertical Transition of 2D Layer Orientation in Low-Temperature Chemical Vapor Deposition-Grown PtSe 2 and Its Influences on Electrical Properties and Device Applications.

Abstract: Two-dimensional (2D) transition-metal dichalcogenides (2D TMDs) in the form of MX2 (M: transition metal, X: chalcogen) exhibit intrinsically anisotropic layered crystallinity wherein their material properties are determined by constituting M and X elements. 2D platinum diselenide (2D PtSe2) is a relatively unexplored class of 2D TMDs with noble-metal Pt as M, offering distinct advantages over conventional 2D TMDs such as higher carrier mobility and lower growth temperatures. Despite the projected promise, much of its fundamental structural and electrical properties and their interrelation have not been clarified, and so its full technological potential remains mostly unexplored. In this work, we investigate the structural evolution of large-area chemical vapor deposition (CVD)-grown 2D PtSe2 layers of tailored morphology and clarify its influence on resulting electrical properties. Specifically, we unveil the coupled transition of structural-electrical properties in 2D PtSe2 layers grown at a low temperature (i.e., 400 °C). The layer orientation of 2D PtSe2 grown by the CVD selenization of seed Pt films exhibits horizontal-to-vertical transition with increasing Pt thickness. While vertically aligned 2D PtSe2 layers present metallic transports, field-effect-transistor gate responses were observed with thin horizontally aligned 2D PtSe2 layers prepared with Pt of small thickness. Density functional theory calculation identifies the electronic structures of 2D PtSe2 layers undergoing the transition of horizontal-to-vertical layer orientation, further confirming the presence of this uniquely coupled structural-electrical transition. The advantage of low-temperature growth was further demonstrated by directly growing 2D PtSe2 layers of controlled orientation on polyimide polymeric substrates and fabricating their Kirigami structures, further strengthening the application potential of this material. Discussions on the growth mechanism behind the horizontal-to-vertical 2D layer transition are also presented.

Effect of Doping Temperatures and Nitrogen Precursors on the Physicochemical, Optical, and Electrical Conductivity Properties of Nitrogen-Doped Reduced Graphene Oxide

Abstract: The greatest challenge in graphene-based material synthesis is achieving large surface area of high conductivity. Thus, tuning physico-electrochemical properties of these materials is of paramount importance. An even greater problem is to obtain a desired dopant configuration which allows control over device sensitivity and enhanced reproducibility. In this work, substitutional doping of graphene oxide (GO) with nitrogen atoms to induce lattice–structural modification of GO resulted in nitrogen-doped reduced graphene oxide (N-rGO). The effect of doping temperatures and various nitrogen precursors on the physicochemical, optical, and conductivity properties of N-rGO is hereby reported. This was achieved by thermal treating GO with different nitrogen precursors at various doping temperatures. The lowest doping temperature (600 °C) resulted in less thermally stable N-rGO, yet with higher porosity, while the highest doping temperature (800 °C) produced the opposite results. The choice of nitrogen precursors had a significant impact on the atomic percentage of nitrogen in N-rGO. Nitrogen-rich precursor, 4-nitro-ο-phenylenediamine, provided N-rGO with favorable physicochemical properties (larger surface area of 154.02 m2 g−1) with an enhanced electrical conductivity (0.133 S cm−1) property, making it more useful in energy storage devices. Thus, by adjusting the doping temperatures and nitrogen precursors, one can tailor various properties of N-rGO.

Chemically Induced Transformation of CVD-Grown Bilayer Graphene into Single Layer Diamond

Abstract: Notwithstanding numerous density functional studies on the chemically induced transformation of multilayer graphene into a diamond-like film, a comprehensive convincing experimental proof of such a conversion is still lacking. We show that the fluorination of graphene sheets in Bernal (AB)-stacked bilayer graphene (AB-BLG) grown by chemical vapor deposition on a single crystal CuNi(111) surface triggers the formation of interlayer carbon-carbon bonds, resulting in a fluorinated diamond monolayer (F-diamane). Induced by fluorine chemisorption, the phase transition from AB-BLG to single layer diamond was studied and verified by X-ray photoelectron, ultraviolet photoelectron, Raman, UV-Vis, electron energy loss spectroscopies, transmission electron microscopy, and DFT calculations.

Statistical, morphological, and corrosion behavior of PECVD derived cobalt oxide thin films

Abstract: Experimental parameters have direct influences on materials properties and therefore their applications. The effect of plasma power on the properties of cobalt oxide thin films, prepared using plasma-enhanced chemical vapor deposition technique, on stainless steel substrates have been addressed in this paper. The structural, morphological, and compositional properties of these films were investigated by means of X-ray diffraction (XRD), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS) technique. The XRD patterns demonstrated the growth of polycrystalline Co3O4 thin film with a cubic spinel structure such that the intensity of (511) and (311) peaks increase as the plasma power increases to 100 W. It is observed that crystallite size increases by increasing the plasma power and the maximum crystallite size is found to be 64.8 nm for 100 W. The AFM results illustrate that the surface roughness and grain size increase by increasing the plasma power, and the film deposited at lower plasma power has more uniform and smoother surface, mainly owing to the increase in surface diffusion that in turn causes the coalescence of the grains. The results of XPS spectra indicated the formation of Co3O4 thin films on stainless steel substrates and there were no other elements other than Co, O in the XPS spectra. Additionally, stereometric analysis and fractal dimension of the 3-D surface microtexture of the AFM micrographs were analyzed and the Kolmogorov–Smirnov test was used to assess the normal distribution of quantitative variables. The results of statistical analysis corroborated the experimental results and proved that the surface roughness increased upon an increase in plasma power. Moreover, the corrosion behavior and the surface morphology of the cobalt oxide thin films were investigated using the potentiodynamic method and scanning electron microscopy. The results of these analysis proved that as the plasma power increases the corrosion resistance improves against the H2SO4. The sample which deposited at 100 W plasma power has the minimum corrosion current and the corrosion resistance of steel substrate was improved by controlling the anodic reactions resulted from a protective Co3O4 thin film. These results are useful for building and designing stainless steel devices in corrosive environments.

Low Contact Barrier in 2H/1T' MoTe2 In-Plane Heterostructure Synthesized by Chemical Vapor Deposition.

Abstract: Metal–semiconductor contact has been a critical topic in the semiconductor industry because it influences device performance remarkably. Conventional metals have served as the major contact material in electronic and optoelectronic devices, but such a selection becomes increasingly inadequate for emerging novel materials such as two-dimensional (2D) materials. Deposited metals on semiconducting 2D channels usually form large resistance contacts due to the high Schottky barrier. A few approaches have been reported to reduce the contact resistance but they are not suitable for large-scale application or they cannot create a clean and sharp interface. In this study, a chemical vapor deposition (CVD) technique is introduced to produce large-area semiconducting 2D material (2H MoTe2) planarly contacted by its metallic phase (1T′ MoTe2). We demonstrate the phase-controllable synthesis and systematic characterization of large-area MoTe2 films, including pure 2H phase or 1T′ phase, and 2H/1T′ in-plane heterostruc...