Highly Enhanced Electromechanical Stability of Large-Area Graphene with Increased Interfacial Adhesion Energy by Electrothermal-Direct Transfer for Transparent Electrodes

Kim, Jangheon,Kim, Gi Gyu,Kim, Soohyun,Jung, Wonsuk American Chemical Society 2016 ACS APPLIED MATERIALS & INTERFACES Vol.8 No.35

<P>Graphene, a two-dimensional sheet of carbon atoms in a hexagonal lattice structure, has been extensively investigated for research and industrial applications as a promising material with outstanding electrical, mechanical, and chemical properties. To fabricate graphene-based devices, graphene transfer to the target substrate with a clean and minimally defective surface is the first step. However, graphene transfer technologies require improvement in terms of uniform transfer with a clean, nonfolded and nontorn area, amount of defects, and electromechanical reliability of the transferred graphene. More specifically, uniform transfer of a large area is a key challenge when graphene is repetitively transferred onto pretransferred layers because the adhesion energy between graphene layers is too low to ensure uniform transfer, although uniform multilayers of graphene have exhibited enhanced electrical and optical properties. In this work, we developed a newly suggested electrothermal-direct (ETD) transfer method for large-area high quality monolayer graphene with less defects and an absence of folding or tearing of the area at the surface. This method delivers uniform multilayer transfer of graphene by repetitive monolayer transfer steps based on high adhesion energy between graphene layers and the target substrate. To investigate the highly enhanced electromechanical stability, we conducted mechanical elastic bending experiments and reliability tests in a highly humid environment. This ETD-transferred graphene is expected to replace commercial transparent electrodes with ETD graphene-based transparent electrodes and devices such as a touch panels with outstanding electromechanical stability.</P>

Sub-μm CVD-grown graphene bridge 의 열전도도 계측

채희범(Heebum Chae),황광석(Gwangseok Hwang),권오명(Ohmyoung Kwon) 대한기계학회 2013 대한기계학회 춘추학술대회 Vol.2013 No.12

For graphene-based electronic devices, it is crucial to analyze the heat transport in graphene in sub-micrometer scale. The heat transport in sub-micrometer graphene devices depends on the characteristic length of the device. As the characteristic length of the device approaches and even gets smaller than the phonon mean free path in graphene, the heat transport in the device becomes ballistic and the thermal conductivity of graphene changes accordingly. Herein, we experimentally observe the ballistic heat transport in graphene by measuring the thermal conductivity of submicrometer CVD-grown graphene bridges. Phonon mean free path of graphene has been predicted to be in the range of 250 ~ 800 nm. However, it is impossible to measure thermal conductivity of graphene in the sub-micrometer scale using optothermal Raman, which has relatively low temperature sensitivity and spatial resolution of about 1 μm. We make the suspended graphene bridges on nano-trenches, heat the bridges electrically, and accurately measure the power applied to the graphene with four-probe configuration. Also, we profile the temperature distribution across graphene bridge by null point scanning thermal microscopy (NP SThM) with ~50 nm resolution and quantitatively measure thermal conductivity using the measured power and temperature profile. In this study, we fabricate the graphene bridges with various lengths ranging from 100 nm to 2 μm and observe the ballistic heat transport.

Efficient inverted polymer Light-emitting diodes using n-type doped graphene cathodes

권성주,한태희,김영훈,김호범,서홍규,이태우 한국공업화학회 2015 한국공업화학회 연구논문 초록집 Vol.2015 No.0

Conventional transparent conducting oxide (e.g. indium-tin oxide (ITO)) should be replaced for flexible electronic applications due to its brittleness. Graphene is one of the excellent candidates for its outstanding electrical, mechanical and optical properties. To apply graphene as a cathode in polymer light-emitting diodes (PLEDs), work function (WF) should be reduced for efficient electron injection. We demonstrated inverted PLED with n-type doped graphene doping using hydrazine and (4-(1,3-dimethyl-2,3-dihydro-1H-benzoimidazol-2-yl)phenyl)dimethyl amine (N-DMBI). Hydrazine and N-DMBI doped graphene showed reduced WF compared to pristine graphene. WF reduction was larger in N-DMBI doped graphene than that of hydrazine doped graphene. (WF decrease of N-DMBI doped graphene: 0.45 eV, WF decrease of hydrazine doped graphene: 0.17 eV) Inverted PLEDs with n-type doped graphene cathode showed improved luminous characteristics. Especially, inverted PLEDs with N-DMBI doped graphene showed even higher luminous efficiency than that with ITO cathode. This results implies that N-DMBI doped graphene is promising cathode in organicoptoelectronics.

산화그래핀 층수에 따른 폴리스타이렌 표면 코팅 특성

이지훈,박재범,박단비,허증수,임정옥,Lee, Jihoon,Park, Jaebum,Park, Danbi,Huh, Jeung Soo,Lim, Jeong Ok 한국재료학회 2021 한국재료학회지 Vol.31 No.7

Graphene, a new material with various advantageous properties, has been actively used in various fields in recent years. Applications of graphene oxide are increasing in combination with other materials due to the different properties of graphene oxide, depending on the number of single and multiple layers of graphene. In this study, single-layer graphene oxide and multi-layer graphene oxide are spray coated on polystyrene, and the physicochemical properties of the coated surfaces are characterized using SEM, Raman spectroscopy, AFM, UV-Vis spectrophotometry, and contact angle measurements. In single-layer graphene oxide, particles of 20 ㎛ are observed, whereas a 2D peak is less often observed, and the difference in surface height increases according to the amount of graphene oxide. Adhesion increases with an increase in graphene oxide up to 0.375 mg, but decreases at 0.75 mg. In multi-layer graphene oxide, particles of 5 ㎛ are observed, as well as a 2D peak. According to the amount of graphene oxide, the height difference of the surface increases and the adhesive strength decreases. Both materials are hydrophilic, but single-layer graphene oxide has a hydrophilicity higher than that of multi-layer graphene oxide. We believe that multi-layer graphene oxide and single-layer graphene oxide can be implemented based on the characteristics that make them suitable for application.

Graphene and graphene‑like carbon nanomaterials‑based electrochemical biosensors for phytohormone detection

Meiqing Yang,Lu Wang,Haozi Lu,Qizhi Dong,Huimin Li,Song Liu 한국탄소학회 2023 Carbon Letters Vol.33 No.5

Phytohormones (plant hormones) are a class of small-molecule organic compounds synthesized de novo in plants. Although phytohormones are present in trace amounts, they play a key role in regulating plant growth and development, and in response to external stresses. Therefore, the analysis and monitoring of phytohormones have become an important research topic in precision agriculture. Among the various detection methods, electrochemical analysis is favored because of its simplicity, rapidity, high sensitivity, and in-situ monitoring. Graphene and graphene-like carbon materials have abundant sources, exhibiting large specific surface area, and excellent physicochemical properties. Thus, they have been widely used in the preparation of electrochemical biosensors for phytohormone detection. In this paper, the research advances of electrochemical sensors based on graphene and graphene-like carbon materials for phytohormone detection have been reviewed. The properties of graphene and graphene-like carbon materials are first introduced. Then, the research advances of electrochemical biosensors (including conventional electrochemical sensors, photoelectrochemical sensors, and electrochemiluminescence sensors) based on graphene and graphene-like carbon materials for phytohormone detection is summarized, with emphasis on their sensing strategies and the roles of graphene and graphene-like carbon materials in them. Finally, the development of electrochemical sensors based on graphene and graphene-like carbon materials for phytohormone detection is prospected.

Graphene/graphene oxide: A new material for electrorheological and magnetorheological applications

Zhang, Wen Ling,Choi, Hyoung Jin Sage Science Press (UK) 2015 Journal of intelligent material systems and struct Vol. No.

<P>The presence of functional groups provides graphene oxide sheets amphiphilic abilities with lower electrical conductivity and relatively high polarizability, which is appropriate for its electrorheological effect. In addition, because the graphene oxide sheets possess high surface area and relatively low particle density, graphene-/graphene oxide–supported materials have also attracted significant interest for fascinating magnetorheological applications. In this article, we briefly review the fabrication mechanisms and electrorheological characteristics of graphene-/graphene oxide–based electrorheological systems, such as pure graphene oxide sheets and various graphene-/graphene oxide–based polymer composites and nanocomposites of graphene/graphene oxide sheets with inorganic particles. As for the magnetorheological fluid application, the fabrication of graphene oxide sheets coated on the surface of carbonyl iron particles and graphene oxide/iron oxide composites are covered regarding improved dispersibility of the magnetorheological suspensions.</P>

그래핀 나노플레이트 및 카본블랙을 첨가한 아스팔트 혼합물의 공용성 평가

고동영,가현길,이시원,문성호 한국도로학회 2021 한국도로학회논문집 Vol.23 No.5

PURPOSES : Graphene nanoplates, which have recently been in the spotlight in various fields, are a layer of graphite used in pencil leads, with carbon arranged in hexagonal honeycomb shapes. The graphene is 0.2 nanometers thick, and it possesses high physical and chemical stability, high strength, and conductivity. These graphene nanoplates have been studied for application in various devices such as semiconductors and batteries, and in the construction sector, where they are used as additives to improve the durability of cement concrete. The purpose of this study was to investigate the physical, and functional properties of graphene-modified asphalt mixtures. METHODS : In this study, the graphene input content of asphalt mixture samples was determined using an asphalt performance grade (PG) test. Based on the results of the test, their strength, stiffness, thermal properties, and electrical conductivity were evaluated. Indirect tensile strength test and dynamic modulus (DM) test were conducted to evaluate the strength and stiffness, and thermal conductivity tests and electrical conductivity evaluations were conducted for determining the functionality of the graphene-modified asphalt mixtures. The thermal conduction test was used to measure the external temperature change over time by placing a general heated asphalt mixture and graphene-modified asphalt with the same raw material-specific mixing ratio inside the temperature chamber in order to measure the heat conductivity. The electrical conductivity was evaluated using a digital multimeter to measure the resistance of DC voltage and DC current via a 4-probe method. RESULTS : The performance grade (PG) test results showed that, for a dynamic shear rheometer (DSR), both tests met the baseline and that physical changes in the binder did not appear evident with graphene addition. Furthermore, each content met the baseline for the bending beam rheometer (BBR). The increasing ratio of flexural creep stiffness approached the maximum when 7.5% graphene was used. In indirect tensile strength test, an average of thrice the indirect tensile strength for graphene-modified asphalt was 0.92 N/mm2, which was approximately 0.04 N/mm2 higher than the average measured three times that of hot mix asphalt mixture, with the same raw material mixing ratio. In the thermal conduction tests, the temperature and the rate of change of temperature of the graphene-modified asphalt mixture were higher than those of the hot-mix asphalt mixture. Lastly, the results of the electric conductivity test using the 4-probe method showed that the electrical conductivity increased slightly as the graphene content increased, but overall, it showed very low electrical conductivity. CONCLUSIONS : In this study, the potential for enhancing the physical and functional performance of graphene nanoplates applied to asphalt mixtures was demonstrated. However, it is practically difficult to arrange graphene particles continuously within an asphalt mixture, which is believed to have very low electrical conductivity.

Unveiling the carrier transport mechanism in epitaxial graphene for forming wafer-scale, single-domain graphene

Bae, Sang-Hoon,Zhou, Xiaodong,Kim, Seyoung,Lee, Yun Seog,Cruz, Samuel S.,Kim, Yunjo,Hannon, James B.,Yang, Yang,Sadana, Devendra K.,Ross, Frances M.,Park, Hongsik,Kim, Jeehwan National Academy of Sciences 2017 PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF Vol.114 No.16

<P>Graphene epitaxy on the Si face of a SiC wafer offers monolayer graphene with unique crystal orientation at the wafer-scale. However, due to carrier scattering near vicinal steps and excess bilayer stripes, the size of electrically uniform domains is limited to the width of the terraces extending up to a few microns. Nevertheless, the origin of carrier scattering at the SiC vicinal steps has not been clarified so far. A layer-resolved graphene transfer (LRGT) technique enables exfoliation of the epitaxial graphene formed on SiC wafers and transfer to flat Si wafers, which prepares crystallographically single-crystalline monolayer graphene. Because the LRGT flattens the deformed graphene at the terrace edges and permits an access to the graphene formed at the side wall of vicinal steps, components that affect the mobility of graphene formed near the vicinal steps of SiC could be individually investigated. Here, we reveal that the graphene formed at the side walls of step edges is pristine, and scattering near the steps is mainly attributed by the deformation of graphene at step edges of vicinalized SiC while partially from stripes of bilayer graphene. This study suggests that the two-step LRGT can prepare electrically single-domain graphene at the wafer-scale by removing the major possible sources of electrical degradation.</P>

Interaction between Metal and Graphene: Dependence on the Layer Number of Graphene

Lee, Jisook,Novoselov, Konstantin S.,Shin, Hyeon Suk American Chemical Society 2011 ACS NANO Vol.5 No.1

<P>The interaction between graphene and metal was investigated by studying the G band splitting in surface-enhanced Raman scattering (SERS) spectra of single-, bi-, and trilayer graphene. The Ag deposition on graphene induced large enhancement of the Raman signal of graphene, indicating SERS of graphene. In particular, the G band was split into two distinct peaks in the SERS spectrum of graphene. The extent of the G band splitting was 13.0 cm<SUP>−1</SUP> for single-layer, 9.6 cm<SUP>−1</SUP> for bilayer, and 9.4 cm<SUP>−1</SUP> for trilayer graphene, whereas the G band in the SERS spectrum of a thick multilayer was not split. The average SERS enhancement factor of the G band was 24 for single-layer, 15 for bilayer, and 10 for trilayer graphene. These results indicate that there is a correlation between SERS enhancement factor and the extent of the G band splitting, and the strongest interaction occurs between Ag and single-layer graphene. Furthermore, the Ag deposition on graphene can induce doping of graphene. The intensity ratio of 2D and G bands (<I>I</I><SUB>2D</SUB>/<I>I</I><SUB>G</SUB>) decreased after Ag deposition on graphene, indicating doping of graphene. From changes in positions of G and 2D bands after the metal deposition on graphene, Ag deposition induced n-doping of graphene, whereas Au deposition induced p-doping.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2011/ancac3.2011.5.issue-1/nn103004c/production/images/medium/nn-2010-03004c_0005.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nn103004c'>ACS Electronic Supporting Info</A></P>

Dimensionality-dependent oxygen reduction activity on doped graphene: Is graphene a promising substrate for electrocatalysis?

Chung, Min Wook,Choi, Chang Hyuck,Lee, Seung Yong,Woo, Seong Ihl Elsevier 2015 Nano energy Vol.11 No.-

<P><B>Abstract</B></P> <P>Graphene, a two-dimensional layer framework of <I>sp</I> <SUP>2</SUP>-hybridized carbon, has attracted tremendous attentions as a promising material for oxygen reduction reactions (ORRs) due to its ideal uniqueness of high surface area and electrical conductivity. Contrary to the general belief, however, graphene catalysts have shown poor catalytic activities compared with those of other carbon-based catalysts. Herein, to understand the low ORR kinetics on the graphene catalysts, the dimensionality of graphene catalysts is sequentially tuned from sheets (2D) to ribbons (1D) and to dots (0D), and then the accompanying changes in terms of physical and electrochemical properties are investigated. In ultraviolet photoelectron spectroscopy, an increment in electropotential is measured as the dimensionality of the graphene catalysts decreases, of which the result infers the enhanced kinetics of the electron transfer from the graphene catalysts to O<SUB>2</SUB> (electropotential: 0D>1D>2D). However, ORR performance does not follow the order of electropotential, and the graphene ribbons show the best activity among the prepared graphene catalysts (ORR activity: 1D>0D>2D). Further electrochemical impedance spectroscopy studies demonstrate that ORR kinetics is primarily determined by charge transfer rates in the fabricated graphene electrodes, which are strongly related to the electrode configurations and thus also to the length-to-width ratios of the graphene catalysts. The graphene sheets and dots, of which the length-to-width ratios are almost 1, handily lay over each other, leading to an impedance of efficient charge transfers. This study suggests the importance of void channels in the fabricated graphene electrode, which have not previously been considered significantly as a factor for improving ORR activity on the graphene catalysts.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The dimensionality of graphene catalysts is sequentially tuned from sheets (2D) to ribbons (1D) and to dots (0D), and then the accompanying changes in terms of physical and electrochemical properties are investigated. </LI> <LI> The prepared graphene catalysts, having N-doped sites as active sites, revealed an increment of electropotential as the dimensionality decreased, but the catalytic activity did not perfectly follow the tendency. </LI> <LI> Electrochemical impedance spectroscopy studies demonstrate that ORR kinetics is primarily determined by charge transfer rates in the fabricated graphene electrodes. </LI> <LI> To achieve a superior ORR performance, the structural constitute for efficient charge accessibility as well increased <I>E</I> <SUB>P</SUB> may be preferentially considered in future design of graphene catalysts. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>