On the mass flow rate from silos with lateral exit holes

The mass flow rate, (m) over dot, associated with the lateral outflow of dry, cohesionless granular material through circular orifices of diameter D made in vertical walls of silos was measured experimentally in order to determine also the influence of the wall thickness of the silo, w. Geometrical arguments, based on the outflow happening, are given in order to have a general correlation for (m) over dot embracing both quantities, D and w. The angle of repose appears to be an important characterization factor in these kinds of flows.

Epitaxial Co metal thin film grown by pulsed laser deposition using oxide target

We report here the growth of epitaxial Co metal thin film on c-plane sapphire by pulsed laser deposition (RD) using Co:ZnO target utilizing the composition inhomogeneity of the corresponding plasma. Two distinct plasma composition regions have been observed using heavily alloyed Co0.6Zn0.4O target. The central and intense region of the plasma grows Co:ZnO film; the extreme tail grows only Co metal with no trace of either ZnO or Co oxide In between the two extremes, mixed phases (Co +Co-oxides +Co:ZnO) were observed. The Co metal thin film grown in this way shows room temperature ferromagnetism with large in plane magnetization similar to 1288 emu cm(-3) and a coerciviLy of similar to 230 Oe with applied field parallel to the film-substrate interface. Carrier density of the film is similar to 10(22) cm(-3). The film is epiLaxial single phase Co metal which is confirmed by both X-ray diffraction and transmission electron microscopy characierizaLions. Planar Hall Effect (PHE) and Magneto Optic Kerr Effect (MOKE) measurements confirm that the film possesses similar attributes of Co metal. The result shows that the epiLaxial Co metal thin film can be grown from its oxides in the PLD. (C) 2014 Elsevier B.V. All rights reserved.

Conductivity noise study of the insulator-metal transition and phase coexistence in epitaxial samarium nickelate thin films

Interaction between the lattice and the orbital degrees of freedom not only makes rare-earth nickelates unusually ``bad metal,'' but also introduces a temperature-driven insulator-metal phase transition. Here we investigate this insulator-metal phase transition in thin films of SmNiO3 using the slow time-dependent fluctuations (noise) in resistivity. The normalized magnitude of noise is found to be extremely large, being nearly eight orders of magnitude higher than thin films of common disordered metallic systems, and indicates electrical conduction via classical percolation in a spatially inhomogeneous medium. The higher-order statistics of the fluctuations indicate a strong non-Gaussian component of noise close to the transition, attributing the inhomogeneity to the coexistence of the metallic and insulating phases. Our experiment offers insight into the impact of lattice-orbital coupling on the microscopic mechanism of electron transport in the rare-earth nickelates.

Application of lateral photovoltage towards contactless light beam induced current measurements and its dependence on the finite beam size

The nature of the signal due to light beam induced current (LBIC) at the remote contacts is verified as a lateral photovoltage for non-uniformly illuminated planar p-n junction devices; simulation and experimental results are presented. The limitations imposed by the ohmic contacts are successfully overcome by the introduction of capacitively coupled remote contacts, which yield similar results without any significant loss in the estimated material and device parameters. It is observed that the LBIC measurements introduce artefacts such as shift in peak position with increasing laser power. Simulation of LBIC signal as a function of characteristic length L-c of photo-generated carriers and for different beam diameters has resulted in the observed peak shifts, thus attributed to the finite size of the beam. Further, the idea of capacitively coupled contacts has been extended to contactless measurements using pressure contacts with an oxidized aluminium electrodes. This technique avoids the contagious sample processing steps, which may introduce unintentional defects and contaminants into the material and devices under observation. Thus, we present here, the remote contact LBIC as a practically non-destructive tool in the evaluation of device parameters and welcome its use during fabrication steps. (C) 2014 AIP Publishing LLC.

Effect of epitaxial strain on phase separation in thin films

In epitaxially grown alloy thin films, spinodal decomposition may be promoted or suppressed depending on the sign of the epitaxial strain. We study this asymmetry by extending Cahn's linear theory of spinodal decomposition to systems with a composition dependent lattice parameter and modulus (represented by Vegard's law coefficients, GRAPHICS] and y, respectively), and an imposed (epitaxial) strain (e). We show analytically (and confirm using simulations) that the asymmetric effect of epitaxial strains arises only in elastically inhomogeneous systems. Specifically, we find good agreement between analytical and simulation results for the wave number GRAPHICS] of the fastest growing composition fluctuation. The asymmetric effect due to epitaxial strain also extends to microstructure formation: our simulations show islands of elastically softer (harder) phase with (without) a favourable imposed strain. We discuss the implications of these results to GeSi thin films on Si and Ge substrates, as well as InGaAs films on GaAs substrates.

Controlling phase separation in La5/8-yPryCa3/8MnO3 (y=0.45) epitaxial thin films by strain disorder

Present study reveals that the length-scale of phase separation in La5/8-yPryCa3/8MnO3 thin films can be controlled by strain disorder invoked during the growth and relaxation process of film. Strain disorder provides an additional degree of freedom to tune colossal magnetoresistance. Magneto-transport measurements following cooling and heating in unequal fields protocol demonstrate that coherent strain stabilizes antiferromagnetic insulating phase, while strain disorder favors ferromagnetic metallic phase. Compared to bulk, antiferromagnetic-insulating phase freezes at lower temperatures in strain disordered films. Raman spectroscopy confirms the coexistence of charge-ordered-insulating and ferromagnetic-metallic phases which are structurally dissimilar and possess P2(1)/m and R-3C like symmetries, respectively. (C) 2015 AIP Publishing LLC.

Investigation on two magnon scattering processes in pulsed laser deposited epitaxial nickel zinc ferrite thin film

Ferromagnetic resonance (FMR) measurements are employed to evaluate the presence of the two magnon scattering contribution in the magnetic relaxation processes of the epitaxial nickel zinc ferrite thin films deposited using pulsed laser deposition (PLD) on the (0 0 1) MgAl2O4 substrate. Furthermore, the reciprocal space mapping reveals the presence of microstructural defects which acts as an origin for the two magnon scattering process in this thin film. The relevance of this scattering process is further discussed for understanding the higher FMR linewidth in the in-plane configuration compared to the out-of-plane configuration. FMR measurements also reveal the presence of competing uniaxial and cubic anisotropy in the studied films.

Effect of lateral substituent and chain length on mesomorphic properties of novel alkoxy benzyloxy benzoates of cyanophenyl rod-shaped compounds

Three novel homologous series of rod-shaped cyanophenyl alkoxy benzoate liquid crystalline compounds with lateral polar fluorine and chlorine substituent were prepared, and chemical structures of novel materials have been characterized by standard spectral technique and elemental analysis. The mesophase characterization was carried out using the combination of polarized optical microscopy and differential scanning calorimetry. All the compounds exhibit wide thermal range of enantiotropic SmA phase.

Investigation on the origin of exchange bias in epitaxial, oriented and polycrystalline Fe3O4 thin films

We observe exchange bias (EB) in a single magnetic film Fe3O4 at temperature T < 200 K. Irrespective of crystallographic orientations of grown Fe3O4; they exhibit similar nature of EB for (100) epitaxial, (111) oriented and polycrystalline Fe3O4 thin films. Growth induced defects such as anti-phase boundaries (APBs) in epitaxial Fe3O4 thin film is known to have an influence on the magnetic interaction. But, it is noticed that according to the common consensus of APBs alone cannot explain the origin of EB. If majority of APBs end up with mainly anti-ferromagnetic interactions across these boundaries together with the internal ordering modification in Fe3O4, then EB can emerge at low temperatures. Hence, we propose the idea of directional anti-ferromagnetic APB induced EB in Fe3O4 triggered by internal ordering for T <= 200 K. Similar arguments are extended to (111) oriented as well as polycrystalline Fe3O4 films where the grain boundaries can impart same consequence as that of APBs. (C) 2015 Author(s).

Enhanced UV detection by non-polar epitaxial GaN films

Nonpolar a-GaN (11-20) epilayers were grown on r-plane (1-102) sapphire substrates using plasma assisted molecular beam epitaxy. High resolution x-ray diffractometer confirmed the orientation of the grown film. Effect of the Ga/N ratio on the morphology and strain of a-GaN epilayers was compared and the best condition was obtained for the nitrogen flow of 1 sccm. Atomic force microscopy was used to analyze the surface morphology while the strain in the film was quantitatively measured using Raman spectroscopy and qualitatively analyzed by reciprocal space mapping technique. UV photo response of a-GaN film was measured after fabricating a metal-semiconductor-metal structure over the film with gold metal. The external quantum efficiency of the photodetectors fabricated in the (0002) polar and (11-20) nonpolar growth directions were compared in terms of responsivity and nonpolar GaN showed the best sensitivity at the cost of comparatively slow response time. (C) 2015 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.

Investigations on the physical origin of lateral photovoltage in PbS-colloidal quantum dot/Si heterojunctions

Restricted area heterojunctions, an array of lead sulfide colloidal quantum dots (PbS-CQDs) and crystalline silicon, are studied with a non-destructive remote contact light beam induced current (RC-LBIC) technique. As well as getting good quality active area images we observed an anomalous unipolar signal response for the PbS-CQD/n-Si devices and a conventionally expected bipolar signal profile for the PbS-CQD/p-Si devices. Interestingly, our simulation results consistently yielded a unipolar and bipolar nature in the signals related to the PbSCQD/n-Si and PbS-CQD/p-Si heterostructures, respectively. In order to explain the physical mechanism involved in the unipolar signal response of the PbS-CQD/n-Si devices, we propose a model based on the band alignment in the heterojunctions, in addition to the distribution of photo-induced excess majority carriers across the junction. Given that the RC-LBIC technique is well suited to this context, the presence of these two distinct mechanisms (the bipolar and unipolar nature of the signals) needs to be considered in order to have a better interpretation of the data in the characterization of an array of homo/heterojunctions.

Stable p-type conductivity in B and N co-doped ZnO epitaxial thin film

We report on the observation of stable p-type conductivity in B and N co-doped epitaxial ZnO thin films grown by pulsed laser deposition. Films grown at higher oxygen partial pressure (similar to 10(-1) Torr) shows p-type conductivity with a carrier concentration of similar to 3 x 10(16) cm(-3). This p-type conductivity is associated with the significant decrease in defect emission peaks due to the vacancy oxygen (V-O) and Schottky type-I native defects compared to films grown at low oxygen partial pressure (similar to 10(-5) Torr). The p-type conductivity is explained with the help of density functional theory (DFT) calculation considering off-stoichiometric BN1+x in the ZnO lattice. (C) 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim