The crystal structure of Fe2In2Se5, a FeIn2Se4-related polytype

Fe₂In₂Se₅, a polytype of FeIn₂Se₄ (a material belonging to the II □ III₂ VI₄ family of semiconducting compounds) has been synthesized by conventional solid-state reaction of their constituent elements. The product of the reaction was sequentially used as starting material in the crystal growth process carried out by chemical transport using I₂ as transporting agent. The crystal structure of a new polytype of this compound was determined using single crystal techniques with data collected with a CCD-based diffractometer. The successful indexing of the data and refinement of the structure led to an hexagonal unit cell with a=4.0371(4) and c=32.746(4) Å. Although the absorption effect in the data was quite noticeable, because of the layered morphology exhibited by the material, a good agreement was obtained for a structural model similar to the structure reported for a related polytype belonging to the ZnIn₂S₄ system.     

Magnetic and dielectric behaviors of Ba0.2Sr0.8Co0.8Fe0.2O3-δ oxide

Ba_0.2Sr_0.8Co_0.8Fe_0.2O_3-δ (BSCFO) ceramic oxide has been synthesized by combined citrate-EDTA complexing method and studied with regard to their structural, magnetic and dielectric properties. It is shown that the compound exhibits perovskite-type cubic structure. It depicts hysteresis loop in presence of magnetic field—indicating its magnetic nature. The dielectric properties of sintered oxide were investigated in temperature range (373-873 K) and frequency (100 kHz-1 MHz).The ferroelectric and ferrimagnetic transition temperatures were found to be around 700 K.     

Influence of lithium potassium zirconate nanoparticles on the electrical properties and structural characteristics of poly(vinyl alcohol) films

We investigated the influence of lithium potassium zirconate (LiKZrO₃) nanoparticles on the electrical properties and structural characteristics of poly(vinyl alcohol) (PVA) films. PVA/LiKZrO₃ nanocomposite films were prepared by casting of aqueous solutions with varying LiKZrO₃ content (0.5, 1.0, and 2.0 wt.%). The dielectric constant (ε′), dielectric loss (ε″), AC conductivity (σ_ac), dielectric loss tangent (tan δ), and electric modulus (M′ and M″) of the nanocomposite films were measured over a range of frequencies at ambient temperature. The results show increases in σ_ac and M′ with frequency, whereas ε′, ε″, and tan δ decreased with increasing frequency. The films were also characterized using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and X-ray diffraction (XRD) techniques. DSC and XRD revealed the nature of LiKZrO₃ nanoparticle interaction with the PVA matrix. TGA analysis revealed an increase in thermal stability of the nanocomposites with increasing nanoparticle concentration. Scanning electron microscopy confirmed uniform dispersion of LiKZrO₃ nanoparticles in the PVA matrix.     

One-step chemically vapor deposited hybrid 1T-MoS2/2H-MoS2 heterostructures towards methylene blue photodegradation

The photocatalytic degradation of methylene blue is a straightforward and cost-effective solution for water decontamination. Although many materials have been reported so far for this purpose, the proposed solutions inflicted high fabrication costs and low efficiencies. Here, we report on the synthesis of tetragonal (1T) and hexagonal (2H) mixed molybdenum disulfide (MoS₂) heterostructures for an improved photocatalytic degradation efficiency by means of a single-step chemical vapor deposition (CVD) technique. We demonstrate that the 1T-MoS₂/2H-MoS₂ heterostructures exhibited a narrow bandgap ∼ 1.7 eV, and a very low reflectance (<5%) under visible-light, owing to their particular vertical micro-flower-like structure. We exfoliated the CVD-synthesised 1T-MoS₂/2H-MoS₂ films to assess their photodegradation properties towards the standard methylene blue dye. Our results showed that the photo-degradation rate-constant of the 1T-MoS₂/2H-MoS₂ heterostructures is much greater under UV excitation (i.e., 12.5 × 10⁻³ min⁻¹) than under visible light illumination (i.e., 9.2 × 10⁻³ min⁻¹). Our findings suggested that the intermixing of the conductive 1T-MoS₂ with the semi-conducting 2H-MoS₂ phases favors the photogeneration of electron-hole pairs. More importantly, it promotes a higher efficient charge transfer, which accelerates the methylene blue photodegradation process.     

The dual of a quantum group

It is shown that the bialgebra (two dimensional pseudo-group) of Woronowicz, with some mild technical conditions, can be embedded into the enveloping algebra of a solvable Lie algebra, with the usual Lie structure and a deformed coproduct. The bialgebra dual of this bialgebra is calculated and found to coincide with U _q,q' (sl₂) after fixing the center. The (associative) bialgebra dual form is calculated explicitly and found to be a product ofq-exponentials. Implications about quantum transfer matrices are discussed.     

Microwave resonant and zero-field absorption study of pure and doped ferrite nanoparticles

Microwave absorption was studied for magnetic nanoparticles of Fe₃O₄ (A) prepared by co-precipitation and Ni_0.35Cu_0.15Zn_0.5Fe₂O₄ (B) nanoparticles prepared by the sol-gel combustion method at different temperature. In all cases only one ferromagnetic resonance line was observed which indicated that the materials were magnetically uniform. The linewidths were large mainly because of the wide variations in particle sizes, shapes and orientations. As expected, A type nanoparticles showed no absorption at zero-field. However, B type nanoparticles exhibited a sizable loss at a zero-field and the effect increases with the increase of reaction temperature. Mechanical crushing of the sample further enhanced the absorption.     

Effect of Si in reactively sputtered Ti-Si-N films on structure and diffusion barrier performance

34 Si₂₃N₄₃ (b3) and Ti₃₅Si₁₃N₅₂ (c3), are synthesized by reactively sputtering a Ti₅Si₃ or a Ti₃Si target, respectively. The silicon-lean film (c3) has a columnar structure closely resembling that of TiN. As a diffusion barrier between a shallow Si n⁺p junction diode and a Cu overlayer, this material is effective up to 700 °C for 30 min annealing in vacuum, a performance similar to that for TiN. The silicon-rich (b3) film contains nanocrystals of TiN, randomly oriented and embedded in an amorphous matrix. A film of (b3) maintains the stability of the same diode structure up to 850 °C for 30 min in vacuum. This film (b3) is clearly superior to TiN or to (c3). Similar experiments performed with Al instead of Cu overlayers highlight the importance of the thermodynamic stability of a barrier layer and demonstrate convincingly that for stable barriers the microstructure is a parameter that directly determines the barrier performance. Received: 18 November 1996/Accepted: 22 January 1997     

Two-wave mixing bistability based on mixed grating formation in photorefractive crystals

1 L) and the relative strength (x) of PCG compared with PRG in two cases: (i) when g₁L>0 and x>1 so that there exists either pure PRG or PRG dominates over PCG, and (ii) when g₁L<0 and x<-1 so that there exists either pure PCG or PCG dominates over PRG. The threshold condition g₁L>(g₁L)_Th=2x(1+1/R) with R>1 and the effective coupling strength, g₂L=g₁L/x>0 with 1<x<-1, need to be satisfied for the bistability. Possible regions of bistability affect the position of the region for the intensity ratio (m) of the incident beams where two branched multiple solutions exist and hysteresis in the gain is expected. Gain solutions are found to be single valued without bistability when g₂L<0. A comparison between the mixed grating gain and pure PRG/PCG gains with the occurance of bistability is presented and interpreted physically. Received: 9 January 1996/Revised version: 17 September 1996     

Structure and magneto-optical properties of (CoPt3)1−xNix alloy films

The effect of the Ni addition on the structure and magneto-optical (MO) properties is investigated with (CoPt₃)_1−xNi_x alloy films. The result shows that, lower T_c and higher H_c could be simultaneously obtained in the Ni range of 0.43–0.7. <111>> texture is not the only reason for perpendicular magnetic anisotropy in the present system. Although Ni addition reduces the Kerr rotation angle value in the blue-wave range, it slightly enhances the value in the red-wave range. The films investigated can be considered as suitable for perpendicular magnetic recording applications if the proper Ni addition range (0.43–0.5) is selected. Received: 2 June 1999 / Accepted: 27 October 1999 / Published online: 23 February 2000     

Mode selectivity in ion–molecule reactions of NH3+

Ammonia ions (NH₃ ⁺) are prepared in two internal states of nearly the same energy, a state with five quanta in the umbrella bending mode (E_int=0.60 eV) and another state with one quantum in the all-symmetric stretch and two quanta in the umbrella bending mode (E_int=0.63 eV). These ions are allowed to react with different neutral reagents, and the product ions are mass analyzed and detected. For each reaction, the product branching ratios are measured as a function of center-of-mass collision energy. Whereas reactions with D₂O, D₂, and CD₄ are found to be uninfluenced by the state preparation of the NH₃ ⁺ reagent, reactions with ND₃, partially deuterated methylamine (CD₃NH₂), and tetrahydrofuran (c-(CH₂)₄O)show varying degrees of mode selectivity, the reaction with tetrahydrofuran to the least extent. We suggest that mode selectivity in these ion–molecule reactions should be a general feature when the charge transfer channel is energetically open, the geometry of the reagent ion differs markedly from the corresponding neutral, and different reaction pathways compete for product production. Received: 14 December 1999 / Published online: 16 August 2000     

Phthalocyanine-C60 composites as improved photoreceptor materials?

2 -Pc, in contact with C₆₀ is studied using photoelectron spectroscopy with ultraviolet and X-ray radiation (UPS and XPS, respectively), X-ray absorption near edge spectroscopy (XANES), and optical transmission spectroscopy. A possible improvement of the charge-carrier generation efficiency, which is essential for the performance as photoreceptor material, is thereby found for these materials upon doping with C₆₀. No ground-state charge transfer is detected for the Pcs in contact with C₆₀. The effect of an enhanced photoconductivity is demonstrated for τ-H₂-Pc when it is doped by 5% C₆₀. Received: 16 March 1998/Accepted: 16 March 1998     

Relationship between shoulder pain and skin temperature measured by infrared thermography in a wheelchair propulsion test

IntroductionWheelchair Users (WCUs) depend on their upper extremities for their daily living. Therefore, it is not unusual to find that shoulder pain (SP) is a problem for WCUs and reduces their participation in sport and leisure activities.ObjectivesThe aims of this study were 1 – to analyse skin temperature measured by infrared thermography (IRT) before (pre-test), one minute after (post-test) and 10 min after (post-10) the kinematic wheelchair propulsion test (T-CIDIF) of athletic wheelchair users; 2 – to evaluate the relationship between shoulder pain (SP) and Skin Temperature Asymmetry (ΔT_sk) before and after (pre-test, post-test, post-10) the T-CIDIF, and to relate the SP with the kinematic variables of the T-CIDIF.Participants & interventions/procedureA volunteer sample of 12 wheelchair athletes completed an exercise test (T-CIDIF) in their own wheelchair. It consisted in a 30-s maximum test performed on two rollers. Two linear transducers connected to the rollers registered the number of propulsions, maximum and mean velocity and power of each arm. SP was assessed with the Wheelchair Users Shoulder Pain Index (WUSPI). Skin temperature (T_sk) of the anterior and posterior upper body was measured before and after the T-CIDIF by using an infrared camera. A total of 26 ROIs were evaluated with respect to the opposite side of the body to identify significant (ΔT_sk).Results/main outcome measure(s)Significant differences were observed between the T_sk of the post-10 and pre-test in 12 ROIs, and between the post-10 and the post-test in most of the ROIs. These differences are attenuated when the ΔT_sk is compared before and after exercise. T_sk tends to initially decrease immediately after the test and then significantly increase after 10 min of completing the T-CIDIF. The ΔT_sk vs SP analysis yielded significant inverse relationships (from r = −0.58 to r = −0.71, p < 0.05) in 5 of the 26 ROI. No significant correlations between propulsion variables and SP questionnaire were found. All T-CIDIF variables were significantly correlated with the temperature asymmetries in multiple ROIs (from r = −0.86 to r = −0.58, from p < 0.05 to p < 0.001).ConclusionsThese results present indications that high performance wheelchair athletes exhibit similar capacity of heat production than able-bodied. The thermographic data inversely correlates with the SP and the kinematic variables, but the last is not related to SP. This work contributes to improve the understanding about temperature changes in wheelchair athletes during exercise, and could be used to assess the efficacy of various sports and rehabilitation programs.     

Evaluating Zn2SiO4:Mn phosphor for use in medical imaging radiation detectors

2 SiO₄:Mn phosphor was evaluated for use in radiation detectors of medical imaging systems. Zn₂SiO₄:Mn was used in the form of laboratory-prepared fluorescent layers (screens) with coating weights from 18 to 150 mg/cm². The phosphor was excited to luminescence by low-energy X-raysusing X-raytube voltages ranging from 15 to 50 kVp. The number of emitted optical photons per incident X-rayquantum was thus determined for various X-rayenergies and phosphor coating weights. The optical emission spectrum was also measured and it was used to evaluate the spectral compatibility of Zn₂SiO₄:Mn with radiographic films, photocathodes and the Si photodiode. Finally, phosphor optical properties were estimated by fitting a theoretical model to experimental data. Results showed that Zn₂SiO₄:Mn is more efficient for low-energy X-rays. Its intrinsic conversion efficiency was found equal to 0.08, which is comparable to that of actually used phosphors. Zn₂SiO₄:Mn was also adequately compatible with orthochromatic films and the ES-20 photocathode, thus being appropriate for low-voltage radiography and fluoroscopy. Received: 31 July 1998/Accepted: 3 August 1998     

Studies on the magnetic viscosity and the magnetic anisotropy of γ-Fe2O3 powders

2 O₃ powders, acicular γ-Fe₂O₃, and CoFe–γ-Fe₂O₃ powders are prepared by different methods. Particle shapes and mean particle sizes of samples are determined by transmission electron microscopy (TEM). Magnetic parameters are measured by a vibrating sample magnetometer (VSM) at different temperatures. Effective magnetic anisotropy constants K_E of granular γ-Fe₂O₃ powders at different temperatures are obtained by using the law of approach to saturation (LATS). K_E values of acicular γ-Fe₂O₃ and CoFe–γ-Fe₂O₃ powders are measured by a magnetotorquemeter. It is found for the first time that the variation tendency of K_E with temperature for granular γ-Fe₂O₃ is about the same as that of shape magnetic anisotropy K_sh. Fluctuation field H_f and activation volume V_f of samples are measured. A theoretical expression of V_f is derived. For granular γ-Fe₂O₃ powders, calculated activation volumes are consistent with experimental ones at different temperatures. But as for acicular γ-Fe₂O₃ powders, calculated activation volumes are larger than experimental ones. Experimental results show that magnetization reversal of granular γ-Fe₂O₃ at different temperatures is close to homogeneous rotation. Received: 27 November 1996/Accepted: 18 April 1997     

Optical transient bleaching/absorption of surface-oxidized CuInS2 nanocrystals

2 nanocrystals in a polymer film have been studied with the picosecond pump-probe technique. The oxidized CuInS₂ nanocrystals have an additional absorption band with a peak at 1.03 eV, which is bleached under picosecond excitation. Rapid (∼50 ps) trapping into midgap surface states results in long-lived (≫300 ps) bleaching and induced absorption features. A schematical energy-level diagram for oxidized CuInS₂ nanocrystals is given based on the experimental results. Received: 7 January 1997/Revised version: 16 April 1997     

Gas contaminant effect in a discharge-excited ArF excimer laser

4 , O₂ and N₂ in a discharge-excited ArF-excimer laser. Measured characteristics include laser pulse energy, small-signal gain, and laser spectrum. Measurement results indicate that laser pulse energy degradation for such impurities (<100 ppm) is mainly due to optical absorption. It has also been found that for O₂ contaminants laser pulse energy degradation is strongly dependent on operational repetition rates; at higher repetition rates, an increased concentration of O₂ impurities results in a reduced small-signal gain and a consequent decline in laser pulse energy. Received: 12 June 1997/Revised version: 3 December 1997     

Linear energy transfer dependence of Al2O3:C optically stimulated luminescence detectors exposed to therapeutic proton beams

Currently, there are no radiation detectors that can be used for routine measurements of linear energy transfer (LET) in particle therapy clinics. In this work, we characterized the LET dependence of Al₂O₃:C optically stimulated luminescence (OSL) detectors (OSLDs) exposed to therapeutic proton beams in order to evaluate their potential for clinical LET measurements. We evaluated OSLDs that were irradiated with an absorbed dose to water of 0.2 Gy in therapeutic proton beams with average energies ranging between approximately 25 MeV and 200 MeV, resulting in LET in water values between 0.45 and 2.29 keV/μm. We examined two properties of the OSL emission signal in terms of LET dependence: the signal intensities of the blue and ultraviolet (UV) emission bands, and the shapes of the OSL curves. We found that the signal intensity of the UV emission band increased consistently with LET within the range investigated, whereas the intensity of the blue emission band remained constant. Our results also demonstrated that the OSL curve shapes were more LET dependent for signals containing both the blue and UV emission bands than for signals containing only one of the bands. Both metrics we examined in this study – the relative UV/blue emission signal intensities and OSL curve shapes – show potential for LET detection in proton therapy.     

Ultrasound assisted synthesis of {[Cu2(BDC)2(dabco)].2DMF.2H2O} nanostructures in the presence of modulator; new precursor to prepare nano copper oxides

As a new precursor to prepare nano copper oxide, nanostructures of porous metal organic framework (MOF) {[Cu₂(BDC)₂(dabco)].2DMF.2H₂O} (1) have been synthesized in the presence of acetic acid as a modulator via sonochemical method. Different concentrations of metal ion, organic linkers, modulator reagent and also different sonication times were held to improve the quality of nanostructures. Ultrasound irradiation helps nucleation step of the oriented attachment of modulation method and nanoparticles with a few nanorods has been prepared. As prepared MOF was calcinated at 500 °C to prepare nano CuO and Cu₂O. Compound 1, CuO and Cu₂O nanostructures were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray powder diffraction (XRD).     

Modeling the optical constants of CuGaSe2 and CuInSe2

The dielectric function data for CuGaSe₂ and CuInSe₂ have been modeled for both perpendicular (E⊥c) and parallel (E∥c) polarizations. We employ the modified Adachi’s model dielectric function model with variable broadening. Variable broadening is accomplished by replacing the damping constant Γ with the energy-dependent expression Γ(E), where the shape of the broadening function is determined by two adjustable model parameters. In spite of one additional parameter per transition, this model requires fewer parameters than the conventional Adachi’s model to achieve equal or better agreement with the experimental data. Our calculations give the relative rms errors for the real and imaginary parts of the index of refraction, δ_n and δ_k, equal to 0.9% and 9.5% for CuGaSe₂ (E⊥c), 0.8% and 7.3% for CuGaSe₂ (E∥c), 1.1% and 3.0% for CuInSe₂ (E⊥c), and 2.5% and 3.7% for CuInSe₂ (E∥c), respectively. Received: 10 July 2000 / Accepted: 10 July 2000 / Published online: 9 November 2000     

Investigating the performance of P3HT:PCBM organic solar cells involving gamma-irradiated PEDOT:PSS layer

In this work, we investigated for the first time the characteristics of (poly (3-hexylthiopene) and [6, 6]-phenyl C61-butyric acid methyl ester) (P3HT:PCBM) blends-based organic solar cell with 1.25?mg/mL boric-acid (H₃BO₃)-doped poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) layer which is irradiated under the 40 Gray (Gy) dose of gamma (γ) ray. Experimental results showed that the parameters of solar cell improved with exposure to low-dose gamma radiation. In particular, it has provided a significant improvement in short-circuit current density (J_sc) and power conversion efficiency (PCE). About 49% increase in PCE to 1.22% and 40% increase in J_sc to 6.28?mA/cm² was obtained between the bare device and the device containing irradiated PEDOT:PSS:H₃BO₃. Also, it was determined that the H₃BO₃-doped PEDOT:PSS is more stable to temperature. More importantly, solar cell containing gamma-irradiated PEDOT:PSS:H₃BO₃ showed best performance comparing to conventional PEDOT:PSS-based cell.