Showing papers on "Chemical vapor deposition published in 2022"

Wafer-scale single-crystal monolayer graphene grown on sapphire substrate

Abstract: The growth of inch-scale high-quality graphene on insulating substrates is desirable for electronic and optoelectronic applications, but remains challenging due to the lack of metal catalysis. Here we demonstrate the wafer-scale synthesis of adlayer-free ultra-flat single-crystal monolayer graphene on sapphire substrates. We converted polycrystalline Cu foil placed on Al2O3(0001) into single-crystal Cu(111) film via annealing, and then achieved epitaxial growth of graphene at the interface between Cu(111) and Al2O3(0001) by multi-cycle plasma etching-assisted-chemical vapour deposition. Immersion in liquid nitrogen followed by rapid heating causes the Cu(111) film to bulge and peel off easily, while the graphene film remains on the sapphire substrate without degradation. Field-effect transistors fabricated on as-grown graphene exhibited good electronic transport properties with high carrier mobilities. This work breaks a bottleneck of synthesizing wafer-scale single-crystal monolayer graphene on insulating substrates and could contribute to next-generation graphene-based nanodevices.

Engineering active sites on nitrogen-doped carbon nanotubes/cobaltosic oxide heterostructure embedded in biotemplate for high-performance supercapacitors

Abstract: At present, both easy agglomeration of carbon nanotubes themselves and waste caused by chemical vapor deposition (CVD) have great pollution, which limits the use of carbon nanotubes (CNTs). A large number of hollow polyhedrons containing N-doped carbon nanotubes and Co3O4 nanoparticles (Co3O4 NPs) were well fabricated on a biotemplate by hydrothermal method, stirring method and pyrolysis process. The regular polyhedron was uniformly arranged on the external surface of diatomite with a natural porous structure, which aims to avoid the agglomeration of CNTs. The electrochemical testing result shows that the composite has promising electrochemical performance, which is embodied in a high specific capacity 894.6 F/g at 2 A/g, good rate performance and high cycling property. Finally, an assembled Co3O4 [email protected]@Diatomite//GR asymmetric supercapacitor has maximal energy density of 36.8 Wh/kg and maximal power density of 16,326.6 W/kg. Indeed, electrode design in this work provides an environmental synthesis idea for the decoration of CNTs on a certain substrate and displays an original electrode material based on diatomite.

The Origin of Mo2C Films for Surface-Enhanced Raman Scattering Analysis: Electromagnetic or Chemical Enhancement?

Abstract: The relatively weak Raman enhanced factors of semiconductor-based substrate limit its further application in surface-enhanced Raman scattering (SERS). Here, a kind of two-dimensional (2D) semimetal material, molybdenum carbide (Mo2C) film, is prepared via a chemical vapor deposition (CVD) method, and the origin of SERS is investigated for the first time. The detection limits of the prepared Mo2C films for crystal violet (CV) and rhodamine 6G (R6G) molecules are low at 10-6 M and 10-8 M, respectively. Our detailed theoretical analysis, based on density functional theory and the finite element method, demonstrates that the enhancement of the 2D Mo2C film is indeed CM in nature rather than the EM effects. Besides, the basic doping strategies are proposed to further optimize the SERS sensitivity of Mo2C for Fermi level regulation. We believe this work will provide a helpful guide for developing a highly sensitive semimetal SERS substrate.

Composition and phase engineering of metal chalcogenides and phosphorous chalcogenides

Abstract: Two-dimensional (2D) materials with multiphase, multielement crystals such as transition metal chalcogenides (TMCs) (based on V, Cr, Mn, Fe, Cd, Pt and Pd) and transition metal phosphorous chalcogenides (TMPCs) offer a unique platform to explore novel physical phenomena. However, the synthesis of a single-phase/single-composition crystal of these 2D materials via chemical vapour deposition is still challenging. Here we unravel a competitive-chemical-reaction-based growth mechanism to manipulate the nucleation and growth rate. Based on the growth mechanism, 67 types of TMCs and TMPCs with a defined phase, controllable structure and tunable component can be realized. The ferromagnetism and superconductivity in FeXy can be tuned by the y value, such as superconductivity observed in FeX and ferromagnetism in FeS2 monolayers, demonstrating the high quality of as-grown 2D materials. This work paves the way for the multidisciplinary exploration of 2D TMPCs and TMCs with unique properties.

Ultralow 0.034 dB/m loss wafer-scale integrated photonics realizing 720 million Q and 380 μW threshold Brillouin lasing.

Abstract: We demonstrate 0.034 dB/m loss waveguides in a 200-mm wafer-scale, silicon nitride (Si3N4) CMOS-foundry-compatible integration platform. We fabricate resonators that measure up to a 720 million intrinsic Q resonator at 1615 nm wavelength with a 258 kHz intrinsic linewidth. This resonator is used to realize a Brillouin laser with an energy-efficient 380 µW threshold power. The performance is achieved by reducing scattering losses through a combination of single-mode TM waveguide design and an etched blanket-layer low-pressure chemical vapor deposition (LPCVD) 80 nm Si3N4 waveguide core combined with thermal oxide lower and tetraethoxysilane plasma-enhanced chemical vapor deposition (TEOS-PECVD) upper oxide cladding. This level of performance will enable photon preservation and energy-efficient generation of the spectrally pure light needed for photonic integration of a wide range of future precision scientific applications, including quantum, precision metrology, and optical atomic clocks.

Large and Uniform Single Crystals of MoS2 Monolayers for ppb-Level NO2 Sensing

Abstract: Recently, unprecedented interest has been immersed toward the synthesis of two-dimensional (2D) transition metal dichalcogenides via the chemical vapor deposition (CVD) system. Synthesis of a uniform and large-sized monolayer MoS2 atomic thin film via CVD is still a major bottleneck owing to strong dependence on diverse associated growth parameters. In this work, we have proposed the most viable recipe which is suitable for controlling the nucleation density of Mo and producing a 90 μm-long MoS2 monolayer crystal and (695 × 394.8) μm2 large MoS2 monolayered film on SiO2/Si and c-plane sapphire, respectively. Moreover, MoS2 monolayer sensing performance has been thoroughly investigated for NO2 exposure at room temperature with a varying response of 4–57.5 for the 100–100 ppm level. Furthermore, the MoS2 monolayer sensor exhibits an ultrasensitive NO2 detection with limit of detection and limit of qualification values of 1.4 and 4.6 ppb, respectively. In addition, the first-principles-based density functional theory has been employed to analyze the adsorption of NO2 on the surfaces of the 2D MoS2 monolayer. It is observed that the electronic band gap of the MoS2 monolayer after NO2 adsorption is reduced by 0.7 eV due to molecular orbital hybridization.

Layer-dependent optical and dielectric properties of centimeter-scale PdSe2 films grown by chemical vapor deposition

Abstract: Abstract Palladium diselenide (PdSe 2 ), a new type of two-dimensional noble metal dihalides (NMDCs), has received widespread attention for its excellent electrical and optoelectronic properties. Herein, high-quality continuous centimeter-scale PdSe 2 films with layers in the range of 3L–15L were grown using Chemical Vapor Deposition (CVD) method. The absorption spectra and DFT calculations revealed that the bandgap of the PdSe 2 films decreased with the increasing number of layers, which is due to the enhancement of orbital hybridization. Spectroscopic ellipsometry (SE) analysis shows that PdSe 2 has significant layer-dependent optical and dielectric properties. This is mainly due to the unique strong exciton effect of the thin PdSe 2 film in the UV band. In particular, the effect of temperature on the optical properties of PdSe 2 films was also observed, and the thermo-optical coefficients of PdSe 2 films with the different number of layers were calculated. This study provides fundamental guidance for the fabrication and optimization of PdSe 2 -based optoelectronic devices.

Grow defect-rich bamboo-like carbon nanotubes on carbon black for enhanced microwave absorption properties in X band

Abstract: Due to the limited electromagnetic wave (EMW) loss capacity and agglomeration, carbon black (CB) gradually fails to meet the increasingly harsh demanding conditions. Herein, defect-rich bamboo-like carbon nanotubes (CNTs) were grown on CB by the process of chemical vapor deposition. CNTs prepared in situ on CB can assist it to build a developed multilevel conductive network and introduce plentiful CB/CNTs nano-interfaces. What's more, the defects that accompany the growth of CNTs endow CNTs with a moderate conductivity and good impedance matching, thereby causing an effective microwave absorption (MA). Meanwhile, the high-density defects on CNTs can induce dipole polarization to further strengthen the EMW loss ability. The influence of CNTs with different growth time on MA performance has been explored. Profiting from the structural merits, the synthesized CB-CNT with CNTs growth time of 40 min exhibits the optimal absorbing property, which has the minimum reflection loss of -53.6 dB and maximum effective absorption bandwidth of 4.1 GHz with the thickness of 2.7 mm, covering almost the entire X band. The introduction of defect-rich CNTs significantly enhances the EMW loss ability of CB, which provides a rational strategy for the design of high-efficient microwave absorption materials.

Two-dimensional covalent organic framework films prepared on various substrates through vapor induced conversion

Abstract: Covalent organic frameworks (COFs) can exhibit high specific surface area and catalytic activity, but traditional solution-based synthesis methods often lead to insoluble and infusible powders or fragile films on solution surface. Herein we report large-area -C=N- linked two-dimensional (2D) COF films with controllable thicknesses via vapor induced conversion in a chemical vapor deposition (CVD) system. The assembly process is achieved by reversible Schiff base polycondensation between PyTTA film and TPA vapor, which results in a uniform organic framework film directly on growth substrate, and is driven by π-π stacking interactions with the aid of water and acetic acid. Wafer-scale 2D COF films with different structures have been successfully synthesized by adjusting their building blocks, suggesting its generic applicability. The carrier mobility of PyTTA-TPA COF films can reach 1.89 × 10-3 cm2 V-1 s-1. When employed as catalysts in hydrogen evolution reaction (HER), they show high electrocatalytic activity compared with metal-free COFs or even some metallic catalysts. Our results represent a versatile route for the direct construction of large-area uniform 2D COF films on substrates towards multi-functional applications of 2D π-conjugated systems.

Red InGaN micro-light-emitting diodes (>620 nm) with a peak external quantum efficiency of 4.5% using an epitaxial tunnel junction contact

Abstract: We present efficient red InGaN 60 × 60 μm2 micro-light-emitting diodes ( μLEDs) with an epitaxial tunnel junction (TJ) contact. The TJ was grown by metal-organic chemical vapor deposition using selective area growth. The red TJ μLEDs show a uniform electroluminescence. At a low current density of 1 A/cm2, the emission peak wavelength is 623 nm with a full-width half maximum of 47 nm. The peak external quantum efficiency (EQE) measured in an integrating sphere is as high as 4.5%. These results suggest a significant progress in exploring high efficiency InGaN red μLEDs using TJ technology.

Optical and Material Characteristics of MoS2/Cu2O Sensor for Detection of Lung Cancer Cell Types in Hydroplegia

Abstract: In this study, n-type MoS2 monolayer flakes are grown through chemical vapor deposition (CVD), and a p-type Cu2O thin film is grown via electrochemical deposition. The crystal structure of the grown MoS2 flakes is analyzed through transmission electron microscopy. The monolayer structure of the MoS2 flakes is verified with Raman spectroscopy, multiphoton excitation microscopy, atomic force microscopy, and photoluminescence (PL) measurements. After the preliminary processing of the grown MoS2 flakes, the sample is then transferred onto a Cu2O thin film to complete a p-n heterogeneous structure. Data are confirmed via scanning electron microscopy, SHG, and Raman mapping measurements. The luminous energy gap between the two materials is examined through PL measurements. Results reveal that the thickness of the single-layer MoS2 film is 0.7 nm. PL mapping shows a micro signal generated at the 627 nm wavelength, which belongs to the B2 excitons of MoS2 and tends to increase gradually when it approaches 670 nm. Finally, the biosensor is used to detect lung cancer cell types in hydroplegia significantly reducing the current busy procedures and longer waiting time for detection. The results suggest that the fabricated sensor is highly sensitive to the change in the photocurrent with the number of each cell, the linear regression of the three cell types is as high as 99%. By measuring the slope of the photocurrent, we can identify the type of cells and the number of cells.

Hard coatings for cutting applications: Physical vs. chemical vapor deposition and future challenges for the coatings community

Abstract: Since decades, protective hard coatings with thicknesses of a few micrometers are grown by physical or chemical vapor deposition (PVD, CVD) on cutting tools to improve their application performance. For the huge variety of cutting applications, different coating materials are used, which typically belong to the material classes of nitrides, carbides, carbonitrides, borides, boronitrides or oxides, frequently in bi- or multilayer stacks. The present work surveys typical hard coatings belonging to the respective material classes, deposited by PVD as well as CVD. Pioneering studies in this field as well as recent findings contributing to the establishment of comprehensive “synthesis – structure – property – application performance” relationships of the respective coatings are discussed and the current state-of-research is reviewed. Condensed summaries and comparisons between PVD and CVD coatings are given at the end of each subsection. In addition, current and future challenges for the hard coatings community are surveyed.

Prospects for phase engineering of semi-stable Ga2O3 semiconductor thin films using mist chemical vapor deposition

Abstract: Routes to semi-stable phases of Ga[Formula: see text]O[Formula: see text] are the subject of extended discussions based on the review of growth methods, growth conditions, and precursors in works that report semi-stable phases other than the thermally stable [Formula: see text] phase. The focus here is on mist chemical vapor deposition because it has produced single-phase Ga[Formula: see text]O[Formula: see text] of [Formula: see text], [Formula: see text], and [Formula: see text] (or [Formula: see text]) in terms of the substrate materials, and features of this growth method for phase control are emphasized. Recent reports of phase control by other growth technology give a deeper understanding of how to determine and control the phases, increasing the opportunities to fully utilize the novel and unique properties of Ga[Formula: see text]O[Formula: see text].

Influence of post-deposition annealing temperature on morphological, mechanical and electrochemical properties of CrN/CrAlN multilayer coating deposited by cathodic arc evaporation- physical vapor deposition process

Abstract: CrN/CrAlN multilayer coatings were deposited on AISI 304 stainless steel substrates utilizing the CAE-PVD process. Then the coatings were annealed at 400, 500, 600, and 700 °C for a duration of 1 h in a vacuum condition. The phases identification, surface morphology, mechanical properties, adhesion, and corrosion behavior of the coating before and after post-deposition annealing treatment were characterized using XRD, SEM, nanoindentation test, Rockwell-C adhesion measurements, and EIS assays, respectively. The results indicated that with increasing post-deposition annealing treatment temperature, the phase structures of the multilayer coating vary from a face-centered cubic CrN to a hexagonal Cr 2 N. Moreover, annealing resulted, in the decrease of the macroparticles on the coating surface decreased. The hardness of the multilayer coating decreased from 19 GPa to 17 GPa, which can be ascribed to the increase in crystallite size and the decrease in the residual stress and annihilation of defects as the temperature increased to 700 °C. Based on the EIS results, the sample annealed at 700 °C had the highest corrosion resistance among other samples, which can be attributed to a decrease in the porosities as corrosion initiation sites, the existence of Cr 2 N as corrosion resistance phase, and an increase in the crystallite size of the multilayer coating. • Comprehensive evaluation on the effect of annealing on CrN/CrAlN multilayer coating. • Significant decrease in residual stress and macrostrain. • Crystallite growth resulted in the decrease in the hardness of the coating by 10%. • Enhancement of electrochemical properties through post-deposition annealing.

High-Mobility MOCVD β-Ga2O3 Epitaxy with Fast Growth Rate Using Trimethylgallium

Abstract: In this work, metalorganic chemical vapor deposition (MOCVD) of (010) β-Ga2O3 with fast growth rates was investigated using trimethylgallium (TMGa) as the gallium (Ga) precursor. Key growth parameters including precursor/carrier gas flow, growth temperature, chamber pressure, and group VI/III molar flow ratio were systematically mapped. Surface morphology and charge transport properties of the homo-epi (010) β-Ga2O3 thin films were probed to correlate with the crystalline quality. The growth rate of (010) β-Ga2O3 thin film increases as the TMGa flow rate increases, and high-quality epi-film is achievable with a fast growth rate up to ∼3 μm/h. By tuning the n-type dopant silane flow rate, the net charge carrier concentration was tuned from ∼1016 to 1019 cm–3. Room-temperature mobility as high as 190 cm2/V·s was measured for a sample grown with a growth rate of 2.95 μm/h and an electron concentration of 1.8 × 1016 cm–3. Temperature-dependent Hall measurement revealed a peak mobility value of ∼3400 cm2/V·s at 53 K. The extracted low compensation level of NA ∼ 1.5 × 1015 cm–3 indicates the high purity of the MOCVD growth of the (010) β-Ga2O3 film using TMGa as the Ga precursor. Quantitative secondary-ion mass spectroscopy characterization revealed a relatively high C concentration of 7 × 1016 cm–3, indicating that C does not serve as a compensator or a donor in MOCVD grown β-Ga2O3. The results from this study demonstrate the feasibility to grow high-quality Ga2O3 thin films with fast growth rates, critical for developing high power electronic device technology.

An electronic nose based on carbon nanotube -titanium dioxide hybrid nanostructures for detection and discrimination of volatile organic compounds

Abstract: Detection and classification of Volatile Organic Compounds (VOCs) that pose risks to human health even at very low concentrations, is a common requirement in the industry. Herein, we apply a modification to the aligned Carbon Nanotubes (CNTs) grown at low temperature (250 °C) using Plasma Enhanced Chemical Vapor Deposition (PECVD). CNTs are used to identify VOCs in an improved sensitivity condition to gas at room temperature. We improve the sensitivity and stability of carbon nanotube sensors via growing Titanium Dioxide Nanowires (TiO2-NW) on the surface of CNTs through the hydrothermal method. A threefold increase in sensitivity and a 30-second decrease in response time were observed as a result of the CNT-TiO2 sensor compared to the pristine CNT sensor. In order to obtain new data, we deposit four different electrodes on the TiO2 surface as virtual arrays of Electronic nose (E-nose). Temperature modulation and Discrete Wavelet Transform (DWT) of virtual arrays, extract new features of the E-nose data. We select 14 different features from E-nose data and apply Principle Component Analysis (PCA) method for data reduction. We categorize the extracted features by using Support Vector Machine (SVM) algorithms and data covariance properties. This paper achieves 97.5% accuracy in classifying four different VOC gases.

Dual-Emitter Graphene Glass Fiber Fabric for Radiant Heating.

Abstract: Radiant heating, as a significant thermal management technique, is best known for its high thermal effect, media-free operation, good penetration, and compatibility for different heated shapes. To promote sustainable development in this area, developing advanced infrared radiation material is in high demand. In this work, a lightweight, flexible dual-emitter infrared electrothermal material, graphene glass fiber (GGF), is developed by chemical vapor deposition (CVD) method, with both graphene and glass fiber as the radiation elements. Large-area GGF fabric (GGFF) exhibits wavelength-independent high infrared emissivity (0.92) and thermal radiation efficiency (79.4%), as well as ultrafast electrothermal response (190.7 °C s-1 at 9.30 W cm-2) and uniform heating temperature. The superior radiant heating capability of GGFF to traditional alloy heating wires can achieve 33.3% energy saving. GGF can promote the development of efficient and energy-saving heat management technology.