Showing papers by "S. Roth published in 2000"

Polarized Raman Spectroscopy on Isolated Single-Wall Carbon Nanotubes

Abstract: Polarized micro-Raman spectroscopy has been performed on spatially separated single-wall carbon nanotubes (SWNTs) in the form of individual nanotubes or thin ropes of only a few SWNTs. Different from bulk samples, the Raman spectra are composed of well-resolved peaks which allow a direct comparison of experimental data with theoretical calculations. Orientation-dependent measurements reveal maximum intensity of all Raman modes when the nanotubes are aligned parallel to the polarization of the incident laser light. The angular dependences clearly deviate from the selection rules predicted by theoretical studies. These differences are attributed to depolarization effects caused by the strongly anisotropic geometry of the nanotubes and to electronic resonance effects for excitation at 633 nm.

Field-effect transistor made of individual V2O5 nanofibers

Abstract: A field-effect transistor (FET) with a channel length of ∼100 nm was constructed from a small number of individual V2O5 fibers of the cross section 1.5 nm×10 nm. At low temperature, the conductance increases as the gate voltage is changed from negative to positive values, characteristic of a FET with n-type enhancement mode. The carrier mobility, estimated from the low-field regime, is found to increase from 7.7×10−5 cm2/V s at T=131 K to 9.6×10−3 cm2/V s at T=192 K with an activation energy of Ea=0.18 eV. The nonohmic current/voltage dependence at high electric fields was analyzed in the frame of small polaron hopping conduction, yielding a nearest-neighbor hopping distance of ∼4 nm.

Raman Imaging of Single Carbon Nanotubes

Abstract: [19] The single crystals of the Bu4NBr0.6I1.4Cl salt, were obtained by addition of IBr to a solution of Bu4NCl in ethanol at a reagent ratio of 1:0.5. Stoichiometry of the anion has been found by EDX. Based on a Raman study the anion consists of the I2Br ‐ (band at 140 cm ‐1 ), IBr2 ‐ (band at 150‐ 176 cm ‐1 ), BrICl ‐ (band at 225 cm ‐1 ), and ICl2 ‐ (band at 250‐263 cm ‐1 ) trihalide anions. [20] The X-ray diffraction data from single crystals for both trihalide salts were measured using an Enraf Nonius CAD4 diffractometer with graphite monochromatic Mo Ka radiation (k = 0.71073 a) at room temperature. Unit cell parameters of the new a¢¢¢- crystal were determined from a leastsquares analysis of 25 reflections. The intensities of 8106 non-zero reflections were collected by the x-scan method up to 2H = 50. The index range was ‐20 2 r(I), Rint = 0.011, were used in the structure analysis. Absorption correction was applied using the DIFABS algorithm. The main room temperature crystal data for the single crystal of 1 are as follows: a = 17.116(2), b = 8.956(1), c = 16.338(2) a, a = 88.09(2), b = 84.22(1), w = 81.22(2), V = 2462.1(5) a 3 , space group P1 ¯ , Z =3 ,M = 1024.89, dcalc =

Phase breaking in three-terminal contacted single-walled carbon nanotube bundles

Abstract: The potential application of carbon nanotubes ~CNT’s ! as molecular wires in submicron devices has initiated a variety of conductance experiments. Phenomena like Coulomb blockade 1,2 and signatures of Luttinger liquids 3 in singlewalled carbon nanotubes ~SWCNT’s!, as well as Aharanov‐ Bohm oscillations, 4 quantized conductance and quasiballistic transport at room temperature ~RT! in multiwalled carbon nanotubes ~MWCNT’s! were reported. 5 Except for the observations of Coulomb blockade, a low contact resistance between leads and the CNT is required in such experiments. In the present study, electron-beam lithography ~EBL! was used to contact SWCNT’s with electrodes on top, similar to Ref. 3. Electrode arrays consisting of three equidistant stripes were prepared from AuPd ~40 wt %/60 wt %!. The electrical transport investigations at room temperature presented here focus on samples with SWCNT bundles, which are connected by three low-Ohmic contacts, in contrast to recent measurements with only two contacts. 3,6 For sample preparation, 7 arc-discharge SWCNT raw material was dispersed by ultrasonic treatment in aqueous surfactant solution, and purified by centrifugation. As substrate, an As doped Si wafer with a thermally grown SiO2 layer was used. Before adsorption of the SWCNT’s, the substrate was treated with a 0.1 wt % aqueous solution of 3-~aminopropyl!triethoxysilane for 2 min. In order to perform EBL ~EBL 100 system, LEICA! on top of the SWCNT’s, a two-layer resist system was used. 2 After EBL, AuPd ~thickness ’17 nm! or Au ~thickness ’24 nm! was thermally evaporated on the substrate at a base pressure of p’10 27 mbar using a rate of 1 A/s.

Ultraviolet Photoelectron Spectroscopy and Surface Potential of π-conjugated Langmuir-Blodgett Films on Gold Metal Electrode

Abstract: The interfacial electronic structure of π-conjugated Langmuir-Blodgett (LB) films [octasubstituted palladiumphthalocyanine (PcPd) and preylene-tetra-carboxyldiimide derivative (PTCDI-Spent)] deposited on Au electrodes was examined by ultraviolet (UV) photoelectron spectroscopy (UPS), and the results were compared with these obtained by the surface potential measurement in a dark vacuum vessel. As the number of deposited layers increases, the energy shift was observed in the UPS spectra, which were found to correspond well with the surface potential change. This result indicates that excess electronic charges are transferred from LB-films to the Au electrodes until a thermodynamic equilibrium is established at the metal-film interface, resulting in the formation of an electrostatic double layer within the range of 1 to 2 nanometers in thickness. The contribution of layers sandwiched between the metal and the PcPd molecular film to the UPS spectra was also examined.

Phase separation of carbon nanotubes and turbostratic graphite using a functional organic polymer (vol 12, pg 213, 2000)

Abstract: sorbed in the vesicle bilayer. Photoinitiated polymerizations were performed in a thermostatted quartz reactor using either an UV-lamp (HPR 125 W, Philips) or a pulsed excimer laser (Lambda Physics XeF, 351 nm, 2 Hz pulse frequency, 30 mJ energy per pulse) as irradiation source. Conversions were determined by HPLC analysis of the residual monomers. Details concerning the use of cryo-electron microscopy have been described earlier [19].