Mechanochemical Adsorption of Phenol by Tot Swelling Clay Minerals

The mechanochemical adsorption of phenol by laponite, saponite, montmorillonite, beidellite and vermiculite was studied by IR and X-ray spectroscopy. Mixtures containing phenol and clay in the ratio of 6:10 were manually ground by a mortar and pestle for 1,3,5 and 10 min and the ground mixtures were investigated. Depending on the basicity of the clay mineral and the time of grinding, two different associations between interlay er cations, water and phenol were identified. In these associations phenol can act either as a proton acceptor or donor (Configurations I and II, respectively). The phenol is more acidic than water and in most cases phenol acts as a proton donor. With montmorillonite and beidellite phenol acts as a proton acceptor. In this association the aromatic ring forms π bonds with atoms of the oxygen planes of the tetrahedral sheets which donate electrons to the anti-bonding π orbitals of the phenol.     

Stress aging in the electron glass

A new protocol for an aging experiment is studied in the electron-glass phase of indium-oxide films. In this protocol, the sample is exposed to a non-Ohmic electric field F for a waiting time t(w) during which the system attempts to reach a steady state (rather than relax towards equilibrium). The relaxation of the excess conductance Delta G after Ohmic conditions are restored exhibits simple aging as long as F is not too large.     

Disorder induced granularity in an amorphous superconductor

We present experimental evidence that shows that the transport mechanism on the insulating side of the superconductor to insulator transition may be modified by the presence of small “droplets” of non-percolating superconducting regions. From the conductivity point of view, the system behaves as a granular system despite the fact that the underlying structure is essentially amorphous.     

Suppression of inelastic electron-electron scattering in anderson insulators

We report on measurements of absorption from applied ac fields in Anderson-localized indium-oxide films. The absorption shows a roll-off at a frequency that is much smaller than the electron-electron scattering rate measured at the same temperature in diffusive samples of this material. These results are interpreted as evidence for discreteness of the energy spectrum.     

Quantum coherent effects in Anderson insulators

During the last two decades quantum interference effects have been extensively studied in the transport properties of diffusive systems such as metals and semiconductors. When the spatial disorder in these systems exceeds a critical value the electronic wavefunctions are localized and their ground state is insulating (the Anderson transition). At finite temperatures charge transport in this phase involves phonon-assisted tunnelling between localized states. This mode of transport is purely quantum mechanical and has no classical analogue. Anderson insulators are therefore the paradigmatic system for studying interference phenomena of electron waves in random media. In this paper we discuss the question of quantum coherence in Anderson insulators and review some of the experimental manifestations of interference phenomena in their transport properties.