Smart Contact Lenses with Graphene Coating for Electromagnetic Interference Shielding and Dehydration Protection

Lee, Sangkyu,Jo, Insu,Kang, Sangmin,Jang, Bongchul,Moon, Joonhee,Park, Jong Bo,Lee, Soochang,Rho, Sichul,Kim, Youngsoo,Hong, Byung Hee American Chemical Society 2017 ACS NANO Vol.11 No.6

<P>Recently, smart contact lenses with electronic circuits have been proposed for various sensor and display applications where the use of flexible and biologically stable electrode materials is essential. Graphene is an atomically thin carbon material with a two-dimensional hexagonal lattice that shows outstanding electrical and mechanical properties as well as excellent biocompatibility. In addition, graphene is capable of protecting eyes from electromagnectic (EM) waves that may cause eye diseases such as cataracts. Here, we report a graphene-based highly conducting contact lens platform that reduces the exposure to EM waves and dehydration. The sheet resistance of the graphene on the contact lens is as low as 593 Omega/sq (+/- 9.3%), which persists in an wet environment. The EM wave shielding function of the graphene-coated contact lens was tested on egg whites exposed to strong EM waves inside a microwave oven. The results show that the EM energy is absorbed by graphene and dissipated in the form of thermal radiation so that the damage on the egg whites can be minimized. We also demonstrated the enhanced dehydration protection effect of the graphene-coated lens by monitoring the change in water evaporation rate from the vial capped with the contact lens. Thus, we believe that the graphene-coated contact lens would provide a healthcare and bionic platform for wearable technologies in the future.</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>

Synthesis of graphene ribbons using selective chemical vapor deposition

An, Hyosub,Lee, Wan-Gyu,Jung, Jongwan Elsevier 2012 CURRENT APPLIED PHYSICS Vol.12 No.4

<P><B>Abstract</B></P><P>A new method for implementing graphene ribbons using selective graphene growth on metal-sidewall by chemical vapor deposition has been proposed. In this method, Ni catalyst is pre-patterned before chemical vapor deposition, and graphene film is selectively grown on the sidewall of the nickel for graphene ribbons. The graphene ribbons were confirmed by TEM image and Raman spectroscopy, and the fabricated graphene ribbon transistors showed well gate-modulated output characteristics. We believe this sidewall-graphene could be useful for applications such as graphene sensors which require high surface area of graphene.</P> <P><B>Highlights</B></P><P>► We propose a new method for implementing graphene ribbons. ► The method uses selective graphene growth on the sidewall of catalyst. ► The graphene ribbons were confirmed by TEM and Raman spectroscopy. ► Finally, the fabricated graphene transistors showed good gate-modulated output characteristics.</P>

Reduction of graphene oxide by resveratrol: a novel and simple biological method for the synthesis of an effective anticancer nanotherapeutic molecule

Gurunathan, Sangiliyandi,Han, Jae Woong,Kim, Eun Su,Park, Jung Hyun,Kim, Jin-Hoi Dove Medical Press 2015 INTERNATIONAL JOURNAL OF NANOMEDICINE Vol.10 No.-

<P><B>Objective</B></P><P>Graphene represents a monolayer or a few layers of sp2-bonded carbon atoms with a honeycomb lattice structure. Unique physical, chemical, and biological properties of graphene have attracted great interest in various fields including electronics, energy, material industry, and medicine, where it is used for tissue engineering and scaffolding, drug delivery, and as an antibacterial and anticancer agent. However, graphene cytotoxicity for ovarian cancer cells is still not fully investigated. The objective of this study was to synthesize graphene using a natural polyphenol compound resveratrol and to investigate its toxicity for ovarian cancer cells.</P><P><B>Methods</B></P><P>The successful reduction of graphene oxide (GO) to graphene was confirmed by UV-vis and Fourier transform infrared spectroscopy. Dynamic light scattering and scanning electron microscopy were employed to evaluate particle size and surface morphology of GO and resveratrol-reduced GO (RES-rGO). Raman spectroscopy was used to determine the removal of oxygen-containing functional groups from GO surface and to ensure the formation of graphene. We also performed a comprehensive analysis of GO and RES-rGO cytotoxicity by examining the morphology, viability, membrane integrity, activation of caspase-3, apoptosis, and alkaline phosphatase activity of ovarian cancer cells.</P><P><B>Results</B></P><P>The results also show that resveratrol effectively reduced GO to graphene and the properties of RES-rGO nanosheets were comparable to those of chemically reduced graphene. Biological experiments showed that GO and RES-rGO caused a dose-dependent membrane leakage and oxidative stress in cancer cells, and reduced their viability via apoptosis confirmed by the upregulation of apoptosis executioner caspase-3.</P><P><B>Conclusion</B></P><P>Our data demonstrate a single, simple green approach for the synthesis of highly water-dispersible functionalized graphene nanosheets, suggesting a possibility of replacing toxic hydrazine by a natural and safe phenolic compound resveratrol, which has similar efficacy in the reduction of GO to rGO. Resveratrol-based GO reduction would facilitate large-scale production of graphene-based materials for the emerging graphene-based technologies and biomedical applications.</P>

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>

Interface engineering for high performance graphene electronic devices

정대율,Yang Sang Yoon,Park Hamin,Shin Woo Cheol,오중건,Cho Byung Jin,최성열 나노기술연구협의회 2015 Nano Convergence Vol.2 No.11

A decade after the discovery of graphene flakes, exfoliated from graphite, we have now secured large scale and high quality graphene film growth technology via a chemical vapor deposition (CVD) method. With the establishment of mass production of graphene using CVD, practical applications of graphene to electronic devices have gained an enormous amount of attention. However, several issues arise from the interfaces of graphene systems, such as damage/unintentional doping of graphene by the transfer process, the substrate effects on graphene, and poor dielectric formation on graphene due to its inert features, which result in degradation of both electrical performance and reliability in actual devices. The present paper provides a comprehensive review of the recent approaches to resolve these issues by interface engineering of graphene for high performance electronic devices. We deal with each interface that is encountered during the fabrication steps of graphene devices, from the graphene/metal growth substrate to graphene/high-k dielectrics, including the intermediate graphene/target substrate.

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.

Fabrication of diverse graphene-conducting polymer composites (graphene-polythiophene, graphene-polyaniline, and graphene-polypyrrole) by facilitating graphene oxide as broad initiator

김민규,장정식 한국공업화학회 2015 한국공업화학회 연구논문 초록집 Vol.2015 No.1

Diverse graphene-conducting polymer (CP) composites (graphene-poly-thiophene, graphene-polyaniline, and graphene-polypyrrole) have been simply and rapidly prepared by facilitating graphene oxide as broad initiator. The UV-vis, SEM, and TEM analysis showed that the graphene-CP composites have successfully been produced. In addition with these, the series of FT-IR analysis were also conducted to investigate how the graphene oxide initiated the polymerizations. Given IR results, plausible polymerization mechanisms were proposed.

A Facile Route for Patterned Growth of Metal–Insulator Carbon Lateral Junction through One-Pot Synthesis

Park, Beomjin,Park, Jaesung,Son, Jin Gyeong,Kim, Yong-Jin,Yu, Seong Uk,Park, Hyo Ju,Chae, Dong-Hun,Byun, Jinseok,Jeon, Gumhye,Huh, Sung,Lee, Seoung-Ki,Mishchenko, Artem,Hyun, Seung,Lee, Tae Geol,Han, American Chemical Society 2015 ACS NANO Vol.9 No.8

<P>Precise graphene patterning is of critical importance for tailor-made and sophisticated two-dimensional nanoelectronic and optical devices. However, graphene-based heterostructures have been grown by delicate multistep chemical vapor deposition methods, limiting preparation of versatile heterostructures. Here, we report one-pot synthesis of graphene/amorphous carbon (a-C) heterostructures from a solid source of polystyrene <I>via</I> selective photo-cross-linking process. Graphene is successfully grown from neat polystyrene regions, while patterned cross-linked polystyrene regions turn into a-C because of a large difference in their thermal stability. Since the electrical resistance of a-C is at least 2 orders of magnitude higher than that for graphene, the charge transport in graphene/a-C heterostructure occurs through the graphene region. Measurement of the quantum Hall effect in graphene/a-C lateral heterostructures clearly confirms the reliable quality of graphene and well-defined graphene/a-C interface. The direct synthesis of patterned graphene from polymer pattern could be further exploited to prepare versatile heterostructures.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2015/ancac3.2015.9.issue-8/acsnano.5b03037/production/images/medium/nn-2015-03037u_0006.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nn5b03037'>ACS Electronic Supporting Info</A></P>

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>