Multilayer Phase Research Articles

Structural phase transitions of FeCo and FeNi nanoparticles: A molecular dynamics study

We have investigated the structural phase transition of FeCo and FeNi nanoparticles by molecular dynamics (MD) simulation using the generalized embedded atom potential (GEAM). It is found that the phase varies with the atomic compositions and annealing processes. By using the Honeycutt and Andersen index (HA index), bond order parameters (BOP) and pair correlation function (PCF), we found that a BCC to defective icosahedra phase transition occurs in the FeCo nanoparticle when Co composition is increased to about 60 at %. In the FeNi nanoparticle, three phases have been identified, namely, the BCC phase, the mixed BCC/FCC phase, and the multilayer defective icosahedral phase, which correspond to the Ni compositions of 0–20 at %, 20–70 at %, and 70–100 at %, respectively. Our simulations have well reproduced the phase transition points and most of the phases observed in recent experiments.

Plasticity in the nanoscale Cu/Nb single-crystal multilayers as revealed by synchrotron Laue x-ray microdiffraction

Abstract

Theory of adsorption equilibria analysis based on general equilibrium constant expression

Adsorption equilibria were analyzed on the basis of general equilibrium constant expression for the development of fundamental adsorption equations (Freundlich, Langmuir, and BET) in connection with the establishment of a general approach towards physical interpretations of adsorption parameters. Theoretically it was proved that Freundlich plot analysis cannot be used to find useful parameters such as the monolayer adsorption capacity of an adsorbent. The present theory also indicated that the adsorption process with known value of monolayer adsorption capacity can be studied for finding various equilibrium constants on the basis of the Fronaeus equation, which is commonly used in the complexation process. The applications of the Langmuir equation in finding the ligand number of a complex as well as the magnitude of equilibrium constant required for the analysis of the BET equation in the multilayer liquid phase adsorption process was also discussed. It was concluded that the general approach towards exploration and physical interpretation of adsorption parameters can be developed by analyzing the adsorption equilibria on the basis of general equilibrium constant expression in accordance with the law of mass action.

Heterolithic azobenzene-containing supermolecular tripedal liquid crystals self-organizing into highly segregated bilayered smectic phases

Synthesis, self-organization, and optical properties of supermolecular tripedal liquid crystals incorporating various prototypical mesogenic units such as alkoxy-azobenzene (AZB), alkoxy-biphenylene (BPH) or alkoxy-cyanobiphenyl (OCB) derivatives are reported. Different molecular systems were designed in order to sequentially incorporate the smectogenic-like alkoxy-azobenzene-based chromophore within the molecular structure, whose relative proportion is selectively varied by exchanging with the other mesogens. A divergent synthetic mode was elaborated for their synthesis, starting from the regioselective functionalization of the phloroglucinol-based (PG) inner core. This methodology allowed the preparation of several sets of unconventional tripedal oligomers with conjugated heterolithic structures (made of different blocks, e.g. PG6AZBxBPH3−x and PG6AZBxOCB3−x, x = 1 or 2) along the homolithic parents (all identical blocks, e.g. PGzAZB3, z = 6 or 11, z is the number of methylene in the spacer between PG and the protomesogen, PG6BPH3, and PG6OCB3), respectively. Essentially all the synthesized systems behave as thermotropic liquid crystals and show various types of highly segregated multilayered smectic phases, or, in one case, a nematic phase, depending on the nature of the constitutive anisotropic blocks and on the molecular topology (homolithic versus heterolithic, mesogenic ratio x:3 − x). The effects of these structural modifications on the mesomorphism (mesophase structures, temperature ranges, and thermodynamic stability) have been investigated by differential scanning calorimetry and small-angle X-ray diffraction experiments combined with dilatometric measurements. Models describing the various supramolecular organizations of these tripedes into such multilayered structures are proposed and discussed. Preliminary results of the investigations of their optical properties will also be presented.

Development of a nanoporous and multilayer drug-delivery platform for medical implants

Biodegradable polymers can be applied to a variety of implants for controlled and local drug delivery. The aim of this study is to develop a biodegradable and nanoporous polymeric platform for a wide spectrum of drug-eluting implants with special focus on stent-coating applications. It was synthesized by poly(DL-lactide-co-glycolide) (PLGA 65:35, PLGA 75:25) and polycaprolactone (PCL) in a multilayer configuration by means of a spin-coating technique. The antiplatelet drug dipyridamole was loaded into the surface nanopores of the platform. Surface characterization was made by atomic force microscopy (AFM) and spectroscopic ellipsometry (SE). Platelet adhesion and drug-release kinetic studies were then carried out. The study revealed that the multilayer films are highly nanoporous, whereas the single layers of PLGA are atomically smooth and spherulites are formed in PCL. Their nanoporosity (pore diameter, depth, density, surface roughness) can be tailored by tuning the growth parameters (eg, spinning speed, polymer concentration), essential for drug-delivery performance. The origin of pore formation may be attributed to the phase separation of polymer blends via the spinodal decomposition mechanism. SE studies revealed the structural characteristics, film thickness, and optical properties even of the single layers in the triple-layer construct, providing substantial information for drug loading and complement AFM findings. Platelet adhesion studies showed that the dipyridamole-loaded coatings inhibit platelet aggregation that is a prerequisite for clotting. Finally, the films exhibited sustained release profiles of dipyridamole over 70 days. These results indicate that the current multilayer phase therapeutic approach constitutes an effective drug-delivery platform for drug-eluting implants and especially for cardiovascular stent applications.

CoMo/Al2O3 catalysts prepared on the basis of Co2Mo10-heteropolyacid and cobalt citrate: Effect of Co/Mo ratio

The effect of Co/Mo ratio in the CoMo/Al2O3 hydrotreating catalysts prepared by simultaneous using of the decamolybdodicobaltate heteropolyacid (Со2Мо10HPA) and cobalt citrate was investigated. Synthesized catalysts were characterized by Raman spectroscopy, N2 adsorption, XRD, XPS, HRTEM techniques and were examined in the model reaction of 4,6-dimethyldibenzothiophene (4,6-DMDBT) HDS, in hydrotreating of straight-run gas oil (SRGO) and mixture of 80vol.% SRGO with 20vol.% light coker gas oil (LCGO). It was established that Co/Mo ratio in the catalysts significantly influences on the structure of CoMoS phase of type II and catalytic activity. Catalysts with λ=Co/(Co+Mo)=0.35 had maximal activities in 4,6-DMDBT HDS and diesel HDT and showed the best stability. Increase of the Co/Mo ratio led to simultaneous growing of both average length and stacking number of CoMoS multilayer active phase of the catalysts. Average length increased from 3.0 to 4.0nm, average staking number increased from 1.4 to 1.6. It was found out that catalysts activity decreased within Co/Mo ratio λ from 0.35 to 0.45. Analysis of textural properties of the catalysts, active phase morphology, phase composition and catalytic activities allowed us to suppose that with increase of Co/Mo ratio blocking the mesopores by sulfides of the active components and by coke species with formation of new micropores would take place. The activity of the best prepared CoMo/Al2O3 catalyst was competitive with the activity of the well-known commercial catalysts for ultra-low sulfur diesel in hydrotreating of SRGO or mixture of SRGO with LCGO.

High-precision soft x-ray polarimeter at Diamond Light Source

The development and performance of a high-precision polarimeter for the polarization analysis in the soft x-ray region is presented. This versatile, high-vacuum compatible instrument is supported on a hexapod to simplify the alignment with a resolution less than 5 μrad, and can be moved with its own independent control system easily between different beamlines and synchrotron facilities. The polarimeter can also be used for the characterization of reflection and transmission properties of optical elements. A W/B(4)C multilayer phase retarder was used to characterize the polarization state up to 1200 eV. A fast and accurate alignment procedure was developed, and complete polarization analysis of the APPLE II undulator at 712 eV has been performed.

A tunable three layer phase mask for single laser exposure 3D photonic crystal generations: bandgap simulation and holographic fabrication

Through the use of a multi-layer phase mask to produce five-beam interference, three-dimensional photonic crystals can be formed through single exposure to a photoresist. In these holographically formed structures, the interconnectivity is controlled by the relative phase difference among contributing beams. Photonic band gaps are calculated and the simulation shows a maximum bandgap of 18% of the middle gap frequency when the phase difference is optimized. A three-layer phase mask is fabricated by placing a spacer layer between two orthogonally-orientated gratings. The phase difference is controlled by thermal-tuning of the spacer thickness. Photonic crystal templates are holographically fabricated in a photosensitive polymer using the phase mask.

Functionalized polymeric stationary phases for ion chromatography

Synthesis and properties of the multilayered stationary phases, which contain quaternary amine functional groups for the analysis of anions by ion chromatography, are described. The bonded phases were characterized by elemental analysis, solid-state (13)C NMR spectroscopy and chromatographic methods. The surface of 1,4-di(2-hydroxy-3-methacryloyloxypropoxy)phenol (solid support) was coated with polymeric layers formed by condensation polymerization of primary amine with diepoxide. Each layer of the anion exchange stationary phase consists of copolymer of methylamine (MA) and 1,4-butanedioldiglycidyl ether (BDDE). A series of stationary phases with different numbers of polymerized layers were tested. The separation of an inorganic anions sample (F(-), Cl(-), NO(2)(-), Br(-), NO(3)(-), additionally HPO(4)(2-) and SO(4)(2-)) was performed. In the measurement, a hydroxide, carbonate, bicarbonate and their mixture were used as mobile phases.

Cloud statistics and cloud radiative effect for a low‐mountain site

AbstractIn 2007, the Atmospheric Radiation Measurement (ARM) Mobile Facility (AMF) was operated for a nine‐month period in the Murg Valley, Black Forest, Germany, in support of the Convective and Orographically‐induced Precipitation Study (COPS). The synergy of AMF and COPS partner instrumentation was exploited to derive a set of high‐quality thermodynamic and cloud property profiles with 30 s resolution. In total, clouds were present 72% of the time, with multi‐layer mixed phase (28.4%) and single‐layer water clouds (11.3%) occurring most frequently. A comparison with the Cloudnet sites Chilbolton and Lindenberg for the same time period revealed that the Murg Valley exhibits lower liquid water paths (LWPs; median = 37.5 g m−2) compared to the two sites located in flat terrain. In order to evaluate the derived thermodynamic and cloud property profiles, a radiative closure study was performed with independent surface radiation measurements. In clear sky, average differences between calculated and observed surface fluxes are less than 2% and 4% for the short wave and long wave part, respectively. In cloudy situations, differences between simulated and observed fluxes, particularly in the short wave part, are much larger, but most of these can be related to broken cloud situations. The daytime cloud radiative effect (CRE), i.e. the difference of cloudy and clear‐sky net fluxes, has been analysed for the whole nine‐month period. For overcast, single‐layer water clouds, sensitivity studies revealed that the CRE uncertainty is likewise determined by uncertainties in liquid water content and effective radius. For low LWP clouds, CRE uncertainty is dominated by LWP uncertainty; therefore refined retrievals, such as using infrared and/or higher microwave frequencies, are needed. Copyright © 2011 Royal Meteorological Society

Effect of the second metal of Anderson type heteropolycompounds on hydrogenation and hydrodesulphurization properties of XMo 6(S)/Al 2O 3 and Ni 3-XMo 6(S)/Al 2O 3 catalysts

The catalysts of the XMo 6(S)/Al 2O 3 and Ni 3-XMo 6(S)/Al 2O 3 structures were prepared from heteropolycompounds (HPCs) of Anderson type (where X = Co, Ni, Cr, Mn, Fe, Cu, Zn, Ga). The precursors and synthesized catalysts were characterized by FTIR, XRD, EXAFS, HRTEM techniques. The prepared catalysts were examined in model reactions of thiophene HDS and benzene HYD and in hydrotreating (HDT) of diesel fraction. The correlations between the catalytic activities in HDS and HYD and the heats of thiophene adsorption depending on the nature of the heteroatom prove that it plays an important role in the formation and behavior of the HYD and HDS active sites. It was found that heteropolycompounds are effective precursors of a multilayered active phase of hydrotreating catalysts.

Development and performance of a versatile soft X-ray polarimeter

With modern undulators generating light of an arbitrary polarization state, experiments exploiting this feature in the soft X-ray region are becoming increasingly widespread. Circularly polarized light in the soft X-ray region is of particular interest to investigate of magnetic metals such as Fe, Co and Ni, and the rare earths. A versatile multilayer polarimeter has been designed and developed to characterize the polarization state of the soft X-ray beam. A W/B4C multilayer transmission phase retarder and reflection analyser has been used for polarimetry measurements on the beamline (I06) at Diamond Light Source. The design details of the polarimeter and preliminary polarimetry results are presented.

Relaxation of shear-enhanced crystallization in impact-resistant polypropylene copolymer: Insight from morphological evolution upon thermal treatment

Relaxation of shear-enhanced crystallization in an impact-resistant polypropylene copolymer (IPC) upon thermal treatment was systematically investigated, from the sight of phase structure and resultant morphological evolution. Shearing was capable of accelerating the crystallization of IPC, while upon melt annealing, a spontaneous morphological evolution can be observed accompanied by a gradual relaxation of shear-enhanced crystallization. It was found the underlying structural motion during relaxation is in essence a phase separation process towards a multi-layered phase structure, in which crystallizable polyethylene segments are spatially entangled with ethylene-propylene random copolymer chains. The shear-enhanced crystallization originates from the destruction of this multi-layered phase structure which releases crystallizable PE segments to contact the matrix serving as nuclei for the crystallization of polypropylene. Upon annealing, reconstruction of the multi-layered structure can be achieved leading to the relaxation of shear-enhanced crystallization. A conceptual model describing this relationship between phase structure and crystallization behavior in IPC has been proposed.

Polymeric Functionalized Stationary Phase for Separation of Ionic Compounds by IC

Synthesis and properties are described of multilayered stationary phases containing quaternary amine functional groups used for the analysis of inorganic anions by ion chromatography. The bonded phases were characterized by elemental analysis, solid state 13C NMR spectroscopy and chromatographic methods. The surface of polyhydroxyethyl methacrylate (solid support) was coated with polymeric layers formed by condensation polymerization of primary amine with diepoxide. Each layer of the anion exchange stationary phase consisted of methylamine and 1,4-butanedioldiglycidyl ether copolymer. A series of stationary phases with different number of polymerized layers were tested. Separation of inorganic anions, such as F−, Cl−, NO2 −, Br−, NO3 −, were performed. Aqueous hydroxide, carbonate and bicarbonate solutions were used as mobile phases.

Simultaneous determination of pyrethrins residues in teas by ultra-performance liquid chromatography/tandem mass spectrometry

A sensitive and effective method for the simultaneous quantitative determination of pyrethrin residues in teas was developed and validated using ultra-performance liquid chromatography coupled with tandem mass spectrometry (UPLC–MS/MS). The six major constituents of the pyrethrins (pyrethrin I and II, jasmolin I and II, and cinerin I and II) were successfully separated and independently confirmed in a single run within approximately 5 min. The multi-residue analysis of pyrethrins in teas involved simply extraction with acetonitrile, clean-up using a multilayer solid phase extraction cartridge, and subsequent separation by a hydrophilic end-capped Aquasil C18 columns with detection by tandem mass spectrometry using an electrospray ionization source in positive mode (ESI+). Recovery studies were carried out at three spiked levels (0.05, 0.1, 0.5 mg kg −1). The overall average recoveries using this method in green teas and black teas at the three concentration levels ranged from 76.15% to 101.86% with relative standard deviations (RSDs) in the range of 2.71–12.93% ( n = 5) for all analytes. The limits of detections (LODs) were below 0.009 mg kg −1, which were lower than the maximum residue limits (MRLs) of 0.5 mg kg −1 in tea samples established by the European Union legislations in 2008, while the limits of quantification (LOQ) did not exceed 0.03 mg kg −1. This study provides a theoretical basis for China to draw up MRLs for pyrethrins in teas.

Portable, lightweight, low power, ion chromatographic system with open tubular capillary columns

Basic operation principles of a lightweight, low power, low cost, portable ion chromatograph utilizing open tubular ion chromatography in capillary columns coated with multi-layer polymeric stationary phases are demonstrated. A minimalistic configuration of a portable IC instrument was developed that does not require any chromatographic eluent delivery system, nor sample injection device as it uses gravity-based eluent flow and hydrodynamic sample injection adopted from capillary electrophoresis. As a detection device, an inexpensive commercially available capacitance sensor is used that has been shown to be a suitable substitute for contactless conductivity detection in capillary separation systems. The built-in temperature sensor allows for baseline drift correction typically encountered in conductivity/capacitance measurements without thermostating device. The whole instrument does not require any power supply for its operation, except the detection and data acquisition part that is provided by a USB port of a Netbook computer. It is extremely lightweight, its total weight including the Netbook computer is less than 2.5 kg and it can be continuously operated for more than 8 h. Several parameters of the instrument, such as detection cell design, eluent delivery systems and data treatment were optimized as well as the composition of eluent for non-suppressed ion chromatographic analysis of common inorganic cations (Na +, NH 4 +, K +, Cs +, Ca 2+, Mg 2+, transition metals). Low conductivity eluents based on weakly complexing organic acids such as tartaric, oxalic or pyridine-2,6-dicarboxylic acids were used with contactless capacitance detection for simultaneous separation of mono- and divalent cations. Separation of Na + and NH 4 + cations was optimized by addition of 18-crown-6 to the eluent. The best separation of 6 metal cations commonly present in various environmental samples was accomplished in less than 30 min using a 1.75 mM pyridine-2,6-dicarboxylic acid and 3 mM 18-crown-6 eluent with excellent repeatability (below 2%) and detection limits in the low micromolar range. The analysis of field samples is demonstrated; the concentrations of common inorganic cations in river water, mineral water and snow samples were determined.

Stability of the nitrogen-deficient Ti2AlN x MAX phase in Ar2+-irradiated (Ti,Al)N/Ti2AlN x multilayers

The effects of 100 keV Ar2+ ion irradiation on the structure and stability of multilayered dc sputtered and annealed thin films of (Ti,Al)N/Ti2AlNx have been investigated with X-ray diffraction and transmission electron microscopy. It is shown that the multilayer structure is preserved as well as the crystalline structures of both components. This demonstrates a high tolerance of the Ti2AlNx MAX phase in multilayers to damage induced by nuclear elastic interactions. It is suggested that damage recovery may originate from native nitrogen vacancies and from the interfaces that act as sinks for point defects, like Frenkel pairs, created during the irradiation.

Interfacial Reaction of Sn and Cu-xZn Substrates After Reflow and Thermal Aging

Zn additions to Cu under bump metallurgy (UBM) in solder joints were the subject of this study. An alternative design was implemented to fabricate pure Sn as the solder and Cu-xZn (x = 15 wt.% and 30 wt.%) as the UBM to form the reaction couple. As the Zn content increased from 15 wt.% to 30 wt.% in the Sn/Cu-Zn system, growth of both Cu 3 Sn and Cu 6 Sn 5 was suppressed. In addition, no Kirkendall voids were observed at the interface in either Sn/Cu-Zn couple during heat treatment. After 40-day aging, different multilayered phases of [Cu 6 Sn 5 /Cu 3 Sn/Cu(Zn)] and [Cu 6 Sn 5 /Cu(Zn,Sn)/CuZn] formed at the interface of [Sn/Cu-15Zn] and [Sn/Cu-30Zn] couples, respectively. The growth mechanism of intermetallic compounds (IMCs) during aging is discussed on the basis of the composition variation in the joint assembly with the aid of electron-microscopic characterization and the Sn-Cu-Zn ternary phase diagram. According to these analyses of interfacial morphology and IMC formation in the Sn/Cu-Zn system, Cu-Zn is a potential UBM for retarding Cu pad consumption in solder joints.

A novel LTCC multilayer SIW linear phase filter

AbstractIn this article, a novel multilayer substrate‐integrated waveguide (SIW) linear phase filter is proposed. Four SIW cavities are placed in two layers based on a standard low temperature cofired ceramic technology. Neural network is used to improve the efficiency of design. One slot which is etched on the top metal layer of SIW cavity is adopted to suppress the first high mode. Flat group delay characteristics can be achieved in the filter that has a rejection level of −25 dB in upper stopband. The filter has a 55% area reduction in comparison with planar structure. Good agreement is acquired between measured and simulated results. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 2357–2360, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24595

Phase-dependent electronic properties of monolayer and multilayer anthracene films on graphite [0001] surfaces

The evolution of the electronic properties of thin anthracene films on highly oriented pyrolytic graphite [0001] substrates as a function of temperature has been investigated using ultraviolet photoelectron spectroscopy. The change in the valence line shape with increasing substrate temperature has been univocally associated with the occurrence of different molecular orientations and structural phases (e.g., ``flat-lying'' mono- and multilayer films and a multilayer phase with a ``standing-up'' orientation). These thin-film phases are characterized by ionization energies varying up to 0.9 eV; the surface dipole and possibly to a minor extent polarization energy contributions are shown to be related to the specific molecular packing/molecular orientation and to the interplay between the molecule-molecule vs molecule-substrate interactions. Furthermore, for the monolayer system, a vibrational fine structure of the highest occupied molecular orbital (HOMO) is clearly revealed, thus allowing a detailed study of the HOMO hole-vibration coupling and the temperature-dependent broadening. Showing a large number of recently discussed contributions to the valence line shape, anthracene thin films emerge as ``benchmark'' systems to study the behavior of holes relevant for the charge transport in organic electronic devices.