Asymmetric Interfaces in Epitaxial Off-Stoichiometric Fe3+xSi1−x/Ge/Fe3+xSi1−x Hybrid Structures: Effect on Magnetic and Electric Transport Properties

Three-layer iron-rich Fe3+xSi1−x/Ge/Fe3+xSi1−x (0.2 < x < 0.64) heterostructures on a Si(111) surface with Ge thicknesses of 4 nm and 7 nm were grown by molecular beam epitaxy. Systematic studies of the structural and morphological properties of the synthesized samples have shown that an increase in the Ge thickness causes a prolonged atomic diffusion through the interfaces, which significantly increases the lattice misfits in the Ge/Fe3+xSi1−x heterosystem due to the incorporation of Ge atoms into the Fe3+xSi1−x bottom layer. The resultant lowering of the total free energy caused by the development of the surface roughness results in a transition from an epitaxial to a polycrystalline growth of the upper Fe3+xSi1−x. The average lattice distortion and residual stress of the upper Fe3+xSi1−x were determined by electron diffraction and theoretical calculations to be equivalent to 0.2 GPa for the upper epitaxial layer with a volume misfit of −0.63% compared with a undistorted counterpart. The volume misfit follows the resultant interatomic misfit of |0.42|% with the bottom Ge layer, independently determined by atomic force microscopy. The variation in structural order and morphology significantly changes the magnetic properties of the upper Fe3+xSi1−x layer and leads to a subtle effect on the transport properties of the Ge layer. Both hysteresis loops and FMR spectra differ for the structures with 4 nm and 7 nm Ge layers. The FMR spectra exhibit two distinct absorption lines corresponding to two layers of ferromagnetic Fe3+xSi1−x films. At the same time, a third FMR line appears in the sample with the thicker Ge. The angular dependences of the resonance field of the FMR spectra measured in the plane of the film have a pronounced easy-axis type anisotropy, as well as an anisotropy corresponding to the cubic crystal symmetry of Fe3+xSi1−x, which implies the epitaxial orientation relationship of Fe3+xSi1−x (111)[0−11] || Ge(111)[1−10] || Fe3+xSi1−x (111)[0−11] || Si(111)[1−10]. Calculated from ferromagnetic resonance (FMR) data saturation magnetization exceeds 1000 kA/m. The temperature dependence of the electrical resistivity of a Ge layer with thicknesses of 4 nm and 7 nm is of semiconducting type, which is, however, determined by different transport mechanisms.

Structural, Morphological, and Magnetic Properties of Nickel Substituted Cobalt Zinc Nanoferrites at Different Sintering Temperature

Co-precipitation was used for the preparation of Co0.5-xNixZn0.5Fe2O4 (x = 0 to 0.3) nanoferrites. The inverse spinel structure of the samples was clearly shown by the structural analysis of X-ray Diffractometer (XRD) and Fourier Transform Infrared (FTIR) Spectroscopy. We have studied the effect of sintering temperature (500oC) on the lattice constant and particle size using XRD. The average lattice parameters for the non-sintered and sintered samples were 8.377 Å and 8.354 Å respectively. For the non-sintered sample, the nickel concentration decreases the lattice parameter from 8.354 Å to 8.310 Å due to its smaller ionic radii than that of cobalt. While for a sintered sample at 500oC, the lattice parameter increases for concentration x=0.3 due to the thermal effect. The particle size calculated by Transmission Electron Microscope (TEM) agrees well with that of XRD. The morphological and compositional analysis was done with the help of Scanning Electron Microscopy (SEM) and the attached Energy Dispersive X-ray (EDX) Analyzer. The increasing percentage of nickel with decreasing percentage of cobalt shows that the cobalt is substituted by Nickel. The magnetic properties were studied by Vibrational Spectrometer (VSM). The value of saturation magnetization is higher for x=0.1 but lower for x=0.2 and 0.3 due to their particle size. The hysteresis loop of the samples their superparamagnetic behavior at room temperature.

Lattice Bounded Distance Equivalence for 1D Delone Sets with Finite Local Complexity

Spectra of suitably chosen Pisot-Vijayaraghavan numbers represent non-trivial examples of self-similar Delone point sets of finite local complexity, indispensable in quasicrystal modeling. For the case of quadratic Pisot units we characterize, dependingly on digits in the corresponding numeration systems, the spectra which are bounded distance to an average lattice. Our method stems in interpretation of the spectra in the frame of the cut-and-project method. Such structures are coded by an infinite word over a finite alphabet which enables us to exploit combinatorial notions such as balancedness, substitutions and the spectrum of associated incidence matrices.

Altering the properties of the magnetic Co ferrite nanoparticles fabricated by modified inverse coprecipitation for high-frequency applications

Magnetic Co ferrite nanoparticles doped with non-magnetic ions (Zn2+) fabricated by modified inverse coprecipitation technique. X-ray calculations show that the average crystallite size (D) and the average lattice constant (a) of CoZn ferrite nanoparticles increase from 32.33 to 52.87 nm and from 8.39 to 8.41Ǻ respectively with increasing non-magnetic Zn2+ ions from 0.00 to 0.55. Morphological forms and M-O at A and B sites studied by SEM and FT-IR spectroscopy. Measurements of the structural, optical, electrical and magnetic characterization of the CoZn ferrite nanoparticles strongly depend on non-magnetic Zn2+ ions content (y). Non-magnetic ions transform Co ferrite from hard and dielectric nature to soft and semiconductor nature. Values of Coercivity and the remanence decrease as non-magnetic Zn2+ ions increases to the minimum values 955 Oe and 6 emu /g for the sample with Zn = 0.55. Co0.45Zn0.55Fe2O4 is might be suitable for high-frequency applications where it has the smallest value of optical gap, the largest value of resistivity and the lowest value of dielectric loss factor.

Green Synthesis and Characterization of Pullulan Mediated Silver Nanoparticles through Ultraviolet Irradiation

Nanoparticles (NPs) are, frequently, being utilized in multi-dimensional enterprises. Silver nanoparticles (AgNPs) have attracted researchers in the last decade due to their exceptional efficacy at very low volume and stability at higher temperatures. Due to certain limitations of the chemical method of synthesis, AgNPs can be obtained by physical methods including sun rays, microwaves and ultraviolet (UV) radiation. In the current study, the synthesis of pullulan mediated silver nanoparticles (P-AgNPs) was achieved through ultraviolet (UV) irradiation, with a wavelength of 365 nm, for 96 h. P-AgNPs were formed after 24 h of UV-irradiation time and expressed spectra maxima as 415 nm, after 96 h, in UV-vis spectroscopy. The crystallographic structure was “face centered cubic (fcc)” as confirmed by powder X-ray diffraction (PXRD). Furthermore, high resolution transmission electron microscopy (HRTEM) proved that P-AgNPs were covered with a thin layer of pullulan, with a mean crystalline size of 6.02 ± 2.37. The average lattice fringe spacing of nanoparticles was confirmed as 0.235 nm with quasi-spherical characteristics, by selected area electron diffraction (SAED) analysis. These green synthesized P-AgNPs can be utilized efficiently, as an active food and meat preservative, when incorporated into the edible films.

An average structure model of the intermediate phase between sodalite and cancrinite

Powder samples of the intermediate phase between sodalite and cancrinite (INT) have been synthesized hydrothermally. The formation of the INT phase was proved by both PXRD and TGA analysis and its stoichiometric composition was found to be |Na6.95(1)(CO3)0.48(2) (H2O)6.18(6)|[AlSiO4]6. The comparison of the intensity ratios of PXRD data with a SCXRD measurement indicates the formation of a comparable phase with the typical strong stacking disorder. The hexagonal lattice parameters with a=1266.3(2) pm and c=1586(1) pm and the unit cell setting were determined by Pawley fits. The average lattice and the stacking disorder along c axis could be confirmed by the reconstruction of three-dimensional ADT data. The average structure of INT was modeled considering only the combination of naturally existing (zeolitic) cages, restricted by the actual number of layers per unit cell. The possible combinations were further reduced by considering the amount of incorporated species. Through the comparison of simulated electron diffraction pattern to measured data the modeled framework could be confirmed. Using relative positions of the incorporated species in the natural cages as well as electron densities calculated by using only the framework of INT the positions of these species could be described.

Average and local strain fields in nanocrystals

This article presents a rigorous and self-consistent comparison of lattice distortion and deformation fields existing in energy-optimized pseudo-spherical gold nanoparticles obtained from real-space and powder diffraction strain analysis techniques. The changes in atomic positions resulting from energy optimization (relaxation) of ideally perfect gold nanoparticles were obtained using molecular dynamics modeling. The relaxed atomic coordinates were then used to compute the displacement, rotation and strain components in all unit cells within the energy-optimized (relaxed) particles. It was seen that all of these terms were distributed heterogeneously along the radial and tangential directions within the nanospheroids. The heterogeneity was largest in the first few atomic shells adjacent to the nanoparticle surface, where the continuity of crystal lattice vectors originating from the interior layers was broken because of local lattice rotations. These layers also exhibited maximum shear and normal strains. These (real-space) strain values were then compared with the average lattice strains obtained by refining the computed diffraction patterns of such particles. The results show that (i) relying solely on full-pattern refinement techniques for lattice strain analysis might lead to erroneous conclusions about the dimensionality and symmetry of deformation within relaxed nanoparticles; (ii) the lattice strains within such relaxed particles should be considered `eigenstrains' (`inherent strains') as defined by Mura [Micromechanics of Defects in Solids, (1991), 2nd ed., Springer]; and (iii) the stress/strain state within relaxed nanoparticles cannot be analyzed rigorously using the constitutive equations of linear elasticity.

Substrate Temperature Effect on the Structural and Optical Properties of Znse Thin Films

Zinc selenide (ZnSe) thin films were deposited on to chemically and ultrasonically cleaned glass substrates at different substrate temperatures from room temperature to 200°C keeping the thickness fixed at 300 nm by using thermal evaporation method in vacuum. The structural properties of the films were ascertained by X-ray diffraction (XRD) method utilizing a diffractometer. The optical properties were measured in the photon wavelength ranging between 300 and 2500 nm by using a UV-VIS-NIR spectrophotometer. The XRD patterns reveal that the films were polycrystalline in nature exhibiting f.c.c zincblende structure with average lattice parameter, a = 5.6873Å. The grain size, strain and dislocation densities of the films have bee calculated. The optical transmittance and reflectance were utilized to compute the absorption coefficient, band gap energy and refractive index of the films. The band gap energy of the films was extracted from the absorption spectra. The direct band gap energy of the films slightly increases with substrate temperature.DOI: http://dx.doi.org/10.3329/jbas.v36i2.12969Journal of Bangladesh Academy of Sciences, Vol. 36, No. 2, 233-240, 2012

Tracking the In-Grain Orientation Spreads in Hot-Deformed Polycrystalline Aluminium: Experiment and Finite Element Simulation

The development of orientation spreads within individual grains of a polycrystal submitted to large deformations is analysed by both experiment and simulation. In the experiment, 176 grains on an internal surface of a split sample were followed by detailed EBSD measurements, at successive strains up to 1.2. In parallel, a high-resolution finite element simulation has been carried out on the same polycrystal configuration. For both experiment and simulation, hundreds to thousands of orientation values were obtained in each grain. Most grains showed a “unimodal” rotation, composed of an average rotation and an orientation spread. The experimental and simulated orientation spreads were compared through different statistical metrics. The average lattice disorientations are found to increase rapidly at the beginning of the deformation and to saturate at high strains. The orientation spreads are also analysed in terms of anisotropy along the sample axes. It is shown that the orientation spreads are aligned preferably along TD at the beginning of the deformation, then tend to move to RD in the experiment, and RD or ND in the simulation.