bluuebunny/crossref_metadata_2025 huggingface dataset:
Laser Deposited Epitaxial Oxide Heterostructures as Prototype Ferroelectric Optical Waveguides
Authors: Fork D. K. , Anderson G. B.
Published: March 2011

The 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

We 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

BaTiO3 (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

High 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

We 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

In 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

Ablation 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

The 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

Particulates 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

The 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

Diamond-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

Collision 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

We 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

A 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

Nanocrystalline 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

Ball 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

The 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

Ultrafine 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

Composite 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

A.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.
Germanium Loaded Zeolite Y: Preparation and Characterization
Authors: Tomiya S. , Petroff P.M. , Margolese D. , Srdanov V. I. , Stucky G. D. , Zhang Y. H.
Published: March 2011

The cavities of molecular sieves offer an opportunity for synthesis of periodically ordered semiconductor nanoclusters. Ge clusters were synthesized in zeolite Y by thermal decomposition of GeH4 absorbed in the zeolite cages. Upon inclusion of germanium in proton exchanged zeolite Y (HY), the X-ray diffraction (XRD) pattern shows a small change in line positions and considerable change in intensities. No extra reflections were detected in either XRD or transmission electron diffraction (TED) for the samples synthesized at 300°C. These observations are in accordance with the energy dispersive X-ray (EDX) spectroscopy data which reveal the presence of germanium within the HY in concentrations higher than 5x1019 cm-3. At annealing temperatures higher than 500°C, small Ge crystallites (∼0.2μm) form on the exterior surface of the HY, as documented by TED, TEM and absorption spectroscopy. The results from the absorption and photoluminescence spectroscopy of the Ge loaded HY will be discussed.
Deposition of Diamond/ Tin Composite Film on Tool Steel Substrate
Authors: Chen X. , Narayan J.
Published: March 2011

TiN/Diamond/TiN composite film has been deposited on tool steel substrate by CVD and laser ablation technique. A TiN film of about 0.5µm thick was first deposited as a buffer layer by laser ablation and then diamond was deposited with proper number density by CVD. After this the diamond layer was covered by a second layer of TiN. It was found that the TiN buffer layer was stable during CVD process of diamond and can chemically isolate the depositing surface from steel substrate. This prevents the reaction between the diamond and the substrate and makes it possible to deposit high quality diamond films on steel. The second TiN layer embeds the diamond particles to form a TiN/diamond composite film and therefore greatly enhances adhesion of the deposited diamond. SEM, Raman. adhesion and hardness measurements show that an extremely hard. adherent and thermalshock-resistant diamond/TiN composite film can be deposited on steel.
Nanocomposites For magnetic Refrigeration
Authors: Shull R.D. , Mcmichael R.D. , Ritter J.J. , Bennett L.H.
Published: March 2011

Upon the application of an external magnetic field, the magnetic spins in a material partially align with the field, thereby reducing the magnetic entropy of the spin system. When performed adiabatically, the specimen's temperature will rise. This temperature rise, δT, related to the entropy change by the heat capacity, is known as the magnetocaloric effect. Upon cycling the magnetic field, this effect can be used for transferring heat from one thermal reservoir to another, forming the basis for a magnetic refrigerator. Recently, NIST scientists predicted composite magnetic materials containing nanometer-size magnetic species could possess enhanced magnetocaloric effects [1-2], especially at high temperatures or low magnetic fields. Magnetic nanocomposites may be prepared in many different ways, and recent magnetocaloric effect data measured on Fe-doped gadolinium gallium garnets are presented to show both the effect of processing and a methodology for optimizing δT.
Evaluation of The Catalytic Activity of A High Surface Area, Regular, Porous Solid Formed From The Clusters of Clusters, MII4O[(CO)9Co3CCO2]6, M = Co, Zn
Authors: Cen Wei , Fehlner Thomas P. , Kalenik Zbigniew , Wolf Eduardo E.
Published: March 2011

The discrete molecular clusters of clusters, M1140[(CO)9Co3CCO2]6, M = Co, Zn undergo thermolysis with the production of highly porous solid materials. Evaluation of the catalytic properties of these materials has been investigated using the hydrogenation of 1,3- butadiene as a test reaction. These experiments suggest it is the unique structure of the porous materials that is responsible for the high activities and the selectivities observed.
Mechano-Chemical Effects of High-Energy Attrition Milling On The Bi2Sr2CaCu2Ox Superconductor
Authors: Luo J. S. , Lee H. G. , Sinha S.
Published: March 2011

The mechano-chemical effects of high-energy attrition milling on the microstructure evolution and superconducting properties of Bi2Sr2CaCu2Ox oxide powder were investigated by a combination of x-ray diffraction, scanning electron microscopy, and magnetization techniques. The powder was attrition-milled under an argon atmosphere, using a standard laboratory attritor with yittria-stabilized ZrO2 balls having a ball-to-powder weight ratio of ∼10:1. After selected time increments the mechanical attrition was interrupted and a small quantity of the milled powder was removed for analysis. The results indicate that (1) the crystal size decreases, (2) this decrease in crystal size is accompanied by degradation of crystallinity of the powder and accumulation of atomic-level strain, (3) the Bi-2212 phase decomposes under conditions of excessive deformation, and (4) the superconducting transition is depressed from 70 K to 60 K in the early stages of milling and completely vanishes upon prolonged deformation. The influence of defects (created during cold work) on the current carrying capacity is also presented and discussed.
Phase Characterization and Grain Size Effects of Nanophase Y2O3, ZrO2 and Y2O3-ZrO2 Composites Produced by the Gas-Phase Condensation Technique
Authors: Foster C. M. , Bai G. R. , Parker J. C. , Ali M. N.
Published: March 2011

Nanophase (n-) ZrO2 was produced in its pure and partially stabilized form by the gas-phase condensation method. The material was examined by x-ray diffraction and Raman scattering to obtain information on the structural evolution of the material during sintering. Two types of Y2O3 doped ZrO2 nanophase materials were made one by co-deposition of n-Y2O3 and n-ZrO2 in a consecutive manner and the second by mechanically mixing n-Y2O3 and n-ZrO2. We have determined that the co-deposition process is the most effect means of doping the n-ZrO2.
Surface Effects on the Properties of Cadmium Selenide Quantum Dots
Authors: Carter A. C. , Majetich S. A.
Published: March 2011

The surface chemistry of 35 Å diameter CdSe quantum crystallites is varied by bonding different molecules to the surface of the crystallites. There are two main variables. The steric hindrance of the molecule is altered to control the density of dangling bonds at the surface. In addition, different bond types between the ligand and surface atoms were used to control the surface electron density. Nanosecond hole burning experiments were used to compare ground state recovery times. Luminescence revealed information on excited state recombination pathways. Analysis suggests that increased surface passivation reduces the fast nonradiative recombination.
Sialons and Silicon Nitrides; Microstructural Design and Performance
Authors: Lewis M.H.
Published: March 2011

survey is presented of developments in silicon nitride and sialon ceramic microstructures designed for application in differing temperature regimes.

For low temperature (< 1000°C) application, pressureless-sinterable sialons with moderate (10-15%) intergranular glass, anisotropic β′ grains and high values of MOR and Kc (1 GPa and 6-10MPa| m respectively) are preferred.

Improved hardness and high temperature capability may be achieved by tailoring intergranularp hases for crystallisation and further enhanced by the introduction of mixed α′/β′ Sialon microstructures. Examples are given of microstructural evolution in β′- Y3Al5O12(garnet), β′-Nd3Si3Al3O12N2 and α′/β′/garnet ceramics and a comparison of their mechanical behaviour.

Novel Sialon ceramics containing dispersed transition metal compounds (TiN, TiB2) may be formed by in-situ redox reaction, utilising the α′ Sialon phase as an oxygen receptor. The dispersed phase may enhance hardness and toughness and confer electro-discharge machinability.

Oxidation instability of Sialon compositions dictates the use of diphasic Si3N4/M2Si2O7 microstructures for application above 1300°C. The thermal cycle during pressurised sintering of these non-sialon compositions is critical in avoiding crystallisation of mixed polymorphs of the intergranular disilicate, with consequent microcracking.
Applications of Silicon Nitride Based Ceramics in the U.S.
Authors: Katz R. Nathan
Published: March 2011

Silicon nitride based ceramics have unique combinations of mechanical, thermal-physical and electrical properties. Additionally, silicon nitride based materials can be fabricated into near net shape components by several processing routes. This unique combination of properties and processing versatility have encouraged the use of silicon nitride based ceramics in a variety of demanding commercial applications over the past decade. In the U.S., these applications currently include cutting tools, bearings, and selected components for diesel engines. Projected future applications include a broader range of reciprocating and gas turbine engine components, and electronic components. For each of these applications examples of use and the key properties of silicon nitride which enable enhanced systems performance will be discussed. Several materials developments which may broaden the range of applicability of silicon nitride based ceramics will be described.
Mg-Si-AI-O-N Glasses Prepared By Nitriding Cordierite Powders Derived from Polymer Precursors
Authors: Laine Richard M. , Bickmore Clint R. , Waldner Kurt F. , Mueller Brian L. , Estry Hal W.
Published: March 2011

We have previously reported the synthesis of cordierite polymer precursors directly from MgO, SiO2 and alumina.1 Removal of organics at 400°C in air and/or in oxygen gave amorphous, atomically mixed, oxide powders with surface areas of 250-400 m2/g. It is possible to convert these high surface area oxide powders to Mg-Si-Al-O-N powders by heating in a flowing NH3 atmosphere. The effects of selected processing conditions on nitrogen incorporation, in a set of well defined oxide powders, were examined. The powders are nitrided in flowing NH3, at temperatures of 700-1200°C, to obtain N contents of up to 5 atomic percent.
Microstructural Characterisation of Microwave Sintered Silicon Nitride Ceramics
Authors: Plucknett Kevin P. , Wilkinson David S.
Published: March 2011

The microstructure of a series of microwave sintered silicon nitride based ceramics have been assessed using a combination of optical microscopy/image analysis and analytical electron microscopy. Materials were studied as-received and after post-sinter hot-isostatic pressing. The grain size of microwave sintered materials was appreciably finer than conventionally processed ceramics of similar composition, although the mechanism involved is not clear. The as-received ceramics exhibited a reverse porosity gradient (with the highest porosity level at the surface) due to heat dissipation to the cooler surroundings during sintering. This also resulted in a small increase in the β′ grain aspect ratio close to the surface arising from an increase in the glass phase viscosity as the temperature decreases. Post-sinter HIPing of microwave sintered samples resulted in the elimination of most of the bulk porosity, but not near the surface. This is due to the reverse porosity gradient previously described, which leads to a transition from closed to open porosity with decreasing density near to the surface.
Elemental Analysis of Matrix Grain Boundaries in Sic Whisker Reinforced Si3N4 Based Composites
Authors: Liu J. , Chowdhury K. Das , Carpenter R. W. , Braue W.
Published: March 2011

The structures of SiC/Si3N4 interfaces and Si3N4 matrix grain boundaries in Ceramic Matrix Composites (CMC) were investigated by high resolution electron microscopy. The light element chemistry of the interfaces was analyzed by high spatial resolution (∼3 nm) position resolved EELS in a field emission TEM and by high spatial resolution EDS in a dedicated scanning transmission electron microscope (STEM). High-angle annular dark-field (HAADF) imaging (resolution < 1 nm) technique was used to determine the distribution of yttrium atoms at matrix grain boundaries and at SiC/Si3N4 interfaces. HAADF images suggest that yttrium might diffuse into Si3N4 crystals bounding the interfacial and grain boundary regions.
Reaction Sintering of β-Si3N4/α'-Sialon Ceramics
Authors: Boskovic S. , Lee K.J. , Tien T.Y.
Published: March 2011

Compositions in the α'-SiAlON-√-Si3N4 solid solution region in the system Si,Al,Y/N,O which contained a third phase as a sintering aid were prepared. Mixtures of starting materials were reaction sintered to full densities without applied pressure. Phases were identified and lattice parameters of β' and √ph ases were measured and compared with standards. The results were used to construct β'-SiAION-√-Si3N4 solidsolution tie lines in the two phase region. As expected, the specimens with a higher β'-SiAION content showed higher hardness and lower toughness values.
Phase Relationship Studies of Silicon Nitride System—A Key to Materials Design
Authors: Yen T.S. , Sun W.Y.
Published: March 2011

Additions and revisions to several of the most important phase diagrams and phase behavior diagrams in the silicon nitride field are reviewed in this work, with emphasis on the Y-Si-A1-O-N system. This information is further used to make observations on the promising silicon nitride systems containing either highly refractory grain boundary phases or compatible matrix phases of desirable properties. Examples are provided to illustrate the advantage of such a basic approach to materials design. Hardness, toughness, strength at room temperature and elevated temperature and even sinterability can all be improved by adopting such an approach.
The Effect of Glass Chemistry on the Microstructub and Properties of Self Reinforced Silicon Nitride
Authors: Pyzik Aleksander J. , Carroll Daniel F. , Hwang C. James
Published: March 2011

The advantage of self-reinforced silicon nitride is the in-situ control of the microstructure. This control is provided in large degree by the chemistry of glassy phase which can be adjusted to tailor the morphology of silicon nitride grains as well as the matrix - reinforcement interface. The presence of high aspect ratio silicon nitride grains is necessary but not sufficient condition to produce materials with optimum properties. For maximum flexure strength and fracture toughness an optimized glass matrix is required.
Characterization of Hot-Pressed Silicon Nitride Ceramics with Alkoxide-Derived Oxide Mixtures As the Sintering Aid
Authors: Sato Y. , Sakurai C. , Ueki M. , Sugita K.
Published: March 2011

A homogeneous mixture of Y2O3, CeO2 and MgO with a final weight ratio of 3:1: 2 was prepared by the alkoxide method. The powder mixture was then added into Si3N4 powder in amounts ranging from 4 to 12 wt%, andconsolidated by hot-pressing. Microstructure and mechanical properties of the sintered bodies were determined and compared to those of materials prepared by the conventional route of mixing the oxide powders as sintering aids individually in essentially same composition. The β-fraction (modification ratio) in same composition was higher in thesintered bodies made through the alkoxide method than those made through the conventional one. The room temperature flexural strength was maximized with 6wt% addition of the alkoxide derived oxide, whereas, 12wt% addition of the total oxide was required to maximize the strength by conventional processing.
Direct Observation of Microstructure Change During Densification of Silicon Nitride Ceramics with A Novel Characterization Method
Authors: Iwamoto Y. , Nomura H. , Sugiura I. , Tsubaki J. , Takahashi H. , Ishikawa K. , Shinohara N. , Okumiya M. , Yamada Y. , Kamiya H. , Uematsu K.
Published: March 2011

A novel characterization method is applied to study the evolution of microstructures during densification of silicon nitride ceramics. This characterization method involves an immersion liquid for making green and sintered bodies transparent, and a subsequent direct optical microscopic examination. Granules were prepared with the spray drying processand formed into green bodies by CIP. After sintering at various temperatures, the specimens were examined for microstructural evolution. Large pores were located at the center and boundary regions of granules left in the green bodies; they were not removed by densification and resulted in large pores in the sintered body, possibly forming fracture origin in ceramics.
Acoustic Emission Study of Si3N4
Authors: Subbarao E. C. , Srikanth V. , Walck J. C. , Tarry C. A.
Published: March 2011

Sintered Si3N4 (with 2 w/o A12O3 and 6 w/o Y2O3) was studied by acoustic emission method during indentation testing and during heating to and cooling from 920ºC in air. The acoustic emission activity was discontinous and its magnitude and duration increased with load applied during indentation testing. Intense acoustic emission signals were detected on cooling Si3N4 ceramics to temperatures below 590ºC, particularly below 450ºC. X-ray diffraction studies showed the presence of SiO2 (Quartz) after heating the sample to 920ºC during acoustic emission study, compared to single phase β Si3N4 before the heat treatment.
High Temperature Fatigue Properties of Silicon Nitride in Nitrogen Atmosphere
Authors: Shigegaki Yasuhiro , Inamura Takashi , Suzuki Akihiko , Sasa Tadashi
Published: March 2011

Cyclic and static fatigue properties of pressure-less sintered silicon nitride were evaluated at 1000° C in air and in nitrogen using four-point bending mode. The data of cyclic fatigue tests or static fatigue tests and the morphology of the fractured surfaces in nitrogen were compared with those in air. The cyclic fatigue behavior was remarkably influenced by the atmosphere, while the static fatigue was less influenced. Crack healing effect due to the oxidation around the crack are thought to be the most probable mechanism to affect the cyclic fatigue rate in air.
Studies on Si3N4 Ceramic Cutting Tool Materials and their Applications
Authors: Miao He-Zhuo , Qi Long-Hao , Ma De-Jin , Jiang Zuo-Zhao
Published: March 2011

Si3N4 ceramics are excellent metal cutting materials. The cutting behavior can be improved by hard particle dispersion phase hardening and heat treatment so as to reduce glass phase in the grain boundaries. Compared with cemented carbide tools, the cutting life of the composite Si3N4 cutting tool is about 10-100 times longer, and the optimum cutting speed is about 3-10 times faster. It performs well in cutting hardened tools, nickel based alloys, and other hard materials and can sustain shock loads in operations such as milling, planing and other types of interrupted cutting. Applications in various fields show that machining efficiency can be increased by 3-10 times resulting in savings of time, electricity, and machining of 30-70% or even more.
Development of Advanced Silicon Nitride Valves for Combustion Engines and Some Practical Experience on the Road
Authors: Hamminger Rainer , Heinrich Juergen
Published: March 2011

One major goal of automotive engineers actually is to reduce fuel consumption and emissions of present internal combustion engines. First promissing results have been achieved by the substitution of conventional by silicon nitride valves. The weight reduction of about 60 % per valve is corresponding with lower inertia and spring forces, which lead to improved emissions, reduced fuel consumptions as well as high performances of the engines. Applying statistical methods, two advanced silicon nitride materials have been developed, concerning their application as “cool” inlet valves and “hot” exhaust valves, respectively. Using high quality powders and combined optimum processing parameters, 4-point-bending strength of more than 1200 MPa (room temperature) and 870 MPa (1000 °C), resp., have been realized. Weibull moduli of more than 30 have been reproduced. Grinding of valves produced from these materials has economically been demonstrated by drastically reducing the machining times. Some results of road tests as well as of simulated engine tests from cooperations with different automotive companies are presented in detail.
Structure and Corrosion Properties of Pvd Coatings in the System Si-AL-O-N
Authors: Knotek Otto , LÖffler Frank , Beele Wolfram
Published: March 2011

Si-Al-O-N ceramics, especially β′-Sialon, are well known as a material offering a very good resistance against aggressive media combined with a good thermal shock behaviour. This combination recommends the Si-Al-O-N ceramics also as coating for products used in applications with high thermal gradients plus corrosion attack.

Therefore this paper presents new developments in the deposition of Si-Al-ON, especially in combination with the aircraft alloy TiAl6V4 as substrate. Investigations of the coating structure in dependence on the deposition parameters were done and the resistance against oxidation and attack of H2SO4 containing media were examined.
Microstructure and Flow Behaviior of Fresh Cement Paste
Authors: Jiang W. , Roy D.M.
Published: March 2011

Characteristics of aqueous cement suspensions and the packing nature during setting were investigated as keys controlling the microstructure and density of a cement paste. The theological properties of the paste were studied as functions of hydration and setting; these properties are influenced by a variety of external factors, which are discussed. The objective of this paper is to sketch a new atomistic approach to a group of rheological phenomena which are as interesting from a scientific viewpoint as they are important for technology. The experiments were carried out by a HAAKE rheometer and an acoustic ultrasonic system. At different flow state, the acoustic emission signal generated from micro-structure is transformed due to wave propagation and due to the transducer response. The scientific information obtained through this study is expected to contribute the establishment of concept of setting processing. The measurements of flow properties relating to flocculation and coagulation were evaluated with respect to the effects of processing conditions on structure development in cement paste.
Cement Viscosity As A Function Of Concentration
Authors: Struble Leslie J. , Sun Guo-Kuang
Published: March 2011

The Krieger-Dougherty equation allows calculation of viscosity as a function of volume fraction for suspensions of noninteracting particles. For model suspensions (of spherical, monosized particles), it has been shown to provide excellent agreement between calculated and measured viscosities. In the present study, this equation was applied to portland cement pastes, also with good correlations between calculated and measured viscosities. Because cement has a broad particle size distribution and its particles are angular and elongated, the two constants in this equation (the maximum volume fraction and the intrinsic viscosity) were estimated using nonlinear optimization techniques. The equation provides an excellent fit to measured viscosity data. However, the nature of the equation makes the estimation somewhat difficult, and the solutions are not well-defined.