ALBERT

Notes: We have developed simple analytical methods to estimate the nonequilibrium thermal effects of pulsed nanosecond lasers on carbon-implanted copper substrates. This analytical method eliminates the use of detailed numerical solutions of the one-dimensional heat flow equation with nonlinear moving boundary conditions. The effect of laser variables, especially energy density and pulse duration, on the maximum melt depths, solidification velocities, and maximum surface temperatures have been determined. Comparison between the analytical and detailed computer solutions of heat flow equations have also been performed to determine the validity of these analytical solutions.

Notes: Europium-doped yttrium oxide (Eu:Y2O3) luminescent thin films have been grown in situ on single crystal (0001) sapphire substrates using a pulsed laser deposition technique. The films grown under different deposition conditions have been characterized using microstructural and luminescent measurements. The photoluminescence (PL) and cathodoluminescence (CL) brightness data obtained from the Eu:Y2O3 films grown under optimized conditions have indicated that sapphire is a promising substrate for the growth of high quality Eu:Y2O3 thin film red phosphor. The success in the fabrication of Eu:Y2O3 films with high PL and CL brightness is attributed to favorable optical properties (low absorption of and low refractive index for red light) of the substrate material and improved growth of grains with unidirectional orientation on (0001) sapphire substrates. © 1998 American Institute of Physics.

Notes: During pulsed laser deposition of thin films, a significant amount of energy is coupled to the laser-generated plasma. The fraction of the energy absorbed in the plasma is a function of the incident laser wavelength, time-dependent plasma dimensions, and electron density. Due to time-varying parameters, a quantitative analysis of the plasma absorption is difficult. A method has been developed to estimate plasma absorption during deposition of thin films. In this model, the time-dependent plasma dimension is replaced by the time-dependent ablation depth, which can be easily determined. Using simulated absorption coefficient values, the ablation depth of the target as a function of energy density and laser wavelengths has been computed. These calculations have been compared with experimental results obtained from excimer laser deposition of high-Tc superconductors. Correlations between plasma absorption coefficient and incident laser photon energy have also been determined.

Notes: In this article we report our studies on the microstructure, magnetoresistance (MR) behavior, and magnetic properties of the La1−x−yCaxMnO3 system in thin-film form. By varying the values of x and y in La1−x−yCaxMnO3, we have synthesized an external- (x=0.3, y=0), an internal- (x=0, y=0.3), and a mixed-doped (x=0.2, y=0.1) system with the same Mn3+/Mn4+ ratio. Thin films of these materials have been grown in situ on (100) LaAlO3 substrates using a pulsed-laser-deposition technique. Atomic force microscopy, x-ray diffraction and high-resolution transmission electron microscopy measurements carried out on these films have shown that the films are smooth, highly crystalline, and epitaxial on the (100) LaAlO3 substrates. Electrical resistance and magnetoresistance have been measured in the 10–300 K range in magnetic fields up to 5 T using a superconducting quantum interference device magnetometer. The MR ratios (calculated using the expression, [R0−RH]/RH, where R0 and RH are resistances in zero and applied fields) of the La0.7Ca0.3MnO3 (x=0.3, y=0), La0.7MnO3 (x=0, y=0.3), and La0.7Ca0.2MnO3 (x=0.2, y=0.1) films are found to be 825%, 700%, and 750% at 200, 240, and 220 K, respectively. The MR ratios of these films, calculated using the expression, [R0−RH]/RH, are 91%, 87%, and 88%, respectively, at the same temperatures. The variation in the insulator-to-metal transition and the MR ratio is attributed to internal chemical pressure and vacancy localization effects. Below Tc/2 (Tc is paramagnetic-to-ferromagnetic transition temperature), resistance increases as T2 for La0.7Ca0.3MnO3 and La0.7Ca0.2MnO3 while it increases as T5/2 for La0.7MnO3. The T2 and T5/2 dependence of resistance suggests that the transport is predominantly governed by an electron–electron scattering and a combination of electron–electron, electron–phonon, and electron–magnon scattering, respectively. High-temperature resistance has been observed to be consistent with small polaron hopping conductivity for all three systems. Magnetization measurements carried out on the films show that the films have reasonably square hysteresis loops with sharp Tc's. Below Tc/2, the magnetization decreases as T2 for La0.7Ca0.2MnO3 and La0.7MnO3, suggesting single-particle excitations in them, while it decreases as T3/2 for La0.7Ca0.3MnO3, representing collective oscillations in this system. © 1999 American Institute of Physics.

Notes: Superlattice structures consisting of La0.7MnO3−δ (LMO) and Pr0.65Ba0.05Ca0.3MnO3−δ (PBCMO) systems, in which the thickness of La0.7MnO3−δ is fixed and that of Pr0.65Ba0.05Ca0.3MnO3−δ varied from 1 to 8 unit cells, have been grown in situ on (100) LaAlO3 substrates using a pulsed-laser deposition technique. Microstructural characterization carried out on these films shows the presence of characteristic intense satellite peaks, indicating the chemical modulation of the superlattice structure. The insulator-to-metal transition and the magnetoresistance (MR) ratio are found to vary with the number of unit cells. The samples with 1, 2, 5, and 8 unit cells of Pr0.65Ba0.05Ca0.3MnO3−δ show transition temperatures of 240, 230, 150, and 160 K and MR ratios of 540%, 592%, 3150%, and 2875%, respectively. We have observed an enhancement of magnetoresistance ratios in the case of superlattices with a thickness of PBCMO greater than 5 unit cells, which may be attributed to a ferromagnetic biasing provided by the LMO layers acting as a ferromagnetic film below its transition temperature. © 2001 American Institute of Physics.

Notes: In this letter, we report enhanced electrical performance of high-dielectric-constant barium strontium titanate (BST) thin films grown by an in situ ultraviolet (UV)-assisted pulsed-laser deposition (UVPLD) technique. In comparison with conventional pulsed-laser deposition (PLD) BST (i.e., films grown under similar conditions but without UV illumination) and films grown by other techniques, the UVPLD-grown films exhibited improved structural and electrical properties. The dielectric constant of 40-nm-thick films deposited at 650 °C by PLD and UVPLD were determined to be 172 and 281, respectively. The density of interface states at the flat-band voltage was found to be approximately 5.6×1011 eV−1 cm−2 for the UVPLD-grown BST films, which was almost an order of magnitude lower than that obtained for conventional PLD films. The leakage current density of the UVPLD-grown films was approximately 4×10−8 A/cm2 at 100 kV/cm, which was nearly 1.5 times lower than that obtained from the PLD deposited films. The equivalent silicon dioxide thickness of the best BST films grown was found to be around 10 Å. © 1999 American Institute of Physics.

Notes: A method for (111) oriented diamond film synthesis has been developed using controlled seeding of micron-sized diamond particles by electrophoresis. Different sizes of diamond powders (0.25 and 5μm) were electrophoretically seeded on silicon substrates using diamond suspensions in organic solvents (acetone, methanol, and ethanol). The seeded samples were then consolidated by the hot filament chemical vapor deposition process. Diamond suspension in acetone was found to be the most suitable for obtaining uniform diamond seeding in electrophoresis. A preferred (111) orientation was obtained for a monolayer of 5 μm seeds. However, when smaller seeds (〈1 μm) were used, randomly oriented films were obtained. The surface morphology, crystal orientation, and quality of diamond films were investigated using scanning electron microscopy, x-ray diffractometry, and Raman spectroscopy. © 1997 American Institute of Physics.

Notes: Europium doped yttrium oxide (Eu:Y2O3) phosphor thin films were grown using a pulsed laser deposition (PLD) technique at varying growth conditions. The structural characterization carried out on a series of Eu:Y2O3 films grown on (100) silicon at substrate temperatures in the range of 250–600 °C and oxygen pressure in the range of 10−5 Torr to 200 mTorr indicated that films were preferentially (111) oriented. Measurements of photoluminescence and cathodoluminescence properties of laser deposited Eu:Y2O3 thin films and powder used for laser target showed that the best in situ grown films were ∼10%–22% as bright as Eu:Y2O3 powder. A postdeposition annealing treatment of Eu:Y2O3 films led to further improvements in their brightness (up to ∼70% with respect to Eu:Y2O3 powder), with cluster sizes of 〈400 nm. © 1997 American Institute of Physics.

Notes: The surfaces of insulating alumina particles have been coated with high-temperature superconducting YBa2Cu3O7−x and colossal magnetoresistive Pr0.65Ba0.05Ca0.3MnO3−x films. These coatings on particulate surfaces have been realized using a technique which is based on laser-assisted generation of a homogeneous flux of ablated materials in front of a fluidized bed of host particles. The coated particulates have been characterized using scanning electron microscopy, energy dispersive x-ray analysis, Auger electron spectroscopy, and superconducting quantum interference device magnetometer. © 1998 American Institute of Physics.

Notes: The growth of continuous adherent diamond thin films on optically transparent substrates is important for the development of corrosion and erosion resistant infrared windows for many applications. Until now, the growth of adherent diamond films on optically transparent substrates like sapphire has been unsuccessful due to the large thermal mismatch between the film and the substrate and the absence of an interfacial carbide "glue'' layer. By employing a low temperature (500–550 °C), low pressure (∼1 Torr) electron–cyclotron–resonance chemical-vapor-deposition process, and utilizing a dispersed–particulate diamond suspension for nucleation, adherent diamond thin films have been fabricated on sapphire substrates. Raman spectroscopy showed that the diamond peak was shifted approximately 6 cm−1 above its equilibrium position, suggesting the presence of very large compressive stresses (∼3.2 GPa) in the film. © 1996 American Institute of Physics.