Observation of the flux line lattice in high Tc-superconductor Bi2.2Sr2CaCu2OX and Ti2Ba2CaCu2OX single crystals

The flux-line lattice (FLL) has been observed on the (001) face of high T_c Bi_2.2Sr₂CaCu₂O_X and Ti₂Ba₂CaCu₂O_X single cristals using the technique of decorating the sample with small ferromagnetic particles. Strong pinning of the Abrikosov vortices by plane defects along (100) and (010) planes has been found out on Bi_2.2Sr₂CaCu₂O_X. The triangular FLL with a long-range order has been observed on the perfect Ti₂Ba₂CaCu₂O_X single crystal. The penetration depth for a magnetic field parallel to (001) axis has been evaluated as ≤0.2μm at 4.2K for both materials.     

Nonmonotonic variation of the electrical conductivity of C<Subscript>60</Subscript> fullerene crystals dynamically compressed to 300 kbar as evidence of anomalously strong reduction of the energy barrier of C<Subscript>60</Subscript> polymerization at high pressures

The electrical conductivity of a C₆₀ fullerene crystal is measured under the conditions of quasi-isentropic loading by a diffuse shock wave to a pressure of 30 GPa at room temperature. Nonmonotonic behavior of the conductivity of the samples with an increase in pressure is observed: first, conductivity increases by several orders of magnitude and, then, decreases rapidly. An increase in conductivity is explained by a decrease in the band gap under pressure, whereas a decrease in conductivity may be explained under the assumption that the energy barrier of C₆₀ polymerization decreases similarly to the band gap with an increase in pressure. As a result, the rate of C₆₀ polymerization at high pressures increases considerably (by more than seven orders of magnitude).     

Electronic structure of the organic semiconductor copper phthalocyanine: experiment and theory

The electronic structure of the organic semiconductor copper-phthalocyanine (CuPc) has been determined by a combination of conventional and resonant photoemission, near-edge x-ray absorption, as well as by the first-principles calculations. The experimentally obtained electronic valence band structure of CuPc is in very good agreement with the calculated density of states results, allowing the derivation of detailed site specific information.     

Electronic properties of C60 single crystals doped with lithium by electrodiffusion

Diffusion of lithium cations in C₆₀ single crystals driven by electric field has been detected and studied. A novel technique for fullerene crystal doping based on injection of ions through a “superionic crystal/C₆₀ single crystal” heterojunction has been suggested. It has been found that lithium doping of C₆₀ single crystals brings about an ESR signal, and this signal as a function of time has been investigated. The electronic conductivity in Li_xC₆₀ crystals has a nonmetallic nature. Reflection spectra measured in the IR band have shown that the reflectivity due to free electrons gradually decreases with time, which correlates with the evolution of signals due to ESR and microwave conductivity. Lithium doping of crystals increases the oscillator strength of the T _1u (4) vibrational mode and shifts it to lower frequencies (from 1429 cm⁻¹ to 1413 cm⁻¹), which indicates that one electron is present at the C₆₀ molecule, and this fact may be treated as evidence that the LiC₆₀ phase is generated in a C₆₀ crystal. Zh. éksp. Teor. Fiz. 116, 1706–1722 (November 1999)     

The electronic structure of cobalt phthalocyanine

The electronic structure and morphology of organic semiconducting cobalt-phtalocyanine (CoPc) films in situ prepared on the Au(001)-5×20 superstructure have been studied by a combination of experimental and theoretical work. The CoPc molecular film was characterized by photoemission spectroscopy (PES, valence band and core-level). The experimental results were simulated and have been explained in the framework of density functional theory (DFT) calculations. The C 1s and N 1s core level spectra were analyzed by taking into account the fact that both types of atoms have different nonequivalent positions in the molecule. And finally, the experimentally obtained electronic valence band structure of CoPc is in very good agreement with ab initio density of state results, allowing a detailed site-specific insight into the system.     

Electronic structure of pristine CuPc: Experiment and calculations

The filled and unoccupied electronic states of the organic semiconductor copper-phthalocyanine (CuPc) have been determined by a combination of direct and resonant photoemission, near-edge X-ray absorption and first principles calculations. The experimentally obtained electronic states of CuPc are in very good agreement with results of ab initio density of states, allowing to derive detailed site specific information.     

Formation of sharp metal-organic semiconductor interfaces: Ag and Sn on CuPc

A detailed investigation of the chemistry and electronic structure during the formation of the interfaces between thin films of the archetypal organic molecular semiconductor copper phthalocyanine (CuPc) and Ag or Sn deposited on it was performed using photoemission and near-edge X-ray absorption spectroscopies with synchrotron light. Our study demonstrates the formation of sharp, abrupt interfaces, a behavior which is of particular importance for applications in organic devices. Moreover, for Ag on CuPc we demonstrate that this interface is free from any reaction, whereas there is slight interface reaction for Sn/CuPc.     

Raman scattering of light and IR absorption in carbon nanotubes

Raman light scattering and IR absorption spectra of samples containing multilayer carbon nanotubes in different stages of purification by the selective oxidation technique have been investigated. It was found that the Raman spectra of carbon nanotubes exhibit softening of the mode at 1582 cm⁻¹ corresponding to E _2g vibrations of graphite hexagons and a line at 120 cm⁻¹ due to the radial vibrations of nanotubes. In IR absorption spectra measured in the region of 0.07–0.3 eV, several sets of lines with a spacing of 15 meV (120 cm⁻¹) between lines of each group have been detected. We suggest that each group corresponds to electron transitions generating electron-hole pairs in semiconducting nanotubes and contains a phononless 00-line and its phonon replicas with spacing between them equal to the “breathing” mode energy of 120 cm⁻¹. Measurements of electric conductivity at a frequency of 9300 MHz indicate that, in addition to semiconducting nanotubes, the samples contain nanotubes with properties of a highly disordered semimetal. Zh. éksp. Teor. Fiz. 113, 1883–1891 (May 1998)     

Gap Reduction of C60 and C70 at High Pressure

Abstract

The absorption spectra of the C₆₀ and C₇₀ are measured at pressures up to 19 GPa. The pressure dependence of the fundamental absorption edge position E(P) is determined for both materials. The initial value of dE/dP=?0.15 eV/GPa for the stronger-absorption region of C₆₀ decreases up to ?0.019 eV/GPa at 12 GPa. The weaker-absorption region located near the fundamental absorption edge shifts slower dE/dP=?0.05 eV/GPa. For the C₇₀ the initial value of dE/dP=?0.1 eV/GPa decreases up to ?0.029 eV/GPa at 10 GPa. All pressure induced changes are reversible in this pressure range.     

Spectrum of gases liberated upon the stepwise heating of single-walled carbon nanotubes deuterated under pressure

JETP Letters - The mass spectra of gases liberated from single-walled carbon nanotubes saturated with deuterium under a pressure of 5 GPa at temperatures up to 50°C (10.8 wt % D) have been...