Microstructural stability and nanoindentation of an electrodeposited nanocrystalline Ni-1.5wt.%P alloy

Microstructural stability of nanocrystalline Ni-1.5wt.%P alloy with an initial grain size of 3 nm processed by pulsed electrodeposition was studied using differential scanning calorimetry (DSC) and annealing. Microstructural characterization suggests that the observed exothermic peak during heating in DSC is related to both concurrent grain growth and Ni3P formation. Nanoindentation on samples with grain sizes from 3 to 50 nm revealed a breakdown in Hall-Petch strengthening in nano Ni-P alloy at grain sizes <= 10 nm, consistent with some previous observations. It is concluded that there is a grain boundary weakening regime for grain sizes < 10 nm, based on analysis which show that the data cannot be rationalized in terms of microstrain relaxation, variation in elastic modulus, texture evolution and duplex structure formation.

Enhanced magnetoresistance in as?deposited oxygen?deficient La0.6Pb0.4MnO3-y thin films

The La0.6Pb0.4MnO3(LPMO) thin films were in situ deposited at different oxygen partial pressure and at a substrate temperature of 630 degrees C by pulsed laser deposition. The films grown at lower oxygen partial pressures showed an increase in lattice parameter and resistivity and a decrease in the insulator-metal transition temperature as compared to the stoichiometric LPMO thin film grown at 400 mTorr. Further, these oxygen-deficient thin films showed over 70% giant magnetoresistance (GMR) near the insulator-metal transition temperature against the 40% GMR in the case of stoichiometric thin films. (C) 1995 American Institute of Physics.

Ferroelectric properties of Bi2VO5.5 thin films on LaAlO3 and SiO2/Si substrates with LaNiO3 base electrode

Ferroelectric bismuth vanadate Bi2VO5.5 (BVO) thin films have been grown on LaAlO3 (LAO) and SiO2/Si substrates with LaNiO3 (LNO) base electrodes by the pulsed laser deposition technique. The effect of substrate temperature on the ferroelectric properties of BVO thin films, has been studied by depositing the thin films at different temperatures. The BVO thin films grown on LNO/LAO were textured whereas the thin films grown on LNO/SiO2/Si were polycrystalline. The BVO thin films grown at 450?°C exhibited good ferroelectric properties indicating that LNO acts as a good electrode material. The remanent polarization Pr and coercive field Ec obtained for the BVO thin films grown at 450?°C on LNO/LAO and LNO/SiO2/Si were 2.5 ?C/cm2, 37 kV/cm and 4.6?C/cm2, 93 kV/cm, respectively. © 1995 American Institute of Physics.

Flow induced by an asymmetrically placed disk rotating coaxially inside a cylindrical casing

In this paper, the flow due to a rotating disk non-symmetrically placed with respect to the height of the enclosing stationary cylinder is analyzed numerically. The full Navier-Stokes equations expressed in terms of stream function and vorticity are solved by successive over-relaxation for different disk radii, its distance from the bottom casing and rotational Reynolds numbers. It is observed that the flow pattern is strongly influenced by the size and the position of the disk. When the disk is very close to the top casing and small in radius, there are two regions of different scales and the vortices in the region of small scale are trapped between the disk and the top casing. Further, the variation of the moment coefficient is determined for different positions and sizes of the rotating disk. The calculations shows that the frictional torque increases rapidly, when the disk approaches the top casing. This finding is of importance for the design of vertical rotating disk reactors applied in chemical vapor deposition.

LaNiO3: a promising material for contact with YBa2 Cu3O7-x thin films

Epitaxial LaNiO3 metallic oxide thin films have been grown on c-axis oriented YBa2Cu3O7-delta thin films on LaAlO3 substrates by pulsed laser deposition technique and the interface formed between the two films has been examined by measuring the contact conductance of the same. The specific contact conductance of the interface measured using a modified four probe method was found to be 1.4 to 6 x 10(4) ohm(-1) cm(-2) at 77 K, There are indications that contact conductance can be brought closer to that obtained for noble metal-YBCO interface.

Nonaxisymmetric convection in stationary Gas Tungsten Arc Weld Pools

Observations of surface flow patterns of steel and aluminum GTAW pools have been made using a pulsed laser visualization system. The weld pool convection is found to be three-dimensional with the azimuthal circulation depending on the location of the clamp with respect to the torch. Oscillation of steel pools and undulating motion in aluminum weld pools are also observed even with steady process parameters. Current axisymmetric numerical models are unable to explain such phenomena. A three-dimensional computational study is carried out in this study to explain the rotational flow in aluminum weld pools.

Enhancement of uniaxial magnetic anisotropy in Fe thin films grown on GaAs(001) with an MgO underlayer

The understanding and control of anisotropy in Fe films grown on cubic systems such as GaAs and MgO has been of interest from the point of view of applications in devices. We report magnetic anisotropy studies on Fe/GaAs(001) and Fe/MgO/GaAs(001) prepared by pulsed laser deposition. In Fe/GaAs(001), magneto optical Kerr effect (MOKE) measurements revealed a dominant uniaxial anisotropy for Fe thickness less than 20 monolayers (ML) and this was confirmed by ferromagnetic resonance (FMR) studies. Multiple steps in the hysteresis loops were observed for Fe films of thickness 20 and 25 ML. Whereas, in Fe/MgO/GaAs(001), even at 25 ML of Fe, the uniaxial anisotropy remained dominant. The anisotropy constants obtained from FMR spectra have shown that the relative strength of uniaxial anisotropy is higher as compared to the cubic anisotropy constant in the case of Fe/MgO/GaAs(001). (C) 2011 American Institute of Physics. doi:10.1063/1.3556941]

Role of silver doping in oxygen incorporation of oxide thin film

A distinctive characteristic of silver in oxygen incorporation of oxide thin films during pulsed laser ablation has been discovered. Optical emission spectroscopy studies of laser-induced plume of Ag-target indicates the presence of AgO species whose concentration increases with an increase in oxygen partial pressure. The formation of AgO in laser-plume has been found to be very useful for the realization of high temperature superconducting YBa2Cu3O7-delta (YBCO) and giant magnetoresistive La0.7MnO3-delta (LMO) thin films with dramatically superior quality if the target materials contained a small amount of silver. The improvement in the quality of these films is brought about by the supply of atomic oxygen to oxide lattices during their formation. This becomes possible due to the fact that Ag, after it is ablated with other constituent materials in the target, gets moderately oxidized in an oxygen atmosphere and the oxidized species dissociate back into Ag and nascent O at the substrate surface. The nascent oxygen is very highly reactive and is easily assimilated into the lattice of these compounds. (C) 1997 Elsevier Science S.A.

ac transport studies of La-modified antiferroelectric lead zirconate thin films

In recent times antiferroelectric thin-film material compositions have been identified as one of the most significant thin films for development of devices such as high charge storage, charge couplers/decouplers, and high strain microelectromechanical systems. Thus, understanding the dielectric and electrical properties under an ac signal drive in these antiferroelectric thin-film compositions, such as lead zirconate thin films, and the effect of donor doping on them is very necessary. For this purpose, thin films of antiferroelectric lead zirconate and La-modified lead zirconate thin films with mole % concentrations of 0, 3, 5, and 9 have been deposited by pulsed excimer laser ablation. The dielectric and hysteresis properties have confirmed that with a gradual increase of the La content, the room-temperature antiferroelectric lead zirconate thin films can be modified into ferroelectric and paraelectric phases. ac electrical studies revealed that the polaronic related hopping conduction is responsible for the charge transport phenomenon in these films. With a La content of less than or equal to3 mole % in pure lead zirconate, the conductivity of the films has been reduced and followed by an increase of its conductivity for a greater than or equal to3% addition of La to lead zirconate thin films. The polaronic activation energies are also found to follow a similar trend as that of the conductivity.

Synthesis and structure of La14V6CuO36.5: a transparent Cu(I) vanadate containing [OCuO](3-) sticks

The title compound, La14V6CuO36.5, was prepared from a stoichiometric mixture of La2O3,V2O5, and CuO at 1050-1080 degreesC. The compound forms transparent, pale green crystals and was characterized by wavelength dispersive spectroscopy and single crystal X-ray diffraction. The structure contains isolated VO43- tetrahedra and [OCuO](3-) sticks dispersed in a lanthanum oxide network. Films of La14V6CuO36.5 were grown on R-plane sapphire by using pulsed laser deposition. Rutherford backscattering spectroscopic and X-ray diffraction analyses of the films showed oriented growth of the title phase, a similar to5 eV optical band gap and n-type conductivity. The compound is an example of a transparent copper(I) oxide.

Dielectric Studies of laser ablated Ca doped BaTiO3 thin films

Recently, there has been growing interest in Ca modified BaTiO3 structures due to their larger electro-optic coefficients for their use in optical storage of information over conventional BaTiO3 crystals. Barium Calcium Titanate (BCT) shows promising applications in advanced laser systems, optical interconnects and optical storage devices. BaTiO3 thin films of varied Ca (3 at. % - 15 at. %) doping were deposited using pulsed laser ablation (KrF excimer laser) technique over Pt/Si substrates. The stoichiometric and the compositional analysis were carried out using EDAX and SIMS. The dielectric studies were done at the frequency regime of 40 Hz to 100 kHz at different ambient temperatures from 200 K to 600 K. The BCT thin films exhibited diffuse phase transition, which was of a typical non lead relaxor behavior and had high dielectric constant and low dielectric loss. The phase transition for the different compositions of BCT thin films was near the room temperature, showing a marked departure from the bulk phase transition. The C - V and the hysteresis behavior confirmed the ferroelectric nature below the phase transition and paraelectric at the room temperature.

Epitaxial LaNiO3 thin films: A normal metal barrier for SNS junction

Epitaxial LaNiO3 thin films have been grown on SrTiO3 and several other substrates by pulsed laser deposition. The films are observed to be metallic down to 15 K, and the temperature dependence of resistivity is similar to that of bulk LaNiO3. Epitaxial, c-axis oriented YBa2Cu3O7-x films with good superconducting properties have been grown on the LaNiO3 (100) films. I-V characteristics of the YBa2Cu3O7-x-LaNiO3 junction are linear, indicating ohmic contact between them.

Interface states of laser ablated BaTiO3 and Ba0.9Ca0.1TiO3 thin films in MFS structure determined by DLTS and C – V technique

BaTiO3 and Ba0.9Ca0.1TiO3 thin films were deposited on the p – type Si substrate by pulsed excimer laser ablation technique. The Capacitance – Voltage (C-V) measurement measured at 1 MHz exhibited a clockwise rotating hysteresis loop with a wide memory window for the Metal – Ferroelectric – Semiconductor (MFS) capacitor confirming the ferroelectric nature. The low frequency C – V measurements exhibited the response of the minority carriers in the inversion region while at 1 MHz the C – V is of a high frequency type with minimum capacitance in the inversion region. The interface states of both the MFS structures were calculated from the Castagne – Vaipaille method (High – low frequency C – V curve). Deep Level Transient Spectroscopy (DLTS) was used to analyze the interface traps and capture cross section present in the MFS capacitor. There were distinct peaks present in the DLTS spectrum and these peaks were attributed to the presence of the discrete interface states present at the semiconductor – ferroelectric interface. The distribution of calculated interface states were mapped with the silicon energy band gap for both the undoped and Ca doped BaTiO3 thin films using both the C – V and DLTS method. The interface states of the Ca doped BaTiO3 thin films were found to be higher than the pure BaTiO3 thin films.

MFIS and MFS structures using SrBi2Ta2O9 thin films for the FRAM applications

Recently there is an increasing demand and extensive research on high density memories, in particular to the ferroelectric random access memory composed of 1T/1C (1 transistor/1 capacitor) or 2T/2C. FRAM's exhibit fast random acess in read/write mode, non - volatility and low power for good performance. An integration of the ferroelectric on Si is the key importance and in this regard, there had been various models proposed like MFS, MFIS, MFMIS structure etc., Choosing the proper insulator is very essential for the better performance of the device and to exhibit excellent electrical characteristics. ZrTiO4 is a potential candidate because of its excellent thermal stability and lattice match on the Si substrate. SrBi2Ta2O9 and ZrTiO4 thin films were prepared on p - type Si substrate by pulsed excimer laser ablation technique. Optimization of both ZT and SBT thin films in MFS and MFIS structure had been done based on the annealing, oxygen partial pressures and substrate temperatures to have proper texture of the thin films. The dc leakage current, P - E hysteresis, capacitance - voltage and conductance - voltage measurement were carried out. The effect of the frequency dependence on MFIS structure was observed in the C – V curve. It displays a transition of C - V curve from high frequency to low frequency curve on subjection to varied frequencies. Density of interface states has been calculated using Terman and high - low frequency C - V curve. The effect of memory window in the C - V hysteresis were analysed in terms of film thickness and annealing temperatures. DC conduction mechanism were analysed in terms of poole - frenkel, Schottky and space charge limited conduction separately on MFS, MIS structure.

MFIS and MFS structures using SrBi2Ta2O9 thin films for the FRAM applications

Recently there is an increasing demand and extensive research on high density memories, in particular to the ferroelectric random access memory composed of 1T/1C (1 transistor/1 capacitor) or 2T/2C. FRAM's exhibit fast random acess in read/write mode, non - volatility and low power for good performance. An integration of the ferroelectric on Si is the key importance and in this regard, there had been various models proposed like MFS, MFIS, MFMIS structure etc., Choosing the proper insulator is very essential for the better performance of the device and to exhibit excellent electrical characteristics. ZrTiO4 is a potential candidate because of its excellent thermal stability and lattice match on the Si substrate. SrBi2Ta2O9 and ZrTiO4 thin films were prepared on p - type Si substrate by pulsed excimer laser ablation technique. Optimization of both ZT and SBT thin films in MFS and MFIS structure had been done based on the annealing, oxygen partial pressures and substrate temperatures to have proper texture of the thin films. The dc leakage current, P - E hysteresis, capacitance - voltage and conductance - voltage measurement were carried out. The effect of the frequency dependence on MFIS structure was observed in the C – V curve. It displays a transition of C - V curve from high frequency to low frequency curve on subjection to varied frequencies. Density of interface states has been calculated using Terman and high - low frequency C - V curve. The effect of memory window in the C - V hysteresis were analysed in terms of film thickness and annealing temperatures. DC conduction mechanism were analysed in terms of poole - frenkel, Schottky and space charge limited conduction separately on MFS, MIS structure.