Hot-wire Chemical Vapor Deposition Research Articles

Effect of hydrogen flow rate on properties of silicon oxycarbide thin films via hot wire chemical vapor deposition

AbstractThis study explores the impact of hydrogen flow as a carrier gas on silicon oxycarbide thin films produced via hot wire chemical vapor deposition (HWCVD) using tetraethyl orthosilicate as a precursor. Systematically varying the hydrogen flow rates, the influence on thin film composition, microstructure, and optical properties is investigated. Employing diverse characterization techniques, such as X‐ray diffraction, field‐emission scanning electron microscopy (FE‐SEM), energy‐dispersive X‐ray spectroscopy, Fourier‐transform infrared (FTIR), X‐ray photoelectron spectroscopy (XPS), ellipsometry, and photoluminescence (PL) spectroscopy, it is revealed that there is a correlation between hydrogen flow rate and thin film elemental composition. Higher hydrogen flow rates result in increased silicon content and reduced contributions of oxygen and carbon. FE‐SEM images show agglomerates with improved homogeneity at higher flow rates. FTIR spectra highlight distinctive vibrational modes, including Si–H bonds. XPS confirms the emergence of Si–H bonds at elevated hydrogen flow rates. Ellipsometry indicates increased thickness and refractive index. PL spectra exhibit a broadband across the visible spectrum, influenced by hydrogen‐related defects and electronic transitions. This study provides findings for optimizing HWCVD parameters to tailor thin films for specific applications, emphasizing the important role of hydrogen flow as a carrier gas.

Improved photoelectrochemical performance of tungsten-catalyzed graphene nanoplatelet electrodes prepared by hot-wire chemical vapor deposition at low substrate temperatures

The current increase in demand for graphene in various energy applications such as electrode materials for supercapacitors, batteries, thermoelectric, and hydrogen production via water-splitting, the production of high-quality graphene, considering its fascinating physical and electrical properties, high-yield, and large-area has becoming more challenging at the research and development level. Therefore, in this work, graphene nanoplatelets (GNPs) were directly grown on tungsten nanoparticle (W NP)-coated p-type crystalline silicon and quartz substrates using hot-wire chemical vapor deposition at low substrate temperatures (<500 °C). Prior to the GNP deposition, a plasma process was employed to induce the formation of W NPs, which act as a metal catalyst for facilitating the growth of large-area and multi-layer GNPs. The W NPs were formed at substrate temperatures ranging from 250 to 550 °C, with the largest graphene sheet was grown at 450 °C. Higher substrate temperatures promote the growth of high-quality graphene layers with high intensities of G (IG) and 2D bands (I2D), and high I2D/IG ratio values. The GNP photoelectrode prepared at 450 °C demonstrated better photoelectrochemical responses with the highest photocurrent density of 1.65 mA/cm2 at 1.5 VAg/AgCl, the lowest charge transfer resistance (14.0 kΩ), and the highest donor density (2.57 × 10 28 cm−3) compared to the tungsten carbide thin film and W NP electrodes prepared at the same temperature. The effects of substrate temperature on the optical, structural, and photoelectrochemical properties of the as-grown GNPs are discussed.

Structural optimization and growth of intrinsic hydrogenated amorphous silicon films by HWCVD

Although the silicon heterojunction (SHJ) solar cell is the crystalline silicon solar cell with highest conversion efficiency at present, its higher cost of production line has been a factor restricting its industrial development. The use of hot wire chemical vapor deposition (HWCVD) technology instead of the mainstream plasma enhanced chemical vapor deposition (PECVD) technology for the deposition of amorphous silicon films can effectively reduce the cost of equipment and processing, and has a bright future. In recent years, i-a-Si:H films grown by PECVD have obtained great improvement in passivation quality, whereas HWCVD technology has been neglected in this field. This has significantly limited the development and application of HWCVD technology in SHJ cell production. In this work, we exploited the differences in the films properties and microstructures deposited by various hot-wire temperatures and successfully developed a structure for the high-passivation-quality i-a-Si:H film grown by HWCVD, consisting of a buffer layer and a double-layer bulk stack. By introducing the buffer layer grown with the 1650 °C hot-wire temperature and pure silane, the effective minority carrier lifetime was improved from 2.3 ms to 7.5 ms, and a cell efficiency enhancement of 0.4%abs was obtained. By depositing the bulk layer sequentially with hot-wire temperatures of 1800 °C and 1900 °C, the passivation quality and the conductance were both improved. An effective minority carrier lifetime of 8 ms and a further cell efficiency enhancement of 0.15%abs were obtained. Finally, SHJ solar cell efficiency of 24.35% was obtained with a home-made HWCVD-based pilot SHJ cell line.

Fabrication of silicon nitride based high-Q microring resonators prepared by the hot-wire CVD method and their applications to frequency comb generation

Fabrication of silicon nitride (SiN) based high-Q microring resonators prepared by the hot-wire chemical vapor deposition (HWCVD) method is presented. By the virtue of low-stress HWCVD films, no special precautions against crack propagation were required for high confinement waveguide device fabrication. By using an additional annealing process, the intrinsic Q factor in excess of 5 × 105 was obtained in the telecommunication C band, and which allowed us to observe frequency comb generation. We also investigated into the anneal temperature dependence of the residual hydrogen concentration in the film as well as the optical properties of the microring resonators.

Polycrystalline GeSn Films Grown by Hot Wire Chemical Vapor Deposition on SiO2/Si(001) Substrates

The conditions for the growth of polycrystalline GeSn films on SiO2/Si(001) substrates by hot wire chemical vapor deposition are determined for the first time. The effect of the introduction of Sn into the Ge lattice on the morphology, structure, and transport properties of films is studied. GeSn films obtained at 300 °C have a uniform surface with a roughness of less than 1.0 nm. It is shown that the introduction of 5% Sn allows, without the use of recrystallization annealing, to significantly increase the hole mobility of polycrystalline GeSn films from 20 to 60 cm2 V−1 × s−1. despite the small grain size of 35 nm. Such films are of great interest for creating thin‐film transistors for active matrices’ liquid crystal displays.

Graphene-All-Around Cobalt Interconnect with a Back-End-of-Line Compatible Process.

The graphene-all-around (GAA) structure has been verified to grow directly at 380 °C using hot-wire chemical vapor deposition, within the thermal budget of the back end of the line (BEOL). The cobalt (Co) interconnects with the GAA structure have demonstrated a 10.8% increase in current density, a 27% reduction in resistance, and a 36 times longer electromigration lifetime. X-ray photoelectron spectroscopy and density functional theory calculations have revealed the presence of bonding between carbon and Co, which makes the Co atom more stable to resist external forces. The ability of graphene to act as a diffusion barrier in the GAA structure was confirmed through time-dependent dielectric breakdown measurement. The Co interconnect within the GAA structure exhibits enhanced electrical properties and reliability, which indicates compatibility applications as next-generation interconnect materials in CMOS BEOL.

Structure and properties of Si3N4-based diamond/MoS2-TiN composite films

This study aims to optimize the performance of silicon nitride (Si3N4) ceramic bearings in high-temperature and heavy-duty environments and to address the issues of insufficient lubrication and heat generation in vacuum environments. To this end, we prepared diamond and MoS2-TiN composite films on silicon nitride ceramic substrates using a hot-wire chemical vapor deposition system and a physical vapor deposition system. The experimental results show that increasing the deposition time of the diamond films can significantly improve their hardness and elastic modulus, enhance the bonding of the films with the substrate, reduce the friction coefficient, and increase the thermal conductivity. Furthermore, by appropriately reducing the sputtering power of the MoS2 film, we can effectively minimize damage to the diamond film and further enhance the overall performance of the composite film. This study offers valuable insights for addressing lubrication and heat dissipation challenges in vacuum environments.

Effects of High-Energy Electron Beam Irradiation on The Structure, Composition and Morphological Properties of Graphene Nanoplatelet Films

This work demonstrated the effects of 1.2 GeV high-energy electron beam irradiation on a few-layers of graphene (FLG) and multi-layer graphene (MLG) films grown via an in-house hot wire chemical vapour deposition (HWCVD) system. The FLG and MLG films were grown on highly doped n-type c-Si (100) substrates which were pre-treated using argon plasma (50 W) for 1 min and 10 min, respectively. The as-prepared samples were then irradiated using a 1.2 GeV high-energy electron beam with a dosage of 1.2 × 109 e-/cm2 at atmospheric and room temperature ambient conditions. The effects of the irradiation-mediated defects on the carbon lattice structure of both graphene samples were validated from the decreased sp2 C=C carbon content, and the increase in the adventitious carbon contamination C-O-C content. Raman results showed an elevation of the ID/IG ratio and blue-shift of the 2D and G band peaks for both the irradiated samples, which validated the mediated defects due to the dislocation of carbon atoms in the graphene sheets. The blue-shifted of 2D and G peaks were much more significant in the MLG than FLG which may indicate a better self-reconstructing property for the MLG atomic network, compared to the FLG. The stability of the films against high-energy electron beam irradiation was validated by their conductivity and surface topography. In conclusion, HWCVD grown graphene nanoplatelet films have high potential for graphene-based high-energy charged particle detectors.

Hot wire-CVD grown molybdenum disulfide (MoS2) thin films for photodetector and humidity sensing applications

Hot wire-CVD grown molybdenum disulfide (MoS2) thin films for photodetector and humidity sensing applications

Oil–Water Separation on Hydrophobic and Superhydrophobic Membranes Made of Stainless Steel Meshes with Fluoropolymer Coatings

In this work, membranes were synthesized by depositing fluoropolymer coatings onto metal meshes using the hot wire chemical vapor deposition (HW CVD) method. By changing the deposition parameters, membranes with different wetting angles were obtained, with water contact angles for different membranes over a range from 130° ± 5° to 170° ± 2° and a constant oil contact angle of about 80° ± 2°. These membranes were used for the separation of an oil–water emulsion in a simple filtration test. The main parameters affecting the separation efficiency and the optimal separation mode were determined. The results reveal the effectiveness of the use of the membranes for the separation of emulsions of water and commercial crude oil, with separation efficiency values that can reach over 99%. The membranes are most efficient when separating emulsions with a water concentration of less than 5%. The pore size of the membrane significantly affects the rate and efficiency of separation. Pore sizes in the range from 40 to 200 µm are investigated. The smaller the pore size of the membranes, the higher the separation efficiency. The work is of great economic and practical importance for improving the efficiency of the membrane separation of oil–water emulsions. It lays the foundation for future research on the use of hydrophobic membranes for the separation of various emulsions of water and oil products (diesel fuel, gasoline, kerosene, etc.).

DEPOSITION OF HYDROPHOBIC FLUOROPOLYMER COATINGS ON A PLASMA-TREATED STAINLESS STEEL SURFACE

A stainless steel surface was treated with a glow discharge plasma. As a result of surface treatment, micro- and nanostructures were obtained. The surface roughness of the samples was increased. Thin fluoropolymer coatings were deposited on treated and untreated surfaces using the hot wire chemical vapor deposition (HWCVD) method. The structure of the obtained samples was studied by scanning and atomic force microscopy. Wetting properties were measured for all samples obtained. It has been shown that pretreatment of the surface before the deposition of fluoropolymer coatings makes it possible to increase the hydrophobicity of the final surfaces. Tests of coatings carried out using an ultrasonic cleaner have shown that plasma pretreatment before deposition and subsequent annealing after deposition make it possible to obtain stable coatings with stable hydrophobic properties.

Epitaxial n+-Ge/p+-Si(0 0 1) heterostructures with ultra sharp doping profiles for light emitting diode applications

The prototype light emitting diodes (LEDs) were fabricated from the n+-Ge/p+-Si(001) heterostructures grown by low-temperature Hot Wire Chemical Vapor Deposition. The n+-Ge epitaxial layers were heavily doped with P from a sublimation solid-phase GaP source. Abrupt profiles of the donor impurity concentrations at the n+-Ge/p+-Si heterojunctions were obtained. Negative differential resistance was observed in the current–voltage curves of the LEDs at forward bias. Electroluminescence (EL) related to the indirect (phonon-assisted) interband radiative optical transitions in the n+-Ge layers (from the l-valleys of the conduction band into the Г-point in the valence band) was observed at room temperature. The EL intensity increased with increasing P concentration in the n+-Ge layers.

In-situ deposition of tungsten oxide hole-contact by Hot-Wire CVD and its application in dopant-free heterojunction solar cells

The tungsten oxide (WO x ) thin films have been deposited by a novel hot filament oxidation-sublimation process and applied in the dopant-free heterojunction solar cells as the hole selective contacts. The oxygen flow ratio plays a significant role during the deposition process. With increasing the oxygen flow ratio from 1.7% to 6.7%, the morphology of WO x films changes from small cauliflower-like particles to large cluster accumulation, and the ratio of W6+ increases from 76.1% to 91.4% with the ratio of W5+ decreasing from 23.9% to 8.6%. The work function of WO x can be tailored in a range of 5.5–6.1 eV by increasing the oxygen flow ratio. Its optical band gap maintains above 3.2 eV with the conductivity of about 10−5 S·cm−1. We have applied the WO x films in dopant-free silicon heterojunction solar cells as the hole selective contact layer by replacing the p-type amorphous silicon layer. By taking advantage of the highly transparent WO x layer, a high photon-current density of 39.6 mA·cm−2 was achieved with the oxygen flow ratio of 1.7%. It is interesting to find that the optimum cell conversion efficiencies of 14.9% were obtained with the oxygen flow ratio of 1.7% and the thickness of 10–20 nm for the deposition of WO x layer. This work proves the feasibility and good potential of Hot-Wire CVD prepared WO x hole selective contact for efficient dopant-free silicon heterojunction solar cells.

Surface treatment technology of downhole water cut sensor

Based on the structure, working principle, and working conditions of conductance water cut sensor, it is revealed that the early failure of the metal electrode of the sensor is due to the comprehensive influence of well fluid erosion, electrochemical corrosion, and oil pollution during its long-term service in the downhole. A technology for electrode surface treatment is proposed using boron-doped diamond (BDD) films to improve the service performance of the modified electrode. The hot wire chemical vapor deposition method was adopted to fabricate BDD film, the boron doping concentration and deposition time were optimized, and fluorination treatment was applied to improve the wear resistance, electrochemical corrosion resistance, and oleophobic property of the BDD film comprehensively. The results showed that BDD film with boron doping concentration of 6×10-3 exhibited high wear resistance and good electrochemical corrosion resistance, and endowed the modified electrode with superior erosion resistance and corrosion resistance. The friction coefficient and wear rate of BDD modified electrode were 92% and 78% lower than those of Invar alloy, also, the low-frequency impedance modulus value of the modified electrode was higher than 1×104 Ω·cm2. The BDD film prepared with a deposition time of 8 h had a favorable micro-nano structure owing to small grain size and uniform distribution. Such morphology was conducive to enhancing the oleophobic performance of the modified electrode, and its contact angle in the simulated well fluid was high to 102°. The engineering applicability of BDD film modified electrode under simulated working conditions indicated that, the modified electrode had excellent comprehensive performances of erosion resistance, electrochemical corrosion resistance and oil adhesion resistance, and can realize the long-term stable operation of the conductance water cut sensor under harsh downhole conditions.

Synaptic mechanisms of four W/WO x /ITO memristors with different WO x structures

Memristor has been an important synaptic device for neuromorphological calculation, but its general model has not been established even though several mechanisms have been accepted widely. Fundamentally, the diversity of mechanisms lies in a wide range of materials that can be used in memristors. Obviously, the top/bottom electrodes and dielectric materials affect the properties/mechanisms of synapses. Hence, we fabricated four different W/WO x /ITO memristors among which the WO x -based layers have different structures due to the different deposition methods employed, i.e. hot wire chemical vapor deposition and magnetron sputtering. Surprisingly, a small change in WO x structure leads to significant differences of synaptic characteristics and mechanisms. By comparing the four W/WO x /ITO memristors, the diversity of mechanisms for memristor synapses is revealed and demonstrated deeply.

Improved Crystallinity of Graphene Grown on Cu/Ni (111) through Sequential Mobile Hot-Wire Heat Treatment

Over the past few years, many efforts have been devoted to growing single-crystal graphene due to its great potential in future applications. However, a number of issues remain for single-crystal graphene growth, such as control of nanoscale defects and the substrate-dependent nonuniformity of graphene quality. In this work, we demonstrate a possible route toward single-crystal graphene by combining aligned nucleation of graphene nanograins on Cu/Ni (111) and sequential heat treatment over pregrown graphene grains. By use of a mobile hot-wire CVD system, prealigned grains were stitched into one continuous film with up to ∼97% single-crystal domains, compared to graphene grown on polycrystalline Cu, which was predominantly high-angle tilt boundary (HATB) domains. The single-crystal-like graphene showed remarkably high thermal conductivity and carrier mobility of ∼1349 W/mK at 350 K and ∼33 600 (38 400) cm2 V-1 s-1 for electrons (holes), respectively, which indicates that the crystallinity is high due to suppression of HATB domains.

Role of H2 and Ar as the diluent gas in continuous hot-wire CVD synthesis of SiC fiber

W-core SiC fiber was synthesized with CH3SiCl3 as the precursor by continuous hot-wire CVD approach. Using H2 and Ar as the diluent gas, the temperature profile and the production of atomic hydrogen (H) in high-speed deposition process were studied by computational flow dynamics (CFD) simulation, and the growth kinetics and microstructure of the deposit were systematically investigated. H2 significantly increases the H production, which reduces the formation of amorphous phase and structural defects (e.g. stacking faults and twins) during SiC growth. Ar could establish a steep thermal gradient in reactor, which enhances the deposit’s surface quality. The mean tensile strength of SiC fiber reaches its peak value (3.15 GPa) with H2 at 1200 sccm, and a high Weibull modulus (14.7) is achieved with Ar at 1600 sccm. These findings indicate H2 is crucial to promote the mechanical performance of SiC fiber, while Ar is beneficial to improving its uniformity.

Preparation and electrochemical properties of nano-diamond/vertical graphene composite three-dimensional electrodes

Diamond/graphene composite three-dimensional electrode has attracted extensive attention because of its low background current, wide potential window from diamond component, and high electrochemical activity from graphite component. In this work, by using the hot wire chemical vapor deposition method, nano diamonds are embedded in the vertical graphene sheet on the surface of single particle layer of nano diamond by regulating the short-term growth time to form a composite three-dimensional electrode. The results show that the electrode exhibits a wide potential window (3.59 V) and a very low background current (1.27 mA/cm&lt;sup&gt;2&lt;/sup&gt;) when nano-diamond crystals grow on the top of the vertical graphene sheet. The composite structure of nano-diamond crystals coated with graphite on the top of the graphene sheet is the key to broadening the potential window and reducing the background current. With the increase of growth time, the vertical graphene sheet grows and nano-diamond grains are embedded into the lamellae, and a novel nano-diamond/graphene composite vertical lamellae structure is constructed. The ordered graphite structure increases the electrochemical active area to 677.19 μC/cm&lt;sup&gt;2&lt;/sup&gt; and the specific capacitance to 627.34 μF/cm&lt;sup&gt;2&lt;/sup&gt;. The increase of graphite components makes the potential window narrow, and the embedded nano-diamond crystals effectively reduce the background current. This study provides a new method for preparing three-dimensional nanodiamond/graphene composite electrodes by hot wire chemical vapor deposition, and provides a new idea for fully exploiting the synergistic effect of diamond/graphene composite films.

Distribution of charge carrier concentrations in epitaxial Ge and GeSn layers grown on n-=SUP=-+-=/SUP=--Si(001) substrates

Heteroepitaxial Ge or Ge1-xSnx layers were grown by hot-wire chemical vapor deposition on Si(001) substrates doped heavily with a donor (As or Sb) impurity. The same layers were also grown on high-resistance Si(001) substrates for comparison. The depth profiles of carrier concentration were measured in both types of layers using the capacitance-voltage method, and carrier mobilities were measured additionally by the Hall effect method in layers on high-resistance silicon. It was found that the layers grown on high-resistance substrates were p-type, while the layers grown in the same regimes on heavily doped substrates were n-type with electron concentration n=(4-9)·1016 cm-3 in Ge layers and n=(2-4)·1017 cm-3 in GeSn layers. It was established experimentally and theoretically that the effect of autodoping of Ge and GeSn layers is lacking in the hot-wire chemical vapor deposition method. In our view, the growth of n-type Ge and GeSn layers on n+-Si(001) substrates doped heavily with a donor (As or Sb) impurity is associated with the segregation of this impurity in the process of growth of a buffer Si layer and its subsequent incorporation into growing Ge or GeSn layers. Keywords: epitaxy, doping, Ge, Si, Sn, concentration.

Contact line dynamics on a substrate coated with a fluoropolymer

This work investigates the dynamics of the contact line during the propagation of a dry spot in a water layer on a solid substrate. The substrate is coated with fluoropolymer by using a hot wire chemical vapor deposition method. The dry spot is generated using a thermocapillary mechanism caused by the heating of the substrate from below by the laser. By analyzing schlieren images, the dependence of the velocity of the contact line during the propagation of a dry spot was obtained for various initial thicknesses of liquid films.