Nanostructured Carbon Films Research Articles

Nanostructured Carbon Films Obtained by CH4 Plasma Deposition and Annealing at High Temperatures: Structural Features and Their Influence on the Electrical and Optoelectronic Properties

Nanostructured Carbon Films Obtained by CH4 Plasma Deposition and Annealing at High Temperatures: Structural Features and Their Influence on the Electrical and Optoelectronic Properties

Nanostructured carbon films obtained by CH4 plasma deposition and annealing at high temperature: structural features and their effects on electrical and optoelectronic properties

This article is dedicated to the study of the structural, electrical, and optoelectronic properties of nanostructured carbon films obtained by methane plasma deposition, followed by annealing at high temperatures (650–800 °C). The conditions for obtaining the films affected the final physicochemical parameters. We studied the film morphology using atomic force microscopy, scanning electron microscopy, Raman spectroscopy, X-ray energy-dispersive analysis, and analysis of the current voltage (C-V) characteristics. The film thickness ranged from 20 to 150 nm, with a C/O ratio of 4:1. Structural studies have shown that the resulting nanostructured carbon films consist mainly of nanographite flakes, the lateral dimensions of which lie in the lateral size (La) range of 5 to 12 nm, and contain different fractional concentrations of sp3/sp2 crystalline phases of carbon. We have established that with an increase in the annealing temperature, the defectiveness of the carbon film structure increases; however, at the same time, the degree of graphitization increases, as indicated by the Raman spectroscopy data and the calculated values of layer resistances from the C-V characteristics. The values of photocurrents were calculated, from which it was found that the samples exhibited photosensitivity in the temperature range of room temperature to –173 °C, based on the temperature dependences of the C-V. The obtained results can be useful in creating day and night light sensors as well as temperature sensors suitable for use at low temperatures.

A comparison between ion irradiation assisted- and electron irradiation assisted-oxygen plasma treatment on modification of nanostructured carbon films

Oxygen plasma treatment has been used for surface modification of carbon materials. However, the working mechanism is not well clarified. Here, the ion irradiation assisted- and electron irradiation assisted-oxygen plasma etching were proposed and realized in an electron cyclotron resonance plasma processing system. The effects of the ion assisted- and electron assisted-argon plasma and oxygen plasma etching on the surface morphology and nanostructure of graphene nanocrystallites embedded carbon film were compared. In the ion assisted plasma etching, compared with argon plasma, the oxygen introduction made the sp2/sp3 and ID/IG of the film upper layer further decrease. While in the electron assisted plasma etching, after O2 introduction, the sp2/sp3 and ID/IG in the film upper layer increased. Then the oxygen plasma treatment mechanism was proposed. In the ion assisted oxygen plasma treatment, the attracted oxygen positive ions took major effect, which would reduce the threshold energy for atom displacement and then implant more carbon or oxygen atoms into the film subsurface to make the film denser. In the electron assisted oxygen plasma treatment, the neutral oxygen took major effect, which would preferentially react with the more unstable amorphous carbon and then make the film equipped with more sp2 bonds.

Tailoring the tribological properties of nanostructured carbon films under water lubrication

Carbon films have been considered suitable to be applied in water lubrication since they exhibit excellent friction-reducing and wear resistance, chemical inertness, etc. However, the basic understanding of tribological behaviors of carbon-based films under water lubrication still needs to be explored. In the present work, carbon films with different nanostructures were prepared by the electron cyclotron resonance (ECR) plasma nano-surface manufacturing system, and micro-textures with different sizes were prepared on the surface of carbon films by plasma etching. The influence of nanostructure and surface texture on the tribological properties of carbon films was investigated. The results show that different nanostructured carbon films can obtain lower friction coefficients and longer wear life under water lubrication than under dry condition. Due to low surface roughness, high hardness, and compact structure, the tribological properties of amorphous carbon (a-C) films under water lubrication are much better than those of graphene sheet-embedded carbon (GSEC) films. The prepared surface texture has a negative effect on the hard a-C film, but it can make the soft GSEC film generate soft wear debris at the initial stage. With the action of water, the soft wear debris is bonded on the surface of the contacting ball to form a silt-like transfer film, which increases the wear life by nearly three orders of magnitude. These results extend the basic understanding of the tribological behavior of carbon film under water lubrication, which is crucial in both fundamental and applied science.

Electrical Contact Properties of Nanostructured Carbon Films under Transverse Current-carrying Condition

Electrical Contact Properties of Nanostructured Carbon Films under Transverse Current-carrying Condition

Delineation of diffusion pathways in nanostructured porous media by applying lattice Boltzmann modeling on scanning electron microscope images

The diffusive transport through a porous electrode is studied here, based on scanning electron microscope (SEM) images of the porous layer, made by electrodeposition of Nickel oxide over nanostructured carbon film. Lattice Boltzmann model (LBM) is employed to simulate the concentration profile in the pore network considering bounceback at the solid nodes of scanning electron images (SEI). The direct use of a grayscale image with probabilistic bounceback as per the pixel-wise intensities is explored vis-à-vis the binarization of images by Otsu’s thresholding with total bounceback at the solid grids. The diffusion pathways are delineated, and the isolated voids are identified from the concentration changes across the pore network. The fraction of isolated voids, the overall diffusivity, and the average concentration in voids are studied for 300 SEIs. The distributions of these three parameters across the SEIs show the heterogeneity in the pore structure.

Photo-induced Electron Emission of Nanostructured Carbon Thin Film Based Transmission Photocathodes at Different Electric Field

Very thin nanostructured carbon films were deposited on quartz substrate by reactive magnetron sputtering using graphite target and gas mixture of Ar and reactive gas N_2 or N_2+H_2. Film thicknesses were in the range of 20-25 nm. Rutherford backscattering spectrometry and Elastic recoil detection analytical method determined the concentration of elements in the films. Scanning electron microscopy scanned the surface morphology of carbon films. Raman spectroscopy was used for chemical structural properties determination of very thin carbon films. Raman spectra intensities were fitted with Gaussian peaks. The photo-induced (pulsed laser - 266 nm) electron emission properties of very thin nanostructured carbon films were investigated by the measurement of cathode bunch charge at different electric field and calculate quantum efficiency. The influence of different electric field on the photo-induced electron emission characteristics of prepared transmission photocathodes are discussed.

Evaporating potential

<h2>Summary</h2> The conversion of ambient heat into electricity through ubiquitous natural evaporation offers hope for new green energy technologies. So far, evaporation-induced electricity has relied mainly on the classical streaming potential, which is an electric potential generated by driving an electrolyte through a narrow channel under a pressure gradient. Here, we show that evaporation of ethanol from nanostructured carbon films can produce a sustainable volt-level potential in an environment free from the streaming potential, which we term the evaporating potential. This evaporating potential is proven to occur within a narrow partially wetted region ahead of the main capillary film and is directly generated by carrier transfer driven by evaporation of ethanol molecules. It is also shown that other polar solvents can generate potentials comparable to those induced by ethanol. The finding could open a new way to harvest environmental energy through natural processes.

Formation and growth characteristics of nanostructured carbon films on nascent Ag clusters during room-temperature electrochemical CO2 reduction.

Synthesis of carbon nanostructures at room temperature and under atmospheric pressure is challenging but it can provide significant impact on the development of many future advanced technologies. Here, the formation and growth characteristics of nanostructured carbon films on nascent Ag clusters during room-temperature electrochemical CO2 reduction reactions (CO2RR) are demonstrated. Under a ternary electrolyte system containing [BMIm]+[BF4]−, propylene carbonate, and water, a mixture of sp2/sp3 carbon allotropes were grown on the facets of Ag nanocrystals as building blocks. We show that (i) upon sufficient energy supplied by an electric field, (ii) the presence of negatively charged nascent Ag clusters, and (iii) as a function of how far the C–C coupling reaction of CO2RR (10–390 min) has advanced, the growth of nanostructured carbon can be divided into three stages: Stage 1: sp3-rich carbon and diamond seed formation; stage 2: diamond growth and diamond–graphite transformation; and stage 3: amorphous carbon formation. The conversion of CO2 and high selectivity for the solid carbon products (>95%) were maintained during the full CO2RR reaction length of 390 min. The results enable further design of the room-temperature production of nanostructured carbon allotropes and/or the corresponding metal-composites by a viable negative CO2 emission technology.

All‐Printed Green Micro‐Supercapacitors Based on a Natural‐derived Ionic Liquid for Flexible Transient Electronics

AbstractThe fabrication and characterization of green, flexible, and ultra‐thin supercapacitors that are able to operate above 1.5 V is reported, using an all‐printed fabrication process. The devices are produced by aqueous spray casting of a natural‐derived electrolyte ionogel composed by 2‐hydroxyethyl cellulose and by the ionic liquid choline lactate, while the electrodes are composed of highly porous nanostructured carbon films deposited by supersonic cluster beam deposition (SCBD). The obtained supercapacitors (device thickness &lt; 10 μm) are stable to bending and they possess power values up to 120 kW kg–1. The combination of aqueous spray casting and SCBD constitutes a versatile, scalable, and eco‐friendly fabrication process able to directly print interconnected elements suitable for transient electronic systems.

Very thin N-doped nanostructured carbon films on quartz and sapphire substrate: Photoelectron emission properties

Very thin N-doped nanostructured carbon films were deposited on quartz and sapphire substrate by radio-frequency reactive magnetron sputtering using carbon target and gas mixture of Ar and N2 or N2+H2 reactive gasses. Rutherford backscattering spectroscopy and Elastic recoil detection analytical methods determined the concentration of elements in the films. Scanning electron microscopy was used to investigate the surface morphology of nanostructured very thin carbon films. Raman spectroscopy was used for the determination of chemical structural properties of the thin nanostructured carbon films. Pulsed laser induced electron emission method was used for the study of photoelectron emission properties of nanostructured carbon films. Measured bunch charge results of fabricated transmission photocathodes showed better photoelectron emission properties of very thin nanostructured carbon films prepared on sapphire substrates. Effects of substrate and technology of very thin nanostructured carbon films on the properties of photo-induced electron emitters as backside illuminated transmission photocathode are discussed.

A strategy to construct long-range fullerene-like nanostructure in amorphous carbon film with improved toughness and carrying capacity

This study demonstrates a novel strategy to construct long-range fullerene-like nanostructures in amorphous carbon films, which we called the ‘external-field-induced growth effect’, i.e. using the target poisoning phenomenon in the magnetron sputtering process and adjusting the target as Ni catalytic material. A fullerene onion precursor can be first produced at an external sputtering target surface through the synergistic catalytic effects of both the Ni catalyst and plasma, and then the fullerene precursor was further sputtered to form fullerene-like nanostructured carbon film with optimized sputtering current, which consists of cross-linked open-loop fullerene sheets with huge amounts and long range sizes. Such a special structure endows the film great toughness and carrying capacity without sacrificing high hardness, so that it has no cracks at high contact stress (maximum Hertz contact stress: 21 GPa), and can work well at high contact stress (maximum Hertz contact stress: 3.2 GPa) with still long wear lifetime similar to that observed at low contact stress, which means it can be reliably applied in high-load conditions, and provides a new way to resolve the brittleness problem of amorphous carbon films by adjusting intrinsic carbon nanostructure.

Effect of helium incorporation on plasma parameters and characteristic properties of hydrogen free carbon films deposited using DC magnetron sputtering

The present work investigates the effects of helium (He) gas mixing with Ar on plasma parameters and examines its effect on film properties of C films. We used a closed-field unbalanced magnetron sputtering system for the deposition of C thin films at a direct current power density of 30 W/cm2 and an operating pressure of ≈3 mTorr. On the basis of systematic analysis, we present an attempt to enhance the electron temperature and investigate the high-energy electron tail, which is required for the efficient ionization in the plasmas, by incorporating He gas in the Ar background. This approach also promotes the plasma density to become high, which is more than two times at a mixing ratio of 80%. Moreover, the present study utilizes these plasma conditions to prepare hydrogen-free highly conductive nanostructured carbon films. Systematic plasma diagnostic and film analysis reveal that a high content of He incorporation is accountable for the fabrication of a highly conductive nanocrystalline carbon film in a high-density plasma environment.

Highly robust nanostructured carbon films by thermal reconfiguration of ionomer binding

A dramatic improvement in the mechanical robustness of fragile carbon nanoparticle films formed by a network of ionomer binders.

Conversion of low-grade heat via thermal-evaporation-induced electricity generation on nanostructured carbon films

Nowadays, due to increasingly serious energy crisis and environmental pollution problems, conversion of ubiquitous low-grade heat to electricity is attracting increasing worldwide interests. Recently, energy-conversion methods mediated by molecular interactions between water and nanostructured carbon materials has been reported to directly harvest the environmental energy without any auxiliary equipment and energy input. Herein, we propose a method of conversion of low-grade heat by the thermal-evaporation-induced electricity generation on a porous nanostructured carbon films (NCFs). These NCFs are directly fabricated on an Al2O3 substrate and then pre-treated by annealing and UV/Ozone treatments to maintain the spontaneous water imbibition at high temperatures. This sample can unremittingly generate electricity at relative large temperature range (~22–82 °C) via the thermal-evaporation of water. This temperature range is a common temperature of low-grade heat sources. The maximum thermal-evaporation-induced voltages are measured to be about 0.79 ± 0.05 V, and the maximum output power is calculated to be approximately 80 nW with a power density of 150 μW/m2. Furthermore, our experimental results and theoretical analysis indicate that the substrate-property of NCFs can seriously influence the performance of thermal-evaporation-induced electricity generation.

Synergistic enhancement of antibacterial activity of Cu:C nanocomposites through plasma induced microstructural engineering

This study presents magnetron plasma co-sputtering process for the synthesis of carbon thin films embedded with Cu nanoparticles (NPs). Varying the working pressure and power density of Cu target, induces control over morphology as well as the amount of Cu ions release while interacting with bacterial aliquots. The crystallographic observations present the formation, growth and orientation of crystals in Cu NPs. Raman spectroscopy depicts that increase in working pressure contributes to the development of carbon matrix structure dominating sp3 hybridizations. The variation in chemical structure with varying the plasma conditions is studied by high resolution x-ray photoelectron spectroscopy. The antibacterial activity, observed against staphylococcus aureus (S. aureus) and Escheria coli (E. coli), is strongly related to the release of Cu ions from the films. The nanocomposite films releasing Cu ions ∼1.68 µg/g of the aliquot, completely inhibit the bacterial growth. Obtained excellent antibacterial activity of presented Cu embedded nanostructured carbon films proves these films as a promising candidate in bio-medical applications.

Thermally induced atomic and electronic structure evolution in nanostructured carbon film by in situ TEM/EELS analysis

The atomic and electronic structures of nanostructured carbon film are of fundamental importance due to their dominant role in carbon films' physical, chemical and mechanical properties. Here, we reported thermally induced atomic and electronic structure evolution of nanostructured carbon film by in-situ transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS). Two nanostructured carbon films were synthesized by electron cyclotron resonance (ECR) plasma sputtering under ion and electron irradiation, respectively. We observed that even though the two carbon films had similar initial sp2/sp3 hybridization ratio, they exhibited very different performance during the same heating process. The electron irradiated film only had a relative slight clustering of sp2 carbon crystallites and almost maintained its sp2/sp3 ratio till 1000 °C; while the ion irradiated film had a significant sp2 crystallites clustering, started its sp3-to-sp2 conversion from 200 °C and almost completed at 400 °C. Argon signal was only found in the ion irradiated carbon film and its content reduced simultaneously with the sp3-to-sp2 conversion process. We suggest that the heated argon trapped inside the carbon film were responsible for triggering the sp3-to-sp2 conversion. The result will guide the future application of the nanostructured carbon film in the proper operation temperature range and help to choose appropriate irradiation method for thin film surface modification.

Electron spectroscopy of various nanostructured carbon films

X-ray photoelectron spectroscopy technique have been used to study carbon films obtained by means of ion-plasma deposition in the plasma of different chemical composition. The detailed analysis of electron spectroscopy data made it possible to determine the structure of the films and the influence of nitrogen and hydrogen admixture in plasma on the structural properties. Diamond-like films are obtained in pure argon plasma, graphite-like and carbon chain structures correspond to nitrogen and hydrogen addition respectively.

Quantitative characterization of the interfacial morphology and bulk porosity of nanoporous cluster-assembled carbon thin films

The deposition of nanoporous carbon thin films with well-controlled morphology, high surface area and porosity is of great interest for different applications requiring autonomous and portable electrochemical devices for energy conversion and storage. The engineering of this class of devices and the evaluation of their performances require the measurement of the porosity and surface area of the active carbon layers. The quantitative characterization of these parameters by gas adsorption techniques is hampered by the small amount of material usually available on a thin film.Here we report a method based on the use of atomic force microscopy (AFM) and nitrogen adsorption technique for the quantitative characterization of the specific surface area and porosity of nanoporous carbon films. In particular, we apply it to nanostructured carbon films fabricated by supersonic cluster beam deposition (SCBD), studying the evolution of their structural properties with film thickness. We exploited the characteristics of SCBD in terms of high-throughput, stability, and reproducibility to fabricate films with controlled nano and microstructure over large substrates compatible with the requirements of gas adsorption measurements. Our approach demonstrates that the combination of AFM and nitrogen adsorption technique provides the possibility of undertaking systematic quantitative characterization of the nano- and mesostructure of cluster-assembled carbon films and of their evolution, which can be easily applied to porous thin films fabricated by many different techniques.

Manipulation of nanostructured carbon films as field emitters in an electric-and-magnetic-field-assisted chemical vapor deposition process

To enhance the field emission performance and understand the emission essence of carbon materials, carbon films with different morphology and phase composition were fabricated by regulating the reactive gas flow ratio in a hot filament chemical vapor deposition system with the assistance of electric field and magnetic field. The characterization of carbon film quality and measurement of their field emission performance indicated that carbon nanostructures, including nanoclusters, nanopillars and nanotips, which were determined by the methane concentration in the process, were formed under the assistance of electric field. Further magnetic field assistance could lead to the formation of finer nanostructures with higher crystallinity. Field emission performance was highly dependent on the morphology and phase composition of the carbon films. Among all the samples, carbon nanotips, deposited in high methane concentration with the co-assistance of magnetic and electric field, possessed the best field emission performance, with the lowest turn-on field of 6.5 V·μm−1 (J = 10 μA·cm−2). Besides, a comparative study on the fitting degree of several conduction mechanisms revealed that the essence of field emission was the combination of several emission mechanisms, which was also dependent on the morphology and phase composition of these carbon films.