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Lee J.H.,Catholic University of Korea | Jung D.-Y.,Sungkyunkwan Advanced Institute of Nanotechnology
Chemical Communications | Year: 2012

A novel controlled molecular release based on highly oriented nanoplates of layered double hydroxide was fabricated on indium tin oxide substrates by electrophoretic deposition of exfoliated LDH nanosheets. The LDH particle coating exhibited a superior release performance of the order of hours. © 2012 The Royal Society of Chemistry. Source


Biswas C.,Sungkyunkwan Advanced Institute of Nanotechnology | Lee Y.H.,Sungkyunkwan Advanced Institute of Nanotechnology
Advanced Functional Materials | Year: 2011

Advances in semiconductor device during last few decades enable us to improve the electronic device performance by minimizing the device dimension. However, further development of these systems encounters scientific and technological limits and forces us to explore better alternatives. Low-dimensional carbon allotropes such as carbon nanotube and graphene exhibit superior electronic, optoelectronic, and mechanical properties compared to the conventional semiconductors. This Feature Article reviews the recent progresses of carbon nanotubes and graphene researches and compares their electronic properties and electric device performances. A particular focus is the comparison of the characteristics in transparent conducting films (transparency and sheet resistance) and field-effect transistors (FETs) (device types, ambipolarity, mobility, doping strategy, FET-performance, logic and memory operations). Finally, the performance of devices that combine graphene and carbon nanotubes is also highlighted. Graphene and CNT exhibit excellent electronic and optoelectronic properties. This Feature Article reviews the recent progresses of carbon nanotubes and graphene research and compares their electronic and optoelectronic properties and device performances, such as transparent conducting films (transparency and sheet resistance) and field-effect transistors (FETs) (device types, ambipolarity, mobility, doping strategy, FET-performance, logic and memory operations), in detail. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source


Ghosh A.,Sungkyunkwan Advanced Institute of Nanotechnology | Lee Y.H.,Sungkyunkwan Advanced Institute of Nanotechnology
ChemSusChem | Year: 2012

Supercapacitors are one of the key devices for energy-storage applications. They have energy densities much higher than those of conventional capacitors and possess much better power delivery capabilities than batteries. This makes them unique devices that can outperform both batteries and conventional capacitors under special circumstances. Nanocarbons are the main electrode materials for supercapacitors. Abundant sources of nanocarbons and facile processes of modification have led to the fabrication of cheap electrodes. In this review, we focus on the capacitance performance of highly porous activated carbons and attempt to determine the role of different pores. Elaborate discussions are presented on individual contributions from micro- and mesopores and their mutual dependence. This article also presents a comparative performance report for both random and ordered porous nanocarbons. Novel carbon materials, such as carbon nanotubes and graphene, and their contributions in this context are discussed. We summarize key techniques for the functionalization of nanocarbons and their pseudocapacitive charge-storage mechanisms. Nanocarbon composites with redox-active transition-metal oxides and conducting polymers are highlighted along with their impact as electrode materials. Ideal composite structures are highlighted and an attempt is made to determine an ideal future electrode structure for capacitors with high energy and power density. Super power! The capacitance performance of highly porous activated carbons is described and the elucidation of the role of different pores is attempted (see picture). Elaborate discussions are also presented on the individual contributions from micro- and mesopores and their mutual dependence. An ideal electrode can be realized when a charge transportation pathway is obtained through the mesopores that channel ions to the micropores available on the surface. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source


Yu W.J.,Sungkyunkwan Advanced Institute of Nanotechnology | Lee Y.H.,Sungkyunkwan Advanced Institute of Nanotechnology
ChemSusChem | Year: 2011

Carbon nanotubes exhibit remarkable mechanical and electronic properties and are, therefore, being regarded as a new functional material for next generation electronics. Nevertheless, several obstacles still exist for an application in industry. The control of carriers in carbon nanotubes is of critical importance prior to an industrial application in transistors. As carbon nanotubes exhibit p-type behavior under ambient conditions, it is difficult to convert them from a p- to an n-type transistor. Also, doping control is a critical issue for applying traditional CMOS technology. Here, we discuss various approaches for preparing operating carbon nanotube transistors: i)impurity doping that employs conventional and interstitial insertion of group III or V materials, ii)chemical doping that induces charge transfer between chemicals and CNTs, iii)carrier control that utilizes the work function difference between metal and CNTs, iv)electrostatic doping that controls the carrier type by using a gate bias, and v)ambipolarity that does not use chemical doping. Advantages and drawbacks of these approaches will be discussed extensively in the text. Have it the carriers way: We discuss various approaches for the doping of operating carbon nanotube transistors: i)impurity doping, ii)chemical doping, iii)control of metal work function, iv) electrostatic doping, and v)ambipolarity. Advantages and drawbacks of these approaches are discussed extensively in the text. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source


Ghosh A.,Sungkyunkwan Advanced Institute of Nanotechnology | Ra E.J.,Sungkyunkwan Advanced Institute of Nanotechnology | Jin M.,Sungkyunkwan Advanced Institute of Nanotechnology | Jeong H.-K.,Daegu University | And 3 more authors.
Advanced Functional Materials | Year: 2011

An ultrathin V2O5 layer was electrodeposited by cyclic voltammetry on a self-standing carbon-nanofiber paper, which was obtained by stabilization and heat-treatment of an electrospun polyacrylonitrile (PAN)-based nanofiber paper. A very-high capacitance of 1308 F g-1 was obtained in a 2 M KCl electrolyte when the contribution from the 3 nm thick vanadium oxide was considered alone, contributing to over 90% of the total capacitance (214 F g-1) despite the low weight percentage of the V2O5 (15 wt%). The high capacitance of the V 2O5 is attributed to the large external surface area of the carbon nanofibers and the maximum number of active sites for the redox reaction of the ultrathin V2O5 layer. This ultrathin layer is almost completely accessible to the electrolyte and thus results in maximum utilization of the oxide (i.e., minimization of dead volume). This hypothesis was experimentally evaluated by testing V2O5 layers of different thicknesses. An ultrathin film of V2O5 is electrodeposited on the surface of carbon nanofibers to obtain a high surface area with an improved electrode conductivity. This provides a high pseudocapacitance of 1308 F g-1 with respect to the effective contribution from the deposited oxide layer. The schematic shows the distribution of V2O5 throughout the nanofiber. The graph shows the dependence of the specific capacitance on the deposited amount of V2O5. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

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