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Author(s):  
Eri Hashimoto ◽  
Keigo Tamura ◽  
Hayato Yamaguchi ◽  
Takeshi Watanabe ◽  
Fumihiko Matsui ◽  
...  

Abstract We characterized CVD-grown graphene with high single-crystallinity on Ir(111)/α-Al2O3(0001) by photoelectron momentum microscopy. A multi-functional photoelectron momentum microscope (PMM), which is installed with element-specific valence band photoelectron spectroscopy and X-ray absorption spectroscopy, is a complementary characterization tool to conventional methods, such as Raman spectroscopy and atomic force microscopy, for comprehensive and quantitative characterization of graphene/Ir(111). Using PMM, we characterized the properties of CVD-grown graphene including the single-crystallinity, number of layers, crystal orientation, and degree of interaction between graphene and Ir(111) and clarified the relationship between these properties and the CVD growth conditions.


2022 ◽  
Author(s):  
Won-Hwa Park

Abstract Graphene can be used as a starting material for the synthesis of useful nano-complexes for flexible, transparent electrodes, therapeutic, bio-diagnostics and bio-sensing. In order to apply graphene in the medical field, chemical vapor deposition (CVD) method has been mainly utilized considering its large and near-homogenious carbon constituents. Especially, the less degree of perturbation of graphene monolayer (GM), which is followed by the underneath catalytic Cu surface morphology, is very crucial in terms of providing the suspended GM and relatively fluent lateral carrier mobility with lower sheet resistance value. In this work, we can suggest a surface-Enhanced Raman Spectroscopic (SERS) indicator in a quantitative way on the status of z-directional morphological corrugation of a CVD–grown GM (CVD-GM) by applying a Nanoparticle-on-Mirror (NPoM) system composed of Au nanoparticle (NP) / CVD-GM / Au thin film (TF) plasmonic junction structure. A new (or enhanced) Radial Breathing Like Mode (RBLM) SERS signal around ~150 cm-1 from CVD-GM spaced in NPoM is clearly observed by employing a local z-polarized incident field formed at the Au NP–Au TF plasmonic gap junctions. With this observation, the value of I[out-of-plane, RBLM] / I[in-plane, [2D] at certain domains, it can be suggested as a new optical nano-metrology value to relatively determine between lower z-directional morphological corrugation (or protrusion) status of a CVD-GM spaced in our NPoM system (lower I[RBLM] / I[2D] value) and higher degree of lateral carrier mobility of the CVD-GM associated with lower sheet resistance values as a result of higher blue-shifted Raman in-plane (G, 2D) peak maximum position. Furthermore, we will also expect the bio-sensing performances by utilizing the high specific surface area and ultrahigh flexibility of the CVD-GM in one of the future prospective works such as pressure-strain, strain-to-electricity and chemical-coupled sensor via I[RBLM] / I[2D] values.


2022 ◽  
pp. 103113
Author(s):  
Hyunkyu Lee ◽  
Jong-Hyurk Park ◽  
Nikhilesh Maity ◽  
Donghoi Kim ◽  
Dongsoo Jang ◽  
...  

2021 ◽  
Author(s):  
Yao Yao ◽  
Ryota Negishi ◽  
Daisuke Takajo ◽  
Makoto Takamura ◽  
Yoshitaka Taniyasu ◽  
...  

Abstract Overlayer growth of graphene on an epitaxial graphene/silicon carbide (SiC) as a solid template by ethanol chemical vapor deposition is performed over a wide growth temperature range from 900 ºC to 1450 ºC. Structural analysis using atomic force and scanning tunneling microscopies reveal that graphene islands grown at 1300 ºC form hexagonal twisted bilayer graphene as a single crystal. When the growth temperature exceeds 1400 ºC, the grown graphene islands show a circular shape. Moreover, moiré patterns with different periods are observed in a single graphene island. This means that the graphene islands grown at high temperature are composed of several graphene domains with different twist angles. From these results, we conclude that graphene overlayer growth on the epitaxial graphene/SiC solid at 1300 ºC effectively synthesizes the twisted few-layer graphene with a high crystallinity.


Author(s):  
Ashish Kumar ◽  
Arathy Varghese ◽  
Vijay Janyani

AbstractThis work presents the performance evaluation of Graphene/ZnO Schottky junctions grown on flexible indium tin oxide (ITO)-coated polyethylene terephthalate (PET) substrates. The fabricated structures include chemical vapour deposition grown graphene layer on ITO-coated PET substrates. Polymethyl methacrylate assisted transfer method has been employed for the successful transfer of graphene from Cu substrate to PET. The smaller D-band intensity (1350 cm−1) compared to G-band (1580 cm−1) indicates good quality of carbon lattice with less number of defects. High-quality ZnO has been deposited through RF sputtering. The deposited ZnO with grain size 50–95 nm exhibited dislocation densities of 1.31270 × 10–3 nm−2 and compressive nature with negative strain of − 1.43156 GPa. Further, the electrical and optical characterization of the devices has been done through device I–V characterization and UV detection analysis. The UV detection capability of the device has been carried out with the aid of a UV-lamp of 365 nm wavelength. The fabricated graphene/ZnO photodetector showed good response to UV illumination. The device performance analysis has been done through a comparison of the device responsivity and detectivity with the existing detectors. The detectivity and responsivity of the fabricated detectors were 7.106 × 109 mHz1/2 W−1 and 0.49 A W−1, respectively.


2021 ◽  
Vol 22 ◽  
pp. 100578
Author(s):  
M. Bahri ◽  
B. Shi ◽  
K. Djebbi ◽  
M.A. Elaguech ◽  
D. Zhou ◽  
...  

2021 ◽  
Vol 11 (22) ◽  
pp. 10833
Author(s):  
Furqan Khairi Mohammed ◽  
Khi Poay Beh ◽  
Asmiet Ramizy ◽  
Naser M. Ahmed ◽  
Fong Kwong Yam ◽  
...  

This work presents the role of graphene in improving the performance of a porous GaN-based UV photodetector. The porous GaN-based photodetector, with a mean pore diameter of 35 nm, possessed higher UV sensitivity, about 95% better compared to that of the as-received (non-porous) photodetector. In addition, it exhibits a lower magnitude of leakage current at dark ambient, about 70.9 μA, compared to that of the as-received photodetector with 13.7 mA. However, it is also highly resistive in nature due to the corresponding electrochemical process selectively dissolute doped regions. Herein, two types of graphene, derived from CVD and the electrochemical exfoliation (EC) process, were cladded onto the porous GaN region. The formation of a graphene/porous GaN interface, as evident from the decrease in average distance between defects as determined from Raman spectroscopy, infers better charge accumulation and conductance, which significantly improved UV sensing. While the leakage current shows little improvement, the UV sensitivity was greatly enhanced, by about 460% and 420% for CVD and EC cladded samples. The slight difference between types of graphene was attributed to the coverage area on porous GaN, where CVD-grown graphene tends to be continuous while EC-graphene relies on aggregation to form films.


Sensors ◽  
2021 ◽  
Vol 21 (21) ◽  
pp. 7262
Author(s):  
Yamujin Jang ◽  
Young-Min Seo ◽  
Hyeon-Sik Jang ◽  
Keun Heo ◽  
Dongmok Whang

We report a novel graphene transfer technique for fabricating graphene field-effect transistors (FETs) that avoids detrimental organic contamination on a graphene surface. Instead of using an organic supporting film like poly(methyl methacrylate) (PMMA) for graphene transfer, Au film is directly deposited on the as-grown graphene substrate. Graphene FETs fabricated using the established organic film transfer method are easily contaminated by organic residues, while Au film protects graphene channels from these contaminants. In addition, this method can also simplify the device fabrication process, as the Au film acts as an electrode. We successfully fabricated graphene FETs with a clean surface and improved electrical properties using this Au-assisted transfer method.


2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Mohammad Salehi ◽  
Parnia Bastani ◽  
Loghman Jamilpanah ◽  
Abbas Madani ◽  
Seyed Majid Mohseni ◽  
...  

AbstractFundamental studies on graphene (Gr) and its real device applications have been affected by unavoidable defects and impurities which are usually present in synthesized Gr. Therefore, post treatment methods on Gr have been an important subject of research followed by the community. Here, we demonstrate a post-treatment of cm-sized CVD-grown graphene in a Radio Frequency-generated low-pressure plasma of methane and hydrogen to remove oxygen functional groups and heal the structural defects. The optimum plasma treatment parameters, such as pressure, plasma power, and the ratio of the gases, are optimized using in-situ optical emission spectroscopy. This way we present an optimal healing condition monitored with in situ OES. A twofold increase in the conductivity of plasma-treated Gr samples was obtained. Plasma treatment conditions give insights into the possible underlying mechanisms, and the method presents an effective way to obtain improved Gr quality.


2021 ◽  
Vol 13 (1) ◽  
Author(s):  
Minseok Lee ◽  
Sangwon Lee ◽  
Jejung Kim ◽  
Jeongsik Lim ◽  
Jinho Lee ◽  
...  

AbstractCortical maps, which are indicative of cognitive status, are shaped by the organism’s experience. Previous mapping tools, such as penetrating electrodes and imaging techniques, are limited in their ability to be used to assess high-resolution brain maps largely owing to their invasiveness and poor spatiotemporal resolution, respectively. In this study, we developed a flexible graphene-based multichannel electrode array for electrocorticography (ECoG) recording, which enabled us to assess cortical maps in a time- and labor-efficient manner. The flexible electrode array, formed by chemical vapor deposition (CVD)-grown graphene, provided low impedance and electrical noise because a good interface between the graphene and brain tissue was created, which improved the detectability of neural signals. Furthermore, cortical map remodeling was induced upon electrical stimulation at the cortical surface through a subset of graphene spots. This result demonstrated the macroscale plasticity of cortical maps, suggesting perceptual enhancement via electrical rehabilitation at the cortical surface.


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