Deposition Of Amorphous Carbon Research Articles

Influence of initiators on the sintering discolouration of PTFE

PTFE homopolymer synthesised using ammonium persulfate initiator discolours at sintering temperatures of approximately 380 °C. No report on this phenomenon is available in the open literature. To shed light on the problem, PTFE samples were synthesised using various initiators and different pH buffers. The initiators used included ammonium persulfate, sodium persulfate, potassium permanganate, di-tertiary butyl peroxide and hydrogen peroxide. Borax and potassium carbonate were used as the buffering agents. The samples were pressed into discs and sintered at 380 °C. The samples were analysed using FTIR and Raman spectroscopy to determine the influence of decomposition of the end-groups during sintering. Each initiator resulted in unique end-groups, with a suggestion of multiple termination reactions in several of the samples. The discolouration of the samples occurs because of amorphous carbon deposition into the polymer matrix after elimination from the end-groups during sintering. The level of discolouration is dependent on the type and concentration of initiator used.

Effects of dealumination on the performance of Ni-containing BEA catalysts in bioethanol steam reforming

The effects of dealumination of BEA zeolite on the formation of nickel active sites and the performance of Ni-containing BEA zeolite catalysts in the steam reforming of ethanol have been studied. Ni-containing BEA zeolite catalysts were prepared by the impregnation of unmodified and dealuminated BEA zeolites with Ni(NO3)2 precursor. The properties of Ni10HAlBEA and Ni10SiBEA zeolite catalysts were studied by means of X-ray diffraction, 1H, 27Al and 29Si magic-angle spinning nuclear magnetic resonance, Fourier-transform infrared and Raman spectroscopy, transmission electron microscopy, temperature-programmed reduction, temperature-programmed ammonia and hydrogen desorption methods. High initial activity and selectivity of Ni10HAlBEA to hydrogen and carbon dioxide with unmodified BEA zeolite support in the steam reforming of ethanol reaction performed at 500 °C was observed. However, fast deactivation of Ni10HAlBEA catalyst, manifested in the decrease of water conversion, drop of selectivity to H2 and CO2, and increase in the selectivity to ethylene with the time-on-stream, was observed. In contrast, Ni10SiBEA zeolite catalyst showed lower initial activity but higher durability and resistance for carbon deposition. It was stated that dealumination of BEA zeolite led to the slight structural changes and simultaneously pronounced decrease of acidity. Formation of the large nickel crystallites was hindered on Ni10SiBEA zeolite catalyst. TEM and Raman spectroscopy studies indicated that deactivation of Ni10HAlBEA was related to formation of nickel mediated filamentous, graphitic and amorphous carbon deposits. Much smaller amounts of filamentous carbons were observed on the Ni10SiBEA zeolite catalyst prepared by the use of dealuminated zeolite support.

Double-sided masking and stress-release etching for the fabrication of high-aspect-ratio graphene micro-cantilever

Well-shaped micro/nano-structured suspended graphene is a versatile building block for micro/nano-electromechanical (MEMS/NEMS) devices. Directly ‘sculpting’ the suspended graphene membrane using an accelerated energetic electron/ion beam to form micro/nano-structured graphene possesses the merits of high resolution and well-processed flexibility. However, both the residual and process-induced stress in the membrane still challenge the obtaining of non-distorted freestanding graphene patterns. We report a featured double-sided masking and stress-release etching method to fabricate well-defined suspended graphene micro-ribbon. We demonstrated that the one-step low-energy (10 keV) electron beam induced the deposition of amorphous carbon (a-C) on both sides of the suspended graphene. The a-C layers were precisely self-aligned, not only allowing its use as reliable masks for the following plasma etch of suspended graphene, but showing potential for future applications of effectively ‘writing’ circuits/devices directly on both sides of a suspended 2D atomic-layered platform. A stress-release plasma etching process and its ‘self-crumpling’ mechanism were demonstrated. High-aspect-ratio micro-structured graphene (bridge and cantilever) with a good shape was obtained. This provides a promising and universal processing method for making suspended structures of 2D materials with in-plane flatness for potential MEMS/NEMS applications.

Growth Mechanism and Origin of High sp^{3} Content in Tetrahedral Amorphous Carbon.

We study the deposition of tetrahedral amorphous carbon (ta-C) films from molecular dynamics simulations based on a machine-learned interatomic potential trained from density-functional theory data. For the first time, the high sp^{3} fractions in excess of 85% observed experimentally are reproduced by means of computational simulation, and the deposition energy dependence of the film's characteristics is also accurately described. High confidence in the potential and direct access to the atomic interactions allow us to infer the microscopic growth mechanism in this material. While the widespread view is that ta-C grows by "subplantation," we show that the so-called "peening" model is actually the dominant mechanism responsible for the high sp^{3} content. We show that pressure waves lead to bond rearrangement away from the impact site of the incident ion, and high sp^{3} fractions arise from a delicate balance of transitions between three- and fourfold coordinated carbon atoms. These results open the door for a microscopic understanding of carbon nanostructure formation with an unprecedented level of predictive power.

Catalytic synthesis of few-layer graphene on titania nanowires.

Growth mechanisms of graphitic nanostructures on metal oxides by chemical vapor deposition (CVD) are observed at 750 °C, using titania nanowire aerogel (NWAG) as a three-dimensional substrate and without metal catalysts. We temporally observed catalytic transformation of amorphous carbon into few-layer graphene on the surface of 5-10 nm diameter titania nanowires. The graphitization spontaneously terminates when the titania nanowires are encapsulated by a shell of approximately three graphene layers. Extended CVD time beyond the termination point (>1125 seconds) yields only additional amorphous carbon deposits on top of the few-layer graphene. Furthermore, it was discovered that the islands of amorphous carbon do not graphitize unless they catalytically grow beyond a threshold size of 5-7 nm along the nanowire length, even after an extended thermal treatment. The electrical conductivity of the NWAG increased by four orders of magnitude, indicating that the graphene shell mediated by titania nanowires yielded a network of graphene throughout the three-dimensional nanostructure of the aerogel. Our results help us understand the growth mechanisms of few-layer graphene on nanostructured metal oxides, and inspire facile and controllable processing of metal oxide-nanocarbon fiber-shell composites.

Detecting and Preventing Gate Oxide Plasma Damage During PECVD Carbon Deposition Through Surface Photovoltage Measurements

For an advanced NAND flash memory device, there is a failure mechanism known as “blown gate oxide” that is commonly sourced to the plasma-enhanced chemical vapor deposition (PECVD) amorphous carbon deposition step. It has been observed that specific maintenance events on the PECVD process chambers will trigger this failure mechanism, most significantly when replacing the showerhead, or installing a “poor quality” showerhead. This paper investigates utilizing surface photovoltage measurements to indicate when a chamber has a high probability to cause blown gates. In this expanded edition of this paper, we also investigate issues concerning chamber cleaning cycles and how they were resolved.

Substrate independent approach for synthesis of graphene platelet networks

Graphene platelet networks (GPNs) comprised of randomly oriented graphene flakes two to three atomic layers thick are synthesized using a novel plasma-based approach. The approach uses a substrate capable of withstanding synthesis temperatures around 800 °C, but is fully independent of the substrate material. The synthesis occurs directly on the substrate surface without the necessity of any additional steps. GPNs were synthesized on various substrate materials including silicon (Si), thermally oxidized Si (SiO2), molybdenum (Mo), nickel (Ni) and copper (Cu), nickel–chromium (NiCr) alloy and alumina ceramics (Al2O3). The mismatch between the atomic structures of sp2 honeycomb carbon networks and the substrate material is fully eliminated shortly after the synthesis initiation, namely when about 100 nm thick deposits are formed on the substrate. GPN structures synthesized on a substrate at a temperature of about 800 °C are significantly more porous in comparison to the much denser packed amorphous carbon deposits synthesized at lower temperatures. The method proposed here can potentially revolutionize the area of electrochemical energy storage by offering a single-step direct approach for the manufacture of graphene-based electrodes for non-Faradaic supercapacitors. Mass production can be achieved using this method if a roll-to-roll system is utilized.

Fabrication of a Schottky diode with transfer-free deposition of multilayer graphene on n-GaN by solid-phase reaction

Transfer-free deposition of multilayer graphene (MLG) on n-GaN by a solid-phase reaction was demonstrated for the first time for the fabrication of a Schottky diode. To improve the crystallinity and uniformity of MLG films, a new approach of heat sputtering for the deposition of amorphous carbon (C) and cobalt (Co) as catalyst layers has been investigated. The characteristics obtained by Raman spectroscopy and scanning electron microscopy (SEM) measurements revealed that the crystallinity and uniformity of MLG films were improved significantly by employing heat sputtering rather than conventional room-temperature sputtering. MLG–GaN Schottky diodes were fabricated with optimized deposition of MLG on n-GaN. The Schottky barrier height determined on the basis of the thermionic emission theory using current–voltage (I–V) data was 0.75 eV. The reverse leakage current was found to be of the order of 10−7 A/mm2. The obtained results indicate the MLG fabrication on n-GaN by our proposed method might have potential applications in the fabrication of Schottky diodes.

Direct growth of coiled carbon nanofibers without nanocatalyst

The paper presents the coiled carbon nanofibers growth on bulk metals without use of nanocatalyst on indigenously developed custom build Chemical Vapour Deposition (CVD) set-up. Transition metal and alloys as substrate were investigated for their effect on morphology during growth of carbon nanofibers. The application of Inconel proved as a very good substrate for homogenous coiled nanofibers growth. Effects of variation in temperature and gas flow ratio were studied on diameter and helix angle of synthesized carbon nanofibers on Inconel as substrate. Experimental results reveal that the range of diameter of carbon nanofibers was 80–150nm. Transmission electron microscopy (TEM) analysis shows stacked-cup type structure with amorphous carbon deposits on carbon nanofibers. As the CVD process is very simple and economical, hence, this process can be effectively used for direct growth of carbon nanofibers.

Nanocomposites Consisting of Carbon Nanotubes and Nanoparticles of Noble Metals

In the framework of the made researches nanocomposite of CNT-NPs type (Carbon Nanotube-Nanoparticles) consisting of multiwalled carbon nanotubes coated by rhodium nanoparticles and/or palladium using the two-step indirect method: chemical reduction have been produced. In the researches high-quality multi-walled carbon nanotubes MWCNTs with a length of 100 to 500 nm and a diameter of 8 to 20 nm previously obtained in the catalytic-chemical vapour deposition CCVD have been used. Nanotubes produced within the framework of own researches contain minor amounts of metallic impurities and amorphous carbon deposits. In order to deposit the noble metal nanoparticles on the surface of carbon nanotubes functionalization of multi-walled carbon nanotubes in a mixture of H2SO4 and HNO3 acids have been used. The prepared material has been subjected chemical reduction using noble metal precursors (RhCI3, PdCl2). The characterization of the produced material including the examination of the structure, morphology, chemical composition and evaluation of the size and distribution of rhodium and/or palladium nanoparticles on the surface of carbon nanotubes has been performed using: scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS). The produced nanomaterials may be used as the active layer of sensors of chemical/biological agents.

La-promoted Ni-hydrotalcite-derived catalysts for dry reforming of methane at low temperatures

La-promoted Ni-containing hydrotalcite-derived catalysts were prepared and tested in dry methane reforming at low-moderate temperatures. The prepared materials were characterized by means of X-ray diffraction (XRD), temperature programmed reduction (H2-TPR) and CO2-temperature programmed desorption (TPD). The presence of lanthanum was found to enhance the reforming reaction, but also direct methane decomposition at low reaction temperatures. This fact was assigned to an increased presence of Ni0 sites as a consequence of improved reducibility of Ni-species in the La-promoted catalysts. Lanthanum can well contribute to the gasification of amorphous carbon deposits, resulting in lower overall carbon deposition at 550°C.

Mixed-mode high-power impulse magnetron sputter deposition of tetrahedral amorphous carbon with pulse-length control of ionization

High-power impulse magnetron sputtering (HiPIMS) is used to deposit amorphous carbon thin films with sp3 fractions of 13% to 82%. Increasing the pulse length results in a transition from conventional HiPIMS deposition to a “mixed-mode” in which an arc triggers on the target surface, resulting in a large flux of carbon ions. The films are characterized using X-ray photoelectron spectroscopy, Raman spectroscopy, ellipsometry, nanoindentation, elastic recoil detection analysis, and measurements of stress and contact angle. All properties vary in a consistent manner, showing a high tetrahedral character only for long pulses, demonstrating that mixed-mode deposition is the source of the high carbon ion flux. Varying the substrate bias reveals an “energy window” effect, where the sp3 fraction of the films is greatest for a substrate bias around −100 V and decreases for higher or lower bias values. In the absence of bias, the films' properties show little dependence on the pulse length, showing that energetic ions are the origin of the highly tetrahedral character.

Value-added functional textiles by plasma-based surface modification

Event Abstract Back to Event Value-added functional textiles by plasma-based surface modification Ranna Tolouei1, Sondes Sondes Gargoubi2, Lucie Levesque1, Pascale Chevallier1, Stephane Turgeon1 and Diego Mantovani1 1 CHU de Quéebec Research Centre, Laval University, Lab. for Biomaterials & Bioengineering (CRC-I), Dept. Min-Met-Materials Engineering, Canada 2 ISET Ksar-Hellal, Textile Engineering Laboratory, Tunisia Recently, there has been a strong interest in providing fabrics with greater wearing comfort while remaining fresh and odor free as well as the ability to impart antimicrobial properties[1]. The innovative combination of controllable topographical and chemical modifications of the material will be a step forward for surface engineering towards real life application: to make surfaces less liable to microbial adhesion, or easier to be cleaned, with the addition of an antimicrobial agent. The fabric surfaces are not only exposed to abrasion and wear caused by daily contacts, but also to aggressive laundry procedures. So far, many different methods have been studied using approaches such as polymeric grafting or polymeric coating accompanied by lack of stability[2]. Thus, higher mechanical and chemical stabilities become mandatory properties for such materials and need to be taken into consideration during the design process. Using plasma-based process techniques, thereby obtaining a highly stable and homogenous functional surface could be a potential alternative. Materials and Methods Cotton knit fabric samples were were cut into size of 1×1 cm2 and cleaned in successive baths of acetone and diethyl ether anhydrous for 10 minutes before being used. Surface modifications were performed using a hybrid plasma enhanced chemical vapor deposition (PE-CVD) reactor, operating at 13.56 MHz at room temperature. Hydrogen and nitrogen (N2:H2) were used as gas precursors for plasma pre-treatment of cotton fabric to enhance antimicrobial dye uptake. Methane was used for deposition of biocidal doped amorphous carbon (aC) nanocoating on the cotton fabric. Chemical state of surface was characterized by X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM). The wettability of the surfaces after each modification has been measured using static water contact angle (WCA). The antibacterial activity of the treated fabric was estimated against Escherichia coli (ATCC 11229). To evaluate durability of wash, a hospital laundry process was chosen[3]. Results: The morphological changes due to plasma treatments were investigated by SEM as shown in Figure 1. It reveals a fairly smooth surface for untreated and N2:H2 pretreated samples, whereas nanocoating deposition caused a significant morphological change. Surface chemical composition analyses, by XPS, exhibited that the aC deposition was efficient as carbon became the major component of the surface: 95.4 at.% for nanocoated sample versus 67 at.% for untreated one. N2:H2 pretreated samples displayed high amount of nitrogen (at.%). Depending on plasma modification process the wetting behavior of cotton fabric could be tailored. Indeed, the WCA demonstrate the effect of plasma treatment by changing untreated cotton fabric wettability from ~ 100° to hydrophobic state (~145°) or hydrophilic state (~ 80°) by aC nanocoating and N2:H2 pretreatment, respectively. Antibacterial test revealed that nanocoated samples as well as N2:H2 pretreated samples with antimicrobial agents shown antibacterial activity against E. Coli as compared to untreated cotton fabric before and after laundry. Discussion and Conclusions: Our results clearly show the feasibility of low temperature plasma based process to modify the surface of fabric towards tuning the wetting behavior and antibacterial property. Moreover, stable antibacterial activity has been achieved by deposition of nanocoating on the surface of cotton fabric. The goal of the present work was to propose an appropriate treatment for functionalization of cotton fabric, which can be applied by textile industry using ecofriendly and non-toxic agents and processes. This work was partially supported by NSERC-Canada, CIHR-Canada, CFI-Canada, FRQ-NT-Quebec, and MRI-Quebec.

Focused particle beam-induced processing.

Focused particle beam-induced processing.

Ethanol conversion at low temperature over CeO2—Supported Ni-based catalysts. Effect of Pt addition to Ni catalyst

The effect of Pt addition on the performance of Ni/CeO2 catalyst for the low temperature steam reforming of ethanol is investigated. The reaction mechanism was explored using diffuse reflectance infrared spectroscopy under reaction conditions and temperature-programmed surface reaction of ethanol. The addition of Pt to Ni/CeO2 catalyst promoted the decomposition of dehydrogenated and acetate species to hydrogen, methane, CO and carbonate species. Furthermore, the presence of Pt reduced the rate of catalyst deactivation. In situ X-ray absorption studies revealed the formation of a nickel carbide phase during steam reforming of ethanol over Ni/CeO2 catalyst, which was associated with amorphous carbon deposition and catalyst deactivation. X-ray photoelectron spectroscopy in combination with kinetic and structural data was consistent with a partial Pt monolayer on Ni in the bimetallic catalyst. The segregation of Pt on the surface of the Ni particles minimized the formation of nickel carbide and promoted catalyst stability.

Iron deposition on multi‐walled carbon nanotubes by fluidized bed MOCVD for aeronautic applications

AbstractThe fluidized bed MOCVD process has been studied in order to uniformly deposit iron nanoparticles on the outer surface of multi‐walled carbon nanotubes (MWCNTs) tangled in balls of 388 µm in diameter. Using ferrocene as organometallic precursor at atmospheric pressure, various reactive atmospheres of deposition (under N2, air and H2) and an ozone O3 surface pre‐treatment of MWCNTs were tested. Around 10 g Fe/100 g MWNCTs were deposited during each run. Under N2 at 650 °C on the raw MWCNTs, nanoparticles formed of Fe and Fe3C were deposited which have catalyzed the formation of carbon nanofibers (CNFs). 20 h of ozone (O3) pre‐treatment improved the number and distribution of iron nanoparticles but without increasing the surface coverage of nanotubes. A more intense amorphous carbon deposit also appeared. Under H2 at 550 °C, the amorphous carbon was partly eliminated but fewer iron nanoparticles were present. Under air at 450 °C, a part of the MWCNTs was lost and a Fe2O3 shell covered each remaining MWCNTs ball. New works are in progress to increase more markedly the surface reactivity of MWCNTs and to deposit pure iron. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The MWCNTs-Rh Nanocomposite Obtained By The New High-Temperature Method

AbstractA nanocomposite was fabricated during the research undertaken, consisting of multiwalled carbon nanotubes coated with rhodium nanoparticles by the new high-temperature method being the subject of the patent claim. High quality multiwalled carbon nanotubes (MWCNTs) with the length of 100÷500 nm and the diameter of 8÷20 nm obtained in advance with Catalytic Chemical Vapour Deposition (CVD) were employed in the investigations. The nanotubes manufactured under the own research contain small amounts of metallic impurities and amorphous carbon deposits. Multiwalled carbon nanotubes functionalisation in acids was applied to deposit rhodium nanoparticles onto the surface of carbon nanotubes, and then the material was placed in a solution being a precursor of rhodium nanoparticles. The material prepared was next placed in a quartz vessel and subjected to high-temperature reduction in the atmosphere of argon to deposit rhodium nanoparticles onto the surface of multiwalled carbon nanotubes. The following examinations were performed, respectively: MWCNTs fabrication, fabrication of a CNT-NPs (Carbon NanoTube-NanoParticles) nanocomposite material; the characterisation of the materials produced including examination of the structure and morphology, and the assessment of rhodium nanoparticles distribution on the surface of carbon nanotubes. Micro- and spectroscopy techniques were employed to characterise the structure of the nanocomposites obtained.

Oxidative and non-oxidative steam reforming of crude bio-ethanol for hydrogen production over Rh promoted Ni/CeO2-ZrO2 catalyst

The catalytic oxidative and non-oxidative steam reforming of crude bio-ethanol for hydrogen production was studied in a tubular fixed bed reaction system over 30wt.%Ni/CeO2-ZrO2 and 1wt.%Rh-30wt.%Ni/CeO2-ZrO2 catalysts. The catalysts were prepared by impregnation-co-precipitation method and characterized by BET, XRD, TPR, TGA, XPS, XANES and EXAFS techniques. Characterization results revealed that the addition of Rh promotes reducibility of NiO at lower temperature for the bimetallic catalysts. Extended X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge structure (XANES) analysis depicted that NiO with 6-fold local co-ordination is present in all the samples. Ethanol conversion, hydrogen yield and product selectivity were investigated at 600°C and space time of 9.17kgcath/kgmol[EtOH]) at atmospheric pressure. In steam reforming of crude bio-ethanol, 81% ethanol conversion was achieved with 59% hydrogen selectivity on Ni/CeO2-ZrO2 catalyst, whereas, higher ethanol conversion (86%) with 73% hydrogen selectivity was achieved using Rh-Ni/CeO2-ZrO2 catalysts. In oxidative steam reforming of crude bio-ethanol, hydrogen yield and selectivity reduced due to the partial oxidation of oxygenate compounds present in the feed. The used catalysts were also analysed by BET, TGA/DTA, TPR, TPO, Raman spectroscopy, SEM, and TEM techniques to identify the cause of catalyst deactivation. The results indicate that the catalyst deactivation occurred mainly due to amorphous and filamentous carbon deposition on the catalysts surface, due to the presence of the impurities in the feed.

Resistance changes of carbon nanotubes decorated with platinum nanoparticles in the presence of hydrogen at different and constant concentrations

This work presents the outcome of research into the structure and resistance changes of composites containing carbon nanotubes (CNT) coated with platinum nanoparticles. High‐quality CNTs obtained in the chemical vapor deposition process (100–200 μm long, 10–20 nm in diameter) were employed in the research. Raw CNTs did not contain metallic impurities or amorphous carbon deposits. An indirect method of bonding the earlier produced platinum nanoparticles to the surface of functionalized CNTs was applied to deposit platinum nanoparticles onto the surface of CNTs. A surface of CNTs with uniformly distributed platinum nanoparticles was achieved as a result of the experiments undertaken. Investigations into the structure and morphology of the materials obtained were carried out with transmission electron microscopy and scanning transmission electron microscopy methods, and the X‐ray structure analysis was used to identify the phase composition of the fabricated nanocomposites. The studies of changes in resistance were carried out with a constant and variable concentration of H2 in the atmosphere of synthetic air. The goal of the research was the multifaceted characterization of the nanomaterials produced and to identify the response of the CNTs–platinum system to hydrogen in the atmosphere of synthetic air.

Oxygen-induced graphitization of amorphous carbon deposit on ohmic switch contacts improves their electrical conductivity and protects them from wear

There has been a resurgence of interest in developing ohmic switches to complement transistors in order to address challenges associated with electrical current leakage and lowering power consumption. A critical limitation is the reliability of their electrical contacts, which are prone to wear and hydrocarbon-induced contamination. These phenomena progressively inhibit signal transmission, eventually leading to device failure. We report on progress made towards converting the contamination into a highly conductive material. We show that Pt-coated microswitch contacts operating in the presence of O2 experience limited contaminant accumulation even in hydrocarbon-rich environments. We then demonstrate that devices that have experienced contamination can recover their original performance when operated in a clean N2:O2 environment. Auger and Raman spectroscopy indicate that this resistance recovery is associated with the structural transformation of the contaminant as opposed to its removal and that the transformed contaminant may shield the Pt coating from wear.