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Van Nang, Lam,Kim, Dong-Ok,Trung, Tran Nam,Arepalli, Vinaya Kumar,Kim, Eui-Tae Korean Society of Microscopy 2017 Applied microscopy Vol.47 No.1
High-quality graphene was synthesized on Cu foil and $Fe_2O_3$ film using $CH_4$ gas via inductively-coupled plasma chemical vapor deposition (ICPCVD). The graphene film was formed on $Fe_2O_3$ at a temperature as low as $700^{\circ}C$. Few-layer graphene was formed within a few seconds and 1 min on Cu and $Fe_2O_3$, respectively. With increasing growth time and plasma power, the graphene thickness was controllably reduced and ultimately self-limited to a single layer. Moreover, the crystal quality of graphene was constantly enhanced. Understanding the ICPCVD growth kinetics that are critically affected by ICP is useful for the controllable synthesis of high-quality graphene on metals and oxides for various electronic applications.
Lam, Do Van,Gong, Tao,Won, Sejeong,Kim, Jae-Hyun,Lee, Hak-Joo,Lee, Changgu,Lee, Seung-Mo The Royal Society of Chemistry 2015 Chemical communications Vol.51 No.13
<P>A small amount of Zn impregnated by ALD triggered enhancement of the mechanical as well as electrical properties of the graphene oxide (GO) membrane. In addition, the Zn-impregnated membranes selectively separated diverse organic vapors while maintaining high water permeability.</P> <P>Graphic Abstract</P><P>A robust and conductive graphene oxide membrane with selective separation properties can be easily prepared by the vapor phase metal-impregnation effect provided by an atomic layer deposition process. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c4cc08896d'> </P>
Region-wide synchrony and traveling waves of dengue across eight countries in Southeast Asia
van Panhuis, Willem G.,Choisy, Marc,Xiong, Xin,Chok, Nian Shong,Akarasewi, Pasakorn,Iamsirithaworn, Sopon,Lam, Sai K.,Chong, Chee K.,Lam, Fook C.,Phommasak, Bounlay,Vongphrachanh, Phengta,Bouaphanh, K National Academy of Sciences 2015 PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF Vol.112 No.42
<P><B>Significance</B></P><P>Persons living in the tropics and subtropics are at risk for dengue fever and dengue hemorrhagic fever, and large epidemics occur unexpectedly that can overburden healthcare systems. The spatial and temporal dynamics of dengue transmission are poorly understood, limiting disease control efforts. We compiled a large-scale dataset and analyzed continental-scale patterns of dengue in Southeast Asia. Our analysis shows that periods of elevated temperatures can drive the occurrence of synchronous dengue epidemics across the region. This multicountry collaborative study improved insight that may lead to improved prediction of dengue transmission patterns and more effective disease surveillance and control efforts.</P><P>Dengue is a mosquito-transmitted virus infection that causes epidemics of febrile illness and hemorrhagic fever across the tropics and subtropics worldwide. Annual epidemics are commonly observed, but there is substantial spatiotemporal heterogeneity in intensity. A better understanding of this heterogeneity in dengue transmission could lead to improved epidemic prediction and disease control. Time series decomposition methods enable the isolation and study of temporal epidemic dynamics with a specific periodicity (e.g., annual cycles related to climatic drivers and multiannual cycles caused by dynamics in population immunity). We collected and analyzed up to 18 y of monthly dengue surveillance reports on a total of 3.5 million reported dengue cases from 273 provinces in eight countries in Southeast Asia, covering ∼10<SUP>7</SUP> km<SUP>2</SUP>. We detected strong patterns of synchronous dengue transmission across the entire region, most markedly during a period of high incidence in 1997–1998, which was followed by a period of extremely low incidence in 2001–2002. This synchrony in dengue incidence coincided with elevated temperatures throughout the region in 1997–1998 and the strongest El NiÉééÉééééño episode of the century. Multiannual dengue cycles (2–5 y) were highly coherent with the Oceanic NiÉééÉééééñño Index, and synchrony of these cycles increased with temperature. We also detected localized traveling waves of multiannual dengue epidemic cycles in Thailand, Laos, and the Philippines that were dependent on temperature. This study reveals forcing mechanisms that drive synchronization of dengue epidemics on a continental scale across Southeast Asia.</P>
Calligraphic ink enabling washable conductive textile electrodes for supercapacitors
Van Lam, Do,Jo, Kyungmin,Kim, Chang-Hyun,Won, Sejeong,Hwangbo, Yun,Kim, Jae-Hyun,Lee, Hak-Joo,Lee, Seung-Mo The Royal Society of Chemistry 2016 Journal of Materials Chemistry A Vol.4 No.11
<P>The appeal of wearable devices for future electronics has stimulated scientists to unearth novel materials to meet the technological demands of modern society. However, the washability issue still remains a significant challenge. We showed that calligraphic ink, used as a writing tool in East Asian areas for thousands of years, could present a route to translate washable and wearable electrodes into a reality. We prepared washable electrodes by simply coating textiles with the ink. It was observed that the electrical and mechanical performance of the fabricated electrodes remained nearly unchanged even after 10 vigorous laundering cycles using a regular washing machine. In addition, supercapacitors made with those electrodes exhibited excellent cycling stability and high energy/power density. These results establish that everyday calligraphic ink is a simple yet powerful resource for fashioning normal textiles into washable and wearable electrodes for supercapacitors.</P>
Activated Carbon Textile <i>via</i> Chemistry of Metal Extraction for Supercapacitors
Lam, Do Van,Jo, Kyungmin,Kim, Chang-Hyun,Kim, Jae-Hyun,Lee, Hak-Joo,Lee, Seung-Mo American Chemical Society 2016 ACS NANO Vol.10 No.12
<P>Carbothermic reduction in the chemistry of metal extraction (MO (s) + C(s) -> M(s) + CO(g)) using carbon as a sacrificial agent has been used to smelt metals from diverse oxide ores since ancient times. Here, we paid attention to another aspect of the carbothermic reduction to prepare an activated carbon textile for high-rate-performance supercapacitors. On the basis of thermodynamic reducibility of metal oxides reported by Ellingham, we employed not carbon, but metal oxide as a sacrificial agent in order to prepare an activated carbon textile. We conformally coated ZnO on a bare cotton textile using atomic layer deposition, followed by pyrolysis at high temperature (C(s) + ZnO(s) -> C'(s) + Zn(g) + CO(g)). We figured out that it leads to concurrent carbonization and activation in a chemical as well as mechanical way. Particularly, the combined effects of mechanical buckling and fracture that occurred between ZnO and cotton turned out to play an important role in carbonizing and activating the cotton textile, thereby significantly increasing surface area (nearly 10 times) compared With the cotton textile prepared without ZnO. The carbon textiles prepared by carbothermic reduction showed impressive combination properties of high power and energy densities (over 20-fold increase) together with high cyclic stability.</P>
Healing defective CVD-graphene through vapor phase treatment
Van Lam, Do,Kim, Sang-Min,Cho, Youngji,Kim, Jae-Hyun,Lee, Hak-Joo,Yang, Jun-Mo,Lee, Seung-Mo The Royal Society of Chemistry 2014 Nanoscale Vol.6 No.11
<P>Structural defects present on chemical vapor deposition (CVD)-graphene have usually originated from the growth stage and transfer process. They limit the electronic transport properties of graphene and degrade performance of related devices. Here we report that these inherent atomic defects could be selectively healed by a simple vapor phase treatment performed in equipment conventionally used for atomic layer deposition (ALD). The unique chemistry of Al2O3ALD facilitated selective depositions of AlxOycompounds on the defects, which could be readily probed and visualized using AFM imaging. The healing agent, AlxOy, was observed to bind tightly to the defects and lead to doping of the CVD-graphene, which was reflected in the noticeable improvement in electrical sheet resistance. In contrast with the chemically doped graphene, the ALD-treated graphenes revealed notable long-term stability under environmental conditions. Our approach promises selective healing of defects present in most materials and possibly ensures considerable improvement in electrical and mechanical properties. ALD with a broad spectrum of material selection could be a versatile tool for upgrading properties of materials.</P>