bluuebunny/crossref_metadata_2025_split huggingface dataset:
Laser Deposited Epitaxial Oxide Heterostructures as Prototype Ferroelectric Optical Waveguides
Authors: Fork D. K. , Anderson G. B. 
Published: March 2011

ABSTRACTThe pulsed laser deposition process is a powerful tool for investigating prototype epitaxial structures. This report outlines recent developments in epitaxial structures which may usefully serve as ferroelectric optical waveguides. Emphasis is given to structures on semiconductor substrates, motivated by hybrid optical/semiconductor integration. Earlier pulsed laser deposited structures, such as BaTiO3/MgO/GaAs (100) are discussed in conjunction with current results on Z-lithium niobate on GaAs (111)A and GaAs (111)B. BaTiO3/MgO/GaAs (100) grows with cube-on-cube crystallography. The epitaxial system z-lithium niobate on GaAs (111)A and GaAs (111)B has been demonstrated both with and without intermediate MgO (111) layers. The in-plane epitaxial relationships are LiNbO3 [110] // GaAs [211] and [211] indicating the existence of 180° boundaries in the LiNbO3 with and without the MgO layer, which grows cube-on-cube with the GaAs. Out-of-plane texture is typically 1.0° and 1.2° for the MgO and LiNbO3 layers respectively. In-plane texture is typically 2.8° and 4.5° for MgO and LiNbO3 layers respectively. These and similar epitaxial systems may be useful for monolithic electro-optic or frequency doubling applications in conjunction with semiconductor laser sources.
Epitaxial growth of LiNbO3 thin films by excimer laser ablation method and their surface acoustic wave properties
Authors: Shibata Yoshihiko , Kaya Kiyoshi , Akashi Kageyasu , Kanai Masaki , Kawal Tomoji , Kawal Shichlo 
Published: March 2011

ABSTRACTWe have formed epitaxial LiNbO3 thin films on sapphire substrates (001),(110) and (012) using an excmer-laser ablation technique. We have fabricated surface acoustic wave (SAW) filters on the films and evaluated SAW properties. It is demonstrated that the LINbO3 thin films on the sapphire substrates are candidates for a high frequency SAW filter because of their high velocities of propagation (5300–5600m/s).
Effect of a Ge Barrier on the Microstructure of BaTiO3 Deposited on Silicon by Pulsed Laser Ablation
Authors: Jacobs Elizabeth G. , Rho Young G. , Pinizzotto Russell F. , Summerfelt Scott R. , Gnade Bruce E. 
Published: March 2011

ABSTRACTBaTiO3 (BT) thin films deposited using pulsed laser ablation on substrates of (100) Si and (100) Si with 0.3 μm Ge were examined. For one set of samples, approximately 2000 Å of BT was deposited at 70°C at O2 pressures of 0, 1.0 and 10.0 mT. In a second set, O2 pressures of 0 and 1.0 mT were used during deposition of 200 Å of BT at 450°C followed by a 5 minute anneal and deposition of an additional 2000 Å at 750°C. This gave a total sample matrix of 10 samples. Cross-sectional TEM revealed that an interfacial layer formed in the BT on Si samples but not in the BT on Ge samples. HREM analysis of the interfaces showed that the interfacial layer was amorphous. On Ge, the BT films were found to have large areas of epitactic growth along the interface. This was confirmed by diffraction tilt angle experiments which showed a strong preferred orientation of BT on Ge. No preferred orientation was found for BT on Si. Statistical grain size analysis of the films using multiple regression showed that the film microstructures were affected most strongly by the substrate type (Ge or Si) followed by the deposition temperature of the substrate. Only a weak effect of O2 pressure was observed.
Characterization of Laser-Assisted Pulseid Laser Deiposited BaFe12O19
Authors: Horwitz J.S. , Chrisey D.B. , Grabowski K.S. , Carosella C.A. , Lubitz P. , Edmondson C. 
Published: March 2011

ABSTRACTHigh quality, epitaxial barium hexaferrite (BaFe12O19) thin films have been deposited by pulsed laser deposition (PLD) onto basal plane sapphire at substrate temperatures of 900°C in 400 mTorr of oxygen. Thin films (< 500 nm) were smooth while thick films (> 1000 nm) had rough, polycrystalline surfaces and “soot-like” appearances. The integration of ferrite films with semiconductors will require thick films (< 70 μm) and low substrate processing temperatures (≤ 600°C). Films deposited at 600°C were mostly amorphous with the presence of some crystalline, non-hexaferrite material. In an effort to improve the quality of barium hexaferrite fihns, we have investigated the effects of excimer-laser-assisted PLD (LAPLD) on the growth of BaFe12O19. During the deposition, the substrate was illuminated with the output of a second pulsed excimer laser (KrF) weakly focused to an energy of 10 to 130 mJ/cm2. The output of the second laser was synchronized such that the delay between the vaporization laser and the annealing laser was 0 to 1 ms. The X-ray diffraction analysis of LAPLD films deposited at 600°C with an annealing fluence of 50 mJ/cm2 indicated that the films were a crystalline mixture of hexaferrite and non-hexaferrite phases. Both phases exhibited a preferred orientation characterized by narrow x-ray rocking curve widths (FWHM ∼ 1°). Magnetic properties (magnetic moment, saturation magnetization and coercive field) detennined from a vibrating sample magnetometer (VSM) also confirmed the presence of oriented hexaferrite material in the laser annealed samples. These results show clear advantages of LAPLD for improved structural and magnetic properties of BaFe12O19 deposited at substrate temperatures compatible with semiconducting materials.
Preparation of Pb(Zr0.54Ti0.46)O3 Thin Films on (100)Si Using Textured YBa2Cu3O7−δ and Yttria-Stabilized Zirconia Buffer Layers by Laser Physical Vapor Deposition Technique
Authors: Tiwari P. , Zheleva T. , Morimoto A. , Shukla V.N. , Narayan J. 
Published: March 2011

ABSTRACTWe have fabricated high-quality <001> textured Pb(Zr0.54Ti0.46)O3 (PZT) thin films on (001)Si with interposing <001> textured YBa2Cu3O7−δ (YBCO) and yttria-stabilized zirconia (YSZ) buffer layers using pulsed laser deposition (KrF excimer laser, λ=248 nm, τ=20 nanoseconds). The YBCO layer provides a seed for PZT growth and can also act as an electrode for the PZT films, whereas YSZ provides a diffusion barrier as well as a seed for the growth of YBCO films on (001)Si. These heterostructures were characterized using X-ray diffraction, high-resolution transmission electron microscopy and Rutherford backscattering techniques. The YSZ films were deposited in oxygen ambient (∼9X10−4 torr) at 775°C on (001)Si substrate having <001>YSZ// <001>Si texture. The YBCO thin films were deposited in-situ in oxygen ambient (200 mtorr) at 650°C. Temperature and oxygen ambient for the PZT deposition were optimized to be 530°C and 0.4–0.6 torr, respectively. The laser fluence to deposit this multistructure was 2.5–5.0 J/cm2. The <001> textured perovskite PZT films showed a dielectric constant of 800–1000, a saturation polarization of 37.81 μC/cm2, remnant polarization of 24.38 μC/cm2 and a coersive field of 125 kV/cm. The effects of processing parameters on microstructure and ferroelectric properties of PZT films and device implications of these structures are discussed.
Pulsed Laser Deposition of High-Epsilon Dielectrics: PMN and PMN-PT
Authors: Saenger K.L. , Roy R.A. , Beach D.B. , Etzold K.F. 
Published: March 2011

ABSTRACTIn this study we report on the KrF excimer laser deposition of crystalline films of lead magnesium niobium oxide (PMN) and solid solutions of PMN and lead titanate (PT) in a 65:35 ratio. These materials have potential microelectronic applications as thin film capacitors due to their high dielectric constants (εPMN(bulk) ≥ 10,000). Films were typically deposited in an oxygen background at elevated substrate temperatures(Ts = 525 °C) on substrates of Pt(111)/SiO2/Si or Pt(111)/glass. The deposited films were characterized by Rutherford Backscattering Spectroscopy (RBS), x-ray diffraction, and capacitance/loss measurements. Films prepared from a nearlystoichiometric commercial PMN target were low in Mg and Pb and yielded only the low-c pyrochlore phase (measured εfilm ≃ 100), even after cx-situ annealing at temperatures up to 650°C. Films deposited from Pb,Mg-rich targets prepared by a sol-gel process (tailored to produce the desired film stoichiometry) contained mixtures of perovskite and pyrochlore, with typical r values of order 600–1200.
Deposition of Thin Films of Silicon Carbide on Fused Quartz and on Sapphire by Laser Ablation of Ceramic Silicon Carbide Targets
Authors: Rimai L. , Ager R. , Hangas J. , Loaothetis E. M. , Abu-ageel Nayef , Aslam M. 
Published: March 2011

ABSTRACTAblation of ceramic silicon carbide with 351 nm excimer radiation was used to depositSIC films on fused silica and on sapphire. For deposition temperatures above 850° C, diffraction shows the films to be crystalline with the [111] axis preferentially oriented normally to the film. Optical spectra show an indirect energy gap at 2.2 eV, near that for the cubic polytype, although the 200 diffractions are absent. Room temperature resistivities range between .02 to .1 Ωcm. Deposition below 600° C yields amorphous SiC with no diffraction bands, low and variable optical band gap and very high resistivity.
An Ion Probe Study of Plasma-Assisted Laser Deposition
Authors: Witanachchi S. , Ahmed K. , Sakthivel P. , Mukherjee P. 
Published: March 2011

ABSTRACTThe ionic content of an excimer laser ablated Yga2Cu3O7−δ (YBCO) plume has been investigated by using an ion probe detection system. The time-of-flight ion signals indicate a bifurcation of the plume, where the degree of bifurcation is dependent on both the oxygen pressure and the laser spot size at the target. A significant enhancement in the ionic content is observed when the plume is passed through a high voltage discharging ring. The results describing the effect of the pressure, laser spot size and the discharge parameters on the propagating laser plume are presented in this paper.
Nature and Application of Particulate Matter Produced by Pulsed Laser Ablation
Authors: Chen Li-Chyong , Hall Ernest L. 
Published: March 2011

ABSTRACTParticulates produced by 248 nm KrF excimer laser ablation were investigated in two systems: Nb-Al and Cr-Nb. Both systems contain intermetallics which are potentially useful high temperature materials. While the melting temperature of Nb is three times higher than that of Al, the melting temperature difference between Nb and Cr is less substantial. This work focuses on the effects of melting temperature difference between the terminal elements in binary alloy systems on the nature of the particulate matter formed by laser ablation.Transmission (TEM) and scanning electron microscopy (SEM), energy dispersive X-rayanalysis (EDX), and optical image analysis were used to characterize the products. The particulate generation rate and the size distribution depend on various growth parameters. In both Nb-Al and Cr-Nb systems, the particulates are all enriched in Nb, with the smallest particulates richest in Nb. Single phase particulates containing barely detectable Al were found in Nb-Al system. In the Cr-Nb system, electron diffraction patterns indicate two types of particulates: one exhibiting a new metastable diamond cubic structure and the other being a two phase mixture of bcc Cr and bcc Nb. A plausible mechanism whereby the lower melting temperature element is depleted as well as the correlation of the particulate size and the overall composition of individual particulate will be discussed. Stoichiometric studies of the particulatesgenerated in the Nb-Al and Cr-Nb systems using the pulsed laser deposition (PLD) technique help illustrate the merits and limitations of the same. One example of the potential applications of the particulate-containing films will be demonstrated.
Pulsed Laser Deposition of Thin Metallic Multilayers and Amorphous Films
Authors: Krebs Hans-Ulrich , Bremert Olaf 
Published: March 2011

ABSTRACTThe method of pulsed excimer laser ablation using KrF radiation was applied for the deposition of thin metallic elementary multilayers. Above an ablation threshold of about 5 J/cm2 an ‘explosive’ evaporation of the metallic targets occurs leading to high deposition rates of up to 5 nm/s. For different metals, the ablation threshold slightly varies leading at the same laser fluence to different growth rates as shown for Ag, Fe, Zr and Nb. By using two elementary targets and adjusting the dwelling times on both targets, Fe/Ag, Fe/Zr and Fe/Nb multilayers of different bilayer thicknesses were deposited. While Fe/Ag superstructures show crystalline phases down to a periodicity of 1 nm, Fe/Zr and Fe/Nb films are amorphous at such wavelengths. On the other side, Fe/Nb multilayers can also be amorphized by a solid state interdiffusion reaction of the elementary multilayers. The surfaces of the grown films are smooth except for a small number of droplets on the film surface.
Laser Ablation Deposition of Diamond-Like Carbon Films
Authors: Leppävuori S. , Levoska J. , Vaara J. , Kusmartseva O. 
Published: March 2011

ABSTRACTDiamond-like carbon (DLC) thin films were prepared by laser ablation deposition. The deposition process was carried out in a vacuum chamber at a base pressure of about 10−5 mbar using the focused beam from either an Nd:YAG laser or an XeCl excimer laser and a pyrolytic graphite target. The peak power density of the laser beam was about 108 W/cm2, and 1010 W/cm2. respectively. The effect of varying power density of the laser beam also was examined. The films were deposited on fused silica and silicon single crystal substrates between room temperature and 600 °C with and without hydrogen addition. The properties of the films were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), micro-Raman and Fourier transform infrared (FTIR) spectrometry, electrical conductivity and optical measurements. The best films were insulating (σ<10−6 Ω−1 cm−1), hard, partly transparent (optical gap 1.3 − 2.2 eV) and smooth without any particulates on the surface.
Oxide Formation During Flight of Ablated Fragments
Authors: Eryu Osamu , Yamaoka Kenji , Masuda Kohzoh 
Published: March 2011

ABSTRACTCollision processes between oxygen molecules and laser ablated fragments from YBa2Cu3Oy superconductor target are described. The space/time resolved photo-emission measurements of Cu and CuO were carried out in order to investigate the oxidation of the laser ablated fragments in O2 atmosphere. Increase of the photo-emission yield of CuO was observed over 100 mTorr and it showed maximum at 2 Torr. Velocity of CuO decreases abruptly at 200 mTorr. The velocity distribution spreads above 500 mTorr. An optimum range of oxygen pressure to fabricate superconducting thin films of Tc = 90 K was from 250 mTorr to 500 mTorr. Process of the reactive collisions of ablated fragments with O2 molecules in this range is discussed.
Time-Resolved Light-Emission Spectroscopy and Ion Current Measurements from Pulsed-Laser-Evaporated Cadmium Plumes
Authors: Rajakarunanayake Y. , Luo Y. , Compaan A. , Tamor M.A. 
Published: March 2011

ABSTRACTWe have investigated the pulsed laser evaporation of elemental Cd targets, with the aim of understanding the velocity distributions in the plumes and the changes which occur under moderate electrical bias. We report detailed kinetic energy distributions of the species in the laser evaporated plumes. In these experiments, frequency doubled, Q-switched pulses of a Nd:YAG laser were used at a 10 Hz repetition rate to generate the plumes. The velocity distributions of individual atomic species were determined by time-of-flight (TOF) light emission spectroscopy, while the time resolved ion/atom currents were measured with a collector above the target. We have simultaneously measured the dependence of the time resolved optical and electrical signals on the electrical bias applied between target and collector. We find that the typical kinetic energies in the plume are on the order of 10-200 eV, while the ionized species travel two to three times faster than the neutral particles. These results provide fundamental information about the physics of the pulsed laser evaporation process, and subsequent evolution of the plume.
Evaluation of the Laser Ablation of Transition Metals/Metal Compounds by Time-of-Flight and Optical Spectroscopy
Authors: Thiem Terry L. , Watson Lyn R. , Gardner James A. , Dressier Rainer A. , Salter Richard H. , Murad Edmond 
Published: March 2011

ABSTRACTA fast pulsed beam of neutral metal atoms is produced by laser vaporization ofa solid metal or metal compound sample in a modified high-temperature mass spectrometer. Atomic beams of several eV kinetic energy are generated as measured using time-of-flight spectroscopy. The energy range can be controlled with the laser power, similar to studies conducted on thin metal films. The solid samples, however, overcome the problem of short sample lifetime associated with irradiating thin films. Samples have been irradiated for several hours without observing a change in beam intensity or energy, thus offering an interesting source for kinetic studies. Initial results of studies done on copper, nickel, zinc and related oxide, sulfide, bromide, and chloride salts will be discussed as to their applicability to serve as a fast atom source. Spectroscopic data from these compounds will also be presented.
Micro-Structure and Electrical Properties of Nanocrystalline Pt Thin Film Prepared By R.F. Sputtering
Authors: Mei Xiangyang , Tao Mingde , Tan Hui , Han Ying , Tao Wei 
Published: March 2011

ABSTRACTNanocrystalline Pt (nc-Pt) thin film was prepared by R. F. sputtering on liquid N2 cooled substrate. Transmission Electron Microscopy (TEM)analyses clearly show that the as prepared film is constructed by numerous nanometer sized particles with average diameter of about 8-9nm. The interfaces between particles can be clearly seen and the interface width is about nmm. Electron Diffraction (ED) photograph and X-ray Diffraction (XRD) spectroscopy both confirm that the nanometer sized particles in the film are ultra fine crystallites with a cubic structure. The crystallite size increases gradually with annealing temperature. The temperature coefficient of resistance (TCR) of nc-Pt film are much lower than that of polycrystalline Pt film. DC conductivity and TCR also increase gradually with the increase of annealing temperature. It is suggested that the interfaces between the nanoorystallites greatly influence the properties of nc-Pt thin film.
A MÖssbauer Study of Nanophase iron Produced by Mechanical Alloying
Authors: Lu Yanxia , Reno R. C. , Takacs L. 
Published: March 2011

ABSTRACTBall milling has been used to mechanically induce the displacement reaction 3Fe3O4 + 8 Al → 9 Fe + 4 A12O3, in which fine magnetite particles (Fe3O4) are reduced to nanophase iron particles. The presence of initial, intermediate, and final phases are easily identified by Mössbauer spectroscopy on samples taken at various stages of the milling process.Our measurements confirm the gradual progress of the above reaction and also verify the presence of FeAl2O4 at intermediate milling times. The concentration of this phase reaches a maximum of 42% at a milling time of 100 minutes. After five hours, the sample is fully reduced and contains ferromagnetic bcc-iron and superparamagnetic iron particles. Further milling reduces the amount of ferromagnetic iron and increases the proportion of the superparamagnetic phase.
Synthesis and Ionic Conductivity of Nanophase Ca1-xLaxF2+x
Authors: Wu Xijun , Su Fang , Qin Xiaoying , Xie Bin , Ji Xiaoli 
Published: March 2011

ABSTRACTThe nanophase ionic conductors Ca1-xLaxF2+x with x=0 and 0.25 were synthesized by an inert gas condensation and in situ compacting technique. The samples with average grain size of 16 na for nanophase CaF2 and 11 nm for nanophase Ca0.75 La0.25F2.25 were prepared under the compacting pressure of 0.5 GPa. The alternating ionic conductivity was deduced from the temperature dependence of the complex impedance.The results indicated that the logarithm of ionic conductivity obeys Arrhenius relation in the temperature range from 300 °C to 530 °C both for nanophase CaF2 and for nanophase Ca0.75La0.25F2.25. Their activation energies are 1.14 eV and 1.00 eV, respectively. The ionic conductivity of nanophase CaF2 is about one and two orders of magnitude higher than that of polycrystalline and single crystal CaF2, respectively. While the ionic conductivity of nanophase Ca0.75La0.25F2.25 is about one order of magnitude higher than that of nanophase CaF2. Further analysis indicated that the enhanced ionic conductivity of nanophase Ca1-xLaxF2+x is related to the large volume fraction of interfaces.
Sintering Behavior of Ultrafine Ceramic Particles
Authors: Bonevich J.E. , Marks L.D. 
Published: March 2011

ABSTRACTUltrafine particles (UFPs) of aluminum oxide, formed by arc discharge, were sintered in an ultrahigh vacuum (UHV) furnace system and characterized by high resolution electron microscopy (HREM) under UHV conditions. The UFPs produced range in size from 20 to 50 nm and have highly faceted surfaces. The atomic structure of the UFPs corresponds to the cubic (γ) and orthorhombic (δ) variants of the spinel structure. In UFPs, surface faceting plays a major role in determining the final sintering geometry with sintering occurring predominantly on the closed-packed (111) facets. Surface diffusion is the predominant mechanism for sintering, as evidenced by the fact that many sintered particles have their initial adhesion structure ‘;lockedin’ during sintering with no reorientation occurring. Furthermore, the necks formed during sintering have well-defined, atomically-sharp contact angles suggesting that the neck growth process is controlled by the faceted structures and may be modeled by a mechanism similar to crystal growth due to ledges, grain boundaries, and twins. The driving force for sintering can be considered as a chemical potential difference between facet surfaces and the neck region.
Control of Particle Size and Orientation during in Situ Precipitation of Oxides in Polymers
Authors: Burdon Jeremy , Calvert Paul 
Published: March 2011

ABSTRACTComposite materials may be prepared by bio-mimetic routes where reinforcing particles are grown by chemical reaction in a polymer matrix, by analogy to the mineralization of collagenous bone matrix by hydroxyapatite. Ideally these resulting composites should resemble bone in having sub-micron, elongated particles packed to high densities in the matrix. The resulting material should have good mechanical properties and may also be fired to a dense ceramic.We have been exploring the control of the precipitation of oxide ceramics, particularly titania, by in situ hydrolysis of metal alkoxides. The size of the precipitate particles can be controlled by variation of the compatibility of polymer and alkoxide. A high level of compatibility leads to particles with sizes below 0.1 microns while less compatible alkoxides give particles up to 1 micron diameter. The kinetics of the hydrolysis also affect the particle size. Elongated and oriented particles can be produced by deformation of the polymer during precipitation. Two-phase polymer blends can be used to provide nanoscale molds within which elongated particles grow. By controlling the scale of phase separation in the blend it is possible to produce rod-shaped particles with diameters in the range from one micron down to a few nanometers.
Ion Transport in Alumina-Pillared Zirconium Phosphate
Authors: Criado C. , Ramos-Barrado J.R. , Maireles-Torres P. , Oliverapastor P. , Jimenez-Lopez A. , Rodriguez-Castellon E. 
Published: March 2011

ABSTRACTA.c. conductivity of a novel large-pore alumina-pillared zirconium phosphate and some lithium ion exchanged samples have been measured by an impedance method. These materials have a conductivity in the range 10-5 to 10-9 Ω-1cm-1 higher than those of alumina-pillared tin phosphate and its lithium derivatives. The electrical behaviour of the pillared zirconium phosphates fits to an equivalent circuit composed by two subcircuits in parallel with a condenser. In a temperature interval (200-500°C), lithium ions are charge carriers and the conductivity increases when heating with activation energies between 0.99 and 1.22 eV.