Surface Of Carbon Films Research Articles

Structuring of the Surface of Thin Carbon Films During Activation by Microsecond Current Pulses

The influence of current activation by electric pulse breakdown on changes in surface morphology and emission characteristics of a field emission cathode made on the basis of carbon films obtained by deposition in a microwave gas discharge plasma was studied. Current activation of these films was carried out by applying voltage pulses of microsecond duration until an electrical breakdown occurred. It is shown that during activation, the morphology of the film surface in the breakdown region changes with the formation of a micro-sized emitting structure, which significantly improves the field emission characteristics of cathodes based on carbon films.

Carbon-Induced Changes in the Morphology and Wetting Behavior of Ionic Liquids on the Mesoscale.

Thin films of ionic liquids (ILs) have gained significant attention due to their unique properties and broad applications. Extensive research has focused on studying the influence of ILs' chemical composition and substrate characteristics on the structure and morphology of IL films at the nano- and mesoscopic scales. This study explores the impact of carbon-coated surfaces on the morphology and wetting behavior of a series of alkylimidazolium-based ILs. Specifically, this work investigates the effect of carbon coating on the morphology and wetting behavior of short-chain ([C2C1im][NTf2] and [C2C1im][OTf]) and long-chain ([C8C1im][NTf2] and [C8C1im][OTf]) ILs deposited on indium tin oxide (ITO), silver (Ag), and gold (Au) substrates. A reproducible vapor deposition methodology was utilized for the deposition process. High-resolution scanning electron microscopy, atomic force microscopy, and X-ray photoelectron spectroscopy were used to analyze the morphological and structural characteristics of the substrates and obtained IL films. The experimental data revealed that the IL films deposited on carbon-coated Au substrates showed minor changes in their morphology compared to that of the films deposited on clean Au surfaces. However, the presence of carbon coatings on the ITO and Ag surfaces led to significant morphological alterations in the IL films. Specifically, for short-chain ILs, the carbon film surface induced 2D growth of the IL film, followed by subsequent island growth. In contrast, for long-chain ILs deposited on carbon surfaces, layer-by-layer growth occurred without island formation, resulting in highly uniform and coalesced IL films. The extent of morphological changes observed in the IL films was found to be influenced by two crucial factors: the thickness of the carbon film on the substrate surface and the amount of IL deposition.

Structuring of the Surface of Thin Carbon Films during Activation by Microsecond Current Pulses

Structuring of the Surface of Thin Carbon Films during Activation by Microsecond Current Pulses

Immersion infrared reflection‐absorption spectroscopy studies on diamond‐like carbon surfaces. I. Formation of electrophilic groups on surfaces of amorphous carbon films aging in ambient air

AbstractTo study chemical functional groups on surfaces of diamond‐like carbon (DLC) films, a highly sensitive infrared reflection‐absorption spectroscopic technique, immersion infrared reflection‐absorption spectroscopy (IRRAS), is applied in the present study. The method employs (i) a conventional attenuated total reflection (ATR) accessory with a Ge crystal as an immersion medium and (ii) an aluminum underlayer beneath the 50–70 nm thick DLC film. Sensitivity, selectivity, and quantifiability of the method can be enhanced by chemical derivatization (CD), coupling chemical moieties with strong characteristic vibrational bands to specific functional groups on the DLC surface. The method is applied to amorphous sputtered carbon films (a‐C) to demonstrate that electrophilic groups, most probably epoxy groups, are formed during aging under ambient conditions.

Scaling up to macroscale superlubricity of sp2-dominated structural carbon films: Graphene and carbon onion

Sp2-dominated structural carbon films exhibit macroscale superlubricity. Nevertheless, the mechanisms governing the superlubricity are still not well comprehended, mainly due to the lack of direct link between graphene (or carbon onion) and superlubricity scale-up. Here, we establish the link by the combination of atomic force microscopy (AFM), transmission electron microscopy (TEM) and Raman analyses of the frictional surfaces of sp2-dominated structural carbon films. The friction-induced graphene and carbon onion products locate strictly at the wear track center and take on flake-like and nanoparticle-like morphologies, respectively. Then they eliminate the cross-interface carbon–carbon interactions and reduce contact area, thereby promoting the achievement of macroscale superlubricity. Atomistic simulations reveal the key role of the curvature and cross-linking degree of graphene basal planes in the sp2-dominated carbon films on their frictional products. The results answer the question how the nanoscale tribology of graphene and carbon onion can be scaled up to macroscale superlubricity.

High-performance amorphous carbon films on titanium foils: Toward industrial preparation of coated metallic bipolar plates for proton exchange membrane fuel cells

The proton exchange membrane fuel cells (PEMFCs) composed of amorphous carbon (a-C) film surface modified metal bipolar plates (BPP) have been widely used as a new generation power source for hydrogen energy applications. However, one of the main challenges limiting the industrial deployment of a-C coated BPP remains the low deposition rate. In this study, arc ion plating with a deposition rate exceeding 100 nm/min was used to rapidly deposit a-C films with excellent performance on the surface of titanium foil (TA1). The experimental results show that the ICR of a-C coated TA1 decreases to 1.125 mΩ cm2 at a pressure of 1.4 MPa and the corrosion current density is about 3.37 × 10−9 A cm−2. In addition, industrially useable BPPs with large-sized coated a-C films has been successfully deposited. This work provides valuable reference for the industrial preparation of low-cost a-C film coating metal BPP for PEMFCs.

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.

Freestanding Ultrathin Precisely Structured Hierarchical Porous Carbon Blackbody Film for Efficient Solar Interfacial Evaporation

Solar‐energy‐powered interfacial evaporation is the most meaningful strategy for energy utilization, water desalination, and mineral purification. It can achieve high efficiency, low‐density energy, and sustainable harvest and utilization. However, the microstructure and surface/interface design still lead to a balance between solar–thermal conversion, water conduction, and thermal management, which also determines the efficiency of photothermal interfacial evaporation. Here, a free‐standing, ultrathin carbon film with a tunable nanopore diameter is prepared and used as a blackbody layer for solar photothermal evaporation. By 3D reconstruction methods, the effect of pore structure on interfacial evaporation is systematically studied. Hierarchical porous carbon film with an average pore size of about 300 nm exhibits outstanding photothermal evaporation performance, reaching up to 1.96 kg m−2 h−1 with excellent stability. Ultra‐hydrophobic, optically enhanced absorption graphene array is constructed on the carbon film surface through femtosecond laser nanoprocessing, further increasing the evaporation rate to 2.12 kg m−2 h−1 (1 sun) and 5.55 kg m−2 h−1 (3 suns).

Facial synthesis of Fe/Fe3N@carbon nanocomposite for simultaneous electrochemical detection of dopamine and acetaminophen

In this work, a serial of Fe/Fe3N based nanocomposites were synthesized by high-temperature pyrolytic method. Structural characterizations show that the small Fe/Fe3N nanoparticles uniformly dispersed on the surface of carbon films, where thin carbon may effectively enhance the stability of Fe/Fe3N and the carbon films can accelerate the migration of electrons. Moreover, Fe/Fe3N based composite can significantly increase the effective area of bare GCE because of its high conductivity, large surface area, and good catalytic property. These structural advantages enhance the electrochemical performance of the constructed electrodes toward simultaneous dopamine (DA) and acetaminophen (AP) sensing. Under optimum condition, the linear ranges for DA and AP detection were 0.05–66.4 μM and 0.05–56.9 μM, respectively. In addition, due to its high sensitivity, good selectivity and strong stability, Fe/Fe3N-900@GCE can also be applied for detecting DA and AP in real samples. This work provides a simple and effective strategy for constructing new electrode materials for small biomolecule sensing.

The synergistic mechanism between graphitized tribofilm and graphitized surface of diamond-like carbon film under different temperature environments

The tribology characteristics of diamond-like carbon (DLC) film are studied under different experiment temperatures. The outcomes reveal the average COF of DLC film will gradually decrease with the increase of temperature from 25 °C to 225 °C, but its wear rate will gradually increase. Especially at 225 °C, the DLC film is worn through in a very short time. The Raman characterizations imply that the low friction behavior of DLC film may be mainly caused by the synergistic effect of graphitized transfer layer and graphitized worn surface of DLC film as the temperature increases from 25 °C to 175 °C. Further analysis shows that the high wear of DLC film at high temperature may be mainly due to the reduction of wear resistance of worn DLC surface and the formation of soft oxide layer at friction interface.

Direct silanol analysis of tribological surfaces using synchrotron radiation

A new direct detection technique for silanol is needed for tribological materials containing silicon. We focused on near-edge X-ray absorption fine structure (NEXAFS), which uses synchrotron radiation as a method for directly detecting silanol. Model samples were prepared, and their spectra were obtained by NEXAFS. The Si and the O K-edge spectra of silanol exhibited peaks at approximately 1843 eV and 535 eV, respectively. Then the surfaces of silicon-containing diamond-like carbon (DLC-Si) films were measured. The amount of silanol on high-silicon-doped DLC, which had a low friction coefficient, was found to be greater than that on low-silicon-doped DLC. In this research, we demonstrated that the silanol on the surface of DLC-Si films can be directly detected and identified by NEXAFS.

The degradation of humidity sensitivity of friction for tetrahedral amorphous carbon film by spin-coating hexagonal boron nitride

At present, the strong friction-dependence on the working environments of amorphous carbon films (a-C) is a troublesome problem that limit theirs wide application, especially the environment humidity. In previous studies, it was shown that the incorporation of other elemental atoms into a-C films could control theirs tribological humidity-sensitivity to some extent. Here, a simple and effective method is employed by spin-coating a hexagonal boron nitride (h-BN) layer on surface of tetrahedral amorphous carbon (ta-C) film. It plays an efficient role on the degradation of humidity-sensitivity of friction for ta-C films, as well as reducing the friction. The underling mechanism is attributed to the enhanced graphitization process catalyzed by h-BN, leading to generation of more ordered carbon, thus enabling the low and stable friction.

Electrochemical activation of graphene sheets embedded carbon films for high sensitivity simultaneous determination of hydroquinone, catechol and resorcinol

In this study, the graphene sheets embedded carbon (GSEC) film was electrochemically activated in KOH solution for high sensitivity simultaneous determination of hydroquinone (HQ), catechol (CC) and resorcinol (RC). The electrochemical activation mechanism of GSEC films in alkaline solution was clarified. We found that the embedded graphene sheets were corroded during activation, resulting in the formation of more defective graphene edges and carbonyl functional groups at the surface of carbon film. These corroded graphene edges provided more electrochemical active sites and accelerated the electron transfer. Thus, the activated GSEC film exhibited highly electrocatalytic activity towards the oxidation of HQ, CC and RC. The redox peak separation for HQ and CC decreased from 366 mV to 62 mV and 262 mV to 54 mV, respectively. The oxidation potential of RC also decreased from 714 mV to 590 mV. The electrochemical sensor showed a wide liner response for HQ, CC and RC in the concentration range of 0.5∼200 μM, 0.5∼200 μM and 0.2∼400 μM with detection limit of 0.1 μM, 0.1 μM and 0.05 μM, respectively. These results demonstrate that the KOH-activated GSEC film is a promising electrode material for constructing highly sensitive and selective biosensors.

Ultrasmooth nanocrystalline carbon film induced by low concentration doping: Carbide disorienting graphene nanocrystallite

The fabrication of nanocrystalline films is usually accompanied by undesired surface roughening, which limits their applications in tribology, optics and electronics. Here, we report a technique to reduce the average roughness of graphene nanocrystalline carbon film from 18.3 nm to 0.66 nm by ∼5 at.% Ti-doping. The surface of the Ti-doped graphene nanocrystalline carbon film stay ultrasmooth from few nanometer thick up to 1 μm thick. Based on the nanostructure characterization, the ultrasmooth mechanism is interpreted that Ti-doping leads to the formation of Ti–C bond, and changes the growth of graphene nanocrystallite from preferred vertical-aligned orientation to random orientation. The ultrasmooth mechanism is general, as shown by similar effects with low concentration doping of Si, Al, Cr, Zr and W. This approach paves a way for fabricating ultrasmooth nanocrystalline carbon films without a requirement of ion-impact-induced downhill current, and significantly improving the hardness of the graphene nanocrystalline carbon film.

Infrared and mechanical properties of the oxygen-doped non-hydrogenated diamond-like carbon film prepared by pulsed laser deposition

The non-hydrogenated diamond-like carbon films were prepared by the femtosecond laser in the oxygen atmosphere, and the influence of the oxygen atmosphere on the microstructural, surface, infrared and mechanical properties of the oxygen-doped diamond-like carbon films were researched. The oxygen atmosphere was propitious to reduce the granules on the surfaces but increase the surface roughness of the diamond-like carbon DLC films. During the pulsed laser deposition, the carbon and oxygen atoms were inclined to form the CO bond, CO bond and CC hybridized bond, when the oxygen pressure was lower than 5 m Torr. Although the CO and CO bonds led one additional absorption band and two additional absorption peaks in the infrared spectra of the oxygen-doped diamond-like carbon films, their transmission in the medium infrared band increased. Nano-hardness of the DLC films was reduced when the oxygen pressure increased dominantly because the CC sp3 bonds with higher atomic binding energy were replaced the CO bonds with lower atomic binding energy.

Precise control of surface texture on carbon film by ion etching through filter: Optimization of texture size for improving tribological behavior

Surface texture is a potential way to promote the tribological behavior of films with a range of tens to hundreds nanometers, but how to precisely control the texture size and find an optimal size for improving the tribological behavior is still challenging. In this paper, we proposed a method to fabricate pit texture with tunable size on the surface of carbon film by ion etching through a filter. The pit depth (10, 30 and 60 nm) was decided by the etching time and the pit diameter (10, 60 and 120 μm) was equal to the through-hole on the filter. The tribological properties of these carbon films were tested using a pin-on-disk tribometer. The results demonstrated that the friction coefficient and wear life were strongly affected by the texture parameter and there were an optimal pit depth and diameter under which the film exhibited the lowest friction coefficient and the longest wear life. The mechanism of the tribological property promotion was further discussed based on the variation of the transfer film structure and contact condition induced by the texture. These results provided an effective way to choose proper texture parameters for better tribological performance of the surface, which can be expected for expanding the texture techniques.

Modifications of surface and bulk properties of magnetron-sputtered carbon films employing a post-treatment of atmospheric pressure plasma

Control of the bonding structure in carbon materials is achieved by a post-treatment of atmospheric pressure plasma (APP) for magnetron-sputtered carbon films. The APP post-treatment changes the films morphologically owing to the removal and modification of sp2 bonds on the basis of the near edge X-ray absorption fine structure analysis of sp2 contents. By APP post-treatment, the resulting changes in surface and bulk properties modify the optical and electrical properties of the carbon films. The control of the film properties can be utilized for various applications, such as gas sensors and solar cells.

OPTICAL PROPERTIES OF THE RAPID ANNEALED OXYGEN-DOPED DIAMOND-LIKE CARBON FILM

The amorphous oxygen-doped diamond-like carbon films were prepared by pulsed laser deposition. Compared with the pure diamond-like carbon film, there were much less graphite clusters on the surfaces of the oxygen-doped diamond-like carbon films, and the average transmission of the oxygen-doped diamond-like carbon films in the medium infrared band increased. However, some new absorption peaks in the infrared spectra of the oxygen-doped diamond-like carbon film were generated. Rapid annealing was experimented to remove the absorption peaks. XPS analysis showed that the fractions of the C–O and C=O bonds that generated the new absorption peaks were reduced more than the fractions of [Formula: see text] bonds by rapid annealing at 400[Formula: see text]C, and the absorption peaks in the medium infrared spectra decreased. It indicated that rapid annealing at right temperature during the right time could reduce greatly the absorption in the medium infrared band of oxygen-doped diamond-like carbon films.

Surface N-doped graphene sheets induced high electrocatalytic activity for selective ascorbic acid sensing

In this study, the graphene sheets embedded carbon (GSEC) film was modified with surface N-doping for highly selective ascorbic acid (AA) sensing. We found that the N-doped graphene sheets formed in-situ at the carbon film surface and induced high electrocatalytic activity for AA oxidation. Although surface N-doping slightly decreased the ID/IG and surface roughness of carbon film, the graphene sheets embedded in amorphous were preserved. With surface N-doping, the charge-transfer resistance was reduced from 22.5 Ω cm2 to 3.9 Ω cm2, the oxidation-reduction peak separation decreased to a low value of 65.7 mV in Fe(CN)64−/3− redox system, and the standard rate constant was increased from 0.24×10-2 to 1.36×10-2 cm·s-1. The surface N-doped graphene sheets embedded carbon (SN-GSEC) decreased the oxidation potential of AA from 0.186 V to 0.025 V (vs. Ag/AgCl) and realized selective detecting of AA. The mechanism may be that the surface N-doping induce the adjacent carbon in graphene sheets to obtain a higher partial density of states and more positive compensating charge. This study provides a simple method for preparing high performance electrochemical biosensor.

Charging of electron beam irradiated amorphous carbon thin films at liquid nitrogen temperature

We studied the charging behavior of an amorphous carbon thin film kept at liquid-nitrogen temperature under focused electron-beam irradiation. Negative charging of the thin film is observed. The charging is attributed to a local change in the work function of the thin film induced by electron-stimulated desorption similar to the working principle of the hole free phase plate in its Volta potential implementation at elevated temperature. The negative bias of the irradiated film arises from the electron beam induced desorption of water molecules from the carbon film surface. The lack of positive charging, which is expected for non-conductive materials, is explained by a sufficient electrical conductivity of the carbon thin film even at liquid-nitrogen temperature as proven by multi-probe scanning tunneling microscopy and spectroscopy measurements.