Pressure Chemical Vapor Deposition Research Articles

Direct Growth Graphene Via Atmospheric Pressure Chemical Vapour Deposition

The integration of graphene in field-effect transistor (FET) has aroused tremendous attention in the field of sensor technology, particularly for electronic biosensors. However, transferring graphene from metal substrates has destructive effects on the electrical characteristics of the graphene film, leading to severe impurities and defects. Here, we investigated a new approach of technique to synthesis direct- growth semiconducting graphene via atmospheric pressure chemical vapour deposition (APCVD) method. In this study we observe the effects of different reaction times, carbon concentrations and temperatures on the carbon arrangement in graphene. The synthesised graphene was characterised by Raman spectroscopy and field emission scanning electron microscopy (FESEM) to observe the quality of graphene formation. From the Raman analysis, the I2D/IG ratio < 1 indicates the formation of graphene in multiple layers. The ID /IG ratio < 1 was also observed, indicating that the graphene has less disorder of defects. Based on the electrical measurement of the material at estimated distance of 250 μm, a higher I2D/IG ratio leads to a higher resistance. Full width at half maximum (FWHM) of 2D band shows graphene with the highest I2D/IG ratio has the lowest value of FWHM. As the conclusion, these directly grown semiconducting graphene layers can be efficiently integrated into biosensors without any complex post-treatment process.

Vanadium pentoxide nanowires preparation via kinetic control of vanadium oxytrichloride catalytic oxidation with APCVD

Vanadium pentoxide nanowires were successfully fabricated using vanadium oxytrichloride oxidation with copper oxide nanoparticles serving as catalysts via atmospheric pressure chemical vapor deposition. Kinetic parameters such as temperature and flow velocity were proved to play important roles in the morphologic control of as-deposited product. Vanadium pentoxide nanowires with an average length of ∼10 μm and a diameter of 50–100 nm, were obtained under the optimum conditions. A root growth mechanism of nanowires was proposed that precursor was readily captured by catalyst nanoparticles at the beginning of deposition, forming nucleation sites. Subsequently, the anisotropic growth of vanadium pentoxide is primarily governed by energy minimization under the reaction rate limited conditions. The presence of oxygen vacancies in the nanowires was confirmed by Raman, XPS and photoluminescence characterization, indicating promising applications in functional materials manufacture. The novel route for preparing vanadium pentoxide nanowires provides an alternative pathway for transitioning traditional vanadium industry towards advanced functional materials development.

Experimental characterization and crystal plasticity finite element simulation of the microstructural evolution in CVD tungsten during multi-step rolling

Atmospheric pressure chemical vapor deposition (CVD) is a promising technique for the preparation of tungsten products with high purity, high density and almost unlimited thickness. The tungsten prepared by using the CVD method (CVD-W) usually has a columnar coarse grain microstructure with strong preferred orientations. Multi-step rolling at gradually decreased operating temperatures is an effective method to lower the ductile-to-brittle transition temperature in pure tungsten. So far, the microstructural evolutions of CVD-W during the multi-step rolling processing is still unclear. In this study, the microstructure evolution and texture development of CVD-W during multi-step rolling are investigated by the coupling of electron backscattering diffraction technique and full-field crystal plasticity finite element simulations. After multi-step rolling, the sample exhibits through-thickness texture gradient. A layered structure with elongated 〈100〉 // ND and 〈111〉 // ND grains is observed in the central region and Goss orientation mainly appears in the surface region. Crystal plasticity finite element simulations show that {001}〈110〉 is a stable orientation under the plane strain compression, which is realized by the rotation of {100} grains around ND. Meanwhile, the shear flow promotes the rotation of {100} grains around TD, leading to the formation of 〈111〉 // ND orientation. 〈110〉 // ND orientation is observed near the shear bands, which is generated through the rotation of {100} grains around <100> // RD axis. The rolled CVD-W exhibits crystallographic orientation dependent recrystallization behavior, which is related to the orientation dependent distortion energy generated in the rolling processing. Our studies provide fundamental insights into the microstructure evolution and texture development of CVD-W under the multi-step rolling processing.

The GeSe/SnSe heterojunction photodetector with self-powered characteristics and high infrared response performance

We present a GeSe/SnSe van der Waals heterojunction fabricated using the wet transfer technique. GeSe and SnSe were synthesized via a low-temperature and atmospheric-pressure chemical vapor deposition method. The GeSe/SnSe heterostructure photodetector demonstrates remarkable rectification characteristics, boasting a rectification ratio of 102, along with an exceptionally low dark current, indicating minimal power consumption. Furthermore, it exhibits a broad optical response, spanning from the visible spectrum (450 nm) to the near-infrared (1064 nm). Under 808 nm laser illumination and reverse bias, the device achieves a responsivity of 19.82 A/W, a detectivity of 4.74 × 109 Jones, and an external quantum efficiency of 3048.32%. Notably, the GeSe/SnSe heterojunction photodetector also exhibits self-powered characteristics, with a responsivity of 0.11 mA/W and a detectivity of 5.44 × 106 Jones at zero bias voltage, accompanied by a fast response time of 23/61 ms (rise/fall). These findings underscore the effectiveness of the GeSe/SnSe heterojunction as a strategy for near-infrared photodetectors to simultaneously achieve low power consumption, high photoresponsivity, and self-powered photodetection, which is promising for optoelectronic device applications.

Two-dimensional GeS synthesized by one-step space-confined APCVD and its self-powered photodetector

Germanium sulfide (GeS) is a notable two-dimensional (2D) layered material that has gained attention across various research domains. However, challenges remain in realizing large areas of high-quality 2D GeS, despite the efforts made. Recently, we have successfully synthesized rectangular 2D single-crystal GeS flakes with a thickness of about 52 nm and a lateral length of 100 μm by one-step space-confined atmospheric pressure chemical vapor deposition (APCVD) using sulfur and germanium powders as raw materials. There is a direct relationship between the area size and the growth time. The further prepared GeS device has good photoresponsivity in the visible range. At 532 nm, it includes a responsivity of 40 mA/W, a detectivity of 8 × 108 Jones and a fast response time of 199 ms. In addition, the GeS device exhibits p-type conductive behavior and a unique self-powered effect. After prolonged storage, the GeS photodetector still exhibits good and stable photoswitching characteristics.

Facet-Dependent Interfacial Charge Transfer between T-Phase VS2 Nanoflakes and Rutile TiO2 Single Crystals.

The hybridizations of two-dimensional (2D) metallic materials with semiconducting transition metal oxides (TMOs) register attractive heterojunctions, which can find various applications in photostimulated circumstances. In this work, we developed an ambient-pressure chemical vapor deposition method to directly grow T-VS2 on atomically smooth rutile TiO2 single crystals with different terminations and thus successfully constructed a heterojunction model of VS2/TiO2 with a well-defined clean interface. Detailed measurements with Kelvin probe force microscopy revealed the facet-dependent charge transfer occurring at the VS2/TiO2 interfaces, seeing variations not only in the amount and direction of the transferred electrons but also in the photoinduced surface potential changes and the dynamics of photogenerated charge carriers under ultraviolet irradiation. Interestingly, ultrathin T-VS2 was found with considerable magnetism at room temperature, disregarding the charge exchange with the TiO2 substrates. These results may bring deep insights into the photoinspired functionalities of the hybridized system combining metallic transition metal dichalcogenides and TMO materials.

Synthesis and Characterization of SiO2-Based Graphene Nanoballs Using Copper-Vapor-Assisted APCVD for Thermoelectric Application.

This study describes a method by which to synthesize SiO2-based graphene nanoballs (SGB) using atmospheric pressure chemical vapor deposition (APCVD) with copper vapor assistance. This method should solve the contamination, damage, and high costs associated with silica-based indirect graphene synthesis. The SGB was synthesized using APCVD, which was optimized using the Taguchi method. Multiple synthesis factors were optimized and investigated to find the ideal synthesis condition to grow SGB for thermoelectric (TE) applications. Raman spectra and FESEM-EDX reveal that the graphene formed on the silicon nanoparticles (SNP) is free from copper. The prepared SGB has excellent electrical conductivity (75.0 S/cm), which shows better results than the previous report. Furthermore, the SGB nanofillers in bismuth telluride (Bi2Te3) nanocomposites as TE materials exhibit a significant increment in Seebeck coefficients (S) compared to the pure Bi2Te3 sample from 109 to 170 μV/K at 400 K, as well as electrical resistivity decrement. This approach would offer a simple strategy to improve the TE performance of commercially available TE materials, which is critical for large-scale industrial applications.

NaCl-assisted chemical vapor deposition growth of MoSe2 and MoSe2/h-BN heterostructure

As a typical two-dimensional (2D) transition metal dichalcogenides (TMDCs), MoSe2 has attracted lots of interest due to its electronic and optical properties in recent years. The controllable synthesis of 2D MoSe2 and its heterostructure is of considerable importance for achieving diverse applications. Herein, we realized the controlled growth of MoSe2 by atmospheric pressure chemical vapor deposition (APCVD) method through using NaCl as the promoter. Raman and photoluminescence (PL) spectroscopy have been used to investigate the optical properties of MoSe2 domains with different layers. The dependence of structures on synthetic parameter is systematically investigated by tuning the growth conditions. On this basis, the monolayer MoSe2 was constructed on CVD-grown hexagonal boron nitride (h-BN) by an all-CVD approach. Detailed characterizations indicate that MoSe2 deposited on h-BN exhibits improved optical properties as compared to those on SiO2/Si. Our results could enrich the understanding for growth of TMDCs, advocating further investigation of their intrinsic properties and a variety of device applications.

Influence of halogen precursors on the growth of InSb nanostructures

The present work highlights the role of halogen compounds in modifying the shape of the InSb nanostructures, while maintaining a high crystalline quality of the nanostructures. One-dimensional (1D) nanowires (NWs) and two-dimensional (2D) nanoplatelets (NPLs) were synthesized by ambient pressure chemical vapor deposition. Our experimental results suggest that at a critical growth temperature of 512 ∘C, InSb NWs grow by the traditional vapor–liquid–solid growth mechanism when gold (Au) nanoparticles are used to initiate growth on an InSb film. The resulting NWs were found to have a cylindrical or tapered shape, were of high crystalline quality, and had stoichiometric composition. In the presence of halogen precursors, a change in morphology was observed and the resulting nanostructures were 2D NPLs and faceted NWs. Using existing models of crystal growth and concepts of volume, surface and edge energies, the experimental results are explained on the basis of chlorine atoms adsorbed on the wide or narrow facets of a nanocrystal, initiating nucleation and facilitating NPL or faceted NW formation. The incorporation of the chlorine atoms add a new degree of freedom to CVD synthesis of nanostructures and the results are promising for the controlled growth of novel 1D and 2D nanostructures for nano-electronic devices.

Niobium doping of CVD-WS2 monolayers using solid precursors with and without salt-KBr as a catalyst: A comparative study

The in situ doping of tungsten disulfide (WS2) monolayers with Niobium (Nb) atoms was obtained through the atmospheric pressure chemical vapor deposition (APCVD) method by controlling the Nb2O5 and WO3 precursors mass ratios. Samples were prepared employing the same growth parameters with and without the use of KBr salt as a catalyst. In both cases, the Nb incorporation quenches the luminescence intensity of the doped samples, and it depends on the Nb2O5:WO3 mass ratio. X-ray photoelectron spectroscopy (XPS) measurements were performed, and the observed redshift at the Fermi level indicated p-type doping. Nb-doped WS2 monolayers synthesized without the use of the catalyst have lower defect density, as revealed by a careful Raman analysis, and are free of agglomerates on their monolayers’ basal plane. The use of KBr as the catalyst increases the average crystal size but also increases the disorder effects compared with samples prepared without the use of salt. The presence of agglomerates of impurities at the surface of doped samples was observed in samples prepared with the use of salt as a catalyst. The controlled synthesis of p-type WS2 with low defect density is essential for developing electronic and photonic devices based on WS2 material.

Magnetoresistance properties in nickel-catalyzed, air-stable, uniform, and transfer-free graphene

A transfer-free graphene with high magnetoresistance (MR) and air stability has been synthesized using nickel-catalyzed atmospheric pressure chemical vapor deposition. The Raman spectrum and Raman mapping reveal the monolayer structure of the transfer-free graphene, which has low defect density, high uniformity, and high coverage (>90%). The temperature-dependent (from 5 to 300 K) current–voltage (I–V) and resistance measurements are performed, showing the semiconductor properties of the transfer-free graphene. Moreover, the MR of the transfer-free graphene has been measured over a wide temperature range (5–300 K) under a magnetic field of 0 to 1 T. As a result of the Lorentz force dominating above 30 K, the transfer-free graphene exhibits positive MR values, reaching ∼8.7% at 300 K under a magnetic field (1 Tesla). On the other hand, MR values are negative below 30 K due to the predominance of the weak localization effect. Furthermore, the temperature-dependent MR values of transfer-free graphene are almost identical with and without a vacuum annealing process, indicating that there are low density of defects and impurities after graphene fabrication processes so as to apply in air-stable sensor applications. This study opens avenues to develop 2D nanomaterial-based sensors for commercial applications in future devices.

Investigation of Contact Resistivities on APCVD (p) Poly-Si for Fired Passivating Contacts

We investigate the properties of boron doped polycrystalline Si (poly-Si) deposited by atmospheric pressure chemical vapor deposition (APCVD) applied to fired passivating contacts (FPC), where no high temperature annealing takes place apart from the contact firing step. X-ray diffraction measurements show that the APCVD poly-Si is already partially crystallized directly after deposition and the crystallite size further increases during firing. Without metallization an implied open circuit voltage of up to 719 mV is achieved. Screen-printing with an Ag paste yields minimal contact resistivities of down to 1 mΩcm² at high firing temperatures. Furthermore, thicker poly-Si layers, accomplished by driving the same wafer multiple times through the APCVD system, generally correspond to lower contact resistivities for the FPC. This can partly be explained by an increasing crystallinity and conductivity during deposition due to the higher thermal budget during deposition for thicker layers as well as by a larger contact area for thicker poly-Si layers. Scanning electron microscopy on sample cross-sections show that almost the entire poly-Si layer is covered with Ag crystallites at high firing temperatures. For lower temperatures a lower density of Ag crystallites in the poly-Si is visible. Both findings hold for planar and textured surfaces.

Investigation on the Long-Term Stability of AlOx/SiNy:H and SiNy:H Passivation Layers During Illuminated Annealing at Elevated Temperatures

Most crystalline Si based solar cells, e.g. passivated emitter and rear cells, rely on SiNy:H and AlOx/SiNy:H passivation layers. In this work, the long-term behavior of minority charge carrier lifetime in such symmetrically passivated samples during illuminated annealing at elevated temperatures is investigated by means of photoconductance decay based lifetime measurements, corona charging and capacitance voltage measurements. Thereby, AlOx layers, which are known to reduce H in-diffusion due to their barrier properties, deposited by atmospheric pressure chemical vapor deposition as well as by atomic layer deposition were considered enabling a comparison of different deposition techniques. The frequently published behavior of the bulk related degradation could be confirmed and the qualitative correlation between maximum defect density and the changing total amount of H in the Si bulk due to the barrier properties of the individual layers dielectric layers could be shown. Furthermore, for the subsequently observed degradation accelerated by a treatment at higher temperatures, literature indicates degradation to be caused by surface related degradation. Investigations on field effect passivation during degradation by means of corona charging and CV measurements showed a large drop in fixed negative charges in the passivation layer stacks.

Investigation of structural, phonon modes and electronic environment of GaP:Si nanostructure thin films

In the present work, silicon-doped gallium phosphide (GaP:Si) nanostructure thin films were deposited using atmospheric pressure chemical vapor deposition (APCVD) with Si doping wt.% varied from 0.5 to 2.5 wt%. AFM revealed the roughness varied from 5.612 to 7.337 nm and the wire-like shape was changed to agglomerated shape with the increase in Si doping from 0.5 to 2.5 wt% in GaP:Si thin films. Fractal dimension varied from 1.931 to 2.519 with an increase in Si doping wt.%. The d-spacing, lattice constant (a), crystallinity fraction and crystallite size (D) increased with an increase in Si wt.% in the GaP:Si films. The dislocation density and microstrain of GaP:Si varied from 0.020 to 0.001 ( × 1014 1/m2) and −0.0052 to 0.0072 respectively due to thermal stress and defect distribution. The TO and LO phonon lifetime varied from 0.41 to 0.33 ps and 0.45 to 0.27 ps respectively for GaP:Si thin films.

TiO2 Thin Films by Atmospheric Pressure Chemical Vapor Deposition for Rear Surface Passivation of p-PERT Solar Cells

TiO2 Thin Films by Atmospheric Pressure Chemical Vapor Deposition for Rear Surface Passivation of p-PERT Solar Cells

Study on the growth mechanism of monolayer and few-layer hexagonal boron nitride films on copper foil.

During the process of synthesizing h-BN on Cu foil via chemical vapor deposition (CVD), low-pressure CVD (LPCVD) typically synthesizes monolayer h-BN films, whereas atmospheric pressure CVD (APCVD) yields few-layer h-BN films. Herein, a growth mechanism for monolayer and few-layer h-BN on Cu foil is proposed using first-principles calculations: Cu(111) passivated h-BN hinders the diffusion of B and N atoms at the subsurface of Cu(111), preventing sufficient transportation of B and N atoms to the existing h-BN layer, thereby leading to the formation of monolayer h-BN in LPCVD. For APCVD, the edges of h-BN are passivated by H, which decreases the barrier energy for the diffusion of B and N atoms on the Cu(111) subsurface, and B and N atoms can easily migrate from the subsurface of Cu(111) to its surface, resulting in the nucleation of h-BN between the existing h-BN and Cu(111), and leading to the formation of few-layer h-BN films. This work provides a theoretical basis at the atomic scale for further understanding the growth of monolayer and few-layer h-BN films on Cu foil.

Modification of the Physical Properties of SnO2 Thin Films for Optoelectronic Applications Combining Rapid Atmospheric Pressure Chemical Vapor Deposition Technique and Heat Treatment

Herein, the influence of the postannealing process on tin oxide thin films deposited by chemical vapor deposition in the atmospheric pressure technique is investigated. The as‐deposited films are heat treated under different environments, including ambient air, oxygen, nitrogen, and vacuum. The postannealing process is performed at 600 ºC for 60 min. It is worth mentioning that no sign of damage or destruction has been observed in samples after the annealing process. The structural characterization of the thin films is studied using X‐ray diffraction analysis, which reveals an increase in the peak intensities after annealing. Field‐emission scanning electron microscope surface morphology shows that heat‐treated tin oxide thin films have larger grain sizes than as‐deposited ones. Hall effect analysis shows a significant reduction in sheet resistance and a substantial increase in mobility after postannealing. The ultraviolet–visible–near‐infrared transmittance spectra in the 300–3000 nm range exhibit near 80% transparency in the visible region after annealing. Furthermore, the estimated bandgap values increase from 2.95 to 3.08 eV as the carrier concentration increases after the heat treatment. The results suggest the superiority of the oxygen‐annealed sample over the other annealing environments.

Numerical and experimental investigation of the effect of side injectors on the deposition rate near the wafer edge during atmospheric pressure chemical vapor deposition

In this study, the effect of side injection on the deposition rate near the wafer edge is investigated through a numerical simulation and in experimental studies. The main purpose is to maintain the uniformity of the silicon epitaxial layer in region of the wafer edge. The results indicate that the deposition rate near the wafer edge can be changed when the momentum of the jet is sufficient to push the streamlines originating from the side injector to touch the wafer edge. The jet momentum can be increased by increasing the inlet velocity and the Trichlorosilane (TCS) mass fraction of the side injector. The deposition rate in the wafer edge region increases when the TCS mass fraction is higher. It is clear that the momentum of the side injector jet determines the region affected, while the TCS mass fraction changes the deposition rate in the affected region. Both experimental and numerical results show that with a suitable jet velocity and TCS mass fraction, the deposition rate in the edge region can be tuned while maintaining almost the same deposition rate in the central region of the wafer. The non-uniformity caused by a sudden drop in the deposition rate in the edge region of the wafer without the use of side injector can be significantly improved by installing a side injector and applying the proper operating conditions. The numerical results are in good agreement with the experimental ones.

Bipolar Resistive Switching in 2D MoSe2 Grown by Atmospheric Pressure Chemical Vapor Deposition.

Two-dimensional (2D) transition metal dichalcogenides (TMDCs) are highly promising nanomaterials for various electronic devices such as field-effect transistors, junction diodes, tunneling devices, and, more recently, memristors. 2D MoSe2 stands out for having high electrical conductivity, charge carrier mobility, and melting point. While these features make it particularly appropriate as a switching layer in memristive devices, reliable and scalable production of large-area 2D MoSe2 still represents a challenge. In this study, we manufacture 2D MoSe2 films by atmospheric-pressure chemical vapor deposition and investigate them on the atomic scale. We selected and transferred MoSe2 bilayer to serve as a switching layer between asymmetric Au-Cu electrodes in miniaturized crossbar vertical memristors. The electrochemical metallization devices showed forming-free, bipolar resistive switching at low voltages, with clearly identifiable nonvolatile states. Other than low-power neuromorphic computing, low switching voltages approaching the range of biological action potentials could unlock hybrid biological interfaces.

Growth of large edge length two-dimensional WS2 using a custom 12-zone atmospheric pressure chemical vapor deposition system

Transition metal dichalcogenides like WS2 exhibit technologically relevant optoelectronic properties. In this work, we report on the growth of two-dimensional tungsten disulfide of various geometries and morphologies using a custom atmospheric pressure chemical vapor deposition system. In triangular flakes, a maximum edge length of ∼110 μm (for multilayer) and ∼60 μm (for monolayer) was observed optically. Energy dispersive x-ray analysis yielded a W:S ratio close to a 1:2 stoichiometry. Two sets of intensity ratios (2LA(M)A1g), derived from Raman measurements, were found: ∼2.15 and ∼0.56, corresponding, respectively, to monolayer and multilayer growth of WS2. Photoluminescence measurements yield peaks at ∼640 and ∼660 nm, with the former peak (assigned to monolayer growth) exhibiting a ∼20-fold enhancement with respect to the latter (multilayer growth), suggesting a radiatively more efficient direct bandgap. It is expected that the process will lead to advancements in the growth of large-area two-dimensional transition metal dichalcogenides for device applications.