时间：5月13日（周一）8:30-11:30

地点：李薰楼468会议室

 

题目1：Grain boundaries in graphene: From control to observations and applications

报告人：Prof. Younghee Lee

单位：IBS Center for Integrated Nanostructure Physics, Institute for Basic Science, Department of Physics, Department of Energy Science, Sungkyunkwan University, Suwon 440-746, Korea

摘要：In spite of successful synthesis of large area single-layer graphene using a simple chemical vapor deposition on transition metals such as Ni and Cu, control of high crystallininity is far from being clearly understood. Some examples of controlling nucleation seeds with polishing of Cu foil will be shown. More importantly, observing grain boundary distributions in large area is highly demanding since this is also related to macroscopic experimental data, for instance, sheet resistance or mobility, although local information at the grain boundary could be obtained from transmission electron microscopy. In this talk, we will demonstrate that the graphene grain boundary distribution could be observed by optical microscopy. This was done by simply oxidizing graphene on Cu substrate, where the selective diffusion took place through graphene grain boundaries but not inside grain. In addition, we will also show our long time effort of using nanocarbons in electronic devices that the CNT-graphene hybridized structures can be used for all-carbon transitors with high transmittance, high flexibility, and high stretchability to demontrate synergistic effect of both materials.

题目2：Fundamental Studies towards (n,m) Controlled CVD Growth of SWCNTs

报告人：Prof. Esko I. Kauppinen (esko.kauppinen@aalto.fi)

单位：Department of Applied Physics, Aalto University School of Science, Puumiehenkuja 2, P.O. Box 16100, FI-00076 Aalto, FINLAND

摘要：We start by reviewing the literature what is known experimentally regarding the chirality i.e. (n,m) as well as chiral angle distributions of SWNTs made via arc discharge, laser and both supported as well as floating catalyst CVD growth. Then we discuss in detail our current understanding of floating catalyst CVD synthesis of SWCNTs from CO using Fe catalyst clusters made via direct evaporation using hot wire generator as well as via thermal decomposition of ferrocene, and with the addition of trace amounts for CO₂, ammonia and water vapor. Here both the tube diameter as well as length can be tailored by changing the reactor temperature profile as well as CO₂ concentration. Chiral i.e. (n,m) distributions as determined with ED/TEM are biased towards large angles with the maximum population at about 23 degrees. Then we proceed to explore the effect of carbon source gas, by adding C₂H₄ together with CO and looking at the effect of temperature when producing catalysts via ferrocene decomposition.

To study the effect of Fe catalyst cluster size and concentration in the floating catalyst synthesis, we have developed a novel catalyst particle production method via physical vapor deposition, based on arc discharge between two electrodes i.e. the spark generator. This methods allows to control separately both the catalyst particle size and concentration when fed into the floating catalyst SWCNT synthesis reactor. Recent results show that when reducing catalyst particle gas phase number concentration, the bundle size of the produced tubes also is reduced, and we reduce the tube diameter below 1 nm and narrow the chiral angle distribution towards armchair when reducing synthesis temperature and CO concentration.

To further understand the growth mechanisms, we have carried out parallel studies on SWCNT growth from carbon monoxide (CO) using supported CVD methods, both at ambient CO pressure in the in-situ Raman microscope as well as at 7 mbar pressure inside the dedicated, Cs-corrected environmental TEM (ETEM). When using supported bimetallic Fe-Cu catalysts, narrow chiral distribution SWCNTs were produced at ambient pressure growth. In addition, epitaxial formation of single crystal cobalt (Co) nanoparticles from Co_xMg_1-xO solid solution reduction (when deposited into MgO via impregnation) in CO enables to grow SWCNTs also with a narrow diameter distribution, and with predominantly (6,5) tubes [1]. (ETEM) studies at reduced pressure reveal that the Co nanoparticles remain in metallic state and their epitaxial contact with MgO support remains coherent during SWCNT root growth process. Interestingly, when depositing Co via atomic layer deposition (ALD) onto MgO surface, we observe tip growth of SWCNTs inside the ETEM at 700℃, with the Co catalyst nanoparticle shape as well as the tube growth direction fluctuating during the growth process.

[1]. He et al., Scientific Reports 3, 1460 (2013).

题目3：Graphene-Based Three-Dimensional Frameworks and Thin Films for High Performance Supercapacitors

报告人：Dr. Zhong-Shuai Wu

单位：Max-Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany

摘要：Graphene-based materials has attracted wide attention for supercapacitors because ofits advantageous features such as large surface area, good flexibility, good chemical and thermal stability, wide potential windows, rich surface chemistry, etc.In this talk, a simplified prototype device of high-performance all solid-state supercapacitors (ASSSs) based on 3D nitrogen and boron co-doped monolithic graphene aerogels (BN-GAs) will be present.The device possesses an electrode-separator-electrolyte integrated structure, in which the GAs serve as additive/binder-free electrodes and a polyvinyl alcohol (PVA)/H₂SO₄ gel as solid-state electrolyte and thinner separator. The as-prepared GAs show 3D interconnected frameworks with a macroporous architecture, which are favorable for ion diffusion and electron transport in bulk electrode.As a consequence, the resulting BN-GAs based device exhibits show high specific capacitance (~ 62 F g^-1), good rate capability, and enhanced energy density (~8.65 Wh kg^-1) or power density (~1600 W kg^-1). Secondly, we will show the designed fabrication of novel graphene-based 3D frameworks with hierarchical macro- and meso-porous structures. Theinterconnected macropores are derived from hydrothermally assembled 3D graphene aerogels (GAs) while themesopores are generated by the silica networks uniformly grown on the surface of graphene, which render it a promising template for creating various 3D porous materials, such as GA basedmesoporous carbons (GA-MC) and metal oxide hybrids (GA-Co₃O₄, GA-RuO₂). Benefiting from the integration of meso- and macro-porous structures, 3D GA-MC manifestsoutstanding specific capacitance (226 F g^-1), high rate capability and excellent cycling stability (no capacitance lossafter 5000 cycles) when it is applied in electrochemical capacitors. Thirdly, the methane plasma reduced graphene-based thin films and CVD graphene for flexible and miniaturized micro-supercapacitors will be present.

References:

[1] Z. S. Wu, A. Winter, L. Chen, Y. Sun, A. Turchanin, X. Feng, K. Müllen, Adv. Mater., 24(2012)5130.

[2] Z. S. Wu, S. B. Yang, Y. Sun, K. Parvez, X. L. Feng, K. Müllen, J. Am. Chem. Soc., 134(2012) 9082.

[3] Z. S. Wu, Y. Sun,Y. Z. Tan,S. B. Yang,X. L. Feng,K. Müllen, J. Am. Chem. Soc.,134(2012) 19532.

Fig. 1: (a) SEM image of the as-prepared BN-GAs (Inset is digital image of the monolithic BN-GAs). (b) Simplified schematic of ASSSs based on BN-GAs. (c) Ragone plot of BN-GAs with undoped GAs (U-GAs), nitrogen-doped GAs (N-GAs), boron-doped GAs (B-GAs) and graphene paper (GP). (d) Fabrication of hierarchical macro- and meso-porous GA-SiO₂ frameworks. (e) SEM image of 3D macro/meso-porous GA-SiO₂ frameworks.