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Synthesis of few-layered graphene by ion implantation of carbon in nickel thin films
Baraton, Laurent,He, Zhanbing,Lee, Chang Seok,Maurice, Jean-Luc,Cojocaru, Costel Sorin,Gourgues-Lorenzon, Anne-Franç,oise,Lee, Young Hee,Pribat, Didier IOP Pub 2011 Nanotechnology Vol.22 No.8
<P>The synthesis of few-layered graphene is performed by ion implantation of carbon species in thin nickel films, followed by high temperature annealing and quenching. Although ion implantation enables a precise control of the carbon content and of the uniformity of the in-plane carbon concentration in the Ni films before annealing, we observe thickness non-uniformities in the synthesized graphene layers after high temperature annealing. These non-uniformities are probably induced by the heterogeneous distribution/topography of the graphene nucleation sites on the Ni surface. Taken altogether, our results indicate that the number of graphene layers on top of Ni films is controlled by the nucleation process on the Ni surface rather than by the carbon content in the Ni film. </P>
Hee Jin Jeong,Laurent Eude,Manoharan Gowtham,Bernd Marquardt,Sung Hun Lim,Shaïma Enouz,Costel Sorin Cojocaru,Kyung Ah Park,이영희,디디에르프리밧 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2008 NANO Vol.3 No.3
The effects of an atomic hydrogen (Hat) pretreatment of the catalyst layer on the low temperature growth of single-walled carbon nanotubes (SWCNTs) have been investigated using a modified catalytic chemical vapor deposition system. Well-defined and isolated individual Fe nanoparticles as a catalyst are successfully formed on the defects with high trapping energy which are created on the Al2O3 surface by Hat pretreatment, yielding highly dense SWCNTs. The pretreatment mechanism of Hat, compared to H2, is also discussed. It was also found that the quality of SWCNTs can be enhanced when Hat is flowed with CH4 during nanotubes growth at low temperature. In this case, the undesired carbon products and defects on catalyst seeds and nanotubes walls can be selectively removed by Hat. Therefore, it is essential to use Hat in pretreatment stage for increasing catalytic activity and keep the size of nanoparticles in the nm range. Hat can also be employed in growth stage for enhancing SWCNTs quality and density at low temperature.
Diffusion Mechanism of Lithium Ion through Basal Plane of Layered Graphene
Yao, Fei,Gü,neş,, Fethullah,Ta, Huy Quang,Lee, Seung Mi,Chae, Seung Jin,Sheem, Kyeu Yoon,Cojocaru, Costel Sorin,Xie, Si Shen,Lee, Young Hee American Chemical Society 2012 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.134 No.20
<P>Coexistence of both edge plane and basal plane in graphite often hinders the understanding of lithium ion diffusion mechanism. In this report, two types of graphene samples were prepared by chemical vapor deposition (CVD): (i) well-defined basal plane graphene grown on Cu foil and (ii) edge plane-enriched graphene layers grown on Ni film. Electrochemical performance of the graphene electrode can be split into two regimes depending on the number of graphene layers: (i) the corrosion-dominant regime and (ii) the lithiation-dominant regime. Li ion diffusion perpendicular to the basal plane of graphene is facilitated by defects, whereas diffusion parallel to the plane is limited by the steric hindrance that originates from aggregated Li ions adsorbed on the abundant defect sites. The critical layer thickness (<I>l</I><SUB>c</SUB>) to effectively prohibit substrate reaction using CVD-grown graphene layers was predicted to be ∼6 layers, independent of defect population. Our density functional theory calculations demonstrate that divacancies and higher order defects have reasonable diffusion barrier heights allowing lithium diffusion through the basal plane but neither monovacancies nor Stone-Wales defect.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jacsat/2012/jacsat.2012.134.issue-20/ja301586m/production/images/medium/ja-2012-01586m_0003.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ja301586m'>ACS Electronic Supporting Info</A></P>
He, Zhanbing,Lee, Chang Seok,Maurice, Jean-Luc,Pribat, Didier,Haghi-Ashtiani, Paul,Cojocaru, Costel Sorin Elsevier 2011 Carbon Vol.49 No.14
<P><B>Abstract</B></P><P>Plasma-enhanced chemical vapor deposition, without a nickel-containing gaseous precursor, was used to synthesize continuous nickel (Ni) nanorods inside the hollow cavity of carbon nanofibers (CNFs), thus forming vertically aligned Ni/CNF core/shell structures. Scanning and transmission electron microscopic images indicate that the elongated Ni nanorods originate from the catalyst particles at the tips of the CNFs and that their formation is due to the effect of extrusion induced by the compressive force of the graphene layers during growth. Different from previous work, each vertically-aligned core/shell structure reported is totally isolated from its neighbors. Continuous Ni nanorods are found to separate into smaller ones with increasing growth time, which was ascribed to (i) the limited amount of Ni available in the tip of the CNF, (ii) the polycrystalline nature of the Ni nanorods and (iii) the combined effects of the compressive stresses on the side of the Ni nanorods and of the tensile stress along their axis.</P>