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Search Results: 1 - 10 of 1292 matches for " Graphene Sheet "
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Synthesis and Characterization of Graphene Oxide and Reduced Graphene Oxide Thin Films Deposited by Spray Pyrolysis Method  [PDF]
M. S. Eluyemi, M. A. Eleruja, A. V. Adedeji, B. Olofinjana, O. Fasakin, O. O. Akinwunmi, O. O. Ilori, A. T. Famojuro, S. A. Ayinde, E. O. B. Ajayi
Graphene (Graphene) , 2016, DOI: 10.4236/graphene.2016.53012
Abstract: 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.
Green and Sustainable Heterogeneous Organo-Catalyst for Asymmetric Aldol Reactions  [PDF]
Mohammad Sadiq, Razia Aman, Khalid Saeed, M. Sohail Ahmad, M. Abid Zia
Modern Research in Catalysis (MRC) , 2015, DOI: 10.4236/mrc.2015.42006
Abstract: Linear amino acids covalently supported on graphene sheet were employed as catalysts for asymmetric aldol reactions between cyclohexanone and aldehydes (aliphatic and/or aromatic) in a batch type reactor in the presence of water. The reactions were found to exhibit high yield as well as excellent ee value. Additionally, the catalysts were found to be truly heterogeneous and eco-friendly.
Graphene as a Strictly 2D Sheet or as a Film of Small but Finite Thickness  [PDF]
Bo E. Sernelius
Graphene (Graphene) , 2012, DOI: 10.4236/graphene.2012.12003
Abstract: We study an interface between two media separated by a strictly 2D sheet. We show how the amplitude reflection coef- ficient can be modeled by that for an interface where the 2D sheet has been replaced by a film of small but finite thick- ness. We give the relationship between the 3D dielectric function of the thin film and the 2D dielectric function of the sheet. We apply this to graphene and show how the van der Waals interaction between two graphene sheets is modified when going from the 2D sheet description to the thin film description. We also show the wrong result from keeping the 2D dielectric function to represent the film medium.
Effects of Surface Charges on the Seawater Desalination Using Functionalized Graphene  [PDF]
Yue Chan, Yong Ren
Journal of Applied Mathematics and Physics (JAMP) , 2016, DOI: 10.4236/jamp.2016.44066
Abstract:

In this paper, we investigate the selection rule for desalinating seawater using functionalized graphene sheet as a semi-permissible membrane. Both the applied mathematical modeling and MD simulations will be used to determine the acceptance conditions for water molecule or sodium ion permeating into the functionalized graphene. Both the Lennard-Jones potential and Coulomb forces are considered by taking into accounts the major molecular and ionic interactions between molecules, ions and functionalized graphene sheet. The continuous approximation will then be used to coarse grain most significant molecular and ionic interactions so that the multi-body problems could be simplified into several two-body problems and the 3D motions are reduced into degenerated 1D motion. Our mathematical model and simulations show that the negatively charged graphene always accepts sodium ions and water; however the permeability of water molecules and sodium ions becomes very sensitive to the presence of positive charges on the graphene.

Effect of the tensile force on the electronic energy gap of graphene sheets
拉伸作用对单层石墨片电子能隙的影响

Wei Yong,Tong Guo-Ping,
韦勇
,童国平

物理学报 , 2009,
Abstract: 基于紧束缚方法,在考虑最近邻相互作用的情况下,研究了拉伸锯齿型边和扶手型边单层石墨的能带结构,得到了两种类型单层石墨片的π电子能带及带隙与拉力的解析关系式.通过数值计算能够发现:拉力不但使单层石墨产生带隙,而且带隙随着拉力的增大而变宽,并且锯齿型比扶手型的带隙更易变宽.
Micro- and nanoscale electrical characterization of large-area graphene transferred to functional substrates
Gabriele Fisichella,Salvatore Di Franco,Patrick Fiorenza,Raffaella Lo Nigro
Beilstein Journal of Nanotechnology , 2013, DOI: 10.3762/bjnano.4.24
Abstract: Chemical vapour deposition (CVD) on catalytic metals is one of main approaches for high-quality graphene growth over large areas. However, a subsequent transfer step to an insulating substrate is required in order to use the graphene for electronic applications. This step can severely affect both the structural integrity and the electronic properties of the graphene membrane. In this paper, we investigated the morphological and electrical properties of CVD graphene transferred onto SiO2 and on a polymeric substrate (poly(ethylene-2,6-naphthalene dicarboxylate), briefly PEN), suitable for microelectronics and flexible electronics applications, respectively. The electrical properties (sheet resistance, mobility, carrier density) of the transferred graphene as well as the specific contact resistance of metal contacts onto graphene were investigated by using properly designed test patterns. While a sheet resistance Rsh ≈ 1.7 kΩ/sq and a specific contact resistance ρc ≈ 15 kΩ·μm have been measured for graphene transferred onto SiO2, about 2.3× higher Rsh and about 8× higher ρc values were obtained for graphene on PEN. High-resolution current mapping by torsion resonant conductive atomic force microscopy (TRCAFM) provided an insight into the nanoscale mechanisms responsible for the very high ρc in the case of graphene on PEN, showing a ca. 10× smaller “effective” area for current injection than in the case of graphene on SiO2.
Photoreduction and Thermal Properties of Graphene-Based Flexible Films  [PDF]
Gautam Naik, Sridhar Krishnaswamy
Graphene (Graphene) , 2017, DOI: 10.4236/graphene.2017.62003
Abstract: In the present study, we report on an efficient method for large-area photoreduction of graphene oxide flexible films. The laser-based reduction can be carried out in situ and can be tuned to attain the properties required. A systematic study has been conducted to evaluate the variation of the degree of reduction with the actual reduction temperature, which is measured using an infrared thermal camera. Local reduction temperature is varied up to 350°C, and the degree of reduction is measured using the C/O ratio. The C/O ratio is increased from 2:1 for graphene oxide to 10:1 for reduced graphene oxide. This high degree of reduction is observed at low temperatures, and also in a short period of time. Thermal conductivity properties calculated using the temperature distribution shows the in-plane thermal conductivities of graphene oxide and reduced graphene oxide are a few orders of magnitude lower than single layer graphene. This can be attributed to oxygen-defect scattering, and also due to the heat conduction through the thickness of the sample by way of contact between adjacent flakes. This photoreduction method provides a way for roll-to-roll scalable production of graphene-based flexible films.
A Two-Step Method for the Preparation of Highly Conductive Graphene Film and Its Gas-Sensing Property  [PDF]
Tran Van Khai, Tran Dai Lam, Le Van Thu, Hyoun Woo Kim
Materials Sciences and Applications (MSA) , 2015, DOI: 10.4236/msa.2015.611097
Abstract: In this research, a highly conductive graphene film was synthesized through the chemical reduction of graphene oxide (RGO) nanosheets followed by thermal treatment at 1100℃ (RGO-1100℃) under H2 ambient. The as-prepared graphene films were characterized by using X-ray photoelectron spectroscopy, fourier transform infrared spectroscopy, X-ray diffractions, raman spectroscopy, transmission electron microscopy, scanning electron microscopy, atomic force microscopy and by electrical conductivity measurements. The results showed that the thermal treatment efficiently removed residual oxygen-containing functional groups on the surface of the RGO sheets and simultaneously restored the sp2 carbon networks in the graphene sheets. As a result, the electrical conductivity of RGO-1100℃ (~210 S/cm) film was greatly improved compared with that of RGO (~24 S/cm) and graphene oxide (4.2 × 10–4 S/m) films. In addition, the NO2 gas sensing characteristics of the as-prepared RGO films were studied. The results indicated that RGO films were highly responsive to NO2 at temperature of 200℃.
Synthesis and Fabrication of Graphene and Graphene Oxide: A Review  [PDF]
Adeniji Adetayo, Damilola Runsewe
Open Journal of Composite Materials (OJCM) , 2019, DOI: 10.4236/ojcm.2019.92012
Abstract: The field of nanotechnology has advanced following the discovery of a two-dimensional material of sp2 hybridized carbon atoms, graphene in 2004 by Geim and Novoselov. Graphene has received so much attention due to its exceptional electronic, thermal, mechanical, and optical properties in addition to its large surface area and single-atom thickness. This has led to the discovery of several techniques to obtain graphene such as chemical exfoliation, chemical vapor deposition (CVD), chemical synthesis etc. However, these techniques are majorly challenged with developing graphene with fewer defects and in large scale; thus, there is an increasing need to produce graphene in large quantities with high quality. Several studies have been carried out to find routes to producing high-quality graphene. This paper focuses majorly on the synthesis and fabrication methods of producing graphene and its derivative, graphene oxide. Characterization techniques to identify graphene such as optical microscopy, scanning electron microscopy (SEM), Raman spectroscopy, scanning probe microscopy (SPM) used to determine number of layers, quality, atomic structures, and defects in graphene is also briefly discussed. This article also covers a short description of graphene applications in transparent electrodes, composites and energy storage devices.
Surgical Approaches to Large Peripheral Nerve Sheets Tumors  [PDF]
Hedaya M. Hendam, Hatem M. El Samouly, Hamdy M. Behairy
Open Journal of Modern Neurosurgery (OJMN) , 2018, DOI: 10.4236/ojmn.2018.81003
Abstract: Peripheral nerve sheath tumors (PNSTs) are not rare tumors. Its sound management is complete surgical excision. The aim of this study was to describe clinical presentation, accuracy of different investigations and ideal surgical approaches in relation to outcomes. The study is a prospective and included 26 surgically treated large PNSTs in 22 patients operated through different surgical approaches according to the site of the tumors. The fellow up period was 6 - 60 months. The mean age was 41.8 years, 9 were males and 13 were females. The common presentations were pain in 12 lesions, swelling in 8 lesions, neural deficits in 4 lesions and positive Tinel’s test in 2 lesions. These lesions were excised through 6 surgical approaches. Histopathological examination showed 20 benign and 6 malignant lesions. Five cases of malignant peripheral nerve sheet tumors (MPNSTs) had local recurrent, 4 cases had distant metastasis, 4 cases received chemotherapy and radiotherapy, and 4 cases were died in the postoperative fellow up period. It was concluded that surgical approaches to the PNSTs, depends on their locations. Adequate exposure with minimal dissection minimized the neurological deficit and decreased rate of local recurrence.
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