Reduced Graphene Oxide Thin Films Research Articles

Characteristics of Thermally Reduced Graphene Oxide Thin Film as DSSC Counter Electrode

We report characteristics of reduced graphene oxide (RGO) as a counter electrode for dye-sensitized solar cell (DSSC). The RGO thin films were prepared on FTO (Fluorine-doped Tin Oxide) substrates and followed by a reduction process. The RGO film was used as a counter electrode in a DSSC device, with a structure of FTO/TiO2/ruthenium dye/mosalyte/RGO/FTO. UV-Vis measurements show an increasing absorption spectrum of RGO film after thermal reduction process and the FT-IR spectrum confirms a removal of the oxygen containing groups after thermal reduction process. The efficiency (η) of the DSSC that applied RGO film as a counter electrode is 0.96%.

Characteristic of Thermally Reduced Graphene Oxide as Supercapacitors Electrode Materials

We investigated graphene like material named reduced graphene oxide (RGO) as an electrode material by employed graphene oxide (GO). Thin film of GO was prepared on the indium thin oxide (ITO) substrate by spin-coating method using varied concentration of GO that dispersed in water. In order to remove its oxygen contained, GO film was thermally reduced at 200 °C for 1 hour. We used cyclic voltammetry to measure its CV characteristic and estimated its specific capacitance. We obtained the highest specific capacitance of 6.53 mF g−1 that measured from 4 mg ml−1 RGO thin film at scan rate 25 mVs−1.

Highly conductive free-standing reduced graphene oxide thin films for fast photoelectric devices

Compared with mechanically exfoliated and chemical vapor deposited graphene, reduced graphene oxide (RGO) possesses unique advantages such as a wet process synthesis, high yield and the ability to assemble large-area thin films on various substrates. However, RGO is normally not recommended for advanced devices owing to its poor electrical conductivity. We report a new method to prepare highly conductive free-standing RGO thin films. The as-prepared RGO thin film possesses the highest conductivity of 87100 S m−1, the second-lowest sheet resistance of 21.2 Ω sq−1 and a medium-level mobility of 16.7 cm2 V−1 s−1 among all of the reported RGO films. To demonstrate the application potential of the free-standing RGO thin films in photoelectric devices, a fully suspended RGO photodetector is constructed using the free-standing RGO thin film, which exhibits the fastest (ca.100 ms) and broadest (from the ultraviolet to terahertz spectral range) photoresponse among all of the RGO film photodetectors that have been reported. The response speed is even comparable with those of CVD-grown graphene photodetectors and mechanically exfoliated graphene photodetectors. These results pave the way towards high-conductivity RGO thin films by a wet process assembly, thus facilitating applications of RGO in advanced electronic, optoelectronic and sensing devices.

Electromechanical properties of reduced graphene oxide thin film on 3D elastomeric substrate

Electrically conducting, 3D elastomeric composite foams are fabricated successfully using multiple cycles of infusing polyurethane foams with graphene oxide sheets followed by reduction, to form coatings of reduced graphene oxide up to ∼1260 nm thick. The reduced graphene oxide coating increases the compression modulus of the composite and lowers the electrical resistance significantly compared with polyurethane foam, the extents of which increase with increasing coating thickness. The electrical resistance of the coated foams varies by as much as three orders of magnitude for coating thickness between ∼150 and ∼1200 nm, whereas the capacitance varies by one order of magnitude. Both the stress-strain and the resistance-strain behavior are highly repeatable with compression cycles performed up to 70% strain. Both SEM and X-ray tomography characterization show that deformation is mostly through bending of the pore walls up to about 20% strain, collapse of pore openings to about 60% strain, and densification beyond that. Micro-fractures also develop on the coating during the first few cycles of compression, but no obvious structural changes can be detected afterwards.

Reduced Graphene Oxide Thin Films with Very Large Charge Carrier Mobility Using Pulsed Laser Deposition

Large area reduced graphene oxide (RGO) thin films have been grown using pulsed laser deposition (PLD) technique. A very large carrier mobility of 372 cm2 V-1s-1 has been observed in a PLD grown RGO thin film with a large sp2 carbon fraction of 87% along with narrow Raman 2D peak profile. The fraction of sp2 carbon and carbon/oxygen ratios are tuned through PLD growth parameters, and these are estimated from X-ray photoelectron spectroscopy (XPS) data. The electrical properties of the RGO thin films are comprehended by the intensity ratios between different optical phonon vibrational modes of Raman Spectra. The photoluminescence spectra also indicate a less intense and broader blue fluorescence spectrum detecting the presence of miniature sized sp2 domains in the near vicinity of π* electronic states which favor the variable range hopping transport phenomena. This study on large area RGO thin films with very large carrier mobility fabricated by PLD process will be very useful for high mobility electronic device applications and could open a roadmap for further extensive research in functionalized 2D materials.

Effect of reduction temperature on structure and hydrogen sensitivity of graphene oxides at room temperature

As precursors exfoliated from graphite oxide gels, graphene oxide thin films are annealed in a temperature range of 100 ℃ to 350 ℃ to obtain a series of reduced graphene oxide samples with different reduction degrees. For the gas sensing experiments, the reduced graphene oxide thin film gas sensing element is prepared by spin coating with Ag-Pd integrated electronic device (Ag-Pd IED). The functional groups, structures, and gas sensing performance of all the samples are investigated by X-ray diffraction, Raman spectroscopy, Fourier transform infrared spectroscopy, and gas sensing measurement. The results show that the structure of the graphene oxide samples are transformed to the graphitic structure after reduction at different thermal treatment temperatures. When the reduction temperature is lower than 150 ℃, materials exhibit features of graphite oxide. When the reduction temperature reaches about 200 ℃, the samples show characteristics transformed from graphite oxide to reduced graphite oxide gradually. When the temperature is higher than 250 ℃, materials show features of reduced graphite oxide. During the reduction process, the disorder degree increases from 0.85 to 1.59, and then decreases slightly to 1.41 with the rise of temperature. Additionally, the oxygen containing functional groups are removed with the increasing reduction temperature, and these functional groups can be removed at specific temperatures. In the lower temperature stage (100-200 ℃), the first kind of oxygen containing functional group removed is the hydroxyl group (C-OH) and the epoxy group (C-O-C) is the second. In the higher temperature stage (250-350 ℃), the main removed oxygen containing functional groups are the epoxy group (C-O-C) and the carbonyl group (C=O). The materials treated at 150, 200, 350 ℃ exhibit n-type, ambipolar, and p-type behaviors, respectively, while rGO-200 exhibits considerable increase in resistance upon exposure to hydrogen gas. rGO-200 exhibits very small decrease of resistance at room temperature and moderate increase of resistance at elevated temperatures upon exposure to hydrogen gas, while rGO-350 exhibits considerable decrease of resistance at room temperature upon exposure to hydrogen gas. These results indicate that the reduction temperature affects the distribution of density of states (DOS) in the band gap as well as the band gap size. The graphene oxide and the reduced products at low temperature show good sensitivity to hydrogen gas. With the increasing reduction temperature, the sensitivity fades while the response time and recovery time increases. The gas sensor exhibits high sensitivity (88.56%) and short response time (30 s) when exposed to the 10-4 hydrogen gas at room temperature.

Physical Properties Investigation of Reduced Graphene Oxide Thin Films Prepared by Material Inkjet Printing

The article is focused on the study of the optical properties of inkjet-printed graphene oxide (GO) layers by spectroscopic ellipsometry. Due to its unique optical and electrical properties, GO can be used as, for example, a transparent and flexible electrode material in organic and printed electronics. Spectroscopic ellipsometry was used to characterize the optical response of the GO layer and its reduced form (rGO, obtainable, for example, by reduction of prepared layers by either annealing, UV radiation, or chemical reduction) in the visible range. The thicknesses of the layers were determined by a mechanical profilometer and used as an input parameter for optical modeling. Ellipsometric spectra were analyzed according to the dispersion model and the influence of the reduction of GO on optical constants is discussed. Thus, detailed analysis of the ellipsometric data provides a unique tool for qualitative and also quantitative description of the optical properties of GO thin films for electronic applications.

Physical investigation of electrophoretically deposited graphene oxide and reduced graphene oxide thin films

Graphene oxide and reduced graphene oxide thin films are very promising materials because they can be used in optoelectronic devices and in a growing range of applications such as touch screens and flexible displays. In this work, graphene oxide (GO) and thermally reduced graphene oxide (rGO) thin films, deposited on Ti/glass substrates, have been obtained by electrophoretic deposition. The morphological and the structural properties of the samples have been investigated by micro-Raman technique, X-ray reflectometry, and SEM analysis. In order to study the optical and electrical properties, variable angle spectroscopic ellipsometry and impedance analysis have been performed. The thermal annealing changes strongly the structural, electrical, and optical properties, because during the thermal processes some amount of sp3 bonds originally present in GO were removed. In particular, the annealing enhances the Ohmic behavior of the rGO film increasing its conductivity and the estimated optical density. Moreover, using electrophoretic deposition, we have found a higher value of optical density for GO thin films, not observed in GO films obtained with other deposition methods.

A facile fabrication of chemically converted graphene oxide thin films and their uses as absorber materials for solar cells

There is a great interest in the use of graphene sheets in thin film solar cells with low-cost and good-optoelectronic properties. Here, the production of absorbent conductive reduced graphene oxide (RGO) thin films was investigated. RGO thin films were prepared from spray-coated graphene oxide (GO) layers at various substrate temperature followed by a simple hydrazine-reducing method. The structural, morphological, optical, and electrical characterizations of graphene oxide (GO) and RGO thin films were investigated. X-ray diffraction analysis showed a phase shift from GO to RGO due to hydrazine treatment, in agreement with the FTIR spectra of the layers. FESEM images clearly exhibited continuous films resulting from the overlap of graphene nanosheets. The produced low-cost thin films had high absorption coefficient up to 1.0 × 105 cm−1, electrical resistance as low as 0.9 kΩ/sq, and effective optical band gap of about 1.50 eV, close to the optimum value for solar conversion. The conductive absorbent properties of the reduced graphene oxide thin films would be useful to develop photovoltaic cells.

Erratum: Reduced Graphene Oxide Thin Film on Conductive Substrates by Bipolar Electrochemistry

Scientific Reports 6: Article number: 21282; Published online: 17 February 2016; Updated: 02 June 2016 The original version of this Article contained errors in the spelling of the authors Anis Allagui, Mohammad Ali Abdelkareem, Hussain Alawadhi and Ahmed S. Elwakil which were incorrectly given as Allagui Anis, Ali Abdelkareem Mohammad, Alawadhi Hussain and S.

Shear-induced dry transfer of reduced graphene oxide thin film via roll-to-roll printing

Here, we report a printing mechanism that utilizes mechanical stress for dry transfer of chemically reduced graphene oxide (r-GO) thin film. We discover that shear stress induced on the elastomeric stamp surface facilitates delamination of the deposited r-GO thin film from the stamp. Shear stress is introduced in a roll-to-roll printing system by rotating the stamp roller faster than the substrate roller. Energy-balance theory for thin film transfer is suggested to analyze the film delamination behavior with induced shear stress. Facile dry transfer of r-GO thin film onto flexible substrates is demonstrated in a roll-to-roll printing system at a printing rate of 5 mm/min with calculated shear stress of 325.43 kPa.

Reduced Graphene Oxide Thin Film on Conductive Substrates by Bipolar Electrochemistry.

Recent years have shown an increased interest in developing manufacturing processes for graphene and its derivatives that consider the environmental impact and large scale cost-effectiveness. However, today’s most commonly used synthesis routes still suffer from their excessive use of harsh chemicals and/or the complexity and financial cost of the process. Furthermore, the subsequent transfer of the material onto a substrate makes the overall process even more intricate and time-consuming. Here we describe a single-step, single-cell preparation procedure of metal-supported reduced graphene oxide (rGO) using the principle of bipolar electrochemistry of graphite in deionized water. Under the effect of an electric field between two stainless steel feeder electrodes, grapheme layers at the anodic pole of the wireless graphite were oxidized into colloidal dispersion of GO, which migrated electrophoretically towards the anodic side of the cell, and deposited in the form of rGO (d(002) = 0.395 nm) by van der Waals forces. For substrates chemically more susceptible to the high anodic voltage, we show that the electrochemical setup can be adapted by placing the latter between the wireless graphite and the stainless steel feeder anode. This method is straightforward, inexpensive, environmentally-friendly, and could be easily scaled up for high yield and large area production of rGO thin films.

Controllable Electrochemical Synthesis of Reduced Graphene Oxide Thin-Film Constructed as Efficient Photoanode in Dye-Sensitized Solar Cells.

A controllable electrochemical synthesis to convert reduced graphene oxide (rGO) from graphite flakes was introduced and investigated in detail. Electrochemical reduction was used to prepare rGO because of its cost effectiveness, environmental friendliness, and ability to produce rGO thin films in industrial scale. This study aimed to determine the optimum applied potential for the electrochemical reduction. An applied voltage of 15 V successfully formed a uniformly coated rGO thin film, which significantly promoted effective electron transfer within dye-sensitized solar cells (DSSCs). Thus, DSSC performance improved. However, rGO thin films formed in voltages below or exceeding 15 V resulted in poor DSSC performance. This behavior was due to poor electron transfer within the rGO thin films caused by poor uniformity. These results revealed that DSSC constructed using 15 V rGO thin film exhibited high efficiency (η = 1.5211%) attributed to its higher surface uniformity than other samples. The addition of natural lemon juice (pH ~ 2.3) to the electrolyte accelerated the deposition and strengthened the adhesion of rGO thin film onto fluorine-doped tin oxide (FTO) glasses.

Synthesis and Characterization of Graphene Oxide and Reduced Graphene Oxide Thin Films Deposited by Spray Pyrolysis Method

Graphene Oxide (GO) was chemically synthesized from Natural Flake Graphite (NFG). The GO was chemically reduced to Reduced Graphene Oxide (RGO) using hydrazine monohydrate. Thin films of GO and RGO were also deposited on sodalime glass substrate using spray pyrolysis technique (SPT). The samples were characterized using Fourier Transform Infrared (FTIR) spectroscopy, Scanning Electron Microscopy (SEM) with Energy Dispersive X-Ray (EDS) facility attached to it, UV-Visible Spectrometry and Four-Point probe. The FTIR spectra showed the addition of oxygen functionality groups in GO while such groups was drastically reduced in RGO. SEM micrograph of GO thin film showed a porous sponge-like structure while the micrograph of RGO thin film showed evenly distributed and well connected graphene structure. The EDX spectrum of RGO showed that there was decrease in oxygen content and increase in carbon content of RGO when compared to GO. The optical analysis of the GO and RGO thin films gave a direct energy bandgap of 2.7 eV and 2.2 eV respectively. The value of sheet resistance of GO and RGO films was determined to be 22.9 × 106Ω/sq and 4.95 × 106Ω/sq respectively.

Work Function Tuning of Reduced Graphene Oxide Thin Films

Graphene oxide (GO) has shown great potential as a component in various devices due to its excellent solution processability and two-dimensional structure. However, the oxygenated form of graphene has a moderate charge-transport capability. The latter parameter may be enhanced through controlled deoxygenation of GO with subsequent tuning of its work function (WF). Various reduction approaches were employed to investigate the effect of the oxygen content on the work function of GO derivatives as thin films on an indium tin oxide substrate. Such films were reduced by stepwise thermal annealing in ultrahigh vacuum up to 650 °C, by chemical reduction with hydrazine, or by a combination of chemical and thermal reduction processes. The effect of the GO film thickness and the flake size on the WF was also investigated. UV photoelectron spectroscopy and X-ray photoelectron spectroscopy were used to correlate the WF of GO derivatives with their oxygen content. The results showed that the WF is strongly dependent o...

Low temperature synthesis of RGO-Au nanocomposite with apparently reduced time and its application as a chemical sensor

For the first time, a reduced graphene oxide (RGO)-Au nanocomposites (NC) is synthesized at a low temperature by refluxing without a surfactant. Transmission electron microscopy suggests that Au nanoparticles (NPs) 10–20nm in size are dispersed on the RGO thin film. X-ray diffraction study, UV–vis spectrometry, and Raman spectroscopy confirmed the reduction of graphene oxide (GO). This RGO-Au NC shows an excellent ability to detect Cr(VI) by electrochemical sensing, with good responses to both current and voltage. A glassy carbon electrode modified with the NC shows a significant voltammetric reduction peak. The voltammetric detection ability is highly dependent on the pH of the electrolyte. The large surface area of RGO's porous structure and the electroactive Au NPs both allow free exchange of reaction intermediates, resulting in significantly enhanced Cr(VI) reduction activity. The RGO-Au electrode shows a good linear response in a range of Cr(VI) concentrations from 10 to 800μM and a high sensitivity of 0.0146μAμM−1 with a 2.10μM detection limit.

Reduction Kinetics of Thermally Reduced Graphene Oxide Thin Films

We report an experimentalstudy of thermal reduction of graphene oxide (GO) under nitrogen flow.Ultrathin films of GO were prepared on quartz glass substrates by spin-coatingfrom 3 mg/ml aqueous solutions of GO. These films were annealed at 50 °C under vacuum overnight before thermal reduction.The films were exposed to temperatures of 100 °C, 150 °C, 200 °C, 300 °C, 400 °C, 500 °C and 800 °C under nitrogen flowing. We used UV-Vis absorption spectroscopy tomonitor the change of absorption spectra caused by thermal reduction. We observed a significant change ofabsorption spectra due to formation of reduced graphene oxide (RGO). We found that thermal reduction startedalready at 100 °C, but proceeded significantly faster at heating temperatures higherthan 200 °C.

Large-area reduced graphene oxide thin film with excellent thermal conductivity and electromagnetic interference shielding effectiveness

In this work, we fabricated reduced large-area graphene oxide (rLGO) with maximum surface area of 1592μm2 through a cost-effective chemical reduction process at low temperature. The product revealed large electrical conductivity of 243±12Scm−1 and thermal conductivity of 1390±65Wm−1K−1, values much superior to those of a conventional reduced small-area graphene oxide (with electrical conductivity of 152±7.5Scm−1 and thermal conductivity of 900±45Wm−1K−1). The rLGO thin film also exhibited not only excellent stiffness and flexibility with Young’s modulus of 6.3GPa and tensile strength of 77.7MPa, but also an efficient electromagnetic interference (EMI) shielding effectiveness of ∼20dB at 1GHz. The excellent performance of rLGO is attributed to the fact that the larger area LGO sheets include much fewer defects that are mostly caused by the damage of graphene sp2 structure around edge boundaries, resulting in large electrical conductivity. The manufacturing process of rLGO is an economical and facile approach for the large scale production of highly thermally conducting graphene thin films with efficient EMI shielding properties, greatly desirable for future portable electronic devices.

Multifunctional Two-Dimensional Reduced Graphene Oxide Thin Film for Gas Sensing and Antibacterial Applications

Multifunctional luminescent chemically reduced graphene oxide (rGO) thin film was fabricated by hydrazine hydrate vapor reduction of graphene oxide (GO) thin film on quartz substrate. Detailed morphogenesis studies have been carried out through various microscopic techniques to explore the surface morphology, uniformity, thickness of the film. The photoluminescence spectroscopy analysis confirms the film quality and extended graphitization of the rGO thin film. Moreover, the electrical and gas sensing properties of the rGO thin film are extensively monitored. It is observed that rGO exhibits good electrical conductivity similar to 104 S m(-1) (1.04 S cm(-1)) at room temperature and good gas sensing properties for variable concentrations of Cl-2 and NO2 gases. The percentage response for NO2 and Cl-2 gases at a fixed 50 ppm concentration are found 27% and 54%, respectively. Additionally, as-synthesized GO and rGO thin films show excellent bacterial toxicity for both Gram +ve (B. cereus) and Gram -ve (E. coli) models of bacteria, which implies that GO and rGO can be used as effective antibacterial coatings. The colligative fast gas sensing response and good antibacterial property of rGO thin film suggest that this material could be an ultimate choice for next generation smart, portable two dimensional (2D) gas sensors as well as in various biomedical applications.

Boron-Doped Reduced Graphene Oxide (B-RGO) and Its Application to L-Cysteine Sensing

In this study, we prepare a boron-doped reduced graphene oxide thin film on the screen printed carbon electrode (SPCE) for the electrochemical sensing of L-cysteine (L-cys). L-cysteine, a sulfur containing amino acid, plays a crucial role in regulating the biological activity of certain proteins, peptides and enzymes. Low level of L-cys is related to myriad of diseases, including slow growth in children, depigmentation of hair, lethargy, liver damage, loss of muscle and fat, skin lesions, and weakness.[1] However, current L-cys sensing techniques require intensive pretreatments[2 , 3]as well as purifications. As a result, developing a relatively easy, selective and sensitive L-cys biosensor in physiological study and clinical diagnosis is highly demanded. In the electron energy loss spectroscopy (Fig. 1 (a)), the peaks of π*(~190 eV) and σ*(~200 eV) anti-bonding orbitals on the K-edge of boron (B) revealed the hybridized sp2-bonded B atoms in the graphene nanosheet. These two peaks indicates that the substitution doping is the dominate type of doping. The STEM-EELS mapping of B-RGO (Fig. 1 (b)) confirms that dopant B (green) is uniformly distributed on the reduced graphene oxide. Electrochemical characterization shows different performances among bare SPCE, RGO/SPCE and B-RGO/SPCE in Fig. 1(c). The results show that with the help of boron, B-RGO (B=9.6%) possesses good electrocatalytic ability to L-cys by decreasing the overpotential and increasing the current density of the irreversible oxidation reaction. Fig. 1(d) shows a plot of the current density of the B-RGO/SPCE as a function time at various L-cys concentrations. The current density increases linearly with the increased L-cys concentration, as shown in the inset. The sensitivity of the B-RGO/SPCE is 20.7 mAcm−2M−1. The limit of detection (LOD), based on a signal-to-noise ratio of 3, for the B-RGO/SPCE is 0.07 μM. [1] S. Shahrokhian, Anal. Chem. 73 (2001), 5972 [2] G. Chwatko, E. Bald, Talanta,52 (2000) 509. [3] K. Arlt, S. Brandt, J. Kehr, Journal of Chromatography A, 926 (2001) 319. Figure 1