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We report on the intershell electron transport in multiwalled carbon nanotubes (MWNTs). To do this, local and nonlocal four-point measurements are used to study the current path through the different shells of a MWNT. For short electrode separations less, similar 1 mum the current mainly flows through the two outer shells, described by a resistive transmission line with an intershell conductance per length of approximately (10 kOmega)(-1)/microm. The intershell transport is tunnel type and the transmission is consistent with the estimate based on the overlap between pi orbitals of neighboring shells. 相似文献
65.
Bourlon B Glattli DC Plaçais B Berroir JM Miko C Forró L Bachtold A 《Physical review letters》2004,92(2):026804
We have studied the high-bias transport properties of the different shells that constitute a multiwalled carbon nanotube. The current is shown to be reduced as the shell diameter is decreased or the length is increased. We assign this geometrical dependence to the competition between the electron-phonon scattering process and Zener tunneling. 相似文献
66.
Optical evidence for the proximity to a spin-density-wave metallic state in $\mathsf{Na_{0.7}CoO_2}$
G.?Caimi L.?DegiorgiEmail author H.?Berger N.?Barisic L.?Forró F.?Bussy 《The European Physical Journal B - Condensed Matter and Complex Systems》2004,40(3):231-234
We present the optical properties of Na0.7CoO2 single crystals, measured over a broad spectral range as a function of temperature (T). The capability to cover the energy range from the far-infrared up to the ultraviolet allows us to perform reliable Kramers-Kronig transformation, in order to obtain the absorption spectrum (i.e., the complex optical conductivity). To the complex optical conductivity we apply the generalized Drude model, extracting the frequency dependence of the scattering rate (
) and effective mass (m
*) of the itinerant charge carriers. We find that
at low temperatures and for
. This suggests that Na0.7CoO2 is at the verge of a spin-density-wave metallic phase.Received: 6 August 2004, Published online: 9 September 2004PACS:
78.20.-e Optical properties of bulk materials and thin films - 74.70.Dd Ternary, quaternary and multinary compounds (including Chevrel phases, borocarbides, etc.) - 75.30.Fv Spin-density waves 相似文献
67.
Sienkiewicz A Vileno B Garaj S Jaworski M Forró L 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2005,177(2):261-273
We present a newly developed microwave probe head that accommodates a gasketed sapphire anvil cell (SAC) for performing sensitive electron spin resonance (ESR) measurements under high-hydrostatic pressures. The system was designed around commercially available dielectric resonators (DRs) having the dielectric permittivity of approximately 30. The microwave resonant structure operates in a wide-stretched double-stacked geometry and resonates in the lowest cylindrical quasi TE(011) mode around 9.2 GHz. The most vital parts of the probe's microwave heart were made of plastic materials, thus making the resonant structure transparent to magnetic field modulation at 100 kHz. The overall ESR sensitivity of the probe was demonstrated for a small speck of 2,2-diphenyl-1-picrylhydrazyl radical (DPPH) positioned in the gasket of the SAC, using water as the pressure-transmitting medium. The system was also used for studying pressure-induced changes in spin-relaxation mechanisms of a quasi-1D-conducting polymer, K(1)C(60). For small samples located in the sample hole of the gasket the probe reveals sensitivity that is only approximately 3 times less than that yielded by regular ESR cavities. 相似文献
68.
Synthesis and conformational study of 1,3,2-oxazaphosphorino[4, 3-a]isoquinolines: a new ring system
Martinek T Forró E Günther G Sillanpää R Fülöp F 《The Journal of organic chemistry》2000,65(2):316-321
A set of 1,3,2-oxazaphosphorino[4,3-a]isoquinolines 6a,b-9a,b, a new ring system, was synthesized, and their stereochemical and conformational analyses were performed by (1)H, (13)C, and (31)P NMR methods. X-ray measurements were also carried out to confirm the stereochemical assignments and conformational results obtained by means of NMR. Intermediate coupling constants (3)J(P,H) were found for compounds 7 and 9; these do not relate to equilibria between previously reported conformers, but are indicative of new distorted conformational states in solution. The connecting isoquinoline and the steric interaction between the aromatic moiety and the Me-1 substituent can block the oxazaphosphorinane ring. The conformational behavior of compounds 6 and 8 was characterized by the usual chair-twist equilibrium. 相似文献
69.
Highly functionalized β-aminocyclohexanecarboxylate regio- and stereoisomers were synthetized from racemic unsaturated bicyclic β-lactams via enzymatic resolution, selective transformation of the C–C double bond by stereoselective epoxidation, and regioselective oxirane ring opening with azide or cyanide as nucleophile. 相似文献
70.
Gyula Lajkó Tímea Orosz Lóránd Kiss Enikő Forró Ferenc Fülöp Antal Péter István Ilisz 《Biomedical chromatography : BMC》2016,30(9):1441-1448
The stereoisomers of five fluorinated cyclic β3‐amino acid derivatives and their nonfluorinated counterparts were separated on chiral stationary phases containing as chiral selectors cellulose tris‐(3,5‐dimethylphenyl carbamate), cellulose tris‐(3‐chloro‐4‐methylphenyl carbamate), cellulose tris‐(4‐methylbenzoate), cellulose tris‐(4‐chloro‐3‐methylphenyl carbamate), amylose tris‐(3,5‐dimethylphenyl carbamate) or amylose tris‐(5‐chloro‐2‐methylphenyl carbamate). The enantioseparations were carried out in normal‐phase mode with n‐hexane/alcohol/alkylamine mobile phases in the temperature range 5–40 °C. The effects of the mobile phase composition, the nature and concentration of the alcohol and alkylamine additives, the structures of the analytes and temperature on the separations were investigated. Thermodynamic parameters were calculated from plots of ln α vs. 1/T. The Δ(ΔH°) values ranged between ?5.0 and +1.6 kJ/mol, while Δ(ΔS°) varied between ?12.6 and +5.7 J/mol/K. The enantioseparation was enthalpically controlled, the retention factor and the separation factor decreasing with increasing temperature, but entropically controlled separation was also observed. The elution sequence was determined for all of the investigated analytes. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献