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Kim, J.,Kim, J.Y.,Pham-Cong, D.,Jeong, S.Y.,Chang, J.,Choi, J.H.,Braun, P.V.,Cho, C.R. Pergamon Press 2016 ELECTROCHIMICA ACTA Vol.199 No.-
The as-electrospun polymeric lithium titanate nanofibers are crystallized into Li<SUB>4</SUB>Ti<SUB>5</SUB>O<SUB>12</SUB> nanofibers (denoted as LTO NFs) via post-annealing. The LTO NFs are coated with a carbon layer using a glucose polymer via hydrothermal synthesis. The GO layer electrostatically attracts to the positively charged LTO NFs, resulting in the uniform wrapping of individual LTO NFs without aggregation. The introduction of uniformly coated carbon and GO double layers led to an enhanced rate capability (110mAhg<SUP>-1</SUP>at 20C) and over two orders of magnitude higher diffusion coefficient (D<SUB>Li</SUB>=~1.04x10<SUP>-11</SUP>cm<SUP>2</SUP>s<SUP>-1</SUP>) of the tailored LTO NFs with carbon and GO network compared with those of the pristine LTO NFs. Extended testing for over 100 cycles demonstrates the cyclic stability and Coulombic efficiency of over 99% of this system. These results indicate that the interconnection and networks of LTO NFs through carbon coating and the individual GO wrapping, which facilitates the lithium ion and electron transportation, may show excellent electrochemical performance.
Pham, D C,Na, K,Piao, S,Cho, I-J,Jhang, K-Y,Yoon, E-S IOP Pub 2011 Nanotechnology Vol.22 No.39
<P>A large number of silicon (Si) patterns consisting of nanopillars of varying diameter and pitch have been fabricated and further coated with diamond-like carbon (DLC) and perfluoropolyether (Z-DOL) films. The wetting behavior and nano-adhesion/friction of the patterns are investigated experimentally in relation to the nanostructures and the hydrophobicity of the materials. Measurements of water contact angle illustrate that the patterning-enhanced wettability of the Si flat surface, along with two distinct wettings which are in good agreement with the Wenzel and hemi-wicking states, depended on the value of the pitch-over-diameter ratio. In the case of the coated patterns, three wetting states are observed: the Cassie–Baxter, the Wenzel, and a transition from the Cassie–Baxter into the Wenzel, which varies with regard to the hydrophobic properties of the DLC and Z-DOL. In terms of tribological properties, it is demonstrated that a combination of the nanopatterns and the films is effective in reducing adhesive and frictional forces. In addition, the pitch and diameter of the patterns are found to significantly influence their adhesion/friction behaviors. </P>
D. Pham-Cong,K. Ahn,홍석원,정세영,J.H. Choi,C.H. Doh,J. S. Jin,정의덕,조채용 한국물리학회 2014 Current Applied Physics Vol.14 No.2
In this study, vanadium pentoxide (V2O5) nanowires (NWs) with a diameter of 100e200 nm and a length of up to several micrometers as cathode for lithium ion batteries are synthesize using an electrospinning method. The reduced graphene oxide (rGO) and V2O5 NWs (GVO) composites are form by wet mixing the electrospun V2O5 NWs and rGO. Surface morphologies, microstructure and elemental mapping, and chemical bonding states of the composites are characterize. The initial and 60 cycles discharge capacities of GVO composite composed of 1 wt% rGO show up to 225 mAh g1 and 125 mAh g1, even higher than pure V2O5 NWs, when the lithium ion battery cycled between 2.0 and 4.0 V with a rate of 0.2 C, because of highly conductive rGO. The GVO composite could be promising as a high performance cathode for lithium ion batteries.
Pham-Cong, D.,Ahn, K.,Hong, S.W.,Jeong, S.Y.,Choi, J.H.,Doh, C.H.,Jin, J.S.,Jeong, E.D.,Cho, C.R. Elsevier 2014 Current Applied Physics Vol.14 No.2
In this study, vanadium pentoxide (V<SUB>2</SUB>O<SUB>5</SUB>) nanowires (NWs) with a diameter of 100-200 nm and a length of up to several micrometers as cathode for lithium ion batteries are synthesize using an electrospinning method. The reduced graphene oxide (rGO) and V<SUB>2</SUB>O<SUB>5</SUB> NWs (GVO) composites are form by wet mixing the electrospun V<SUB>2</SUB>O<SUB>5</SUB> NWs and rGO. Surface morphologies, microstructure and elemental mapping, and chemical bonding states of the composites are characterize. The initial and 60 cycles discharge capacities of GVO composite composed of 1 wt% rGO show up to 225 mAh g<SUP>-1</SUP> and 125 mAh g<SUP>-1</SUP>, even higher than pure V<SUB>2</SUB>O<SUB>5</SUB> NWs, when the lithium ion battery cycled between 2.0 and 4.0 V with a rate of 0.2 C, because of highly conductive rGO. The GVO composite could be promising as a high performance cathode for lithium ion batteries.
Pham, T.D.,Lee, B.K.,Lee, C.H. Elsevier 2016 Applied Catalysis B Vol.182 No.-
<P>In this study, we used Cu(NO3)(2) as a precursor of Cu dopants, which defected the TiO2 lattice and copper oxides, which in turn distributed on the TiO2 surface to enhance the photocatalytic oxidation activity of the TiO2. Porous polyurethane (PU) was used as a substrate for the immobilization of the enhanced TiO2, to increase the adsorption capacity of the photocatalyst. Therefore, the synthesized Cu-TiO2, immobilized on PU (Cu-TiO2/PU) materials, exhibited both improved photocatalytic oxidation and adsorption activity for the effective removal of benzene from indoor aerosols. The benzene removal, by Cu-TiO2/PU under visible light conditions, was due to the combination of improved adsorption and photocatalytic oxidation. The removal of benzene from the aerosol was strongly dependent on humid environmental conditions, and the amount of Cu in the Cu/TiO2. Optimal humidity conditions and the amount of Cu in the Cu/TiO2, for the photocatalytic oxidation of benzene in the aerosol by the Cu-TiO2/PU photocatalyst, were 60% RH and 6 wt%, respectively. Under visible light irradiation, and at a relative humidity of 60% RH, the 6% Cu-TiO2/PU material removed 86% of the benzene in 100 ppm inlet gas, while 91% of the removed amount was mineralized into CO2 and H2O. (C) 2015 Elsevier B.V. All rights reserved.</P>
Multiferroic CoFe2O4-Pb(Zr,Ti)O3 Nanostructures
Pham Duc Thang,Mai T. N. Pham,G. Rijnders,D. H. A. Blank,Nguyen Huu Duc,J. C. P. Klaasse,E. Bruck 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.52 No.5
Multiferroic CoFe₂O₄-Pb(Zr,Ti)O₃ films were prepared on TiO₂-terminated (001) Nb-doped SrTiO3 substrates by using pulsed laser deposition (PLD). The lms were epitaxial and exhibited a large in-plane magnetic anisotropy and good ferroelectric properties. A decrease in the magneti- zation around the ferroelectric Curie temperature indicated magnetoelectric coupling between the magnetostrictive and the piezoelectric phases, which allows interconversion of energy stored in the electric and the magnetic elds and provides great potential for applications as next-generation multi-functional devices. Multiferroic CoFe₂O₄-Pb(Zr,Ti)O₃ films were prepared on TiO₂-terminated (001) Nb-doped SrTiO3 substrates by using pulsed laser deposition (PLD). The lms were epitaxial and exhibited a large in-plane magnetic anisotropy and good ferroelectric properties. A decrease in the magneti- zation around the ferroelectric Curie temperature indicated magnetoelectric coupling between the magnetostrictive and the piezoelectric phases, which allows interconversion of energy stored in the electric and the magnetic elds and provides great potential for applications as next-generation multi-functional devices.
Search-based Sentiment and Stock Market Reactions: An Empirical Evidence in Vietnam
Du D. Nguyen,Minh C. Pham 한국유통과학회 2018 The Journal of Asian Finance, Economics and Busine Vol.5 No.4
The paper aims to examine relationships between search-based sentiment and stock market reactions in Vietnam. This study constructs an internet search-based measure of sentiment and examines its relationship with Vietnamese stock market returns. The sentiment index is derived from Google Trends’ Search Volume Index of financial and economic terms that Vietnamese searched from January 2011 to June 2018. Consistent with prediction from sentiment theories, the study documents significant short-term reversals across three major stock indices. The difference from previous literature is that Vietnam stock market absorbs the contemporaneous decline slower while the subsequent rebound happens within a day. The results of the study suggest that the sentiment-induced effect is mainly driven by pessimism. On the other hand, optimistic investors seem to delay in taking their investment action until the market corrects. The study proposes a unified explanation for our findings based on the overreaction hypothesis of the bearish group and the strategic delay of the optimistic group. The findings of the study contribute to the behavioral finance strand that studies the role of sentiment in emerging financial markets, where noise traders and limits to arbitrage are more obvious. They also encourage the continuous application of search data to explore other investor behaviors in securities markets.