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Graphene films grown by chemical vapour deposition have unusual physical and chemical properties that offer promise for applications such as flexible electronics and high-frequency transistors.sup.1-10. However, wrinkles invariably form during growth because of the strong coupling to the substrate, and these limit the large-scale homogeneity of the film.sup.1-4,11,12. Here we develop a proton-assisted method of chemical vapour deposition to grow ultra-flat graphene films that are wrinkle-free. Our method of proton penetration.sup.13-17 and recombination to form hydrogen can also reduce the wrinkles formed during traditional chemical vapour deposition of graphene. Some of the wrinkles disappear entirely, owing to the decoupling of van der Waals interactions and possibly an increase in distance from the growth surface. The electronic band structure of the as-grown graphene films shows a V-shaped Dirac cone and a linear dispersion relation within the atomic plane or across an atomic step, confirming the decoupling from the substrate. The ultra-flat nature of the graphene films ensures that their surfaces are easy to clean after a wet transfer process. A robust quantum Hall effect appears even at room temperature in a device with a linewidth of 100 micrometres. Graphene films grown by proton-assisted chemical vapour deposition should largely retain their intrinsic performance, and our method should be easily generalizable to other nanomaterials for strain and doping engineering. A growth process in which protons decouple graphene from the underlying substrate greatly reduces the number of wrinkles that usually degrade large graphene films grown by chemical vapour deposition., Author(s): Guowen Yuan [sup.1] [sup.2] , Dongjing Lin [sup.1] [sup.2] , Yong Wang [sup.1] [sup.2] , Xianlei Huang [sup.1] [sup.2] , Wang Chen [sup.1] [sup.2] , Xuedong Xie [sup.1] [sup.2] [...]

Abstract: This study was designed to determine if surface modification via photo-initiated chemical vapor deposition (PICVD) affects the physicochemical properties of polyethylene glycol (PEG) and poly(vinyl alcohol) (PVA) differently, given [...]

Diamonds, one of the hardest materials on Earth, are so strong that they can protect fragile quantum states that would otherwise survive only in a vacuum or at ultra-cold temperatures. Engineers are mastering the art of growing diamonds with special properties and detecting their quantum spins -- opening up a range of sensing applications in the life sciences and elsewhere. Diamonds, one of the hardest materials on Earth, are so strong that they can protect fragile quantum states that would otherwise survive only in a vacuum or at ultra-cold temperatures. Engineers are mastering the art of growing diamonds with special properties and detecting their quantum spins -- opening up a range of sensing applications in the life sciences and elsewhere., Author(s): Neil Savage Author Affiliations: How quantum diamonds work: from imaging magnetic fields to detecting viruses Download a PDF of the graphic Growing diamonds Engineers can synthesize diamonds in several [...]

Film properties of hydrogenated amorphous silicon (a-Si:H) fabricated by 'liquid-Si printing' (LSP) were investigated in detail and compared to the conventional plasma enhanced chemical deposition (plasma-CVD) method. LSP a-Si:H films (LSP films) had lower film density and larger size void than the a-Si:H films deposited by plasma-CVD (CVD films). On the other hand, the LSP films had high photoconductivity comparable to device grade a-Si:H films and higher photostability than the CVD films. Thus, the LSP films were drastically different from conventional CVD films. The conversion efficiency of the bifacial solar cells (glass/TCO/n(LSP film)/i(LSP film)/p(CVD film)/TCO/electrode), which was a problem because of the missing link between high photoconductivity and low cell performance, were improved. Undoped CVD film was inserted between the i- and p-layers to suppress the plasma damage to the active layer printed by LSP when depositing a B doped a-Si:H by plasma-CVD. As a result, we achieved conversion efficiencies of 1.1% with n side incidence and 3.1% with p side incidence. PACS Nos.: 78.56.-a, 61.43.Dq. Nous etudions en detail des films de a-Si:H fabriques a l'aide d'une imprimante au Si liquide (LSP) et les comparons a ceux obtenus par la methode conventionnelle de depot chimique en phase vapeur avec traitement au plasma (plasmaCVD). Les films a-Si:H fabriques a l'aide d'une imprimante (LSP) ont une densite de film plus faible et des lacunes plus grosses que des films deposes par plasma-CVD. D'un autre cote, les films LSP ont une haute photoconductivite comparable a des films a-Si:H de haute qualite et une plus grande photo-stabilite que des films CVD. Les films LSP sont notablement differents des films CVD conventionnels. Nous ameliorons le rendement de conversion de cellules solaires bifaciales (verre/TCO/n(film LSP)/i(film LSP)/p(film CVD)/TCO/electrode) qui etait un probleme a parce qu'il n'y avait pas de lien entre haute conductivite et basse performance de la cellule. Nous inserons un film CVD non dope entre la couche i et la couche p pour eliminer le dommage plasma a la couche active imprimee par LSP, lorsqu'on depose un a-Si:H dope au B par plasma-CVD. Le resultat est que nous realisons un rendement de conversion de 1.1 % pour une incidence cote n et de 3.1 % pour une incidence cote p. [Traduit par la Redaction], 1. Introduction Thin-film silicon solar cells are a candidate for high cost-performance solar cells. We successfully obtained the deposition criteria for high quality amorphous Si (a-Si:H) films deposited by plasma [...]

Monolayer graphene was first obtained (1) as a transferable material in 2004 and has stimulated intense activity among physicists, chemists and material scientists (1-4). Much research has been focused on developing routes for obtaining large sheets of monolayer or bilayer graphene. This has been recently achieved by chemical vapour deposition (CVD) of C[H.sub.4] or [C.sub.2][H.sub.2] gases on copper or nickel substrates (5-7). But CVD is limited to the use of gaseous raw materials, making it difficult to apply the technology to a wider variety of potential feedstocks. Here we demonstrate that large area, high-quality graphene with controllable thickness can be grown from different solid carbon sources--such as polymer films or small molecules--deposited on a metal catalyst substrate at temperatures as low as 800 °C. Both pristine graphene and doped graphene were grown with this one-step process using the same experimental set-up., With its extraordinary electronic and mechanical properties, graphene is showing promise in a plethora of applications (7-13). Graphene can now be obtained by several different approaches. The original mechanical peeling [...]

The synthesis of the gas chromatography stationary phase by molecular self-assembly of carbon nanotubes (CNTs) via a novel ethanol chemical vapor deposition process is presented. A major advantage is that ethanol was found to be an excellent carbon source that generated highly pure multiwalled carbon nanotubes with very little nontubular carbon impurities. The nanotubes were not vertically aligned but lay fiat out on the column surface in a randomly distributed configuration. The CNT phase was able to separate a wide range of organic compounds with diverse polarity and volatility, where the number of plates per meter ranged from 900 to 1280. It also showed classical chromatographic behavior and good precision. 10.1021/ac100428m

A dielectric barrier discharge is generated by flowing helium and hydrogen through a microreactor capillary which contains a coating of Ni/alumina catalyst to activate carbon nanofiber (CNF) synthesis. Optical and electrical measurements have been done to characterize the discharge during catalyst treatment. A sinusoidal voltage of 6 kV (peak) with a frequency of 50 kHz has been applied to a high-voltage electrode, and a helium gas flow stabilizes the discharge to have a uniform and high-power-density surface treatment. Cold-plasma operation for 15 min is simple and audiovisual, increases the CNF yield significantly compared to nonactivated samples, and can compete with high-temperature treatment at 973 K for 2 h. Increasing the discharge treatment duration to 30 min results in sintering of catalyst particles and nonuniform growth of the nanofibers. Index Terms--Barrier discharge, carbon nanofiber (CNF), catalyst, chemical vapor deposition (CVD), microplasma, microreactor.

Plasma polymerization at atmospheric pressure is used to obtain stable hydrophobic coatings onto various substrates. Plasma is generated in a dielectric barrier discharge configuration using a mixture of helium gas and styrene vapors. The discharge is characterized by means of electrical measurements and optical emission spectroscopy. Since the styrene vapors introduced in plasma provide a significant decrease of the discharge current, we established the optimum parameters (voltage waveform, gap length, and gas flow rates) for plasma polymerization, assuring a maximum discharge current. The plasma-polymerized films (polystyrene), deposited onto the glass or silicon substrates, are analyzed by contact angle measurements, ellipsometry, IR spectroscopy, and atomic force microscopy (AFM). The film thickness is measured by light interferometry and confirmed by AFM analysis. The water contact angles are higher than 130[degrees], proving the hydrophobic characteristics of the film, and the refractive index is around 1.5, corresponding to the values of commercial polystyrene. Index Terms--Coatings, materials science and technology, plasma applications, plasma chemical vapor deposition, plasma diagnostics, polymers.

In this paper, homogeneous and dense silicon-based coatings have been deposited from hexamethyldisiloxane (HMDSO: [Si.sub.2]O[(C[H.sub.3]).sub.6]) on patterned silicium in a Townsend dielectric barrier discharge operating at atmospheric pressure. A brief description of the physical mechanisms ruling the step coverage is first described, followed by a description of the atmospheric pressure plasma process used. The step coverage is discussed with regard to the aspect ratio of the patterned wafers. Coatings deposited in and after the discharge region have also been characterized to understand the influence of plasma activation. In order to understand the experimental results, numerical simulations have been performed using a simplified reactive transport model. These results provide information and first general insight on the physical mechanisms ruling the conformity of silicon-based films deposited with this technique. Index Terms--Atmospheric pressure Townsend discharge (APTD), dielectric barrier discharge (DBD), glow discharges, plasma-enhanced chemical vapor deposition (PECVD), reactive transport modeling, silicon oxide, step coverage.

In this paper, the deposition and characterization of plasma-polymerized polystyrene (pp-PS) using PECVD under atmospheric pressure on a variety of substrates was investigated. An atmospheric RF plasma torch and an HF dielectric-barrier-discharge (DBD) system were used to deposit thin pp-PS coatings on PTFE, HDPE, stainless steel, glass, and silicon wafer. The styrene vapor was carried by Ar or He. The pp-PS films were characterized by Fourier transform infrared spectroscopy (FTIR) (infrared reflection absorption spectroscopy), X-ray photoelectron spectroscopy (XPS), water contact angle (WCA), static secondary ion mass spectroscopy (SSIMS), and optical microscopy, and the plasma phase was studied by optical-emission spectroscopy. The major features that characterize PS are present in the FTIR, SSIMS, and XPS spectra of our films, although some differences are observed between pp-PS and their conventionally polymerized counterparts: oxygenation, branching, degree of cross-linking, and unsaturation. According to the WCA and XPS results, the films deposited by the RF plasma torch (placed in a Plexiglass chamber) are more oxygenated than those deposited by DBD, which is operated under a much more controlled atmosphere. A comparison of the chemical structure of the deposited coatings (branching, cross-linking) as a function of the nature of the carrier gas was established by FTIR: pp-PS synthesized in the presence of Ar (for both processes) exhibit more branching and a higher degree of cross-linking than pp-PS synthesized with He as the main plasma gas. The optical microscopy points out a diversity of structures that depend on the nature of the substrate and the plasma parameters. Index Terms--Plasma CVD, plasma materials-processing applications, plasmas, plastics.

A large-scale atmospheric pressure plasma has been generated in helium, and the time-resolved optical and electrical properties have been shown to produce a homogeneous dielectric barrier discharge. Introducing tetraethyl orthosilicate as a liquid aerosol into this plasma produced clear, uniform, and smooth plasma polymerized coatings. Optical imaging studies have shown that adding 1% oxygen to the gas mixture induced a switch from a homogeneous plasma to a filamentary or microdischarge mode of operation, and this has been shown to dramatically alter the morphology of the deposited coatings. Surface analysis reveals significant particulate inclusions in coatings deposited from the filamentary mode of operation. Index Terms--CVD, optical imaging, plasma properties, thin films.

Pulsed dielectric-barrier discharge was used to modify polycarbonate surfaces by applying a thin film of silicone oxide. The discharge was supplied by alternating voltage pulses that lasted for about 50 ns. The generated current pulses were shorter and lasted for about 20 ns. For this reason, high power is concentrated in short time. Analysis of the composition thin film by means of the X-ray photoelectron spectroscopy method shows that it consists mainly of silicon, oxygen, and carbon. Based on the concentrations of these elements, films can be divided into three parts. In this paper, the influences of parameters characterizing the plasma reactor are attributed to a charge transferred in the single pulse of discharge, a power of discharge, and a microstructure of discharge. The influences of these parameters on deposition rate are shown. Index Terms--Dielectric breakdown, plasma CVD, thin films.

We have demonstrated resonant frequency tuning of nanowire resonator operated in both atmospheric circumstance and high vacuum environment using electrostatic spring-softening effect. The nanowire is synthesized at any desired position by focused ion beam-chemical vapor deposition (FIB-CVD) on the sidewall of batch-processed micro electrode. The resonant frequency in a vacuum chamber of 2.5 x [10.sup.-4] Pa is 1.564 MHz under the driving voltage of 5 [V.sub.DC] [+ or -] 5 [V.sub.AC]. When 30 [V.sub.DC] tuning bias is applied on tuning electrode, the resonant frequency is reduced to 1.529 MHz due to the electrostatic spring-softening effect while the driving bias is maintained. For the tuning bias of 60 V, the resonant frequency at atmospheric pressure has been tuned from 1.49 MHz to 1.41 MHz under the c riving voltage of 30 [V.sub.DC] [+ or -] 10 [V.sub.AC]. The method demonstrated both in high vacuum and at atmospheric pressure is a simple and effective way to tune the deviated resonant frequency of nanowire resonator to the desired value without the alteration of the structure or post fabrication process. Index Terms--Electrostatic force, electrostatic spring effect, focused ion beam-chemical vapor deposition (FIB-CVD), frequency tuning, nanowire resonator, resonant frequency.

Polycrystalline artificial diamond produced by chemical vapor deposition (pCVD) is a possible sensor material for the beam calorimeter of the ILC. The requirements are linearity over a large range of flux and radiation hardness against a total ionizing dose of several MGy per year of operation. A hadron test beam at the CERN PS was used to study the linearity of the response of pCVD sensors. An electron test beam at the S-DALINAC was used to measure the charge collection distance (CCD) as a function of the absorbed dose up to several MGy. Current-voltage characteristics of these sensors were measured before and after the irradiation as well as the dependence of the CCD on the applied electric field before and after the irradiation. Index Terms--BeamCal, charge collection distance, CVD diamond sensor, FCAL, forward calorimetry, ILC, irradiation, pumping, radiation hardness.