L. Forró

Elastic modulus of ordered and disordered multiwalled carbon nanotubes

Reference LNNME-ARTICLE-1999-005doi:10.1002/(SICI)1521-4095(199902)11:2 3.0.CO;2-JView record in Web of Science Record created on 2007-04-23, modified on 2016-08-08

PATTERNED FILMS OF NANOTUBES USING MICROCONTACT PRINTING OF CATALYSTS

change in the vibrational structure of the PL spectrum were effected by MWNTs. The reduction of the PL efficiency can be a result of energy transfer and partial hole transfer from PPV chains to MWNTs, together with scattering and absorption by MWNTs. Using the composite, photovoltaic devices have been fabricated by employing MWNT as a hole-collecting electrode. We obtained good quantum efficiency (1.8 % at 2.9±3.2 eV), about twice that of the standard ITO device. It is considered that the high efficiency arises from a complex interpenetrating network of PPV chains with MWNTs and the relatively high work function of the MWNT film. The present results suggest the possible application of carbon nanotubes as a new interesting electrode material in macroscale devices.

Synthesis of MWNT-based composite materials with inorganic coating

Abstract Multiwalled carbon nanotube (MWNT) based metal oxide composites were prepared by an impregnation method using organometallic compounds as precursor. Aluminium isopropoxide (AlIP), tetraethyl orthosilicate (TEOS), and tetraethyl orthotitanate (TEOTi) were used as inorganic sources and decomposed by hydrolysis on the surface of carbon nanotubes. The composites were subsequently investigated by transmission electron microscopy and their coverage was compared. A direct, solvent-free impregnation technique turned out to be the most successful for all organometallic compounds and provided homogeneous inorganic cover layer on the surface of purified MWNTs.

Synthesis and manipulation of carbon nanotubes

This paper reviews recent results in the field of carbon nanotube (CNT) research obtained at our institute at EPFL. We show in particular that CNTs can be synthesized by the catalytic vapour deposition (CVD) technique with high efficiency and purity. Furthermore, we present recent examples of advances in the large-scale production of CNTs as well as in the chemical and mechanical manipulation of CNTs. The chemical manipulation involves covalent and non-covalent sidewall functionalization of single-wall CNTs and preparation of inorganic coatings on CVD-grown nanotubes for the realization of fibres and CNT-reinforced composites. Mechanical manipulation aims at the application of CNTs as tips for scanning probe microscopy.

Femtosecond snapshots of gap-forming charge-density-wave correlations in quasi-two-dimensional dichalcogenides 1 T − TaS 2 and 2 H − TaSe 2

Time-resolved optical spectroscopy of collective and single-particle excitations of 1 T-TaS2 and 2H-TaSe2 reveals the presence of a large gap in the excitation spectrum on the femtosecond time scale, associated with the formation of various degrees of charge-density-wave order. In common with superconducting cuprates, excitations with energies less than the full gap show much slower relaxation. This separation of time scales cannot be explained in a quasi-two-dimensional Fermi-liquid picture with an anisotropic gap but rather suggests the formation of a fluctuating spatially inhomogeneous state eventually forming a long-range ordered state at low temperatures.

Orbitally driven spin pairing in the three-dimensional nonmagnetic Mott insulator BaVS3: Evidence from single-crystal studies

Static electrical and magnetic properties of single crystal BaVS_3 were measured over the structural (T_S=240K), metal-insulator (T_MI=69K), and suspected orbital ordering (T_X=30K) transitions. The resistivity is almost isotropic both in the metallic and insulating states. An anomaly in the magnetic anisotropy at T_X signals a phase transition to an ordered low-T state. The results are interpreted in terms of orbital ordering and spin pairing within the lowest crystal field quasi-doublet. The disordered insulator at T_X<T<T_MI is described as a classical liquid of non-magnetic pairs.

Electronic and Mechanical Properties of Carbon Nanotubes

Interest in carbon nanotubes has grown at a very rapid rate because of their many exceptional properties, which span the spectrum from mechanical and chemical robustness to novel electronic transport properties. Their physics, chemistry and perspectives for applications are very challenging. Below we highlight the main results of the Lausanne group and their collaborators on transport, electron spin resonance, elastic and field emission properties of single wall (SWNT) and multi-wall (MWNT) carbon nanotubes.

Estimation of matrix element effects and determination of the Fermi surface in Bi2Sr2CaCu2O8+d systems using angle-scanned photoemission spectroscopy

The strong dependence of the momentum distribution of the photoelectrons on experimental conditions raises the question as to whether angle-resolved photoemission spectroscopy is able to provide an accurate reflection of the Fermi surface in Bi-based cuprate superconductors. In this paper we experimentally prove that the main contribution to the intensity variation comes from matrix-element effects and develop an approach to overcome this problem. We introduce a concept of ‘‘self-normalization’’ that makes the spectra essentially independent of both the matrix elements and particular experimental parameters. On the basis of this concept we suggest a simple and precise method of Fermi-surface determination in quasi-two-dimensional systems.

Pressure induced quantum critical point and non-Fermi-liquid behavior in BaVS3

The phase diagram of BaVS3 is studied under pressure using resistivity measurements. The temperature of the metal to nonmagnetic Mott insulator transition decreases under pressure, and vanishes at the quantum critical point p(cr) = 20 kbar. We find two kinds of anomalous conducting states. The high-pressure metallic phase is a non-Fermi liquid described by Deltarho approximately T(n) where n = 1.2-1.3 at 1<T<40 K. At p<p(cr), the transition is preceded by a wide precursor region with critically increasing resistivity which we ascribe to the opening of a soft Coulomb gap.

Gaps and excitations in fullerides with partially filled bands: NMR study of Na 2 C 60 and K 4 C 60

We present a nuclear magnetic resonance (NMR) study of