Publications

The pressure response of CeAg(1-x)Ni(x)Sb(2) is Studied by means of electrical resistivity measurements. The ferromagnetic ordering temperatures T(c) of this series decrease as pressure is applied, except CeNiSb(2), showing a pressure driven continuous increase of T(c). This refers to crystalline electric field effects originating distinct different magnetic ground states. Concomitantly, the pressure response of various material dependent parameters also behave in the opposite direction.

A typical facility for fabrication of devices based on high temperature superconducting (HTS) films grown on the less-expensive CeO2-buffered sapphire substrates comprises a transfer chamber, a chamber for CeO2 growth, a chamber for YBa2Cu3Oy (YBCO) growth, and a chamber for Au deposition at room temperature. Here we present the adaptation of our previously-reported method to create artificial pinning centres in HTS films through self-assembled nano-scale islands for this type of facility without making any modifications. We succeeded to grow Au nano-dots from an ultra-thin layer of Au grown at room temperature subsequently annealed in the chamber for YBCO deposition, in the same conditions as for YBCO growth. AFM and RBS were used to investigate the formation of Au nano-dots, while XRD and susceptibility measurements were used to study the properties of nano-structured YBCO films.

Micro and nanorods of potassium acid phthalate (KAP) with diameters ranging from a hundred nanometers to tens of microns were obtained by solution growth in polycarbonate (PC) ion track templates. The ion track templates were produced by swift heavy ion irradiation of PC foils (e.g. U with 11.4 MeV/nucleon specific energy) and subsequently etching. After the growth the host templates were partially dissolved in dichlormethane and imagined by scanning electron microscopy. The template approach allows the fabrication of arrays of uniform nanostructures with a controlled morphology.

A new anisotropic size-broadening model based on a spherical-harmonics representation allowing determination of both volume-and area-averaged apparent crystallites and convenient for implementation into Rietveld programs is described. The model effectiveness is demonstrated on a ZnO powder pattern exhibiting strongly anisotropic size broadening and pronounced super-Lorentzian peak shapes. Moreover, it is shown how the apparent crystallites can be interpreted in terms of physical models by using ellipsoidal and cylindrical crystallites with lognormal size distributions. This interpretation is critically assessed and it is argued that both simplified physical models and a priori complementary information (obtained by transmission electron microscopy, for instance) are often needed to avoid unstable and non-unique solutions.

We investigate the output performance of the 1.06 mu m(4)F(3/2)-->I-4(11/2) transition in Nd:GdVO4 and Nd:YVO4 thin-disk lasers under multi-pass pumping with diode lasers at 0.81 mu m and at 0.88 mu m, which corresponds to direct in-band pumping of the F-4(3/2) emitting level. The use of a pump module with 24 passes through the crystal allowed the realization of an in-band pumped Nd:GdVO4 thin-disk laser with 14.9 W of continuous wave (cw) output power at 1.06 mu m; the overall optical-to-optical efficiency was 0.50 and the slope efficiency with respect to the incident pump power was 0.52. Intracavity frequency-doubling of the Nd:GdVO4 thin-disk laser with a LiB3O5 (LBO) nonlinear crystal yielded 9.1 W of cw output power in the green at 0.53 mu m with an overall optical-to-optical efficiency of 0.31.

Several hole trapped centres, namely Tl2+, self-trapped hole and A-type centres, were observed by ESR in PbBr2:Tl single crystals after X-ray irradiation at 77 K. The corresponding spectra are visible up to 200 K for all three defect centres. The STH centres are observed at higher temperatures than in the undoped PbBr2 single crystals, probably due to the stabilising effect of the Tl+ impurities. The ESR parameters of the Tl2+ centre point to stronger covalency effects in PbBr2 than in the isostructural PbCl2 crystals. All hole trapped centres started decaying around 160 K, probably due to recombination with nonparamagnetic electron trapped centres. Besides a small concentration of self-trapped electron centres, no other electron trapped centres were observed. (c) 2008 Elsevier B.V. All rights reserved.

The hyperfine interactions and dynamics aspects in nanoparticles system of the xSnO(2)-(1-x)alpha-Fe2O3 (x = 0.0-1.0) have been investigated by Sn-119-Mossbauer and XRD techniques. The change revealed by the XRD (XRDSs) and Mossbauer spectra (MSs) vs. x was discussed in terms of the phase and lattice-dynamics changes. The evidences of the triple hyperfine magnetic fields' distributions (MHFDs) and their dependencies x (< 0.175) are discussed taking into account the super-transferred hyperfine interactions (STHI), the local disorder Sn4+/Fe3+ around the tin isotope probe and the reduced dimension effect.

Single crystallites of superhard, semiconducting, n-type, amber colored and p-type, blue colored, Be-doped cubic boron nitride have been irradiated either with UV (350 nm) light or with an intense beam of accelerated (1 MeV) electrons. The examination of the irradiated samples at low temperatures by high frequency W (95 GHz)-band electron spin resonance reveals several new, radiation-induced, isotropic paramagnetic centers. The UV irradiation of both types of crystals yields centers involving very likely protons. In the amber c-BN crystals the irradiation with I MeV electrons results in the formation of vacancy associated paramagnetic defects and quasi-free electrons in colloidal particles. (C) 2008 Elsevier B.V. All rights reserved.