Semiconductor-enriched single wall carbon nanotube networks applied to field effect transistors

Substantial progress on field effect transistors "FETs" consisting of semiconducting single wall carbon nanotubes "s-SWNTs" without detectable traces of metallic nanotubes and impurities is reported. Nearly perfect removal of metallic nanotubes is confirmed by optical absorption, Raman measurements, and electrical measurements. This outstanding result was made possible in particular by ultracentrifugation (150 000 g) of solutions prepared from SWNT powders using polyfluorene as an extracting agent in toluene. Such s-SWNTs processable solutions were applied to realize FET, embodying randomly or preferentially oriented nanotube networks prepared by spin coating or dielectrophoresis. Devices exhibit stable p-type semiconductor behavior in air with very promising characteristics. The on-off current ratio is 10^5, the on-current level is around 10 $\mu$A, and the estimated hole mobility is larger than 2 cm2 / V s

Fictions, Fault, and Forgiveness: Jury Nullification in a New Context

Recently, critics of the Anglo-American jury system have complained that juries in criminal trials have been ignoring the law, in favor of defendants who claim that they lack criminal responsibility because they are afflicted by the various victimization syndromes now popularized in the mass media. In this Article, Professors Dorfman and Iijima counter this characterization of the runaway jury and argue that juries are not ignoring the law, but rather, are exercising a primary power of the jury, to nullify the application of the law when such application to a particular defendant is unjust. The Authors trace the development of the jury nullification power from its beginnings in the late seventeenth century to the present. The Authors then counter the standard arguments against jury nullification. Finally, the Authors propose an explicit jury nullification instruction and accommodating adjustments to other trial procedures that would solve the deficiencies of the current manner in which juries exercise their nullification power

Pressure dependence of the thermoelectric power of single-walled carbon nanotubes

We have measured the thermoelectric power (S) of high purity single-walled carbon nanotube mats as a function of temperature at various hydrostatic pressures up to 2.0 GPa. The thermoelectric power is positive, and it increases in a monotonic way with increasing temperature for all pressures. The low temperature (T < 40 K) linear thermoelectric power is pressure independent and is characteristic for metallic nanotubes. At higher temperatures it is enhanced and though S(T) is linear again above about 100 K it has a nonzero intercept. This enhancement is strongly pressure dependent and is related to the change of the phonon population with hydrostatic pressure.Comment: 4 pages, 3 figure

Neutral B Flavor Tagging for the Measurement of Mixing-induced CP Violation at Belle

We describe a flavor tagging algorithm used in measurements of the CP violation parameter sin2phi_1 at the Belle experiment. Efficiencies and wrong tag fractions are evaluated using flavor-specific B meson decays into hadronic and semileptonic modes. We achieve a total effective efficiency of $ 28.8 +- 0.6 %.Comment: 28 pages, 9 figure

Curvature, hybridization, and STM images of carbon nanotubes

The curvature effects in carbon nanotubes are studied analytically as a function of chirality. The pi-orbitals are found to be significantly rehybridized in all tubes, so that they are never normal to the tubes' surface. This results in a curvature induced gap in the electronic band-structure, which turns out to be larger than previous estimates. The tilting of the pi-orbitals should be observable by atomic resolution scanning tunneling microscopy measurements.Comment: Four pages in revtex format including four epsfig-embedded figures. The latest version in PDF format is available from http://fy.chalmers.se/~eggert/papers/hybrid.pd

Dimerization structures on the metallic and semiconducting fullerene tubules with half-filled electrons

Possible dimerization patterns and electronic structures in fullerene tubules as the one-dimensional pi-conjugated systems are studied with the extended Su-Schrieffer-Heeger model. We assume various lattice geometries, including helical and nonhelical tubules. The model is solved for the half-filling case of $\pi$-electrons. (1) When the undimerized systems do not have a gap, the Kekule structures prone to occur. The energy gap is of the order of the room temperatures at most and metallic properties would be expected. (2) If the undimerized systems have a large gap (about 1eV), the most stable structures are the chain-like distortions where the direction of the arranged trans-polyacetylene chains is along almost the tubular axis. The electronic structures are ofsemiconductors due to the large gap.Comment: submitted to Phys. Rev. B, pages 15, figures 1

Magnetic Structure of Nano-Graphite Moebius Ribbon

We consider the electronic and magnetic properties of nanographite ribbon with zigzag edges under the periodic or Moebius boundary conditions. The zigzag nano-graphite ribbons possess edge localized states at the Fermi level which cause a ferrimagnetic spin polarization localized at the edge sites even in the very weak Coulomb interaction. The imposition of the Moebius boundary condition makes the system non-AB-bipartite lattice, and depress the spin polarization, resulting in the formation of a magnetic domain wall. The width of the magnetic domain depends on the Coulomb interaction and narrows with increasing U/t.Comment: 4 pages; 6 figures; published at J. Phys. Soc. Jpn. Vol. 72 No. 5 pp. 998-1001 (2003

Spin configurations of carbon nanotube in a nonuniform external potential

We study, theoretically, the ground state spin of a carbon nanotube in the presence of an external potential. We find that when the external potential is applied to a part of the nanotube, its variation changes the single electron spectrum significantly. This, in combination with Coulomb repulsion and the symmetry properties of a finite length armchair nanotube induces spin flips in the ground state when the external potential is varied. We discuss the possible application of our theory to recent measurements of Coulomb blocked peaks and their dependence on a weak magnetic field in armchair carbon nanotubes.Comment: RevTeX, 5 pages + two figure