Structure and stability of Fe−Mg amorphous alloys prepared by coevaporation

The structure, stability and magnetic properties at 77K of Fe₆₀Mg₄₀ amorphous thin films prepared by coevaporation are investigated using mainly Mössbauer effect working in scattering geometry and transmission electron microscopy. The temperature range of the amorphous to crystal transition is determined; moreover a superparamagnetic-like behaviour of the films is pointed out at 77K.

     

Damage distribution and measure of projected range in proton bombarded GaAs

Abstract

The technique of cross-sectional transmission electron microscopy has been applied to obtain information on the projected range of protons and their damage distribution in gallium arsenide. The crystals were subjected to dosages of 1 × 10¹⁵ to 1 × 10¹⁷ protons cm^?2 and proton energies of 100, 200 and 300 keV. Within this energy range the damage shows a Gaussian distribution about a mean range which correlates closely with LSS values. The experimentally determined damage profiles are found to be essentially independent of proton energy and the temperature of post implantation anneal for a given dosage. The displacement damage as reflected by the damage profiles is found to be linear with proton dose. Finally, it is estimated that defects became visible in unannealed crystals when each atom is, on the average, displaced at least once during irradiation.     

Magnetic nanoparticles trigger cell proliferation arrest of neuro-2a cells and ROS-mediated endoplasmic reticulum stress response

The synthesis, morphological characterization, and optical properties of colloidal, Eu(III) doped Gd₂O₃ nanoparticles with different sizes and shapes are presented. Utilizing wet chemical techniques and various synthesis routes, we were able to obtain spherical, nanodisk, nanotripod, and nanotriangle-like morphology of Gd₂O₃:Eu³⁺ nanoparticles. Various concentrations of Eu³⁺ ions in the crystal matrix of the nanoparticles were tested in order to establish the levels at which the concentration quenching effect is negligible. Based on the luminescence spectra, luminescence lifetimes and optical parameters, which were calculated using the simplified Judd–Ofelt theory, correlations between the Gd₂O₃ nanoparticles morphology and Eu³⁺ ions luminescence were established, and allowed to predict the theoretical maximum quantum efficiency to reach from 61 to 98 %. We have also discussed the impact of the crystal structure of Gd₂O₃ nanoparticles, as well as coordinating environment of luminescent ions located at the surface, on the emission spectra. With the use of a tunable femtosecond laser system and the Z-scan measurement technique, the values of the effective two-photon absorption cross-section in the wavelength range from 550 to 1,200 nm were also calculated. The nonlinear optical measurements revealed maximum multi-photon absorption in the wavelength range from 600 to 750 nm.

     

Scanning tunnelling microscopy of charge-density waves in transition metal chalcogenides

We have used scanning tunnelling microscopes (STMs) operating at liquid helium and liquid nitrogen temperatures to image the charge-density waves (CDWs) in transition metal chalcogenides. The layer structure dichalcogenides TaSe₂, TaS₂, NbSe₂, VSe₂, TiSe₂ and TiS₂ have been studied including representative polytype phases such as 1T, 2H and 4Hb. Experimental results are presented for the complete range of CDW amplitudes and structures observed in these materials. In most cases both the CDW and the surface atomic structure have been simultaneously imaged. Results on the trichalcogenide NbSe₃ are also included.

The formation of the CDW along with the associated periodic lattice distortion gaps the Fermi surface (FS) and modifies the local density-of-states (LDOS) detected by the tunnelling process. The tunnelling microscopes have been operated mostly in the constant current mode which maps the LDOS at the position of the tunnelling tip. The relative amplitudes and profiles of the CDW superlattice and the atomic lattice have been measured and confirm on an atomic scale the CDW structures predicted by X-ray, electron and neutron diffraction. The absolute STM deflections are larger than expected for the CDW induced modifications of the LDOS above the surface and possible enhancement mechanisms are reviewed.

In the 2H trigonal prismatic coordination phases the CDWs involve a relatively small charge transfer and the atomic structure dominates the STM images. In the 1T octahedral coordination phases the charge transfer is large and the CDW structure dominates the STM image with an anomalously large enhancement of the STM profile. Systematic comparison of the STM profiles with band structure and FS information is included.

In the case of the 4Hb mixed coordination phases at the lowest temperatures two nearly independent CDWs form in alternate sandwiches. STM studies on 4Hb crystals with both octahedral and trigonal prismatic surface sandwiches have been carried out. The STM scans detect the relative strengths of the two CDWs as well as the interactions between the two types of CDW structure.

The STM scans are also able to detect defects and domain structure in the CDW image. Several examples will be given demonstrating the potential of the STM to detect these local variations in LDOS on an atomic scale. In contrast to the layer structure crystals the linear chain compound NbSe₃ shows a complex surface atomic structure as well as the formation of two CDWs. The surface atomic structure is resolved in the STM scans and profiles have detected the presence of the CDW modulation at 77K and 4.2K. These results demonstrate the feasibility of detecting CDW structure in the presence of complex atomic structure and using materials where dynamical CDW effects can also be studied by STM.

The range of STM results presented here show that the STM scans are extremely sensitive to the detail of the CDW structure and its effect on the LDOS. Although much of this structure has been deduced from diffraction studies, the ability to examine the CDW structure on an atomic scale with the STM is new. The sensitivity of the STM method suggests potential applications to a wide range of electronic structures in materials.     

Structural,morphologic and optical characterization of In(2−x)Al x S3

Aluminum-doped indium sulfide thin films are deposited on glass by spray pyrolysis technique. The structure and the surface morphology of these films were characterized by X-ray diffraction and atomic force microscopy. The effects of aluminum ratio z and substrate temperature T _s, on the film structure and grain size are discussed. The influence of aluminum ratio on surface morphology is revealed by scanning electron microscope. Besides, energy dispersive spectrometry technique is used to compare atomic aluminum concentration in the film with aluminum ratio z in spray solution. Optical properties are studied by a spectrophotometer in the wavelength range 350–850 nm, at room temperature. Optical transmission and grain size are found to be maximal for z = 1.8 %. Moreover, band-gap energy is found to increase with aluminum ratio.     

Structural and phase analysis of rapidly solidified Al-Fe alloys

The structure and phase composition of lightly-doped Al-Fe alloys obtained by ultrarapid quenching from the melt are investigated. The surface of foils was studied using scanning electron microscopy, atomic-force microscopy, and Rutherford backscattering technique. The variation in the phase composition of alloys during annealing was studied by x-ray diffraction technique and by resistivity and microhardness measurements. The Al-Fe alloys have microcrystalline structure with a nonuniform iron content in the near-surface region of the samples. A correlation of depth profiles of iron and phase composition of the foils is observed. It is found that decomposition of the supersaturated α solid solution proceeds in the temperature range 250–350°C. As the annealing temperature increases, a metastable Al₆Fe phase is precipitated. In the range 300–500°C, the metastable Al₆Fe phase decomposes, and a stable Al₃Fe phase is precipitated.     

Application of Advanced Synchrotron Radiation–Based and Conventional Molecular Techniques in Recent Research on Molecular Structure,Metabolic Characteristics,and Nutrition in Coproducts from Biofuel Processing

Abstract

Advanced synchrotron radiation infrared microspectroscopy, as a nondestructive and rapid analytical technique, is able to simultaneously reveal the structural, chemical, and environmental features of biomaterials at cellular and molecular levels within intact tissue. However, to date, this advanced synchrotron-based technique is still seldom used by feed and nutrition scientists. This article aims to provide detailed information regarding how to apply advanced synchrotron radiation–based and conventional molecular techniques to research in coproducts from biofuel processing on the molecular structure, metabolic characteristics, and nutrition. The information described in this article provides better insight on coproduct research progress and updates with advanced synchrotron radiation-based and globar-based (conventional) molecular spectroscopy.     

Omega phase of zirconium: Formation under shock wave compressin and stability at atmospheric pressure

Abstract

The structure of Zr after shock compression in the 8–32 GPa range at initial tempertures 290 K and 90 K has been investigated by X-ray diffraction and transmission electron microscopy. ω-phase fraction vs. peak pressure and crystallographic relationship between α- and ω-phases have been obtained. A dilatometric study of Zr samples containing ω-phase has been performed.     

Tapped granular packings described as complex networks

Abstract

We characterize the structure of simulated two-dimensional granular packings using concepts from complex networks theory. The packings are generated by a simulated tapping protocol, which allows us to obtain states in mechanical equilibrium in a wide range of densities. We show that our characterization method is able to discriminate non-equivalent states that have the same density. We do this by examining differences in the topological structure of the contact network of the packings. In particular, we find that the polygons of the network are specially sensitive probes for the contact structure. Additionally, we compare the network properties obtained in two different scenarios: the tapped and a compressed system.     

Study of quasi-two- and three-dimensional ordered porous structures by means of small-angle X-ray scattering in the grazing incidence geometry

The structure of surface layers of thin metal inverse opals has been studied first by the grazing-incidence small-angle X-ray scattering technique. Contributions of the form factor and structure factor to the small-angle diffraction pattern have been separated using a numerical model of the scattering process. The complementary use of the small-angle X-ray scattering and grazing-incidence small-angle X-ray scattering techniques has provided independent information about the bulk and surface properties of the samples and allowed a type of defect in the investigated structures to be determined. The measurement results have been verified by atomic force microscopy.

     

1.25μm近红外场助光阴极材料InGaAsP/InP的液相外延

本文简要阐述了近红外场助光阴极的原理及对外延材料的要求。利用液相外延工艺并采用独特的掺杂技术生长出了用于近红外光电阴极的InP/InGaAsP 异质结结构。显微分析。x射线双晶衍射、电子探针、电化学C-V等测试结果表明外延层的结晶质量及电学性能符合设计的特殊要求,在此基础上制作的场助光电阴极量子效率在1.20μm处为3.5×10^-4,其响应波长可达1.25μm。     

Monte Carlo simulations of magnetic particle suspensions with a simple assessment method for the particle overlap between magnetic spheroids

We have developed a simple assessment method for the overlap between spheroidal particles, which neither requires the complex manipulation of vectors and matrices that is indispensable in the ordinary methods, nor is based on a model potential. Moreover, we have developed an evaluation method for the interaction energy arising from the overlap of the steric layer coating spheroidal particles. This is based on a sphere-connected particle model, but some modifications are introduced in order to express an appropriate repulsive interaction energy at the deepest overlapping position. We have investigated the phase change in a magnetic spheroidal particle suspension for a two-dimensional system by means of Monte Carlo simulations. In the case of no external magnetic field, if the magnetic particle-particle interaction is sufficiently strong to favour cluster formation, long raft-like clusters tend to be formed in a dilute situation. With decreasing values of area fraction, a chain-like structure in a dense situation transforms into a raft-like structure within a narrow range of the particle area fraction. Similarly, the raft-like clusters are preferred in a weak applied magnetic field, but an increase in the field strength induces a phase change from a raft-like into a chain-like structure.

Highlights of the present paper:

1. A simple assessment method has been proposed for the overlap between two spheroidal particles.

2. The particle overlap assessment is free from a complex mathematical manipulation regarding vectors and matrices.

3. A modified sphere-connected model has been proposed in order to more accurately evaluate a repulsive interaction due to the overlap of the steric layers coating spheroidal particles.

4. 2D Monte Carlo simulations have been performed to elucidate the phenomenon of a phase change by magnetic spheroidal particles on a material plane surface.

5. A phase change between a raft-like and a chain-like aggregate structure is able to be controlled by the area fraction of particles and an external magnetic field.

     

On the formation of lamellae during annealing of extended chain crystals of radiation-polymerized trioxane

The structure changes of radiation-polymerized trioxane taking place during annealing have been studied by means of electron microscopy, X-ray small- and wide-angle scattering, and differential thermal analysis. The original fibrillar crystals, supposedly consisting of extended chains, change into lamellar crystals due to annealing at temperatures between 150° and 190°C. Lamella formation can be connected with the appearance of a long period of about 200A which is not observed in the unannealed sample.

During annealing within the same temperature range the X-ray reflections due to the twin structure of the original polytrioxane disappear, whereas the orientation of the fraction with its c-axis parallel to the c-axis of the parent trioxane remains unaltered.

The melting point of the lamellar crystals obtained by annealing is 186°-187°C and, therefore, considerably higher than the melting point (175°C) of crystals grown during cooling of a polytrioxane melt. The equilibrium melting point of an undisturbed extended-chain poly-oxymethylene single crystal must be still higher and may even approach 200°C.

On the basis of the electron-microscopical observations and the X-ray results, it is supposed that the process of lamella formation takes place continuously by reorganization of the whole structure including the already grown lamellae. The rate of this process is the faster the higher the annealing temperature. Some possible mechanisms are discussed but the final reasons for the observed structure changes are not known.     

Formation of Germanium–Vacancy Color Centers in CVD Diamond

We study Ge-doped polycrystalline diamond films synthesized, using microwave plasma chemical vapor deposition (CVD) in CH₄-H₂ base mixtures. We compare two sources of the dopant – gaseous monogermane (GeH₄) and solid Ge plates. We investigate the structure and phase composition of the obtained films, using scanning electron microscopy, photoluminescence (PL), and Raman spectroscopy. We vary the precursor gas composition to maximize the intensity of the Germanium–vacancy (Ge-V) PL signal at 602 nm and discover that, using [C]-rich gas mixtures ([CH₄]=20%), we are able to increase the intensity of Ge-V signal by two orders of magnitude in comparison with Ge-doped high-quality microcrystalline films of the same thickness but grown at [CH₄]=4%. The attained results may be used for the fabrication of polycrystalline diamond films and plates with high concentrations of Ge-V centers, which may serve as source material for the fabrication of submicrometer-sized luminescent diamond particles for local optical thermometry.

     

The Technique of Studying X-Ray Scattering over Wide Temperature Range in an Electric Field

The technique of studying the synchrotron radiation scattering on single crystals over wide temperature range using an original miniature device for applying an electric field to a sample is described. A specific feature of the device is the possibility of its application with various heating and cooling systems. The technique was used at BM01 beamline at the European Synchrotron Radiation Facility (ESRF) for the study of the influence of electric field on the processes of structural transformation in lead zirconate–titanate single crystal with a low titanium concentration. The efficiency of the technique proposed in this work is demonstrated and the results of the preliminary analysis of the results are presented.

     

High-gain erbium-doped fiber amplifier incorporating a double-pass amplification technique as a preamplifier

We present a high-gain erbium-doped fiber amplifier to be utilized as a preamplifier. A double-pass amplification technique is used in the first-stage amplifier together with a tunable bandpass filter. The secondstage amplifier is a counter-pumped configuration and another tunable bandpass filter is utilized to filter out amplified spontaneous emission from the first-stage amplifier. This design is able to produce a high gain of 55.6 dB and a noise figure of 6.02 dB at 1530 nm with a signal power of ?45 dBm. The receiver sensitivity measurement shows that the proposed amplifier improves the minimum detectable power from ?33.7 to ?40.8 dBm for a bit-error rate of 10^?11 at 155 Mbps.

     

A maze structure for sound attenuation

Sonic crystals are periodic arrangement of scatterers made of material with low acoustic impedance or sound hard materials [1]. Sonic crystals have numerous applications such as green belts and sound barriers. Here we showed that a typical maze structure at children playground can attenuate noise effectively for frequencies ranging from 12.5 Hz to 20,000 Hz. The original designer for the maze structure probably does not have that in mind. The maze structure can be viewed as a sonic crystal structure with sound attenuation characteristics. We found that the maze was able to attenuate noise up to 17.9 dBA for frequency range below 1000 Hz and 23 dBA for higher frequency range up to 20,000 Hz. The maze structure was able to mitigate noise at a wide range of frequencies in addition to the center frequency (f_c$f_c$) of 478 Hz which was estimated based on the Bragg’s Law. The periodic effects of the maze was also proven by numerical studies. Our results demonstrated that the maze structure commonly found in children playgrounds was able to attenuate noise covering the whole human hearing range.     

The nucleation,growth, structure and epitaxy of thin surface films

A review is given of the evidence available on the mechanism of growth and the structure of thin deposited films. The main attention is devoted to the growth of metals onto single crystal substrates, particularly those formed by the evaporation technique. Some consideration of other types of deposit is also given, including chemically formed films and epitaxial silicon layers. A survey of the various experimental techniques which can be used for structural studies on thin films is given, but the main evidence presented is based upon electron diffraction and transmission electron microscopy.

The mode of nucleation of the layers is described, and the evidence for the way in which the nuclei develop into a continuous deposit film is outlined. This includes the evidence obtained from growing films inside the electron microscope, which reveals two important processes. These are the ‘liquid-like’ coalescence of nuclei and islands, and recrystallization of islands.

The various imperfection structures observed in thin films are described, and an attempt is made to explain the mechanisms by which these imperfections are formed during the growth of the film.

Finally, the significance of the experimental evidence on growth and structure is discussed in relation to the occurrence of epitaxy, and an attempt is made to determine the most important directions for future studies of epitaxy.