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Catalyst faceting during graphene layer crystallization in the course of carbon nanofiber growth
Maurice, J.L.,Pribat, D.,He, Z.,Patriarche, G.,Cojocaru, C.S. Pergamon Press ; Elsevier Science Ltd 2014 Carbon Vol.79 No.-
The low temperature catalytic growth of multiwall carbon nanotubes (MWCNTs) rests on the continuous nucleation and growth of graphene layers at the surface of crystalline catalyst particles. Here, we study the atomic mechanisms at work in this phenomenon, by observing the growth of such layers in situ in the transmission electron microscope, in the case of iron-based catalysts. Graphene layers, parallel to the catalyst surface, appear by a mechanism of step flow, where the atomic layers of catalyst are ''replaced'' by graphene planes. Quite remarkably, catalyst facets systematically develop while this mechanism is at work. We discuss the origin of faceting in terms of equilibrium particle shape and graphene layer nucleation. Step bunching due to impeded step migration, in certain growth conditions, yields characteristic catalyst nail-head shapes. Mastering the mechanisms of faceting and step bunching could open up the way to tailoring the structure of low temperature-grown MWCNTs, e.g. with highly parallel carbon walls and, ultimately, with controlled structure and chirality.
Sub ppm Gas Sensing Using a CNTFET-Based Sensor Array Fabricated Using Dierent Metals as Electrodes
Paolo Bondavalli,Pierre Legagneux,Didier Pribat 한국물리학회 2009 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.54 No.1
This paper deals with the fabrication of carbon nanotube eld effect transistors (CNTFETs) for gas sensing applications. The aim of this study is to achieve a sort of fingerprinting of a specific gas by using an array of CNTFET-based sensors. The electronic ngerprinting will be obtained by exploiting the change of the metal electrode work function after gas exposure. This one strictly depends on the metal/gas interaction and consequently in uences univocally the transfer characteristics of each transistors. To demonstrate this original concept, we have fabricated different CNTFETs using different metal contacts: Au, Pt and Mo. Using these transistors, we have shown that a specific gas, in our case DiMethyl-Methyl-Phosphonate (DMMP, a sarin simulant), interacts specifically with each metal: exposure to 0.5 ppm of DMMP reduces the transistor ON current by 10 %, 60 % and 25 % after 5 minutes respectively for Au, Pt, Mo-based CNTFETs at V<SUB>GS</SUB> = -25 Volt. We think that this new approach can be applied for highly selective sensing of various gases using ultra-compact, room temperature and very low power devices. This paper deals with the fabrication of carbon nanotube eld effect transistors (CNTFETs) for gas sensing applications. The aim of this study is to achieve a sort of fingerprinting of a specific gas by using an array of CNTFET-based sensors. The electronic ngerprinting will be obtained by exploiting the change of the metal electrode work function after gas exposure. This one strictly depends on the metal/gas interaction and consequently in uences univocally the transfer characteristics of each transistors. To demonstrate this original concept, we have fabricated different CNTFETs using different metal contacts: Au, Pt and Mo. Using these transistors, we have shown that a specific gas, in our case DiMethyl-Methyl-Phosphonate (DMMP, a sarin simulant), interacts specifically with each metal: exposure to 0.5 ppm of DMMP reduces the transistor ON current by 10 %, 60 % and 25 % after 5 minutes respectively for Au, Pt, Mo-based CNTFETs at V<SUB>GS</SUB> = -25 Volt. We think that this new approach can be applied for highly selective sensing of various gases using ultra-compact, room temperature and very low power devices.
Etchant-induced shaping of nanoparticle catalysts during chemical vapour growth of carbon nanofibres
He, Z.B.,Maurice, J.L.,Lee, C.S.,Gohier, A.,Pribat, D.,Legagneux, P.,Cojocaru, C.S. Pergamon Press ; Elsevier Science Ltd 2011 Carbon Vol.49 No.2
Carbon nanofibres (CNFs) obtained by plasma-enhanced chemical vapour deposition are made of cone-shaped graphene layers, the opening angle of which has a significant influence on their properties: the smaller the angle, the closer the properties to those of carbon nanotubes. That angle is determined by the shape of the metal nanoparticle used to catalyse the growth. We show in this paper that the shape of Ni nanoparticle catalysts, and in turn the CNF properties, can be tuned during plasma-enhanced chemical vapour deposition, by the choice of the etchant gas. We show in particular that a water-containing etchant (H<SUB>2</SUB>O or H<SUB>2</SUB>O+H<SUB>2</SUB>) increases the growth rate by an order of magnitude at 600<SUP>o</SUP>C compared to an ammonia-containing etchant (NH<SUB>3</SUB> or NH<SUB>3</SUB>+H<SUB>2</SUB>), and leaves more elongated Ni particles with a cone angle three times smaller. We conclude that the cone angle and the growth rate are directly related, and propose a mechanism to explain that large difference between the two etchants
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>
Alumina-coated silicon-based nanowire arrays for high quality Li-ion battery anodes
Nguyen, Hung Tran,Zamfir, Mihai Robert,Duong, Loc Dinh,Lee, Young Hee,Bondavalli, Paolo,Pribat, Didier The Royal Society of Chemistry 2012 Journal of materials chemistry Vol.22 No.47
<P>Amongst other requirements, a good anode for Li-ion battery applications must exhibit dimensional stability upon Li insertion, as well as chemical inertness with respect to the electrolyte. This latter characteristic is usually provided by the so-called solid electrolyte interphase (SEI), a passivating film that is formed at the end of the first lithiation step, originating from the partial reduction of the electrolyte and Li salt. However, silicon, which exhibits the highest known capacity for Li alloying, possesses none of the above attributes when used as an anode material. Actually, the large volume expansion of Si upon alloying with Li induces a mechanical instability of the SEI film, which therefore fails to provide its protective role. In this paper, we have studied the effect of thin alumina deposits on top of Si-based nanowires. A thin alumina deposit will act as a substitute for the SEI, preventing electrolyte decomposition. We observe that even if alumina films crack during lithiation–delithiation steps of the Si-based nanowires, they still provide some kind of protection, prolonging the lifetime of the anode. Using Al<SUB>2</SUB>O<SUB>3</SUB>-coated Si-based nanowires, we have been able to obtain a lifetime of 1280 cycles when the capacity of the anode was limited to 1200 mA h g<SUP>−1</SUP>. We also show that uncoated Si nanowires degrade more rapidly when cycled under identical conditions.</P> <P>Graphic Abstract</P><P>We have studied the effect of thin Al<SUB>2</SUB>O<SUB>3</SUB> coatings on Si-based nanowires for Li-ion battery anodes. We report a lifetime of 1280 cycles when the capacity is limited to 1200 mA h g<SUP>−1</SUP>. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c2jm35125k'> </P>
Singh, Swati,Hong, Seunghyun,Jeon, Wonjae,Lee, Dongmok,Hwang, Jae-Yeol,Lim, Seulky,Kwon, Gi Duk,Pribat, Didier,Shin, Hyunjung,Kim, Sung Wng,Baik, Seunghyun American Chemical Society 2015 Chemistry of materials Vol.27 No.7
<P>The successful mechanical exfoliation and chemical synthesis of graphene has attracted considerable attention for the synthesis of other two-dimensional materials on graphene template. Chalcogenide materials such as Sb2Te3 are of interest due to the rhombohedral lattice structure with two-dimensional hexagonally closed-packed atomic layers along the c-axis. Here we synthesized c-axis-oriented Sb2Te3 nanoplates (NPs) on graphene substrates by the microwave-assisted solvothermal method. The microwave irradiation resulted in a higher temperature of graphene, compared with the synthesis solution, which was revealed by the single-mode microwave experiments and an analytical model based on energy balance and convective heat transfer. Besides, the lattice mismatch between c-axis-oriented Sb2Te3 and bridge sites of graphene was only 4%, which is also favorable for the graphene-templated Sb2Te3 synthesis. c-Axis-oriented single-crystalline Sb2Te3 NPs as large as 7 mu m could be successfully synthesized on graphene with negligible damage of the graphene template. Larger surface coverage could be obtained by merging Sb2Te3 NPs. The merged Sb2Te3 NPs were polycrystalline with rotated grain boundaries. This work provides a facile, rapid, and low-cost synthesis route of c-axis-oriented Sb2Te3 NPs on graphene templates, which may be extended for the synthesis of various two-dimensional materials with hexagonally closed-packed atomic layers along the c-axis.</P>