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Insight of cleaning, doping and defective effects on the graphene surface by using methanol
Rai, Krishna Bahadur,Khadka, Ishwor Bahadur,Koirala, Agni Raj,Ray, Schindra Kumar Techno-Press 2021 Advances in materials research Vol.10 No.4
Graphene has attracted enormous interest to researchers because of its remarkable electrical, mechanical, and optical properties. Chemical vapor deposition (CVD) method was used to synthesize the graphene. The methanol (CH<sub>3</sub>OH) was used to investigate the cleaning, doping and defective effect in the graphene surface. The samples were characterized by X-ray diffraction patterns (XRD), field emission scanning electron microscope (FESEM) images, Xray photoelectron spectroscopy (XPS) measurements, and Raman spectroscopy. XRD indicates the introduction of oxygen in graphene layer. FESEM images of samples suggest the sheet like morphology. XPS measurements confirm the existence of large number of oxygen containing functional groups (C=O, COOH, and C-O) and C-C in the graphene surface. The Raman spectra confirm the n-doping and cleaning effects on graphene surface through the red shifts of G and 2D peaks. Furthermore, the optical images were used to observe the residues in graphene. The residues are obtained due to adsorption of CH<sub>3</sub>OH in graphene surface. Therefore, this work provides a simple and effective approach to investigate the cleaning, doping and defective effects on the surface of graphene using CH<sub>3</sub>OH solvent that can be applied in tunable electronic devices and gas sensor.
Highly Efficient Trans-Reflective Color Filters Incorporating TiO2-MgF2 Multilayer Stacks
Vivek Raj Shrestha,이상신,박철순,Ishwor Koirala,최덕용 한국광학회 2015 Current Optics and Photonics Vol.19 No.6
We report for the first time highly efficient trans-reflective color filters capable of demonstratingcoloration in both transmission and reflection modes by taking advantage of a multilayer stack consistingof MgF2 and TiO2 used respectively as the low and high index materials. In order to enable suchtrans-reflective performance, securing an optimal stop band assuming an appropriate bandwidth within thevisible regime is pivotal, which was realized by tailoring the thicknesses and the numbers of TiO2-MgF2bi-layers. Three devices were designed through rigorous simulations and developed via e-beam evaporationto demonstrate vivid blue, green, and red colors in the reflection mode, and yellow, magenta, and cyancolors in the transmission mode, featuring an enhanced efficiency exceeding 90% under normal incidence. The color performance of the filters was examined by referring to the chromaticity coordinates of thetransmission and reflection spectra, alongside photographed color images. The dependence of theperformance on the angle of incidence was explored with respect to incident polarization, indicating thata transmission surpassing 60% could be stably maintained up to an angle of 75°. Polarization independenttransfer characteristics were especially achieved for the normal incidence. The proposed devices may bereadily extended to other spectral regimes by adjusting the thicknesses of the films