Wave Plasma Chemical Vapor Deposition Research Articles

Effect of TiO2 nanoparticle load on photoelectric properties of TiO2/VGs heterojunction

Preparation of Titanium dioxides loaded vertical graphene nanosheets (TiO2/VGs) composite films with heterojunctions by a multi-plasma combination method. Highly vertically oriented VGs were prepared by helicon wave plasma chemical vapor deposition (HWP-CVD), and TiO2 nanoparticles were deposited on VGs templates by ultra-high vacuum magnetron sputtering (UH-MS). By controlling the sputtering time of TiO2 nanoparticles to modulate the nanoparticle loading content. The morphology, structure, and photocatalytic performance of heterojunction TiO2/VGs composite films were investigated. The characterization results of morphology and structure show that the structure of VGs nanosheets is not altered by the increase of the deposited particle content, indicating that VGs have excellent mechanical properties as a template for TiO2 loading. As the deposition time of the TiO2 nanoparticles increases, the loading type progresses from epitaxial growth at the beginning to conformal deposition and eventually to gap-filling growth. Photoelectric performance tests showed that the heterojunctions were formed at the interface between TiO2 and VGs. The photovoltage test results show that the photogenerated carriers are effectively separated at the interface, and the nanosheets can promote the migration of separated electrons to the external circuit. The variation in photocurrent density shows a positive correlation with the number of TiO2 attachment sites and loading content on the surface of the VGs nanosheets.

Morphological changes of carbon thin films with nitrogen doping synthesized by microwave-excited surface wave plasma CVD

Nitrogen (N) doped graphene-based materials are of significant interest for various applications, such as, catalytic reactions, tribological energy generation, sensor devices and other electronic device applications. Most recently, the catalytic and noncatalytic growth of graphene structures at a low substrate temperature were explored by using the microwave-excited surface wave plasma (MW-SWP) chemical vapor deposition (CVD) technique. In this study, growth of carbon thin films is investigated by the MW-SWP CVD technique with nitrogen doping at various temperatures on the insulating substrates. It is obtained that partially graphitized carbon thin films can be obtained at a temperature as low as 150 °C on the quartz substrates. Interestingly, the morphological changes are observed with nitrogen doping and change in synthesis temperature for the carbon thin films grown by the MW-SWP CVD method. The partially graphitized carbon thin films form irregular morphologies at a lower temperature, while the morphology transforms with increase in temperature. At a certain growth temperature (500 and 700 °C), the carbon film shows granular morphology without addition of nitrogen, whereas the addition of nitrogen reduces the granular morphology and forming planar structures. Thus, these studies reveal the growth of carbon films with control morphology with respect to incorporation of nitrogen, which can be significant to develop carbon films and nanostructures for diverse fields of applications.

Effect of nitrogen doping on the structure and electrochemical properties of vertical graphene sheets prepared by HWP-CVD

3D nitrogen-doped vertically-oriented graphene nanosheets (3D N/VGs) were controllably prepared by helicon wave plasma chemical vapor deposition (HWP-CVD) employing argon, methane, and nitrogen by varying the N2 flow rate (RN2) without any catalyst and substrate heating during the growth. The effect of plasma gas phase species on the growth structure of N/VGs thin films was studied. The influence of nitrogen doping content on the structure and properties of VGs was analyzed. A growth model for the preparation of N/VGs by HWP-CVD was proposed. The results show that the elevated doping content of nitrogen atoms promotes enhanced CH4 dissociation and access to more H atoms, leading to an elevated nanosheet number density and a reduced growth rate. More excited N atoms could be embedded into the C vacancy to replace the missing C atom and restore the hexagonal network and increasing the nitrogen content. N/VGs with lower defect densities obtained with enhanced doping of nitrogen. The effective average distance between defects increases with nitrogen content, and the tunneling phenomenon is apparent, increasing resistance. Electrochemical performance tests showed that VGs with high nitrogen atomic content have higher specific capacitance and rate performance, up to 1340 μF/cm2 and 91.7%, respectively.

Polycrystalline Diamond Coating on Orthopedic Implants: Realization and Role of Surface Topology and Chemistry in Adsorption of Proteins and Cell Proliferation.

Polycrystalline diamond has the potential to improve the osseointegration of orthopedic implants compared to conventional materials such as titanium. However, despite the excellent biocompatibility and superior mechanical properties, the major challenge of using diamond for implants, such as those used for hip arthroplasty, is the limitation of microwave plasma chemical vapor deposition (CVD) techniques to synthesize diamond on complex-shaped objects. Here, for the first time, we demonstrate diamond growth on titanium acetabular shells using the surface wave plasma CVD method. Polycrystalline diamond coatings were synthesized at low temperatures (∼400 °C) on three types of acetabular shells with different surface structures and porosities. We achieved the growth of diamond on highly porous surfaces designed to mimic the structure of the trabecular bone and improve osseointegration. Biocompatibility was investigated on nanocrystalline diamond (NCD) and ultrananocrystalline diamond (UNCD) coatings terminated either with hydrogen or oxygen. To understand the role of diamond surface topology and chemistry in the attachment and proliferation of mammalian cells, we investigated the adsorption of extracellular matrix proteins and monitored the metabolic activity of fibroblasts, osteoblasts, and bone-marrow-derived mesenchymal stem cells (MSCs). The interaction of bovine serum albumin and type I collagen with the diamond surfaces was investigated by confocal fluorescence lifetime imaging microscopy (FLIM). We found that the proliferation of osteogenic cells was better on hydrogen-terminated UNCD than on the oxygen-terminated counterpart. These findings correlated with the behavior of collagen on diamond substrates observed by FLIM. Hydrogen-terminated UNCD provided better adhesion and proliferation of osteogenic cells, compared to titanium, while the growth of fibroblasts was poorest on hydrogen-terminated NCD and MSCs behaved similarly on all tested surfaces. These results open new opportunities for application of diamond coatings on orthopedic implants to further improve bone fixation and osseointegration.

Synthesis of Graphene and Related Materials by Microwave-Excited Surface Wave Plasma CVD Methods

Several kinds of chemical vapor deposition (CVD) methods have been extensively used in the semiconductor industries for bulk crystal growth, thin film deposition, and nanomaterials synthesis. In this article, we focus on the microwave-excited surface wave plasma CVD (MW-SWP CVD) method for growth of graphene and related materials. The MW-SWP CVD system consisting of waveguide, slot antenna, and dielectric windows is significant for generating high density plasma with low electron temperature, enabling low temperature growth of materials without damaging the surface of base substrates. The synthesis of graphene and hexagonal boron nitride (hBN) films has been achieved on metals, semiconductors, insulators, and dielectric substrates for application in photovoltaics, sensors, batteries, supercapacitors, fuel cells, and various other electronic devices. The details of the synthesis process for graphene films, vertically-oriented graphene, doped-graphene, and hBN films by the MW-SWP CVD method are summarized to understand the growth mechanism, which will enable further development of the plasma CVD process for material synthesis at a low temperature for industrial applications.

The effect of nitrogen concentration on the properties of N-DLC prepared by helicon wave plasma chemical vapor deposition

Nitrogen-doped diamond-like carbon (N-DLC) films were synthesized by helicon wave plasma chemical vapor deposition (HWP-CVD). The mechanism of the plasma influence on the N-DLC structure and properties was revealed by the diagnosis of plasma. The effects of nitrogen doping on the mechanical and hydrophobicity properties of DLC films were studied. The change in the ratio of precursor gas flow reduces the concentration of film-forming groups, resulting in a decrease of growth rate with increasing nitrogen flow rate. The morphology and structure of N-DLC films were characterized by scanning probe microscopy, Raman spectroscopy, and X-ray photoemission spectroscopy. The mechanical properties and wettability of N-DLC were analyzed by an ultra-micro hardness tester and JC2000DM system. The results show that the content ratio of N+ and is positively correlated with the mechanical properties and wettability of N-DLC films. The enhancement hardness and elastic modulus of N-DLC are attributed to the increase in sp3 carbon–nitrogen bond content in the film, reaching 26.5 GPa and 160 GPa respectively. Water contact measurement shows that the increase in the nitrogen-bond structure in N-DLC gives the film excellent hydrophobic properties, and the optimal water contact angle reaches 111.2°. It is shown that HWP technology has unique advantages in the modulation of functional nanomaterials.

Synthesis of Ag-decorated vertical graphene nanosheets and their electrocatalytic efficiencies

Herein we report the successful preparation of silver (Ag)-decorated vertically oriented graphene sheets (Ag/VGs) via helicon wave plasma chemical vapor deposition (HWP-CVD) and radiofrequency plasma magnetron sputtering (RF-PMS). VGs were synthesized in a mixture of argon and methane (Ar/CH4) by HWP-CVD and then the Ag nanoparticles on the prepared VGs were modified using the RF-PMS system for different sputtering times and RF power levels. The morphology and structure of the Ag nanoparticles were characterized by scanning electron microscopy and the results revealed that Ag nanoparticles were evenly dispersed on the mesoporous wall of the VGs. X-ray diffraction results showed that the diameter of the Ag particles increased with the increase in Ag loading, and the average size was between 10.49 nm and 25.9 nm, consistent with the transmission electron microscopy results. Ag/VGs were investigated as effective electrocatalysts for use in an alkaline aqueous system. Due to the uniquely ordered and interconnected wall structure of VGs, the area of active sites increased with the Ag loading, giving the Ag/VGs a good performance in the oxygen evolution reaction. The double-layer capacitance (C dl) of the Ag/VGs under different Ag loadings were studied, and the results showed that the highest Ag content gave the best C dl (1.04 mF cm−2). Our results show that Ag/VGs are likely to be credible electrocatalytic materials.

Laser-assisted doping of graphene for transparent conducting electrodes

In this work, we study the role of laser irradiation in the control of the doping processing for directly grown graphene using microwave surface wave plasma chemical vapor deposition (MW-SWP-CVD) on the glass substrates. Raman spectrum and X-ray photoelectron spectroscopy (XPS) were used to investigate the evolution of the structure of doping graphene as a function of laser irradiation. Also, the effect of laser on the morphology for doping graphene using AuCl3 was observed by field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), and optical microscope techniques. The gold particles were collected on graphene network wrinkles, which were resulted from laser irradiation. These gold network wrinkles were further used to enhance the electrical properties of the graphene, resulting in a significant reduction in sheet resistance and an improvement of its stability after storage in ambient air. The presented approach paves the way to design promising transparent conductive electrodes for optoelectronic devices such as light-emitting diodes (LED), photodiodes and solar cells.

<i>In-situ</i> diagnosis of Ar/CH<sub>4</sub> helicon wave plasma for synthesis of carbon nanomaterials

A variety of carbon-based thin films are prepared by self-developed helicon wave plasma chemical vapor deposition (HMHX, HWP-CVD) through changing the parameters of plasma discharge. The Ar/CH<sub>4</sub> plasma discharge is diagnosed <i>in situ</i> by Langmuir probe, emission spectroscopy and mass spectrometry. The carbon thin films are characterized by scanning electron microscopy (SEM) and Raman spectroscopy (Raman). The results show that under the given parameters, the plasma discharge modes are all helicon wave discharge modes. Under a given CH<sub>4</sub> flow rate, the energy distribution in the plasma is enough to dissociate the methane molecules and form carbon free radicals. The preparation of different carbon-based films is realized by adjusting the CH<sub>4</sub> fluence. The research result shows that when the plasma is rich in CH and H radicals, it is suitable for growing diamond-like carbon films. When the plasma is rich in C<sub>2</sub> radicals and less H, it is favorable for growing vertical graphene nanosheets. According to the results of plasma diagnosis and material characterization, the decomposition mechanism of methane molecules under the action of Ar helicon wave plasma (HWP) is proposed, and the growth model of carbon-based materials is established, the feasibility of Ar/CH<sub>4</sub>-HWP in the preparation of carbon-based nanomaterials is verified, which provides a reference for preparing the carbon-based materials by HWP-CVD technology.

Direct Synthesis of Graphene on Silicon at Low Temperature for Schottky Junction Solar Cells

Graphene thin films synthesized directly at low temperature (550˚C) on silicon substrate by microwave (MW) surface wave plasma (SWP) chemical vapor deposition (CVD) using the cover on substrates for avoiding plasma emission ultraviolet ray’s effect during film deposition. Analytical methods such as Raman spectroscopy, Transmission electron microscopy (TEM) and Scanning electron microscopy (SEM), four-point probe method, and JASCO V-570 UV/VIS/NIR spectrophotometer were employed to characterize the properties of the graphene films. Here, we report that it is possible to grow graphene directly on the silicon substrate (without using catalyst) due to the high radical density of MW SWP CVD. Furthermore, we fabricated graphene/silicon Schottky junction solar cells with an efficiency of up to 6.39%. Compared to conventional silicon solar cells, the fabrication process is greatly simplified; just graphene is synthesized directly on n-type crystalline Si substrate at low temperate.

Hydrogen-modulated Ar/CH4 HWP-CVD for fast preparation of multi-wall carbon nanotube arrays with high specific capacitance

Two-dimensional Multiwalled Carbon Nanotube arrays (MWCNTs) were prepared by a novel high-density helicon wave plasma chemical vapor deposition (HWP-CVD) at room temperature. Preliminary studies show that the MWCNTs prepared by this method has strong orientation and is perpendicular to the substrate surface, and exhibit a highly ordered array distribution. The addition of hydrogen can effectively improve the growth rate of MWCNTs and increase the aspect ratio. The height and aspect ratio of MWCNTs can be effectively increased with the increase of growth time. Electrochemical investigation indicated that MWCNTs have high specific capacitance (1.96 mF/cm−2) and excellent rate capability (81.6%).

The structure and properties of amorphous diamond-like carbon films deposited by helicon wave plasma chemical vapor deposition

The diamond-like carbon (DLC) films have been synthesized on silicon substrates by using chemical vapor deposition assisted with a high-density m=+1 mode helicon wave-excited plasma in Ar/CH4 gas mixtures. The structure and morphology of the DLC films are characterized by scanning electron microscopy (SEM), Raman spectroscopy and atomic force microscopy (AFM). The surface energies of the DLC films are calculated by the the Owens–Wendt–Rabel–Kaelble (OWRK) method. SEM results show that the surfaces of DLC films are found to be very uniform and dense, and the deposition rate of the film can reach up to 45 μm/h. The Young's modulus of the DLC films reaches the maximum (11 GPa) value at 25 sccm CH4 flow rate. With the increase of CH4 flow rate from 5 sccm to 35 sccm, the surface energy and friction coefficient of the DLC films decrease from 73.5 to 37.6 mJ m − 2 and from 0.56 to 0.25, respectively. It indicates that the deposited DLC films have good friction properties.The Young's modulus value is obtained here using AFM [48]. The results show that the Young's modulus increases from 4.1 to 10. 77 GPa, as the CH4 flow rate increases from 5 to 25 sccm. However, with further increasing the CH4 flow rate, the Young's modulus decreases gradually. This is consistent with the trend of sp3 bond content in Raman results. According to literature [49], CC sp3 bond of DLC films has a certain influence on Young's modulus. The result shows that the CC sp3 content reaches its maximum when the CH4 flow rate reaches 25 sccm. Moreover, the RMS results of DLC films show that the smoother the film is, the higher the Young's modulus is, likewise the rougher the DLC film is, the lower the Young's modulus is. It can be inferred that when DLC film is rough, the accumulated carbon polymer sp3 content in DLC film is low.

Fast preparation of vertical graphene nanosheets by helicon wave plasma chemical vapor deposition and its electrochemical performance

We investigated the growth process of vertically-oriented graphene nanosheets (VGs) on a Si substrate by helicon wave plasma chemical vapor deposition (HWP-CVD). The results show that VGs has good vertical orientation on Si and the growth process does not require the catalyst. Modulation of height, thickness and mesh size of vertical graphene nanosheets can be achieved by changing the growth time. It is found that the height of VGs is linear with time. Extremely high growth rate, approximately 0.26 μm/min, is achieved, in contrast to previous studies. The results of Cyclic voltammetry (CV) measurement indicating that VGs have a very rapid current–voltage response, an excellent electrochemical reversibility and excellent capacitive behavior. The VGs was able to deliver an outstanding specific capacitance value of 345 μF/cm2, and demonstrated an excellent rate capability, which retained 94.41%.

A review of graphene synthesisatlow temperatures by CVD methods

Chemical vapor deposition (CVD) is the most effective method for the synthesis of large-scale and high-quality graphene. However, the growth temperature of graphene is high, about 1000 °C, using conventional CVD, meaning that it is expensiveand thus limits the use of the material. The synthesis of CVD graphene at low temperatures(<600°C) is therefore the focus of many researchers. Recent research on the production of CVD graphene at low temperaturesis reviewed. Comprehensive comparison, analysis and discussion of quality, number of layers, domain size and the uses of graphenesynthesized at low temperatures using different precursors (gas, liquid and solids) and substrates (metals, metal alloys and dielectric materials) are given for different CVD methods (atmospheric pressure CVD, plasma enhanced CVD, catalyst-enhanced CVD, surface wave plasma CVD, microwave plasma CVD, radio frequency plasma enhanced CVD and electron cyclotron resonance CVD). The future prospects and challenges of preparing graphene at low temperatures are discussed.

Effect of DC negative bias on microstructure and surface morphology of amorphous silicon carbide films prepared by HWP-CVD

The effect of DC negative bias (− Vs) on microstructure and surface morphology of amorphous silicon carbide thin films prepared by helicon wave plasma chemical vapor deposition is reported. Microstructure and surface morphology were obtained by scanning electron microscope (SEM) and atomic force microscope (AFM). The results show that the increase of − Vs on the substrate make a more compact film and lower surface roughness, which can reach 0.56 nm. The XRD analysis reveals that the SiC thin films are of an amorphous structure. Percentages of carbon and silicon atoms (C/Si) were measured by energy dispersive spectrometer (EDS), and the C/Si ratio can reach 1.45. The structural properties of the films were studied by Raman spectroscopy techniques and Fourier transform infrared (FTIR). It is found that the films contain not only Si–C bonds but also Si–CHx bonds. Raman spectra results show that the proportion of disordered carbon in the films decreases with the increase of − Vs. The results of ultra-microhardness tester show that the hardness of the films increases with the increase of − Vs and the maximum mechanical hardness can reach 18.5 GPa at − Vs = − 60 V.

Synthesis, characterization, and thermal properties of novel silicon 1,1,3,3‐tetramethylguanidinate derivatives and use as single‐source chemical vapor deposition precursors

AbstractA series of chemical vapor deposition (CVD) precursors have been synthesized by a single‐step reaction of 1,1,3,3‐tetramethylguanidine and a variety of silicon chlorides. The structures of the 1,1,3,3‐tetramethylguanidinate‐based compounds were verified by 1H NMR, 13C NMR, XPS, EI‐MS, and elemental analysis. The thermal stability, transport behavior, and vapor pressures of these compounds were evaluated by simultaneous thermal analyses (STA). These compounds are highly stable and those in liquid form are very volatile. Silicon carbonitride (SiCN) thin films were prepared by using bis (tetramethylguanidine)‐dimethyl‐silane as the precursor in helicon wave plasma chemical vapor deposition (HWP‐CVD). The properties of the films were investigated by SEM, AFM, and XPS. The results showed that the films have good uniformities, low friction coefficient, and high hardness, enabling the films for fabrication of semiconductor devices.

Gas dependent growth study of hexagonal boron nitride synthesized by microwave assisted surface wave plasma chemical vapor deposition process

Gas dependent growth study of hexagonal boron nitride synthesized by microwave assisted surface wave plasma chemical vapor deposition process

The properties of N-doped diamond-like carbon films prepared by helicon wave plasma chemical vapor deposition

In this paper, N-doped diamond-like carbon (DLC) films were deposited on silicon substrates by using helicon wave plasma chemical vapor deposition (HWP-CVD) with the Ar/CH4/N2 mixed gas. The surface morphology, structural and mechanical properties of the N-doped DLC films were investigated in detail by scanning electron microscopy (SEM), x-ray photoelectron spectroscopy (XPS), Raman spectra, and atomic force microscopy (AFM). It can be observed from SEM images that surface morphology of the films become compact and uniform due to the incorporation of N. The maximum of the deposition rate of the films is 143 nm min−1, which is related to the high plasma density. The results of XPS show that the N incorporates in the films and the C−C sp3 bond content increases firstly up to the maximum (20%) at 10 sccm of N2 flow rate, and then decreases with further increase in the N2 flow rate. The maximum Young’s modulus of the films is obtained by the doping of N and reaches 80 GPa at 10 sccm of N2 flow rate, which is measured by AFM in the scanning probe microscope mode. Meanwhile, friction characteristic of the N-doped DLC films reaches a minimum value of 0.010.

Mechanism of high growth rate for diamond-like carbon films synthesized by helicon wave plasma chemical vapor deposition

A high growth rate fabrication of diamond-like carbon (DLC) films at room temperature was achieved by helicon wave plasma chemical vapor deposition (HWP-CVD) using Ar/CH4 gas mixtures. The microstructure and morphology of the films were characterized by Raman spectroscopy and scanning electron microscopy. The diagnosis of plasma excited by a helicon wave was measured by optical emission spectroscopy and a Langmuir probe. The mechanism of high growth rate fabrication for DLC films by HWP-CVD has been discussed. The growth rate of the DLC films reaches a maximum value of 54 μm h−1 at the CH4 flow rate of 85 sccm, which is attributed to the higher plasma density during the helicon wave plasma discharge. The CH and Hα radicals play an important role in the growth of DLC films. The results show that the Hα radicals are beneficial to the formation and stabilization of C=C bond from sp2 to sp3.

Catalyst-Free Growth of Graphene by Microwave Surface Wave Plasma Chemical Vapor Deposition at Low Temperature

Catalyst-free graphene films has been synthesized by microwave (MW) surface wave plasma (SWP) chemical vapor deposition (CVD) using hydrogenated carbon source on silicon substrates at low temperature (500℃). The synthesized process is simple, low-cost and possible for application on transparent electrodes, gas sensors and thin film resistors. Analytical methods such as Raman spectroscopy, transmission electron microscopy (TEM) and four points prove resistivity measurement and UV-VIS-NIR spectroscopy were employed to characterize properties of the graphene films. The formation of multilayer of graphene on silicon substrate was confirmed by Raman spectroscopy and TEM. It is possible to grow graphene directly on silicon substrate (without using catalyst) due to high radical density of MW SWP CVD. In addition, we also observed that the hydrogen had significant role for quality of graphene.