CVD Technique Research Articles

Carbon coated iron pyrite (C–FeS2) photo-electrode for photo-electrochemical water splitting

In this paper, we present fabrication of ‘FeS2’ and carbon coated FeS2 (C–FeS2) photo-electrodes and demonstrated that coating of carbon on FeS2 significantly enhanced photo-electrochemical properties. The hydrothermal method has been adopted for the synthesis of FeS2 and carbon coating on FeS2 was achieved by CVD technique. The materials are subsequently characterized using X-ray diffraction, Raman spectroscopy and Field enhanced scanning electron microscope (FESEM) techniques for phase identification and morphological studies, respectively. The photo-electrochemical measurements revealed significant enhancement in the current density from ∼2 to 3.7 mA/cm2 (∼1.8 times higher) for C–FeS2 in comparison to the FeS2 photo-electrode under visible light. The enhancement in FeS2 after carbon coating has been attributed to reduction in recombination of photo generated charge carriers, enhancement in the band bending and lowering the charge transfer resistance at the semiconductor/electrolyte interface. To date, very few studies have been reported on FeS2 based composites for water splitting applications and use of carbon coating can be a novel approach for developing efficient solar to hydrogen conversion devices. The mechanism for the photocurrent enhancement was supported by Mott-Schottky and electrochemical impedance spectroscopy measurements.

Plasmonic Au3Cu Ordered Nanocrystals Induced Phase Transformation in 2D‐MoS2 for Efficient Hydrogen Evolution

AbstractThe synthesis of ordered gold‐copper (Au3Cu) alloy nanocrystals (≈10 nm) is reported and used in the semiconductor (2H) to metallic (1T) phase transformation of an atomically thin large‐area 2D‐MoS2 grown via CVD technique. The ordered Au3Cu nanocrystals are dispersed over 2D‐MoS2, and the phase transformation is confirmed via Raman spectroscopy followed by X‐ray photoelectron spectroscopy (XPS), while the surface properties of the Au3Cu/2D‐MoS2 is determined by the XPS valence band analysis and ultra‐violet photoemission spectroscopy (UPS). By comparing overpotential and Tafel slopes for Hydrogen Evolution Reaction (HER), a decrease is observed in overpotential by 83.2 mV and Tafel slope by ≈58.25 mV per decade for Au3Cu/MoS2 on light irradiation. This electrocatalytic enhancement of Au3Cu/MoS2 refers to the transformation of semiconducting 2D‐MoS2 to metallic phase under light illumination, thereby altering the surface electronic structures, improving carrier concentrations, lowering the valence band edge, and lowering the free energy of H* adsorption/desorption. Density functional theory (DFT) calculations, along with other surface characterizations, further illustrate that the ordered nanocrystal‐induced phase transformation in 2D‐MoS2 leads to a more durable metallic characteristic, thus, enhancing the surface electrical conductivity, reducing surface potential and Gibbs free energy, and improving the kinetics of photoelectrocatalytic performance of the hybrid structure.

Nanocatalysis MoS2/rGO: An Efficient Electrocatalyst for the Hydrogen Evolution Reaction.

In this study, a systematic investigation of MoS2 nanostructure growth on a SiO2 substrate was conducted using a two-stage process. Initially, a thin layer of Mo was grown through sputtering, followed by a sulfurization process employing the CVD technique. This two-stage process enables the control of diverse nanostructure formations of both MoS2 and MoO3 on SiO2 substrates, as well as the formation of bulk-like grain structures. Subsequently, the addition of reduced graphene oxide (rGO) was examined, resulting in MoS2/rGO(n), where graphene is uniformly deposited on the surface, exposing a higher number of active sites at the edges and consequently enhancing electroactivity in the HER. The influence of the synthesis time on the treated MoS2 and also MoS2/rGO(n) samples is evident in their excellent electrocatalytic performance with a low overpotential.

Investigation of structural and optical properties of Mg doped ZnS thin films prepared by Mist-CVD technique: Experimental and theoretical aspects

In the present study, undoped and magnesium (Mg)-doped zinc sulfide (ZnS) thin films were prepared using the low-cost Mist CVD technique on a soda-lime glass substrate in a reactor chamber maintained at a high temperature of 450 °C ± 10 °C. The structural, vibrational, chemical compositional, morphological, optical and electric characteristics of the prepared Zn1-xMgxS thin films were studied using X-ray diffraction (XRD), Raman spectroscopy, energy dispersive spectrometer (EDS), scanning electron microscopy (SEM), photoluminescence emission (PL), atomic force microscopy (AFM) analysis, and Hall effect measurements. The aim of the present work is to examine the effect of incorporation of Mg into ZnS thin films matrix. XRD and Raman spectroscopy investigations confirmed the formation of polycrystalline micro structured films. The presence of Zn, S, and Mg elements was confirmed by EDS Analysis. The growth of the surface roughness of the films with increasing Mg content, as well as the crystalline size lead to a higher carrier concentration (5.103 × 1018 cm−3), and lower resistivity of the thin films (5.021 × 10−3 Ω cm). Furthermore, DFT investigation of the electronic properties using the GGA/PBE + U functional provides a detailed explanation of the band structure and confirms the band gap reduction after doping wurtzite ZnS with Mg (12 at.%). Therefore, the outcome of this of this study might provide an experimental and theoretical background for future research on Mg-doped ZnS.

Fabrication of a-Ga2O3:Sn/a-Cr2O3/a-Al2O3 heterostructure by mist CVD and HVPE

Corundum-structured chromium oxide (a-Cr2O3), exhibiting p-type conductivity, is a highly attractive candidate for forming high-quality p-n heterojunctions with a-Ga2O3. Two CVD growth techniques were employed in the fabrication of the heterostructure. A ~ 0.2-micron a-Cr2O3 layer was grown on a (0001) sapphire substrate using mist CVD at 800 °C. It possesses high morphological homogeneity and low roughness, which is acceptable for further epitaxial processes. Subsequently, Sn-doped a-Ga2O3 with a thickness of ~ 1.5 µm was grown on the a-Cr2O3 layer using HVPE at 500 °C. The feasibility of fabricating this heterostructure with the specified layer thickness and acceptable surface morphology using CVD techniques has been demonstrated

Fabrication of highly sensitive visible photodetector based on SnS2 Terrazzo-like structure for weak signal detection

Chemically inert and van der Waal-structured tin-disulfide (SnS2) has become a potential candidate for optoelectronics due to its ultra-sensitivity and high performance resulting from high light absorption coefficient and thickness-dependent electrical properties. We report the facile synthesis of SnS2 Terrazzo-like structure using the CVD technique. A highly responsive MSM SnS2-based device is designed to detect optical radiation ranging from 300 to 800 nm. The fabricated device exhibits excellent responsivity (external quantum efficiency) of 2240 mAW−1 (522%) under 532 nm wavelengths for a 5 μW optical signal. The other merits, like detectivity and noise equivalent power, are 1.4 × 1010 Jones and 2.6 × 10−12 WHz−1/2, respectively, with a linear dynamic range (LDR) of ∼41 dB. The low LDR plays a vital role in evaluating light intensity from the corresponding generated photocurrent. The weak optical signal detection capability of SnS2-based photodetector paves the way for its application in astronomy, communication systems, and biomedical imaging.

Influence of Deposition Time on Titanium Nitride (TiN) Thin Film Coating Synthesis Using Chemical Vapour Deposition

Titanium nitride (TiN) thin film coatings were grown over silicon (p-type) substrate using the atmospheric pressure chemical vapour deposition (APCVD) technique. The synthesis process was carried out to evaluate the effect of deposition time on the physical and mechanical characteristics of TiN coating. Thin films grown over Si substrate were further characterised to evaluate the morphological properties, surface roughness and mechanical properties using a scanning electrode microscope (SEM), atomic force microscopy (AFM) and nanoindentation, respectively. EDS equipped with SEM showed the presence of Ti and N elements in considerable amounts. TiN morphology obtained from the SEM test showed small-sized particles on the surface along with cracks and pores. AFM results revealed that by increasing the deposition time, the surface roughness of the coating also increased. The nanomechanical properties such as nanohardness (H) and Young’s modulus (E), etc., evaluated using the nanoindentation technique showed that higher deposition time led to an increase in H and E. Overall, it was observed that deposition time plays a vital role in the TiN coating deposition using the CVD technique.

Growth of few layers of WS2 thin films by pulsed laser deposition

Tungsten disulphide (WS2) is a notable material among 2D transition metal dichalcogenides (TMDCs) for the next generation of optoelectronic devices. Therefore, the fabrication of good quality thin films with controlled growth parameters is essential for device level applications. Pulsed laser deposition (PLD) can be replacement for the conventionally used CVD technique. We report the growth of few layers of 2D WS2 thin films on Si/SiO2 substrates by PLD. A sintered WS2 target was ablated at room temperature using the fourth harmonics of Q-switched Nd:YAG laser (λ = 266 nm, pulse width = 10 ns) followed by a post deposition annealing at different temperatures. Deposited films were characterized by RAMAN, Atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). Controlled growth of few layers of WS2 thin films can make a remarkable change in the development of novel optoelectronic devices.

Graphene: The Revolutionary 2D Material

Graphene is considered as the initial laboratory-made 2D material which initiated a new revolution in the field of materials science. Since its discovery, lots of researchers have discovered various properties and tested it for many potential applications. The present report discusses a brief overview of graphene, mainly concentrating on the structure, synthesis, and applications of graphene. The mechanical exfoliation and CVD techniques for the synthesis of graphene. Some of the applications of graphene in the field of flexible electronics, sensing, and photovoltaic are reviewed in this report

Non-toxic precursor for chemical vapor deposition of borophene on Cu(111) surface

In this work, conventional CVD technique, which had already been available in industries and laboratory, was proposed to utilize as an alternating method to synthesize borophene. This approach used the boron and diboron trioxide as boron source, Therefore, there was no extra cost for the toxic waste treatment. In addition, by blending their adjusted similar size into homogeneous mixture, it had demonstrated to improve the efficiency of overall process, and was able to achieve thin film layer of borophene with approximately 500 × 300 nm2 and about 3 nm thick. The metallic boron (B1s (Metal)) and crystalline systems in both single boron form (α-B) of borophene and copper-boron alloy form (β-B) were present. This report of facile borophene fabrication would potentially open up the feasibility of synthesizing methods in similar systems that will help the further application and development of 2-dimensional materials.

CVD Synthesis of Graphitic Carbon Nitride Films from Melamine

A CVD technique has been developed for the deposition of homogeneous graphitic carbon nitride films on silicon and quartz glass substrates using melamine as a precursor. Layer-by-layer deposition at low precursor loadings makes it possible to deposit a film up to 1.4 µm thick; however, it is possible to achieve large thicknesses by multiple repetition of the experimental cycle. The effect of synthesis parameters on the surface morphology of deposited layers has been studied by scanning electron microscopy. The chemical composition and structure of graphitic carbon nitride films are confirmed by a set of spectroscopic methods and X-ray diffraction. The optical properties have been studied using diffuse reflectance spectroscopy. Scanning electron microscopy and X-ray diffraction analysis have shown that films deposited at temperatures of 550–650°C have a layered microcrystalline structure. The bandgap of the obtained samples was 2.76–2.93 eV.

Synthesis of B[sbnd]C[sbnd]N nanotubes by CVD method and their electrochemical performance towards supercapacitors

Energy transition to renewables necessitate efficient energy storage systems such as super capacitors. Hence Boron carbon nitride (BCN) nanotubes were synthesized using CVD technique at 800, 900 and 1000 °C, using N-Dimethyl formamide and trimethyl borate as precursors and ferrocene as the catalyst. Increase in CVD temperature from 800 to 1000 °C increased the conductance and specific capacitance. Supercapacitor device fabricated with BCN synthesized at 1000 °C showed specific capacitance of 68.125F/g, energy density of 1.51 Wh/Kg, energy efficiency of 53.17 % and power density of 100 W/Kg. It retained 73.6 % of initial capacitance for 1000 charge/discharge cycles.

In Ukrainian

There are influence of Fe/C as polymer composition component studied, for use as PCM of special purposes, on structure, mechanical, and electrophysical properties, when regarding to goal for usage possibilty establishing for carbon and iron-containing material of Fe/C, and last was synthesized with CVD technique on iron-containing catalyst. There were PEHD- and nano-disperse addition of Fe/C - based composite films prepared, with hot pressing method, of mass equation in 42/58 for Fe/C, and addition content in PCM of 1 – 15 % mass. Then, there were films oriented with thermogradient hot stretching.. It is established, that Fe/C presence is decreasing for maximal stretching value λmax, for pure HDPE, to 5 for highly-loaded compositions. There are addition’s influence on PE phase transitions in composite films: when at low addition’s contents, then, there are forming more perfect crystallic structure of more larger and uniform crystallites by dimensions, but, at those higher - less uniform one. It is established, that specific saturation magntetization values (σs ), for composite and non-oriented films, are increasing, from 1.1 Gs∙cm3/g for film of 5 %mass. of Fe/C, to 5.6 Gs∙cm3/g (film of 15 % mass. Fe/C). There are cohertzitive power values, changing dependently from Fe/C comtent, from 97 to 99 E. It is founded, that electrical conductivity values (s), at frequency of 1 kHz , is absent, for non-oriented film of 1 %mass. Fe/C (σ=9,4∙10-11 Om-1cm-1), but, for those non-oriented ones of 5- 15 %mass. are 2,4∙10-5 ‒ 1∙10 Om-1cm-1. Where are orientational stretching actions, there are decreasing in electrical conductivity values - σ=1,4∙10-12‒2,7∙10‑1 Om-1cm-1 for films of λ=5‒6. Those films, when at own intrinsic structure-mechanical, electrical and magnetic properties, depending of Fe/C content, are perspective ones as magnetic, anti-static and electrical conductive materials.

Interaction study of molten uranium with multilayer SiC/Y2O3 and Mo/Y2O3 coated graphite

Graphite crucibles are used for melting uranium and its alloys in VIM furnace. Various coating materials namely Al2O3, ZrO2, MgO etc. are applied on the inner surface of the crucibles using paint brush or thermal spray technique to mitigate U-C interaction. These leads to significant amount of carbon pick-up in uranium. In this study, the attempts are made to develop multilayer coatings comprising of SiC/Y2O3 and Mo/Y2O3 on graphite to study the feasibility of minimizing U-C interaction. The parameters are optimized to prepare SiC coating of about 70μm thickness using CVD technique on graphite coupons and subsequently Y2O3 coating of about 250μm thickness using plasma spray technique. Molybdenum and Y2O3 layers were deposited using plasma spray technique with 70μm and 250μm thickness, respectively. Interaction studies of the coated graphite with molten uranium at 1450°C for 20 min revealed that Y2O3 coating with SiC interlayer provides physical barrier for uranium-graphite interaction, however, this led to the physical separation of coating layer. Y2O3 coating with Mo interlayer provided superior barrier effect showing no degradation and the coatings remained intact after interaction tests. Therefore, the Mo/Y2O3 coating was found to be a promising solution for minimizing carbon pick-up during uranium/uranium alloy melting.

Growth of MoS2 Thin Films Using the Two-step Approach

In this study, MoS2 thin films were grown using two-step approach, which is based on employing both PVD and CVD techniques. The films were obtained initially by sputtering 1nm Mo film in the PVD system and followed by sulphurization of the film in CVD at 700 oC. The grown films were optimized employing different sulphurization times. The main difference in our study from the current literature is using preheated CVD furnace (700 oC) ahead of sulphurization. The films quality are then investigated using Raman and Photoluminance spectrometer as well as AFM measurements. The Raman spectrums indicate that two characteristic vibration modes of 2H-MoS2 phase were observed in all samples, however, vibration modes of 1T-MoS2 phase were also observed in some films at low sulphurization time. These results were also in line with PL measurements that confirm the direct band transition of the MoS2 films. The surface topography of the films were investigated by AFM for MoS2 films obtained by the sulfurization of 1 nm-thick Mo film in 15 minutes at 700 oC which shows MoS2 crystals in triangle shape

A template approach to designing and synthesizing hierarchical porous carbon with tri-modal pore structure and its application for high performance oxygen reduction electrocatalyst support

A new type of hierarchical porous carbon with tri-modal pore structure (Tri-PC), i.e., ordered micropores (1.3 nm), uniformly distributed mesopores (2–10 nm) and “earthworm-shaped” mesochannels (with a diameter of 20 nm) running through the whole particle was successfully realized via a novel and facile template approach, in which zeolite Y was firstly gone through a pore expansion using oxalic acid-ammonium fluoride mixture to prepare hierarchical porous zeolite. The hierarchical porous zeolite was subsequently used as the template to catalytically grow carbon via CVD technique. Tri-PC was then obtained after the removal of the template. The as synthesized Tri-PC showed great potential as the catalyst support. We evaluated the ORR catalytic activity of Tri-PC supported platinum nanoparticles (Pt/Tri-PC) in alkaline electrolyte, which exhibits 20 mV higher onset potential (0.95 V) and 30 mV higher half-wave potential (0.87 V) than commercial 10 wt% Pt/C catalyst. Meanwhile, the electrochemical impedance spectroscopy measurement showed that Pt/Tri-PC had lower charge transfer resistance. High performance benefits from a collaborative hierarchical architecture. Micropores offer a large specific surface area and sufficient active sites, mesopores increase the accessibility of active sites and shorten the diffusion path of fuels and products, and mesochannels further enhance the connectivity of the entire pore network. The present work highlights the significance of the hierarchical porous structure for enhancing the catalytic performance of catalysts and suggests that Tri-PC could be used as an advanced catalyst support in many fields.

Utilization of catalytically active metals in mining waste and water for synthesis of carbon nanotubes

This study presents the application of fine-grained precipitates from mine waters for the synthesis of carbon nanotubes. Experimental synthesis of carbon nanotubes was carried out on natural substrates taken from the Slovak mining localities Markušovce, Smolník and Poproč. The substrates were obtained from mining waste taken from the shore dark sediment settling ponds in Markušovce, from the water flowing out of the mine in Smolník and from the sediment collected from the mine of Poproč. The main components of the colloidal residues resulting from the extraction of ores are particles containing catalytically active metals. Microscopic analysis of nanocomposites synthetized in a hot filament chemical vapour deposition reactor shows that the sediments from all residues after ore mining have a high ability to catalyse the synthesis of carbon nanotubes. The combination of catalyst particles and co-catalyst plays an essential role in the formation of carbon nanotubes. • Precipitates from mining waste and water were used for catalyst preparation. • Colloidal residues are particles containing catalytically active metals. • Catalytically active metals are used for synthesis of carbon nanotubes and for nanocomposite formation by CVD technique. • Combination of catalyst particles and co-catalyst plays an essential role in the formation of carbon nanotubes and nanofibers.

Performance Analysis of n-ZnO/p-Si Heterojunction Diode as Function of Zinc Oxide Thin Films Thickness

The n-type Zinc oxide (n-ZnO) nanostructured thin films (TFs) with different thicknesses (211, 325, 433 and 552 nm) were grown onto glass substrates employing the CVD technique at atmospheric pressure. Deposited films were characterized by EDX spectroscopy attached with FE-SEM and XRD techniques to determine the influence of thickness on elemental compositions and crystalline structure of ZnO films, respectively. Also, ZnO TFs were deposited on the p-Si(111) substrates to form different structures of n-ZnO/p-Si heterojunction diodes and then I-V characteristics were studied in the dark. The electrical parameters of the diodes such as rectification ratio (RR), reverse saturation current (Is), ideality factor (), barrier height (b) and series resistance (Rs) were calculated from the I-V measurements. EDX spectra showed that these films were only made from Zn and O elements. XRD patterns presented that the ZnO films possess hexagonal wurtzite structure with preferred orientation along [002] direction. I-V characteristics of the heterojunction diodes revealed rectification behavior and depend on ZnO TFs thickness. Also, electrical parameters of diodes were affected by the prepared film's thickness. It was found that the crystalline structure of the films and electrical properties of diodes were improved with increasing the thickness of ZnO films. It is noted that the best heterojunction diodes were that prepared with thickness (552 nm), where possess lowest value of ideality factor (3.38) and a series resistance (0.84 k) with a highest rectification ratio (1517), compared with other structures. This study offers a simple model for fabricating diodes from semiconductor films.

Optimisation of cutting parameters in face milling of cryogenic treated 6061 aluminium alloy and effects on surface roughness, wear, and cutting temperatures

In addition to its usage in the defence industry, 6061 aluminium is prevalent in heavy industries like the aviation, shipbuilding and space industries. In this study, cryogenic processing was applied on the 6061-T651 aluminium alloy and the cutting inserts used, face milling procedures were carried out, and the effects of cutting parameters were examined. For the face milling procedure, cutting inserts with three different coatings (coated with TiN-TiCN-Al2O3 by CVD technique, coated with TiAlN-Nano by PVD technique, and coated with AlTiN by PVD technique), three different cutting speeds (250, 350 and 450 m min−1) and three different feed rates (0.15, 0.30 and 0.45 mm tooth−1) were used. The Taguchi method was used for experimental design and optimisation, and by selecting the Taguchi L9 (33) orthogonal array, nine experiments were carried out. Surface roughness and flank wear were measured after each experiment while cutting zone temperatures were measured during the experiments. The values obtained from the experiments were optimised and assessed with analysis of variance (ANOVA), three-dimensional plots, and the regression method. After the experiments, the lowest surface roughness, flank wear, and cutting temperatures were successfully optimised with the Taguchi method. The R2 values of the mathematical models for these three parameters were obtained as 100%.

PdO and PtO loaded WS2 boosts NO2 gas sensing characteristics at room temperature

In this work tungsten disulphide nanostructures loaded with platinum-oxide (PtO), or palladium-oxide (PdO) were grown directly onto alumina substrates. This was achieved using a combination of aerosol-assisted chemical vapour deposition (AA-CVD) method with atmospheric pressure CVD technique. At first, tungsten oxide nanowires loaded with either PtO or PdO nanoparticles were successfully co-deposited via AA-CVD followed by sulfurization at 900 °C in the next step. The morphological, structural, and chemical characteristics were investigated using FESEM, TEM, XRD, XPS and Raman spectroscopy. The results confirm the presence of PdO and PtO in the WS2 host matrix. Gas sensing attributes of loaded and pristine WS2 sensors were investigated, at room temperature, towards different analytes (NO2, NH3, H2 etc.). Both pristine and metal-oxide loaded WS2 gas sensors show remarkable responses at room temperature towards NO2 detection. Further, the loaded sensors demonstrated stable, reproducible, ultrasensitive, and enhanced gas sensing response, with a detection limit below 25 ppb. Additionally, the effect of ambient humidity on the sensing response of both loaded and pristine sensors was investigated for NO2 gas. The response of PtO loaded sensor considerably decreased in humid environments, while the response for pristine and PdO loaded sensors increased. However, slightly heating (at 100 °C) the sensors, suppresses the influence of humidity. Finally, the long-term stability of different sensors is investigated, and the results demonstrate high stability with repeatable results after 6 weeks of gas sensing tests. This work exploits an attractive pathway to add functionality in the transition metal dichalcogenide host matrix.