Graphene Oxide Thin Films Research Articles

Effect of potassium permanganate on morphological, structural and electro-optical properties of graphene oxide thin films

This work investigated the effect of Potassium Permanganate (KMnO4) on graphene oxide (GO) properties, especially on electrical properties. The GO thin films were deposited on a glass substrate using drop casting technique and were analysed by using various type of spectroscopy (e.g. Scanning Electron Microscopy (SEM), Ultra- Violet Visible (UV–VIS), Fourier Transform Infrared (FTIR), X-Ray Diffraction (XRD), optical band gap, Raman Spectroscopy). Furthermore, the electrical experiments were carried out by using current–voltage (I-V) characteristic. The GO thin film with 4.5 g of KMnO4 resulted in higher conductivity which is 3.11 × 10−4 S/cm while GO with 2.5 g and 3.5 g of KMnO4 achieve 2.47 × 10−9 S/cm and 1.07 × 10−7 S/cm, respectively. This further affects the morphological (SEM), optical (band gap, UV–Vis, FTIR, and Raman), and crystalline structural (XRD) properties of the GO thin films. The morphological, elemental, optical, and structural data confirmed that the properties of GO is affected by different amount of KMnO4 oxidizing agent, which revealed that GO can potentially be implemented for electrical and electronic devices.

Reduced Graphene Oxide Thin Film with Strong Optical Nonlinearity

Herein, a simple, low‐cost, and scalable process is developed to prepare the reduced graphene oxide (rGO) thin films (TFs) with strong optical nonlinearity. To do so, a chemical reduction method (using inorganic agent hydroiodic acid) and drop‐casting technique are used. Optical nonlinearity of the prepared thin rGO film is measured by the Z‐scan technique at low light intensity (continuous‐wave wavelength of 632 nm). The result of optical nonlinearity responses is illustrated by a remarkable nonlinear refraction index (n2 ≈ 10−4 cm2 W−1) as well as a considerable nonlinear absorption coefficient (β = 1.43 × 10−8 cm2 W–1) compared with similar reported results. Moreover, experimental results show that the prepared film enjoys a positive nonlinear refractive index with strong optical nonlinearity. Results also confirm that the changes made in optical absorption of rGO TFs are due to state filling effects and the optical nonlinearity proportional to the carriers’ density is in fact due to thermal effects of SiO2 substrate.

Graphene Oxide for Integrated Photonics and Flat Optics.

With superior optical properties, high flexibility in engineering its material properties, and strong capability for large-scale on-chip integration, graphene oxide (GO) is an attractive solution for on-chip integration of 2D materials to implement functional integrated photonic devices capable of new features. Over the past decade, integrated GO photonics, representing an innovative merging of integrated photonic devices and thin GO films, has experienced significant development, leading to a surge in many applications covering almost every field of optical sciences such as photovoltaics, optical imaging, sensing, nonlinear optics, and light emitting. This paper reviews the recent advances in this emerging field, providing an overview of the optical properties of GO as well as methods for the on-chip integration of GO. The main achievements made in GO hybrid integrated photonic devices for diverse applications are summarized. The open challenges as well as the potential for future improvement are also discussed.

Synthesis of Sodium Alginate Graphene Oxide Thin Film for Adsorption Application

This paper essentially describes the synthesis of sodium alginate graphene oxide silver (SA-(GOAg)) composite thin film for adsorption of methylene blue. The composite thin film is synthesized using simple solvent casting method by varying the amount of GOAg (20 ml, 40 ml, 60ml, 80ml and 100 ml) into SA solution. The thin film then characterized by using UV-Visible absorption spectroscopy (UV-Vis), Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) analysis. The degradation of methylene blue was observed by using UV-Vis and recorded in every 5 minutes for one hour. The results reveal that the combination of SA and 100 ml GOAg shows the highest adsorption rate in one hour compared to other value of SA-GOAg thin films. The SA-GOAg thin film is believed to have a huge potential in adsorption application such as water treatment.

Porous Graphene Oxide Films Prepared via the Breath-Figure Method: A Simple Strategy for Switching Access of Redox Species to an Electrode Surface.

Porous materials can be modified with physical barriers to control the transport of ions and molecules through channels via an external stimulus. Such capability has brought attention toward drug delivery, separation methods, nanofluidics, and point-of-care devices. In this context, gated platforms on which access to an electrode surface of species in solution can be reversibly hindered/unhindered on demand are appearing as promising materials for sensing and microfluidic switches. The preparation of a reversible gated device usually requires mesoporous materials, nanopores, or molecularly imprinted polymers. Here, we show how the breath-figure method assembly of graphene oxide can be used as a simple strategy to produce gated electrochemical materials. This was achieved by forming an organized porous thin film of graphene oxide onto an ITO surface. Localized brushes of thermoresponsive poly(N-isopropylacrylamide) were then grown to specific sites of the porous film by in situ reversible addition-fragmentation chain-transfer polymerization. The gating mechanism relies on the polymeric chains to expand and contract depending on the thermal stimulus, thus modulating the accessibility of redox species inside the pores. The resulting platform was shown to reversibly hinder or facilitate the electron transfer of solution redox species by modulating temperature from the room value to 45 °C or vice versa.

Towards In-Situ Environmental Monitoring: On-Chip Sample Preparation and Detection of Lead in Sediment Samples Using Graphene Oxide Sensor

This manuscript reports, a novel, integrated on-chip sample-to-answer platform capable of detecting lead ions (Pb <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+2</sup> ) directly in sediment samples. As sediment is one of the main sources of hazardous heavy metals in aquatic ecosystems, rapid and real-time detection of heavy metals in sediment is crucial in the field of environmental monitoring. Electrochemical sensors can provide rapid detection capability, but in-situ measurement of heavy metals with such sensors has been limited by complicated pretreatment steps. To overcome this drawback, an integrated system was developed consisting of a porous matrix for purification and extraction of Pb <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+2</sup> onto a graphene oxide thin film that serves as an active sensing material. The integrated sensor with a 3D porous matrix was used as an in-situ platform to detect lead directly in complex sediment samples. The proposed electrochemical sensor has a detection limit of 4 ppb and a linear working range. The ability to directly detect lead in sediment samples with minimal pretreatment agents and time makes this system a promising solution for on-site monitoring of heavy metals in environmental samples. Although the current study focused on lead for platform validation, the proposed sensing platform can be further developed for the detection of a wide panel of toxic metals.

Fabrication of layer-by-layer graphene oxide thin film on copper substrate by electrophoretic deposition

In this paper, we investigate the fabrication of graphene oxide (GO) films on copper substrates by means of an electrophoretic technique, with the aim of realizing conductive thin films that could be applied as reliable electrical contacts for use in various applications. Uniform films were fabricated, and the film thickness measured using atomic force microscopy. The graphene oxide film thickness is estimated to range from a few manometers to several tens of manometers, depending on the deposition time. Cross-sectional transmission electron microscopy images indicate that the films possess a multi-layered structure, and that the distance between layers is approximately 0.5 nm. Furthermore, the electrical contact resistance of the films was measured, using conductive probe atomic force microscopy. The prepared GO films exhibit electrical conductivity due to their layered structure, which affects their electrical properties.

Transfer of printed electronic structures using graphene oxide and gelatin enables reversible and biocompatible interface with living cells

We present a low-cost, easy-to-implement platform for printing materials and interfacing them with eukaryotic cells. We show that thermal or chemical reduction of a graphene oxide thin film allows water-assisted delamination of the film from glass or plastic. The chemical and physical properties and permeability of the resulting film are dependent on the method of reduction and deposition of the graphene oxide, with thermal reduction removing more oxidized carbon functionality than chemical reduction. We also developed a method to attach the films onto cell surfaces using a thin layer of gelatin as an adhesive. In general, the films are highly impermeable to nutrients and we observed a significant amount of cell death when gelatin was not used; gelatin enables diffusion of nutrients for sustained cell viability. The combination of nanoscale membranes with a low melting point biopolymer allows us to reversibly interface cells with cargo transferred by graphene oxide while maintaining cell viability. To demonstrate delivery of electronic structures, we modified a commercial off-the-shelf printer to print a silver-based ink directly onto the reduced graphene oxide films which we then transferred to the surface of the cells.

Graphene Oxide Thin Films: Synthesis and Optical Characterization

AbstractThe oxidized derivative of graphene named Graphene oxide (GO) are attractive materials as optoelectronic devices due to their optical response in the mid‐infrared wavelength spectral range; however, very large‐scaled synthesis methods and optical characterization are required. Here, GO thin films are fabricated on quartz by implementing simple two‐step pyrolysis processes by using renewable bamboo as source material. The effect of carbonization temperature (TCA) on the compositional, vibrational, and optoelectronic properties of the system are investigated. It was found that as TCA increases, graphite conversion rises, oxygen coverage reduces from 17 % to 4 %, and the band‐gap energy monotonically decreases from 0.30 to 0.11 eV. Theoretical predictions of the energy band‐gap variations with the oxide coverage obtained via density functional theory (DFT) computational simulations agree well with the experimental results, providing evidence of oxygen‐mediated charge‐transport scattering. Interestingly, in the optical response, increased TCA results in a blue‐shift of the absorption and the absorbance spectrum can be correlated with the large size distribution of the graphitic nano‐crystals of the samples. These results suggest that graphene oxide‐bamboo pyroligneous acid (GO) thin films exhibit optoelectronic response useful in developing photodetectors and emitter devices in the mid‐infrared (MIR) spectral range.

GO film on flexible substrate: An approach to wearable colorimetric humidity sensor

Graphene and graphene oxides have outstanding electrical and optical properties, making it particularly interesting in the field of gas sensing. In this study, colorimetric humidity sensor based on graphene oxide (GO) thin film on different substrates was fabricated by using dip coating technique. The fabrication conditions that influence the humidity response were systematically investigated and optimized. Our results indicated that GO thin film on metallized polyethylene terephthalate (mPET) film displayed poor resolution and sensitivity if it was fabricated from aqueous dispersion. However, both spectra resolution and reflectance color of GO film on mPET are enhanced, if it was fabricated from acetone dispersion. It was attributed to the wetting property of solvent that help to form uniform d-spacing of GO sheet assemblies as revealed from XRD analysis. Bending test of the formed GO film on mPET showed an extreme spectra stability upon 10,000 cycles of bending, suggesting that the devices are quite suitable for flexible device applications in both personal physiological condition monitoring and environment condition change detection.

Multilayer Engineering of Polyaniline and Reduced Graphene Oxide Thin Films on a Plastic Substrate for Flexible Optoelectronic Applications Using NIR

This article describes the photoconductive properties of a multilayer uniform ultrathin film comprising alternating polyaniline (PANi) and reduced graphene oxide (RGO) layers, fabricated on a poly(ethylene terephthalate) (PET) sheet. The fabrication of the two electron-rich layers on the PET substrate is successfully completed using a layer-by-layer (LBL) deposition technique under mild conditions and HI/H2O vapor treatment at 100°C. The photocurrent under illumination of >300 nm light exhibits 80 µA compared with that of obtained in the dark. However, it decreases to 75 µA under >460 nm light illumination and further increases to 80 µA under >600 nm light illumination (0.64 mW) at an applied voltage of 1.0 V. The PET sheets coated with (PANi/RGO)20 films (d = 46.3 nm) exhibits a photoresponsivity of 125 mA/W at an illunination intensity of 0.64 mW using red light (> 600 nm). The extraordinary optoelectronic characteristics of the (PANi/RGO) films are ascribed to the charge transfer complex formation of the two PANi and RGO layer components and also to the structural uniformity of the LBL-assembled optoelectronic thin films, which tended to favor the rapid interfacial charge transfer to the electrodes.

Chemical-free transfer of patterned reduced graphene oxide thin films for large area flexible electronics and nanoelectromechanical systems

In this paper, a wet-dry hybrid technique to transfer patterned reduced graphene oxide (rGO) thin film to arbitrary substrates at predetermined locations without using any chemicals is reported. The transfer process involves water-assisted delamination of rGO, followed by dry transfer to an acceptor substrate using viscoelastic stamp. Patterned reduced graphene oxide films are transferred to silicon dioxide (SiO2/Si) substrate to begin with. Subsequently, the method is deployed to transfer rGO to different polymer substrates such as poly(methyl methacrylate) (PMMA), and crosslinked poly(4-vinylphenol) (c-PVP), which are commonly used as gate dielectric in flexible electronic applications. The credibility of the transfer process with precise spatial positioning on the target substrate leads to fabrication of freely suspended reduced graphene oxide membrane towards nanoelectromechanical systems (NEMS) based devices such as nanomechanical drum resonators.

Spatio-temporal Analysis of the Electric Field-Induced Solid-State Reduction Dynamics of Graphene Oxide Thin Films for Controlled Band-Gap Modulation

An electric field-induced reduction mechanism studied for tuning the band gap of graphene oxide thin films in a two-electrode configuration on a SiO2/Si substrate is presented. During the reduction...

Comparison of low cost lasers for graphene oxide thin films reduction

In this work we made reduction of graphene oxide films with different low-cost lasers (near IR (1060 nm) and blue (445 nm) to investigate possibility of such films usage for flexible electronic and nanoelectronic applications. We successfully showed possibility of graphene oxide reduction with both types of laser but blue laser showed better uniformity of reduced graphene oxide film parameters including film morphology, resistance and Raman intensity ratios. We showed that reduction with near IR laser spills out into large nonuniformity of resistance with relatively high values. Thus the usability of commercially available laser facility for graphene oxide modification without adjusting control settings (on hardware and software levels) is poor. On the other hand, relatively laboratory device based on low-power blue laser showed much better usability an it’s perspective to future market of low-cost modification facilities for thin carbon-based films.

Graphene oxide thin film structural dielectric capacitors for aviation static electricity harvesting and storage

In this paper, we demonstrate the feasibility of using carbon fibre reinforced polymer (CFRP) laminates for the dual functions on aircraft as high load-bearing structural materials as well as for the harvesting and storage of static electricity during flight which can be used to power navigation lights and other electrical systems. CFRP laminate was fabricated into a structural dielectric capacitor (SDC) composite by sandwiching graphene oxide (GO) film between two electrically-conductive carbon fabric layers. To meet the high requirements of aviation applications, the mechanical properties of the GO-based SDC composite were increased using a polymer cross-linking agent in the GO film. This work opens a new concept and possibility of converting the safety threatening static charges into useful electrical energy, which not only reduces the safety hazard, but also improves the energy efficiency of aircraft without compromising the mechanical performance.

Variable Angle Spectroscopic Ellipsometry Characterization of Reduced Graphene Oxide Stabilized with Poly(Sodium 4-Styrenesulfonate)

Lately, the optical properties of Graphene Oxide (GO) and Reduced Graphene Oxide (RGO) films have been studied in the ultraviolet and visible spectral range. However, the accurate optical properties in the extended near-infrared and mid-infrared range have not been published yet. In this work, we report a Variable Angle Spectroscopic Ellipsometry (VASE) characterization of GO thin films dip-coated on SiO2/Si substrates and thermally reduced GO films in the 0.38–4.1 eV photon energy range. Moreover, the optical properties of RGO stabilized with poly(sodium 4-styrenesulfonate) (PSS) films dip-coated on SiO2/Si substrates are studied in the same range for the first time. The Lorentz optical models fit well with the experimental data. In addition, the morphological properties of the samples were investigated by Scanning Electron Microscopy (SEM) analysis.

Green Solid-State Chemical Reduction of Graphene Oxide Supported on a Paper Substrate

The reduction of graphene oxide (GO) thin films deposited on substrates is crucial to achieve a technologically useful supported graphene material. However, the well-known thermal reduction process cannot be used with thermally unstable substrates (e.g., plastics and paper), in addition photo-reduction methods are expensive and only capable of reducing the external surface. Therefore, solid-state chemical reduction techniques could become a convenient approach for the full thickness reduction of the GO layers supported on thermally unstable substrates. Here, a novel experimental procedure for quantitative reduction of GO films on paper by a green and low-cost chemical reductant (L-ascorbic acid, L-aa) is proposed. The possibility to have an effective mass transport of the reductant inside the swelled GO solid (gel-phase) deposit was ensured by spraying a reductant solution on the GO film and allowing it to reflux in a closed microenvironment at 50 °C. The GO conversion degree to reduced graphene oxide (r-GO) was evaluated by Fourier transform infrared spectroscopy (FT-IR) in attenuated total reflectance (ATR) mode and X-ray Diffraction (XRD). In addition, morphology and wettability of GO deposits, before and after reduction, were confirmed by digital USB microscopy, scanning electron microscopy (SEM), and contact angle measurements. According to these structural characterizations, the proposed method allows a bulky reduction of the coating but leaves to a GO layer at the interface, that is essential for a good coating-substrate adhesion and this special characteristic is useful for industrial exploitation of the material.

Transparent and flexible humidity sensor based on graphene oxide thin films prepared by electrostatic spray deposition technique

In this work, transparent and flexible humidity sensors based on graphene oxide film were prepared using the electrostatic spray deposition technique. Graphene oxide (GO) powder was synthesized using the modified Hummer’s method, which was used as a precursor for thin-film deposition. The properties of GO films were characterized by X-ray diffraction, field-emission scanning electron microscope, Raman spectroscopy, Fourier transform infrared spectroscopy, and UV–Vis spectrophotometer. The effect of substrate temperature on the sensor properties was observed. The impedance of the device exhibited a lower value when increasing the relative humidity level. In addition, the device showed high sensitivity of more than 1117.3, fast response with 5 s, more than 60% optical transparency, and flexible property more than 2000 cycles. In addition, the equivalent circuit models of the devices were evaluated from complex impedance measurements used to explain the sensing mechanisms of the device.

Electrochemically deposited graphene oxide thin film supercapacitors: Comparing liquid and solid electrolytes

In the present work, graphene oxide (GO) thin films were prepared on ITO substrates by electrochemical deposition for different voltages and deposition times and were further electrochemically reduced by cyclic voltammetry (CV). Reduced GO films (rGO) were used in the manufacturing of supercapacitors with solid-state electrolyte based on a freeze-thawed PVA-Na2SO4 hydrogel. GO and rGO films were tested using SEM, XRD, RAMAN and XPS techniques for comparative reasons. The specific capacitance of the electrodes and supercapacitors were estimated by electrochemical methods. XRD analysis revealed increase of the rGO interlayer spacing after multiple CV cycles that was assigned to incorporation of the electrolytic agents such as sodium ions of the electrolyte. Raman spectra showed that the ID/IG ratio associated with the graphene matrix defects remained fairly constant even after several CV cycles, meaning that no new defects were added. It was the XPS analysis that confirmed the reduction of GO to rGO as well as the presence of sodium in the rGO films. The optimum value of the electrode capacitance of the constructed model supercapacitor with thin rGO films and PVA-20%Na2SO4 electrolyte was 8.55 mF/cm2 that approaches the electrode capacitance value of 10.67 mF/cm2 measured with liquid Na2SO4 electrolyte.

Optical properties of graphene oxide thin film reduced by low-cost diode laser

A non-toxic, fast, low-cost, single step and highly efficient reduction method is proposed in this research for the development of high-quality multilayer graphene film using laser diode. Graphene oxide film is irradiated with a diode laser (808 nm, 6 W) for different exposure times (1, 1.5, 2, 2.5, and 3 min.) to reduce it. Surface damage was observed on the graphene oxide (GO) film for exposure time greater than 3 min and at power 6 W. Different measurement techniques (Raman spectroscopy, Uv–visible absorption, photoluminescence and FTIR) are used to study the optical properties of rGO films. After laser irradiation, the Raman spectra of rGO films showed peaks for the D, G, and 2D bands centered at 1335, 1581, and 2710 cm−1, respectively. A small increase in the (ID/IG) ratio was observed and showed that greater reduction occurred after the graphene oxide film exposure time of 3 min. The as-prepared film of graphene oxide that showed absorption peak at 235 nm was red-shifted to 270 nm after 3 min of laser diode irradiation for reduction. The PL measurements were performed, where the sample was excited by Ar-ion laser (488 nm) and the PL signal was amplified using lock in techniques. The photoluminescence emission spectrum was measured at different positions on the graphene oxide film reduced for 3 min to show the effect of the energy spatial distribution of the laser diode beam on the rGO film. The maximum PL peaks gradually blue shifted and the peak intensities decreased as the measurements go toward the center of the reduced film. The FT-IR spectrum revealed that there are no hydroxyl, carboxyl, and epoxy groups and new peaks were found assigned to functional groups such as CH2, C–H by reducing the graphene oxide with laser diode for 3 min.