Theory of the thermally-stimulated-current transport peak. Application to a dispersive transport case

13 págs.; 6 figs.Thermally-stimulated-current (TSC) technique consists of heating a dielectric, with excess carriers having been introduced. The current flowing under the effect of applied electric field is then recorded as a function of increasing temperature. The current maximum obtained is called a >transport TSC peak> if it appears due to thermally activated transport of carriers initially generated at one electrode and collected at the other. In this paper the transport of carriers, controlled by multiple trapping, is studied when the temperature of the system is increased linearly with time. The general equations for current density in a TSC experiment are obtained and are applied for the cases of a single trap and an exponential trap distribution. The condition for a TSC current maximum, initial rise of current, and partial heating technique are studied in detail. The properties of the transport TSC peak differ considerably from those of the classical TSC; the position of the current maximum and activation energy found from partial heating at the maximum depend on the field applied and on sample thickness. It is also found that there exists a correlation between the transport TSC peak and time-of-flight signal, and the transport parameters found from TSC (activation energy of mobility, parameter of dispersion ±, etc.) correspond to those of the time of flight measurements. The critical trap criterion and concepts of lifetime and transit time are extended to the general case of nonisothermal transport. © 1981 The American Physical Society.Peer Reviewe

Matter-screened Casimir force and Casimir-Polder force in planar structures

Using a recently developed theory of the Casimir force (Raabe C and Welsch D-G 2005 Phys. Rev. A 71 013814), we calculate the force that acts on a plate in front of a planar wall and the force that acts on the plate in the case where the plate is part of matter that fills the space in front of the wall. We show that in the limit of a dielectric plate whose permittivity is close to unity, the force obtained in the former case reduces to the ordinary, i.e., unscreened Casimir-Polder force acting on isolated atoms. In the latter case, the theory yields the Casimir-Polder force that is screened by the surrounding matter.Comment: 11 pages, 1 figure -- published online at J. Opt. B on Nov 16 200

Quantum properties of the parametric amplifier with and without pumping field fluctuations

The parametric amplifier with and without the pumping fluctuations of coupling function is considered when the fields are initially prepared in coherent light. The pumping fluctuations are assumed to be normally distributed with time-dependent variance. The effects of antibunching and anticorrelation of photons on the photon distribution, correlation between modes and factorial moments are demonstrated. A possible enhancement of photon antibunching for certain values of initial mean photon numbers is shown and discussed. We have shown also that new states (called modified squeezed vacuum states or even thermal states) can be generated from such an interaction. Further, we have demonstrated that the sum photon-number distribution can exhibit collapses and revivals in the photon-number domain somewhat similar to those known in the Jaynes-Cummings model.Comment: 17 pages, 6figure

Markovian Master Equations: A Critical Study

We derive Markovian master equations of single and interacting harmonic systems in different scenarios, including strong internal coupling. By comparing the dynamics resulting from the corresponding Markovian master equations with exact numerical simulations of the evolution of the global system, we precisely delimit their validity regimes and assess the robustness of the assumptions usually made in the process of deriving the reduced dynamics. The proposed method is sufficiently general to suggest that the conclusions made here are widely applicable to a large class of settings involving interacting chains subject to a weak interaction with an environment.Comment: 40 pages, 14 figures, final versio

Fifty Years of Study of the Piezoelectric Properties of Macromolecular Structured Biological Materials

The piezoelectricity of biopolymers was discovered by E. Fukada for wood and bone in the fifties. This paper induced a number of studies on piezoelectric behaviour of bone collagen and tendon in wet and dry conditions as well as in many biological substances: polysaccharides, proteins, and biodegradable, optically active oriented films of poly(L-lactic acid). The implantation of this polymer induced the growth of bone, possibly because the ionic current caused by piezoelectric polarization stimulated the activity of bone cells. The phenomenon of bone growth has been discussed in terms of application of various substances, particularly modified collagen. The healing process of bone growth is still open both from the view of mechanism and biocompatibilities of materials used for this purpose. Fukada's group has a leading position in these studies. The fifty years of study of piezoelectricity in biomaterials resulted in many important observations and indication for further promising experimental and theoretical studies which will help to discover new ways and new materials for the tissue reconstruction

Fifty Years of Study of the Piezoelectric Properties of Macromolecular Structured Biological Materials

The piezoelectricity of biopolymers was discovered by E. Fukada for wood and bone in the fifties. This paper induced a number of studies on piezoelectric behaviour of bone collagen and tendon in wet and dry conditions as well as in many biological substances: polysaccharides, proteins, and biodegradable, optically active oriented films of poly(L-lactic acid). The implantation of this polymer induced the growth of bone, possibly because the ionic current caused by piezoelectric polarization stimulated the activity of bone cells. The phenomenon of bone growth has been discussed in terms of application of various substances, particularly modified collagen. The healing process of bone growth is still open both from the view of mechanism and biocompatibilities of materials used for this purpose. Fukada's group has a leading position in these studies. The fifty years of study of piezoelectricity in biomaterials resulted in many important observations and indication for further promising experimental and theoretical studies which will help to discover new ways and new materials for the tissue reconstruction

Application of Conducting Organic Solids for Biological Sensors: Successes and Problems

Studies on the basic properties and fabrication of biosensors based on conducting organic polymers have been reviewed. Several types of biosensors and some classes of conducting polymers used in biosensors are described. It is shown that their selective responses towards a dissolved analyte have lead to their successful application in a new generation of ion, molecular and biosensors. Some important open problems in this fast growing field have also been indicated. They are related with the complex interactions of biomolecules and/or cells with the conducting transducers. The present tendency to extreme miniaturization of biosensors related to the utilization of a few biomolecules and/or a single cell as a heart of biosensing devices seems to be very close to molecular electronics

FORMATION OF SUPERMOLECULAR STRUCTURES IN THIN POLYMER LAYERS

ABSTRACT Thin polymer films can be prepared by polymerization of a monomer in the gas phase. The polymerization may be initiated by light, pyrolysis, electron bom bardment, or by glow discharge. The formation of polymers occurs mainly in the adsorbed monomer layer on a suitable support. The glow discharge technique is most effective. It was originally considered that such films are rather amorphous irrespective of the support material, but later investigations on organosilicon compounds have shown that during polymerization, or immediately after, some supermolecular structures are formed. Supermolecular structure formation was observed in the preparation of organic polymers by the glow discharge technique. Poly(benzene) films are at first amorphous but later exhibit birefringent areas and supermolecular structures. Similar phenomena were observed in other polymers. The origin of these supermolecular structure formations is not exactly known at this time. It is supposed that the local stresses due to further polymerization processes (related to trapped tree radicals) and crosslinking enhance the structural changes. With more polar monomers some orientation may occur during polymerization. The crystallinity of these layers is low. The structure of thin polymer layers depends on the temperature and the kinds of support. Some characteristic features of epitaxial growth were observed for layers obtained on sodium chloride crystal surfaces. When metals are used as supports the capacity for supermolecular structure formation depends on the purity of the surface. Typical spherulitic structures are not formed but hedrite-like structures may be observed