Graphene Oxide Ink Research Articles

Formation of Etch Pits on Germanium Surfaces Loaded with Reduced Graphene Oxide in Water

Metal-assisted chemical etching is a simple and low-cost etching process for semiconductor surfaces. There have been many reports on Si surfaces loaded with noble metals in HF solutions with oxidants such as H2O2.[1,2] Noble metals catalyze the reduction of the oxidant (H2O2), resulting in enhanced oxidation of the Si surface around the loaded metals. Because the oxide is immediately dissolved in the HF solution, selective etching of the Si surface occurs. This etching mode is used to form a variety of three-dimensional nanostructures not only on Si but also on other semiconductor surfaces.We have applied this etching mode to the machining of a Ge surface in O2-containing water. So far, we revealed fundamental etching properties such as pore formation and patterning in this system with noble metals (Pt and Ag),[3] and recently, we demonstrated Pt-assisted chemical flattening.[4,5] In this scheme, a catalyst plate comprising a soft elastomer coated with a sputtered Pt film, and a Ge wafer were brought into contact and rotated independently in the same plane in water. The processed Ge surface includes few protrusions with a lateral size on the order of 10 nm, which is probably caused by the selective removal of protrusions from the Ge surface by the catalytic activity of Pt.However, a problem in this system is the use of noble metals as catalysts. After metal-assisted chemical etching, residual metals on a semiconductor surface have to be removed. For example, aqua regia is effective for dissolving Pt. However, such a strong oxidative solution causes severe damage to a Ge surface. To solve this issue, graphene can be used as a substitute for noble metals to achieve catalyst-assisted chemical etching.[6] In this talk, we discuss the etching properties of a p-type Ge(100) surface loaded with reduced graphene oxide (RGO) in O2-containing water. In order to obtain the RGO, a graphene oxide (GO) ink, used as a starting material, was either heated at 900°C in Ar ambient for 10 min or immersed in a solution comprising the GO ink, hydrazine and N,N-dimethylformamide.[7] Then we deposited the obtained RGO on a Ge surface in the form of aggregated particles or dispersed flakes. After immersing the samples into water exposed to air, we found that the Ge surface was preferentially etched around the loaded RGO. The etching rate as well as the etched morphology was revealed by atomic force microscopy observations, and the etching mechanism is proposed. These findings show the possibility of using RGO as a catalyst to enhance the chemical etching of a Ge surface in water. [1] Z. Huang, N. Geyer, P. Werner, J. de Boor and J. Gösele, Adv. Mat., vol. 23, no. 2, pp. 285-308 (2011).[2] X. Li, Current Opinion in Solid State and Materials Science, vol. 16, pp. 71-81 (2012).[3] T. Kawase, A. Mura, K. Nishitani, Y. Kawai, K. Kawai, J. Uchikoshi, M. Morita and K. Arima, J. Appl. Phys., vol. 111, no. 12, pp. 126102 1-3 (2012).[4] T. Kawase, Y. Saito, A. Mura, T. Okamoto, K. Kawai, Y. Sano, M. Morita, K. Yamauchi, and K. Arima, ChemElectroChem, vol. 2, no. 11, pp. 1656-1659 (2015).[5] T. Kawase, A. Mura, Y. Saito, T. Okamoto, K. Kawai, Y. Sano, K. Yamauchi, M. Morita, and K. Arima, ECS Transactions, vol. 75, no. 1, pp. 107-112 (2016).[6] J. Kim, D.H. Lee, J.H. Kim and S.-H. Choi, ACS Appl. Mat. and Inter., vol. 7, no. 43, pp. 24242-24246 (2015).[7] S. Park, J. An, I. Jung, R.D. Piner, S.J. An, X. Li, A. Velamakanni and R.S. Ruoff, Nano Lett., vol. 9, no. 4, pp. 1593-1597 (2009).

Role of reduced graphene oxide as nano-electrocatalyst in carbon felt electrode of vanadium redox flow battery

Carbon-based electrodes are usually used in vanadium redox flow batteries and electrochemical performance of these electrodes can be modified by electrocatalysts. In the current study, reduced graphene oxide inks with different concentrations were used to modify a carbon felt electrode. It was observed that CF which was modified in 2 mg/ml ink (CF-G-2) had the optimum combination of electrochemical properties, because no significant peak current improvement was observed at higher graphene contents and it also had the minimum value of ΔEp. The anodic and cathodic peak currents for positive redox couple reaction in CF-G-2 reached to 45.3 and 21.1 mA respectively, in comparison with 14.2 and 4.7 mA values for bare felt. Linear diffusion coefficient was also enhanced more than two times with the incorporation of graphene. Nyquist plots of CF-G in different electrolytes (VOSO4/V2O5 and VOSO4) showed different shapes and equivalent circuit data indicated much lower charge transfer resistance for modified carbon felts with graphene. The diffusion process was remarkably facilitated with the incorporation of reduced graphene oxide and graphene had desirable influence on the electrolyte absorption of carbon felt. Finally, scanning electron micrographs of electrodes demonstrated loaded graphene nanosheets on the surface of carbon felt fibers.

Highly selective organic transistor biosensor with inkjet printed graphene oxide support system.

Most of the reported field effect transistors (FETs) fall short of a general method to uniquely specify and detect a target analyte. For this reason, we propose a pentacene-based FET with a graphene oxide support system (GOSS), composed of functionalized graphene oxide (GO) ink. The GOSS with a specific moiety group to capture the biomaterial of interest was inkjet printed on the pentacene FET. It provided modular receptor sites on the surface of pentacene, without alteration of the device. To evaluate the performance of a GOSS-pentacene FET biosensor, we detected the artificial DNA and circulating tumor cells as a proof-of-concept. The mobility of the FET dramatically changed upon capturing the target biomolecule on the GOSS. The FET exhibited high selectivity with 0.1 pmoles of the target DNA and a few cancer cells per detection volume. This study suggests a valuable sensor for medical diagnosis that can be mass produced effortlessly at low-cost.

Rapid and efficient intense pulsed light reduction of graphene oxide inks for flexible printed electronics

Inkjet-printed GO patterns without additives were reduced by IPL treatment and achieved resistance as low as 760.4 Ω and acceptable flexibility.

Controlling “coffee staining” effect of inkjet-printed droplets from graphene oxide inks

Controlling “coffee staining” effect of inkjet-printed droplets from graphene oxide inks

Controlling “coffee staining” effect of inkjet-printed droplets from graphene oxide inks

Here, we investigate the formation of inkjet-printed graphene oxide (GO) droplets with different flake size. It is shown that the size of GO flakes has strong influence to the drop morphology and can be used to control the CRE. The CRE was eliminated gradually with increased mean GO flake size (from 0.68 to ~ 36 µm). The result suggests a new strategy to control the CRE, and our observation about the morphology of inkjetprinted droplets with different flake size will be very effective to print uniform two-dimensional materials based patterns.

Graphene-oxide films printed on rigid and flexible substrates for a wide spectrum of applications

Structures of films produced from a water-based graphene oxide ink by 2D printing on various substrates, including those of the flexible type, are compared. It was shown that the deposition of a thin polyvinyl alcohol film making substrates hydrophilic leads not only to more uniform application of the ink, but also to a denser film structure with a shallower surface profile. The processing of a graphene-oxide suspension in a blender additionally reduces the particle size of the suspension, which results in improvement of the structure and, on the whole, a shallower surface profile of the film. Comparison of the electrical properties of films on silicon with various coatings hydrophilizing the substrates demonstrated that the properties of the structures strongly depend on the type of coatings, which can change the conductivity type of the silicon substrate and lead to doping of the graphene-oxide film. At graphene-oxide film thicknesses not exceeding 25 nm, noticeable currents (>1 µA) appear in the films at voltages higher than 1–1.5V. The graphene-oxide layers are promising for the fabrication of protective and insulating coatings and sensors and, in the case of reduction, for the deposition of transparent electrodes.

Writable electrochemical energy source based on graphene oxide.

Graphene oxide (GO) was mainly used as raw material for various types of reduced graphene oxide (rGO) as a cost effective method to make graphene like materials. However, applications of its own unique properties such as extraordinary proton conductivity and super-permeability to water were overlooked. Here GO based battery-like planar energy source was demonstrated on arbitrary insulating substrate (e.g. polymer sheet/paper) by coating PEDOT, GO ink and rGO on Ag charge collectors. Energy from such GO battery depends on its length and one unit cell with length of 0.5 cm can generate energy capacity of 30 Ah/L with voltage up to 0.7 V when room temperature ionic liquid (RTIL) is added. With power density up to 0.4 W/cm3 and energy density of 4 Wh/L, GO battery was demonstrated to drive an electrochromic device. This work is the first attempt to generate decent energy using the fast transported water molecules inside GO. It provides very safe energy source that enables new applications otherwise traditional battery technology can not make including building a foldable energy source on paper and platform for futuristic wearable electronics. A disposable energy source made of GO was also written on a plastic glove to demonstrate wearability.

Graphene Oxide for Ink-Jet Printing Technology

In order to acquire a suitable ink for ink-jet printing technology, a graphene oxide ink was explored based on the GO aqueous dispersion. The GO dispersion was characterized by field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD). The average particle diameter and zeta potential of the GO dispersion was determined by zeta potential & particle size analyzer. The GO ink is composed of 1,2-propanediol, diethylene glycol monobutyl ether, glycerol, polyvinyl pyrrolidone (PVP) and GO dispersion. The surface tension and viscosity of the GO ink was tested by surface tension meter and rheometer. The GO ink was inkjet printed on polyethylene terephthalate (PET) substrate. The optimal inkjet printing parameters were obtained and the printing quality was characterized by confocal laser scanning microscopy. The results show that the GO ink is suitable for inkjet printing technology and the morphology of the GO film with one printing pass has good uniformity.

Graphene oxide overprints for flexible and transparent electronics

The overprints produced in inkjet technology with graphene oxide dispersion are presented. The graphene oxide ink is developed to be fully compatible with standard industrial printers and polyester substrates. Post-printing chemical reduction procedure is proposed, which leads to the restoration of electrical conductivity without destroying the substrate. The presented results show the outstanding potential of graphene oxide for rapid and cost efficient commercial implementation to production of flexible electronics. Properties of graphene-based electrodes are characterized on the macro- and nano-scale. The observed nano-scale inhomogeneity of overprints' conductivity is found to be essential in the field of future industrial applications.

Efficient anti-corrosive coating of cold-rolled steel in a seawater environment using an oil-based graphene oxide ink.

We report the production of an efficient anti-corrosive coating of cold-rolled (CR) steel in a seawater environment (∼3.5 wt% NaCl aqueous solution) using an oil-based graphene oxide ink. The graphene oxide was produced by heating Aeschynomene aspera plant as a carbon source at 1600 °C in an argon atmosphere. The ink was prepared by cup-milling the mixture of graphene oxide and sunflower oil for 10 min. The coating of ink on the CR steel was made using the dip-coating method, followed by curing at 350 °C for 10 min in air atmosphere. The results of the potentiodynamic polarization show that the corrosion rate of bare CR steel decreases nearly 10,000-fold by the ink coating. Furthermore, the salt spray test results show that the red rusting in the ink-coated CR steel is initiated after 100 h, in contrast to 24 h and 6 h in the case of oil-coated and bare CR steel, respectively. The significant decrease in the corrosion rate by the ink-coating is discussed based on the impermeability of graphene oxide to the corrosive ions.

Flexible, transparent, and conductive defrosting glass

Flexible and transparent electronics play a predominant role in the next-generation electrical devices. In this study, a printable aqueous graphene oxide (GO) ink that enables direct deposition of GO onto flexible glass substrates is demonstrated and its application on fabricating a transparent, conductive, and flexible glass device by solution coating process is investigated as well. A uniform GO layer is formed on the flexible glass through Meyer-rod coating followed by an annealing process to reduce GO into graphene. The obtained thermally reduced graphene oxide (RGO) flexible glass has a transmittance of over 40%, as well as a sheet resistance of ~5×103Ω/sq. In addition, a defrosting window fabricated from the RGO coated flexible glass is demonstrated, which shows excellent defrosting performance.

Graphene ink as a corrosion inhibiting blanket for iron in an aggressive chloride environment

Corrosion resistance of iron (Fe) was achieved by coating it with a reduced graphene oxide ink. The Fe surface with the graphene oxide ink coating exhibited improved corrosion resistance in an aggressive chloride environment, which is attributed to the excellent barrier property of graphene. The advantage of this method is that graphene can be deposited by using a solution process that is easy, reproducible, and can be used to coat objects of any dimensions just like conventional paints or coatings.

Electrospray deposition of a graphene-oxide thin film, its characterization and investigation of its resistive switching performance

A novel route to thin-film fabrication of graphene oxide (GO) is presented using a well-known technique, i.e., electrospray deposition. For deposition of the graphene-oxide thin film, grapheneoxide ink containing 0.025 wt% graphene oxide flowing through a metal capillary was subjected to a static electric field in order to generate atomized droplets, thereby depositing a uniform thin film of graphene oxide on an indium-tin-oxide coated polyethylene terephthalate substrate. The quality of the layer was characterized by analyzing the surface morphology and the thickness, and the electrical measurements on the single film were performed. In order to study the resistive switching behavior of GO, a prototype GO-based resistive switching device having an active area of 0.026 mm2 was developed and was analyzed by current voltage measurements. The IV characteristics of the device successfully showed a typical non-volatile resistive switching behavior for a GO layer having the retention times of ∼103 s, thus highlighting the electrospray deposition technology as a reliable candidate for the fabrication of GO layers.

Micropatterning of Graphene Sheets by Inkjet Printing and Its Wideband Dipole‐Antenna Application

Patterned graphene sheets are fabricated by an inkjet printing technique. High line resolution and sustained electrical conductivity is achieved, and tuning of the sheet resistance is dependent on the concentration of graphene oxide ink and the number of print layers. A patterned graphene-based thin film is also applied as a practical wideband dipole antenna.

Submillimeter-scale Graphene Patterning through Ink-jet Printing of Graphene Oxide Ink

Abstract Patterning of reduced graphene is successfully demonstrated through ink-jet printing of graphene oxide (GO) ink and subsequent reduction with hydrazine vapor in submillimeter scale. GO plate size is the most critical parameter for the success of facile ink-jet printing of GO ink. Prepared graphene lines show conductivity of 1.1 S m−1, which is a fifth of typical conductivity of graphene film, which might result from decreased percolation of graphene plates in ink-jet printing.