Graphene Sheets Embedded Carbon Film Research Articles

Effect of Graphene Sheets Embedded Carbon Films on the Fretting Wear Behaviors of Orthodontic Archwire-Bracket Contacts.

Carbon films were fabricated on the orthodontic stainless steel archwires by using a custom-designed electron cyclotron resonance (ECR) plasma sputtering deposition system under electron irradiation with the variation of substrate bias voltages from +5 V to +50 V. Graphene sheets embedded carbon (GSEC) films were fabricated at a higher substrate bias voltage. The fretting friction and wear behaviors of the carbon film-coated archwires running against stainless steel brackets were evaluated by a home-built reciprocating sliding tribometer in artificial saliva environment. Stable and low friction coefficients of less than 0.10 were obtained with the increase of the GSEC film thickness and the introduction of the parallel micro-groove texture on the bracket slot surfaces. Particularly, the GSEC film did not wear out on the archwire after sliding against three-row micro-groove textured bracket for 10,000 times fretting tests; not only low friction coefficient (0.05) but also low wear rate (0.11 × 10−6 mm3/Nm) of the GSEC film were achieved. The synergistic effects of the GSEC films deposited on the archwires and the micro-groove textures fabricated on the brackets contribute to the exceptional friction and wear behaviors of the archwire-bracket sliding contacts, suggesting great potential for the clinical orthodontic treatment applications.

Surface/interface texture enhanced tribological properties of graphene sheets embedded carbon films

Texture could improve the tribological properties of thin films effectively. The mechanism of surface texture improving tribological performance has been extensively studied. However, the coupling effect of surface texture and interface texture on tribological performances needs to be comprehensively understood. In this work, we fabricated surface/interface textured carbon films. The experimental results proved that the tribological properties of carbon films had a remarkable enhancement after adding surface/interface texture and they were strongly related to the texture parameters. The mechanism of the enhanced performance was discussed based on the promotion of transfer films and the enhancement of film-substrate adhesion strength induced by the surface/interface texture. Finally, a coupling effect of surface/interface texture on the tribological performance was proposed.

Robust low friction performance of graphene sheets embedded carbon films coated orthodontic stainless steel archwires

Reducing the friction force between the commercial archwire and bracket during the orthodontic treatment in general dental practice has attracted worldwide interest. An investigation on the friction and wear behaviors of the uncoated and carbon film coated stainless steel archwires running against stainless steel brackets was systematically conducted. The carbon films were prepared at substrate bias voltages from +5 to +50 V using an electron cyclotron resonance plasma sputtering system. With increasing substrate bias voltage, local microstructures of the carbon films evolved from amorphous carbon to graphene nanocrystallites. Both static and stable friction coefficients of the archwire-bracket contacts sliding in dry and wet (artificial saliva) conditions decreased with the deposition of carbon films on the archwires. Low friction coefficient of 0.12 was achieved in artificial saliva environment for the graphene sheets embedded carbon (GSEC) film coated archwire. Deterioration of the friction behavior of the GSEC film coated archwire occurred after immersion of the archwire in artificial saliva solution for different periods before friction test. However, moderate friction coefficient of less than 0.30 sustained after 30 days immersion periods. The low friction mechanism is clarified to be the formation of salivary adsorbed layer and graphene sheets containing tribofilm on the contact interfaces. The robust low friction and low wear performances of the GSEC film coated archwires make them good candidates for clinical orthodontic treatment applications.

Electrochemical corrosion behaviors of N-doped graphene sheets embedded carbon films in acid

Electrochemical corrosion behaviors of N-doped graphene sheets embedded carbon (N-GSEC) film in H2SO4 solutions were investigated. We found that the corrosion of N-GSEC film originated from the oxidation of carbon, and the sp2-hybridized carbon was more susceptible to be oxidized than the sp3-hybridized carbon. The corrosion resulted in the formation of N-doped graphene oxides and more exposed graphene edges, which highly improved the electron transfer rates as well as the electrochemical activity of N-GSEC films. The corroded N-GSEC exhibited much higher electrocatalytic activity for phenol biomolecules. These findings shed light on the surface functional modification and application of N-GSEC films.

High Electrochemical Activity Induced by Doping Oxygen in Graphene Sheets Embedded Carbon Film

AbstractIn this work, the high electrochemical activity induced by doping different contents of oxygen on the surface of graphene sheets embedded carbon (GSEC) film is studied, which is prepared by electron cyclotron resonance (ECR) plasma sputtering system under electron irradiation. Transmission electron microscopy observation and Raman analysis confirm that doping oxygen induced more graphene edges and oxygen‐containing functional groups on the surface. The electrochemical activities of the films are measured in the redox system and the results show that a proper doping content of oxygen is beneficial to reduce the oxidation‐reduction peak separation. The surface O‐doped GSEC film with 5% content realizes the simultaneous detection of uric acid (UA), xanthine (XA) and hypoxanthine (HXA) with high sensitivity. The mechanism could be that the isolated electron at graphene edge and the polar fraction of oxygen‐containing functional groups provide more active sites to accelerate the electron transfer. These results indicate that surface O‐doped GSEC films are promising electrode materials to construct sensitive electrochemical biosensors.

Magnetostrictive friction of graphene sheets embedded carbon film

We report a magnetostrictive friction phenomenon in atomic force microscopy (AFM) silicon probe sliding against graphene sheets embedded carbon (GSEC) film under external magnetic field. A special electromagnet device was designed on AFM to generate controllable magnetic field for the magnetostrictive friction measurements. GSEC films possessing self-magnetism were prepared by electron irradiation in electron cyclotron resonance (ECR) plasma. The magnetostrictive friction was investigated by adjusting the external magnetic field intensity and self-magnetism of the film. The results showed that the presence of the magnetic field resulted in an evident increment of the friction force of GSEC films with different magnetism, while the friction of nonmagnetic silicon wafer was not affected, indicating that the interaction between external magnetic field and the self-magnetism of the carbon film contributes to the friction increment, i.e. magnetostrictive friction. The mechanism of the magnetostrictive friction was ascribed to the atomic scale real contact area increment induced by the magnetostrictive strain of the graphene sheets. This finding may shed light on the new applications of magnetostrictive friction of carbon film.

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.

Nanosized graphene sheets enhanced electron field emission behavior in pure carbon film

We reported the field emission behavior of pure carbon films deposited by low-energy electron irradiation in electron cyclotron resonance plasma. First, the field emission behaviors of amorphous, graphene sheets embedded and graphite-like structures were investigated, and the graphene sheets embedded carbon film exhibited an enhanced performance. Then by controlling the electron irradiation energies and densities, the effects of the graphene sheets on the field emission properties were examined. The best electron emission property (turn-on field of 8.4 V/μm and maximum current density of 2.10 mA/cm2 at electric field of 16 V/μm) was obtained with the carbon film under the electron irradiation energy of 50 eV and density of 65 mA/cm2. The mechanism of enhanced field emission was attributed to the nanosized graphene sheets which acted as electron emitters and transport channels. The method of controlling nanosized graphene sheets is important for developing the nanostructured carbon coatings in field emission applications.

Study on friction-electrification coupling in sliding-mode triboelectric nanogenerator

Triboelectric nanogenerator (TENG) is regarded as a revolutionary technology for harvesting clean and sustainable energy with low cost. Here, sliding-mode TENGs based on both graphene sheets embedded carbon (GSEC) and amorphous carbon (a-C) films were designed and their friction-electrification coupling properties were studied. The GSEC and a-C films were fabricated by electron irradiation assisted physical vapor deposition in an electron cyclotron resonance (ECR) plasma system. A novel testing platform that can simultaneously measure friction force, output voltage and output current was designed and assembled for studying the friction-electrification coupling of sliding-mode TENG. In the case of GSEC and a-C films slid against Polytetrafluoroethylene (PTFE) film, the open-circuit output voltage, the short-circuit output current density, the peak power density and the maximum instantaneous energy conversion efficiency were 13.5 V, 0.35 μA/cm2, 0.63 mW/cm2 and 8.61% for the GSEC film based TENG, and 8.5 V, 0.24 μA/cm2, 0.5 mW/cm2 and 7.71% for the a-C film based TENG, respectively. The results implied that the GSEC film exhibited a higher electric output performance compared with the a-C film. The origin of high electric output performance of the GSEC film based TENG was ascribed to the edge and channel effects of graphene sheets. These findings shed light on the application of carbon films in friction-induced nanoenergy field.

Nanosized graphene sheets induced high electrochemical activity in pure carbon film

We found that nanosized graphene sheets induced high electrochemical activity in pure carbon films, which prepared by electron cyclotron resonance (ECR) plasma sputtering under low-energy electron irradiation condition. The electrochemical properties were studied by electrochemical impedance spectroscopy and cyclic voltammetry. The graphene sheets embedded carbon (GSEC) films showed a wide potential window over 3.2 V. The charge transfer resistance and the oxidation-reduction peak separation (ΔEP) of the GSEC films are lower than amorphous carbon films in several redox systems (Fe(CN)64−/3-, Ru(NH3)62+/3+, dopamine and ascorbic acid), especially in the inner-sphere system, the ΔEP is only half of amorphous carbon films. The high electrochemical activity of GSEC films originated from the nanosized graphene sheets, which offered faster electron transfer path and more reaction active sites. Our results indicate the GSEC films have great potential to be an electrochemical biosensor in detecting biomolecules with high oxidation potential.

Nanosized graphene sheets enhanced photoelectric behavior of carbon film on p-silicon substrate

We found that nanosized graphene sheets enhanced the photoelectric behavior of graphene sheets embedded carbon (GSEC) film on p-silicon substrate, which was deposited under low energy electron irradiation in electron cyclotron resonance plasma. The GSEC/p-Si photodiode exhibited good photoelectric performance with photoresponsivity of 206 mA/W, rise and fall time of 2.2, and 4.3 μs for near-infrared (850 nm) light. The origin of the strong photoelectric behavior of GSEC film was ascribed to the appearance of graphene nanosheets, which led to higher barrier height and photoexcited electron-collection efficiency. This finding indicates that GSEC film has the potential for photoelectric applications.

Restructured graphene sheets embedded carbon film by oxygen plasma etching and its tribological properties

An oxygen plasma etching technique was introduced for improving the tribological properties of the graphene sheets embedded carbon (GSEC) film in electron cyclotron resonance plasma processing system. The nanostructural changing in the film caused by oxygen plasma etching was examined by transmission electron microscope, Raman spectroscopy and X-ray photoelectron spectroscopy, showing that the 3nm thick top surface layer was restructured with smaller graphene nanocrystallite size as well as higher sp3 bond fraction. The surface roughness, mechanical behavior and tribological properties of the original GSEC and oxygen plasma treated GSEC films were compared. The results indicated that after the oxygen plasma treatment, the average roughness decreased from 20.8±1.1nm to 1.9±0.1nm, the hardness increased from 2.3±0.1GPa to 2.9±0.1GPa, the nanoscratch depth decreased from 64.5±5.4nm to 9.9±0.9nm, and the wear life increased from 930±390 cycles to more than 15,000 frictional cycles. The origin of the improved tribological behavior was ascribed to the 3nm thick graphene nanocrystallite film. This finding can be expected for wide applications in nanoscale surface engineering.

Magnetic behavior of graphene sheets embedded carbon film originated from graphene nanocrystallite

We found paramagnetic behavior at 300 K of graphene sheets embedded carbon (GSEC) film, which is deposited under low energy electron irradiation in electron cyclotron resonance plasma. The origin of the magnetic properties of GSEC film is ascribed to the formation of graphene nanocrystallite. With higher irradiation energy, the size of nanocrystallite barely changed, while the density in GSEC film became higher, leading to a dramatically increase of saturation magnetization and residual magnetism. This finding indicates that GSEC film with higher magnetization can be expected, which has the potential for magnetic and spintronics applications.

Graphene sheets embedded carbon film prepared by electron irradiation in electron cyclotron resonance plasma

We used a low energy electron irradiation technique to prepare graphene sheets embedded carbon (GSEC) film based on electron cyclotron resonance plasma. The particular π electronic structure of the GSEC film similar to bilayer graphene was verified by Raman spectra 2D band analyzing. The phase transition from amorphous carbon to GSEC was initiated when electron irradiation energy reached 40 eV, and the growth mechanism of GSEC was interpreted as inelastic scattering of low energy electrons. This finding indicates that the GSEC film obtained by low energy electron irradiation can be excepted for widely applications with outstanding electric properties.