http://chineseinput.net/에서 pinyin(병음)방식으로 중국어를 변환할 수 있습니다.
변환된 중국어를 복사하여 사용하시면 됩니다.
Development of a 60 Hz Power Standard Using SNS Programmable Josephson Voltage Standards
Burroughs, C.J.,Benz, S.P.,Dresselhaus, P.D.,Waltrip, B.C.,Nelson, T.L.,Yonuk Chong,Williams, J.M.,Henderson, D.,Patel, P.,Palafox, L.,Behr, R. Institute of Electrical and Electronics Engineers 2007 IEEE transactions on instrumentation and measureme Vol.56 No.2
<P>We are implementing a new standard for 60 Hz power measurements based on precision sinusoidal reference voltages from two independent programmable Josephson voltage standards (PJVS): one for voltage and one for current. The National Institute of Standards and Technology PJVS systems use series arrays of Josephson junctions to produce accurate quantum-based DC voltages. Using stepwise-approximation synthesis, the PJVS systems produce sinewaves with precisely calculable RMS voltage and spectral content. We present measurements and calculations that elucidate the sources of error in the RMS voltage that are intrinsic to the digital-synthesis technique and that are due to the finite rise times and transients that occur when switching between the discrete voltages. Our goal is to reduce all error sources and uncertainty contributions from the PJVS synthesized waveforms to a few parts in 10 <SUP>7</SUP> so that the overall uncertainty in the AC-power standard is a few parts in 10<SUP>6</SUP></P>
The effect of copper pre-cleaning on graphene synthesis
Kim, Soo Min,Hsu, Allen,Lee, Yi-Hsien,Dresselhaus, Mildred,Palacios, Tomá,s,Kim, Ki Kang,Kong, Jing IOP Pub 2013 Nanotechnology Vol.24 No.36
<P>Copper foil is the most common substrate to synthesize monolayer graphene by chemical vapor deposition (CVD). The surface morphology and conditions of the copper foil can be very different depending on the various suppliers or different batches. These surface properties of copper strongly affect the growth behavior of graphene, thus rendering the growth conditions irreproducible when different batches of Cu foil are used. Furthermore, the quality of the graphene is severely affected as well. In this work, we report a facile method of copper pre-cleaning to improve the graphene quality and the reproducibility of the growth process. We found that the commercial Ni etchant (based on nitric acid) or nitric acid is the most effective cleaning agent among various acidic or basic solutions. The graphene grown on thus-treated copper surfaces is very clean and mostly monolayer when observed under scanning electron microscopy (SEM) and optical imaging, as compared to the graphene grown on untreated copper foil. Different batches (but with the same catalog number) of copper foil from Alfa Aesar Company were examined to explore the effect of copper pre-cleaning; consistent growth results were obtained when pre-cleaning was used. This method overcomes a commonly encountered problem in graphene growth and could become one of the standard protocols for preparing the copper foil substrate for growing graphene or other 2D materials.</P>
Synthesis of Patched or Stacked Graphene and hBN Flakes: A Route to Hybrid Structure Discovery
Kim, Soo Min,Hsu, Allen,Araujo, P. T.,Lee, Yi-Hsien,Palacios, Tomá,s,Dresselhaus, Mildred,Idrobo, Juan-Carlos,Kim, Ki Kang,Kong, Jing American Chemical Society 2013 Nano letters Vol.13 No.3
<P>Two-dimensional (2D) materials such as graphene and hexagonal boron nitride (hBN) have attracted significant attention due to their remarkable properties. Numerous interesting graphene/hBN hybrid structures have been proposed but their implementation has been very limited. In this work, the synthesis of patched structures through consecutive chemical vapor deposition (CVD) on the same substrate was investigated. Both in-plane junctions and stacked layers were obtained. For stacked layers, depending on the synthesis sequence, in one case turbostratic stacking with random rotations were obtained. In another, “AA-like”, slightly twisted stacking between graphene and hBN was observed with lattice orientation misalignment consistently to be <1°. Raman characterizations not only confirmed that hBN is a superior substrate but also revealed for the first time that a graphene edge with hBN passivation displays reduced D band intensity compared to an open edge. These studies pave the way for the proposed well-ordered graphene/hBN structures and outline exciting future directions for hybrid 2D materials.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/nalefd/2013/nalefd.2013.13.issue-3/nl303760m/production/images/medium/nl-2012-03760m_0008.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nl303760m'>ACS Electronic Supporting Info</A></P>
Double-walled carbon nanotubes: synthesis, structural characterization, and application
Kim, Yoong Ahm,Yang, Kap-Seung,Muramatsu, Hiroyuki,Hayashi, Takuya,Endo, Morinobu,Terrones, Mauricio,Dresselhaus, Mildred S. 한국탄소학회 2014 Carbon Letters Vol.15 No.2
Double walled carbon nanotubes (DWCNTs) are considered an ideal model for studying the coupling interactions between different concentric shells in multi-walled CNTs. Due to their intrinsic coaxial structures they are mechanically, thermally, and structurally more stable than single walled CNTs. Geometrically, owing to the buffer-like function of the outer tubes in DWCNTs, the inner tubes exhibit exciting transport and optical properties that lend them promise in the fabrication of field-effect transistors, stable field emitters, and lithium ion batteries. In addition, by utilizing the outer tube chemistry, DWCNTs can be useful for anchoring semiconducting quantum dots and also as effective multifunctional fillers in producing tough, conductive transparent polymer films. The inner tubes meanwhile preserve their excitonic transitions. This article reviews the synthesis of DWCNTs, their electronic structure, transport, and mechanical properties, and their potential uses.
Role of Intertube Interactions in Double- and Triple-Walled Carbon Nanotubes
Hirschmann, Thomas Ch.,Araujo, Paulo T.,Muramatsu, Hiroyuki,Rodriguez-Nieva, Joaquin F.,Seifert, Max,Nielsch, Kornelius,Kim, Yoong Ahm,Dresselhaus, Mildred S. American Chemical Society 2014 ACS NANO Vol.8 No.2
<P>Resonant Raman spectroscopy studies are performed to access information about the intertube interactions and wall-to-wall distances in double- and triple-walled carbon nanotubes. Here, we explain how the surroundings of the nanotubes in a multiwalled system influence their radial breathing modes. Of particular interest, the innermost tubes in double- and triple-walled carbon nanotube systems are shown to be significantly shielded from environmental interactions, except for those coming from the intertube interaction with their own respective host tubes. From a comparison of the Raman results for bundled as well as individual fullerene-peapod-derived double- and triple-walled carbon nanotubes, we observe that metallic innermost tubes, when compared to their semiconducting counterparts, clearly show weaker intertube interactions. Additionally, we discuss a correlation between the wall-to-wall distances and the frequency upshifts of the radial breathing modes observed for the innermost tubes in individual double- and triple-walled carbon nanotubes. All results allow us to contemplate fundamental properties related to DWNTs and TWNTs, as for example diameter- and chirality-dependent intertube interactions. We also discuss differences in fullerene-peapod-derived and chemical vapor deposition grown double- and triple-walled systems with the focus on mechanical coupling and interference effects.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2014/ancac3.2014.8.issue-2/nn500420s/production/images/medium/nn-2014-00420s_0008.eps'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nn500420s'>ACS Electronic Supporting Info</A></P>
Jung, Yong Chae,Muramatsu, Hiroyuki,Hayashi, Takuya,Kim, Jin Hee,Kim, Yoong Ahm,Endo, Morinobu,Dresselhaus, Mildred S. WILEY‐VCH Verlag 2010 European journal of inorganic chemistry Vol.2010 No.27
<P><B>Abstract</B></P><P>We carried out covalent functionalization of single‐ and double‐walled carbon nanotubes (SWNTs and DWNTs) comparatively by using isocyanate chemistry. The introduction of aromatic diisocyanate on the sidewalls of the tubes was verified by the strong IR peak around 2272 cm<SUP>–1</SUP> arising from the NCO asymmetric stretching mode, by the intensified sp<SUP>3</SUP> peak at 285.2 eV in the C1s photoemission spectra, and by a typical TEM image of the amorphous‐like coating. The suppression of the optical properties in a covalently isocyanate‐functionalized SWNT is due to a breakdown of the van Hove singularities, whereas the strong optical activity in a covalently isocyanate‐functionalized DWNT originates from the geometrically shielded inner tubes. The chemically active isocyanate groups at the end of the phenyl diisocyanate that are covalently attached to the sidewalls of the DWNTs will allow us to utilize isocyanate chemistry in synthesizing functional organic–inorganic hybrid materials as well as high‐performance polymer composites.</P>
Linear Carbon Chains under High-Pressure Conditions
Andrade, N. F.,Aguiar, A. L.,Kim, Y. A.,Endo, M.,Freire, P. T. C.,Brunetto, G.,Galvã,o, D. S.,Dresselhaus, M. S.,Souza Filho, A. G. American Chemical Society 2015 The Journal of Physical Chemistry Part C Vol.119 No.19
<P>A high-pressure resonance Raman spectroscopy study of linear carbon chains encapsulated inside multiwalled carbon nanotubes (MWCNTs) is reported. While the frequencies of the tangential modes of carbon nanotubes (G band) harden as the pressure increases, the vibrational frequencies of the chain modes (around 1850 cm<SUP>–1</SUP>) decrease, thus indicating a softening of the carbon–carbon bonds in this 1D solid. Pressure-induced irreversible structural changes in the linear carbon chains are unveiled by the red shift in the vibrational modes when pressure is released. These results have been interpreted as being due to a coalescence of carbon chains, and this hypothesis is supported by state-of-the-art atomistic reactive molecular dynamics simulations.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpccck/2015/jpccck.2015.119.issue-19/acs.jpcc.5b00902/production/images/medium/jp-2015-00902g_0012.gif'></P>
Kang, C.S.,Fujisawa, K.,Ko, Y.I.,Muramatsu, H.,Hayashi, T.,Endo, M.,Kim, H.J.,Lim, D.,Kim, J.H.,Jung, Y.C.,Terrones, M.,Dresselhaus, M.S.,Kim, Y.A. Pergamon Press ; Elsevier Science Ltd 2016 Carbon Vol.107 No.-
<P>Linear carbon chains (LCCs) consisting of sp-hybridized carbon atoms are considered a fascinating 1D system and could be used in the fabrication of the next-generation molecular devices because of its ideal linear atomic nature. A large portion of long LCCs inside multi-walled carbon nanotubes (MWCNTs) were synthesized by atmospheric arc discharge in the presence of boron. Closed-end growth of MWCNTs in the arc process is suggested as a critical condition for the simultaneous growth of LCCs within the inner cores of carbon nanotubes. The strong Raman line around 1850 cm(-1) was used to characterize the degree of filling as well as their structural stability under high temperature thermal treatments. We observed a distinctive change in the electrical conductivity of the MWCNT assembly before and after the disappearance of LCCs due to the expected strong coupling interaction between the LCCs and the innermost tube. This work demonstrates for the first time the enhanced effect of confined linear carbon chains on the overall electrical conductivity of MWCNT assemblies. (C) 2016 Elsevier Ltd. All rights reserved.</P>