bluuebunny/crossref_metadata_2025 huggingface dataset:
Growth of Epitaxial ZnS Films by Pulsed-Laser Ablation
Authors: McCamy J. W. , Lowndes D. H. , Budai J. D. , Chakoumakos B. C. , Zuhr R. A.
Published: March 2011

Pulsed KrF (248nm) laser ablation of a polycrystailine ZnS target has been used to grow high quality, carbon-free, epitaxial ZnS thin films on GaAs(OOl), GaAs(111), and GaP(OOl). The films were grown at temperatures of 150–450°C, using a rotating substrate heater and deposition geometry that produces films with highly uniform thickness. X-ray rocking curves are consistent with (111) stacking faults being the dominant defects in the ZnS films grown on GaAs. The estimated stacking fault density is ∼6 × 1010 cm-3, comparable to the best MOCVD ZnS films. RBS analysis shows that these defects are located predominantly near the GaAs-ZnS interface. The anisotropy of the ZnS growth rate, between the GaAs(001) and GaAs(111) surfaces, was found to be temperature-dependent.
Synthesis, Structural and Optical Characterization of Zinc Chalcogentdes in Novel Solid State Hosts
Authors: Moran Kelly L. , Ott Andrew W. , Gier Thurman E. , Harrison William T. A. , Eckert Hellmut , Stucky Galen D.
Published: March 2011

Several series of sodali te analogues of unit cell composition M8X2(TO2)12, where M is Zn or Cd, X is a chalcogen, and T is a tetrahedral cation B, or Be in combination with Si or Ge, have been prepared. An M4X tetrahedron, which is the first coordination sphere of the bulk semiconductor MX, sits at the center of each sodalite cage. These materials have been structurally characterized by solid state 77Se and 125STe MAS NMR and by powder X-ray diffraction. Diffuse reflectance optical absorption spectra are reported for each series. The borates have optical properties similar to the bulk MX whereas the beryllosilicates and germanates exhibit large blue shifts in the absorption spectra.
Optical Transitions on CdS/CdTe CVD Heterostructures
Authors: Boemare Claude , Nazare M H
Published: March 2011

Wide-band gap II-VI semiconductors have direct bandgaps which cover the energy range from the red to the u-v. This makes such compounds ideal for optoelectronic applications. CdS has a band gap of 2.42 eV and becomes potentially useful for the green region of the spectrum. However, because CdS has a preference to adopt the hexagonal wurtzite structure, epitaxial growth of this semiconductor is complicated. Nevertheless succesful growth of CdS layers onto CdTe is possible. We report a detailed photoluminescence study of CdS/CdTe heterostructures grown by CVD. The CdS layers have high quality hexagonal structure. Luminescence lines are narrow enough and we could detect a splitting ocurring on the excited state of a neutral acceptor bound exciton, at 2.5462 eV.
Remote Ecr Plasma Deposition of Diamond Thin Films from Water-Methanol Mixtures
Authors: Singh R. K. , Gilbert D. , Tellshow R. , Koba R. , Ochoa R. , Simmons J. H. , Holloway P. H. , Rodgers J. , Buckle K.
Published: March 2011

We have applied an electron cyclotron resonance technique to deposit diamond thin films on various substrates under remote plasma, low temperature (600°C) and low pressure (60 mTorr) conditions. Diamond films were grown on different substrates (silicon, molybdenum) with varying concentrations of precursor gases (methanol and water). A positive substrate bias (50 to 60 V) was found to be essential for the growth of diamond films onto substrates positioned 16 cm below the ECR plasma. The films were characterized by Raman, X-ray diffraction and scanning electron microscopy for microstructure, phase purity and chemical bonding characteristics. The effect of various processing parameters including gas pressure, gas composition, substrate temperature and bias have also been analyzed.
Self-Compensation and Doping Problems in ZnSe
Authors: Laks David B. , Van de Walle Chris G.
Published: March 2011

We examine native-defect compensation, solubility limits, and dopant self-compensation in ZnSe. Our results are based on a formalism, using first-principles density-functional theory, that treats dopant atoms and native defects on an equal footing. For the case of acceptor doping of ZnSe with Li, we find that compensation due to interstitial Li donors and to native donor defects can be reduced to a tolerable level by carefully adjusting the growth conditions. A more serious impediment to Li doping comes from the solubility limit of Li in ZnSe.
A Comparison of the Wurtzite and Zincblende Band Structures for SiC, AlN and GaN
Authors: Lambrecht W. R. L. , Segall B.
Published: March 2011

Total energy and band structure results of linear-muffin-tin orbital calculations within the atoiuic-spliere-approxiiuation are presented for SiC, GaN and A1N in the zincblende and the wurtzite structure. We discuss the origin of the directness or indirectness and the relative magnitudes of the band gaps.
Deposition of Flame Grown Diamond Films in a Controlled Atmosphere
Authors: Doverspike Kathleen , Butler James E. , Freitas Jaime A.
Published: March 2011

Polycrystalline diamond films were synthesized both by using an open atmosphere combustion flame, and also using a combustion flame in an enclosed chamber. By operating the pre-mixed oxy-acetylene torch in a chamber, we were able to vary the atmosphere around the flame in a controlled manner and study the effects on the diamond films. Varying the atmosphere around the flame is of interest to control the incorporation of unwanted gases, such as room air, and to obtain finer control over the flame properties. We report on the properties of films grown in the open atmosphere and in the chamber with oxygen and argon.
The Einstein Relation in Superlattices OP Wide-Band Gap Semiconductors Onder Cross-Field Configuration
Authors: Ghatak Kamakhya P. , De Badal
Published: March 2011

in this paper we study the Einstein relation in superlattices of wide-band gap semiconductors under crossfield configuration and the for.-ning materials incorporating spin and broadening of Landau levels, it is found, taking GaAs/AÀAs superlattice as an example that the diffusivity-mobility ratio increases with increasing electron concentration and oscillates with inverse quantizing magnetic field due to SdH effect. Thetheoretical analysis is in agreement with the suggested experimental method of determining the same ratio in degenerate materials having arbitrary dispersion laws.
Conductivity Control of AlGaN. Fabrication of AlGaN/GaN Multi-Heterośtructure and their Application to UV/Blue Light Emitting Devices
Authors: Akasaki I. , Amano H.
Published: March 2011

The method for controlling the electrical properties of n-type GaN and AIGaN have been established. Both GaN and AIGaN films having p - type conduction have been realized for the first time. High quality AIGaN/GaN mu I t i-he t er ostrueture showing clear quantum size effect has been fabricated. P-n junction type UV/blue LED with double he t e ros t rue ture have been developed for the first time.
Systematic Studies on Magnetron-Sputtered Indium Nitride
Authors: Bryden W. A. , Ecelberger S. A. , Morgan J. S. , Poehler T. O. , Kistenmacher T. J.
Published: March 2011

Extensive and systematic studies on reactive magnetron sputtering of InN thin films are summarized. The films have been deposited onto several types of substrates, with variations in such process parameters as deposition temperature, partial pressures of reactive and inert gases, sputtering power and gas flows. These films have been characterized by measuring their electrical, optical, structural and morphological properties. It has been shown that epitaxial growth of InN occurs on the basal plane of single-crystal (00.1) sapphire and (001) mica substrates and on the (111) face of cubic substrates such as silicon and zirconia.

Two principal problems currently limit the usefulness of thin films of InN. First, although epitaxy can be attained with the proper choice of substrate type and deposition temperature, the resulting film is an agglomerate of epitaxial grains -- not a single crystal. Second, all magnetron sputtered InN films prepared to date have low mobility and high carrier concentration (likely due to nitrogen vacancies). In an attempt to address these problems, experiments on the growth and characterization of sputtered InN films have been carried out and are discussed here with particular emphasis on seeded heteroepitaxial growth and the effects of film deposition temperature.

For example, it was found early that the growth of InN on the bare surface of several crystalline substrates at growth temperatures near 350°C results in a morphological transition that causes a degradation of semiconducting properties. The predeposition of an AIN seed layer inhibits this morphological transition and stabilizes a relatively high mobility state, but a still too high carrier concentration obtains. Further progress critically depends on optimizing the seeded heteroepitaxial growth technique in conjunction with the achievement of InN films with lower density of nitrogen vacancies.
A Comparative Study of GaN Epitaxy on Si(001) and SI(111) Substrates
Authors: Lei T. , Moustakas T. D.
Published: March 2011

Epitaxial GaN films were grown on Si(001) and (111) substrates, using a two-step process. The films on Si(001) are single crystalline having the zincblende strucutrue, while those on Si(111) have the wurtzite structure. The crystalline qualities of the films were studied by X-ray diffraction. While the zincblende GaN has a perfect cubic structure, the wurtzitic GaN on Si(111) has a considerable amount of stacking faults along (0002) direction, which gives rise to significant zincblende component with (111) orientation. Room temperature resistivity for both type of GaN films was found to be larger than 100 Ω· cm. The temperature dependence of th resistivity gives a defect level at HOmeV for wurtzitic GaN and 80meV for cubic GaN. Optical studies show that GaN on Si(001) has a gap 3.2eV, and GaN on Si(111) has a gap of 3.4eV at room temperature.
Growth Dependence of Thickness, Morphology and Electrical Transport of InN Over Layers on Ain-Nucleated (00.1) Sapphire
Authors: Kistenmacher T. J. , Ecelberger S. A. , Bryden W. A.
Published: March 2011

The seeded-heteroepitaxial growth, morphology and electrical transport properties of InN overlayers deposited by reactive magnetron sputtering on AIN-nucleated (00.1) sapphire have been investigated. For comparison, InN films were grown directly onto (00.1) sapphire under identical experimental conditions. These unseeded films showed a unimodal growth and were a mixture of textured and broadly heteroepitaxial grains. Low Hall mobility and carrier concentration and high resistivity were typical. In contrast, the AIN-nucleated InN overlayers exhibited a bimodal growth, strongly heteroepitaxial grains, and high Hall mobility. A particularly interesting aspect of the films grown on seeded (00.1) sapphire is the preservation of electrical continuity and high Hall mobility even in the limit of InN overlayers with thicknesses only on the order of 20–40Å.
Epitaxial Growth of AlN on 3C-SiC and Al2O3 Substrates
Authors: Sywe B. S. , Yu Z. J. , Edgar J. H.
Published: March 2011

A1N films were grown on the (100) plane of 3C-SiC/Si and the (0001) plane of A12O3 substrates by metalorganic chemical vapor deposition (MOCVD) using trimethylaluminum (TMA) and ammonia (NH3) as the precursors. The deposited films were characterized by X-ray diffraction (XRD) and a Read thin film camera. At 1150°C, preferentially oriented polycrystalline AlN films were obtained on both substrates and the crystal structure was wurtzite. The epitaxial relations were (1010)AlN//(100)SiC//(100)Si and (0001)AlN// (0001)Al2O3. The attempt to grow cubic AlN on 3C-SiC/Si was not successful.
Electrical Properties of Thermally Grown SiO2-SiC Interfaces
Authors: Singh Nitya N. , Rys A. , Ahmed A. U.
Published: March 2011

Fabrication processes of metal-oxide semiconductor (MOS) capacitors on n-type, Si-face, 6H-SiC were studied. The effects of thermal oxidation conditions at temperatures between 1100 and 1250°C on the electrical properties of MOS capacitors were determined. The wafers were annealed under argon to improve the C-V characteristics. C-V characteristics of AI-SiO2-SiC metal-oxide-semiconductor were measured at high frequency in the dark and under illumination. In the dark inversion does not occur, probably owing to the absence of minority carriers due to the large band gap of 6H-SiC. The accumulation, depletion, and inversion regions were clearly observed when the C-V measurements were made under illumination for both wet and dry thermally grown oxides. The interface trap densities and emission time constants of fast states were determined by ac conductance measurements. From the analysis of data we obtained a total of Fixed charges and the slow interface traps, Nf + NssSlow of 1.5 to 3.3 × 1012 cm-2, fast interface trap densities, NssFast of 0.5 to 1.7 × 1011 cm-2 eV-1 and emission times constant of 0.3 to 1.4 μsec for wet oxidation. For dry oxidation, Nf + N, ssSlow of 3.5 to 11.2 × 10cm-2, NssFast of 0.7 to 1.25 × 1010 cm-2 eV-1 and emission time constants of 0.6 to 2 μsec were obtained.
Submillimeter Optical Properties of Hexagonal Boron Nitride
Authors: Gatesman A. J. , Giles R. H. , Waldman J.
Published: March 2011

The submillimeter optical properties of hot-pressed boron nitride with a hexagonal crystal structure were studied at room temperature from approximately 20 cm-1 to 120 cm-1 (500μm -84 μm) with a Fourier Transform Spectrometer. Several grades were studied and probed both parallel and perpendicular to the material's optic axis. The material was found to behave as a negatively uniaxial birefringent crystal. In one case, the birefringence (Δ = ne - no) was quite large with a value of-0.152. The material's absorption properties were also studied. For certain grades, a modest dichroism was observed. The low absorption (α < 1 cm-1) for grade A at frequencies below 38 cm-1 suggests the possibility for millimeter/submillimeter wave applications. Results are compared with data by other researchers on related materials.
Effects of Reactive Sputtering Parameters on the Growth and Properties of Acoustooptic ZnO Films
Authors: Jacobsohn E. , Shechtman D.
Published: March 2011

1 μm ZnO films were deposited on SiO2 by reactive sputtering using a D. C. magnetron gun. The microstructure, orientation and chemistry of the deposited layers were examined. It is shown that the oxygen partial pressure plays an important role in the structure of the layer through a mechanism of surface diffusion.
Effect of Laser Irradiation on Carbon-Implanted Copper Substrates
Authors: Singh Rajiv K. , Viatella John
Published: March 2011

We have analyzed the non-equilibrium thermal effects of pulsed nanosecond lasers on carbon-implanted copper substrates. The thermal effects of pulsed nanosecond lasers were simulated by numerically solving the heat flow equation and taking into account the phase changes which occur at the surface of the irradiated solid. Intense pulsed laser irradiation induces rapid heating at the near surface resulting in melting, followed by rapid quenching of the melt phase. The effect of laser variables (energy density, etc.) on the maximum melt depth, melt-in and solidification velocities and transient temperature profiles have been computed. Maximum melt depths and the surface temperatures were found to increase approximately in a linear manner with pulse energy density. Extremely high average solidification velocities (20–45 m/sec) were calculated which may give rise to solute trapping and other non-equilibrium segregation effects. The change in laser-irradiated characteristics of copper substrates as a result of carbon-ion implantation is also discussed.
Preparation of Pb-Based Ferroelectric thin films by Ion- and Photo-Assisted Deposition
Authors: Hayashi Shigenori , Iijima Kenji , Hirao Takashi
Published: March 2011

Thin film process for Pb-based perovskite ferroelectrics has been investigated. Synthesis of epitaxial PLZT, PLT and PZT thin films by rfmagnetron sputtering in our laboratory was reviewed. Basic thin film process and applications were discussed. For further investigation, film preparation process was developed by co-deposition and assisted deposition techniques. The substrate temperature required for in-situ preparation of perovskite could be reduced to room temperature by an ion- and photoassisted co-evaporation technique.
Ferroelectric PbZrxTi1-xO3 Thin Films Grown by Organometallic Chemical Vapor Deposition
Authors: Dormans G.J.M. , de Keijser M. , Veldhoven P. J. van
Published: March 2011

For the successful integration of ferroelectric thin films in IC technology, there is a need for a deposition technique capable of growing homogeneous layers at high growth rates over large-area structured substrates. Organometallic chemical vapor deposition (OMCVD) is a promising technique for meeting these demands.

Ferroelectric layers of PbZrxTi1-xO3 (PZT) were grown by OMCVD on Pt-coated 10 cm diameter Si-substrates using the precursors tetra-ethyl-lead, tetra-iso-propoxy-titanium and tetra-tertiary-butoxy-zirconium at 700 °C without any post anneal. At this temperature the layers are single phase and highly (h00) and/or (00l) oriented. The layers show good ferroelectric switching properties with high remanent polarizations, but also with high coercive field strengths. Fatigue measurements are presented for these OMCVD grown PZT layers. The layers have a switching lifetime exceeding 1011 cycles at a switching amplitude of 5 V.
Spectroscopic and Microstructural Characterization of Solution Chemistry Effects in Pzt Thin Film Processing
Authors: Schwartz Robert W. , Ink R. A. Ass , Headley T. J.
Published: March 2011

Ferroelectric PZT 53:47 thin films were prepared by two different solution deposition methodologies. Both routes utilized carboxylate and alkoxide precursors and acetic acid, which served as both a solvent and a chemical modifier. We have studied the effects of solution preparation conditions on film microstructure and ferroelectric properties, and have used NMR spectroscopy to characterize chemical differences between the two precursor solutions. Films prepared by a sequential precursor addition (SPA) process were characterized by slightly lossy hysteresis loops, with a Pr of 18.7 μC/cm2 and an Ec of 55.2 kV/cm. Films prepared by an inverted mixing order (IMO) process were characterized by well saturated hysteresis loops, a Pr of 26.2 μC/cm2 and an Ec of 43.3 kV/cm. While NMR investigations indicated that the chemical environments of both the proton and carbon species were similar for the two processes, differences in the amounts of by-products (esters, and therefore, water) formed were noted. These differences apparently impacted ceramic microstructure. Although both films were characterized by a columnar growth morphology, the SPA derived film displayed a residual pyrochlore layer at the film surface, which did not transform into the stable perovskite phase. The presence of this layer resulted in poor dielectric properties and lossy ferroelectric behavior.
Structural and Electrical Properties of BaTiO3 Thin Film Capacitors
Authors: Shi Z.Q. , Jia Q.X. , Anderson W.A.
Published: March 2011

Thin film BaTiO3 capacitors were deposited by RF magnetron sputtering. The leakage current was suppressed by more than 3 orders of magnitude if a trace of hydrogen was introduced into the sputtering chamber during film deposition. The introduction of hydrogen gas during sputtering makes the dc conductivity as low as 1×10−13 (Ω−cm)−1 for the amorphous films but still gives the dielectric constant a value of around 17. However, this accomplishment could not be achieved for polycrystal BaTiO3 thin film capacitors. As the substrate temperature increased from room temperature to 700°C, the dielectric constant was increased from 16 to 300 by using Ar + O2 gas. But, the dielectric constant was only around 30 at a deposition temperature of 700°C while the leakage current was decreased when using a gas mixture of Ar + H2 + O2 during sputtering.
Electrochemical Preparation of Barium Titanate Films at Ultra-Low Temperatures
Authors: Venigalla S. , Bendale P. , Ambrose J.R. , Verink E.D. , Adair J.H.
Published: March 2011

Preparation of BaTiO3 thin films on titanium substrates by hydrothermal-electrochemical methods at temperatures ranging from 80 to 200°C have recently been reported in literature. In the present work, polycrystalline, homogeneous, and electrically insulating films of BaTiO3 have been electrochemically synthesized at temperatures as low as 55°C. Effects of various electrochemical and thermodynamic parameters such as temperature, solution pH, electrolyte composition, current density, and atmosphere on phase stability and film characteristics have been investigated. Formation of BaTiO3 is favored only under highly alkaline conditions. This finding is consistent with the reported phase stability criteria for BaTiO3 in Ba-Ti-CO2-H2O system. Auger spectroscopic analyses with depth profiling indicate a titanium oxide layer, whose thickness depends on current density, acts as a precursor to BaTiO3. Use of highly oxidizing atmospheres promotes the formation of thick, well-crystallized and electrically insulating films of BaTiO3 at low temperatures. Films synthesized at 55'C exhibit a characteristic bilayer structure consisting of a large grained porous top layer above a fine grained and dense bottom layer. In contrast, the films prepared at higher temperatures are uniform, fine grained but porous. Preliminary experiments indicate the feasibility to electrochemically synthesize BaTiO3 at temperatures near 25°C.
Modeling of Hysteresis Properties of Lead Zirconate Titanate Thin Films
Authors: Yoo In K. , Desu Seshu B.
Published: March 2011

It is proposed that the polarization reversal mechanism in ferroelectric ceramics such as titanates is controlled by nucleation, growth, merging and shrinkage of ferroelectric domains. These domain phenomena are in turn determined by the nature of Barkhausen jumps, internal electric field, and dielectric relaxation times of the dipoles. Based on the proposed polarization reversal mechanism, a quantitative model was developed for simulating the hysteresis properties of lead zirconate titanate (PZT) thin films. The simulated hysteresis loops are in good agreement with the experimental results.

It was observed that dielectric viscosity, which is very useful in understanding fatigue and aging behavior of PZT thin films, is one of the key parameters that controls the hysteresis properties.
Crystallization Dynamics and Rapid Thermal Processing of PZT Thin Films
Authors: Chen Jiayu , Brooks Keith G. , Udayakumar K.R. , Cross L. Eric
Published: March 2011

The crystallization process of PZT thin films has been studied in situ by means of Environmental Scanning Electron Microscopy ( ESEM ). Based on the ESEM observations, the Rapid Thermal Processing (RTP) technique has been employed to crystallize ferroelectric thin films. Various annealing temperature-time combinations were investigated; the results indicate the crystallization process to be very fast. X-ray diffraction data shows the crystallization to be complete in 10 seconds at 600°C, and in 1 second at 700°C. In comparison with conventionally furnace processed films, the RTP films have comparable ferroelectric and dielectric properties, but are distinguished by superior breakdown strengths and morphologically smoother surface. The relation between microstructure of films and crystallizing parameters has been studied.
Analyses of Pt/Ti Electrodes for Plzt Capacitors
Authors: Olowolafe J. O. , Jones R. E. , Campbell A. C. , Maniar P. D. , Hegde R. I. , Mogab C. J.
Published: March 2011

A suitable choice of an electrode material is important for an acceptable electrical contact to a high-permittivity dielectric, such as PLZT. A material which does not form a low-permittivity oxide is necessary, since these dielectrics generally require high temperature deposition or annealing in an oxidizing environment. Platinum, which is one of the few metals that satisfy this requirement, has been widely employed for contacting PLZT. However, for integrated circuit applications, an adhesion layer must be superposed between Pt and the substrate, and Ti is used frequently. Therefore, we have investigated the Pt/Ti combination to determine its suitability as an electrode for contacting PLZT. Using x-ray diffraction, Rutherford backscattering spectrometry, Auger electron microscopy, and scanning electron microscope techniques, interdiffusion of Pt/Ti bilayers has been investigated. Pt/Ti films with or without PLZT overlay were annealed in either O2 or N2 ambients or in N2 followed by O2. Annealing temperatures varied from 500 to 800 °C. It was observed that the anneal ambient has a marked effect on the interdiffusion processes, the reaction products, the morphology of the structures, and the crystallization of PLZT.
Integrated Piezoelectric and Pyroelectric Devices from Thin Film Ferroelectrics
Authors: Sayer M. , Kumar C.V.R. Vasant , Barrow D. , Zou Li , Amm D.T.
Published: March 2011

Thin PZT films 1-4 μm in thickness prepared by sputtering or sol gel methods allow PZT films to be integrated with silicon technology to achieve piezoelectric or pyroelectric structures having small size or mass. Design criteria, materials and processing techniques for such devices are discussed, and the implementation of small size devices on silicon substrates is demonstrated. Factors of importance are the piezoelectric and pyroelectric characteristics achievable in the films, mechanical strength and fatigue, and the stability and compatibility of the films and electrodes with device fabrication procedures and operating conditions.
Ferroelectricity of Lead-Zirconate-Titanate Thin Films Prepared by Laser Ablation
Authors: Ogawa Toshio , Kidoh Hideo , Yashima Hideyuki , Morimoto Akiharu , Shimizu Tatsuo
Published: March 2011

Lead-zirconate-titanate films were prepared by excimer laser ablation. The coercive field of films deposited on MgO substrates with an electrode was lower than that of films deposited on sapphire substrates. Laser fluence influenced the grain and crystalline size, resulting in a change in the Ec. Film thicknesses were varied over a range from 0.3 to 2.41μm, with the thinnest film showing a large remanent polarization even at an applied effective voltage of 5V.
Preparation of Epitaxial BaTiO3 Thin Films by Plasma-Enhanced Metalorganic Chemical Vapor Deposition (Pe-Mocvd)
Authors: Chern C.S. , Zhao J. , Norris P. E. , Li Y.Q. , Gallois B. , Kear B. , Luo L. , Maggiore C. J. , Wilkens B. J.
Published: March 2011

The plasma-enhanced metalorganic chemical vapor deposition (PE-MOCVD) process has been successfully used to achieve high quality epitaxial growth of BaTiO3 thin films on (001) LaA103 and (001) NdGaO3 substrates at a substrate temperature of 680°C. The PEMOCVD system, which incorporates a 300-Watt microwave cavity, introduces excited species from an oxygen plasma to lower the required deposition temperature, as compared to thermal MOCVD growth of BaTiO3. X-ray diffraction (XRD) θ-20 scan patterns indicate that there are few randomly oriented grains and impurity phases in the epitaxial BaTiO3 films. Results of XRD ϕ-scans of the BaTiO3 (202) reflection show a modulation pattern of peaks every 90°, which demonstrates that the BaTiO3 thin films have no misorientation along the [100] and [010] directions of the substrates. An XRD ω rocking curve of the BaTiO3 (200) reflection had a narrow FWHM of 0.25°, indicating that the films have a high degree of preferred orientation of <100> perpendicular to the substrates. The high degree of epitaxial crystallinity is further confirmed by Rutherford Backscattering Spectrometry which gives a minimum yield of 7.5% and 11% for the films deposited on LaAIO3 and NdGaO3, respectively. Scanning electron micrographs show that these films have very smooth surface morphologies, which are desirable for device applications.
Lead Scandium Tantalate Thin Films for Thermal Detectors
Authors: Patel A. , Shorrocks N.M. , Whatmore R.W.
Published: March 2011

Thin films of lead scandium tantalate (Pb(Sc½Ta½)03) (PST) have been prepared by a novel modified sol-gel process. The process involves two deposition steps. In the first, layers of amorphous ScTaO4 are deposited by spin coating a solution of metallorganic compounds of scandium and tantalum. A film of lead oxide is then deposited onto the surface using a solution of lead acetate, and the process repeated to obtain thicker films. After firing the composite film, a pale yellow transparent film of PST is obtained. The films are highly orientated and 100% perovskite.

The film's electrical properties have been measured against field and temperature, showing a strong induced pyroelectric response (peak value of 3.8 x 10−3C/m2K), peak permittivities of 4500 and low loss. The figure-ofmerit of these films (11 x 10−5Pa−½) indicates a performance equivalent to conventional bulk ceramic pyroelectric wafers prepared by slicing, lapping and polishing of ceramic blocks.
Quantitative Determination of Er in Silica-Based Matrices
Authors: Oblas Daniel W. , Pink Francis , Singh Mahendra P. , Connolly Joseph , Dugger Donald , Wei T. Michael
Published: March 2011

The distribution and concentration of dopants in the core of an optical fiber, at low concentrations, particularly the rare earth dopants, are difficult to measure quantitatively. However, such information is critical to the determination of absorption cross sections of rare earth dopants in fiber amplifiers and the optimization of their performance. A number of different analytical techniques, such as secondary ion mass spectrometry (SIMS) and the electron probe microanalyzer (EPMA) were used here, along with prepared glass standards, to determine the Er concentration and distribution in optical fiber preforms containing Al, Ge and P. These results were compared with data obtained by neutron activation analysis (NAA) and x-ray fluorescence (XRF) which measure the average concentration of Er in the core. It has been shown that SIMS (and EPMA), in conjunction with NAA data can be used to establish, quantitatively, the Er concentration in the preform core, without the need for glass standards.
Excited State Absorption in Pr3+ Doped Fluorozirconate Glass
Authors: Quimby R. S. , Zheng B.
Published: March 2011

The excited state absorption (ESA) spectrum for Pr3+ doped ZBLAN glass is determined using a new technique based on the McCumber theory [D.E. McCumber, Phys. Rev. 136, A954 (1964)]. ESA peaks at 1380 and 840 nm are found, corresponding to transitions from the 1G4 to the 1D2 and 1I6 levels, respectively. ESA at the fiber amplifier pump wavelength 1.017 μm is found to be very small. The new method is also applied to Er+ doped glass, and good agreement is obtained between the resulting ESA spectrum and previous measurements using a traditional pump-probe technique.
The Role of Glass Composition in the Performance of Er3+-, Nd3+-, and Pr3+-Doped Fiber Amplifiers
Authors: Miniscalco W. J. , Pedersen B. , Zemon S. , Thompson B. A. , Lambert G. , Hall B. T. , Folweiler R. C. , Wei T. , Dakss M. L. , Andrews L. J.
Published: March 2011

The role of glass composition is examined theoretically and experimentally for fiber amplifiers. Simple analysis procedures can be used to set limits on performance and identify more favorable glass types for detailed investigation.
Polymeric Integrated Optics
Authors: Lösch Kurt H. , Kersten Peter , Wischmann Wiltraud
Published: March 2011

Since the realization of first polymer channel waveguides in the early 70ths and the market introduction of polymer fibres research work is aiming to increase the integration level of photonic circuits. This paper reports the state of the art in passive and active polymeric integrated optics in view of the requirements for practical applications in telecom and data processing systems.
Segmented proton exchange waveguide on LiNbO3 for SHG using simultaneous modulation of the indices and nonlinear coefficients
Authors: He Q. , Chen S. , Micheli M. P. De , Ostrowsky D. B. , Armani F. , Delacourt D. , Lallier E. , Papuchon M.
Published: March 2011

With proton exchange on LiNbO3 or LiTaO3 it is possible to fabricate waveguides presenting simultaneous modulation of the refractive indices and nonlinear coefficients. This allows us to realize a new kind of Quasi Phase Matching, and we will describe the first experimental results.
Low Loss Rib-Waveguides in SOI
Authors: Schmidtchen J. , Schüppert B. , Splett A. , Petermann K.
Published: March 2011

The realization of single-mode rib-waveguides with dimensions of several micrometers in Silicon-On-Insulator (SOI) is reported. The predicted monomode behaviour is confirmed by comparison of a simulated and a measured nearfield intensity distribution. Waveguide losses below 0.5dB/cm were obtained at wavelengths of 1.3μm and 1.55μm, respectively, independent of the polarization state.
A General Analytical Solution for the Concentration Profiles of Ion-Exchanged Planar Waveguides
Authors: Li Xiaoming , Johnson Paul F.
Published: March 2011

During the recent years, a great variety of ion-exchange processes, including one-step or two-step electric field assisted ion-exchange processes, have been developed to fabricate different kinds of passive planar glass waveguides, e.g., surface waveguides, which correspond to surface maximum concentration, or buried waveguides, which correspond to inside maximum concentration [1,2,3]. Theoretical calculation of ionic concentration distribution has been of interest since refractive index is generally a linear function of concentration. A general analytical solution to calculate both surface and buried concentration distributions from different ion-exchange processes, however, has not yet been presented. In addition, traditional ion-exchange has been carried out only with constant surface concentration boundary conditions. Little attention has been paid, either experimentally or theoretically, to ion-exchange processes with variable boundary conditions. In fact, the time-dependent surface concentration is experimentally observed for the ion-exchange of GRIN glass in molten salt bath [4]. Very recently, a novel one-step technique [5,6] involving electric field assisted ion-exchange of Na+ in glass by Ag+ from molten AgNO3 bath with decaying silver concentration has been developed to produce buried Ag+ concentration profiles in glass. As the accurate and reproducible processes are very important for fabricating ion-exchanged glass waveguides, theoretical modeling and analysis on the new process are needed.

In this paper, the one-dimensional field-assisted linear diffusion equation has been analytically solved by Laplace transformation to theoretically calculate concentration profiles produced by field enhanced ion-exchange process with exponentially decaying surface concentration boundary conditions. The applications of the solution to a variety of ion-exchange processes with different boundary or processing conditions for optical waveguide fabrication have been discussed. The theoretical results prove that the solution is a general analytical solution which can be used to calculate either surface concentration profiles or buried concentration profiles.
Picosecond Nonlinear Optical Response of Copper Clusters Created by Ion Implantation in Fused Silica
Authors: Magruder R. H. , Haglund R. F. , Yang L. , Wittig J. E. , Becker K. , Zuhr R. A.
Published: March 2011

We have embedded nm-size Cu clusters in optically dense, thin (∼ 150 nm) layers using standard ion implantation techniques. The size and size distribution of the clusters can be altered by varying such ion-implantation parameters as total dose and current density. The layers exhibit both a thermo-optic and an electronic nonlinear optical response, depending on the mode of laser excitation. The electronic nonlinearity has a response time no longer than 5 ps.
Optical Waveguides in Thermally Grown SiO2 on Si Using Nitrogen Ion Implantation
Authors: Wong S. P. , Pun E. Y. B. , Lam W. T. , Chung P. S.
Published: March 2011

Multi-energy nitrogen implantation into thermally grown SiO2 on silicon substrates has been performed and the optical wave-guiding properties of this structure has been studied. The implantation energy used was in Ie range of 40 KeV to 150 keV, and the doses used were typically 2×1016 to 2×10−2. The energies and doses were chosen to achieve relatively flat implanted nitrogen profiles. It is found that optical waveguides can be formed when the implanted nitrogen concentration is sufficiently high. Both prism-coupling technique and end-fire coupling technique were used to test the implanted waveguides fabricated. Many m-lines including dark modes were observed by the prism-coupling method. This structure is found to be very stable against thermal annealing and there is no significant change observed in the waveguiding properties even after annealing at 1000 °C for four hours. The waveguide loss was found to be typically 0.6 dB/cm before annealing and can be further reduced to about 0.3 dB/cm after annealing.
Cold Cap Grout Formulation for Waste Containment at DOE Site, Hanford, Washington
Authors: Wakeley Lillian D. , Ernzen James J.
Published: March 2011

WES developed a grout to be used as a cold (non-radioactive) cap or void-fill material between the solidified low-level waste and the cover blocks of near-surface disposal vaults at the U.S. Department of Energy (DOE) Hanford Facility. The project consisted of formulation and evaluation of candidate grout, followed by a physical scale-model test to verify grout performance under project-specific conditions and provide data to verify numerical models of stresses and isotherms inside the Hanford demonstration vault. Evaluation of unhardened grout included segregation, bleed, flow, and working time. For hardened grout, strength, volume stability, thermal heat rise, and geochemical compatibility with surrogate wasteform grout were examined.

The grout was formulated to accommodate unique environmental boundary conditions (vault temperature = 45 °C) and exacting regulatory requirements (mandating less than 0.1% shrinkage with no expansion and no bleeding); and to remain pumpable for a minimum 2 hr. A grout consisting of API Class H cement, an ASTM C 618 Class F fly ash, sodium bentonite clay, and a natural sand from the Hanford area met all performance requirements in laboratory studies.
Degradation of Portland Cements Exposed to Evaporite Brine at Hydrothermal Temperatures
Authors: Krumhansl James L. , Lambert Steven J.
Published: March 2011

The long-term integrity of cementitious materials is of interest where cement is used as part of the isolation system in underground workings sited in evaporite rocks. However, the slow rates of cement/fluid interactions at room temperature provide minimal guidance for predicting long-term cement behavior. To accelerate reactions that degrade cement, hydrothermal brine/cement interaction experiments were carried out at temperatures between 100° and 250° C. The pastes used in these experiments were two batches containing 65 (weight) % Class H cement and 35 % fly ash (one with Class C and one Class F, both with 10 mass equivalent % plaster), and one batch of Type K expansive cement, all with NaCl-saturated mix water. The brine used in testing was based on a composite representation of groundwaters from the Rustler formation of southeastern New Mexico, a mixed evaporite/clastic rock sequence. This brine was sufficiently concentrated that its use afforded an opportunity to study several mechanisms likely to degrade cement performance. At the conclusion of each experiment solid products were characterized and the coexisting fluids analyzed. In general, the cement was extensively altered by the brine at all temperatures assessed. In addition to the expected sulfate attack, it was found that magnesium effectively displaced calcium from the CSH gels that impart strength to cementitious materials. Sodium and potassium did not play a role in altering the cement.
Uptake of Metal Ions by Autoclaved Cement Pastes
Authors: Shi Caijun , Day Robert L. , Wu Xuequan , Tang Mingshu
Published: March 2011

This paper deals with the hydration products and pore structure of Portland cement (PC) and alkali-phosphorus slag cement (APSC) pastes, and the uptake of metal ions (Sr2+, Co2+, Cd2+, and Cu2+) in pastes which have been hydrated at 150°C for 25 days. Results indicate that the hydration products of PC are crystalline Ca(OH)2 and C2SH(A); for APSC the products are poorly crystallized low-basic CSH(B) and crystalline tobermorite. The PC pastes have a lower total porosity than APSC pastes, but the PC pastes consist mainly of larger pores with r> 1000Å, while the APSC pastes consist mainly of smaller pores with r< 100Å. The two types of paste were immersed for 19 days at room temperature in Sr2+, Co2+, Cd2+ and Cu2+ solutions with concentrations of 100, 200, 500 and 1000 ppm. It was found that all Ca(OH)2, in the PC pastes was dissolved. Except for Sr2+, the uptake of metal ions by PC paste is mainly due to the formation of insoluble hydroxides. The uptake of metal ions by APSC pastes is due to physical adsorption and the formation of some insoluble compounds. The APSC pastes show a stable structure after immersion in these metal ion solutions.
The Influence of Moisture on the Expansion of Macro-Defect-Free Cements
Authors: Igarashi H. , Takahashi T.
Published: March 2011

MDF(Macro-Defect-Free ) cement pastes, which consist of portland cement and polyvinyl alcohol/acetate, were prepared by varying the temperature during pressing and drying operations. We then examined the expansion of MDF cement pastes at various constant humidities. There was a large difference in expansion above 60%R.H. between samples prepared varying temperature at which samples were pressed. Samples pressed at 90 °C showed less expansion than samples pressed at 40 °C.

The pore structure of MDF cement pastes before exposure to moisture was measured by nitrogen adsorption, mercury intrusion porosimetry and image analysis. The properties of a matrix containing polyvinyl alcohol/acetate and cemnt hydrates were also investigated by TEM, IR and XPS.

There were not large differences in the result of IR and XPS measurement between the MDF cement pastes prepared at various temperatures. Calcium hydroxide crystal, lying perpendicular to cement particles, were often observed only in the MDF cement pastes pressed at 90 °C which occurs by water absorption, seems to be suppressed by calcium hydroxide crystal.
Processing-Property Interactions in Macro-Defect-Free Cements
Authors: McHugh A. J. , Tan L. S.
Published: March 2011

Relationships between mixing conditions, viscoelastic paste properties and flexural strength of hardened matrices have been investigated for an MDF cement. The correlation of paste relaxation times and matrix mechanical properties with mixing intensity suggests the build up and eventual breakdown of a network structure during mixing.
Gel-Cast Organic-Inorganic Systems
Authors: Maes K. , Silsbee M.R. , Roy D.M. , Adair J.H. , Scheetz B.E.
Published: March 2011

The studies reported herein were designed to develop a better understanding of the influence of different crosslinking agents on the polymerization of acrylamide gel systems and upon the resulting physical properties of the composites. Specimens were developed via a gel-casting process for viscoelastic and diametral tensile strength testing and the chemical reactions were monitored by Raman spectroscopy and isothermal calorimetry. The studies have demonstrated the ability to tailor the properties of a gel-cast system over a relatively wide range of reaction rates and the resulting mechanical properties by utilizing small adjustments to the overall chemistry of the system.
New Experimental Techniques for Characterizing Cement-Based Materials
Authors: Jennings Hamlin M. , Sujata K.
Published: March 2011

Materials science is the discipline of studying the relationships between structures and properties of materials. In the case of concrete as an engineering material most research has focussed on properties or on microstructure, but only modest progress has been made on establishing relationships between them. In other words a lot of work has been done in the area of strength, fracture toughness [1], shrinkage [2,3], creep and microcracking [2,4], and microstructure each as somewhat isolated subjects [5]. Microstructure has not been related to properties in a quantitative manner.
Investigation of Pozzolanic Binders Containing Calcined Laterites
Authors: Pera Jean , Ambroise Jean , Momtazi Ali Sadr
Published: March 2011

When heated at 750°C for five hours, African laterites show good pozzolanic activity. The kaolin content of the materials affects their pozzolanicity as indicated by lime reactivity. Blended cements containing 20, 30, 40, and 50% calcined laterite admixture were examined.

The rate of hydration was studied from compressive strength up to 90 days of curing and the hydrates formed as measured by DTA and XRD. The burnt laterite addition considerably reduced calcium hydroxide content and contributed to the formation of hydrated gehlenite (C2 ASH8) and gismondine (CASH).

The best compressive streng hs were obtained with blended cements containing 30% calcined laterite. In some cases, there was no more portlandite in binders where the replacement level of cement by burnt laterite was 50% by mass.
Impedance Spectroscopy and the Role of Admixtures in the Hydration of Portland Cement Pastes
Authors: Christensen Bruce J. , Mason Thomas O. , Jennings Hamlin M.
Published: March 2011

Measurements of the bulk electrical properties of cement pastes were made using impedance spectroscopy (IS) and are useful for studying hydration. Normalization of these quantities by dividing out changes in the pore fluid reveals information pertinent to the microstructural development of these materials. In this study, observations are made on the influence of accelerators, retarders and silica fume (SF) on pastes of white and ordinary portland cements (OPC). All systems show variations in the normalized electrical properties at the same degree of hydration, as compared to a control. Changes in the microstructure that are implied by these measurements are consistent with the observations of others.
A Chemical Image Analysis Method for Portland Cements
Authors: Diamond Sidney , Bonen David
Published: March 2011

A method is described for carrying out image analysis on portland cements in which the differing chemical compositions of the particles are specifically recognized. Representative fields of ca. 100 individual particles are imaged by a backscatter detector in an SEM, then ported to the attached image analyzer. After preliminary procedures, the image analyzer takes control of the SEM and individually rasters over each particle in turn to acquire both chemical (EDX) and geometrical information. The recorded EDX spectra are used to automatically assign each particle to its predominant mineralogical phase At the same time, conventional feature analysis parameters are acquired for each particle, including measurements of area, length, width, perimeter, shape, etc. The results of the analysis of a given cement constitutes a data base of all of the particles analyzed. It can be used to provide global characterization, or features can be broken out by size class, mineralogical type, shape, or various combinations of parameters. Illustrations are provided of the results of such analysis for a cement, and possible applications to clinker, cement paste, and concrete are considered.
Strength and Microstructural Properties of Water Glass Activated Slag
Authors: Qing-Hua Cheng , Tagnit-Hamou Arezki , Sarkar Shondeep L.
Published: March 2011

Slag as a supplementary cementitious material is known for its latent hydraulic properties. Thus, constant efforts are being directed towards improving its reactivity. This mostly involves the use of alkali salts. The authors present the results of alkali activation of a slag from Hamilton, Ontario, Canada, by means of water glass (Na2SiO3). Distinct improvement in early and late age strength was noted when water glass was used in combination with CH. The microstructure of this activated slag paste at 28 days is described. The microanalytical techniques used included SEM/EDXA, and XRDA.