Plasma-assisted Chemical Vapor Deposition Method Research Articles

Electrochemical Recovery of Copper from Model Wastewater Using Boron-Doped Diamond Electrodes

Introduction The recovery of Cu from wastewater is a key issue for environmental and economic aspects1. The wastewater treatment containing Cu has been carried out by various techniques such as chemical precipitation, coagulating sedimentation, and electrochemical methods. Although chemical precipitation method is the most commonly used technique due to relatively simple operation, the process needs to put additional chemicals and generates large amounts of sludge. On the other hand, electrodeposition is known as the “clean” method because it is able to achieve the recovery of Cu without requiring addition of chemicals and generating sludge. However, the current efficiency tends to decrease especially in a dilute solution, because hydrogen evolution and oxygen reduction reaction occur as competition reaction. Boron-doped diamond (BDD) electrode is a candidate for resolving the above problem because it has the excellent electrochemical properties2. Along these lines, we study on the recovery of Cu from dilute cupric sulfate solution as a model wastewater by electrodeposition method using BDD electrodes, and glassy carbon (GC) as a comparative carbon electrode. Experimental Two types of BDD films with different boron doping level (B/C = 0.1%, 1%) were deposited onto silicon wafer substrates by a microwave plasma-assisted chemical vapor deposition method. Electrochemical measurements were carried out using a conventional three-electrode system: BDD and GC as a working electrode, Pt plate as a counter electrode, and Ag/AgCl (saturated KCl) as a reference electrode. The surface of BDD electrodes was oxidized in 0.1 M H2SO4 at 2.0 V for 10 min before electrochemical measurements. The electrochemical behavior of Cu ions was evaluated by cyclic voltammetry (CV) in an aqueous solution of 0.5 mM CuSO4 and 0.1 M H2SO4 with a scan rate of 0.3 V s−1. Before CV measurements, the solution was deoxidized by bubbling with nitrogen for 10 min. Electrodeposition of Cu was carried out by chronoamperometry at various potentials from 0 to −0.8 V in 9-ml aqueous solution of 0.5 mM CuSO4 and 0.1 M H2SO4. During the electrodeposition, nitrogen kept bubbling in the solution. After electrodeposition, concentration of residual Cu ions was measured by an inductively coupled plasma atomic emission spectroscopy. Results and Discussion Figure 1 showed the time-dependent Cu recovery rates and current efficiencies at the various potentials on BDD and GC electrodes. When the electrodeposition was carried out at 0 V on all electrodes, Cu could hardly deposit on the electrodes. The Cu recovery rates on 0.1%BDD increased with increasing the applied negative potential, whereas the Cu recovery rates on GC decreased at −0.8 V, compared to the other potentials. On 1%BDD, Cu recovery rates hardly changed at any potential except 0 V. From CV measurements, reduction potentials corresponding to Cu2+ ions to metal Cu were −0.48 V, −0.28 V, and −0.20 V on 0.1%BDD, 1%BDD, and GC, respectively. Since the nucleation potential of Cu on 0.1%BDD is the most negative, Cu recovery rates at −0.2 V was lower than the other potentials. The nucleation overpotentials were different between 0.1%BDD and 1%BDD due to the difference of their conductive properties. As 0.1%BDD has a characteristic of a p-type semiconductor, a depletion layer occurs at the surface of the electrode with a band bending when the electrode contacts the solution. Therefore, cathodic reactions are inhibited due to increasing the depletion layer when applying the negative potential. On the other hand, 1%BDD has a characteristic of metal-like conductivity, so charge transfer from the electrode to Cu ions easily occurs. Also, the hydrogen evolution potential on 0.1%BDD was the most negative, followed in order by 1%BDD, and GC. Therefore, Cu recovery rates at −0.8 V on GC decreased due to the hydrogen evolution. The current efficiencies decreased with increasing the applied negative potentials on the all electrodes, because hydrogen evolution reaction easily occurs at more negative potential. Also, the current efficiencies on BDD were higher than GC at any potential. It is assumed that the current efficiency was improved using BDD electrodes due to inhibition of hydrogen evolution reaction, compared to GC electrode. Moreover, the current efficiency using 0.1%BDD was the higher than 1%BDD due to higher hydrogen overpotential, whereas 0.1%BDD also required high Cu deposition overpotential. Therefore, it was found that the recovery of Cu was achieved with high current efficiency using 1%BDD along with the lower power consumption. References (1) F. Fu and Q. Whang, J. Environ. Manage. 92, 407 (2011). (2) Y. Einaga, J. Appl. Electrochem. 40, 1807 (2010). Figure 1

Formation of Nitrogen-Vacancy Centers in Homoepitaxial Diamond Thin Films Grown via Microwave Plasma-Assisted Chemical Vapor Deposition

A model for controlling the two-dimensional distribution of negatively charged nitrogen-vacancy (NV - ) fluorescent centers near the surface of a diamond crystal is presented, using only a microwave plasma-assisted chemical vapor deposition (CVD) method. In this approach, a CVD diamond layer is homoepitaxialy grown via microwave plasma-assisted CVD using an isotopically enriched methane ( 12 CH4), hydrogen (H2), and nitrogen (N2) gas mixture on patterned diamond (0 0 1). When the surface is imaged by means of confocal microscope photoluminescence mapping, fine grooves are observed to have been generated artificially on the diamond surface. NV - centers are found to be distributed selectively into these grooves. These results demonstrate an effective means for the formation of NV - centers of selectable size and density via microwave plasma-assisted CVD, with potential application in the production of diamond quantum sensors.

Formation of SixNy(H) and C:N:H layers by Plasma-Assisted Chemical Vapor Deposition method

This work includes the results of growth rate of the silicon nitride layers and layers of carbon doped nitrogen deposition on (001) Si substrate as a function of time in the process of chemical vapor deposition, assisted with the plasma generated by radio frequency waves RF CVD (13,56MHz, 300W). On the basis of measurements of thickness of the layers it was observed that kinetic curves are not linear but consist of stages, which regularly recur and are characterized at first by the rapid growth rate and then by slowing down at the end of each stage. The spectroscopic ellipsometry investigations allowed us to determine layer thickness and optical constants parameters, versus deposition time.The obtained results allow us to conclude that the growth process within this system is limited by the number of active centers on the substrate surface, and at the next stages, on the surface of growing layers. A possible mechanism based on the theory on of transition state has been discussed.

Mechanical characterization of a-C:H:SiOx coatings synthesized using radio-frequency plasma-assisted chemical vapor deposition method

A series of SiOx containing a-C:H films was deposited on polished silicon substrates by RF PACVD (Radio Frequency Plasma Assisted Chemical Vapour Deposition) method using methane and hexamethyldisiloxane (HMDSO). Three CH4/HMDSO flow ratios and four self-bias voltages were applied for the synthesis of 12 different a-C:H:SiOx coatings having different properties and silicon/oxygen concentrations. The chemical structure of the deposited films was determined by Fourier transform infrared spectroscopy. Detailed characterization of the mechanical properties of SiOx incorporated carbon coatings was made using the nanoindentation (hardness and modulus) and profilometry (residual stress) methods. Hardness and elastic modulus were used for the evaluation of the endurance capability (H/E) and resistance to plastic deformation (H3/E2). The elastic recovery was calculated based on loading and unloading curves. The residual stress of diamond-like carbon coatings can be effectively reduced by the incorporation of SiOx. The mechanism of reducing the residual stress depending on the applied self-bias voltage is proposed. In the case of all of the examined coatings the addition of SiOx reduces the hardness, while for high self-bias voltages an increase of endurance capability and resistance to plastic deformation is observed.

Formation and field emission properties of multilayer graphene hybrid films grown on laser pretreated Ni layer

A series of petaloid few-layer graphene–aggregated state multilayer graphene hybrid films with large areas (∼500 mm2) were made on Ni-coated Al2O3 ceramic substrate utilising a microwave plasma-assisted chemical vapour deposition method. Nickel layers were pretreated by laser etching technology. A Raman spectra, field emission scanning electron microscope and field emission I–V measurements were used for the detection of the film properties. Test results indicated that the laser etched region (groove region) and the un-etched region (prominent ridge region) surface topography had significant differences between the two, and a petaloid few-layer graphene film was found in the laser-etched region while in the un-etched region, an aggregated state multilayer graphene film was formed. The influence of the laser etching pretreatment on surface microstructure and morphologies of the graphene films was investigated. Moreover, synthesis mechanisms of the films were discussed. Field emission results showed a turn on the field was 4·5 V μm−1 and the current density was 0·1 mA cm−2 in an electric field of 6·1 V μm−1.

Surface-Morphology-Induced Hydrophobicity of Fluorocarbon Films Grown by a Simultaneous Etching and Deposition Process

Development of facile methods to prepare hydrophobic films is of great important. We report fluorocarbon films deposited by a simple plasma-assisted chemical vapor deposition method using C3F8 and C2H2 with extra Ar and/or O2 gases. The surface characteristics of the films were examined by scanning electron microscopy, atomic force microscopy, and x-ray photoelectron spectroscopy. The hydrophobic and oleophobic properties of the films were evaluated by measurements of static contact angle. The results showed that the film deposited with C3F8, C2H2, Ar, and O2 exhibited a water contact angle of 114°, hexadecane contact angle of 45°, and transmittance of 94.5%. Photoelectron spectra further revealed that the films contained mainly CF and CF2 bonds and thus a high F/C ratio. Introduction of O2 increased the F/C ratio, which combined with the stripe-like surface of the films achieved better hydrophobicity.

Surface Modification of the Ti6Al4V Alloy with Silicon Carbonitride Layer Deposited by PACVD Method

AbstractFour different layers of various silicon, carbon and nitrogen contents on the Ti6Al4V alloy and (001)Si wafers have been deposited by means of Plasma Assisted Chemical Vapor Deposition (PACVD) method. The layers were obtained from reactive gas mixture containing SiH4, CH4, NH3 and Ar. After deposition the structure and chemical composition of modified surfaces have been analyzed with use of SEM/EDS technique. Based on these results and thermodynamic calculations, the diffusion coefficients, D, for nitrogen and carbon in alloy were discussed. Scratch test shown that silicon carbonitride layers have good adhesion to metal surface. In order to determine atomic structure of obtained layers, FTIR spectra for layer-(001)Si and layer-Ti6Al4V were registered.

Size-dependency of corrosion behavior for TiN nanostructure coatings deposited by the PACVD method

This paper evaluates the corrosion resistance of duplex treated AISI H11 tool steel. The duplex treatment involves cold wall plasma nitriding and plasma assisted chemical vapor deposition (PACVD). Plasma nitriding was carried out in a chamber including 25vol.% of N2 and 75vol.% of H2 at 500°C for 4h. PACVD treatment was performed in the same chamber containing Ar, N2, and H2 gases along with TiCl4 vapor for 4h at a chamber pressure of 3mbar, for different process temperatures of 470, 495, and 520°C. Field emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), and potentiodynamic polarization test in 3.5% NaCl solution were used to study the samples. The results indicate that samples coated with TiN at lower temperature exhibit a 10 times improvement in corrosion resistance relative to the coated samples at higher temperatures. It was found that the grain size is about 4–7nm which plays an important role in corrosion behavior. Furthermore, this study demonstrates that surface roughness increases by raising the deposition temperature of the PACVD treatment from 470°C to 520°C, leading to a lower corrosion resistance of the coated samples.

Effectiveness of a hot-filament chemical vapor deposition method for preparation of a boron-doped superconducting diamond film with higher superconducting transition temperature

We have investigated the effectiveness of a hot-filament chemical vapor deposition (HFCVD) method for preparation of a boron-doped superconducting diamond film with higher superconducting transition temperature (Tc). A boron-doped superconducting diamond film has been fabricated on a diamond (111) substrate using the HFCVD method, and studied by means of scanning electron microscopy, X-ray photoelectron spectroscopy (XPS), and resistivity. The film consists of grains with an average size of 200mm. Analyses of valence band and boron 1s core-level XPS spectra indicate the formation of boron-doped diamond film on the substrate. From the resistivity measurements, the film is found to be a superconductor with onset Tc of 7.1K. Carrier concentration determined by Hall conductivity measurements is 1.1×1021cm−3. The value of Tc is higher compared with that in boron-doped superconducting diamond films prepared by a commonly used microwave plasma-assisted chemical vapor deposition (MPCVD) method, at the same carrier concentration [A. Kawano et al., Phys. Rev. B 82 (2010) 085318]. The result of higher Tc in the film by the HFCVD method is consistent with the previous one [Wang et al., Diamond Relat. Mater. 15 (2006) 659], suggesting that the HFCVD method is effective for preparation of boron-doped superconducting diamond films showing higher Tc.

Electrochemical oxidation of aqueous phenol at low concentration using Ti/BDD electrode

The high quality boron-doped diamond (BDD) film electrodes deposited on titanium (Ti) substrate have been prepared by a microwave plasma-assisted chemical vapor deposition (MP-CVD) method. The products consist of high quality dense grains characterized by Raman spectroscopy and scanning electron microscopy (SEM) employed. The BDD electrodes have wide electrochemical window (approximate 4.0V) and low background current (near zero) and the oxidation peak of phenol appears before the discharge of water, examined by cyclic voltammetry and linear sweep voltammetry. Compared with the fluorine-doped lead dioxide anodes (Ti/F-PbO2), the Ti/BDD anodes showed higher current efficiency and lower power consumption with degradation of low concentration phenol. The experimental results demonstrated that the BDD electrode on the Ti substrate possesses the excellent electrocatalytic activity in dilute solution.

Preparation of carbon-coated stainless steels and their properties as bipolar plate materials of polymer electrolyte fuel cells

In order to develop metal bipolar plates for polymer electrolyte fuel cells (PEFC), various grades of stainless steels (SUS304, SUS316, and SUS430) were coated with carbonaceous thin films by plasma-assisted chemical vapor deposition method. The resulting carbon-coated stainless steels were characterized by Raman spectroscopy, interfacial contact resistance (ICR) measurement, and scanning electron microscopy (SEM). Corrosion properties were examined by dynamic polarization measurement in H2SO4 solution. ICR values were decreased by carbon coating due to the deposition of a conductive carbonaceous thin film. The corrosion resistance of carbon-coated SUS304 and SUS430 was superior to that of carboncoated SUS316 at ambient temperature. Based on the SEM images obtained after dynamic polarization measurements, it was found that carbonaceous thin-film layers on SUS304 and SUS430 were dense and did not peel. At 80°C (simulated operating temperature of PEFCs), corrosion resistance of carbon-coated SUS304 was superior to that of carbon-coated SUS430. The influence of the stainless steel grade on the corrosion properties provided by carbon-coating was discussed in relation to the carbon deposition mechanism.

Preparation of carbon-coated stainless steels and their properties as bipolar plate materials of polymer electrolyte fuel cells

In order to develop metal bipolar plates for polymer electrolyte fuel cells (PEFC), various grades of stainless steels (SUS304, SUS316, and SUS430) were coated with carbonaceous thin films by plasma-assisted chemical vapor deposition method. The resulting carbon-coated stainless steels were characterized by Raman spectroscopy, interfacial contact resistance (ICR) measurement, and scanning electron microscopy (SEM). Corrosion properties were examined by dynamic polarization measurement in H2SO4 solution. ICR values were decreased by carbon coating due to the deposition of a conductive carbonaceous thin film. The corrosion resistance of carbon-coated SUS304 and SUS430 was superior to that of carboncoated SUS316 at ambient temperature. Based on the SEM images obtained after dynamic polarization measurements, it was found that carbonaceous thin-film layers on SUS304 and SUS430 were dense and did not peel. At 80°C (simulated operating temperature of PEFCs), corrosion resistance of carbon-coated SUS304 was superior to that of carbon-coated SUS430. The influence of the stainless steel grade on the corrosion properties provided by carbon-coating was discussed in relation to the carbon deposition mechanism.

Influence of atomic bonds on electrical property of boron carbon nitride films synthesized by remote plasma-assisted chemical vapor deposition

Boron carbon nitride (BCN) films are synthesized with various growth conditions by remote plasma-assisted chemical vapor deposition method. The chemical bonding in the BCN film is modified by the growth condition. Optical and electrical properties are investigated for BCN films with various chemical bonding. Electrical characterization is carried out for the BCN films which have the same bandgap energy and different C composition ratio and have the same C composition ratio and different bandgap energy.

Diamond coating on hard metals by traveling methods in a plasma-assisted chemical vapor deposition method above the liquid

In this work, two approaches were developed to extend the coating area of diamond by continuous deposition in a plasma-assisted chemical vapor deposition (CVD) method above the liquid. The techniques were based on the methods previously developed by our research group and the characteristic was to use dc (direct current) plasma generated between the liquid surface and the metal electrode. In the first approach, a tungsten rod was rotated in a chamber at reduced pressure so that a diamond film was formed as a ‘belt’ in 6 mm width around the side of the rod. The deposited diamond was polycrystalline with a grain size of 1–3 μm. The film thickness increased almost linearly with deposition time, whereas the grain size was almost constant against the deposition time. The second approach was for a plate substrate. A tungsten plate was hung with an iron wire and the plasma was horizontally generated between the liquid and plate surfaces. When the W plate was vertically slid down slowly, a diamond film was continuously deposited on the surface. The deposited film was covered with a soot-like carbon layer on the top and the post-treatment with H 2O/N 2 gas at 600 °C was effective in removing it. The continuous deposition successfully demonstrated the expansion of the deposition area with the novel plasma CVD method above the liquid.

Selective Growth of Boron Nitride Nanotubes by the Plasma-Assisted and Iron-Catalytic CVD Methods

Boron nitride nanotubes (BNNTs) were selectively synthesized on patterned bilayer (Fe/Al) catalysts by the plasma-assisted chemical vapor deposition (PACVD) method. The as-grown nanotubes comprise both coaxial and cup-stacking tubular structures. Optical transitions on cup-stacking BNNTs are investigated for the first time. The observed red-shift of free excitonic luminescence was attributed to the excitonic recombination in terms of defect trapping in the tube's surface. The O 2 additives during the synthetic process were found to balance the excess H radicals that in turn enhance the growth yield of BNNTs. Moreover, our elemental mapping results provide direct evidence of the metal catalytic mechanism and the influence of the as-formed Al 2 O 3 underlayer.

Self-assembled growth of carbon nitride nanocones using abnormal glow discharge

Crystalline carbon nitride nanocones with intact appearances and the minimum apex diameter of 2–3 nm have been grown vertically on Co-covered Si substrates, using the direct-current abnormal glow discharge plasma-assisted chemical vapor deposition method. The abnormal glow discharges for growth of carbon nitride nanocones were carried out in the ambience of mixtures of methane and nitrogen, with a total pressure of 30 Torr and a CH4/N2 pressure ratio of 1/50. Energy-dispersive X-ray spectroscopy and selected-area electron diffraction results indicated that the as-grown carbon nitride nanocones have the atomic [C]:[N] ratio of nearly 3:4 and the crystallinity close to the β-C3N4 structure. Based on the characterizations and analyses for the as-grown carbon nitride nanocones, two main growth ways with different Co-layer thicknesses are presented.

Atomic bonds in boron carbon nitride films synthesized by remote plasma-assisted chemical vapor deposition

Boron carbon nitride (BCN) films are synthesized by remote plasma-assisted chemical vapor deposition (RPCVD) method. The present experimental apparatus is featured by introducing BCl 3 gas near the substrate without mixing to plasma consisting of N 2 and CH 4 gases. Two sample groups of the BCN films are prepared. One is grown with various CH 4 flow rates, and another is grown with various BCl 3 flow rates. The composition ratio of the constituent atoms, atomic bonds and optical bandgap are investigated. C composition ratio of the BCN film increases with increasing CH 4 flow rate, leading to a reduction in the optical bandgap with increasing C composition ratio. On the other hand, it is found that no significant variation in the composition ratio occurs for the BCN films grown with various BCl 3 flow rates and that the optical bandgap decreases with increasing BCl 3 flow rate. This behavior of the optical bandgap is related to a change of the atomic bonds in the BCN film grown with various BCl 3 flow rates.

Hemocompatibility of surface-modified, silicon-incorporated, diamond-like carbon films

The hemocompatibility of plasma-treated, silicon-incorporated, diamond-like carbon (Si-DLC) films was investigated. Si-DLC films with a Si concentration of 2 at.% were prepared on Si (100) or Nitinol substrates using a capacitively coupled radiofrequency plasma-assisted chemical vapor deposition method using a mixed gas of benzene (C 6H 6) and diluted silane (SiH 4:H 2 = 10:90). The Si-DLC films were then treated with O 2, CF 4 or N 2 glow discharge for surface modification. The plasma treatment revealed an intimate relationship between the polar component of the surface energy and its hemocompatibility. All in vitro characterizations, i.e. protein absorption behavior, activated partial thromboplastin time measurement and platelet adhesion behavior, showed improved hemocompatibility of the N 2-- or O 2-plasma-treated surfaces where the polar component of the surface energy was significantly increased. Si–O or Si–N surface bonds played an important role in improving hemocompatibility, as observed in a model experiment. These results support the importance of a negatively charged polar component of the surface in inhibiting fibrinogen adsorption and platelet adhesion.

Chemical Analysis of Impurity Boron Atoms in Diamond Using Soft X-Ray Emission Spectroscopy

To analyze the local structure and/or chemical states of boron atoms in boron-doped diamond, which can be synthesized by the microwave plasma-assisted chemical vapor deposition method (CVD-B-diamond) and the temperature gradient method at high pressure and high temperature (HPT-B-diamond), we measured the soft X-ray emission spectra in the CK and BK regions of B-diamonds using synchrotron radiation at the Advanced Light Source (ALS). X-ray spectral analyses using the fingerprint method and molecular orbital calculations confirm that boron atoms in CVD-B-diamond substitute for carbon atoms in the diamond lattice to form covalent B-C bonds, while boron atoms in HPT-B-diamond react with the impurity nitrogen atoms to form hexagonal boron nitride. This suggests that the high purity diamond without nitrogen impurities is necessary to synthesize p-type B-diamond semiconductors.

Improved field emission characteristics of individual carbon nanotube coated with boron nitride nanofilm

An individual multiwall carbon nanotube (CNT) synthesized without a catalyst by an arc discharge method is bonded to a tungsten tip. Field emission characteristics of the individual CNT coated with a boron nitride (BN) nanofilm are investigated. The BN film is synthesized by plasma-assisted chemical vapor deposition method in which boron trichloride (BCl3) and nitrogen (N2) are used as source gases. Deposition of the BN film with a thickness less than 10nm onto the individual CNT is attempted. Field emission characteristics are measured in the chamber evacuated to 2×10−8Pa. An anode electrode is set 25mm away from the CNT sample. The turn-on electric field, designated as an electric field at an emission current of 1.0nA, is compared between individual CNTs with and without the BN nanofilm. A significant reduction in the turn-on electric field is achieved by coating with the BN nanofilm. The turn-on electric field is estimated to be 1.2×10−2V∕μm for the uncoated individual CNT sample, and the turn-on electric field is estimated to be 8.2×10−3V∕μm for the CNT sample coated with BN nanofilm. Moreover, stable operation is demonstrated at an emission current as high as 1×10−5A.