Influence of annealing temperature on structural,electrical and optical properties of WSi2

WSi₂ polycrystalline films of different thicknesses were prepared by low pressure chemical vapor deposition on silicon wafers, and their crystallization properties were studied as a function of the annealing temperature. Structural measurements were performed by X-ray diffraction, detailing for the first time the phase transition from the amorphous to the hexagonal structure at an annealing temperature 380° C and from hexagonal to tetragonal above 700° C. The electrical sheet resistance showed the same transition temperatures.Optical characterization was performed by spectroscopic ellipsometry, and the real and imaginary part of the complex refractive index were obtained as a function of the annealing temperature in the 0.25–0.9 m wavelength range. A broad optical band was found for samples annealed up to 700° C, while for higher annealing temperatures a transparency region for wavelengths greater than 0.5 m and some significant structures appear. A corresponding behavior was observed in the infrared reflectance spectra. Furthermore, it was shown that the determination of the thickness of SiO₂ grown on WSi₂ requires a multilayer model, taking into account the transparency of tetragonal WSi₂.     

Propellanes—XXXIX : 13C NMR-spectra of configurationally different propellane isomers containing cyclopropane rings

The mono- and bis-adducts obtained in the reaction of carbethoxycarbene with 12-methyl-11,13-dioxo-12-aza[4.4.3]propella-3,8-diene have established configurations of cyclopropane rings and ester groups with respect to the hetero-ring. Thus ¹³C NMR measurements afford data which correlates the ¹³C absorptions of these isomers with their configurations.     

Unification of the quality assurance systems of public health laboratories conformed to ISO 17025, ISO 15189, and ISO 9000: a major organizational change

The Department of Public Health Laboratories consists of five major laboratories located across the country of Israel: four environmental laboratories performing microbiological and chemical testing of food and water products [accredited according to International Organization for Standardization (ISO) 17025 since 1999) and a fifth laboratory that is dedicated to virology testing (certified according to ISO 9000 since 2003). Historically, each laboratory operated independently and developed its own quality assurance (QA). On November 2004, an important strategic decision was made: to unify all five laboratories’ QA systems conformed to ISO 17025, ISO 15189, and ISO 9000—a transition from five laboratories operating independently in the field of QA toward establishing a multisite laboratory. This process was considered and visualized as a major organizational change and therefore raised some resistance among both QA managers and the professional laboratories’ management. Thus, it was necessary to overcome the resistance and at the same time induce thoughts of ways of reshaping and formatting the new and uniform quality manual and uniform standard operating procedures (SOPs). In September 2005, the first phase of the process was completed, and all four environmental public health laboratories successfully passed a reaccreditation audit using a uniform QA manual guide and partially uniform SOPs. We shall share our experience and discuss the major contributions of this process to overall laboratory management. Presented at the 3rd International Conference on Metrology, November 2006, Tel Aviv, Israel.     

Synthesis and characterization of ABA triblock copolymers containing poly(2,6-dimethyl-1,4-phenylene oxide) as A blocks and tetramethyl bisphenol-A polysulfone as B blocks

α, β-Bis(hydroxyphenol) tetramethyl bisphenol-A polysulfone (PSUT) was synthesized by two different methods, one using a strong base, the other using a weak base. The bifunctional polysulfone containing tetramethyl bisphenol-A chain ends was exploited as a model telechelic that can be used for the preparation of ABA triblock copolymers containing poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) as A segments and PSUT as B segments. PSUT and PPO were incorporated into triblock copolymers by an oxidative coupling copolymerization of PSUT with 2,6-dimethylphenol or by the redistribution of PPO in the presence of PSUT. The mechanism of block copolymerization is discussed. DSC studies indicate that short immiscible PPO and PSUT segments incorporated into a triblock copolymer do not exhibit phase separation. Polymer blends of the PPO–PSUT–PPO triblock copolymers with PPO homopolymer were analyzed by DSC. Both miscible and phase-separated blends can be prepared depending on the molecular weight of both PPO homopolymer and of the PPO segment present in the triblock copolymer. Polymer blends of the PPO–PSUT–PPO triblock copolymer with PSUT were miscible at all compositions.     

The use of thermogravimetry as a means of predicting the performance of coke in delayed coking of a residue of Venezuelan origin

Journal of Thermal Analysis and Calorimetry - A study, which shows the similarities in the results obtained through this technique and those corresponding to a process of delayed coking at...     

Mössbauer spectroscopy of lanthanum and holmium ferrites

PrRh₂Si₂ is highly anisotropic Ising-type antiferromagnetic system. The ordering temperature (T _N~ 68 K) of PrRh₂Si₂ is exceptionally high on the de-Gennes scale in the family of RRh₂Si₂ (R = rare earths). The reason for this anomalous behaviour is not clear. It is believed that the presence of uniaxial anisotropy assists in enhancing the T _N. The Mössbauer study was performed on a 10% Fe-doped PrRh₂Si₂ sample to understand the magnetic coupling between different sites of PrRh₂Si₂. The Mössbauer spectra together with the magnetic susceptibility data suggest that the magnetic coupling in PrRh₂Si₂ is provided mainly by the RKKY interaction between Pr-moments.     

1<Emphasis Type="Italic">∕</Emphasis><Emphasis Type="Italic">f</Emphasis><Superscript><Emphasis Type="Italic">β</Emphasis></Superscript> noise for scale-invariant processes: how long you wait matters

We study the power spectrum which is estimated from a nonstationary signal. In particular we examine the case when the signal is observed in a measurement time window [t _w , t _w + t _m ], namely the observation started after a waiting time t _w , and t _m is the measurement duration. We introduce a generalized aging Wiener–Khinchin theorem which relates between the spectrum and the time- and ensemble-averaged correlation functions for arbitrary t _m and t _w . Furthermore we provide a general relation between the non-analytical behavior of the scale-invariant correlation function and the aging 1∕f ^β noise. We illustrate our general results with two-state renewal models with sojourn times’ distributions having a broad tail.     

The influence of polyvinylpyrrolidone on thick and optical properties of BaTiO<Subscript>3</Subscript>:Er<Superscript>3+</Superscript> thin films prepared by sol–gel method

Erbium (Er³⁺) 0.5% mol doped barium titanate (BaTiO₃) thin films were elaborated via sol–gel method and dip-coating technique using titanium alkoxide and barium pentanedionate. Two syntheses were performed [with and without polyvinylpyrrolidone (PVP)] in order to obtain thick films. The BaTiO₃:Er³⁺ thin films prepared from the sol with PVP were elaborated with 1 layer and those without PVP and were elaborated with 17 layers. In both cases, the films were deposited on silica quartz substrates. Both BaTiO₃:Er³⁺ films presented a cubic phase, as determined by X-ray diffraction. BaTiO₃:Er³⁺ films elaborated with PVP via single-step dip coating produced crack-free films with thicknesses of ~800 nm. SEM micrographs for the obtained BaTiO₃:Er³⁺ films revealed high homogeneity and density. Mapping images obtained from BaTiO₃:Er³⁺ revealed homogeneous distribution of Er³⁺ ions on the surface. XPS analyses of the chemical state and chemical environment of the constituent elements in the compositions showed that Er³⁺ ions in (Ba_1−x Er _x )TiO₃ are in mixed valence of Er³⁺/Er²⁺. The BaTiO₃:Er³⁺-PVP film exhibited luminescent properties under near-infrared excitation, as revealed by green emissions. The BaTiO₃:Er³⁺-PVP film has good potential for optical applications.