Measurements of the actual fluorine content x in the RO1−xFxFeAs-samples by wavelength-dispersive X-ray spectroscopy (WDX) reveal sample dependent discrepancies to the nominal fluorine content (initial weight). In particular for SmO1−xFxFeAs, the measured value only reached approximately half of the required value. In the lanthanum compound LaO1−xFxFeAs, we found a good agreement mainly for x>0.05, but the fluorine hardly goes into the sample for x<0.05. We used the measured fluorine content when plotting the electronic phase diagrams again and find a more consistent picture occurs as well for our samples as for comparison with the divers published data.

Current-voltage dependence for In2O3-SrO ceramics contains three regions: linear at low voltages, superlinear at intermediate voltages (current is increased stronger than voltage) and sublinear at higher voltages (current is increased weaker than voltage). The appearance of sublinear region after superlinear one cannot be explained by the existing theory. Based on the experimental data (electrical measurements, SEM and XPS) a modified grain-boundary model is suggested. In the model the additional adsorption of oxygen due to a capture of electrons at the grain-boundary states is assumed. Accordingly, the barrier height is increased and current is saturated. Calculated current-voltage dependences correspond experimentally observed ones.

Concerns about violent conduct of service users towards healthcare staff have prompted a ‘zero tolerance’ policy within the National Health Service. This policy specifically excludes users of mental health services. We attempt to challenge artificial distinctions between users of mental health and other services, and propose an ethical underpinning to the implementation of this policy.

In the title of this paper (and also in several places in the text), the chemical notation for the orthorhombic semiconducting iron disilicide is given incorrectly. In the whole paper, the chemical formula “β-FeSi2.5” should be replaced by the formula “β-FeSi2”.

A new THz/IR/UV photon source at Jefferson Lab is the first of a new generation of light sources based on a Energy-Recovered, (superconducting) Linac (ERL). The machine has a 160 MeV electron beam and an average current of 10 mA in 75 MHz repetition rate hundred femtosecond bunches.

These electron bunches pass through a magnetic chicane and therefore emit synchrotron radiation. For wavelengths longer than the electron bunch the electrons radiate coherently a broadband THz ∼ half cycle pulse whose average brightness is > 5 orders of magnitude higher than synchrotron IR sources. Previous measurements showed 20 W of average power extracted[1]. The new facility offers simultaneous synchrotron light from the visible through the FIR along with broadband THz production of 100 fs pulses with >200 W of average power (see G. P. Williams, this conference).

The FELs also provide record-breaking laser power [2]: up to 10 kW of average power in the IR from 1 to 14 microns in 400 fs pulses at up to 74.85 MHz repetition rates and soon will produce similar pulses of 300–1000 nm light at up to 3 kW of average power from the UV FEL. These ultrashort pulses are ideal for maximizing the interaction with material surfaces. The optical beams are Gaussian with nearly perfect beam quality. See www.jlab.org/FEL for details of the operating characteristics; a wide variety of pulse train configurations are feasible from 10 microseconds long at high repetition rates to continuous operation.

The THz and IR system has been commissioned. The UV system is to follow in 2005. The light is transported to user laboratories for basic and applied research. Additional lasers synchronized to the FEL are also available. Past activities have included production of carbon nanotubes, studies of vibrational relaxation of interstitial hydrogen in silicon, pulsed laser vapor deposition, nitriding of metals, and energy flow in proteins. This paper will present the status of the system and discuss some of the opportunities provided by this unique light source for modifying and studying materials.

Results of magnetization and magnetic susceptibility measurements on undoped and Co-doped FeSi2.5 single crystals are presented. The temperature dependence of the magnetic susceptibility of the Co-doped sample in the range of 5–300 K can be explained by temperature-dependent contributions due to paramagnetic centers and the carriers excited thermally in the extrinsic conductivity region. The values of the paramagnetic Curie temperature and activation energy of the donor levels were estimated. It is also shown that the magnetic susceptibility of Co-doped samples cooled in zero external field and in a field are different. This resembles the properties of spin-glasses and indicates the presence of coupling between magnetic centers.

The influence of composition and high-temperature heat treatment on phase content and superconducting properties of the Yni2B2C phase was investigated. Phase relations in those parts of the Y–Ni–B–C quaternary phase diagram, which are relevant for the YNi2B2C intermetallic phase formation, were revealed by x-ray diffraction, optical and scanning electron microscopy, and high-temperature differential thermoanalysis. A widespread interval of superconducting transition temperatures TC = 10.4–15.2 K and small transition width <0.3 K were determined from samples of different nominal compositions after high-temperature annealing. The different intrinsic properties are ascribed to composition variations of the YNi2B2C phase and related to structure parameters, residual resistance ratios, and element concentrations determined by the electron probe microanalysis.

Epitaxial ReSi1.75 thin films of variable thickness between 15nm and 150nm have been prepared in an one step process by Facing Target Sputtering (FTS) onto heated (100) and (111)Si and SOS wafers. The epitaxial relations and film structure have been investigated by Xray diffraction and transmission electron microscopy. Epitaxial growth was found at a substrate temperature of 1070K. Thermoelectric properties were measured between 100K and 450K and compared to the transport behavior of bulk ReSi1.75 and polycrystalline films. A distinct dependence of both the conductivity and thermopower was found on the film thickness, on unintentional doping and on the film structure. The results show that epitaxial ReSi1.75 films prepared by FTS can be a basis for further investigations of thermoelectric silicide/silicon multilayers.

The electrical transport properties of β-FeSi2 single crystals have been investigated in dependence on the purity of the source material and on doping with 3d transition metals. The transport properties included are electrical conducticvity, Hall conductivity and thermopower mainly in the temperature range from 4K to 300K. The single crystals have been prepared by chemical transport reaction in a closed system with iodine as transport agent. In undoped single crystals prepared with 5N Fe both electrical conductivity and thermopower depend on the composition within the homogeinity range of β-FeSi2 which is explained by different intrinsic defects at the Sirich and Fe-rich phase boundaries. In both undoped and doped single crystals impurity band conduction is observed at low temperatures but above 100K extrinsic behaviour determined by shallow impurity states. The thermopower shows between 100K and 200K a significant phonon drag contribution which depends on intrinsic defects and additional doping. The Hall resistivity is considered mainly with respect to an anomalous contribution found in p-type and n-type single crystals and thin films. In addition doped single crystals show at temperatures below about 130K an hysteresis of the Hall voltage. These results make former mobility data uncertain. Comparison will be made between the transport properties of single crystals and polycrystalline material.