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Mesoscale Imperfections in MoS<sub>2</sub> Atomic Layers Grown by a Vapor Transport Technique
Liu, Yingnan,Ghosh, Rudresh,Wu, Di,Ismach, Ariel,Ruoff, Rodney,Lai, Keji American Chemical Society 2014 NANO LETTERS Vol.14 No.8
<P>The success of isolating small flakes of atomically thin layers through mechanical exfoliation has triggered enormous research interest in graphene and other two-dimensional materials. For device applications, however, controlled large-area synthesis of highly crystalline monolayers with a low density of electronically active defects is imperative. Here, we demonstrate the electrical imaging of dendritic ad-layers and grain boundaries in monolayer molybdenum disulfide (MoS<SUB>2</SUB>) grown by a vapor transport technique using microwave impedance microscopy. The micrometer-sized precipitates in our films, which appear as a second layer of MoS<SUB>2</SUB> in conventional height and optical measurements, show ∼2 orders of magnitude higher conductivity than that of the single layer. The zigzag grain boundaries, on the other hand, are shown to be more resistive than the crystalline grains, consistent with previous studies. Our ability to map the local electrical properties in a rapid and nondestructive manner is highly desirable for optimizing the growth process of large-scale MoS<SUB>2</SUB> atomic layers.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/nalefd/2014/nalefd.2014.14.issue-8/nl501782e/production/images/medium/nl-2014-01782e_0006.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nl501782e'>ACS Electronic Supporting Info</A></P>
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Thermal Oxidation of WSe<sub>2</sub> Nanosheets Adhered on SiO<sub>2</sub>/Si Substrates
Liu, Yingnan,Tan, Cheng,Chou, Harry,Nayak, Avinash,Wu, Di,Ghosh, Rudresh,Chang, Hsiao-Yu,Hao, Yufeng,Wang, Xiaohan,Kim, Joon-Seok,Piner, Richard,Ruoff, Rodney S.,Akinwande, Deji,Lai, Keji American Chemical Society 2015 NANO LETTERS Vol.15 No.8
<P>Because of the drastically different intralayer versus interlayer bonding strengths, the mechanical, thermal, and electrical properties of two-dimensional (2D) materials are highly anisotropic between the in-plane and out-of-plane directions. The structural anisotropy may also play a role in chemical reactions, such as oxidation, reduction, and etching. Here, the composition, structure, and electrical properties of mechanically exfoliated WSe<SUB>2</SUB> nanosheets on SiO<SUB>2</SUB>/Si substrates were studied as a function of the extent of thermal oxidation. A major component of the oxidation, as indicated from optical and Raman data, starts from the nanosheet edges and propagates laterally toward the center. Partial oxidation also occurs in certain areas at the surface of the flakes, which are shown to be highly conductive by microwave impedance microscopy. Using secondary ion mass spectroscopy, we also observed extensive oxidation at the WSe<SUB>2</SUB>–SiO<SUB>2</SUB> interface. The combination of multiple microcopy methods can thus provide vital information on the spatial evolution of chemical reactions on 2D materials and the nanoscale electrical properties of the reaction products.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/nalefd/2015/nalefd.2015.15.issue-8/acs.nanolett.5b02069/production/images/medium/nl-2015-02069p_0005.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nl5b02069'>ACS Electronic Supporting Info</A></P>
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Political Ties and Firm Performance in China: Evidence from a Quantile Regression
Wenjing Xie,Keji Liu,Fei Xie,Haoyuan Ding 동아시아연구원 2017 Journal of East Asian Studies Vol.17 No.3
Whether political ties enhance or weaken firm performance has been widely investigated in a number of studies, including some on China. Based on a database of non-financial A-share listed firms from 2004 to 2012, we study the effects of political ties on firm performance within a quantile regression framework. We find that there is a positive relationship between political ties and economic performance, but that it is diminishing with respect to firm performance. Political ties appear particularly important for weaker firms.
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Jinsong Liang,Qibao Xie,Wenjie Feng,Bo Li,Tao Peng,Kejie Liu,Mengjin Jiang 한국섬유공학회 2023 Fibers and polymers Vol.24 No.11
The spinnability of semi-dilute poly(p-phenylene-benzimidazole-terephthamide) (PBIA) spinning solution was regulated by a small amount of polyethylene glycol (PEG) to make it suitable for dry-jet wet spinning. The effects of different molecular weights and contents of PEG on the rheological properties and spinnability of PBIA spinning solution were investigated. Results show that the PBIA spinning solution with PEG 50,000 has the highest viscosity and the best spinnability, which can be smoothly spun by dry-jet wet spinning. The dynamic viscoelasticity study shows that the energy storage modulus and loss modulus of the PBIA spinning solution keeps increasing with PEG 50,000 and achieves the maximum value of 0.5% wt. The maximum draw ratio between the first roll and the spinneret (Dm) also reached a maximum value of 3.0 when the addition of PEG 50,000 reached 0.5% wt. Moreover, primary PBIA fibers prepared by dry-jet wet spinning and a higher draw ratio have a smoother surface appearance and better mechanical properties.
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