CRYSTAL RESEARCH AND TECHNOLOGY, Issue 1-2 2005
D. C. Meyer
Abstract Thermal evolution of the structure of Fe/Al multilayers (MLs) with nominal composition 5*(5 nm Al / 5 nm Fe) prepared by crossed-beam pulsed laser deposition is studied by wide-angle X-ray scattering and X-ray reflectometry after different temperature-time procedures of thermal treatments under high-vacuum conditions. In comparison to direct thermal annealing at temperatures of 250 °C and 275 °C, respectively, which results in nearly complete mixing of the MLs and formation of the FeAl intermetallic compound, quite different behaviour was found after dedicated thermal pretreatment. Annealing at successive growing temperatures before final annealing at temperatures mentioned, resulted in conservation of pronounced multilayer structure. From the results it is generalised, that also in the case of ML systems, the tendency of mixing a dedicated tuning of interface characteristics by thermal treatment allows for formation of diffusion-hindering interlayers. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Annealing of Biodegradable Polymer Induced by Femtosecond Laser Micromachining,

ADVANCED ENGINEERING MATERIALS, Issue 4 2010
Wai Yee Yeong
Abstract Femtosecond laser is a potential tool for net shape processing of biodegradable polymers. However, laser processing of polymeric material is still a challenge and the effects induced by laser ablation needs to be investigated. Poly(, -caprolactone) was micromachined at high fluence and the heat affected zone was characterized. Two different phases of microstructure, namely the annealed spherulite zone and the amorphous zone, are found. [source]

Photophysics and Photocurrent Generation in Polythiophene/Polyfluorene Copolymer Blends

ADVANCED FUNCTIONAL MATERIALS, Issue 19 2009
Christopher R. McNeill
Abstract Here, studies on the evolution of photophysics and device performance with annealing of blends of poly(3-hexylthiophene) with the two polyfluorene copolymers poly((9,9-dioctylfluorene)-2,7-diyl-alt-[4,7-bis(3-hexylthien-5-yl)-2,1,3-benzothiadiazole]-2,,2,,-diyl) (F8TBT) and poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT) are reported. In blends with F8TBT, P3HT is found to reorganize at low annealing temperatures (100,°C or below), evidenced by a redshift of both absorption and photoluminescence (PL), and by a decrease in PL lifetime. Annealing to 140,°C, however, is found to optimize device performance, accompanied by an increase in PL efficiency and lifetime. Grazing-incidence small-angle X-ray scattering is also performed to study the evolution in film nanomorphology with annealing, with the 140,°C-annealed film showing enhanced phase separation. It is concluded that reorganization of P3HT alone is not sufficient to optimize device performance but must also be accompanied by a coarsening of the morphology to promote charge separation. The shape of the photocurrent action spectra of P3HT:F8TBT devices is also studied, aided by optical modeling of the absorption spectrum of the blend in a device structure. Changes in the shape of the photocurrent action spectra with annealing are observed, and these are attributed to changes in the relative contribution of each polymer to photocurrent as morphology and polymer conformation evolve. In particular, in as-spun films from xylene, photocurrent is preferentially generated from ordered P3HT segments attributed to the increased charge separation efficiency in ordered P3HT compared to disordered P3HT. For optimized devices, photocurrent is efficiently generated from both P3HT and F8TBT. In contrast to blends with F8TBT, P3HT is only found to reorganize in blends with F8BT at annealing temperatures of over 200,°C. The low efficiency of the P3HT:F8BT system can then be attributed to poor charge generation and separation efficiencies that result from the failure of P3HT to reorganize. [source]

Microstructural and crystallographic surface changes after grinding zirconia-based dental ceramics

JOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 2 2006
I. L. Denry
Abstract The purpose of this study was to evaluate microstructural and crystallographic phase changes after grinding 3Y-TZP dental ceramics. Ceramic blanks were sintered according to manufacturer's recommendations and divided into four groups: (A) as-sintered control, (B) diamond-ground manually under water, (C) ground and polished, and (D) ground and annealed at 1000°C for 1 h. Bulk specimens were analyzed by X-ray diffraction to characterize the crystalline phases. The microstructure was investigated by SEM. XRD analyses showed that the control group and the group that was ground and annealed contained only tetragonal zirconia. However, after grinding or after grinding followed by polishing, rhombohedral zirconia and strained tetragonal zirconia were present, without any detectable amount of monoclinic zirconia. Annealing led to the disappearance of both residual lattice strain and the rhombohedral phase. The microstructure of the ground and polished specimens was characterized by significant residual surface damage associated with grain pullout to a depth of about 20 ,m. This type of damage could have an impact on the long-term fatigue behavior of 3Y-TZP. © 2005 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2006 [source]

Freeze-drying of tert- butanol/water cosolvent systems: A case report on formation of a friable freeze-dried powder of tobramycin sulfate

JOURNAL OF PHARMACEUTICAL SCIENCES, Issue 4 2002
Sakchai Wittaya-Areekul
Abstract A case study is presented in which a tert -butanol (TBA)/water cosolvent system was found to be a useful means of producing freeze-dried tobramycin sulfate that readily forms a loose powder upon agitation in a specialized application in which a critical quality attribute is the ability to pour the sterile powder from the vial. Both formulation and processing variables are important in achieving acceptable physical properties of the cake as well as minimizing residual TBA levels. Liquid/liquid phase separation was observed above critical concentrations of both drug and TBA, resulting in a two-layered lyophilized cake with unacceptable appearance, physical properties, and residual TBA levels. However, the choice of tobramycin sulfate and TBA concentrations in the single-phase region of the phase diagram resulted in a lyophilized solid that can readily be poured from vials. Crystallization of TBA before drying is critical to achieving adequately low residual TBA levels, and this is reflected in the effect of thermal history of freezing on residual TBA levels, where rapid freezing results in incomplete crystallization of TBA and relatively high levels of residual solvent. Annealing at a temperature above T,g of the system after an initial freezing step significantly reduces the level of residual TBA. Secondary drying, even at increased temperature and for extended times, is not an effective method of reducing residual TBA levels. © 2002 Wiley-Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 91: 1147,1155, 2002 [source]

Exuding Liquid from Grain Boundaries in Alumina

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2001
N. Ravishankar
Bicrystals of alumina with anorthite glass in the boundary were prepared by hot pressing. Annealing of the bicrystals leads to the migration of the intergranular liquid to the free surface of the sample. It is proposed that the migration is driven by the difference in the wetting behavior of the free surface and the boundary. [source]

Blue-shift of absorption edge in LaTiO2N by controlling the anion nonstoichiometry

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 11 2006
Toshihiro Moriga
Abstract The perovskite-type oxynitride LaTiO2N was prepared by heating an oxide precursor at 950 °C for 5 hours under NH3 atmosphere at a flow rate of 1 dm3/min. The precursor was prepared by the polymerized complex method. The oxynitride obtained was almost stoichiometric, LaTi(O0.68N0.32)2.9, with a reddish orange color. The oxynitride was successively annealed at 950 °C for 3 hours under a NH3 atmosphere at flow rates of 50 cm3/min, 30 cm3/min and 10 cm3/min, respectively. The color and composition varied from yellow LaTi(O0.89N0.11)2.8 through green-yellow LaTi(O0.93N0.07)2.9 to light-blue LaTi(O0.98N0.02)2.9 in accordance with the decreased flow rate. The absorption edges varied from 2.28 eV for the reddish orange, 2.56 eV for the yellow, 3.17 eV for the green-yellow, to 3.44 eV for the light-blue oxynitrides. Annealing under NH3 is therefore effective in color tuning, mainly resulting in a blue-shift of the absorption edge. DV-X, calculations support the conclusion that the lower flow rate of NH3 led to a lower amount of nitrogen and higher oxygen levels in the oxynitrides. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Atomic structure of pyramidal defects in GaN:Mg: Influence of annealing

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 7 2006
Z. Liliental-Weber
Abstract The atomic structure of the characteristic defects (Mg-rich hexagonal pyramids) in p-doped bulk and MOCVD GaN:Mg thin films grown with Ga polarity was determined at atomic resolution by direct reconstruction of the scattered electron wave in a transmission electron microscope. Small cavities were present inside the defects, confirmed also with positron annihilation. The inside walls of the cavities were covered by GaN of reverse polarity compared to the matrix. Annealing of the MOCVD layers lead to slight increase of the defect size and an increase of the room temperature photoluminescence intensity. Positron annihilation confirms presence of vacancy clusters of different sizes triggered by the Mg doping in as-grown samples and decrease of their concentration upon annealing at 900 and 1000 °C. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Effect of structural disordering on magnetic properties of stoichiometric Ni2MnGa alloy films

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 1 2003
Y. V. Kudryavtsev
Abstract Ordered and disordered Ni2MnGa alloy films have been prepared by flash evaporation. We show that the ordered films are ferromagnetic and exhibit the same magnetic and transport properties as those of crystalline bulk Ni2MnGa with the martensite transformation near 200 K. The structural disorder in Ni2MnGa alloy films destroys the ferromagnetic order. The disordered Ni2MnGa films are shown to behave like a highly resistive Pauli paramagnet with a nearly linear negative temperature coefficient of resistivity. Annealing of the disordered films at 680 K restores the L21 structure and the magnetic and transport properties of the ordered state. [source]

Formation of ohmic contacts to ultra-thin channel AlN/GaN HEMTs

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2008
Tom Zimmermann
Abstract AlN/GaN-based high electron mobility transistors with ultra-thin AlN barriers of 2.3 - 5 nm are attractive candidates for very high speed applications owing to the aggressive scalability such structures afford. We report the first study on formation of ohmic contacts to these high quality ultra-thin channel heterostructures (ns > 1x1013 cm,2 and , > 900 cm2/Vs) with systematically varying barrier thicknesses. While the conventional ohmic contacts to AlGaN/GaN structures generally require high temperature annealing, these ohmic contacts were found to behave ohmic or near ohmic as-deposited. Annealing (400-860 0C) improves the contact resistance to a range of 0.8 - 2 ohm-mm but the annealing conditions strongly depend on the AlN thickness as well as the heterostructure quality (,). All alloyed contacts show smooth morphology, making them suitable for e-beam lithographically defined gate patterning. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Interdiffusion effect on exchange coupling in annealing NiFe/FeMn and FeMn/NiFe systems

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 12 2007
Kuang-Ching Chen
Abstract The effect of interdiffusion on the exchange coupling field (Hex) and coercivity (Hc) in annealing NiFe/FeMn and FeMn/NiFe systems was investigated in the study. Type I samples: Silicon substrate/Ta/NiFe/FeMn/Ta and Type II samples: Silicon substrate/Ta/FeMn/NiFe/Ta were prepared. Annealing was carried out at 200 to 450 °C for two hours under 720 Oe, respectively. The results show that the Hex and Hc in two types samples were dependent on the annealing temperature. For both types the magnetization loss ratio (,M/MS) is negative, which reflects a loss of magnetization associated with interfacial mixing caused by annealing. The magnetization loss ratio becomes larger when the annealing temperature increases. The exchange coupling of these two types samples is associated with interfacial diffusion between the NiFe and FeMn interface. The annealing treatment also affected the Hc. In these two types samples, the exchange coupling was improved from modification of the interface between layers by annealing. The extended annealing (above 375 °C) changes the exchange coupling in these two types samples due to serious interdiffusion of the interface between NiFe and FeMn layers. It results in unwanted interdiffusion effects at the interface and a concomitant reduction in the exchange bias field. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Magnetic properties of spin valves having extremely thin underlayers

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 12 2007
Jiwon Kim
Abstract Magnetic properties of spin valve elements having Mo(N) and Ta(N) underlayers were studied by varying their thickness. Spin valve structure was Si/SiO2/Underlayer(tÅ)/NiFe(21 or 42Å)/CoFe(28Å)/Cu(22Å)/CoFe(18Å)/IrMn(65Å)/Ta(25Å). Spin valve elements having exteremely thin Mo(N) and Ta(N) underlayers showed high MR ratio of about 7 - 8%. Annealing of such spin valve elements having underlayer thickness of 7 to 8 Å showed comparable behavior with the spin valve elements with thicker (35Å) underlayer, which can be utilized to reduce overall device thickness. Also, it was found that Mo(N) underlayers for spin valve elements may be used as diffusion barriers between Si substrate and ensuing active spin valve layers, simultaneously. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Electrodeposited CuGa(Se,Te)2 thin-film prepared from sulfate bath

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 8 2006
Yusuke Oda
Abstract CuGa(Se,Te)2 (CGST) thin films were prepared on a soda-lime glass substrate sputter coated with molybdenum by electrodeposition. The aqueous solution which contained CuSO4 -5H2O, Ga2(SO4)3 -19.3H2O, H2SeO3, H6TeO6, Li2SO4 and gelatin was adjusted to pH 2.6 with dilute H2SO4 and NaOH. It has been observed that (i) a crack-less and smooth CGST film with a composition close to the stoichiometric ratio was deposited at -600 mV (vs. Ag/AgCl) when Te was hardly included in the film and (ii) cracks and products on the surface increased with increasing Te content in the film. Annealing at 600 °C for 10 min improved the crystallinity of the as-deposited films. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Effect of annealing and orientation on microstructures and mechanical properties of polylactic acid

POLYMER ENGINEERING & SCIENCE, Issue 4 2008
Long Yu
Two types of polylactic acid (PLA) films (one amorphous and one semi-crystalline) were produced by sheet extrusion. Talc was used as a nucleation agent for the semi-crystalline PLA. The films were annealed above their Tg or were uniaxially orientated in two ways: (1) via a drawing system in front of the extruder and die or (2) via a three-roller stretching system. The slower crystallization rate and lower melting stress of the PLA resulted in amorphous film using the drawing system. Annealing above Tg increased crystallinity and polymer chain relaxation, which resulted in increases in both strength and toughness. Stretching above Tg also produced simultaneous crystallization and chain relaxation, which resulted in increases in both modulus and toughness. Both modulus and tensile strength in the stretching direction were higher than in the crosswise direction. Talc acted not only as a rigid filler to reinforce the PLA, but also as a nucleation agent for the PLA, especially during annealing. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers [source]

Ab initio structure determination of phase II of racemic ibuprofen by X-ray powder diffraction

ACTA CRYSTALLOGRAPHICA SECTION B, Issue 1 2010
Patrick Derollez
Annealing of the quenched ibuprofen at 258,K yielded a new crystalline form, called phase II. Powder X-ray diffraction patterns of this phase II were recorded with a laboratory diffractometer equipped with an INEL G3000 goniometer and a curved position-sensitive detector CPS120. The starting structural model was found by a Monte-Carlo simulated annealing method. The final structure was obtained through Rietveld refinements with rigid-body constraints for the phenyl group and soft restraints on the other interatomic bond lengths and bond angles. The cell volume is 5% larger than that of the conventional phase I at 258,K. It is also shown that the orientation of the propanoic acid group is drastically changed with respect to phase I, leading to strong modifications of the orientation of the O,H...O hydrogen bonds with respect to the chains of dimers. These structural considerations could explain the metastable character of this phase II. [source]

Hybrid Meta-Heuristic Algorithm for the Simultaneous Optimization of the O,D Trip Matrix Estimation

COMPUTER-AIDED CIVIL AND INFRASTRUCTURE ENGINEERING, Issue 6 2004
Antony Stathopoulos
These include a genetic algorithm (GA), a simulated annealing (SA) algorithm, and a hybrid algorithm (GASA) based on the combination of GA and SA. The computational performance of the three algorithms is evaluated and compared by implementing them on a realistic urban road network. The results of the simulation tests demonstrate that SA and GASA produce a more accurate final solution than GA, whereas GASA shows a superior convergence rate, that is, faster improvement from the initial solution, in comparison to SA and GA. In addition, GASA produces a final solution that is more robust and less dependent on the initial demand pattern, in comparison to that obtained from a greedy search algorithm. [source]

Three-Dimensional Optimization of Urban Drainage Systems

COMPUTER-AIDED CIVIL AND INFRASTRUCTURE ENGINEERING, Issue 6 2000
A. Freire Diogo
A global mathematical model for simultaneously obtaining the optimal layout and design of urban drainage systems for foul sewage and stormwater is presented. The model can handle every kind of network, including parallel storm and foul sewers. It selects the optimal location for pumping systems and outfalls or wastewater treatment plants (defining the natural and artificial drainage basins), and it allows the presence of special structures and existing subsystems for optimal remodeling or expansion. It is possible to identify two basic optimization levels: in the first level, the generation and transformation of general layouts (consisting of forests of trees) until a convergence criterion is reached, and in the second level, the design and evaluation of each forest. The global strategy adopted combines and develops a sequence of optimal design and plan layout subproblems. Dynamic programming is used as a very powerful technique, alongside simulated annealing and genetic algorithms, in this discrete combinatorial optimization problem of huge dimension. [source]

Preparation, structure and photoluminescence properties of SiO2,coated ZnS nanowires

CRYSTAL RESEARCH AND TECHNOLOGY, Issue 10 2010
Changhyun Jin
Abstract It is essential to passivate one-dimensional (1D) nanostructures with insulating materials to avoid crosstalking as well as to protect them from contamination and oxidation. The structure and influence of thermal annealing on the photoluminescence properties of ZnS-core/SiO2 -shell nanowires synthesized by the thermal evaporation of ZnS powders followed by the sputter deposition of SiO2 were investigated. Transmission electron microscopy and X-ray diffraction analyses revealed that the cores and shells of the core-shell nanowires were single crystal zinc blende-type ZnO and amorphous SiO2, respectively. Photoluminescence (PL) measurement showed that the core-shell nanowires had a green emission band centered at around 525 nm with a shoulder at around 385 nm. The PL emission of the core-shell nanowires was enhanced in intensity by annealing in an oxidative atmosphere and further enhanced by subsequently annealing in a reducing atmosphere. Also the origin of the enhancement of the green emission by annealing is discussed based on the energy-dispersive X-ray spectroscopy analysis results. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Interdiffusion phenomena in InGaAs/GaAs superlattice structures

CRYSTAL RESEARCH AND TECHNOLOGY, Issue 5 2010
B. Sar, kavak
Abstract We have studied structural properties of InGaAs/GaAs superlattice sample prepared by Molecular Beam Epitaxy (MBE) using high resolution X-ray diffractometer (HRXRD). Increasing strain relaxation and defect generations are observed with the increasing Rapid Thermal Annealing (RTA) temperature up to 775 °C. The higher temperatures bring out relaxation mechanisms; interdiffusion and favored migration. The defect structure and the defects which are observed with the increasing annealing temperature were analyzed. Firstly, the in-plane and out-of-plane strains after the annealing of sample were found. Secondly, the structural defect properties such as the parallel X-ray strain, perpendicular X-ray strain, misfit, degree of relaxation, x composition, tilt angles and dislocation that are obtained from X-ray diffraction (XRD) analysis were carried out at every temperature. As a result, we observed that the asymmetric peaks especially in asymmetric (224) plane was affected more than symmetric and asymmetric planes with lower polar or inclination angles due to c-direction at low temperature. These structural properties exhibit different unfavorable behaviors for every reflection direction at the increasing temperatures. The reason is the relaxation which is caused by spatially inhomogeneous strain distribution with the increasing annealing temperature. In the InGaAs superlattice samples, this process enhances preferential migration of In atoms along the growth direction. Further increase in the annealing temperature leads to the deterioration of the abrupt interfaces in the superlattice and degradation in its structural properties. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Oxide layer dissolution in Si/SiOx/Si wafer bonded structures

CRYSTAL RESEARCH AND TECHNOLOGY, Issue 10 2009
N. Zakharov
Abstract The evolution of the interfaces of hydrophilic-bonded Si wafers and the corresponding low-angle twist boundary have been analysed in relation to thermal annealing and their relative crystallographic orientation. Two orientation relationships were investigated: Si<001>/Si<001> and Si<001>/Si<110>, where the interfaces are seperated by thin native SiO2 layers. The interfaces were analysed by TEM and STEM/EELS. It is found that the decomposition rate of the intermediate oxide layer and the formation of a Si(Si bonded interface depend very much on the lattice mismatch and on the twist angle. The velocity of the dissolution of the thin oxide layers and the formation of Si(Si bonds at the bonding interface depend on the orientation relations of the corresponding wafers. The processes of interface fusion and the dissolution of oxide layer are discussed. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Effect of AlN doping on the growth morphology of SiC

CRYSTAL RESEARCH AND TECHNOLOGY, Issue 9 2009
N. B. Singh
Abstract AlN doped SiC films were deposited on on-axis Si-face 4H-SiC (0001) substrates by the physical vapor transport (PVT) method. Thick film in the range of 20 ,m range was grown and morphology was characterized. Films were grown by physical vapor deposition (PVD) in a vertical geometry in the nitrogen atmosphere. We observed that nucleation occurred in the form of discs and growth occurred in hexagonal geometry. The X-ray studies showed (001) orientation and full width of half maxima (FWHM) was less than 0.1° indicating good crystallinity. We also observed that film deposited on the carbon crucible had long needles with anisotropic growth very similar to that of pure AlN. Some of the needles grew up to sizes of 200 ,m in length and 40 to 50 ,m in width. It is clear that annealing of SiC-AlN powder or high temperature physical vapor deposition produces similar crystal structure for producing AlN-SiC solid solution. SEM studies indicated that facetted hexagons grew on the top of each other and coarsened and merged to form cm size grains on the substrate. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Effect of annealing on the structural, electrical and optical properties of nanostructured TiO2 thin films

CRYSTAL RESEARCH AND TECHNOLOGY, Issue 9 2009
S. Sankar
Abstract Nanostructured titanium dioxide thin films were prepared using reactive pulsed laser ablation technique. Effects of annealing on the structural, morphological, electrical and optical properties are discussed. The structural, electrical and optical properties of TiO2 films are found to be sensitive to annealing temperature and are described with GIXRD, SEM, AFM, UV-Visible spectroscopy and electrical studies. X-ray diffraction studies showed that the as-deposited films were amorphous and at first changed to anatase and then to rutile phase with increase of annealing temperature. Optical constants of these films were derived from the transmission spectra and the refractive index dispersion of the films, subjected to annealing at different temperatures, is discussed in terms of the single oscillator-Wemple and Didomenico model. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Effects of annealing on structural, electrical and optical properties of AgGa(Se0.5S0.5)2 thin films deposited by using sintered stoichometric powder

CRYSTAL RESEARCH AND TECHNOLOGY, Issue 4 2009
H. Karaagac
Abstract The structural, electrical and optical properties of AgGa(Se0.5S0.5 )2 thin films deposited by using the thermal evaporation method have been investigated as a function of annealing in the temperature range of 450,600 °C. X-ray diffraction (XRD) analysis showed that the structural transformation from amorphous to polycrystalline structure started at 450 oC with mixed binary phases of Ga2Se3, Ga2S3, ternary phase of AgGaS2 and single phase of S. The compositional analysis with the energy dispersive X-ray analysis (EDXA) revealed that the as-grown film has different elemental composition with the percentage values of Ag, Ga, Se and S being 5.58, 27.76, 13.84 and 52.82 % than the evaporation source powder, and the detailed information about the stoichometry and the segregation mechanisms of the constituent elements in the structure have been obtained. The optical band gap values as a function of annealing temperature were calculated as 2.68, 2.85, 2.82, 2.83, and 2.81 eV for as-grown, annealed at 450, 500, 550, and 600 °C samples, respectively. It was determined that these changes in the band gap are related with the structural changes with annealing. The temperature dependent conductivity measurements were carried out in the temperature range of 250-430 K for all samples. The room temperature resistivity value of as-grown film was found to be 0.7x108 (,-cm) and reduced to 0.9x107 (,-cm) following to the annealing. From the variation of electrical conductivity as a function of the ambient temperature, the activation energies at specific temperature intervals for each sample were evaluated. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Synthesis and crystal structure determination of two dispiro compounds from laboratory x-ray powder diffraction data

CRYSTAL RESEARCH AND TECHNOLOGY, Issue 2 2008
A. M. Moustafa
Abstract The crystal structures of the dispiro compounds 1,3,4,8,10,11-Hexaphenyl-13-methyl-1,2,8,9,13-pentaazadispiro[4.1.4.3]tetradeca-2,9-dien-6-one (3a) and 4,11-Bis(4-methoxyphenyl)-13-methyl-1,3,8,10-tetraphenyl-1,2,8,9,13-pentaazadispiro-[4.1.4.3]tetradeca-2,9-dien-6-one (3b) have been determined at room temperature from X-ray powder diffraction data using the method of simulated annealing as implemented in the programs DASH and TOPAS. Subsequent Rietveld refinements using the data collected to 1.5 Å resolution yielded R-Bragg values of 2.2% for (3a) and 3.7% for (3b). It was found, that both compounds crystallize in the monoclinc space group P 21/n with lattice parameters of a = 17.1656(5) Å, b =13.8128(3) Å, c = 16.1016(5) Å, and , = 103.7330(2)° for (3a) and a = 17.2529(8) Å, b = 13.8729(5) Å, c =16.1287(10) Å, and , = 103.6910(3)° for (3b). Both compounds exhibit a distorted hexagonal close type of packing (hcp) of the molecular centers of gravity. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Photoelectrical properties of crystalline titanium dioxide thin films after thermo-annealing

CRYSTAL RESEARCH AND TECHNOLOGY, Issue 5 2007
R. Sathyamoorthy
Abstract This paper reports the photoelectrical properties of sol gel derived titanium dioxide (TiO2) thin films annealed at different temperatures (425-900°C). The structure of the as-grown film was found to be amorphous and it transforms to crystalline upon annealing. The trap levels are studied by thermally stimulated current (TSC) measurements. A single trap level with activation energy of 1.5 eV was identified. The steady state and transient photocurrent was measured and the results are discussed on the basis of structural transformation. The photocurrent was found to be maximum for the films annealed at 425°C and further it decreases with annealing at higher temperatures. The photoconduction parameters such as carrier lifetime, lifetime decay constant and photosensitivity were calculated and the results are discussed as a function of annealing temperature. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Growth of big single crystals of a new magnetic superconducting double perovskite Ba2PrRu1,xCuxO6

CRYSTAL RESEARCH AND TECHNOLOGY, Issue 2 2006
S. M. Rao
Abstract Single crystals of Ba2PrRu1,xCuxO6 with x = 0 to 0.2, have been grown from high temperature solutions of a mixture of PbO-PbF2 in the temperature range 1100,1200 °C. Thin crystals with mostly a hexagonal and triangular plate like habit measuring up to 1,2 mm across and 0.1,0.2 mm thick were obtained. The size, quality and morphology of the crystals were improved by varying the solution volume as well as additives like B2O3. Large crystals measuring up to 3 mm across and 0.3 to 0.5 mm thick were obtained with 5,7 wt% solute concentration and 0.51 wt% of B2O3. The ZFC curves exhibit a spin glass like behavior with x = 0 and a superconducting transition at 8 to 11 K depending on x = 0.05 to 0.1. The transition was also influenced by the growth temperature and post growth annealing. Powder x-ray diffraction, EDS and Raman spectroscopic measurements confirm the presence of Cu in the crystals. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Formation of diffusion-hindering interlayers in metals in contact by dedicated thermal treatment

Influence of nanocrystalization on magnetoelastic Villari effect in Fe73.5Nb3Cu1Si13.5B9 alloy

CRYSTAL RESEARCH AND TECHNOLOGY, Issue 3-5 2003
R. Szewczyk
Abstract The results of an investigation of the influence of thermal annealing on the magnetoelastic properties of Fe73.5Nb3Cu1Si13.5B9 soft magnetic alloy in both amorphous and nanocrystalline state are presented. A new method developed was used to apply uniform compressive stresses to the investigated ring core made of the alloy. The compressive stresses produced by external mechanical forces were applied perpendicularly to the direction of the magnetizing field. Due to the uniform distribution of stresses in the core brittle nanocrystalline alloys may be tested for stresses up to 10 MPa. The results revealed, that process of nanocrystallisation causes significant increase in the stress sensitivity of the Fe73.5Nb3Cu1Si13.5B9 alloy. Moreover the influence of stresses caused by external forces is more significant at relatively low values of the magnetizing field suggesting that these nanocrystalline soft magnetic materials are stress sensitive in the range of technical operation of inductive components based on such materials. [source]

Challenging Wallacean and Linnean shortfalls: knowledge gradients and conservation planning in a biodiversity hotspot

DIVERSITY AND DISTRIBUTIONS, Issue 5 2006
Luis Mauricio Bini
ABSTRACT Knowledge about biodiversity remains inadequate because most species living on Earth were still not formally described (the Linnean shortfall) and because geographical distributions of most species are poorly understood and usually contain many gaps (the Wallacean shortfall). In this paper, we developed models to infer the size and placement of geographical ranges of hypothetical non-described species, based on the range size frequency distribution of anurans recently described in the Cerrado Biome, on the level of knowledge (number of inventories) and on surrogates for habitat suitability. The rationale for these models is as follow: (1) the range size frequency distribution of these species should be similar to the range-restricted species, which have been most recently described in the Cerrado Biome; (2) the probability of new discoveries will increase in areas with low biodiversity knowledge, mainly in suitable areas, and (3) assuming range continuity, new species should occupy adjacent cells only if the level of knowledge is low enough to allow the existence of undiscovered species. We ran a model based on the number of inventories only, and two models combining effects of number of inventories and two different estimates of habitat suitability, for a total of 100 replicates each. Finally, we performed a complementary analysis using simulated annealing to solve the set-covering problem for each simulation (i.e. finding the smallest number of cells so that all species are represented at least once), using extents of occurrence of 160 species (131 real anuran species plus 29 new simulated species). The revised reserve system that included information about unknown or poorly sampled taxa significantly shifted northwards, when compared to a system based on currently known species. This main result can be explained by the paucity of biodiversity data in this part of the biome, associated with its relatively high habitat suitability. As a precautionary measure, weighted by the inferred distribution data, the prioritization of a system of reserves in the north part of the biome appears to be defensible. [source]

Using geostatistics to elucidate temporal change in the spatial variation of aeolian sediment transport

EARTH SURFACE PROCESSES AND LANDFORMS, Issue 6 2003
Adrian Chappell
Abstract Little is known about the spatial and temporal scales of variation in aeolian processes. Studies that aim to investigate surface erodibility often sample aeolian sediment transport at the nodes of a regular grid of arbitrary size. Few aeolian transport investigations have the resources to obtain sufficient samples to produce reliable models for mapping the spatial variation of transport. This study reports the use of an innovative nested strategy for sampling multiple spatial scales simultaneously using 40 sediment samplers. Reliable models of the spatial variation in aeolian sediment transport were produced and used for ordinary punctual kriging and stochastic simulated annealing to produce maps for several wind erosion events over a 25 km2 playa in western Queensland, Australia. The results support the existence of a highly dynamic wind erosion system that was responding to possibly cyclic variation in the availability of material and fluctuations in wind energy. The spatial scale of transport was considerably larger than the small scale expected of the factors controlling surface erodibility. Thus, it appears that transport cannot be used as a surrogate of erodibility at the scale of this investigation. Simulation maps of transport provided considerably more information than those from kriging about the variability in aeolian sediment transport and its possible controlling factors. The proposed optimal sampling strategy involves a nested approach using ca 50 samplers. Copyright © 2003 John Wiley & Sons, Ltd. [source]