Reinvestigation of the thermoelectric properties of Ag8GeTe6

High‐density polycrystalline samples (above 98% of the theoretical density) of Ag₈GeTe₆ were prepared by solid‐state reactions of Ag₂Te, GeTe, and Te, followed by hot‐pressing. The thermoelectric properties were measured at temperatures ranging from room temperature to around 700 K. The thermal conductivity values were extremely low (0.25 Wm^–1 K^–1 at room temperature), and consequently Ag₈GeTe₆ exhibited a relatively high thermoelectric figure of merit, ZT = 0.48 at 703 K. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

On kaonic hydrogen. Phenomenological quantum field theoretic model revisited

We argue that due to isospin and U-spin invariance of strong low-energy interactions the S-wave scattering lengths a ⁰ ₀ and a ¹ ₀ of ˉN scattering with isospin I = 0 and I = 1 satisfy the low-energy theorem a ⁰ ₀ +3a ¹ ₀ = 0 valid to leading order in chiral expansion. In the model of strong low-energy ˉN interactions at threshold (Eur. Phys. J. A 21, 11 (2004)) we revisit the contribution of the Σ(1750) resonance, which does not saturate the low-energy theorem a ⁰ ₀ +3a ¹ ₀ = 0, and replace it by the baryon background with properties of an SU(3) octet. We calculate the S-wave scattering amplitudes of K^-N and K^-d scattering at threshold. We calculate the energy level displacements of the ground states of kaonic hydrogen and deuterium. The result obtained for kaonic hydrogen agrees well with recent experimental data by the DEAR Collaboration. We analyse the cross-sections for elastic and inelastic K^-p scattering for laboratory momenta 70MeV/c < p _K < 150MeV/c of the incident K^--meson. The theoretical results agree with the available experimental data within two standard deviations.     

Investigation of the interaction of evaporated aluminum with vapor deposited Teflon AF films via X-ray photoelectron spectroscopy

The interfacial bonding and mixing between evaporated aluminum and a vapor deposited Teflon AF (abbreviated to AF) film have been investigated with X-ray photoelectron spectroscopy. Graphite carbon (C–C), and aluminum carbide (Al–C), oxide (Al–O–C) and fluoride (Al–F) are formed when aluminum atoms are deposited on to the AF film. With increasing deposition of aluminum, the concentrations of these newly formed components increase gradually. Moreover, in situ annealing results in remarkable increases in the C–C, Al–C, Al–O–C and Al–F configurations and a decrease in metallic aluminum. No significant diffusion of aluminum into the AF film was observed during the annealing. The Al compounds form a layer at the Al/AF interface that acts as an adhesion promoter and diffusion barrier. Received: 21 October 2002 / Accepted: 22 October 2002 / Published online: 15 January 2003 RID="*" ID="*"Corresponding author. Fax: +49-431/880-6229, E-mail: sjding@yahoo.com     

Electrical Characteristics of Copper Phthalocyanine Thin-Film Transistors with Polyamide-6/Polytetrafluoroethylene Gate Insulator

Polyamide-6（PA 6）/polytetrafluoroethylene is studied as a potential gate dielectric for flexible organic thin film transistors. The same method used for the formation of organic semiconductor and gate dielectric films greatly simplifies the fabrication process of devices. The fabricated transistors show good electrical characteristics. Ambipolar behaviour is observed even when the device is operated in air.     

Silver oligomer and single fullerene electronic properties revealed by a scanning tunnelling microscope

Clusters on surfaces have been investigated with low-temperature scanning tunnelling microscopy and spectroscopy. Constant current spectra acquired on Ag oligomers and one-dimensional chains on a Ag(111) reveal a single resonance peak whose energy shifts towards the Fermi level with increasing cluster size. Next, controlled and reproducible contact between a STM tip and a C₆₀ molecule adsorbed on Cu(100) is reported. The transition from tunnelling to contact is discussed in terms of local heating of the tip-molecule junction.     

Exact solutions for network rewiring models

Evolving networks with a constant number of edges may be modelled using a rewiring process. These models are used to describe many real-world processes including the evolution of cultural artifacts such as family names, the evolution of gene variations, and the popularity of strategies in simple econophysics models such as the minority game. The model is closely related to Urn models used for glasses, quantum gravity and wealth distributions. The full mean field equation for the degree distribution is found and its exact solution and generating solution are given.     

Structure of low-lying <Superscript>12</Superscript>C resonances

The hyperspherical adiabatic expansion is combined with complex scaling and used to calculate low-lying nuclear resonances of ¹²C in the 3α model. We use Ali-Bodmer potentials and compare results for other potentials α-α with similar ⁸Be properties. A three-body potential is used to adjust the ¹²C resonance positions to desired values extending the applicability of the method to many-body systems decaying into three α-particles. For natural choices of three-body potentials we find 14 resonances below the proton separation threshold, i.e. two 0⁺, three 2⁺, two 4⁺, one of each of 1^±, 2^-, 3^±, 4^-, and 6⁺. The partial-wave decomposition of each resonance is calculated as a function of the hyperradius. Strong variation is found from small to large distance. The connection to previous experimental and theoretical results is discussed and agreements as well as disagreements are emphasized.     

Stabilizing the intensity of a wave amplified by a beam of particles

The intensity of an electromagnetic wave interacting self-consistently with a beam of charged particles as in a free electron laser, displays large oscillations due to an aggregate of particles, called the macro-particle. In this article, we propose a strategy to stabilize the intensity by re-shaping the macro-particle. This strategy involves the study of the linear stability (using the residue method) of selected periodic orbits of a mean-field model. As parameters of an additional perturbation are varied, bifurcations occur in the system which have drastic effect on the modification of the self-consistent dynamics, and in particular, of the macro-particle. We show how to obtain an appropriate tuning of the parameters which is able to strongly decrease the oscillations of the intensity without reducing its mean-value.     

Growth of GaN single crystals with extremely low dislocation density by two-step dislocation reduction

We have discovered a mechanism which can significantly reduce the dislocation density during the growth of GaN single crystals in the Na flux method. The significant reduction of the dislocation density occurs in the later stage of LPE growth, rather than solely at the seed-LPE interface for which we have already reported evidence indicating the presence of bundling dislocations. The two-step dislocation reduction is the key in achieving extremely low dislocation density using this method.     

In situ spectroscopic ellipsometry: Application to Sb coverage measurement in the monolayer range on Si (111)

In this paper, we present an analysis of antinomy deposition on silicon in the range of 0.1 to 1 monolayer by in situ spectroscopic ellipsometry. After a careful choice of viewpoint material, ellipsometric measurements are found to be sensitive to small surface perturbations, especially with antimony. In fact, less than a 0.1 monolayer of antimony on silicon at room temperature is detectable. Moreover, a linear dependence of the ellipsometric signal on Sb coverage is observed in the monolayer range. Consequently, the signal versus time variation directly gives the Sb adsorption kinetics on silicon. The saturation to one monolayer of compact antimony on silicon surface is used in order to calibrate the spectra.