Plasma Chemical Vapor Deposition System Research Articles

One-Step Fabrication of Carbon Nanotubes Decorated with Graphitic Nanoflakes for Energy Storage Systems

We have used a bias-assisted microwave plasma chemical vapor deposition system to synthesize carbon nanotubes presenting graphitic nanoflakes, named coral-like carbon nanotubes, and well-aligned carbon nanotubes on carbon cloth substrates. Applying an external bias of -100 V led to the growth of well-aligned carbon nanotubes. In the absence of an external bias, the coral-like nanotubes presenting graphite nanoflakes were formed. The specific surface areas of the well-aligned and coral-like carbon nanotubes electrodes were 90.31 and 143.69 m2/g, respectively. In terms of energy storage, we estimated the capacitance of the coral-like carbon nanotube electrode to be ca. 194 F/g in an electrolyte of 1 M H2SO4. This value is almost double that of the well-aligned carbon nanotubes electrode (104 F/g), presumably because the presence of the carbon nanoflakes had a positive influence on the migration and adsorption of ions within the electrode. The fitting results indicated that the coral-like carbon nanotubes electrode behaved as a traditional electrochemical capacitor. Durability tests revealed that the coral-like carbon nanotube electrode was reliable, with a decay of 9% in capacitance over 1000 cycles.

Development of fine-particle plasma systems for basic and applied research

Two plasma systems for basic and applied research on fine-particle plasmas have been developed. One is a planar-magnetron plasma system, by which fine particles are suspended apart from the region of plasma production and are driven upward, for the basic research of fine-particle plasmas. Fine particles are observed to be horizontally arranged even when they have a size of 6.5 µm. The other one is a hot-filament-assisted plasma chemical vapor deposition system for nano-carbon synthesis. Synthesis processes have been analyzed by mass spectroscopy, light scattering and self-bias voltage. It was shown that negatively charged carbon fine particles were confined for a long time in plasmas during generation and growth. Synthesized carbon fine particles were confirmed to contain single-walled carbon nanotubes by analyzing the results of Raman spectroscopy and transmission electron microscopy.

Growth of high-quality carbon nanotubes on free-standing diamond substrates

Carbon nanotubes (CNTs) were grown on diamond-coated Si substrates and free-standing diamond wafers to develop efficient thermal interface materials for thermal management applications. High-quality, translucent, free-standing diamond substrates were processed in a 5kW microwave plasma chemical vapor deposition (CVD) system using CH4 as precursor. Ni and Ni–9%W–1.5%Fe catalyst islands were deposited to nucleate CNTs directly onto the diamond substrates. Randomly-oriented multi-walled CNTs forming a mat of ∼5μm thickness and consisting of ∼20nm diameter tubes were observed to grow in a thermal CVD system using C2H2 as precursor. Transmission electron microscopy and Raman analyses confirmed the presence of high-quality CNTs on diamond showing a D/G peak ratio of 0.2–0.3 in Raman spectra.

The metal-induced crystallization of poly-Si and the mobility enhancement of thin film transistors fabricated on a glass substrate

In this study, we report on the fabrication of poly-crystalline silicon (poly-Si) using the metal-induced crystallization (MIC) method and its application to thin film transistors (TFTs). The top gate of the p-type TFTs, whose active layer used MIC poly-Si annealed for 1 h at 650 °C, showed a field effect mobility ( μ FE) of 7.5 cm 2/V s. By increasing the crystallization time to 5 h, the quality of the MIC poly-Si was improved. The μ FE increased from 7.5 to 15 cm 2/V s. In order to enhance the channel mobility, the Si dangling bonds, which were produced during the transformation from the amorphous phase to the poly-crystalline phase of silicon (Si), were reduced by using plasma hydrogenation. Measurements show that the μ FE reached 45 cm 2/V s after passivation by an inductively coupled plasma chemical vapor deposition (ICPCVD) system.

The Field Emission Properties of Graphene Aggregates Films Deposited on Fe‐Cr‐Ni alloy Substrates

The graphene aggregates films were fabricated directly on Fe‐Cr‐Ni alloy substrates by microwave plasma chemical vapor deposition system (MPCVD). The source gas was a mixture of H2 and CH4 with flow rates of 100 sccm and 12 sccm, respectively. The micro‐ and nanostructures of the samples were characterized by Raman scattering spectroscopy, field emission scanning electron microscopy (SEM), and transparent electron microscopy (TEM). The field emission properties of the films were measured using a diode structure in a vacuum chamber. The turn‐on field was about 1.0 V/μm. The current density of 2.1 mA/cm2 at electric field of 2.4 V/μm was obtained.

Metal Oxide Film for Growing Vertically Aligned Single-Walled Carbon Nanotubes

In the present study, we use a method that uses the oxidation state of platinum in Co–Cr–Pt oxide films to cause a volume expansion to form isolated nanoparticles through exposure to H2 microwave plasma. The generated nanoparticles are then used to grow single-walled carbon nanotubes (SWCNTs) at ∼600 °C without the application of a buffer layer using a microwave plasma chemical vapor deposition system. The effects of metal oxide film thickness on the growth of SWCNTs are investigated. The characterization techniques including X-ray photoelectron spectroscopy, scanning electron microscopy, and transmission electron microscopy are carried out, with the results showing that this method used is highly efficient in generating very small and dense catalytic nanoparticles. The results also show that, when the metal oxide film thickness is no more than 2 nm, the nanoparticles produced with diameters ranging from 2 to 3 nm can be effective for growing vertically and densely aligned SWCNTs.

Nanocrystalline Silicon Thin-Film Transistor Fabricated without Substrate Heating for Flexible Display

We fabricated nanocrystalline silicon (nc-Si) thin-film transistors (TFTs) without any substrate heating. High quality nc-Si and silicon dioxide films were deposited at room temperature employing an inductively coupled plasma chemical vapor deposition (ICP-CVD) system. For the nc-Si film, a crystalline phase was grown as a columnar structure and the crystalline volume fraction was 27%. On the silicon dioxide film, hydrogen plasma post-treatment was performed, and the electrical characteristics of silicon dioxide film improved owing to charge reduction and the annealing effect. The nc-Si and silicon dioxide films were used for the fabrication of nc-Si TFTs without substrate heating. Although there was no external heating, a mobility of 6.42 cm2·V-1·s-1 was achieved. This result indicates that nc-Si TFTs fabricated without substrate heating may be a suitable devices for a flexible display.

Capillary jet injection of SiH4 in the high density plasma chemical vapor deposition of SiO2

In this article, the authors compare the thickness profiles and OH content of SiO2 films deposited using capillary jet injection of silane in a high density plasma chemical vapor deposition (HDP CVD) system with the results of phenomenological modeling using direct simulation Monte Carlo (DSMC) gas flow calculations. A tube with an internal diameter of 1mm is located vertically at 3cm in front of the substrate surface and is used for the injection of the silane. The deposition plasma is characterized using optical emission spectroscopy (OES) and differentially pumped quadrupole mass spectrometry (QMS). Studying the thickness-normalized OH absorption in the deposited film at various points on the substrate, the authors gain insight into the contribution of the water flux to the OH content in the deposited SiO2 film. Gas flow simulations using the DSMC technique are used to study the fluxes of the species onto the substrate plane. From the results the authors conclude that (i) the flux of the H2O onto the substrate holder is uniform, while the SiH4 flux varies considerably along the substrate holder, which leads to a lower level of hydroxyl incorporated into the deposited film in regions of high deposition rate; (ii) HDP CVD systems cannot be considered as well mixed when using SiH4 because its reaction products have high sticking coefficients and the ground-state molecules have the possibility to be consumed on the surface through reactions with oxygen radicals and ions when depositing SiO2; (iii) the primary beamlike flux of undissociated SiH4 onto the substrate surface has an important influence on the film’s deposition rate; and (iv) the SiH4 reactive sticking coefficient is estimated to be between 0.01 and 0.03.

Effect of rapid thermal annealing treatment on the field-emission characteristics of nanocrystalline diamonds grown on various metal/silicon substrates

In this study, nanocrystalline diamond (NCD) films were deposited on various metal/silicon substrates using a microwave plasma chemical vapor deposition system. Metal layers used are chromium, titanium, aluminum and were used as the electron source for field emitters. These NCD/metal/silicon structures were subsequently annealed at 500 °C in a rapid thermal annealing (RTA) furnace. After RTA treatment, the surface of NCD films becomes flat and the grain boundaries can no longer be clearly seen. The intensity of graphitic peak is substantially decreased and the sp3 content of NCD films is increased. The chemical composition of NCD film remains unchanged after RTA treatment, but the sp3/sp2 ratio in C 1s has been increased. It is found that the field-emission characteristics of diamond emitter not only can be effectively controlled by the metal used in the metal/NCD/Si structure, but also can be further enhanced by the improved microstructure of the NCD film obtained after RTA treatment.

Deposition of low dielectric constant SiOC films by using an atmospheric pressure microplasma jet

Low dielectric constant (low-k) SiOC films have been prepared by using an atmospheric pressure microplasma jet (APPJ) from mixtures of tetraethoxysilane (TEOS) and argon (Ar). By decreasing the Ar flow rate from 10 to 2 slm, the dielectric constant of films can be reduced almost linearly to values of about 2.1. Moreover, the film deposition rate increases dramatically to the maximum value of 23 nm s−1, which is much higher than that in a low pressure plasma chemical vapour deposition (LPCVD) system. The leakage current density of films increases with increasing electric field, but has a low value of 1 × 10−8 A cm−2 at 1 × 106 V cm−1, which is similar to the value of samples deposited by LPCVD. It has promising applications as interconnect dielectrics for future generations of advanced integrated circuits (ICs), in addition, demonstrating the feasibility of using APPJ as a substitute for costly and cumbersome low pressure equipment in the production process.

Pore sealing of mesoporous silica low- k dielectrics by oxygen and argon plasma treatments

In this study, we have prepared surfactant templated mesoporous silica thin films as the ultralow- k dielectrics and a TaN X thin film deposited by plasma enhanced atomic layer chemical vapor deposition (PE-ALCVD) using TaCl 5 as the gas precursor was used as the diffusion barrier. Without any surface modification for the dielectric layer, Ta atoms could easily diffuse into the mesoporous layer seriously degrading dielectric properties. O 2 and Ar plasmas have been used to modify the surface of the mesoporous dielectric in a high density plasma chemical vapor deposition (HDP-CVD) system, and both of the treatments produced a densified oxide layer a few nanometer thick. According to transmission electron microscopy and Auger electron spectroscopy, the pore sealing treatment could effectively prevent Ta atoms from diffusing into the mesoporous dielectric during the PE-ALCVD process.

Synthesis and structural characterization of highly 〈1 0 0〉-oriented {1 0 0}-faceted nanocrystalline diamond films by microwave plasma chemical vapor deposition

We report the synthesis and characterization of high-quality highly 〈1 0 0〉 oriented nanocrystalline diamond (NCD) films consisting of {1 0 0} nano-facets with a high growth rate of 2.6 μm/h. The NCD samples were grown on large (1 0 0) silicon wafers of 5.08 cm in diameter by employing CH 4/H 2/O 2/N 2 chemistries without the aid of bias for orientation, microwave power 3 kW and the substrate temperature about 700 °C using a 5 kW-type high-power microwave plasma chemical vapor deposition (CVD) system. The strong 〈1 0 0〉 preferred orientation is unambiguously demonstrated by a detailed crystallographic texture analysis and the conventional X-ray diffraction. Moreover, a detailed morphological characterization by the high-resolution scanning electron microscopy (SEM) and the atomic force microscopy (AFM), reveal that the growth surface consists of square (1 0 0) facets with an average size of about 60 nm and has a cylindrical microstructure. We demonstrate that the root-mean-square surface roughness as low as ∼15 nm, measured by AFM on 1 μm 2 scan areas, can be obtained even for considerably thick (76 μm) films. The high quality of these films is confirmed by the Raman and Fourier-transformer infrared spectra. The high-quality smooth 〈1 0 0〉-oriented {1 0 0}-faceted NCD films may have high potential in mechanical, tribological and micro-electromechanical system (MEMS) applications.

Field Emission Properties of Ball-Like Nano-Carbon Thin Films Deposited on Mo Films with Accidented Topography

Ball-like nano-carhon thin films (BNCTs) are grown on Mo layers by microwave plasma chemical vapour deposition (MPCVD) system. The Mo layers are deposited on ceramic substrates by electron beam deposition method and are pretreated by ultrasonically scratching. The optimization effects of ultrasonically scratching pretreat-ment on the surface micro-structures of carbon films are studied. It is found from field-emission scanning electron microscope (FE-SEM) images and Raman spectra that the surface structures of the carbon films deposited on Mo pretreated are improved, which are composed of highly uniform nano-structured carbon balls with considerable disorder structures. Field emission (FE) measurements are carried out using a diode structure. The experimental results indicate that the BNCTs exhibit good FE properties, which have the turn on field of 1.56 V/μm, and the current density of 1.0mA/cm2 at electric field of 4.0 V/μm, the uniformly distributed emission site density from a broad well-proportioned emission area of 4 cm2 are also obtained. Linearity is observed in Fowler–Nordheim (F–N) plots in higher Geld region, and the possible emission mechanism of BNCTs is discussed.

Highly Stable Bottom-Gate Nanocrystalline Silicon Thin Film Transistor Fabricated Employing ICP-CVD

Bottom-gate nanocrystalline silicon (nc-Si) thin film transistors (TFTs) were fabricated and evaluated their characteristics and electrical stability under various stress condition. nc-Si with high crystallinity was deposited employing Inductively coupled plasma chemical vapor deposition(ICP-CVD) system. We employed helium gas diluted deposition and all the process temperature was kept under 350oC. We fabricated conventional inverted-staggered nc-Si TFTs. Fabricated nc-Si TFTs showed fine electrical characteristics, such as electrical mobility of 0.64~0.77 cm2/V⋅sec. We investigated its stability through constant-voltage stress and constant-current stress. The threshold voltage shift after 30,000 seconds gate bias (10V) stress was only 0.098V, which is considerably less compared to a-Si:H TFT. Under the static current stress condition, the threshold voltage of the nc-Si TFT was shifted less than that of a-Si:H TFT. It demonstrates that nc-Si TFT exhibit better stability than conventional a-Si:H TFT.

The effect of Ni catalytic nanoparticle on the growth of carbon nanotubes: A perspective from nanotribological characterization

Characteristics of section structure, surface morphology, topography and tribology of catalyst nanoparticles synthesized with a microwave plasma chemical vapor deposition system on Ni/TaN/Si substrate are achieved by means of scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), ex situ atomic force microscopy (AFM), and nanoscratch techniques. In this study, we propose that the effect of catalyst nanoparticles on the growth of carbon nanotubes (CNTs) can be characterized by its tribological behavior. The results show that the temperature and the plasma treatment resulted in melting and roughening of the substrate surface, and promoted the formation of uniformly separated metal particles at 550 °C. This is due to the catalyst conglomerate forming particles with more uniform size under higher temperature. Our nanoscratch analysis indicates that the coefficient of friction of Ni nanoparticles/TaN/Si system increases from 0.77 to 1.2 while the pretreatment temperature increases from 450 °C to 550 °C. Furthermore, the scratch wear depth under ramping load show that higher pretreatment temperature leads to Ni nanoparticles with higher shear resistance, which enhances the well-aligned CNTs. These findings reveal that the role of pretreatment catalytic nanoparticles on the growth of CNTs can be identified by its nanotribological behavior.

Field emission characteristics of nano-structured carbon films deposited on differently pretreated Mo films

Nano-structured carbon films (NCFs) were grown on Mo layers by microwave plasma chemical vapor deposition (MPCVD) system. The Mo layers were deposited on ceramic substrates by electron beam deposition method and were pretreated by different techniques, which include ultrasonically scratching and laser-grooving technology (10 line/mm). NCFs were characterized by a field emission type scanning electron microscope (FE-SEM), Raman spectra and field emission (FE) I– V measurements. Effects of process parameters on morphologies, structures and FE properties of NCFs were examined. The experimental results show that two kinds of NCFs deposited at the same parameters employed for the MPCVD process were respectively composed of carbon nano-balls and reticular carbon nano-tubes inlayed by carbon nano-balls with dissimilar disorder structures, both NCFs showed each merits and exhibited good field emission properties, especially shown in the uniformity of FE, the uniform field emission images with areas of 4 cm 2 were obtained. Growth mechanism influenced by different pretreated method was discussed and the possible FE mechanisms of the NCFs were also investigated. Finally, the process characteristics of laser-grooving technology were analyzed, and its potential applications were predicted.

Interface structure of microcrystalline silicon deposited by inductive coupled plasma using internal low inductance antenna

Hydrogenated microcrystalline silicon (µc-Si:H) films were prepared by inductive coupled plasma chemical vapor deposition (ICP-CVD) system using internal low inductance antenna (LIA) units on various under layer composed of Si, O, and N. The resultant changes in the crystallinity of the µc-Si:H films were investigated using Raman scattering spectroscopy and the details of the interface structure were observed by high resolution transmission electron microscope. We had found that µc-Si:H film on the SiNx layer treated by O2 plasma has good interface quality. The highly crystallized µc-Si:H films with no amorphous incubation layer at interface of Si/SiNx could be directly deposited on the SiNx layer.

Luminescence behavior from amorphous silicon-carbide film-based optical microcavities

All solid-state optical microcavities based on amorphous silicon-carbide films were designed and prepared in conventional plasma chemical vapor deposition system. The resonant cavity mode was clearly observed in the transmission spectrum, which is in well agreement with the pre-designed value. Room temperature photoluminescence spectra were studied which contain both the enhanced emission band at resonant mode and the stop-band edge emission bands. The luminescence intensity is significantly enhanced and the bandwidth is obviously narrowed at the resonant wavelength due to the Si-based optical cavity structures. The modulation effect of cavity on the transmission and emission behaviors was investigated by angle-dependent transmission, photoluminescence spectra together with photoluminescence excitation spectra.

Low Temperature Synthesis of Single-Walled Carbon Nanotubes in an Inductively Coupled Plasma Chemical Vapor Deposition System

In this work, we present a parametric study on the low temperature synthesis of single-walled carbon nanotubes (SWNTs) in an inductively coupled plasma (ICP) CVD system using dry bi-layered catalytic thin-films (Fe/Al and Ni/Al, deposited by electron-beam evaporation method) as the catalysts. With a low substrate temperature of 550 degrees C and above, SWNTs were successfully synthesized on both catalysts, as revealed from the characteristic peaks of SWNTs in the micro-Raman spectra. By the reduction of plasma power and the shortening of the process times, the lowest synthesis temperature of SWNTs achieved in our system was approached to 500 degrees C on Ni/Al catalysts; on the other hands, the lowest temperature for Fe/Al catalysts was 550 degrees C. Our results suggest that as compared with Fe/Al, Ni/Al is more favorable for plasma-enhanced CVD (PECVD) synthesis of SWNTs at low temperatures. This work can be used for further improvements and better understanding on the production processes of SWNTs by PECVD methods.

Optical band gap of nitrogenated amorphous carbon thin films synthesized by microwave surface wave plasma CVD

Nitrogenated amorphous carbon (a-C:N) thin films were prepared on silicon and quartz substrates by microwave surface wave plasma chemical vapor deposition system, aiming to control optical band gap ( E g) of the films for photovoltaic solar cells application. For films deposition, we used argon as carrier gas, nitrogen as dopant and hydrocarbon source gases, such as camphor dissolved with ethyl alcohol (3:7) and acetylene. The E g of the films has been decreased from 4.1 to 2.4 eV and 2.2 to 1.6 eV with alcohol plus camphor and acetylene source gases respectively by nitrogen doping. The E g of the a-C:N films can be tuned from 2.4 to 0.95 eV by thermal annealing treatment. These results show that it is possible to control the E g by nitrogen doping with different carbon source gases and by post growth annealing of the films.