Thermo-optic coefficients of monoclinic KLu(WO<Subscript>4</Subscript>)<Subscript>2</Subscript>

The three thermo-optic coefficients of the biaxial laser host KLu(WO₄)₂ are measured at 633 nm by a deflection method. Their values at 300 K amount to ∂ n _g /∂ T=−7.4×10⁻⁶ K⁻¹; ∂ n _m /∂ T=−1.6×10⁻⁶ K⁻¹ and ∂ n _p /∂ T=−10.8×10⁻⁶ K⁻¹. Nearly athermal propagation directions are found for polarizations along the N _m and N _p dielectric axes.     

Structural transformation of MoO<Subscript>3</Subscript> nanobelts into MoS<Subscript>2</Subscript> nanotubes

The structural transformation of MoO₃ nanobelts into MoS₂ nanotubes using a simple sulfur source has been reported. This transformation has been extensively investigated using electron microscopic and spectroscopic techniques including scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), electron diffraction (ED), and energy-dispersive X-ray analysis (SEM-EDAX and TEM-EDX). The method described in this report will serve as a generic route for the transformation of other oxide nanostructures into the chalcogenide nanostructures.     

Growth and magneto-optical properties of LiTb(MoO<Subscript>4</Subscript>)<Subscript>2</Subscript> crystal

Lithium terbium molybdate (LiTb(MoO₄)₂) single crystal was grown by the Czochralski method. The lattice parameters of the crystal were determined by X-ray diffraction analysis. The absorption coefficient and the Faraday rotation spectrum (B=1.07 T) were investigated at wavelengths of 400–1500 nm at room temperature. Verdet constants of LiTb(MoO₄)₂ crystal at 532-, 633- and 1064-nm wavelengths were measured by the extinction method. The results show that LiTb(MoO₄)₂ crystal has a larger magneto-optical figure of merit than that of terbium gallium garnet at wavelengths of 600–1500 nm.     

Spectroscopic properties of Nd<Superscript>3+</Superscript>:CaNb<Subscript>2</Subscript>O<Subscript>6</Subscript> crystal

The absorption spectra, fluorescence spectrum and fluorescence decay curve of Nd³⁺ ions in CaNb₂O₆ crystal were measured at room temperature. The peak absorption cross section was calculated to be 6.202×10⁻²⁰ cm² with a broad FWHM of 7 nm at 808 nm for E//a light polarization. The spectroscopic parameters of Nd³⁺ ions in CaNb₂O₆ crystal have been investigated based on Judd-Ofelt theory. The parameters of the line strengths Ω _t are Ω ₂=5.321×10⁻²⁰ cm²,Ω ₄=1.734×10⁻²⁰ cm²,Ω ₆=2.889×10⁻²⁰ cm². The radiative lifetime, the fluorescence lifetime and the quantum efficiency are 167 μs, 152 μs and 91%, respectively. The fluorescence branch ratios are calculated to be β ₁=36.03%,β ₂=52.29%,β ₃=11.15%,β ₄=0.533%. The emission cross section at 1062 nm is 9.87×10⁻²⁰ cm².     

Magnetic properties of DyNi<Subscript>2</Subscript>B<Subscript>2</Subscript>C studied with a two-ion model for antiferromagnets

In a rare-earth antiferromagnet, two neighboring magnetic ions order spontaneously in opposite directions below the Néel temperature. Especially when it is placed in an external magnetic field, the two magnetic ions react to the field in different ways, so that they usually have different magnitudes and orientations below the magnetic transition temperature. Therefore, to describe the magnetic structure of an antiferromagnet, the single-ion ferromagnetic-like model is inadequate. To solve this problem, a two-ion model for rare-earth antiferromagnets is proposed and used in this work to investigate the magnetic properties of DyNi₂B₂C. The magnetic susceptibility curves obtained with this model show good agreements with experimental data.     

Structural and dehydriding properties of Ca(BH<Subscript>4</Subscript>)<Subscript>2</Subscript>

We have investigated the structural and dehydriding properties of Ca(BH₄)₂. It was found that Ca(BH₄)₂ undergoes a structural phase transformation from an orthorhombic low-temperature (LT) modification into a tetragonal high-temperature (HT) modification between 433 K and 523 K. The amount of hydrogen desorbed from Ca(BH₄)₂ during the pressure–composition (p–c) isotherm measurement was 5.9 mass%. This hydrogen desorption is caused by the partial dehydrogenation of Ca(BH₄)₂ accompanied by the formation of CaH₂ and orthorhombic intermediate phases.     

High pressure study of the organic compound (TMTTF)<Subscript>2</Subscript>BF<Subscript>4</Subscript>

High pressure resistivity measurements of the organic compound (TMTTF)₂BF₄ have been performed in a newly developped Bridgman cell providing good pressure conditions on a wide pressure range. For the first time in this compound a zero resistance superconducting state is observed between 3 and 4 GPa. At temperatures above the superconducting transition, the resistivities of the two high quality samples show a different behavior. One sample, provides indications for a magnetic quantum critical point at the maximum of T_c, whereas in the other antiferromagnetic spin-fluctuations are present above T_c.     

Electronic properties of orthorhombic LiGaS<Subscript>2</Subscript> and LiGaSe<Subscript>2</Subscript>

We report theoretical calculations of the band structure and density of states for orthorhombic LiGaS₂ (LGS) and LiGaSe₂ (LGSe). These calculations are based on the full potential linear augmented plane wave (FP-LAPW) method within a framework of density functional theory. Our calculations show that these crystals have similar band structures. The valence band maximum (VBM) and the conduction band minimum (CBM) are located at Γ, resulting in a direct energy band gap. The VBM is dominated by S/Se-p and Li-p states, while the CBM is dominated by Ga-s, S/Se-p and small contributions of Li-p and Ga-p. From the partial density of states we find that Li-p hybridizes with Li-s below the Fermi energy (E _F), while Li-s/p hybridizes with Ga-p below and above E _F. Also, we note that S/Se-p hybridizes with Ga-s below and above E _F.     

Post-deposition processes for nanostructures formed by electron beam induced deposition with Pt(PF<Subscript>3</Subscript>)<Subscript>4</Subscript> precursor

Electron beam induced deposition was performed using a Pt(PF₃)₄ precursor gas. Self-standing nanowires were produced on the edge of a molybdenum film, followed by two post-deposition processes; electron beam irradiation at room temperature and heating at about 400 K in vacuum. The as-deposited nanowires were composed of an amorphous phase, of which the dominant composition was platinum but containing a small amount of phosphorus impurity. After irradiating with a 300 keV electron beam, the amorphous nanowires were transformed to crystalline ones. By heating, the as-deposited nanowires became single-crystal platinum with a large grain size and the phosphorus content disappeared.     

Recent high-<Emphasis Type="Italic">p</Emphasis><Subscript><Emphasis Type="Italic">T</Emphasis></Subscript> results from STAR

We present selected recent results of multi-hadron correlation measurements in azimuth and pseudorapidity at intermediate and high p _T in Au+Au collisions at , from the STAR experiment at RHIC. At intermediate p _T , measurements are presented that attempt to determine the origin of the associated near-side (small Δφ) yield at large pseudo-rapidity difference Δη that is found to be present in heavy ion collisions. In addition, results are reported on new multi-hadron correlation measures at high-p _T that use di-hadron triggers and multi-hadron cluster triggers with the goal to constrain the underlying jet kinematics better than in the existing measurements of inclusive spectra and di-hadron correlations.     

Wave mixing in nominally undoped Sn<Subscript>2</Subscript>P<Subscript>2</Subscript>S<Subscript>6</Subscript> at high light intensities

The intensity dependence of the photorefractive response of Sn₂P₂S₆ is studied for the Kr⁺-laser wavelength of 647 nm and pump-beam intensities of up to 10 W/cm². A considerable enhancement of the two-beam coupling gain factor with increasing intensity at a grating spacing of ≃1 μm is attributed to a light-induced increase of the effective trap density. The large gain reached at high intensities is applied for the build up of a double phase conjugate mirror with a sub-millisecond switch-on time.     

Incubation in the UV irradiation of condensed CHCl<Subscript>3</Subscript> solids

Matrix-Assisted-Pulsed-Laser-Evaporation (MAPLE) has emerged as a very promising technique for the deposition of polymers and biopolymers in intact and functional form. However, our understanding of the mechanism of the procedure is still limited. Here, we examine laser-induced (248 nm) desorption from condensed CHCl₃ solid, which has been employed as a potential matrix in MAPLE. We find that the absorption of the condensed halocarbon increases significantly with successive laser pulses, as a result of the formation and accumulation of strongly absorbing products. This results in a significant increase of the ejection efficiency in the irradiation with successive laser pulses. Thus, in studies employing multi-pulse irradiation protocols, the attained laser-induced temperatures are considerably higher than what is estimated on the basis of the absorption coefficient of CHCl₃. Thus, contrary to previous suggestions, ablation of CHCl₃ frozen solid at 248 nm may be due to explosive boiling. A number of additional implications are also discussed.     

Dielectric investigations in Sr<Subscript>0.75</Subscript>Ba<Subscript>0.25</Subscript>Nb<Subscript>2</Subscript>O<Subscript>6</Subscript> relaxor ferroelectric thin films

The dielectric properties of Sr_0.75Ba_0.25Nb₂O₆ relaxor ferroelectric thin films were carefully analyzed. In contrast to bulk samples which present three distinct dielectric relaxation phenomena Sr_0.75Ba_0.25Nb₂O₆ thin films present only two of them. The suppression of the third anomaly can be mainly attributed to the narrow grain size distribution of nanograins and weak tensile strains imposed to the film from the substrate. The whole set of results point to the interpretation of a dielectric response characteristic of mesoscopic structure, which is composed of clusters and nanodomains.     

Effect of tetragonal lattice distortion of Co<Subscript>70</Subscript>Fe<Subscript>30</Subscript> on the tunneling magnetoresistance of AlO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> based magnetic tunnel junction

The tunneling magnetoresistance of Co₇₀Fe₃₀/AlO _x /Co₇₀Fe₃₀ magnetic tunnel junctions with epitaxial bottom electrode annealed at different temperatures was studied. The TMR was significantly enhanced when the bottom electrodes were annealed at 300°C and above. The interface roughness, barrier width and height are almost identical within the experimental uncertainty. However, high resolution reciprocal space mapping studies showed that the lattice distortion of the epitaxial bottom electrodes from body centered cubic to body centered tetragonal had the same trend as the TMR. The tetragonal lattice distortion is attributed to be the dominant factor for this spin polarization enhancement.     

Deposition and stoichiometry control of Nd-doped gadolinium gallium garnet thin films by combinatorial pulsed laser deposition using two targets of Nd:Gd<Subscript>3</Subscript>Ga<Subscript>5</Subscript>O<Subscript>12</Subscript> and Ga<Subscript>2</Subscript>O<Subscript>3</Subscript>

We have demonstrated pulsed laser deposition of Nd-doped gadolinium gallium garnet on Y₃Al₅O₁₂ by the simultaneous ablation of two separate targets of Nd:Gd₃Ga₅O₁₂ (GGG) and Ga₂O₃. Such an approach is of interest as a method of achieving stoichiometry control over films whilst the growth parameters are kept constant and optimal for high quality crystal growth. We show here how the stoichiometry and resultant lattice parameter of a film can be controlled by changing the relative deposition rates from the two targets. Films have been grown with enough extra Ga to compensate for the deficiency that commonly occurs when depositing only from a GGG target. We have also grown crystalline GGG films with an enriched Ga concentration, and this unconventional approach to film stoichiometry control may have potential applications in the fabrication of films with advanced compositionally graded structures.     

The structure and photoluminescence properties of TiO<Subscript>2</Subscript>-coated ZnS nanowires

The structure and photoluminescence properties of TiO₂-coated ZnS nanowires were investigated. ZnS nanowires were synthesized by thermal evaporation of ZnS powder and then coated with TiO₂ by using the metal organic chemical vapor deposition (MOCVD) technique. We performed scanning electron microscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy, and photoluminescence (PL) spectroscopy to characterize the as-synthesized and TiO₂-coated ZnS nanowires. TEM and XRD analyses revealed that the ZnS core and the TiO₂ coatings had crystalline zinc blende and crystalline anatase structures, respectively. PL measurement at room temperature showed that the as-synthesized ZnS nanowires had two emissions: a blue emission centered in the range from 430 to 440 nm and a green emission at around 515 nm. The green emission was found to be dominant in the ZnS nanowires coated with TiO₂ by MOCVD at 350°C for one or more hours, while the blue emission was dominant in the as-synthesized ZnS nanowires. Also the mechanisms of the emissions were discussed.     

Ferroelectric and dielectric properties of SrBi<Subscript>4</Subscript>Ti<Subscript>4</Subscript>O<Subscript>15</Subscript> thin films grown on Bi<Subscript>4</Subscript>Ti<Subscript>3</Subscript>O<Subscript>12</Subscript> film layer

Ferroelectric and dielectric properties of bilayered ferroelectric thin films, SrBi₄Ti₄O₁₅ grown on Bi₄Ti₃O₁₂, were investigated. The thin films were annealed at 700°C under oxygen atmosphere. The bilayered thin films were prepared on a Pt(111)/Ti/SiO₂/Si substrate by a chemical solution deposition method. The dielectric constant and dielectric loss of the bilayered thin films were 645 and 0.09, respectively, at 100 kHz. The value of remnant polarization (2P _r) measured from the ferroelectric thin film capacitors was 60.5 μC/cm² at electric field of 200 kV/cm. The remnant polarization was reduced by 22% of the initial value after 10¹⁰ switching cycles. The results showed that the ferroelectric and dielectric properties of the SrBi₄Ti₄O₁₅ on Bi₄Ti₃O₁₂ ferroelectric thin films were better than those of the SrBi₄Ti₄O₁₅ grown on a Pt-coated Si substrate suggesting that the improved properties may be due to the different nucleation and growth kinetics of SrBi₄Ti₄O₁₅ on the c-axis-oriented Bi₄Ti₃O₁₂ layer or on the Pt-coated Si substrate.     

Application of MEH-PPV/SnO<Subscript>2</Subscript> bilayer as hybrid solar cell

The effects of oxygen content in the sputtering gas on the crystallographic and optoelectronic properties of 210 nm-thick Zr–doped In₂O₃ (Zr–In₂O₃) films by rf magnetron sputtering were initially studied. The results of X-ray diffraction show that the Zr–In₂O₃ films grown on glass substrates exhibit mixed crystallographic orientations. Moreover, the Zr–In₂O₃ film grown in an Ar atmosphere promotes the appearance of crystallographic orientation of (222). The surface of the Zr–In₂O₃ film becomes rougher as the oxygen content in the sputtering gas decreases; the current images obtained by conductive atomic force microscopy reveal that the surfaces of the Zr–In₂O₃ films exhibit a distribution of coexisting conducting and nonconducting regions, and that the area of the nonconducting surface increases with the oxygen content in the sputtering gas. The resistivity is minimized to 3.51×10⁻⁴ Ω cm when the Zr–In₂O₃ film is grown in an Ar atmosphere and the average transmittance in the visible light region is ∼85%. The optical band gap decreases as the oxygen content in the sputtering gas increases.     

Microstructures and impedance studies of Bi<Subscript>3.15</Subscript>Nd<Subscript>0.85</Subscript>Ti<Subscript>3</Subscript>O<Subscript>12</Subscript> thin films

Microstructures and impedance characteristics of chemical-solution-derived Bi_3.15Nd_0.85Ti₃O₁₂ thin films were studied as functions of temperature. A dielectric anomaly was found at around 450°C, corresponding to the paraelectric to ferroelectric transition. Via complex impedance studies, grain and grain boundary contributions to the impedance were separated. The resistance of grain and grain boundaries is found governed by the same kind of space charge with an activation energy around 1.1 eV, close to that of oxygen vacancies in perovskite ferroelectrics. The low temperature ac conductance of BNdT thin films shows a frequency dispersion, which can also be ascribed to space charges mainly due to oxygen vacancies. The results were compared with SrBi₂Ta₂O₉ in terms of oxygen vacancy conductivity.     

Infrared absorption spectra of pure and doped YAl<Subscript>3</Subscript>(BO<Subscript>3</Subscript>)<Subscript>4</Subscript> single crystals

Several weak absorption bands have been observed in the optical absorption spectra of pure and rare-earth-doped YAl₃(BO₃)₄ single crystals in the 3350– 3650 cm⁻¹ wave number region. Two of them, peaking at about 3377 cm⁻¹ and 3580 cm⁻¹ in the 8 K spectra, appear in most of the samples. They are tentatively attributed to the stretching mode of OH⁻ ions incorporated in the crystal during the growth. An additional absorption band at about 5250 cm⁻¹ at 8 K has also been detected in almost all samples. The temperature and polarization dependences of these bands, and their possible origin, are discussed.