• Tribology and Lubricants
• /
• 제38권6호
• /
• pp.235-240
• /
• 2022

Atomically-thin 2D nanomaterials can be easily deformed and have surface corrugations which can influence the frictional characteristics of the 2D nanomaterials. Chemical vapor deposition (CVD) graphene can be grown in a wafer scale, which is suitable as a large-area surface coating film. The CVD growth involves cooling process to room temperature, and the thermal expansion coefficients mismatch between graphene and the metallic substrate induces a compressive strain in graphene, resulting in the surface corrugations such as wrinkles and atomic ripples. Such corrugations can induce the friction anisotropy of graphene, and therefore, accurate imaging of the surface corrugation is significant for better understanding about the friction anisotropy of CVD graphene. In this work, the combinatorial analysis using friction force microscopy (FFM) and transverse shear microscopy (TSM) was implemented to unveil the friction anisotropy of CVD bi-layer graphene. The periodic friction anisotropy of the wrinkles was measured following a sinusoidal curve depending on the angles between the wrinkles and the scanning tip, and the two domains were observed to have the different friction signals due to the different directions of the atomic ripples, which was confirmed by the high-resolution FFM and TSM imaging. In addition, we revealed that the atomic ripples can be easily suppressed by ironing the surface during AFM scans with an appropriate normal force. This work demonstrates that the friction anisotropy of CVD bilayer graphene is well-correlated with the corrugated structures and the local friction anisotropy induced by the atomic ripples can be controllably removed by simple AFM scans.

• 한국진공학회:학술대회논문집
• /
• 한국진공학회 2011년도 제41회 하계 정기 학술대회 초록집
• /
• pp.157-157
• /
• 2011

Graphene has generated significant interest in the recent years as a functional material for electronics, sensing, and energy applications due to its unique electrical, optical, and mechanical properties. Much of the considerable interest in graphene stems from results obtained for samples mechanically exfoliated from graphite. Practical applications, however, require reliable and well-controlled methods for fabrication of large area graphene films. Recently high quality graphene layers were fabricated using chemical vapor deposition (CVD) on nickel and copper with methane as the source of the carbon atoms. Here, we report a simple and efficient method to synthesize graphene layers using solid carbon source. Few-layer graphene films are grown using filtered vacuum arc source (FVAS) technique by evaporation of carbon atom on Ni catalytic metal and subsequent annealing of the samples at 800$^{\circ}$C. In our system, carbon atoms diffuse into the Ni metal layer at elevated temperatures followed by their segregation as graphene on the free surface during the cooling down step as the solubility of carbon in the metal decrease. For a given annealing condition and cooling rate, the number of graphene layers is easily controlled by changing the thickness of the initially evaporated amorphous carbon film. Based on the Raman analysis, the quality of graphene is comparable to other synthesis methods found in the literature, such as CVD and chemical methods.

• Carbon letters
• /
• 제15권3호
• /
• pp.151-161
• /
• 2014

Exceptional progress has been made with chemical vapor deposition (CVD) of graphene in the past few years. Not only has good monolayer growth of graphene been achieved, but large-area synthesis of graphene sheets has been successful too. However, the polycrystalline nature of CVD graphene is hampering further progress as graphene property degrades due to presence of grain boundaries. This review will cover factors that affect nucleation of graphene and how other scientists sought to obtain large graphene domains. In addition, the limitation of the current research trend will be touched upon as well.

• 한국진공학회:학술대회논문집
• /
• 한국진공학회 2013년도 제44회 동계 정기학술대회 초록집
• /
• pp.590-590
• /
• 2013

Direct growth of graphene using CVD method has been done on CVD grown boron nitride substrate. From the SEM image, we have shown that the size of grain of graphene could be clearly controlled by varying the amount of injected hydrocarbon. To convince the existence of graphene on boron nitride, XPS and Raman has been checked. Both B1s and N1s peaks in XPS spectra and the Raman peak around 1,370 $cm^{-1}$ demonstrated that boron nitride did remain after high temperature treatment during the graphene growth process. And along the graphene grain boundary, the Raman fingerprint of graphene was neatly appeared.

• 한국진공학회:학술대회논문집
• /
• 한국진공학회 2014년도 제46회 동계 정기학술대회 초록집
• /
• pp.434.2-434.2
• /
• 2014

We observe enhanced pH response of solution-gated field-effect transistors (SG-FET) having 1D-2D hybrid channel of vertical grown ZnO nanorods grown on CVD graphene (Gr). In recent years, SG-FET based on Gr has received a lot of attention for biochemical sensing applications, because Gr has outstanding properties such as high sensitivity, low detection limit, label-free electrical detection, and so on. However, low-defect CVD Gr has hardly pH responsive due to lack of hydroxyl group on Gr surface. On the other hand, ZnO, consists of stable wurtzite structure, has attracted much interest due to its unique properties and wide range of applications in optoelectronics, biosensors, medical sciences, etc. Especially, ZnO were easily grown as vertical nanorods by hydrothermal method and ZnO nanostructures have higher sensitivity to environments than planar structures due to plentiful hydroxyl group on their surface. We prepared for ZnO nanorods vertically grown on CVD Gr (ZnO nanorods/Gr hybrid channel) and to fabricate SG-FET subsequently. We have analyzed hybrid channel FETs showing transfer characteristics similar to that of pristine Gr FETs and charge neutrality point (CNP) shifts along proton concentration in solution, which can determine pH level of solution. Hybrid channel SG-FET sensors led to increase in pH sensitivity up to 500%, compared to pristine Gr SG-FET sensors. We confirmed plentiful hydroxyl groups on ZnO nanorod surface interact with protons in solution, which causes shifts of CNP. The morphology and electrical characteristics of hybrid channel SG-FET were characterized by FE-SEM and semiconductor parameter analyzer, respectively. Sensitivity and sensing mechanism of ZnO nanorods/Gr hybrid channel FET will be discussed in detail.

• 한국진공학회:학술대회논문집
• /
• 한국진공학회 2011년도 제41회 하계 정기 학술대회 초록집
• /
• pp.114-114
• /
• 2011

Graphene is the hottest topic in condensed-matter physics due to its unusual electronic structures such as Dirac cones and massless linear dispersions. Graphene can be epitaxially grown on various metal surfaces with chemical vapor deposition (CVD) processes. Such epitaxial graphene shows modified electronic structures caused by substrates. In the method for removal of the effect of substrate, there are bi, tri-layer graphene, gold intercalation, and oxygen intercalation. Here, We will present the changes of geometric and electronic structure of graphene grown on Ru(0001) by oxygen intercalation between graphene and Ru(0001). Using Scanning tunneling microscopy (STM) and spectroscopy (STS), we observed the aspect that the band gap features near the fermi level of graphene on Ru(0001) system is shifted and narrow. Based on the observed results, two effects by intercalated oxygen were considered.

• 한국진공학회:학술대회논문집
• /
• 한국진공학회 2014년도 제46회 동계 정기학술대회 초록집
• /
• pp.114.1-114.1
• /
• 2014

Copper is considered to be the most promising substrate for the growth of high-quality and large area graphene by chemical vapor deposition (CVD), in particular, on the (111) facet. Because the interactions between graphene and Cu substrates influence the orientation, quality, and properties of the synthesized graphene, we studied the interactions using angle-resolved photoemission spectroscopy. The evolution of both the Shockley surface state of the Cu(111) and the p band of the graphene was measured from the initial stage of CVD growth to the formation of a monolayer. Graphene growth was initiated along the Cu(111) lattice, where the Dirac band crossed the Fermi energy ($E_F$) at the K point without hybridization with the d-band of Cu. Then two rotated domains were additionally grown as the area covered with graphene became wider. The Dirac energy was about 0.4 eV and the energy of the Shockley surface state of Cu(111) shifted toward the $E_F$) by 0.15 eV upon graphene formation. These results indicate weak interactions between graphene and Cu, and that the electron transfer is limited to that between the Shockley surface state of Cu(111) and the p band of graphene. This weak interaction and slight lattice mismatch between graphene and Cu resulted in the growth of rotated graphene domains ($9.6^{\circ}$ and $8.4^{\circ}$), which showed no significant differences in the Dirac band with respect to different orientations. These rotated graphene domains resulted in grain boundaries which would hinder a large-sized single monolayer growth on Cu substrates.

• 한국전기전자재료학회논문지
• /
• 제25권5호
• /
• pp.387-391
• /
• 2012

Graphene was fabricated onto Ni/Si substrate using a rapid-thermal pulse CVD and they were transferred onto the Ti/PES flexible substrate. For top electrode applications of the BMNO dielectric films, graphene was patterned using a argon plasma. Through an AFM image and a leakage current density of the BMNO films grown onto various bottom electrodes before and after bending test, BMNO films grown onto the graphene bottom electrode showed no change of the microstructure and the leakage current density after the bend.

• 한국진공학회:학술대회논문집
• /
• 한국진공학회 2016년도 제50회 동계 정기학술대회 초록집
• /
• pp.298.1-298.1
• /
• 2016

Two-dimensional materials have been received significant interest after the discovery of graphene due to their fascinating electronic and optical properties for the application of novel devices. However, graphene lack of certain bandgap which is essential requirement to achieve high performance field-effect transistors. Analogous to graphene materials, molybdenum disulfide ($MoS_2$) as one of transition-metal dichalcogenides family presents considerable bandgap and exhibits promising physical, chemical, optical and mechanical properties. Here we studied nonvolatile memory based on $MoS_2$ which is grown by chemical vapor deposition (CVD) method. $MoS_2$ growth was taken on $1.5{\times}1.5cm^2$ $SiO_2$/Si-substrate. The samples were analyzed by Raman spectroscopy, atomic force microscopy and X-ray photoelectron spectroscopy. Current-voltage (I-V) characteristic was carried out HP4156A. The CVD-$MoS_2$ was analyzed as few layers and 2H-$MoS_2$ structure. From I-V measurement for two metal contacts on CVD-$MoS_2$ sample, we found typical resistive switching memory effect. The device structures and the origin of nonvolatile memory effect will be discussed.

• 한국재료학회지
• /
• 제28권5호
• /
• pp.279-285
• /
• 2018

Graphene is an interesting material because it has remarkable properties, such as high intrinsic carrier mobility, good thermal conductivity, large specific surface area, high transparency, and high Young's modulus values. It is produced by mechanical and chemical exfoliation, chemical vapor deposition (CVD), and epitaxial growth. In particular, large-area and uniform single- and few-layer growth of graphene is possible using transition metals via a thermal CVD process. In this study, we utilize polystyrene and boron oxide, which are a carbon precursor and a doping source, respectively, for synthesis of pristine graphene and boron doped graphene. We confirm the graphene grown by the polystyrene and the boron oxide by the optical microscope and the Raman spectra. Raman spectra of boron doped graphene is shifted to the right compared with pristine graphene and the crystal quality of boron doped graphene is recovered when the synthesis time is 15 min. Sheet resistance decreases from approximately $2000{\Omega}/sq$ to $300{\Omega}/sq$ with an increasing synthesis time for the boron doped graphene.