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Nanocarbonic transparent conductive films
Roth, Siegmar,Park, Hye Jin Royal Society of Chemistry 2010 Chemical Society reviews Vol.39 No.7
<P>This <I>tutorial review</I> discusses the contradictory material properties of electrical conductivity and optical transparency for the examples of graphene films and carbon nanotube networks. It is argued that for homogeneous films both properties are linked by basic laws of physics and that for perfect monoatomic layers conductivity and transparency can be calculated from the fine structure constant. To beat these limitations, inhomogeneous films are required, such as graphene with an array of holes or nanotube networks. An overview is given on literature values of transparency and conductivity, both for graphene films and for nanotube networks.</P> <P>Graphic Abstract</P><P>Light emitting diode behind electrically contacted large area graphene film to demonstrate transparency and conductivity at the same time. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c003813j'> </P>
Hyocheon Kweon,이규원,이철의,Siegmar Roth 한국물리학회 2011 Current Applied Physics Vol.11 No.3
Room-temperature ferromagnetism, concurrent with antiferromagnetic order, was observed in dodecylamine-intercalated vanadium oxide nanosheets by the magnetization and electron spin resonance measurements. Charge disproportionation arising from charge localization around T_P = 375 K appears to be associated with the ferromagnetic order. The ferromagnetic and the antiferromagnetic spins are found to be exchange-decoupled.
Improved field emission stability of thin multiwalled carbon nanotube emitters
Chen, Guohai,Shin, Dong Hoon,Kim, Suki,Roth, Siegmar,Lee, Cheol Jin IOP Pub 2010 Nanotechnology Vol.21 No.1
<P>The improved field emission stability of thin multiwalled carbon nanotube (thin-MWCNT) emitters using a tip sonication process has been investigated. The thin-MWCNTs showed short lengths and many open tips after the tip sonication treatment. The field emission properties of the thin-MWCNT emitters were investigated. Field emission stability dramatically increased as the tip sonication time increased. In particular, field emission current at an acceleration condition was quite stable and showed no degradation for over 19 h after tip sonication treatment of 30 min. Tip sonication could effectively cut CNTs short and regulate the length of CNTs. Therefore, field emission stability was significantly improved during a long period of operation because many shortened thin-MWCNTs could participate in field emission after the treatment. </P>
Field emission characteristics of point emitters fabricated by a multiwalled carbon nanotube yarn
Chen, Guohai,Shin, Dong Hoon,Roth, Siegmar,Lee, Cheol Jin IOP Pub 2009 Nanotechnology Vol.20 No.31
<P>We fabricated point emitters using a multiwalled carbon nanotube (MWCNT) yarn which was treated by ethylene glycol. The point emitter showed a very high emission current of 3.01 mA (current density of 1.1 × 10<SUP>8</SUP> A cm<SUP>−2</SUP>) and good emission stability of over 20 h. We attributed the excellent field emission properties to a large field enhancement factor caused by the large aspect ratio of the sharp tip of the point emitter and the tight bonding of neighboring MWCNTs due to the ethylene glycol treatment. We investigated the field enhancement factor according to the gap between the anode and the emitter tip at a macroscopic gap regime. The measured field enhancement factor of the MWCNT point emitter was in good agreement with theoretical models. </P>
Urszula Dettlaf-Wegl,Viera Skakalova,Jannik Meyer,Jiri Cech,Bernd G. Mueller,Siegmar Roth 한국물리학회 2007 Current Applied Physics Vol.7 No.1
We present a comparative study of uorinated single wall carbon nanotubes and C60 peapods. The uorination was carried out byxenon diuoride treatment at moderate temperature (100.C). The uorination level was determined by EDX. In empty nanotubes aometry of C4F). TEM images show that this uorination procedure does not aect the peapod structure. The elemental mapping carriedout by EELS reveals homogenous distribution of uorine along the carbon nanotube bundle. This chemical treatment is found to changethe electrical properties of carbon nanotubes in bucky papers. Four-probe measurements indicate a conductivity decrease by up to twoorders of magnitude at room temperature. The temperature dependence of the conductivity indicates a signicant change in the chargecarrier density of this system. Moreover, a non-linear behavior of theIV characteristic is observed below 50 K in uorinated peapods.
Nanotube actuators for nanomechanics
Andrew Minett,Jerome Fr?ysse,Gu Gang,Gyu-Tae Kim,Siegmar Roth 한국물리학회 2002 Current Applied Physics Vol.2 No.1
Carbon nanotubes are unique nanostructures with interesting properties that suit them to a range of diverse applications including nanoscale electronics, use in composites, as gas storage media and scanning probe tips. An exciting property of carbon nanotubes is their ability to efficiently convert electrical energy into mechanical energy (actuation). Nanotube actuation is caused by the geometrical expansion of the carbon–carbon covalent bond caused by charge transfer into the nanotube [Abstract American Chemical Society 22 (1999); Abstract American Chemical Society 20 (2000)]. This ability to actuate, in addition to their high strength (1 TPa), makes macro-scale sheets of nanotubes termed ‘bucky paper’, ideal for artificial muscles [Science 284 (1999) 1340]. Carbon nanotube actuators based on bucky paper have been shown to generate an order of magnitude higher stresses than those observed for natural muscle. These promising results suggest that carbon nanotube actuators based on a single (or a few hundred) nanotubes will also lead to enhanced applications on the micro- or nano-scale in the biomedical or electronic fields. This paper provides an overview of carbon nanotube actuators, their exceptional properties, current research ideas and possibilities for future applications. 2002 Elsevier Science B.V. All rights reserved.
Random telegraph noise in carbon nanotubes and peapods
장성호,이상욱,이동수,H.Y. Yu,Urszula Dettlaf-Wegl,캠벨,Siegmar Roth,박영우 한국물리학회 2006 Current Applied Physics Vol.6 No.6
The switching of resistance between two discrete values, known as random telegraph noise (RTN), was observed in individualsingle-walled carbon nanotubes (SWNTs) and C60-lled SWNTs (the so-called peapods). The RTN has been studied as a functionof bias-voltage and gate-voltage as well as temperature. By analyzing the features of the RTN, we identify three dierent types ofRTN existing in the SWNT related systems. While the RTN can be generated by the various charge traps in the vicinity of theSWNTs, the RTN for metallic SWNTs is mainly due to reversible defect motions between two metastable states, activated by inelas-tic scattering with ballistic electrons. On the other hand, the noise for peapods can be attributed to the motion of C60 molecules inhollow space of SWNTs.
Electrical Properties of the ZnO Nanowire Transistor and its Analysis with Equivalent Circuit Model
C. Y. Yim,우윤성,김규태,전대영,이종수,김강현,S. Kim,Siegmar Roth 한국물리학회 2006 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.48 No.6
A single ZnO nanowire .eld-eect transistor(FET) was fabricated and its current-voltage char- acteristics were recorded at the temperatures ranging from T = 107 K to 300 K. Current-voltage characteristics showed typical non-ohmic behaviors with noticeable temperature dependence of the carrier concentration and the mobilities, re°ecting the in°uence of the contact barriers formed be- tween the ZnO nanowire and metal electrodes. In this paper, an equivalent circuit model of the ZnO nanowire FET and its analysis methods with PSPICE simulation are suggested in order to model the contact barriers in nanowire devices.?