Dc Plasma-enhanced Chemical Vapor Deposition Research Articles

CVD-diamond nanoparticle synthesis for DLC film application

Diamond-like carbon (DLC) films have been extensively applied as a solid lubricant and as a protective coating due to their attractive chemical, mechanical, and tribological properties. Furthermore, these properties of DLC coatings can be improved with the incorporation of nanoparticles of different materials, especially diamond nanoparticles (DNPs). Herein, the incorporation of chemical vapor deposition (CVD) DNPs was done from a deionized aqueous colloidal solution by using a controlled pulsed valve, which is an innovative aspect of this work. The CVD DNPs were pulverized into the plasma region and incorporated in the DLC films bulk with controllable size particle distribution and density. In addition, an enhanced process to obtain DNPs with suitable size distribution was established by using a high energy ball milling technique, centrifugation, and a special chemical cleaning process. The DLC films were deposited on a metallic substrate via a modified, pulsed DC plasma-enhanced chemical vapor deposition (PECVD) technique, with an additional cathode. X-ray diffractometry (XRD) and scanning electronic microscopy (SEM) techniques showed that an aqueous colloidal solution of high-purity DNPs with a mean diameter of 32 nm was obtained. Dynamic light scattering (DLS) results showed that it is possible to control particle size distribution by varying the milling and centrifugation time lengths. Therefore, a valuable result was that DLC films could be deposited with DNPs by using clean water without affecting deposition rate, the adhesion between the DLC films and substrates, the structural quality of the film, and keeping lower coefficient of friction.

Impact of pressure on carbon films by PECVD toward high deposition rates and high stability as metallic bipolar plate for PEMFCs

Stainless-steel bipolar plates (BPPs) are widely used in place of graphite bipolar plates in proton exchange membrane fuel cells (PEMFCs). Amorphous hydrogenated carbon (a-C:H) coatings are widely used to improve the conductivity and corrosion resistance of metal bipolar plates. However, a-C:H coatings prepared by the sputtering method cannot be applied to quantity production on account of its low deposition rate. Our paper focuses on a-C:H coatings applied at metallic BPPs for PEMFCs produced by direct-current plasma-enhanced chemical vapor deposition (DC-PECVD) with high deposition rates. The effects of adjusting deposition pressures on the structure and properties of coatings have been investigated. The results show that the a-C:H coating deposited at 8 Pa deposition pressure have high stability, with a high deposition rate of 37.5 nm/min. As the deposition pressure increased, sp2-hybridized carbon atoms increased, the larger microcrystalline carbon clusters are found, and the structure will undergo different structural transformations in a-C:H coatings. Overall, the a-C:H coatings deposited at 8 Pa are attractive to be applied in metallic bipolar plate with have high deposition rates, dense coating structure, and proper carbon structure.

Improving field emission properties of vertically aligned carbon nanotube arrays through a structure modification

Vertically aligned carbon nanotube (VACNT) emitters were synthesized directly on stainless steel substrate using DC plasma-enhanced chemical vapor deposition. Remarkable field emission (FE) properties, such as low turn-on electric field (ETO = 1.40 V/μm) and low threshold electric field (ETH = 2.31 V/μm), were observed from VACNT arrays with long length and moderate density. The FE performance was significantly enhanced by a uniquely bundled structure of VACNTs formed through a simple water treatment process. The FE properties of VACNTs were further improved by coating the exterior of CNTs with a uniform layer of crystalline SnO2 nanoparticles; the ETO and ETH were reduced to 1.18 and 2.01 V/μm, respectively. The enhancement of FE properties by SnO2 coating can be attributed to the morphological change of VACNTs caused by the solution phase coating process. The coated samples also exhibited an improved FE stability which is attributed to the enhancement of the mechanical strength and chemical stability of the VACNTs after the SnO2 coating. The VACNT emitters with characteristic features such as a conductive substrate, low contact resistance between the VACNTs and the substrate, uniform coating, and bundled morphology can be ideal candidates for FE devices.

Spectroscopic studies to investigate the effect of different plasma parameters on the geometrical and electronic structure of graphene

Spectroscopic studies were carried out on monolayer, trilayer, and few layers of graphene sheets to investigate the effect of plasma parameters such as the electric current, substrate temperature, and the effect of the acetylene and hydrogen gases mixture ratios on the geometrical structure, electronic and optical properties of the synthesized films. Single-, triple- and few-layer graphene sheets were deposited on copper substrates by using self-assembled direct current plasma enhanced chemical vapor deposition (DC-PECVD) reactor. The deposited graphene samples were characterized by high resolution transmission electron microscope (HRTEM), X-ray diffraction (XRD), Raman and photoluminescence (PL) spectroscopy. The results demonstrated that the number of graphene layers as well as the defects ratio of sp2 hybridization size domain have been changed notably with changing the preparation conditions, where a single layer graphene sheet was obtained at preparation conditions of H2:C2H2 ratio of 100:4 sccm, plasma electric current of 130 mA, and substrate temperature of 750 °C. The recorded PL spectrum for the single layer graphene shows one weak and broad band at 348 nm. We have recorded an exponential relation between the blue shift of the PL peak and the changing in the size domain of the sp2 hybridization.

Electron field emission property of nanostructure wrinkle thin film induced by amorphous diamond like carbon

The electron field emission property of nanostructure wrinkle created by silver doped amorphous diamond like carbon (a-Ag:DLC) thin film have been reported. The amorphous Ag:DLC thin film have been deposited on elastomeric polymer of poly-dimenthylsiloxane (PDMS) and silicon substrate by direct current plasma enhanced chemical vapor deposition (DC-PECVD) process. Due to difference in elastic moduli of PDMS substrate and a-Ag:DLC thin films, a well-defined nanostructure wrinkle pattern have formed on PDMS surface. Is has been observed that the wavelength of the created wrinkle decreased as increased the Ag content in the DLC film. Due to the surface nanostructure as well as change in electronic structure by Ag doping, the a-Ag:DLC wrinkled film showed good electron field emission properties with a low threshold field.

Coin-cell Supercapacitors Based on CVD Grown and Vertically Aligned Carbon Nanofibers (VACNFs)

Complete supercapacitors (SCs) comprising vertically aligned carbon nanofibers (VACNFs) as electrode materials have been assembled as coin-cells. The VACNFs were grown directly onto the current collector by direct current plasma enhanced chemical vapor deposition (DC-PECVD), thereby providing excellent contact with the current collector, but also eliminating the need of any binder. The vertical alignment facilitates fast ion transport and the electrolyte to access the entire surface of the CNFs. The morphology of the VACNFs was evaluated by scanning electron microscopy (SEM), while the performance was assessed by several methods: cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and device related cycling by galvanostatic charge/discharge. The capacitance, 3.64 mF/cm2 , is >15 times higher than the capacitance of a coin-cell without CNFs and the cyclic performance shows these proof-of-concept SCs to retain >80% of the capacitance after 2000 full charge/discharge cycles. The direct growth of VACNFs as electrodes at the current collector opens pathways for SC production using existing coin-cell battery production technology.

The growth of patterned carbon nanotube arrays on Si pillar arrays

ABSTRACTVertically aligned carbon nanotube (CNT) arrays were prepared using dc plasma-enhanced chemical vapor deposition (DC-PECVD). For uniform growth of the vertically aligned CNTs in the patterned array, the conventional photolithography technique and oblique angle deposition technique were utilized. The pattern of the CNTs was defined by the silicon pillar configuration fabricated by the conventional photolithography. The characteristics of the vertically aligned CNTs were dependent on conditions of catalyst metals using the oblique angle deposition technique. Using the conventional photolithography and oblique angle deposition techniques, the well-defined and well-separated CNT pattern arrays were successfully grown. In order to improve the electrical properties of the grown CNTs, nitrogen (N) was doped using NH3. This low-cost and simplified fabricating method would be an effective growth process for the CNT array which can be used in field emitter applications.

Recent Research Progress of Carbon Nanotube Arrays Prepared by Plasma Enhanced Chemical Vapor Deposition Method

Preparing carbon nanotube (CNT) arrays by plasma enhanced chemical vapor deposition (PECVD) method can dramatically reduce the deposition temperature, which makes it possible for in-situ fabrication of CNT-based nanoelectronic devices. In this paper, up to date research progress of CNT arrays prepared by PECVD method was presented, including radio frequency PECVD, direct current PECVD and microwave PECVD. Then, morphology and quality of CNT arrays were compared. In the end, we analyzed the possible challenges encountered through CNT array preparation by PECVD method at the moment and in the future.

Effect of Plasma Power on Growth of Multilayer Graphene on Copper Using Plasma Enhanced Chemical Vapour Deposition

Large-area multilayer graphene was synthesised on Cu foil by DC plasma-enhanced chemical vapour deposition (DC PECVD) at a relatively low temperature. We discuss the growth mechanism of graphene in the plasma environment by the PECVD method based on the results of X-ray photoelectron spectroscopy, scanning electron microscopy and Raman scattering. Also, the I–V characteristics of graphene synthesised at different plasma powers was studied with a Keithley 2361 system. Due to the advantages of plasma growth, graphene synthesised under DC plasma exhibits better crystallinity, higher growth rate and large grain size at relatively low temperatures. At a plasma power of 100 W, the grain size of graphene (~5 μm) can be increased by a factor of 5. Raman spectroscopy showed D, G and 2D bound in our graphene samples while we find that the intensity of the D peak decreases by increasing the plasma power in growth conditions, which means that the defect density is reduced by the use of the plasma. The XPS results from the sample with maximum plasma power confirm the existence of sp2 carbon atoms (C=C), which indicates the successful formation of graphene onto Cu foil by PECVD. In addition the increase of plasma power is attributed to larger grain sizes, thus leading to the increase of mobility and current change. This investigation shows that DC PECVD is a simple and effective technique to synthesise large-area multilayer graphene, which has potential for application as electronic devices.

Pt nanoparticles supported on carbon nanowalls with different domain sizes for oxygen reduction reaction

Carbon nanowalls (CNWs) with different domain sizes were synthesized by a dc plasma-enhanced chemical vapor deposition. Platinum (Pt) loading on the CNWs (Pt/CNW) was carried out by a solution reduction method. As a result, Pt nanoparticles were preferentially deposited along the domain boundaries in CNWs as reported previously. It should be noted that the Pt particle size strongly depends on the domain size. Namely, the smaller the domain size is, the smaller the Pt particle size is. Moreover, the Pt/CNW with smaller Pt particles exhibit high catalytic activity. Especially, the mass activity related to cathodic oxygen reduction reaction (ORR) is high and reach about five times as much as that of commercial T-Pt/CB with good performance. The high ORR activity can be attributed to the domain boundaries in CNWs, which might lower not only the activation energy of O2 dissociation on Pt particles but also the energy barrier of the rate-limiting step in the ORR process.

A catalyst free method to grow GaN nanowires on porous Si at low temperature

GaN nanowires (NWs) were synthesized on porous silicon (PSi) as a substrate using pulsed direct current plasma enhanced chemical vapor deposition (DC-PECVD) method at 600°C. The precursors were gallium (Ga) metal and nitrogen (N) plasma. The GaN NWs were grown as a result of direct reaction between Ga atoms and excited N atoms in the plasma environment on PSi substrate, without using any catalyst. Self-induced mechanism is suggested to grow GaN NWs on PSi. Characterizations of GaN NWs were carried out by field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), photoluminescence (PL) and Raman spectroscopy. These measurements showed that the hexagonal structure of GaN NWs were synthesized with diameters from 20 to 50nm. The band gap energy of GaN NWs was obtained about 3.42eV. Further optical analysis using Raman spectra displayed two Raman active optical phonons at 535cm−1 and 730cm−1 due to A1 (TO) and A1 (LO), respectively.

Field emission current from a junction field-effect transistor

Fabrication of a titanium dioxide/carbon nanotube (TiO2/CNT)-based transistor is reported. The transistor can be considered as a combination of a field emission transistor and a junction field-effect transistor. Using direct current plasma-enhanced chemical vapor deposition (DC-PECVD) technique, CNTs were grown on a p-typed (100)-oriented silicon substrate. The CNTs were then covered by TiO2 nanoparticles 2–5 nm in size, using an atmospheric pressure CVD technique. In this device, TiO2/CNT junction is responsible for controlling the emission current. High on/off-current ratio and proper gate control are the most important advantages of device. A model based on Fowler–Nordheim equation is utilized for calculation of the emission current and the results are compared with experimental data. The effect of TiO2/CNT hetero-structure is also investigated, and well modeled.

CMOS compatible on-chip decoupling capacitor based on vertically aligned carbon nanofibers

On-chip decoupling capacitor of specific capacitance 55pF/μm2 (footprint area) which is 10 times higher than the commercially available discrete and on-chip (65nm technology node) decoupling capacitors is presented. The electrodes of the capacitor are based on vertically aligned carbon nanofibers (CNFs) capable of being integrated directly on CMOS chips. The carbon nanofibers employed in this study were grown on CMOS chips using direct current plasma enhanced chemical vapor deposition (DC-PECVD) technique at CMOS compatible temperature. The carbon nanofibers were grown at temperature from 390°C to 550°C. The capacitance of the carbon nanofibers was measured by cyclic voltammetry and thus compared. Futhermore the capacitance of decoupling capacitor was measured using different voltage scan rate to show their high charge storage capability and finally the cyclic voltammetry is run for 1000 cycles to assess their suitability as electrode material for decoupling capacitor. Our results show the high specific capacitance and long-term reliability of performance of the on-chip decoupling capacitors. Moreover, the specific capacitance shown is larger for carbon nanofibers grown at higher temperature.

パルスDC-PCVD法による各種硬質皮膜の金型への応用

パルスDC-PCVD法による各種硬質皮膜の金型への応用

Effect of Substrate Temperature on Structural and Optical Properties of Un-Doped Diamond Thin Film

Un-doped diamond thin films were deposited at various substrate temperatures (from 300 °C to 500 °C) onto glass substrates by using direct current plasma enhanced chemical vapour deposition (DC-PECVD) system. The fabricated films were having amorphous phase which shown by X-ray diffraction (XRD). Atomic force microscopy (AFM) has discovered that the RMS surface roughness and the thickness which were obtained in the range of 0.69 nm to 1.67 nm and 4.8 nm to 0.83 nm, respectively as increasing substrate temperatures. From UV visible spectroscopy (UV-VIS), it was found that the optical transition had changed from forbidden indirect transition to allowed indirect transition as the substrate temperature increased. The optical band gaps were increased (3.14 eV, 3.93 eV and 4.09 eV) when the substrate temperatures increased. Hence, the higher the substrate temperatures, the larger the cluster size and RMS surface roughness and result in decreasing of films thickness and increasing the optical band gap.

Gold catalyst effect on the morphological and structural properties of GaN nanostructures deposited by plasma enhanced chemical vapor deposition

Wurtzite type structure of GaN nanowires and nanograins were synthesized by pulsed direct current plasma enhanced chemical vapor deposition (DC-PECVD) at low temperature (600°C). The GaN nanostructures were grown using gallium atoms and excited nitrogen species in the plasma on Si substrates either with or without catalyst. Structural and morphological characterizations of GaN nanostructures were carried out using X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS) and field emission electron microscopy (FESEM). GaN nanowires were grown on the gold-coated Si with average diameters of 20–30nm. However, nanoislands appeared over uncoated Si substrates. Using catalyst can increase the concentration of nitrogen and gallium atoms and GaN nanowires can be formed on the gold-coated Si substrate.

Aerosynthesis: Growth of Vertically-Aligned Carbon Nanofibres with Air DC Plasma

Vertically-aligned carbon nanofibres (VACNFs) have been synthesized in a mixture of acetone and air using catalytic DC plasma-enhanced chemical vapour deposition. Typically, ammonia or hydrogen is used as an etchant gas in the mixture to remove carbon that otherwise passivates the catalyst surface and impedes growth. Our demonstration of the use of air as the etchant gas opens up the possibility that ion etching could be sufficient to maintain the catalytic activity state during synthesis. It also demonstrates a path toward growing VACNFs in the open atmosphere.

Synthesis of GaN Nanoparticles by DC Plasma Enhanced Chemical Vapor Deposition

The unique optical properties of nanostructured GaN basically, turn it as a very important part of many electronic and optoelectronic devices such as high power transistors, UV detectors, solar cells, lasers and blue LED. The aim of the current study is GaN nanoparticle deposition at low temperature in preferred direction. In this work, GaN nanoparticles were prepared using direct current plasma enhanced chemical vapor deposition (DC-PECVD) method on Si (100) wafer as a substrate at 700°C. Gallium metal and nitrogen plasma were used as precursors. GaN nanoparticles were grown based on the direct reaction between gallium atoms and excited nitrogen species in the plasma. Structural and morphological characterizations of GaN nanoparticles were carried out using X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS) and field emissions electron microscopy (FE-SEM). Preferred (100) direction of GaN nanostructures which obtained by careful control of processing parameters, were revealed by XRD. FE-SEM images show the average diameter of nanoparticles is 37 nm. The EDS results show the Ga to N ratio in the sample was 8.8 to 1.2 by weight which is very close to the Ga to N ratio of prefect GaN crystal. The deviance is related to the nitrogen vacancy of the sample. These results demonstrate a simple inexpensive method for GaN nanoparticle deposition at low temperature which is critical for many of applications.

Atomic force microscopy and Raman spectroscopy study of the early stages of carbon nanowall growth by dc plasma-enhanced chemical vapor deposition

The early stage of carbon nanowall (CNW) growth on Si substrate by dc plasma-enhanced chemical vapor deposition (PECVD) was investigated by means of atomic force microscopy and Raman spectroscopy. First nanodiamond particles with highly defective graphene layers are shown to be formed over the substrate. Subsequently nanographite grains are formed on the nanodiamond film. The density of nanographite grains increases with increasing deposition time, and they coalesce to form a continuous graphite film. Finally CNWs are shown to grow vertically on the graphite film. Such understanding of the interface layers between the substrate and CNWs will be useful for not only the growth control but also device applications.

Mediator-less highly sensitive voltammetric detection of glutamate using glutamate dehydrogenase/vertically aligned CNTs grown on silicon substrate

A sensitive glutamate biosensor is prepared based on glutamate dehydrogenase/vertically aligned carbon nanotubes (GLDH, VACNTs). Vertically aligned carbon nanotubes were grown on a silicon substrate by direct current plasma enhanced chemical vapor deposition (DC-PECVD) method. The electrochemical behavior of the synthesized VACNTs was investigated by cyclic voltammetry and electrochemical impedance spectroscopic methods. Glutamate dehydrogenase covalently attached on tip of VACNTs. The electrochemical performance of the electrode for detection of glutamate was investigated by cyclic and differential pulse voltammetry. Differential pulse voltammetric determinations of glutamate are performed in mediator-less condition and also, in the presence of 1 and 5μM thionine as electron mediator. The linear calibration curve of the concentration of glutamate versus peak current is investigated in a wide range of 0.1–500μM. The mediator-less biosensor has a low detection limit of 57nM and two linear ranges of 0.1–20μM with a sensitivity of 0.976mAmM−1cm−2 and 20–300μM with a sensitivity of 0.182mAmM−1cm−2. In the presence of 1μM thionine as an electron mediator, the prepared biosensor shows a low detection limit of 68nM and two linear ranges of 0.1–20 with a calibration sensitivity of 1.17mAmM−1cm−2 and 20–500μM with a sensitivity of 0.153mAmM−1cm−2. The effects of the other biological compounds on the voltammetric behavior of the prepared biosensor and its response stability are investigated. The results are demonstrated that the GLDH/VACNTs electrode even without electron mediator is a suitable basic electrode for detection of glutamate.