Preparation and structural stability investigation of CoN/CN soft X-ray multilayers

The structural stability of heat-treated CoN/CN soft X-ray multilayers fabricated by dual-facing-target sputtering has been investigated by using complementary measurement techniques. The high temperature annealing results imply that the destructive threshold of the Co/C multilayers is improved by 100–200 degrees centigrade through doping with N. The low-angle X-ray diffraction of CoN/CN soft X-ray multilayers indicates that the period expansion of the multilayers is only 4 % at 400°C, and the interface pattern still exists even if they were annealed at 700°C. The Raman spectra analyses give the evidence that the formation of the sp³ bonding in the CN sublayers can be suppressed effectively by doping N with atoms, and thus the period expansion resulting from the changes in the density of CN layers can be decreased considerably. The X-ray photoelectron spectra analyses present the information of the existence of the strong covalent bonding betweenC andN atoms, and the ionic bonding between Co and N atoms, which can slow down the tendency of the structural relaxation. The interstitial N atoms decrease the mobility of Co atoms, and thus the fcc-Co and hcp-Co coexist even though the annealing temperature is much higher than the phase transformation temperature of 420°C, leading to the suppression of the grain growth.     

Solid State Amorphisation in Magnetic Multilayers: the Interface Structure and the Electrical Transport Properties

The structure and electrical conductivity properties of the R.F. sputtered FeZr and FeTi multilayers with ultrathin layer thicknesses, in as-deposited states, have been studied using X-ray diffraction, low-angle X-ray and neutron reflectometry, conversion electron Mössbauer spectroscopy (CEMS), resistivity and magnetoresistivity measurements. The thickness ratio (β=d_Fed_Zr and d_Fed_Ti) of analysed multilayers was 0.5 and 1, the values of the bilayer thickness (λ=d_Fe+d_Ti,Zr) was varied from 9 Å to 600 Å, maintaining constant the total thickness of the samples by controlling the number of bilayers. The results obtained from CEM-spectroscopy and X-ray diffraction show that Fe layers of the thickness below 20 Å are alloyed forming an amorphous phase during deposition. This amorphous phase is distributed in the plane between the crystalline sublayers as well as in the grain boundaries according with the proposed model of the interpretation of the electrical conductivity as a function of the bilayer thickness (λ).     

Multiscale Modeling for the Simulation of Damage Processes at Refractory Materials under Thermal Shock

Refractory materials, for example ceramic materials, initially contain a multitude of defects such as voids, microcracks, grain boundaries etc. The deformation process and failure mechanisms due to thermal shock at high temperatures above 1000°C are going along with the creation of new micro defects as well as the growth and coalescence of cracks. A material damage model based on the theoretical concept of damage mechanics and the mechanics of microcracks is presented in this paper. Cell models are developed as representative volume elements (RVE) including crack initiation and growth as well as microstructural shielding effects. For simple configurations of the microstructure, the relation between stress, strain and temperature is derived from analytical considerations. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Formation of nanocrystalline Fe73.5Cu1Nb3Si13.5B9 alloy under high pressure

The formation of nanocrystalline Fe_73.5 Cu₁Nb₃Si_13.5 B₉ alloy by annealing an amorphous Fe_73.5Cu₁Nb₃Si_13.5B₉ alloy at a temperature of 823 K under pressures in the range of 1–5 GPa is investigated by using X-ray diffraction, electron diffraction, and transmission electron microscopy. The high pressure experiments are carried out in belt-type pressure apparatus. Experimental results show that the initial crystalline phase in these annealed alloys is a-Fe solid solution (named a-Fe phase below), and high pressure has a great influence on the crystallization process of the a-Fe phase. The grain size of the a-Fe phase decreases with the increase of pressure (P). The volume fraction of the a-Fe phase increases with increasing the pressure as the pressure is below 2 GPa, and then decreases (Pδ2 GPa). The mechanism for the effects of the high pressure on the crystallization process of amorphous Fe_73.5Cu₁Nb₃Si_13.5B₉ alloy is discussed Project supported by the National Natural Science Foundation of China (Grant No. 19674070) and the Natural Science Foundation of Hebei Province.     

Ag/Si multilayers with nanometer sized particles of silver during annealing process

Thein situ low angle X-ray diffraction and transmission electron microscopy were used to monitor the interdiffusion characteristics as well as the microstructure in Ag/Si multilayers with modulated wavelength 7. 64 nm when annealing from 323 to 573 K. The interdiffusion mechanism of Ag/Si multilayers with immiscibility is different from that of other metal/Si multilayers which are miscible. Phase separation takes place at 323 K, then silicon atoms diffuse into silver sublayers through silver grain boundaries and separate silver sublayers into nanometer sized silver particles gradually at higher temperature. The mean size of silver particles is about 5 nm. The activation energy and frequency factor are determined to be 0.24 eV and 2.02 x⁻²⁰m²/s, respectively. An erratum to this article is available at .     

Diamagnetism of organic liquid mixtures at different temperatures

The diamagnetic susceptibilities of mixtures of benzene-acetone, chloroformacetone and nitrobenzene-acetone have been studied at different temperatures ranging from 15°;C to 50°;C, using the Quincke method with very large magnetic fields. The factors influencing the measurements made by such a method are critically considered and natural explanations are offered to the anomalous results obtained by different investigators. The susceptibilities of these mixtures obey the additive law in this range of temperature. Further the pure liquids do not show any variation in their susceptibility values between 15°;C and 50°;C. A large amount of evidence is presented to show that association in organic liquids does not produce any change in the specific susceptibility and that the additive law of mixtures is true unless chemical combination in the mixture changes entirely the nature of the bonds linked to the carbon atom.     

Magneto-optical Kerr effect in CoxAg1-x nanostructured granular films

A series of Co_xAg_{1 - x} nanostructured granular films have been prepared by ion beam sputtering and annealed at 100, 250, 400, 500°C. The optical constants, the complex dielectric function and magneto-optical Kerr parameters were measured at room temperature. For the samples having low Co compositions, the strong Kerr effect enhancement is observed around the Ag plasma edge. With an increase in annealing temperature, the resonance-like peaks appear in the Kerr rotation, and the peak positions are shifted toward the low photon energy region. From the analysis of the numerical calculations, it is concluded that the magneto-optical Kerr effect enhancement (MOKE) is due to the presence of the steep plasma edge.     

Magneto-optical Kerr effect in Co x Ag1-x nanostructured granular films

A series of Co_xAg_{1 - x} nanostructured granular films have been prepared by ion beam sputtering and annealed at 100, 250, 400, 500°C. The optical constants, the complex dielectric function and magneto-optical Kerr parameters were measured at room temperature. For the samples having low Co compositions, the strong Kerr effect enhancement is observed around the Ag plasma edge. With an increase in annealing temperature, the resonance-like peaks appear in the Kerr rotation, and the peak positions are shifted toward the low photon energy region. From the analysis of the numerical calculations, it is concluded that the magneto-optical Kerr effect enhancement (MOKE) is due to the presence of the steep plasma edge.     

Properties of GaAs single crystals grown by molecular beam epitaxy at low temperatures

Properties of GaAs single crystals grown at low temperatures by molecular beam epitaxy (LTMBE GaAs) have been studied. The results show that excessive arsenic atoms of about 10²⁰ cm⁻³ exist in LTMBE GaAs in the form of arsenic interstitial couples, and cause the dilation in lattice parameter of LTMBE GaAs. The arsenic interstitial couples will be decomposed, and the excessive arsenic atoms will precipitate during the annealing above 300°C. Arsenic precipitates accumulate in the junctions of epilayers with the increase in the temperature of annealing. The depletion regions caused by arsenic precipitates overlap each other in LTMBE GaAs, taking on the character of high resistivity, and the effects of backgating or sidegating are effectively restrained.     

Control of biopolymer poly-β-hydroxybutyrate characteristics by γ-irradiation

The influence of γ-irradiation on the structure and some mechanical properties of poly-β-hydroxybutyrate was studied. Specimens of PHB were γ-irradiated with various doses (1–20 Mrad) in air and vacuum. The molecular weight, structural characteristics of the crystalline and amorphous phases, characteristics of thermal degradation, and deformation of the polymer were determined. The crystallinity was found to increase with increase in the radiation dose and with the corresponding reduction in molecular weight. The increase of crystallinity was the greater the smaller the length of macromolecules (higher radiation dose). The melting temperature T _m , which characterizes the crystalline order, decreased with decrease in the molecular weight. The results of calorimetric studies suggest that radiation-caused degradation, which occurs at a temperature at which “cold” crystallization (60°C) is possible, might also affect the crystalline part of the polymer.     

Simulating resistance switching in amorphous carbon

The resistance switching in amorphous carbon (a-C) is mathematically simulated on the basis of quantum molecular dynamics. The electric conductivity in thin a-C films is related to a phase transition due to an electric field and corresponding Joule heating and cooling. Simulations show that the transition mechanism is related to the clusterization of existing conducting regions of graphite (sp ²) in a nonconducting diamond (sp ³) matrix. Simulations yield the conditions for the phase transition in a-C from one state to another. Excited molecular orbitals and the energy gap at different temperatures are also calculated.     

α-Sn thin film grown on GaAs substrate by MBE and investigation of its multiquantum well structure

α-Sn thin films have been grown on GaAs (001) single crystal substrates by molecular beam epitaxy (MBE). The α-Sn growth process has been characterizedin situ by reflection high energy electron diffraction (RHEED), and the transmission electron microscope (TEM) was used to analyze the interface structures. The measurement results indicate that our metastable a-Sn films have both higher temperature stability which increases by 30°C (from 70 to 100°C) and thickness stability which increases by 200 nm (from 500 to 700 nm) in comparison with previous reports. Other improvements in electrical properties have also been observed. In addition, a new model of multiquantum well structure has been suggested. Project supported by the National Natural Science Foundation of China (Grant No. 69586001).     

Determining Net Requirements for Material Requirements Planning

This paper presents a design guideline for netting systems that determine net requirements, for push-type production ordering. Two alternative netting systems (full and single) are formulated in an N stage production and inventory system. The performances of the two alternatives are discussed through numerically analysing production ordering variations and inventory level variations at each stage in the processes. The results obtained suggest that: (1) the full netting system is preferable at the production stages, where variance in the accumulated forecast consumption error by the immediately succeeding stage is smaller than the variance in the accumulated forecast market demand error over a production ordering interval and the lead time for the stage. (2) The single netting system may be preferable at the other stages, particularly in regard to production ordering variations.     

Synthesis and surface reactivity of phosphide nanocrystals

Gap and InP nanocrystals were synthesized from Na₃P and GaCI₃ at low temperature (80–100°C) and atmospheric pressure. The samples were characterized by XRD and TEM measurements. The surface reactivity of Gap nanocrystals was studied by heating in N₂. The weight of the nanocrystals increased at the temperature between 370°C and 480°C. It can be concluded that N, molecule was absorbed and reactivated on the surface of Gap nanocrystals. Keywords: gallium phosphide, indium phosphide, nanocrystal, surface reactivity.     

Thermal conductivity of micro-and nanostructural epoxy composites at low temperatures

The thermal conductivity of epoxy composites containing not only the traditional fillers quartz, talc, carbon black, and aerosil, but also the very promising carbon nanomaterials is investigated. Two kinds of carbon nanomaterials — multi-wall (MWNT) and single-wall (SWNT) carbon nanotubes — were considered. The influence of their content (from 0.05 to 3.0 wt.%) on the thermal conductivity of MWNT-epoxy composites was studied. The thermal conductivity of epoxy composites was examined in the temperature range from −150 to 150°C. It was found that the introduction of 0.1–1.0 wt.% MWNT enhanced the thermal conductivity of pure epoxy resin by about 40%. A further increase in content of the nanotubes decreased the thermal conductivity. This can be explained by the worsening of nanotube dispersion at their high concentrations. The maximum growth in the thermal conductivity of the epoxy composites, on the entire range of temperatures considered, was observed at a 0.1 wt.% content of MWNT. __________ Translated from Mekhanika Kompozitnykh Materialov, Vol. 44, No. 1, pp. 117–126, January–February, 2008.     

Adhesive ability of a heat-resistant double-chain polymer and the strength of CFRP based on it

The adhesive ability of a heat-resistant polyiminoquinazolindione (PIQD) binder, based on a double-chain polymer, and the physicomechanical characteristics of unidirectional CFRPs made with it are investigated. It is shown that, at room temperature, the strength of model adhesive joints (PIQD-steel wire) and of the CFRPs in shear and bending is rather low — about half of that of similar specimens based on an epoxy binder. At the same time, all their mechanical characteristics, to a large measure (50%), are retained at temperatures up to 450°C, which considerably exceeds the heat resistance of all polymer matrices used at the present time. The elastic modulus of the CFRPs in bending practically remains the same up to 450°C. __________ Translated from Mekhanika Kompozitnykh Materialov, Vol. 44, No. 4, pp. 535–546, July–August, 2008.     

Synthesis of C3N4 crystals under high pressure and high temperature

C₃N₄ crystals with the size of several micrometers have been synthesized from C₃N₄H₄ in the presence of nickel-based alloy or cobalt as catalyst under high pressure of 7 GPa and temperature of about 1400°C for 10 min. Scanning electron microscopy, energy-disperse X-ray analysis, and X-ray diffraction were used to examine the grown crystals. The general rule on selecting the starting materials for synthesis of carbon nitride crystals at high pressures and high temperatures is suggested.     

A Microcomputer Based Solution to a Practical Scheduling Problem

This paper presents a scheduling problem with constraints imposed on the waiting time between stages. The process in which it occurs involves the preparation, cooking and chilling of meals. A maximum of 30 min is permitted for waiting between the completion of the cooking stage and the start of chilling down to temperature of <3°C. If this is not achieved, then the food has to be discarded. Clearly the scheduling of the final cooking stage and chilling facilities is crucial in this context. The development of a procedure to do this scheduling, using a microcomputer, is described and some typical results presented. Further uses of the model are briefly outlined.