Graphite-like Films Research Articles

Influencing mechanisms of deposition bias voltage on superlubricious a-C:H films: Key role of nanoclustering structures in controlling structural evolution of transfer film

Hydrogenated amorphous carbon (a-C:H) films exhibit super-low friction coefficient but high wear rate in vacuum, while adjusting the deposition bias voltage is a practical method to enhance their anti-wear abilities. However, the inherent mechanisms are still no well comprehended. Here, systematic characterizations were conducted to unveil the intrinsic relationship between the superlubricious transfer films and their corresponding initial ion-energy induced bonding structures. The results indicated that the establishment of hydrogen-rich, graphite-like transfer films was the key factor for the ultra-low friction. The elevated deposition ion energy can cause structural changes of the initial film from layered-like nanoclustering structures to disordered bonding network, which could hamper the graphitization of transfer films and lead to the failure of superlubricity after the depletion of the sp2-rich, highly hydrogenated surface nanolayers. For the sustainable structural evolution from the inherent nanoclusters to superlubricious transfer films, sufficient hydrogen and mechanical stiffness of the film bulk were necessary, which can be optimized by balancing the growth process of subplantaion and chemical adsorption via controlling the carbon ion energy to approach the theoretical surface penetration threshold of 30 eV. Under this condition, the films can achieve an ultra-low wear rate of 6.6 × 10−8 mm3N−1m−1 with a lowest friction coefficient of 0.007 in vacuum. These findings can provide guidance for the design of superlubricious carbon coatings for aerospace applications.

Measurement of Thin Carbon Films Absorption in the Visible Spectrum

The article is devoted to studying radiation absorption in the visible spectrum by thin carbon films. Two types of carbon films, diamond-like and graphite-like, with different structures, are investigated. The films are produced using laser vaporization of the initial material with a further coating of glass substrates. Measurements of light transmission through several samples of films with different thicknesses at three (or more) different areas are obtained for the wavelength range of 400-800 nm using the USB4000 compact fiber-optic spectrometer. The obtained results for the films with different thicknesses demonstrate scant differentiation of values (limiting to the same type of films). The imaginary parts of the films' complex refractive indices (absorption indices) are calculated. The comparison reveals the significant differences (by a factor of two or three) of the absolute values and trends of the absorption indices of diamondlike and graphite-like films. Both types of films are characterized by the expected increase in absorption when transitioning from the long-wavelength spectral region to the short-wavelength one. However, the rate of increase in absorption during such a transition is higher for the diamond-like films. These differences are related to the structure of the films.

Graphitic Nanoporous Carbon Thin Films: Fabrication Method, Structural, Electrical and Gas Sensor Properties

Carbon nanoporous thin films are very attractive for application in fields of supercapacitors, fuel cells, gas sensors and others. However due to it very high resistance an employment of this material for resistance gas sensor is problematic. At the same time graphene based materials are very sensitive to different gas ambient and have a resistivity suitable for testing. In this work the new method of formation of high porous graphite-like thin films by RF magnetron plasma enhanced chemical vapor deposition (MPECVD) from argon-methane/argon-acetylene gas mixture followed by annealing at 650ºC, is suggested. A comparative study of transformation of nanoporous carbon film produced in different carbon-hydrogen atmosphere into graphitic one, their structural and electrical properties are presented. The films of nanoporous carbon were fabricated on silicon or SiO2/Si wafers. To clarify chemical structure of the film FTIR spectroscopy and XPS were used. Micro-Raman spectroscopy and AFM were applied to determine of structure and surface morphology correspondingly. X-ray refraction (XRR) method allows us to determine a density and a thickness of the films. Four point probe method and transmittance line (TSL) technique were used for the analysis of electrical properties. Additionally, electrical conductivity at different temperature and frequency was examined by measurement of resistance between two nearest Ni contacts. The same contacts were used to estimate of the gas sensitivity.It was shown that initial deposited films have mainly sp3 C-H bonds without appearance of silicon bonds. AFM demonstrates nanostructured surface morphology with size of the surface fluctuation about 3 nm; a density of the films is about 1.3 g/cm3 for both carbon films, that corresponds to nanoporous carbon; resistivity is about 108 Ohm×cm. After thermal annealing at 650°C for 30 min in N2 atmosphere the sp3 C-H bonds are disappeared, and C=C sp2 bonds are formed. Besides the resistivity the films synthesized in argon-methane gas mixture decreases to 104 Ohm×cm whereas the films synthesized in argon-acetylene gas mixture decreases their resistivity up to 102 Ohm×cm. The density of the C films synthesized in in argon-methane gas mixture reaches about 1.5 g/cm3 that corresponds to 34% of porosity, and material shows layered structure. The density of the C films synthesized in in argon-acetylene gas mixture falls to 1.01 g/cm3 that corresponds to 55% of porosity. Graphitized films synthesized in argon-methane gas mixture appears sensory sensitivity to moisture and ammonia whereas the films synthesized in argon-acetylene gas mixture show low sensitivity to these gases. The nature of the gas sensor resistor sensitivity is discussed.

Chemical vapor deposition growth and characterization of graphite-like film

Thick graphene film can be widely used in surface protection, heat dissipation, heating devices and other fields. Here we present a study on the growth and characterization of large area continuous and patterned graphite-like films prepared on Ni foil through CVD. Effects of parameters on the material growth are studied experimentally and theoretically in detail. Thickness of the graphite-like film in this work can reach 500 nm and can be regulated by growth process. Characterization results show that the graphite-like film is formed by free stacking of large area graphene continuous films and possesses strong mechanical strength, chemical stability, good electrical conductivity and flexibility. The graphite-like film shows potential for application in metal surface protection, flexible conduction, heating and electromagnetic shielding.

Highly porous carbon films fabricated by magnetron plasma enhanced chemical vapor deposition: Structure, properties and implementation

The new method is suggested of formation of highly porous graphite-like thin films by radio frequency magnetron plasma enhanced chemical vapor deposition from argon-methane gas mixture. The prepared films were characterized before and after thermal annealing by XPS, XES, FTIR, Raman spectroscopy, XRD, XRR, AFM, and electrical measurements. Deconvolution of XPS spectra has demonstrated a significant growth of sp2/sp3 ratio from 1 for as-deposited films to 12 for the films annealed at 650 °C for 5 min. FTIR spectra have confirmed that thermal annealing results in reduction of H– and OH– functional groups and formation of СС bonds. The analysis of Raman spectra has shown that the annealing incorporates additional defects in graphite plane. XRD has shown that films are amorphous. Estimation of porosity from XRR measurements gave values of about 59% for as-deposited films and 34% for annealed films. AFM has shown that roughness of the films decreases from 3.3 to 0.6 nm during treatment at 650 °C in inert atmosphere. The size of pores was found to be few tens of nanometers. The electrical measurements have shown that after annealing the resistivity decreases by up to 5 orders of magnitude. Annealed films have demonstrated perceptible sensitivity to ammonia and water vapor.

Formation of Highly Conducting Optically Transparent Films with Multigraphene Structure via Carbonization of Polyimide Langmuir–Blodgett Films

Multigraphene films have been for the first time obtained on the surface of quartz glass via carbonization of polyimide Langmuir–Blodgett films. The Raman spectra of the films show bands G and D and a broad band at 2300–3200 cm–1, which are characteristic of graphite-like films. The transmission electron microscopy demonstrated that the films are constituted by “stacks” of layers spaced by 0.36 nm. The surface resistance of the 5-nm-thick films was 1.2 ± 0.2 kΩ, and the transmittance was 87% at λ = 550 nm. The transmittance was 97% in the IR part of the spectrum and 70–80% in the UV part.

The Effects of Precursor C₂H₂ Fraction on Microstructure and Properties of Amorphous Carbon Composite Films Containing Si and Ag Prepared by Magnetron Sputtering Deposition.

Hydrogenated graphite-like carbon composite films containing silicon (Si) and silver (Ag) (g-C:H:Si:Ag) were prepared by middle frequency magnetron sputtering deposition in argon (Ar) and acetylene (C2H2) mixture gases. The effects of precursor C2H2 fraction on the microstructure and properties were studied. The results of Raman and X-ray photoelectron spectroscope (XPS) revealed that the films were dominated by sp2 carbon sites. It was observed from transmission electron microscope (TEM) that the films contained nanoparticles mainly consisting of Ag, and their size increased with the decrease in the C2H2 fraction. Si was also found to aggregate in the areas where Ag nanoparticles formed in films with high Si content. The comparative studies on the frictional behaviors of films sliding against aluminum oxide were carried out in ambient air and saline solution. The g-C:H:Si:Ag films still exhibited outstanding frictional properties even when the test environment shifts from ambient air to saline solution.

A Carbon Nanostructure for a Thermoelectric Generator

We demonstrate that it is technologically possible to obtain graphite-like films which can be used for the creation of a thermoelectric generator. The proposed technology ensures uniformity and rather small thickness of these films and allows them to be formed on a diamond-like film substrate with deposited contacts at acceptable interface. Measurements show that the electron-phonon drag effect in this system ensures thermo-emf values about 100 times as large as those provided by the diffusion process. Arrangement of the graphite-like material on a diamond-like film substrate also favors increase in the thermo-emf, which is a manifestation of the electron–ballistic phonon drag. It is established that conditions necessary for the creation of a thermoelectric generator can be achieved based on the proposed carbon nanostructures.

Углеродная наноструктура для термоэлектрического генератора

AbstractWe demonstrate that it is technologically possible to obtain graphite-like films which can be used for the creation of a thermoelectric generator. The proposed technology ensures uniformity and rather small thickness of these films and allows them to be formed on a diamond-like film substrate with deposited contacts at acceptable interface. Measurements show that the electron-phonon drag effect in this system ensures thermo-emf values about 100 times as large as those provided by the diffusion process. Arrangement of the graphite-like material on a diamond-like film substrate also favors increase in the thermo-emf, which is a manifestation of the electron–ballistic phonon drag. It is established that conditions necessary for the creation of a thermoelectric generator can be achieved based on the proposed carbon nanostructures.

Structure and Properties of Thin Graphite-Like Films Produced by Magnetron-Assisted Sputtering

The structural, electrical, and optical properties of thin graphite-like films produced by magnetron- assisted sputtering onto crystalline silicon and quartz at substrate temperatures in the range from 320 to 620°C are studied. From analysis of the Raman spectra, it is established that, as the substrate temperature is elevated, the crystallite size increases and the concentration of structural defects and the content of amorphous carbon in the phase composition of the films decrease. It is found that, as the substrate temperature is elevated, the maximum of the absorption intensity in the ultraviolet spectral region of the optical absorption spectra shifts to longer wavelengths and the absorption intensity in the visible and near-infrared spectral regions increases. As the deposition temperature is elevated, the conductivity of the films increases from 0.2 Ω–1 cm–1 at 320°C to 30 Ω–1 cm–1 at 620°C.

Структура и свойства полученных методом магнетронного распыления тонких графитоподобных пленок

AbstractThe structural, electrical, and optical properties of thin graphite-like films produced by magnetron- assisted sputtering onto crystalline silicon and quartz at substrate temperatures in the range from 320 to 620°C are studied. From analysis of the Raman spectra, it is established that, as the substrate temperature is elevated, the crystallite size increases and the concentration of structural defects and the content of amorphous carbon in the phase composition of the films decrease. It is found that, as the substrate temperature is elevated, the maximum of the absorption intensity in the ultraviolet spectral region of the optical absorption spectra shifts to longer wavelengths and the absorption intensity in the visible and near-infrared spectral regions increases. As the deposition temperature is elevated, the conductivity of the films increases from 0.2 Ω^–1 cm^–1 at 320°C to 30 Ω^–1 cm^–1 at 620°C.

Cm-Length free-standing Fe3C-filled thin graphite-like films and buckypaper-like films with high smoothness

We report the fabrication of cm-length smooth graphitic-films filled with Fe3C particles and of cm-length smooth buckypaper-like films comprising thin walled carbon nanotubes filled with Fe3C nanowires with reflectance in the 450–1000 nm region.

The microstructure and properties of energetically deposited carbon nitride films

Abstract The intrinsic stress, film density and nitrogen content of carbon nitride (CN x ) films deposited from a filtered cathodic vacuum arc were determined as a function of substrate bias, substrate temperature and nitrogen process pressure. Contour plots of the measurements show the deposition conditions required to produce the main structural forms of CN x including N-doped tetrahedral amorphous carbon (ta-C:N) and a variety of nitrogen containing graphitic carbons. The film with maximum nitrogen content (~ 30%) was deposited at room temperature with 1.0 mTorr N 2 pressure and using an intermediate bias of − 400 V. Higher nitrogen pressure, higher bias and/or higher temperature promoted layering with substitutional nitrogen bonded into graphite-like sheets. As the deposition temperature exceeded 500 °C, the nitrogen content diminished regardless of nitrogen pressure, showing the meta-stability of the carbon–nitrogen bonding in the films. Hardness and ductility measurements revealed a diverse range of mechanical properties in the films, varying from hard ta-C:N (~ 50 GPa) to softer and highly ductile CN x which contained tangled graphite-like sheets. Through-film current–voltage characteristics showed that the conductance of the carbon nitride films increased with nitrogen content and substrate bias, consistent with the transition to more graphite-like films.

Influence of carbon content and nitrogen vacancies on the bonding structure and mechanical performance of graphite-like BCxN thin films

X-ray absorption near edge structure (XANES) was used to investigate two sets of graphite-like BCxN thin films with similar B:C:N ratios but different amounts of nitrogen vacancies, which become oxygen-filled in the surface-most region. The two sets of samples were grown on Si (100) at room temperature by ion beam assisted deposition using two different ion/atom ratios. Nitrogen vacancy defects were detected in the B1s XANES spectra due to an oxygen decoration mechanism taking place at the film surface, which is correctly described by a core-level shift model. Analysis of the O1s XANES spectra showed two different types of oxygen incorporation in the samples under study. The tribomechanical properties of the BCxN samples were tested by the pin-on-disk technique, revealing the substantial role played by both the carbon intake in the hexagonal BCN planes and the concentration of nitrogen vacancies generated during the growth.

Modification of Fullerene Nanocolumn Structure by Accelerated C60 Ions

Crystalline C60 and amorphous graphite-like films of nanocolumn arrays fabricated by glancing angle deposition of C60 fullerene at substrate temperatures of -425 K were studied by transmission electron microscopy (TEM) and atomic-force microscopy (AFM). Characteristic dimension of columns is 200-400 nm. We used co-deposition of C60 molecules and accelerated C60 ions to modify the structure and properties of nanocolumn arrays. Influence of incidence angle for C60 ions on formation of film morphology was revealed. Raman spectrum analysis showed that amorphous carbon nanocolumns consist of nanographite areas with average size of -1.5 nm. The films have high conductivity (close to graphite) and have no mechanical stresses. The carbon films were applied in all-solid-state rechargeable thin-film battery as an anode layer. The nanocolumn amorphous carbon film as anode electrode showed the discharge capacity of about 50 microAh cm(-2)microm(-1) and good cycling ability over 100 times in full cell system.

Conducting and ordered carbon films obtained by pyrolysis of covalently attached polyphenylene and polyanthracene layers on silicon substrates

Graphite-like thin films with excellent electrode properties were obtained by pyrolysis of nanometer thick electrografted layers of polyphenylene and polyanthracene layers on silicon substrates in a forming gas atmosphere. The pyrolyzed grafted films, characterized by using different surface analytical techniques such as ellipsometry, cyclic voltammetry, Raman spectroscopy, X-ray photo-electron spectroscopy, atomic force microscopy, and transmission electron microscopy, consist of graphite-like layers of ∼6 nm crystallite thickness with electrochemical properties that are similar to those of pyrolyzed photoresist films. Hence, pyrolysis of covalently bonded organic layers is an alternative approach to obtain very thin conducting carbon films strongly attached to a substrate. Furthermore, this technique can be applied to substrates of any geometrical structure, in contrast to spin coating techniques. It is suggested that thin graphite-like films on silicon produced in this manner could serve as substrate for spectroelectrochemical investigations of surface reactions by attenuated total reflectance experiment or in the production of optically transparent electrodes.

Correlations between switching of conductivity and optical radiation observed in thin graphite-like films

The satisfactory explanation of anomalous electromagnetics in thin graphite-like carbon films till now is absent. The most comprehensible explanation may be the high-temperature superconductivity (HTSC). The pulse widths of spasmodic switching of electrical conductivity measured in this work in the graphite-like nanostructured carbon films, produced by methods of the carbon arc (CA) and chemical vapor deposition (CVD), are 1 and 2 ns correspondingly. Such fast switching completely excludes the thermal mechanism of the process. According to HTSC logic, in the time vicinity close to jump of electroresistance, it is necessary to expect the generation of optical radiation in the infrared (IR) range. This work presents the first results on registration of IR radiation caused by the sharp change of conductivity in thin graphite-like carbon films.

Structural changes in amorphous carbon nitride films due to bias voltage

The effect of bias voltage on the structural properties of amorphous carbon nitride films deposited by plasma decomposition of methane (CH 4) and nitrogen (N 2) is investigated. A series of films was deposited under conditions in which diamond-like a-C:H films are obtained, i.e., bias of − 200 V, and pressure of 1.0 Pa. Another series of films was deposited under conditions where graphite-like films are obtained, i.e., bias of − 800 V, and pressure of 12 Pa. To investigate the effect of these conditions on the properties of the films, FTIR, Raman, nanohardness, and ESR measurements were undertaken. It was observed that the incorporation of nitrogen and the investigated properties depend on the base structure (diamond-like vs. graphite-like).

Microtopography and field emission properties of carbon films grown in a microwave gas discharge plasma

Graphite-like carbon films are grown in an ethanol vapor plasma in a microwave gas discharge. The electrical parameters controlling the microtopography and electronic properties of carbon films are determined. It is shown that electron bombardment affects the fine structure of graphite-like nanocrystallites and their emissive power with characteristics close to those of carbon nanotubes. The emission properties of layered graphite-like films can be improved by metal (cadmium) impurity doping. For nanocrystalline graphite-like films, emission currents with a density of 0.3 A/cm2 are induced at an electric field strength of less than 7 V/µ m in the gap.

Preparation and properties of COx films

New types of amorphous graphite-like COx films were obtained by two ways: (i) magnetron sputtering of a graphite target in the gas mixture Ar+O2; and (ii) air annealing at 250–300 °C of a-C films deposited by magnetron sputtering in Ar. These films contain at most 18–22% atomic oxygen, depending on the way of preparation. They remain stable in air and vacuum up to 300 °C. The transition from graphite-like a-C to a-CO0.2 is accompanied by a sharp increase in electrical resistivity and IR transmittance. Two characteristic absorption bands at approximately 1700 and 1605 cm-1 appear and the G band in the Raman spectrum shifts to approximately 1605 cm-1. Electron diffraction reveals that only those films with 002 interlayer distance increased with respect to that of graphite may be saturated with oxygen up to approximately 22 at. %, until they become strongly vaporized.