Bias-assisted Hot Filament Chemical Vapor Research Articles

Nanostructured boron-doped diamond electrode for degradation of the simulation wastewater of phenol

The applications of a boron-doped diamond (BDD) used in electrode application for toxic and refractory organic degradation have attracted much attention, and its efficiency is considered to be an important factor for its practical application. In this study, BDD thin films were prepared on Ti plates by double bias-assisted hot filament chemical vapor deposition (HFCVD) technique. A reactive ion etching process was introduced by a positive grid bias and a negative substrate bias which can generate an electric field in HFCVD system. Then a novel structure of BDD electrode with nanocone arrays was successfully etched from a flat diamond thin film by this system. The addition of the bias greatly improved the etching efficiency and promoted the formation of nanocones structures. The cyclic voltammograms (CV) test showed nanostructured BDD (NBDD) electrodes had excellent electrochemical performance almost the same as that of the electrodes with untreated surfaces. It had a large effective electroactive surface area (EASA), which was 31.0% greater than the unetched electrode. As a result, the NBDD electrode exhibited improved electrocatalytic performance as compared with the untreated one, i.e., an about 24.3% increase of chemical oxygen demand (COD) removal efficiency. Among them, the superiority of NBDD electrode was obvious in the initial stage due to its highest concentration in the initial stage. In addition, the NBDD electrode achieved higher average current efficiency (ACE) as compared with the untreated one.

Assessment of carbon nanotubes and silver nanoparticles loaded clays as adsorbents for removal of bacterial contaminants from water sources.

This work evaluated the antimicrobial efficacy of kaolin clay and its loaded forms with carbon nanotubes (CNTs) and silver nanoparticles (AgNPs) against bacterial isolates from different water supplies (tap, underground and surface water) in addition to wastewater. A total of 160 water samples were collected from different water sources in the investigated districts. Samples were cultured for isolation and serological identification of pathogenic bacteria. AgNPs were synthesized by a typical one-step synthesis protocol, where CNTs were carried out in a reactor employing the double bias-assisted hot filament chemical vapor deposition method. Both were characterized using transmission electron microscopy, infrared and X-ray fluorescence (XRF) spectroscopy. The antimicrobial efficacy of each of natural kaolin clay, AgNPs- and CNTs-loaded clays were evaluated by their application in four concentrations (0.01, 0.03, 0.05 and 0.1 ppm) at different contact times (5 min, 15 min, 30 min and 2 h). AgNPs-loaded clays at concentrations of 0.05 and 0.1 mg/l for 2 h contact time exhibited a higher bactericidal efficacy on Escherichia coli and Salmonella spp. (70, 70, 80 and 90%, respectively) compared to CNTs-loaded clay. Concluding, the application of AgNPs-loaded clay for removal of water bacterial contaminants at a concentration of 0.1 ppm for 2 h contact times resulted in highly effective removals.

General fabrication of ordered nanocone arrays by one-step selective plasma etching

One-step selective direct current (DC) plasma etching technology is employed to fabricate large-area well-aligned nanocone arrays on various functional materials including semiconductor, insulator and metal. The cones have nanoscale apexes (∼2 nm) with high aspect ratios, which were achieved by a selective plasma etching process using only CH4 and H2 in a bias-assisted hot filament chemical vapor deposition (HFCVD) system without any masked process. The ions play a major role to etch the roughened surface into a conical structure under the auxiliary of H+ ions. Randomly formed nano-carbon may act as an original mask on the smooth surface to initiate the following selective ions sputtering. Physical impinging of energetic ions onto the concave regions is predominant in comparison with the etching of convex parts on the surface, which is identified as the key mechanism for the formation of conical nanostructures. This one-step maskless plasma etching technology enables the universal formation of uniform nanocone structures on versatile substrates for many promising applications.

Metallic electrical transport in inter-graphitic planes of an individual tubular carbonnanocone

Tubular carbon cones (TCCs) with a herring-bone-like graphitic structure are synthesizedon gold wire via the bias-assisted hot filament chemical vapor deposition (HFCVD)method. The electrical transport properties of an individual TCC are studied in thetemperature range from 300 to 500 K by using a double probe scanning electronmicroscopy (DPSEM) in situ electrical measurement system. The high-resistanceI–V characteristics of W–TCC–Au back-to-back double junctions show that electrons tunnelthrough the W–TCC junction, while thermoionic transport through the Au–TCC junctioncontributes to low-resistance properties. Temperature dependence of the electricalcharacteristics indicates that inter-graphitic-plane electrical transport in TCC is metallic.

Effect of grain size and pores on the dielectric constant of nanocrystalline diamond films

The nanocrystalline diamond films with different morphologies and roughness were synthesized by a bias-assisted hot filament chemical vapor deposition method. It was found that the nanocrystalline diamond film exhibited low-k dielectric properties with the increase of CH4 concentration during diamond deposition. The low-k nanocrystalline diamond film with grain size of around 40nm and dielectric constant of 2.4 was obtained at the CH4 concentration of 16% and the bias of −140V. The low dielectric constant can be mainly attributed to the decrease of diamond grain sizes and the formation of more nanopores in as-grown nanocrystalline diamond film, both of which were discussed in details based on the grain size determined band gap expansion effect and the two-phase dielectric mixing model, respectively.

Field electron emission from individual diamond cone formed by plasma etching

Field electron emission properties of individual diamond cone were investigated using a customized double-probe scanning electron microscope system. The diamond cone was formed by maskless ion sputtering process in bias-assisted hot filament chemical vapor deposition system. The as-formed sharp diamond cone coated with high-sp2-content amorphous carbon exhibited high emission current of about 80μA at an applied voltage of 100V. The field emission was stable and well in consistent with the conventional Fowler-Nordheim emission mechanism, due to a stabilization process in surface work function. It has demonstrated the possibility of using individual diamond cone as a point electron emission source, because of its high field electron emission ability and stable surface state after the process of work function stabilization.

Raman characterization of boron carbonitride nanotubes

A systematic Raman study of boron carbonitride (BCN) nanotubes, synthesized by bias-assisted hot filament chemical vapor deposition, is reported. Raman spectra up to the fourth order are observed from the BCN nanotubes. Comparing with pure carbon nanotubes, the Raman bands in BCN nanotubes are broadened and the relative intensity of the D mode with respect to the G mode varies with increasing B and N atomic concentrations. The underlying mechanism has been studied on the basis of the microstructures obtained by high-resolution transmission electron microscopy.

Adjustable boron carbonitride nanotubes

The adjustable photoluminescence (PL) and field electron emission (FEE) properties of boron carbonitride (B–C–N) nanotubes grown under well-controlled conditions are studied systematically. Large-scale highly aligned B–C–N nanotubes are synthesized directly on Ni substrates by the bias-assisted hot filament chemical vapor deposition method. Single-walled B–C–N nanotubes and nanometric B–C–N heterojunctions are obtained by the pulsed-arc-discharge technique and pause-reactivation two-stage process, respectively. It is found that the microstructures, orientations, and chemical compositions of the nanotubes can be controlled by varying growth parameters. The mechanism of the controllable growth is also investigated. Intense and stable PL from the nanotubes is observed in both blue-violet (photon energies 3.14–2.55 eV) and yellow-green bands (photon energies 2.13–2.34 eV) and the emission bands are adjusted by varying the compositions of the nanotubes. FEE properties are also studied and optimized by varying the B or N atomic concentrations in the nanotubes. All these results verify the controllability of the electronic band structure of the B–C–N nanotubes.

Blue–violet photoluminescence from large-scale highly aligned boron carbonitride nanofibers

We report on the strong blue–violet photoluminescence (PL) at room temperature from the large-scale highly aligned boron carbonitride (BCN) nanofibers synthesized by bias-assisted hot filament chemical vapor deposition. The photoluminescence peak wavelength shifts in the range of 470–390 nm by changing the chemical composition of the BCN nanofibers, which shows an interesting blue and violet-light-emitting material with adjustable optical properties. The mechanism for the shift of the PL peaks at room temperature is also discussed.

Highly oriented rich boron B–C–N nanotubes by bias-assisted hot filament chemical vapor deposition

Highly oriented rich boron B–C–N nanotubes, prepared by bias-assisted hot filament chemical vapor deposition, have been examined by scanning electron microscopy, transmission electron microscopy, and Raman spectroscopy. The compositions of the nanotubes have been analyzed by Auger electron spectroscopy and electron energy loss spectroscopy. The results show that the compositions can be controlled by changing the B 2H 6 concentration in the reactive gas mixture and the highest boron content of 45% at atomic percentage can be obtained for the B–C–N nanotubes. As a new kind of semiconducting material, the photoluminescence of the B–C–N nanotubes is also studied.

Turbostratic boron carbonitride films produced by bias-assisted hot filament chemical vapor deposition

Boron carbonitride (BCN) films with various compositions have been prepared by bias-assisted hot filament chemical vapor deposition. The three elements of B, C, and N are chemically bonded with each other and an atomic-level BCN hybrid has been formed in the films. The deposited films are composed of turbostratic structural regions ranging from a few to a few tens of nanometers. Besides, there exist some amorphous domains in the films. Boron atoms have been confirmed to be incorporated into the films with a concentration up to 70 at. %. The interplanar spacing of 3.49 Å is found to be independent of the film composition in this range. These films show a blueshift in photoluminescence peak with increasing B content. These findings show that the electronic structure of BCN compounds can be controlled by changing compositions and the BCN compounds are blue-light emitting materials.

Heteroepitaxial nucleation of diamond on Si(100) via double bias-assisted hot filament chemical vapor deposition

A new process has been developed to obtain high density epitaxial diamond nucleation via a double bias-assisted hot filament chemical vapor deposition (HFCVD). In the process, a negative bias voltage is applied to the Si substrate and a positive bias voltage is applied to a steel grid placed on top of the hot filaments. With this arrangement, a stable plasma can be generated between the grid and the hot filaments. Ions in the plasma are then drawn to the substrate by a negative substrate bias voltage. The impinging rate of these ions can be easily controlled by adjusting the grid current, and the ion energy can be independently controlled by adjusting the substrate bias voltage. Hence, the energy and dosage of ion bombardment onto the Si(100) substrate can be controlled easily and independently. With the controlled ion bombardment, high density and heteroepitaxial nucleation can be achieved routinely. After the nucleation process, highly textured diamond films were grown by either the HFCVD or the microwave plasma chemical vapor deposition process (MPCVD).

Growth of epitaxial β-SiC films on silicon using solid graphite and silicon sources

Epitaxial β-SiC films have been grown on mirror-polished Si(111) substrates using bias-assisted hot filament chemical vapor deposition at a substrate temperature of 1000°C. A graphite plate was used as the carbon source, and the silicon source came from the silicon substrate itself. The gas phase in the system is hydrogen only. Atomic hydrogen produced by hot filaments reacted with the graphite to form hydrocarbon radicals, which further reacted with the silicon substrate and deposited as β-SiC. The effect of negative bias applied to the substrate is the key factor for epitaxial growth. Under the growth conditions without the negative bias applied, only polycrystalline β-SiC was obtained.

Influence of deposition condition and hydrogen on amorphous-to-polycrystalline SiCN films

Synthesis of SiCN thin films on mirror-polished Si(100) substrates has been achieved by performing a bias-assisted hot filament chemical vapor deposition. High purity nitrogen, methane, and hydrogen were used as reactant gases. Incorporated Si element in the films totally came from the Si surface of the substrate. Scanning electron microscopy showed two categories of morphologies of the films according to the introduction of hydrogen. Energy-dispersive X-ray analysis and Auger electron spectroscopy depth profiling were used to measure the chemical composition of the samples. With no hydrogen applied, the film was found to be a nitride layer over the Si substrate with some nanosize columnal silicon-containing CN crystals embedded. With hydrogen added, the film was uniformly composed of smaller SiCN particles. On both conditions, the overall carbon content was rather limited. X-ray photoelectron spectroscopy revealed the chemical environment of C, N, and Si atoms in the samples. The effect of methane flow ratio and substrate temperature were investigated on the conditions without hydrogen flow. The effects of hydrogen flow ratio on the films were also studied.

Synthesis and characterization of B–C–N compounds on molybdenum

B–C–N compounds were prepared on molybdenum by means of bias-assisted hot filament chemical vapor deposition (HFCVD). Effect of the substrate temperature (Ts) on the growth of B–C–N films has been investigated systematically by x-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) based on the detailed analysis and calculation of the XPS. The substrate temperature plays a key role in the formation of the bonding states, the composition, and the surface morphology. Boron carbonitride is the main phase at all depositing temperatures, and the obtained compounds are as follows: B0.83C0.17 + B0.39C0.35N0.26 at 873 K, B0.30C0.34N0.36 at 973 K, B0.64C0.36 + B0.51C0.23N0.26 at 1073 K, B0.51C0.31N0.18 at 1173 K, and B0.37C0.54N0.09 at 1273 K.

Epitaxial growth of β–SiC on silicon by bias-assisted hot filament chemical vapor deposition from solid graphite and silicon sources

Epitaxial β–SiC film has been grown on a mirror-polished Si(111) substrate using bias-assisted hot filament chemical vapor deposition (BA-HFCVD) at a substrate temperature of 1000 °C. A graphite plate was used as the only carbon source, and hydrogen was the only feeding gas to the deposition system. Atomic hydrogen, produced by hot filaments, reacted with the graphite to form hydrocarbon radicals which further reacted with the silicon substrate and deposited as β–SiC. The effect of negatively biasing the substrate is the key factor for epitaxial growth. Under the same growth conditions without negative bias, polycrystalline β–SiC resulted.

Uniform and rapid nucleation of diamond via bias-assisted hot filament chemical vapor deposition

A new method was developed to obtain high density, uniform diamond nuclei via bias-assisted hot filament chemical vapor deposition. A negative bias was applied between a mesh (installed above the filament) and the substrate to produce abundant uniform ions at the growth surface. Raman spectroscopy, scanning electron microscopy, and Auger electron microscopy were used to analyze the films obtained. The results show that a layer of diamond film with a nucleation density of 109/cm2 can be obtained after 10 min deposition under 1 Torr.

Synthesis and characterization of C3N4 crystal (II)

A successful experimental synthesis of pure crystalline β- and α-C3N4 films on Si(100) substrate was carried out by bias-assisted hot filament chemical vapor deposition (bias-HFCVD). It is found that a mixed-phase C3-I-SixNy buffer layer was formed between the Si substrate and the C-N film. A “lattice match selection” was proposed to study the growth mechanism of C3N4 clusters composed of many crystal columns with hexagonal facets.

Effect of methane concentration on the growth of crystalline C3N4 films

The effect of methane concentration on the growth of crystalline α- and β-C 3 N 4 films have been studied in bias-assisted hot filament chemical vapor deposition system by using a low-pressure methane-nitrogen gas mixture. Scanning electron microscopy, energy dispersive X-ray analysis, and X-ray diffraction have been used to characterize the films obtained. The results indicate that a methane concentration of 0.5 vol% leads to a compatible growth of α- and β-C 3 N 4 ; 1.0 and 2.0 vol% lead to the selected growth of β- and α-C 3 N 4 , respectively. The lattice constants of the C 3 N 4 phases synthesized at different methane concentrations coincide very well with the ab initio calculation results. Moreover, two recently identified CN new phases with tetragonal and monoclinic structure are found in all of the depositions.

Synthesis and characterization of C3N4 crystal (I)

A successful experimental synthesis of pure crystalline β- and α-C3N4 films on Si(100) substrate was carried out by bias-assisted hot filament chemical vapor deposition (bias-HFCVD). It is found that a mixed-phase C3-I-SixNy buffer layer was formed between the Si substrate and the C-N film. A “lattice match selection” was proposed to study the growth mechanism of C3N4 clusters composed of many crystal columns with hexagonal facets.