Plasma Jet Chemical Vapor Deposition Research Articles

Electrochemical biosensor based on one-dimensional MgO nanostructures for the simultaneous determination of ascorbic acid, dopamine, and uric acid

One-dimensional (1D) MgO nanostructures of various morphologies including tadpole-like nanobelts (tadpoles), nanobelts, and nanorods were synthesized via direct current (DC) arc plasma jet chemical vapor deposition (CVD). The effect of morphology on the biosensing properties of the nanostructures was investigated by comparing their electrochemical properties. Compared with tadpoles and nanorods, the MgO nanobelts had excellent electrocatalytic activity toward ascorbic acid (AA), dopamine (DA) and uric acid (UA). The response of the MgO nanobelts to the analytes was twice that of the tadpoles. A MgO nanobelt-modified electrode was thus fabricated for the simultaneous determination of AA, DA, and UA. The peak separations between AA and DA, DA and UA, and AA and UA for this electrode were 111, 161, and 272mV, respectively. The linear response ranges of the electrodes were 2.5–15 and 25–150μM for AA, 0.125–7.5μM for DA, and 0.5–3 and 5–30μM for UA. The calculated detection limits were 0.2, 0.05, and 0.04μM (S/N=3), respectively. The excellent electrocatalytic activity of the MgO nanobelts can be attributed to various surface defects such as low-coordination anions (O5C2− and O4C2− at the terrace and edge sites, and O3C2− at the corner and kink sites). Additionally, electron tunneling between these surface defects is possible. These defects have a strong adsorption capacity toward AA, DA, and UA. This affinity improves sensitivity and decreases the detection limits of the MgO nanobelt electrodes.

Effects of Nitrogen Doping on Nanocrystalline Diamond/p-Type Si toward Solar Cell Applications

In this work, a solar cell structure of nitrogen-doped nanocrystalline diamond (NCD:N)/p-type silicon was fabricated using microwave plasma jet chemical vapour deposition technique. The effects of nitrogen doping level on the structure, optical, and electrical of the as-grown NCD:N was discussed. The results showed that the micro structure, surface roughness, electrical properties, and optical properties were affected by the nitrogen doping. Additionally, the agglomeration of the film was increased with the higher concentration of CN species when the ratio of doped nitrogen increased. The roughness of the film was Rms:16.5 nm ~ 20.4 nm and the wettability was increased (contact angle 94.4o~ 64.6o). The optical transmittance was decreased (87% ~ 72%) with the higher nitrogen. The results of Hall measurements showed that the carrier concentration increased 2 order (1016 cm-3to 1018 cm-3) through nitrogen doping. The solar cell was made by NCD: N compound with p-type silicon. The photoelectric conversion efficiency was 2.8%. The open-circuit voltage was 0.52 V. The short-circuit current was 3 mA and the fill factor was 0.38.

Analysis of Fracture Behavior of Thin Polycrystalline Diamond Films

The effect of the substrate temperature and CH4 concentrations on the fracture behavior of thin polycrystalline diamond films was systematically investigated by X-ray diffraction and scanning electron microscopy. The results show that the fracture behavior of thin polycrystalline diamond films synthesized by direct current plasma jet chemical vapor deposition is closely related to the substrate temperature and CH4 concentrations. A high substrate temperature, due to difference in the thermal expansion coefficients of the substrate and the diamond film, causes thin polycrystalline diamond films to generate high residual stresses, which usually exceed fracture strength of thin diamond film and even that of diamond. The fracture toughness is found to drop with the increasing ratio of CH4 concentration. In case of high CH4 concentrations, various defects and impurities, such as cracks, microscopic holes, graphite, and amorphous carbon were observed in the films. Thus, the substrate temperature and CH4 concentrations should be strictly controlled within an appropriate range

Nanocrystalline Diamond Thin Films Synthesis on Curved Surface

Thin films of curved surface nanocrystalline diamond (CS-NCD) are a category of important materials. However, the development of such materials is still a highly challenging task. Here we present a novel approach to synthesizing CS-NCD thin films deposited on non-spherical surfaces of molybdenum substrate using direct current plasma jet chemical vapor deposition. A special cooling system was designed and applied to ensure uniform substrate temperature. It is demonstrated from simulation and experimental results that this system is favorable for the production of thin films. The results show that the quality of CS-NCD thin films depends on the selection of optimal values of parameters including CH4 concentration, substrate temperature, and chamber pressure. If the CH4 concentration and/or the substrate temperature is too high or low, it results in non-diamond phase or micron-crystalline diamond thin films. Synthetic CS-NCD thin films using the proposed method have a smooth surface and uniform thickness. The average grain size and the mean surface roughness are approximately 30 and 4.3 nm respectively. Characteristics of CS-NCD thin film spectra comprised of the full width at half maximum with broad Raman peaks around 1,140 and 1,480 cm−1, confirming the presence of the NCD phase.

Synthesis and Characterization of Porous ZnO-CNT Nanocomposites Prepared by Microwave Plasma Jet Chemical Vapor Deposition System

In the present study, we fabricated the CNT-porous ZnO composite by Microwave Plasma Jet Chemical Vapor Deposition (MPJCVD) System. The morphology and characteristics of the CNT-porous ZnO were examined by SEM, EDS and Raman spectrometer. Finally, a few carbon content was found to exist within the CNT-porous ZnO nanocomposite.

The effect of microstructure and crystal defect on electrochemical performances of MgO nanobelts

The electrochemical properties of one-dimensional (1-D) nanomaterials are highly sensitive to their surface microstructure and crystal defects. MgO nanobelts were obtained by magnesium nitrate decomposition using the direct arc plasma jet chemical vapor deposition technique, with a molybdenum substrate at 950°C for 5min. The structural details, defects, and electrochemical properties of MgO nanobelts were determined. From high-resolution transmission electron microscopy, the nanobelts contain numerous contacts, rough edges, vacancies, and doping defects. Nanobelts with large surface area and oxide ions in low coordination (with O5C2− and O4C2−, for terrace and edge sites, and O3C2− for corner and kink sites) were seen by various analytical studies. The electrochemical performances of the MgO nanobelts-modified electrode were investigated using standard techniques. The unique nanostructural features and crystal defects endow MgO nanobelt with excellent electrochemical performance as demonstrated in their application in the selective determination of hydroquinone (HQ) and catechol (CC); both can be oxidized at the MgO nanobelt-modified electrode. This nanomaterial allows the sensitive determination of HQ and CC without cross-interference. The MgO nanobelts/glassy-carbon electrode exhibited high sensitivity in the selective determination of HQ and CC, with detection limits of 1×10−8M.

Effects of Surface Modification of Nanodiamond Particles for Nucleation Enhancement during Its Film Growth by Microwave Plasma Jet Chemical Vapour Deposition Technique

The seedings of the substrate with a suspension of nanodiamond particles (NDPs) were widely used as nucleation seeds to enhance the growth of nanostructured diamond films. The formation of agglomerates in the suspension of NDPs, however, may have adverse impact on the initial growth period. Therefore, this paper was aimed at the surface modification of the NDPs to enhance the diamond nucleation for the growth of nanocrystalline diamond films which could be used in photovoltaic applications. Hydrogen plasma, thermal, and surfactant treatment techniques were employed to improve the dispersion characteristics of detonation nanodiamond particles in aqueous media. The seeding of silicon substrate was then carried out with an optimized spin-coating method. The results of both Fourier transform infrared spectroscopy and dynamic light scattering measurements demonstrated that plasma treated diamond nanoparticles possessed polar surface functional groups and attained high dispersion in methanol. The nanocrystalline diamond films deposited by microwave plasma jet chemical vapour deposition exhibited extremely fine grain and high smooth surfaces (~6.4 nm rms) on the whole film. These results indeed open up a prospect of nanocrystalline diamond films in solar cell applications.

In situ doping of diamond coatings with silicon, aluminum and titanium through a modified laser-based CVD process

Abstract The aim of this study was to demonstrate the feasibility of in situ doping of chemical vapor deposition (CVD) fabricated diamond coatings through simultaneous evaporation of solids in a CVD plasma-based process. In order to achieve maximum flexibility and energy density, a laser-based plasma-jet CVD process was chosen, and expanded with the introduction of dopant rods. The rods, with diameters varying from 0.5 mm to 3.0 mm, were fed at rates from 0.25 mm/min to > 100 mm/min, and positioned 3 mm below the optical breakthrough which generates the plasma. Gas flows of 20.0 slm (standard liters per min) argon, 2.0 slm hydrogen and 0.02 slm methane were used for diamond coating deposition. At a surface temperature of about 1100 °C, an average linear diamond growth rate of 20 μm/h was achieved. The materials selected as solid precursors for the rods were SiO2, Al2O3, and Ti due to their differing electrical characteristics, as they are an insulator, semiconductor, and conductor, respectively. The evaporation rate of these rods varied by more than six orders of magnitude, from 7 × 10− 2 g/min (SiO2). The doped diamond coatings were produced by simultaneous evaporation and CVD. To prove that the precursors were vaporized and the atomic bonds were broken by the plasma, the optical emission spectra are compared with published and calculated spectral lines. Analyses of the layers were performed using EDX (energy-dispersive X-ray) spectroscopy and WDS (wavelength dispersive X-ray spectroscopy). As a result, the maximum doping densities in the diamond coating were determined, and were 3.460 wt.% for silicon, 0.957 wt.% for aluminum, and 0.03 wt.% for titanium. To prove the diamond-like characteristics of these coatings, Raman measurements were performed.

Field emission characteristics study for ZnO–CNTs composites by the microwave plasma jet chemical vapor deposition system

The field emission (FE) properties of the carbon nanotubes (CNTs) grown on zinc oxide (ZnO) films have been reported in the present study. The ZnO films were first spun on a Si substrate by a spin coater, and then the grown CNTs were grown on the surface of the ZnO films by the microwave plasma jet chemical vapor deposition (MPJCVD) system. The experimental results showed that ZnO–CNT composite exhibited superior FE performance compared to that of CNTs and ZnO nanowires. The turn-on field of an emission device constructed with the ZnO–CNT composite was 0.31Vμm−1, which was lower than that of the common CNTs and ZnO nanowires/nanorods. As the results of field emission tests, the CNTs on ZnO films could be a useful material in the emission applications.

Electrochemical properties of tadpole-like MgO nanobelts

Tadpole-like MgO nanobelts have been grown on Mo substrates via DC arc plasma jet chemical vapor deposition. The 10−30nm wide nanobelts have spherical caps of 30−50nm diameter. The nanobelts contain numerous contacts and oxide ions in low coordination (with O5C2− and O4C2−, for terrace and edge sites, and O3C2− for corner and kink sites). Hydroquinone (HQ) and catechol (CC) can be oxidized on MgO nanobelt-modified electrodes. The electrochemical properties of the modified electrode were investigated using cyclic voltammetry and differential pulse voltammetry techniques. This modified electrode exhibited high sensitivity in the determination of HQ and CC, with the limits of detection for HQ and CC being 1×10–11M and 1×10−9M, respectively. The strong electrocatalytic properties were correlated with large surface area and presence of numerous defects.

Synthesis and optical properties of single-crystal MgO nanobelts

MgO nanobelts were obtained by the decomposition of magnesium nitrate in a direct current arc plasma jet chemical vapor deposition process, with a Mo substrate at 950°C for different durations. The products formed in the first 0.5min were nanobelts, some of which possessed spherical particles on tips of nanobelts, forming “tadpole-like” nanostructures. When the reaction time was extended to 1min, nanobelts become longer although spherical particles were still observed. When the reaction time was 3min, nanobelts became even longer, and no spherical particles were observed. Extending the reaction time to 5min significantly widened the nanobelts, with widths ranging from 10 to 100nm. The MgO nanobelt growth occurred along the 〈100〉 and the 〈111〉 axes. The growth mechanism of the MgO nanobelts was a combination of axial VLS and side VS growth. Nanobelts exhibited strong ultraviolet–blue photoluminescence emission under excitation at 350nm.

Preparation of photoluminescent single crystalline MgO nanobelts by DC arc plasma jet CVD

Magnesium oxide (MgO) nanostructures were synthesized by DC arc plasma jet chemical vapor deposition, which possesses the advantages of being simple, economical, fast, effective and environmentally benign. The formation of “tadpole”-, dendrite-, belt- and rod-like MgO nanostructures was confirmed by scanning electron microscopy and high-resolution transmission electron microscopy. Powder X-ray diffraction analysis revealed that the nanostructures consist of cubic phase MgO. Nanobelts that were 30–50nm wide with a width/thickness ratio of 1–2 were synthesized in just 5min. Most of the nanobelts were connected to others, and the connected nanobelts possessed a single-crystal structure. A formation mechanism for MgO nanostructures was proposed. Fourier transform infrared spectra indicated the adsorption of water and CO2 on the MgO surface. The nanobelts exhibited relatively strong blue-green luminescence.

A study of growth and surface performance analysis of nanographites grown using microwave plasma jet chemical vapor deposition system

Nanographites were grown using a microwave plasma jet chemical vapor deposition (MPJCVD) system. The E-H tuner of the MPJCVD was controlled by a personal computer. Monitoring of plasma jet was done through an optical emission spectroscopy and a charge coupled detector camera. High frequency structure simulator software was used to calculate electrical fields around specimens at different positions of the E-H tuner of the MPJCVD. Nanographites, composed of sp2 hybrid orbital, were grown at a microwave power of 800 W. The carbon bonds, both C–C and C=C bonds, of as-grown nanographites were measured to have characteristic peaks at 1309 and 1595 cm−1 using Raman spectroscopy. The mean size of the nanostructured graphite was nearly 50 nm under scanning electron microscopy observation. The measurement of contact angle on such graphite films was made by laying drops of deionized (DI) water, 0.03 and 0.09 M sodium chloride (NaCl) and was found to be 153°, 147°, and 136°, respectively. An electro-wetting test was also performed on the graphite films by adding electrical voltage through the CA measurement. It was found that contact angles of electro-wetting test for graphite films become 110° and 37° for DI water and NaCl solution, respectively.

Improvement on the synthesis technique of ultrananocrystalline diamond films by using microwave plasma jet chemical vapor deposition

In this paper, a particular class of smooth ultrananocrystalline diamond (UNCD) films synthesized by home-made microwave plasma jet chemical vapor deposition system (MPJCVD) with gas chemistry of Ar–1%CH 4–10%H 2 is presented. This synthesis by MPJCVD yields UNCD films identical to those UNCD films fabricated with Ar/CH 4 chemistry by MPCVD, but using relatively low Ar introduction, low pressure, and low power due to the focused microwave plasma jet enhanced the dissociation of react gases to form energetic species during the deposition. The transition from microcrystalline to ultrananocrystalline diamond films grown from Ar/Ar+H 2 0% to 90% plasmas using MPJCVD has been systematically studied. The results of this study showed that the grain size, surface roughness, and sp 3 bonding carbon concentration in the films decreased with the increase in Ar concentration. The reason is due to the great increase in renucleation during the films growth. The TEM images clearly exhibited the grain size of the films (Ar/Ar+H 2: 90%) in the range of 3–8 nm. The near-edge X-ray absorption fine structure spectrum also exhibited the clear bonding characteristics of diamond. Moreover, the plasma precarbonization was employed by MPJCVD prior to UNCD films synthesis in order to markedly enhance the smoothness of UNCD films. The UNCD film was synthesized via unique MPJCVD-enhanced nucleation and growth, which produced films with high growth rate (315 nm/h), smooth surfaces (∼11.7 nm rms), and extremely fine-grained (3–8 nm) distribution in the whole film.

Deposition and structure characterization of carbon films prepared at atmospheric pressure by plasma jet

Amorphous carbon films were deposited on stainless steel substrates by plasma jet chemical vapor deposition (PJCVD). The carbon coatings have been prepared at atmospheric pressure in an argon/acetylene mixture. The Ar/C2H2 gas volume ratio varied from 100:1 to 200:1, while the distance between the plasma torch nozzle exit and the samples was 0.005–0.02m. Scanning electron microscope analysis demonstrated that the surface roughness and growth rate of the coatings increase with the decrease of the Ar/C2H2 ratio. The ERDA results showed that the hydrogen concentration rises from 5at.% to 27at.% with the increase of the distance from 0.005 to 0.02m. The increase of the Ar/C2H2ratio from 100:1 to 200:1 slightly increases the hydrogen and oxygen concentration in the films. The Raman spectroscopy results indicated that the sp3 C–C carbon sites are replaced by sp3 CH2–3 bonds with the increase of the deposition distance. The microhardness of the carbon films deposited at 0.005m was in range of 7.1–9.3GPa.

Fabrication of nanogranular diamond films by MPJCVD system

Nanogranular diamond films have been prepared by microwave plasma jet chemical vapor deposition system (MPJCVD) with argon-rich (Ar/H2:90%) plasma. In this work, the plasma pre-carbonization (P.P.) pre-treatment was employed to obtain uniform and smooth (13.3nm rms) diamond films with high nucleation density. The diamond films were fabricated in various Ar/H2 concentrations from 0% to 100% and fixed at CH4 concentration of 1%. It can be clearly observed that the grain size of diamond films changed from micrometer to nanometer scale and down to 5nm at the concentration of 90% Ar/H2. The reason is due to the rise of C2 dimer in the plasma, which could be proved from the analysis of OES analysis.

Formation of ultrananocrystalline diamond films with nitrogen addition

Nitrogen-doped ultrananocrystalline diamond (UNCD) films have been prepared by the microwave plasma jet chemical vapor deposition system (MPJCVD) using a gas mixture of Ar-1%CH 4-10%H 2 and addition of 0.5–7% nitrogen. This growth process by MPJCVD with 10% hydrogen addition that yields UNCD films compared with those UNCD films produced by MPCVD with a high Ar/CH 4 ratio due to the focused microwave plasma jet greatly enhanced the enough dissociation of react gases and formed C 2 species with an energetic state at lower argon concentration. The surface morphologies were changed drastically from continuous to rough granular surface with increasing the nitrogen content due to the great rise of CN species in the plasma. The width of grain boundaries composed of sp 2-bonded carbon increased with increasing nitrogen content in the films. Moreover, the seldom defects in the UNCD films induced by the addition of nitrogen in the plasma were identified and investigated by using a scanning transmission electron microscope (STEM). The highest nitrogen-doped benefit with a N/C atomic ratio of 3.25% in UNCD films was reached by addition of only 3% N 2 in plasma (Ar-1%CH 4-10%H 2-3%N 2), showing the MPJCVD can greatly reduce the used amount of nitrogen in the synthesis of nitrogen-doped UNCD films.

Deposition of crackless freestanding diamond films on Mo substrates with Zr interlayer

The Mo substrate with Zr interlayer, namely composite substrate, was employed to solve the problem of crack formation in the freestanding diamond film deposition. Freestanding diamond films deposited on the composite substrates by the direct current arc plasma jet chemical vapor deposition (CVD) method were investigated with scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and Raman spectroscopy. In addition, the stress distribution during the large area freestanding diamond film deposition on the composite substrate was analyzed based on the finite element model ANSYS. The results reveal that Zr interlayer can be easily destroyed during the post-deposition cooling process, which is helpful for stress release and crack avoiding in diamond films.

Stress in Freestanding CVD Diamond Thick Film

The present paper describes research on stress in freestanding diamond thick film, diameter of 60mm, prepared on Mo substrate by DC arc plasma jet chemical vapor deposition (DCPCVD) method. The stress in the CVD diamond film was investigated by X-ray diffraction and Raman spectrum. The results show that the stress in the film is compressive. The stress changes little at the same homocentric round. The compressive stress along radial direction is that the stress in the centre of the film is lower than that in the edge at both the final surface and the original surface.

Thermal Stress in Free-standing Diamond Films with Cr Interlayer Destroyed

Thermal stress in large area free-standing diamond films was remarkable during the post-deposition cooling of direct current (DC) arc plasma jet chemical vapor deposition (CVD) process. In this research, the stress release caused by delamination of Cr interlayer was of great importance to ensure the integrity of free-standing diamond film. The effects of Cr interlayer on Mo substrate, namely composite substrate, on thermal stress were investigated. Thermo-mechanical coupling analysis of the thermal stress was applied by finite element analysis (FEA) using ANSYS code. It was found that the interlayer could be destroyed first by the large thermal stress, and then the stress could be released and the probability of diamond film crack initiation would be reduced. The stress concentration at the bent edge of diamond film was also discussed. In addition, diamond films deposited on Mo substrates with and without Cr interlayer were prepared by DC arc plasma jet CVD system and experimental measurements were used to characterize these films. It was found that composite substrate could be an effective method of growing free-standing crack-free diamond films by DC arc plasma jet CVD system when there is no special requirement to the film strength.