Rita John

Synthesis and Characterization of Rare Earth Ion Doped Nano ZnO

Zinc oxide (ZnO) doped with erbium at different concentrations was synthesized by solid-state reaction method and characterized by X-ray diffraction (XRD), scanning electron microscopic (SEM), UV-absorption spectroscopy, photoluminescence (PL) study and vibrating sample magnetometer. The XRD studies exhibit the presence of wurtzite crystal structure similar to the parent compound ZnO in 1% Er3+ doped ZnO, suggesting that doped Er3+ ions sit at the regular Zn2+ sites. However, same studies spread over the samples with Er3+ content>1% reveals the occurrence of secondary phase. SEM images of 1% Er3+ doped ZnO show the polycrystalline nature of the synthesized sample. UV-visible absorption spectrum of Er3+ doped ZnO nanocrystals shows a strong absorption peak at 388 nm due to ZnO band to band transition. The PL study exhibits emission in the visible region, due to excitonic as well as defect related transitions. The magnetization-field curve of Er3+ doped ZnO nanocrystals showed ferromagnetic property at room-temperature.

Double-layer fabrication of cubic-manganites/hexagonal-ZnO on various substrates by ion beam sputtering, and variable electrical property

Hetero double-layers of LaBaMnO3 (LBMO)/ZnO were fabricated by ion beam sputtering on substrates of MgO, sapphire (SP), LaAlO3 (LAO), and SrTiO3 (STO). All the surfaces of substrates, ZnO and LBMO have step-terrace morphology. The p-LBMO/n-ZnO/SP shows junction rectification at different temperatures. The junction resistance follows from colossal magnetoresistance (CMR) of LBMO based on DEC model. The different LBMO/ZnO junctions on the different substrates show different junction behaviors at room temperatures. LBMO/ZnO/STO has the largest rectification factor of 210. After running measurement currents, LBMO/ZnO/STO shows current?voltage (I?V) switchings. LBMO/ZnO/MgO shows very clear switching and large hysteresis between upward and downward voltage sweeps. These are interpreted by CMR and DEC model, and phase separation. The switching is caused by disconnection of percolation path consisting of ferromagnetic metallic grains. The higher resistant state cannot be quickly transformed back to the lower resistant state during the downward sweep.

Evolution of I-V Characteristics and Photo Effects of Heterojunction LBMO/ZnO Prepared by IBS

The hetero p-n junctions of LBMO/ZnO were fabricated by ion beam sputtering. The sample shows clear temperature-dependent rectifying current (I)-voltage (V) characteristics, and junction resistance vs temperature curve is reflected by the CMR nature based on DEC model. The sample shows two-step switching, then the I-V is composed of very-low-resistance (VLR), low-resistance (LR) and high-resistance (HR) regions. The whole I-V behavior is changed by measurement running current. The switching is caused by the spot current, and the original VLR is restored when the current is reduced. The mechanism of switching is proposed in terms of the percolation paths composed of metallic FM-grains. Photo illumination effect on the I-V was investigated. The currents are increased in VLR and HR regions by the illumination. Two origins are possible, electronic process due to hole injection, and phase process. The percolation path might be reinforced by the light.

Influence of structural parameters to engineer the band gaps in ternary pnictide semiconductors - : Theory as a tool

The band gap anomaly exhibited by ABC2 : A = Cd; B = Si,Ge,Sn; C = P,As pnictides with respect to their binary analogs GaP, Ga0.5In0.5P, InP, GaAs, Ga0.5In0.5As, InAs is studied using Tight Binding Linear Muffin Tin Orbital (TBLMTO) method as an investigating theoretical tool. The influence of the structural parameters, η and u are analyzed to enable one to tune energy gap to make tailor made compounds.

Tuning of Energy Band Gaps in Ternary Semiconductors

The first principle investigations on electronic structure of ABC2 (A = Cd; B = Si, Ge, Sn; C= P, As) pnictides using the Tight Binding Linear Muffin Tin Orbital (TB-LMTO) method within the Atomic Sphere Approximation (ASA) is reported. Variation of Eg with pressure reveals the direct and pseudodirect natures of these compounds. CdSiP2 shows a pseudo direct and CdGeP2, CdSnP2, CdSiAs2, CdGeAs2 and CdSnAs2 show direct band gap natures. Semiconductor to metal transition at high pressures is observed. Metallisation volumes (V/Vo) m and pressures (Pm), bulk modulus (Bo) and its pressure derivative (Bo 1) are reported. Correlation connecting Bo and the unit cell volume (Vo) is established.

Tailoring of Morphology and Optical Properties of Bishydrazone-Capped ZnSe Nanorods

Hydrazone derivatives containing heterocyclic moieties have interesting ligational features. Various heterocyclic base ligands have been gradually used to synthesize nanomaterials; however, adapting task-specific ligand systems to guide the synthesis path towards desirable nanostructures and morphologies is rare. In this article, bishydrazone was used as a ligand to purposely modify the morphological structure of the zinc selenide nanostructures via wet chemical reaction method at room temperature. The as-prepared ZnSe nanorods are relatively uniform with an average diameter of ~100 nm at the core and top diameter of 8–10 nm. UV-Vis spectrum of the products displayed absorption maxima at 390 nm. Therefore, the obtained ZnSe nanorods may have promising applications in blue emitters, catalysts, and gas sensors. The presence of bishydrazone in the ZnSe nanorods is confirmed by the Fourier transform infrared spectrum. It would be expected that bishydrazone could be used to prepare other nanoscale metal selenides with special morphologies and improved properties on a large scale.

Micropatterned Arrays of ZnSe Nanospheres as Antireflection Coatings

In this work, we demonstrate deposition of micro-arrays of ZnSe nanospheres on Si (100) substrate using simple thermal evaporation on a self-assembled sacrificial polystyrene (PS) mask. The results have been compared with the deposition on unpatterned gold catalyst- and SU-8 (negative photoresist)-coated Si substrates. The deposited ZnSe nanospheres properties were characterised by X-ray diffraction, atomic force microscopy (AFM), scanning electron microscopy (SEM), Raman, photoluminescence, and UV-vis spectroscopies. The X-ray diffraction patterns of the films exhibited reflection corresponding to the cubic (111) phase and showed polycrystallinity with a cubic (zinc blende) structure. The SEM and AFM images indicated that the particles were well dispersed and spherical in shape. The micro-arrays of ZnSe nanospheres on a self-assembled sacrificial PS mask showed excellent structural, morphological, and optical properties and demonstrated its usage in photovoltaic devices as an improved superior antireflective coating. The reflectance of the micro-arrays of ZnSe nanospheres on a self-assembled sacrificial PS mask decreased to nearly half of that of the ZnSe nanospheres fabricated on Au- and SU-8-coated Si substrates in the range of 300–800 nm. Due to the well aligned and patterned surfaces, these noble textured ZnSe nanospheres may be suitable for low cost, large area photovoltaic devices and other antireflection applications.

First principle calculations on the effect of addition of X (Co, Rh, Ir) on TiPd

I two-dimensional (2D) electron system, electrons can move in two dimensions but are confined in the third, pretty much like billiard balls. Low-disorder 2D electron systems are currently the focus of a great deal of attention, particularly for low electron densities, where the interactions between them dominate their behavior, theoretical methods are still poorly developed, and new experimental results are of great interest. Consistent with Fermi liquid theory at high electron densities, these 2D systems are expected to freeze into a Wigner crystal in the dilute, strongly-interacting limit. In the intermediate regime, where interactions are not yet strong enough to cause crystallization, the electrons behave like a strongly-correlated liquid. Our recent data show that the low-temperature (fractions of 1 kelvin) properties of this strongly correlated electron liquid are unusual and very interesting. For example, the spin susceptibility grows and seemingly diverges as the electrons become more dilute, which indicates transition to a new state of matter (Wigner crystal or a precursor). Moreover, I will report the observation of strongly nonlinear voltage-current characteristics that display two distinct thresholds and a dramatic increase in noise at the breakdown of the insulating state. With the roles of voltage and current interchanged, this behavior is strikingly like that observed for the depinning of the vortex lattice in Type-II superconductors. Adapting the model used for vortexes to the case of an electron solid yields good agreement with our experimental results. This strongly favors the formation of the electron solid in the insulating phase as the double threshold behavior cannot be described within existing alternative models.W use the SU(3) Schwingers boson theory to study the spin transport properties of two-dimensional anisotropic frustrated Heisenberg model at T=0. We have investigated the behavior of the spin conductivity in diferent frustrated spin systems that presents exchange interactions J1, J2 and J3. We have studied the spin transport in the Bose-Einstein condensation regime where the bosons tz are condensed. Our results show an influence of the quantum phase transition point on the spin conductivity behavior. We also have made a diagrammatic expansion for the green-function and do not have obtained any significative change on the results.N methods for differential equations are one of the notable glories of contemporary science. Coupled with much algorithmic ingenuity, numerical methods are widely applied across science and engineering fields. One of the most important numerical methods is the numerical integration which has been the focus of intense research since its development in 1915 by David Gibb. In this abstract, we present the study of numerical integrator based on Fer expansion in the integration of the time-dependent Schrodinger equation (TDSE) which is a central problem to nuclear magnetic resonance (NMR) in general and solid-state NMR in particular. Numerical simulations of NMR experiments are often required for the development of new techniques and for the extraction of structural and dynamic information from the spectra. The development and design of various pulse sequences and understanding of different NMR experiments are based on the form of effective Hamiltonian or effective propagator that satisfies the TDSE which is difficult to solve unless the Hamiltonian is time independent or commutes with itself at two different times. The evolution operator allows obtaining the density matrix of the spin system that has evolved from the equilibrium density matrix due to the application of RF irradiation. The signal intensity depends on the final density matrix of the spin system. For example, if the numerical model is implemented with the approximate solutions of Fer or Magnus, the results of the simulation will show incorrect or undesirable effects of finite pulses and ring-down mainly when dealing with quadrupolar nuclei (I>1/2). In this study we proposed an efficient numerical integrator based on Fer expansion for solving the TDSE to obtain an effective propagator that continually improves the detected NMR signal. We will also compare the performance of the numerical integrator based on Fer expansion with respect to other Lie-group solvers, namely Magnus and Cayley methods.