William Perez | UPB - Universidad Pontificia Bolivariana - Medellín (original) (raw)

Papers by William Perez

Research paper thumbnail of Anharmonic interactions in beryllium oxide

Physical Review B, 1996

BeO is an insulator with an unusually high thermal conductivity (92% that of Cu at 25 C) and a hi... more BeO is an insulator with an unusually high thermal conductivity (92% that of Cu at 25 C) and a high Debye temperature (1280 K). We measured its first-order Raman scattering as a function of temperature from 300 down to 30 K. The temperature dependence of the ...

Research paper thumbnail of Ferroelectric properties of laser-ablated Sr1-xAxBi2Ta2O9 thin films (where A=Ba, Ca)

Applied Physics Letters, 2002

Bismuth-layered ferroelectric thin films of Sr1-xAxBi2Ta2O9, with composition x=0 and 0.2, were f... more Bismuth-layered ferroelectric thin films of Sr1-xAxBi2Ta2O9, with composition x=0 and 0.2, were fabricated by using the pulsed-laser deposition technique. Structural characterization of the films by x-ray diffraction and atomic force microscopy, revealed that the films are polycrystalline in nature with average grain size of 180 nm. The films displayed spherical grains with a surface roughness of 12 nm. The ferroelectric

Research paper thumbnail of Self-aligned, buried heterostructure AlInGaAs laser diodes by micro-selective-area epitaxy

Applied Physics Letters, 2004

We describe the growth and characteristics of AlInGaAs, self-aligned buried heterostructure quant... more We describe the growth and characteristics of AlInGaAs, self-aligned buried heterostructure quantum well lasers deposited by micro-selective-area growth. The lateral waveguide is defined by metalorganic vapor-phase epitaxy in narrow stripe openings; and the natural tendency to form smooth, no-growth {111} sidewall planes produces a low-loss, single-mode waveguide. By proper adjustment of the growth conditions after the waveguide formation, the waveguide

Research paper thumbnail of Phonons and magnetic excitation correlations in weak ferromagnetic YCrO3

Journal of Applied Physics, 2014

Here, we report the temperature dependent Raman spectroscopic studies on orthorhombically distort... more Here, we report the temperature dependent Raman spectroscopic studies on orthorhombically distorted perovskite YCrO 3 over a temperature range of 20-300 K. Temperature dependence of DC-magnetization measurements under field cooled and zero field cooled protocols confirmed a N eel transition at T N $ 142 K. Magnetization isotherms recorded at 125 K show a clear loop opening without any magnetization saturation up to 20 kOe, indicating a coexistence of antiferromagnetic (AFM) and weak ferromagnetic (WFM) phases. Estimation of exchange constants using mean-field approximation further confirm the presence of a complex magnetic phase below T N . Temperature evolution of Raman line-shape parameters of the selected modes (associated with the octahedral rotation and A(Y)-shift in the unit-cell) reveal an anomalous phonon shift near T N . An additional phonon anomaly was identified at T * $ 60 K, which could possibly be attributed to the change in the spin dynamics. Moreover, the positive and negative shifts in Raman frequencies between T N and T * suggest competing WFM and AFM interactions. A close match between the phonon frequency of B 3g (3)-octahedral rotation mode with the square of sublattice magnetization between T N and T * is indicative of the presence of spin-phonon coupling in multiferroic YCrO 3 . V C 2014 AIP Publishing LLC. [http://dx.

Research paper thumbnail of Pressure effect on electronic properties of Sc 0.5 In 0.5 N compound

physica status solidi (b), 2009

Research paper thumbnail of Mechanical Measurements of Multilayer Thin Films Obtained by a PAPVD System

Microscopy and Microanalysis, 2005

The need of techniques for determining the mechanical properties of thin films, e.g. hardness coa... more The need of techniques for determining the mechanical properties of thin films, e.g. hardness coatings on ion beam treated surfaces has prompted a study of the microindentation hardness technique. The present interest is driven to a good understanding of the adhesion, friction, wear, and indentation processes. In most of the solid-solid interfaces of technological relevance, it occurs contact in many asperities, and this is why the study of fundamental properties of micro-mechanic and tribology of surfaces and interfaces is very important. The recent developments of different microscopic techniques based on tips and force surface devices (i.e. AFM, FM, LFM) allowed investigations of interfacial problems with high resolution and have led to the nanoscale regime the mechanical properties study for a wide spectrum of materials. In this work a method for Young's modulus determination of hard coatings multilayers of TiN/ZrN is evaluated. This method is based on AFM and spectroscopy-force modes [1-2].

Research paper thumbnail of Pressure effects on the electronic and magnetic properties of GaxV1−xN compounds: Ab-initio study

Materials Science and Engineering: B, 2009

We report an ab-initio study of the pressure effects on the electronic and the magnetic propertie... more We report an ab-initio study of the pressure effects on the electronic and the magnetic properties of Ga x V 1−x N compounds (x = 0.25, 0.50 and 0.75) in wurtzite-derived structures. We use the full-potential linearized augmented plane wave plus local orbitals method (LAPW + lo) within of the spin density functional theory framework. The lattice constant is found to vary linearly with Ga-concentration. The magnetic moment changes for a critical pressure. At x = 0.75, a rather abrupt onset of the magnetic moment from 0 to 2 B at P cr ∼22.8 GPa is observed. For x = 0.25 and 0.50 Ga concentrations, the magnetic moment increases gradually when the pressure decreases toward the equilibrium value. We study the transition pressure dependence to a ferromagnetic phase near the onset of magnetic moment for each Ga x V 1−x N compounds. The calculation of the density of states with Ga concentration is carried out considering two spin polarizations. The results reveal that for x = 0.75 the compound behaves as a conductor for the spin-up polarization and that the density of states for spin-down polarization is zero at the Fermi level. At this concentration the compound presents a half metallic behavior; therefore this material could be potentially useful as spin injector. At high pressures P > P cr the compounds exhibit a metallic behavior.

Research paper thumbnail of BDNF: A missing link between sympathetic dysfunction and inflammatory disease?

Journal of Neuroimmunology, 2006

Nerve growth factor (NGF) plays a role in sympathetic neuron integrity and survival. Brain-derive... more Nerve growth factor (NGF) plays a role in sympathetic neuron integrity and survival. Brain-derived neurotrophic factor (BDNF) also has trophic effects on sympathetic neurons. We report here the serendipitous finding that co-treatment of hippocampus with BDNF and the NGF antagonist TrkA-Fc leads to perivascular inflammation and marked vasoconstriction. This effect is not observed with either reagent alone or in combination with other control proteins. Because NGF supports sympathetic neuron health, we tested the hypothesis that BDNF combined with sympathetic compromise caused this effect. Superior cervical ganglia were removed bilaterally with concurrent BDNF infusion into hippocampus. Perivascular inflammation was observed at 3 days, but not 12 days post treatment, when sympathetic terminals had receded, suggesting that the presence of these terminals was necessary for inflammation. Since sympathetic dysfunction may lead to compensatory overactivity of norepinephrine (NE) signaling, we co-infused BDNF with NE in the hippocampus and observed perivascular inflammation. In humans, sympathetic overactivity has been reported in a variety of vascular diseases. Some of these diseases, e.g. primary Raynaud's, are not accompanied by serious inflammatory disease whereas others, such as scleroderma and systemic lupus, are. We speculate that BDNF may contribute to the transformation of sympathetic dysfunction to inflammatory disease. D

Research paper thumbnail of Micro-Raman and infrared reflectivity spectra of YBa2Cu3O7−δ deposited on LaAlO3 and stainless steel/inconel substrates

Journal of Applied Physics, 1995

Abstract The motivation for this article has been to try to understand the relative phenomenologi... more Abstract The motivation for this article has been to try to understand the relative phenomenological differences between the behavior of the films of the high‐temperature superconductors like YBa 2 Cu 3 O 7-δ deposited on (a) relatively insulating substrates ( ...

Research paper thumbnail of In-composition effect on band gap width of Sc1−xInxN alloys

Journal of Alloys and Compounds, 2009

We report first-principles calculations to analyze the In-composition effect on band gap width of... more We report first-principles calculations to analyze the In-composition effect on band gap width of Sc 1−x In x N alloys in wurtzite structure for the compositions x = 0, 0.25, 0.5, 0.75, 1. The calculations were performed in the framework of the density functional theory (DFT) using the full potentiallinearized augmented plane-wave (FP-LAPW) method as implemented in the WIEN2k code. We used both Perdew-Burke-Ernzerhof (PBE) and Engel-Vosko (EV) functional of generalized gradient approximation (GGA) for the exchange-correlation potential. First, the lattice parameters with PBE functional were optimized. Subsequently, using PBE and EV functional, the band structure at equilibrium volume for each In-concentration was calculated. The gap bowing in wurtzite structure was obtained and analyzed. The calculated band structure with PBE and EV functional for all the compounds are similar, however a band gap wider with EV functional was obtained.

Research paper thumbnail of Influence of Ca on Structural and Ferroelectric Properties of Laser Ablated SrBi 2 Ta 2 O 9 Thin Films

Japanese Journal of Applied Physics, 2003

抄録 Bismuth layered perovskites of composition Sr1-xCaxBi2Ta2O9 (SCBT) with $ x= 0, 0.1, 0.2$, and... more 抄録 Bismuth layered perovskites of composition Sr1-xCaxBi2Ta2O9 (SCBT) with $ x= 0, 0.1, 0.2$, and 0.3 were grown using pulsed laser deposition technique. Influence of Ca on the structural and ferroelectric properties of SrBi2Ta2O9 (SBT) thin films have been ...

Research paper thumbnail of Studies on Laser Ablated SrBi 2 Ta 2 O 9 and Sr 0.8 Ca 0.2 Bi 2 Ta 2 O 9 Ferroelectric Thin Films

Integrated Ferroelectrics, 2002

Ferroelectric thin films of SrBi 2 Ta 2 O 9 (SBT) and (Sr 0.8 Ca 0.2 )Bi 2 Ta 2 O 9 (SCBT) were g... more Ferroelectric thin films of SrBi 2 Ta 2 O 9 (SBT) and (Sr 0.8 Ca 0.2 )Bi 2 Ta 2 O 9 (SCBT) were grown on platinized silicon substrates by using pulsed laser deposition technique. The effect of annealing temperature on the structural and electrical properties of the films was studied. Films were grown at 200 mTorr oxygen pressure with

Research paper thumbnail of Raman scattering in the aurivillius-layered ferroelectric SrBi 2 Ta 2 O 9 – Bi 3 TiNbO 9 thin films

Integrated Ferroelectrics, 2000

Abstract We have used Raman spectroscopy to investigate thin films of ferroelectric (SrBi2Ta2O9) ... more Abstract We have used Raman spectroscopy to investigate thin films of ferroelectric (SrBi2Ta2O9) x (Bi3TiNbO9) 1− x layered structures and to compare them with the corresponding bulk materials. Various compositions, with x'0.0, 0.2, 0.4, 0.6, 0.8, and 1.0, ...

Research paper thumbnail of Polycrystalline SrBi 2 Ta 0.8 Nb 1.2 O 9 thin films

Integrated Ferroelectrics, 2000

The growth, microstructure and micro-Raman properties of SrBi2Tao0.8Nb1.2O9 (SBTN) thin films dep... more The growth, microstructure and micro-Raman properties of SrBi2Tao0.8Nb1.2O9 (SBTN) thin films deposited on Si(100) substrates using pulsed laser deposition (PLD) technique were studied at various substrate temperatures. Films were characterized using X-ray diffraction(XRD), atomic force microscopy(AFM), energy dispersive X-ray analysis (EDAX) and micro-Raman studies. AFM studies indicated that the average grain size of the films increased between 0.08 μm to

Research paper thumbnail of Raman study of SrBi 2 Ta 2 O 9 thin films

Ferroelectrics Letters Section, 1999

Abstract Thin films of SrBi2Ta2O9 (SBT) were deposited on Si using Sol-Gel technique. The thickne... more Abstract Thin films of SrBi2Ta2O9 (SBT) were deposited on Si using Sol-Gel technique. The thicknesses of the films 200 nm (SBT2) and 400 nm (SBT4), respectively. SEM were studies showed most of the grains in the film are smaller than 0.1 μ. FTIR reflectivity ...

Research paper thumbnail of A low frequency Raman study of SrBi 2 Ta 2 O 9 -Bi 3 TiNbO 9

Ferroelectrics Letters Section, 1999

Abstract Raman spectra of SrBi2Ta2O9 (SBT), Bi3TiNbO9 (BTN), and x (SBT)+(1-x)(BTN) samples were ... more Abstract Raman spectra of SrBi2Ta2O9 (SBT), Bi3TiNbO9 (BTN), and x (SBT)+(1-x)(BTN) samples were studied for the first time in the low frequency region. The BTN spectra show two features around 33 and 41 cm− 1, while only one feature, around 30 cm− 1, is found in ...

Research paper thumbnail of Ruthenium adsorption and diffusion on the GaN(0001) surface

Applied Surface Science, 2009

... They found that Ga-T 4 model is more stable in Ga-rich conditions and N-H 3 model is more sta... more ... They found that Ga-T 4 model is more stable in Ga-rich conditions and N-H 3 model is more stable in N-rich conditions. A similar first principle study on the GaN(0 0 0 1)surface reports a Ga-adlayer reconstruction stable in Ga-rich conditions [14]. Northrup et al. ...

Research paper thumbnail of Structural stability and electronic structure of iron adsorption on the GaN(0001) surface

Applied Surface Science, 2011

Structural and electronic properties of main YCu 2 and YZn 2 binary compounds with C14, C15, C36 ... more Structural and electronic properties of main YCu 2 and YZn 2 binary compounds with C14, C15, C36 Laves phases and CeCu 2 structure in Cu-Y-Zn alloy are investigated by first-principles calculations. The related total energies versus occupations of nonequivalent lattice sites in all four structural forms were studied. Density functional theory is considered within framework of both pseudo-potentials and plane waves basis using VASP (Vienna ab initio Software Package). The optimized structural parameters were in very good agreement with the experimental values. Formation heat has been computed and showed that the CeCu 2 -YCu 2 and YZn 2 Laves phases have the strongest alloying ability and structural stability. Electronic density of states (DOSs) and charge density distribution were calculated and discussed in terms of structure stability.

Research paper thumbnail of SX SJOGREN

Research paper thumbnail of Anharmonic interactions in beryllium oxide

Physical Review B, 1996

BeO is an insulator with an unusually high thermal conductivity (92% that of Cu at 25 C) and a hi... more BeO is an insulator with an unusually high thermal conductivity (92% that of Cu at 25 C) and a high Debye temperature (1280 K). We measured its first-order Raman scattering as a function of temperature from 300 down to 30 K. The temperature dependence of the ...

Research paper thumbnail of Ferroelectric properties of laser-ablated Sr1-xAxBi2Ta2O9 thin films (where A=Ba, Ca)

Applied Physics Letters, 2002

Bismuth-layered ferroelectric thin films of Sr1-xAxBi2Ta2O9, with composition x=0 and 0.2, were f... more Bismuth-layered ferroelectric thin films of Sr1-xAxBi2Ta2O9, with composition x=0 and 0.2, were fabricated by using the pulsed-laser deposition technique. Structural characterization of the films by x-ray diffraction and atomic force microscopy, revealed that the films are polycrystalline in nature with average grain size of 180 nm. The films displayed spherical grains with a surface roughness of 12 nm. The ferroelectric

Research paper thumbnail of Self-aligned, buried heterostructure AlInGaAs laser diodes by micro-selective-area epitaxy

Applied Physics Letters, 2004

We describe the growth and characteristics of AlInGaAs, self-aligned buried heterostructure quant... more We describe the growth and characteristics of AlInGaAs, self-aligned buried heterostructure quantum well lasers deposited by micro-selective-area growth. The lateral waveguide is defined by metalorganic vapor-phase epitaxy in narrow stripe openings; and the natural tendency to form smooth, no-growth {111} sidewall planes produces a low-loss, single-mode waveguide. By proper adjustment of the growth conditions after the waveguide formation, the waveguide

Research paper thumbnail of Phonons and magnetic excitation correlations in weak ferromagnetic YCrO3

Journal of Applied Physics, 2014

Here, we report the temperature dependent Raman spectroscopic studies on orthorhombically distort... more Here, we report the temperature dependent Raman spectroscopic studies on orthorhombically distorted perovskite YCrO 3 over a temperature range of 20-300 K. Temperature dependence of DC-magnetization measurements under field cooled and zero field cooled protocols confirmed a N eel transition at T N $ 142 K. Magnetization isotherms recorded at 125 K show a clear loop opening without any magnetization saturation up to 20 kOe, indicating a coexistence of antiferromagnetic (AFM) and weak ferromagnetic (WFM) phases. Estimation of exchange constants using mean-field approximation further confirm the presence of a complex magnetic phase below T N . Temperature evolution of Raman line-shape parameters of the selected modes (associated with the octahedral rotation and A(Y)-shift in the unit-cell) reveal an anomalous phonon shift near T N . An additional phonon anomaly was identified at T * $ 60 K, which could possibly be attributed to the change in the spin dynamics. Moreover, the positive and negative shifts in Raman frequencies between T N and T * suggest competing WFM and AFM interactions. A close match between the phonon frequency of B 3g (3)-octahedral rotation mode with the square of sublattice magnetization between T N and T * is indicative of the presence of spin-phonon coupling in multiferroic YCrO 3 . V C 2014 AIP Publishing LLC. [http://dx.

Research paper thumbnail of Pressure effect on electronic properties of Sc 0.5 In 0.5 N compound

physica status solidi (b), 2009

Research paper thumbnail of Mechanical Measurements of Multilayer Thin Films Obtained by a PAPVD System

Microscopy and Microanalysis, 2005

The need of techniques for determining the mechanical properties of thin films, e.g. hardness coa... more The need of techniques for determining the mechanical properties of thin films, e.g. hardness coatings on ion beam treated surfaces has prompted a study of the microindentation hardness technique. The present interest is driven to a good understanding of the adhesion, friction, wear, and indentation processes. In most of the solid-solid interfaces of technological relevance, it occurs contact in many asperities, and this is why the study of fundamental properties of micro-mechanic and tribology of surfaces and interfaces is very important. The recent developments of different microscopic techniques based on tips and force surface devices (i.e. AFM, FM, LFM) allowed investigations of interfacial problems with high resolution and have led to the nanoscale regime the mechanical properties study for a wide spectrum of materials. In this work a method for Young's modulus determination of hard coatings multilayers of TiN/ZrN is evaluated. This method is based on AFM and spectroscopy-force modes [1-2].

Research paper thumbnail of Pressure effects on the electronic and magnetic properties of GaxV1−xN compounds: Ab-initio study

Materials Science and Engineering: B, 2009

We report an ab-initio study of the pressure effects on the electronic and the magnetic propertie... more We report an ab-initio study of the pressure effects on the electronic and the magnetic properties of Ga x V 1−x N compounds (x = 0.25, 0.50 and 0.75) in wurtzite-derived structures. We use the full-potential linearized augmented plane wave plus local orbitals method (LAPW + lo) within of the spin density functional theory framework. The lattice constant is found to vary linearly with Ga-concentration. The magnetic moment changes for a critical pressure. At x = 0.75, a rather abrupt onset of the magnetic moment from 0 to 2 B at P cr ∼22.8 GPa is observed. For x = 0.25 and 0.50 Ga concentrations, the magnetic moment increases gradually when the pressure decreases toward the equilibrium value. We study the transition pressure dependence to a ferromagnetic phase near the onset of magnetic moment for each Ga x V 1−x N compounds. The calculation of the density of states with Ga concentration is carried out considering two spin polarizations. The results reveal that for x = 0.75 the compound behaves as a conductor for the spin-up polarization and that the density of states for spin-down polarization is zero at the Fermi level. At this concentration the compound presents a half metallic behavior; therefore this material could be potentially useful as spin injector. At high pressures P > P cr the compounds exhibit a metallic behavior.

Research paper thumbnail of BDNF: A missing link between sympathetic dysfunction and inflammatory disease?

Journal of Neuroimmunology, 2006

Nerve growth factor (NGF) plays a role in sympathetic neuron integrity and survival. Brain-derive... more Nerve growth factor (NGF) plays a role in sympathetic neuron integrity and survival. Brain-derived neurotrophic factor (BDNF) also has trophic effects on sympathetic neurons. We report here the serendipitous finding that co-treatment of hippocampus with BDNF and the NGF antagonist TrkA-Fc leads to perivascular inflammation and marked vasoconstriction. This effect is not observed with either reagent alone or in combination with other control proteins. Because NGF supports sympathetic neuron health, we tested the hypothesis that BDNF combined with sympathetic compromise caused this effect. Superior cervical ganglia were removed bilaterally with concurrent BDNF infusion into hippocampus. Perivascular inflammation was observed at 3 days, but not 12 days post treatment, when sympathetic terminals had receded, suggesting that the presence of these terminals was necessary for inflammation. Since sympathetic dysfunction may lead to compensatory overactivity of norepinephrine (NE) signaling, we co-infused BDNF with NE in the hippocampus and observed perivascular inflammation. In humans, sympathetic overactivity has been reported in a variety of vascular diseases. Some of these diseases, e.g. primary Raynaud's, are not accompanied by serious inflammatory disease whereas others, such as scleroderma and systemic lupus, are. We speculate that BDNF may contribute to the transformation of sympathetic dysfunction to inflammatory disease. D

Research paper thumbnail of Micro-Raman and infrared reflectivity spectra of YBa2Cu3O7−δ deposited on LaAlO3 and stainless steel/inconel substrates

Journal of Applied Physics, 1995

Abstract The motivation for this article has been to try to understand the relative phenomenologi... more Abstract The motivation for this article has been to try to understand the relative phenomenological differences between the behavior of the films of the high‐temperature superconductors like YBa 2 Cu 3 O 7-δ deposited on (a) relatively insulating substrates ( ...

Research paper thumbnail of In-composition effect on band gap width of Sc1−xInxN alloys

Journal of Alloys and Compounds, 2009

We report first-principles calculations to analyze the In-composition effect on band gap width of... more We report first-principles calculations to analyze the In-composition effect on band gap width of Sc 1−x In x N alloys in wurtzite structure for the compositions x = 0, 0.25, 0.5, 0.75, 1. The calculations were performed in the framework of the density functional theory (DFT) using the full potentiallinearized augmented plane-wave (FP-LAPW) method as implemented in the WIEN2k code. We used both Perdew-Burke-Ernzerhof (PBE) and Engel-Vosko (EV) functional of generalized gradient approximation (GGA) for the exchange-correlation potential. First, the lattice parameters with PBE functional were optimized. Subsequently, using PBE and EV functional, the band structure at equilibrium volume for each In-concentration was calculated. The gap bowing in wurtzite structure was obtained and analyzed. The calculated band structure with PBE and EV functional for all the compounds are similar, however a band gap wider with EV functional was obtained.

Research paper thumbnail of Influence of Ca on Structural and Ferroelectric Properties of Laser Ablated SrBi 2 Ta 2 O 9 Thin Films

Japanese Journal of Applied Physics, 2003

抄録 Bismuth layered perovskites of composition Sr1-xCaxBi2Ta2O9 (SCBT) with $ x= 0, 0.1, 0.2$, and... more 抄録 Bismuth layered perovskites of composition Sr1-xCaxBi2Ta2O9 (SCBT) with $ x= 0, 0.1, 0.2$, and 0.3 were grown using pulsed laser deposition technique. Influence of Ca on the structural and ferroelectric properties of SrBi2Ta2O9 (SBT) thin films have been ...

Research paper thumbnail of Studies on Laser Ablated SrBi 2 Ta 2 O 9 and Sr 0.8 Ca 0.2 Bi 2 Ta 2 O 9 Ferroelectric Thin Films

Integrated Ferroelectrics, 2002

Ferroelectric thin films of SrBi 2 Ta 2 O 9 (SBT) and (Sr 0.8 Ca 0.2 )Bi 2 Ta 2 O 9 (SCBT) were g... more Ferroelectric thin films of SrBi 2 Ta 2 O 9 (SBT) and (Sr 0.8 Ca 0.2 )Bi 2 Ta 2 O 9 (SCBT) were grown on platinized silicon substrates by using pulsed laser deposition technique. The effect of annealing temperature on the structural and electrical properties of the films was studied. Films were grown at 200 mTorr oxygen pressure with

Research paper thumbnail of Raman scattering in the aurivillius-layered ferroelectric SrBi 2 Ta 2 O 9 – Bi 3 TiNbO 9 thin films

Integrated Ferroelectrics, 2000

Abstract We have used Raman spectroscopy to investigate thin films of ferroelectric (SrBi2Ta2O9) ... more Abstract We have used Raman spectroscopy to investigate thin films of ferroelectric (SrBi2Ta2O9) x (Bi3TiNbO9) 1− x layered structures and to compare them with the corresponding bulk materials. Various compositions, with x'0.0, 0.2, 0.4, 0.6, 0.8, and 1.0, ...

Research paper thumbnail of Polycrystalline SrBi 2 Ta 0.8 Nb 1.2 O 9 thin films

Integrated Ferroelectrics, 2000

The growth, microstructure and micro-Raman properties of SrBi2Tao0.8Nb1.2O9 (SBTN) thin films dep... more The growth, microstructure and micro-Raman properties of SrBi2Tao0.8Nb1.2O9 (SBTN) thin films deposited on Si(100) substrates using pulsed laser deposition (PLD) technique were studied at various substrate temperatures. Films were characterized using X-ray diffraction(XRD), atomic force microscopy(AFM), energy dispersive X-ray analysis (EDAX) and micro-Raman studies. AFM studies indicated that the average grain size of the films increased between 0.08 μm to

Research paper thumbnail of Raman study of SrBi 2 Ta 2 O 9 thin films

Ferroelectrics Letters Section, 1999

Abstract Thin films of SrBi2Ta2O9 (SBT) were deposited on Si using Sol-Gel technique. The thickne... more Abstract Thin films of SrBi2Ta2O9 (SBT) were deposited on Si using Sol-Gel technique. The thicknesses of the films 200 nm (SBT2) and 400 nm (SBT4), respectively. SEM were studies showed most of the grains in the film are smaller than 0.1 μ. FTIR reflectivity ...

Research paper thumbnail of A low frequency Raman study of SrBi 2 Ta 2 O 9 -Bi 3 TiNbO 9

Ferroelectrics Letters Section, 1999

Abstract Raman spectra of SrBi2Ta2O9 (SBT), Bi3TiNbO9 (BTN), and x (SBT)+(1-x)(BTN) samples were ... more Abstract Raman spectra of SrBi2Ta2O9 (SBT), Bi3TiNbO9 (BTN), and x (SBT)+(1-x)(BTN) samples were studied for the first time in the low frequency region. The BTN spectra show two features around 33 and 41 cm− 1, while only one feature, around 30 cm− 1, is found in ...

Research paper thumbnail of Ruthenium adsorption and diffusion on the GaN(0001) surface

Applied Surface Science, 2009

... They found that Ga-T 4 model is more stable in Ga-rich conditions and N-H 3 model is more sta... more ... They found that Ga-T 4 model is more stable in Ga-rich conditions and N-H 3 model is more stable in N-rich conditions. A similar first principle study on the GaN(0 0 0 1)surface reports a Ga-adlayer reconstruction stable in Ga-rich conditions [14]. Northrup et al. ...

Research paper thumbnail of Structural stability and electronic structure of iron adsorption on the GaN(0001) surface

Applied Surface Science, 2011

Structural and electronic properties of main YCu 2 and YZn 2 binary compounds with C14, C15, C36 ... more Structural and electronic properties of main YCu 2 and YZn 2 binary compounds with C14, C15, C36 Laves phases and CeCu 2 structure in Cu-Y-Zn alloy are investigated by first-principles calculations. The related total energies versus occupations of nonequivalent lattice sites in all four structural forms were studied. Density functional theory is considered within framework of both pseudo-potentials and plane waves basis using VASP (Vienna ab initio Software Package). The optimized structural parameters were in very good agreement with the experimental values. Formation heat has been computed and showed that the CeCu 2 -YCu 2 and YZn 2 Laves phases have the strongest alloying ability and structural stability. Electronic density of states (DOSs) and charge density distribution were calculated and discussed in terms of structure stability.

Research paper thumbnail of SX SJOGREN