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van der Waals Layered Materials: Opportunities and Challenges
Duong, Dinh Loc,Yun, Seok Joon,Lee, Young Hee American Chemical Society 2017 ACS NANO Vol.11 No.12
<P>Since graphene became available by a scotch tape technique, a vast class of two-dimensional (2D) van der Waals (vdW) layered materials has been researched intensively. What is more intriguing is that the well-known physics and chemistry of three-dimensional (3D) bulk materials are often irrelevant, revealing exotic phenomena in 2D vdW materials. By further constructing heterostructures of these materials in the planar and vertical directions, which can be easily achieved <I>via</I> simple exfoliation techniques, numerous quantum mechanical devices have been demonstrated for fundamental research and technological applications. It is, therefore, necessary to review the special features in 2D vdW materials and to discuss the remaining issues and challenges. Here, we review the vdW materials library, technology relevance, and specialties of vdW materials covering the vdW interaction, strong Coulomb interaction, layer dependence, dielectric screening engineering, work function modulation, phase engineering, heterostructures, stability, growth issues, and the remaining challenges.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2017/ancac3.2017.11.issue-12/acsnano.7b07436/production/images/medium/nn-2017-074362_0021.gif'></P>
Duong, Dinh Loc,Lee, Il Ha,Kim, Ki Kang,Kong, Jing,Lee, Seung Mi,Lee, Young Hee American Chemical Society 2010 ACS NANO Vol.4 No.9
<P>The mechanism of doping carbon nanotubes (CNTs) with a salt solution was investigated using the density functional theory. We propose that the anion−CNT complex is a key component in doping CNTs. Although the cations play an important role in ionizing CNTs as an intermediate precursor, the ionized CNTs are neutralized further by forming a stable anion−CNT complex as a final reactant. The anion−CNT bond has a strong ionic bonding character and clearly shows p-type behavior by shifting the Fermi level toward the valence band. The midgap state is introduced by the strong binding of carbon and anion atoms. These localized charged anion sites are highly hygroscopic and induce the adsorption of water molecules. This behavior provides a new possibility for using anion-functionalized CNTs as humidity sensors.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2010/ancac3.2010.4.issue-9/nn1011489/production/images/medium/nn-2010-011489_0006.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nn1011489'>ACS Electronic Supporting Info</A></P>
Breaking AB stacking order in graphite oxide: <i>ab initio</i> approach
Loc Duong, Dinh,Kim, Gunn,Jeong, Hae-Kyung,Hee Lee, Young Royal Society of Chemistry 2010 Physical chemistry chemical physics Vol.12 No.7
<P>Different bulk structures of graphite oxide were systematically investigated using density functional theory (DFT). Our model consisted of a hexagonal in-plane structure of graphene with hydroxyl and epoxide groups, and different oxidation levels and water content. The graphitic AB stacking order was stable in anhydrous graphite oxide, independent of oxidation levels. The hydrogen bonding interaction of layers became weaker as the oxidation level increased to the saturation limit. When water molecules were present in highly oxidized graphite oxide, the AB stacking order was broken due to entropic disorder. The interlayer distances increased with the oxidation level: the interlayer distance was 5.1 Å for low oxidation graphite oxide and 5.8 Å for high oxidation graphite oxide. The calculated interlayer distance of hydrated graphite oxide was 7.3 Å, which is in excellent agreement with experimental observations.</P> <P>Graphic Abstract</P><P>The AB stacking order is no longer maintained in hydrated high oxidation graphite oxide because of weak interlayer interaction and entropic disorder. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=b919683h'> </P>
Probing graphene grain boundaries with optical microscopy
Duong, Dinh Loc,Han, Gang Hee,Lee, Seung Mi,Gunes, Fethullah,Kim, Eun Sung,Kim, Sung Tae,Kim, Heetae,Ta, Quang Huy,So, Kang Pyo,Yoon, Seok Jun,Chae, Seung Jin,Jo, Young Woo,Park, Min Ho,Chae, Sang Hoo Nature Publishing Group, a division of Macmillan P 2012 Nature Vol.490 No.7419
Grain boundaries in graphene are formed by the joining of islands during the initial growth stage, and these boundaries govern transport properties and related device performance. Although information on the atomic rearrangement at graphene grain boundaries can be obtained using transmission electron microscopy and scanning tunnelling microscopy, large-scale information regarding the distribution of graphene grain boundaries is not easily accessible. Here we use optical microscopy to observe the grain boundaries of large-area graphene (grown on copper foil) directly, without transfer of the graphene. This imaging technique was realized by selectively oxidizing the underlying copper foil through graphene grain boundaries functionalized with O and OH radicals generated by ultraviolet irradiation under moisture-rich ambient conditions: selective diffusion of oxygen radicals through OH-functionalized defect sites was demonstrated by density functional calculations. The sheet resistance of large-area graphene decreased as the graphene grain sizes increased, but no strong correlation with the grain size of the copper was revealed, in contrast to a previous report. Furthermore, the influence of graphene grain boundaries on crack propagation (initialized by bending) and termination was clearly visualized using our technique. Our approach can be used as a simple protocol for evaluating the grain boundaries of other two-dimensional layered structures, such as boron nitride and exfoliated clays.
Oxidize Graphene by UV-Ozone Treatment in Vacuum Chamber
Dinh, S. Thach,Pham, T. H. Nhung,Nguyen, T. T. Hien,Dinh, N. T. Nghia,Vu, V. Quang,Hoang, T. K. Dung,Duong, D. Loc American Scientific Publishers 2016 Journal of nanoscience and nanotechnology Vol.16 No.8
<P>As changing graphene properties is vital to promote it as electronic device, we developed graphene modified method with epoxy group by two simple methods: ultraviolet irradiation with various partial oxygen pressures and ultraviolet irradiation under rich oxygen condition with various temperatures. By Hall measurement, the electric mobility in graphene was decreased with increasing temperature during UV-ozone treatment at 50 degrees C, 80 degrees C, 100 degrees C and 120 degrees C. At low partial oxygen pressure (less than 160 Torr) the oxidation degree is not significant. Additionally, Raman spectroscopy showed the disrupted pi-pi structure in graphene. Based on the above identification we supposed that epoxy group might establish on graphene surface.</P>
Yao, Fei,Duong, Dinh Loc,Lim, Seong Chu,Yang, Seung Bum,Hwang, Ha Ryong,Yu, Woo Jong,Lee, Il Ha,Gü,neş,, Fethullah,Lee, Young Hee Royal Society of Chemistry 2011 Journal of materials chemistry Vol.21 No.12
<P>In spite of the technical importance of detecting environmental SO<SUB><I>x</I></SUB> and NO<SUB><I>x</I></SUB> gases, a selective detection has not been realized because of their similar chemical properties. In this report, adsorption and desorption of SO<SUB>2</SUB> and NO<SUB>2</SUB> gas on carbon nanotubes are investigated in terms of different humidity levels at room temperature. A random-network single walled carbon nanotube (SWCNT) resistor is constructed by a dip-pen method using a SWCNT/dichloroethane (DCE) solution. In the case of SO<SUB>2</SUB> gas adsorption, the resistance increases at high humidity level (92%) and shows no obvious change at low humidity levels. On the other hand, in the case of NO<SUB>2</SUB> gas adsorption, the resistance always decreases independent of moisture levels. Our density functional theory (DFT) calculations show that this selective behavior originates from cooperative charge compensation between the SO<SUB>2</SUB>–<I>n</I>H<SUB>2</SUB>O complex and the p-type CNT resistor. The change of response time and recovery time with different moisture levels is further investigated. This humidity-assisted gas reaction provides a simple route to detect these two gases selectively.</P> <P>Graphic Abstract</P><P>Selective detection of SO<SUB>2</SUB> and NO<SUB>2</SUB> gas has been successfully realized on carbon nanotubes by introducing humidity in this study. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c0jm03227a'> </P>
임성주,윤정현,DINH LOC DUONG,조영우,김태형,김수민,황하룡,이영희 한국물리학회 2015 Current Applied Physics Vol.15 No.3
Semiconducting single-walled carbon nanotubes (s-SWCNTs) with lower absorption energy of NO2 gas exhibited higher sensitivity than metallic SWCNTs. The result originated from quantum capacitance of s- SWCNTs, which was readily affected by charge transfer, whereas that of m-SWCNTs showed no change with even more transferred charges. However, m-SWCNT that were aligned polarize adsorbed gases on the surface by a local field that contributed the capacitance changes of m-SWCNT networks. This is a newly introduced detection mechanism of gas sensing using m-SWCNTs.
Efficient Photothermoelectric Conversion in Lateral Topological Insulator Heterojunctions
Mashhadi, Soudabeh,Duong, Dinh Loc,Burghard, Marko,Kern, Klaus American Chemical Society 2017 Nano letters Vol.17 No.1
<P>Tuning the electron and phonon transport properties of thermoelectric materials by nanostructuring has enabled improving their thermopower figure of merit. Three-dimensional topological insulators, including many bismuth chalcogenides, attract increasing attention for this purpose, as their topologically protected surface states are promising to further enhance the thermoelectric performance. While individual bismuth chalcogenide nanostructures have been studied with respect to their photothermoelectric properties, nanostructured p-n junctions of these compounds have not yet been explored. Here, we experimentally investigate the room temperature thermoelectric conversion capability of lateral heterostructures consisting of two different three-dimensional topological insulators, namely, the n-type doped Bi2Te2Se and the p-type doped Sb2Te3. Scanning photocurrent microscopy of the nanoplatelets reveals efficient thermoelectric conversion at the p-n heterojunction, exploiting hot carriers of opposite sign in the two materials. From the photocurrent data, a Seebeck coefficient difference of Delta S = 200 mu V/K was extracted, in accordance with the best values reported for the corresponding bulk materials. Furthermore, it is in very good agreement with the value of Delta S = 185 mu V/K obtained by DFT calculation taking into account the specific doping levels of the two nanostructured components.</P>