Showing papers in "Advances in Physics in 1989"

Noise in solid-state microstructures: A new perspective on individual defects, interface states and low-frequency (1/ƒ) noise

Abstract: In very small electronic devices the alternate capture and emission of carriers at an individual defect site generates discrete switching in the device resistance—referred to as a random telegraph signal (RTS) The study of RTSs has provided a powerful means of investigating the capture and emission kinetics of single defects, has demonstrated the defect origins of low-frequency (1/ƒ) noise in these devices, and has provided new insight into the nature of defects at the Si/SiO2 interface

Linear and nonlinear optical properties of semiconductor quantum wells

Abstract: In this article we review the experimental and theoretical investigations of the linear and nonlinear optical properties of semiconductor quantum well structures, including the effects of electrostatic fields, extrinsic carriers and real or virtual photocarriers.

Artificial metallic superlattices

Abstract: Vue d'ensemble sur la preparation, la caracterisation, les proprietes de transport et les proprietes magnetiques des superreseaux

Localized states in glasses

Abstract: The properties of amorphous materials determined by the presence of localized atomic and electronic states are reviewed. Experimental data on atomic dynamics in glasses are described. The two-level-system (TLS) model is presented, and the limits of its applicability analysed. The concept of soft atomic potentials, allowing generalization of the TLS model to higher energies, is introduced. Atomic dynamics in soft potentials, as well as soft-potential coupling with phonons and thermal expansion of glasses, are described. Localized electronic states in glasses are investigated and different theoretical models of such states in glassy semiconductors are reviewed. The connection between localized electronic states and soft potentials is studied. Particular attention is paid to low-relaxation processes in glasses controlled by two-well soft potentials; specifically, low-frequency noise in disordered conductors is considered. The possibility of investigating the localized states in question with the hel...

The electronic and magnetic properties of the 3d transition metal intercalates of TiS2

Abstract: The introduction of 3d transition metals (M) into the van der Waals gaps between the weakly coupled layers of transition metal dichalcogenides TX2 (T:transition metal, X:chalcogen) produces an interesting family of intercalation compounds, M x TX2, the physical properties of which are different from those of the host TX2 matrix because of ‘host-guest’ interactions. In this article we shall review the salient features of the M x TiS2 family with the simple 1T-CdI2 type layered structure, which have been extensively studied by structural, transport, specific heat and lattice dynamic, magnetic and photoemission spectroscopic measurements. In contrast with the previously reported series of intercalation complexes of the Group V transition metal dichalcogenides, a characteristic of the M x TiS2 materials is strong hybridisation between the guest atom M 3d orbitals and the host Ti 3d and S 3p orbitals, leading to changes in the Fermi energy E F of the conduction band, the density of states at E F and v...

Kinetic properties of metals near electronic topological transitions (2 1/2-order transitions)

Abstract: Under external influences, the electronic topological transition (ETT) may be realized in metals: the topological properties of the metal Fermi-surface are changed, that is, either its separate voids are generated or disappear, or the closed Fermi surface is transformed into an open one. The peculiarity of the density of states, appearing at the ETT, involves a number of peculiarities of the thermodynamical and kinetic properties of the metal. In the present review we shall describe the significant successes achieved in the past decade in the experimental and theoretical investigations of the kinetic properties of metals undergoing the ETT. The exposed microscopic ETT theory takes into account the temperature diffuseness of the Fermi surface, as well as possible processes of electron scattering. The peculiarities of the metal thermopower and conductivity in the ETT vicinity are discussed in detail and an analysis of the abundant experimental data is carried out. The influence of the ETT upon the ...

The structure of amorphous hydrogenated silicon and its alloys: A review

Abstract: The atomic structure of hydrogenated amorphous silicon is discussed from the point of view of three length scales, related to short-, medium- and long-range structure, and also from the viewpoint of Si-related, H-related and dopant-related environments. The results of the use of various techniques such as extended X-ray absorption fine structure, nuclear magnetic resonance and vibrational spectroscopy are discussed. The use of such chemically-specific structural probes has allowed information to be obtained for the first time on the local structural environments of the incorporated hydrogen and dopant atoms, and it is this structure which is crucial in controlling the electronic properties of this material.

Curved crystals, defects and disorder

Abstract: The structure of media whose short-range order cannot be extended crystallographically in flat space (disordered metallic and covalent systems, Frank-Kasper phases, quasicrystals, blue phases and various molecular phases) is describable in terms of distributions of defects in a crystal situated in a space of constant curvature. This paper reviews the geometrical and topological properties of curved crystals and of their defects, the relations between defects and the mapping on flat space, and how certain universal properties generally attributed to disordered systems can be inferred from this model. A number of topics which have not yet received full recognition as belonging to the subject of frustration and curvature are emphasized, such as the role of other defects than disclinations (in particular disvections), the curved space description of incommensurate structures such as quasicrystals, and in these latter the concept of phase.