bluuebunny/crossref_metadata_2025 huggingface dataset:
Integrated Optical Isolator Employing Nonreciprocal Phase Shift by Wafer Direct Bonding
Authors: Yokoi H. , Mizumoto T.
Published: April 2011

A novel configuration of an integrated optical isolator employing a nonreciprocal phase shift is proposed. The isolator is equipped with a cladding layer of magnetic garnets by means of wafer direct bonding technique. This device has a semiconductor guiding layer, so high compatibility in integrating with other semiconductor optical devices is expected.
Radiatively Coupled Waveguide Concept for an Integrated Magneto-Optic Circulator
Authors: Lohmeyer M. , Shamonin M. , Bahlmann N. , Hertel P. , Dotsch H.
Published: April 2011

Three-guide couplers with multimode central waveguides allow for remote coupling between optical channels. A simple three mode approximation turns out to be sufficient for the description of the main features of the power transfer behavior. The specific form of the relevant modes suggests the design of integrated optical isolators and circulators based on magnetic garnet materials. These novel devices are superior to conventional nonreciprocal couplers with respect to the total length and admissible fabrication tolerances. We characterize the isolation performance and the transmission loss for the proposed devices by propagating mode simulations and estimate the influence of geometry parameter deviations.
The Precipitation of the Nanoparticles by the Thermophoresis at the Cryogenic Temperatures
Authors: Khasanov O.L. , Pokholkov Yu.P , Krivobokov V.P. , Milovanova T.V.
Published: April 2011

The conditions of nanodispersed particles precipitation from a gas flow on the surface cooled to cryogenic temperatures are analyzed. The range of allowable values of precipitation surface temperature has been defined in dependence of dispersed flow characteristics. The method can be used both for catching of nanopowders, and for gas cleaning from aerosol and dust particles for ecological purposes.
Agglomerate-Free Silica-Tin Oxide Particles
Authors: Gellermann Carsten , Wolter Herbert , Storch Werner
Published: April 2011

Monodisperse silica-tin oxide particles of the core-shell type were prepared via a sol-gel process without formation of agglomerates. After synthesis of silica cores the surface was coated with tin oxide by controlled hydrolysis and condensation of tin(IV) tertiary butoxide. Particle properties were characterized by electron microscopy, dynamic light scattering, N2-sorption (BET), zeta potential and X-ray fluorescence analysis. As a consequence of the variable content of tin oxide numerous possible applications arise, for example introducing X-ray opacity in dental filling materials. In order to use such particles as fillers, an additional surface functionalization with 3-methacryloxypropyltrimethoxysilane was created matching the C=C-functional groups of the polymer resins, e.g. ORMOCER*s. Characterization methods such as diffuse reflectance infrared Fourier transform spectroscopy and elemental analysis were used to confirm the surface coverage.
Electrically Assisted Aerosol Reactors using Ring Electrodes
Authors: Briesen H. , Fuhrmann A. , Pratsinis S. E.
Published: April 2011

Nanostructured materials have distinctly different properties than the bulk because the number of atoms or molecules on their surface is comparable to that inside the particles creating a number of new materials and applications. Despite this potential for nanoparticles, very few practical applications have been developed because of the current high cost of these materials ($100/lb). On the other hand, flame aerosol reactors are routinely used for inexpensive production (∼$1/lb) of submicron sized commodities such as carbon blacks, pigmentary titania, fumed silica and preforms for optical fibers in telecommunications. Flame technology can be used also for synthesis of nanoparticles with precisely controlled characteristics. In these reactors, gas mixing is used to widely control the primary particle size and crystallinity of product powders while electric fields can be used to narrowly control the primary, and aggregate particle size and crystallinity. Here the application of axial electrical fields on a silica producing flame using hexamethyldisiloxane (HMDS) as precursor is presented. Experiments varying the precursor delivery rate corresponding to total production rates of 10, 20 and 30 g/h are presented. Electric fields decreased the particle size by electrostatic dispersion and repulsion of charged particles and by the reduced particle residence time inside the flame.
Physical Characterization of Zirconium Doped Zinc Oxide Thin Firms Deposited by Spray Pyrolysis
Authors: Maldonado A. , Acosta D.R. , De La Luz Olvera M. , Castanedo R. , Torres G. , Ortega J.Cañetas , Asomoza R.
Published: April 2011

Zinc oxide thin films doped with zirconium were prepared from solutions with doping material dispersed at several concentrations and using the spray pyrolysis technique.The films were deposited over sodocalcic glasses at different substrate temperatures. Effects of doping material concentration and substrate temperatures on electrical, optical, structural and morphological film properties are presented. Results show an evolution in morphology and grains size as the doping concentration is increased. Preferential growth in the (002) orientation was detected for each thin film from X ray diffractograms.
Novel Hollow Powder Porous Structures
Authors: Sypeck David J. , Parrish Phillip A. , Wadley Haydn N.G.
Published: April 2011

Recent finite element calculations [1] indicate that structures constructed from partially compacted hollow spheres exhibit a greater stiffness and strength than many other cellular structures at comparable density. It has been observed that gas atomization of metallic powders often leads to entrapment of the flow field gas [2]. The resulting hollow powders are an unwanted by-product in the sense that they lead to porosity and future sites of defect in solid parts. Here a method is developed to separate the hollow powders according to their size, shape and density. They are then consolidated to a porous structure. Examples of this are given for both a titanium alloy and a nickel-base superalloy. The compressive mechanical properties are measured and compared to those of other porous structures.
Superplastic Foaming of Titanium and Ti-6Al-4V
Authors: Dunand D. C. , Teisen J.
Published: April 2011

Solid-state foaming of metals can be achieved by hot-isostatic pressing of powders in presence of argon followed by expansion of the resulting high-pressure argon bubbles at ambient pressure and elevated temperature. This foaming technique was first demonstrated by Kearns et al. [1] for Ti-6Al-4V, but is limited by its low creep rate and ductility, which lead to early cell wall fracture. We address these issues by performing the foaming step under superplastic conditions. Rather than using microstructural superplasticity (requiring fine grains which are difficult to achieve in porous powder-metallurgy materials), we used transformation superplasticity, which occurs at all grain sizes by biasing with a deviatoric stress (from the pore pressure) of internal stresses (from the allotropic mismatch during thermal cycling about the allotropic temperature range). As compared to control experiments performed under isothermal creep conditions, superplastic foaming under temperature cycling of unalloyed titanium and alloyed Ti-6Al-4V led to a significantly higher pore volume fraction and higher foaming rate.
Lightweight Products with Metal Foam - Properties and Methods of Processing
Authors: Neugebauer R. , Brdunlich H. , Wagner U.
Published: April 2011

The aim of future production technology is the economic application of lightweight components with improved property profiles.

Demands for weight reduction made by both the automotive industry and the machine-building industry can be met through selective utilization of metal foam composite _ structures. To that end, basic investigations into material behavior and the machineability of metal foam composites are necessary.

The presentation will submit an overview of the properties and processing parameters of selected composites based on an analysis of industrial requirements. The development of analytical models of the process mechanics will contribute to the creation of preconditions for a numerical simulation of selected processes. Innovative applications and the potential for future use of metal foam composites in lightweight construction will be shown as well.

Finally, results from projects of the Fraunhofer-Institut für Werkzeugmaschinen und Umformtechnik together with industrial companies in Saxony will be presented.
Influence of Imperfections on Effective Properties of Cellular Solids
Authors: Grenestedt Joachim L.
Published: April 2011

The mechanical properties of cellular solids, or solid foams, is affected by “imperfections” such as wavy distortions of cell walls, variations in cell wall thickness, non-uniform cell shape, etc. The present paper is focused mainly on elastic stiffnesses of closed cell cellular solids. A “perfect” model is first discussed and shown to predict the behavior of PVC foams well. However, this model over-estimates the stiffnesses of aluminum foams. The relatively poor properties of the aluminum foam are believed to be caused by imperfections in the cells. The main body of the paper focuses on modeling different kinds of imperfections, and analyzing their impact on foam properties.
A Continuum Plasticity Model for the Constitutive Behaviour of Foamed Metals
Authors: Miller Ronald E. , Hutchinson John W.
Published: April 2011

A yield surface is proposed that can be fit to the plastic flow properties of a broad class of solids which exhibit plastic compressibility and different yield points in tension and compression. The yield surface is proposed to describe cellular solids, including foamed metals, and designed to be fit to three simple experimental results: (1) the compressive stress-strain response (including densification), (2) the difference between the tensile and compressive yield points and (3) the degree of compressibility of the foam, as measured by the lateral expansion during a uniaxial compression test. The model is implemented using finite elements and used to study the effects of plastic compressibility on two problems: the compression of a doubly notched specimen and indentation by a spherical indenter.
Elastic Properties of Porous Structural Ceramics Produced by Plasma-Spraying
Authors: Wanner A.
Published: April 2011

This study focuses on the relationship between porosity and elastic stiffness of structural ceramic materials produced by plasma-spraying. Mg-AI-spinel was chosen as a model material and studied in as-sprayed condition as well as upon annealing to increasingly higher temperatures up to 1650°C. The detailed analysis of the stiffness and mass density evolution offers a deep insight into the initial microstructural state of the material and into the morphological changes that occur upon heat treatment.
High Cycle Fatigue Properties of Aluminium Foams
Authors: Zettl B. E. , Stanzl-Tschegg S. E. , Gradinger R. , Degischer H. P.
Published: April 2011

Fatigue lifetime measurements have been performed on foamed Al-Mg-Si wrought alloys and Al-Si cast alloys in the high cycle range using an ultrasonic resonance testing method. The porous structure of the material is described by quantitative image analysis of optical micrographs and non destructively by X-ray computer tomography. The static mechanical properties as determined by tensile, compression and bending tests in earlier studies are used for material characterisation in this paper. The evaluation of the stress strain curves is specified for porous structures to obtain the stiffness and the plateau strength. The influence of the surface skin on the mechanical properties as well as on oscillation behaviour during lifetime measurements was studied.
RTP Temperature Measurements Using Si Grating Prepared by Laser Ablation for Large Diameter Wafer Applications
Authors: Liu C. W. , Lee M. H. , Chao C. Y. , Chen C. Y. , Yang C. C. , Chang Y.
Published: April 2011

Although a resolution of 1 °C of the grating temperature measurements has been demonstrated in RTP process[l], the conventional etching process to fabricate gratings on large diameter wafers makes it impractical for the production purpose. We, therefore, used the laser ablation technique to fabricate such Si gratings without any lithography and etching process. To increase the sensitivity of measurements, a large-angle diffracted beam was used by optimizing the incident angle and the grating period. As a result, an improvement of sensitivity could be obtained. The Si gratings were fabricated by the interference of two high power laser beams with the wavelength of 266 nm. The grating period was determined by interference condition, and could be varied from 180 to 550 nm, which would be beneficial to increase the measurement sensitivity. HeNe laser was used as the light source to measure the thermal expansion of grating periods for the temperature measurements. The temperature measurement of Si wafer from room temperature to 800 °C was demonstrated.
Novel Applications of Rapid Thermal Chemical Vapor Deposition for Nanoscale MOSFET’s
Authors: Sturm J. C. , Yang M. , Chang C. L. , Carroll M. S.
Published: April 2011

In this paper we examine several applications of Rapid Thermal Chemical Vapor Deposition (RTCVD) for the fabrication of sub-100 rum MOSFET's. Vertical dual-gated MOSFET’s are used as a test vehicle to implement FET's of very short channel length. To realize such devices, the ability of epitaxial Si1-x-y, GexCy layers for suppressing the thermal diffusion, transient enhanced diffusion, and oxidation enhanced diffusion of boron both in the Si1-x-y, GexCy and in nearby Si layers is very useful Novel gate electrodes deposited by RTCVD also showed the ability to greatly reduce boron penetration in ptype polycrystalline gates for p-channel FET’s.
Comparison of the Performance of Single Wafer and Batch Systems for Identical Processes
Authors: Claasen T. , Van Driel R. , Hasper A. , Radelaar S.
Published: April 2011

We compare single wafer systems, conventional batch systems and fast ramp batch systems in terms of throughput, cycle time and cost per wafer for four different processes. Comparison is based on dynamic fab simulations done with proprietary software package. The results show that vertical furnaces are the best choice in terms of throughput and cost per wafer for those processes for which both a single wafer and a batch process exist. Fast ramp furnaces are an attractive option to conventional batch furnaces in case a shorter cycle time is needed. Single Wafer systems show a substantially lower cycle time, but a higher cost per wafer. These additional costs might be justified by short cycle times in e.g. ASIC's manufacturing and in product development.
Chemical Ordering Along the Growth Direction in Epitaxial [0002] Co1−xRux Alloy Thin Films
Authors: Ersen O. , Bouzidi L. , Pierron-Bohnes V. , Cadeville M.C.
Published: April 2011

The occurrence of metastable long range order (LRO) along the growth direction with a periodicity twice that of a disordered alloy is now a well established result in epitaxial hcp [0002] Co-Ru and Co-Pt alloy thin films. We first present a review of previous results obtained in Co-rich Co1−xRux alloy thin films (x = 0.25) prepared at various growth temperatures (TG) and the diffusive model developed to account for the observed behavior. This model which takes into account the competition between surface and bulk interactions and surface and bulk diffusion during the growth time reproduces the TG dependence of the LRO parameter (η) and of the lattice constants. Then we present new results on the occurrence of this LRO in Co1−xRux films for higher Ru concentrations (0.22 ≤ x ≤ 0.78) prepared at the optimal temperature for the occurrence of this LRO (570-595 K). Chemical ordering is observed over the whole explored concentration range and it is found to be in agreement with results obtained in a previous series prepared at 610 K with lower Ru content. The LRO parameter deduced from the difference in composition between two successive planes normalized with respect to the concentration of the minonty element displays a nearly symmetric dependence with concentration characterized by a maximum around x = 0.2 and a minimum around the equiatomic composition. These results are qualitatively discussed in terms of a balance between the different energetic contributions to the surface segregation that arise from the release of the elastic energy and the difference in the wetting energy of each element. The important role played by the quality of the substrate in determining the value of η is outlined.
Coarsening Simulations of Two-Dimensional Islands on Solid Surfaces
Authors: Metiu H. , Mattsson T. R. , Mills G.
Published: April 2011

Using simulations, we have studied the coarsening of an ensemble of atom-high two-dimensional islands on a square lattice. The parameters are chosen to represent metal-on-metal homogeneous epitaxy. We study first the elementary processes controlling coarsening: the evaporation of atoms from islands of various sizes and the migration of these islands due to material transport along their edges. The information obtained from these preliminary studies is used to produce a very efficient simulation of coarsening. This allows us to study how coarsening modifies the number of islands, the distribution of their sizes, and the positions of the islands on the surface.
Cosegregation-Induced Epitaxial Growth of Two- and Three-Dimensional Compounds on Multicomponent Alloy Surfaces
Authors: Clauberg E. , Dziakova A. , Eltester B. , Hammer L. , Hüning B. , Kottcke M. , Müller C. , Rath C. , Uebing C. , Heinz K.
Published: April 2011

In this contribution the cosegregation-induced epitaxial growth of two- and three-dimensional chromium nitrides on ferritic Fe-15%Cr-N(100) (CN= 30 wt-ppm) single crystal surfaces will be discussed. The two-dimensional CrN surface compound is stable between 600 and 720°C. From the (1 × 1) LEED pattern it is inferred that the surface compound is epitaxial to the bcc(100) alloy surface. XPD and LEED-IV investigations have revealed that this surface compound consists of a single CrN compound layer plus an additional subsurface chromium layer with a huge interlayer expansion between both layers. The CrN surface precipitate formed at temperaturesT< 600°C is also epitaxially arranged on the bcc(100) substrate surface. Its structure corresponds to the rocksalt structure, i.e. the structure of the well-known bulk CrN. Starting from a sputter cleaned alloy surface the growth of the epitaxial CrN surface precipitate proceeds via the two-dimensional CrN surface nitride. After completion of this two-dimensional CrN layer the nucleation and growth of the three-dimensional CrN surface precipitate takes place.
Energetics of Fullerene Clusters
Authors: Rotkin Slava V. , Suris Robert A.
Published: April 2011

A new phenomenological model for calculation of formation energy of carbon nano-clusters of definite shape is proposed. The model uses only three energetic parameters: two first, Ec and ω5, being determined from comparison with experimental data, results of computer simulation for various carbon nano clusters, and the last one is dangling bond energy. Eb Energies of formation of carbon clusters shaped as cylinder, sphere, icosahedral polyhedra, capsule, were calculated in frame of unified phenomenological approach, which allows to judge relative energetical stability of these clusters.
The Influence of Anisotropic Grain Boundary Energy on Triple Junction Morphology and Grain Growth
Authors: King Alexander H.
Published: April 2011

We consider some examples of triple junction equilibration in the presence of grain boundary energy anisotropy. It is shown that the presence of one or two cusp-trapped grain boundaries can reduce the restrictions upon the dihedral angles formed with the remaining (isotropic) boundaries This allows for a reduction in the average grain boundary curvature, and thus in the driving force for grain boundary migration.
Calculation of Residual Stress in F-Doped Depressed Inner Cladding (DIC) Fiber
Authors: Park Y. W. , Oh K. , Paek U. C. , Kurkjian C. R.
Published: April 2011

The analytic calculation and the measurement of thermal stresses have been performed for concentric three layered structures of a fiber-core, inner, and outer cladding. Especially the effects of F-doped inner cladding on the residual stress have been parametrically studied.
Magnetosensitive Ni-Coated Optical Fibers
Authors: Biriukov A. S. , Belovolov M. I. , Bogatyrjov V. A. , Dianov E. M. , Lebedev V. F. , Sysolyatin A. A. , Khitun A. G.
Published: April 2011

We report, for the first time, optical fibers coated with Ni by the freezing technique. Ni-coated fibers demonstrate acceptable mechanical strength and effects related to magnetoactivity of the coating. Mechanical and optical characteristics of Ni-coated fibers along with their promising applications are discussed.
Near Defect Free GaN Substrates
Authors: Porowski S.
Published: April 2011

The current status of GaN crystallization under high nitrogen pressure will be presented. Both conductive and semi-insulating GaN crystals will be characterized.

In particular the influence of Mg on the growth mechanisms will be discussed. The influence of Mg doping on morphology of Mg-doped crystals grown under pressure and Mg-doped homoepitaxial layers will be shown. It will be also shown that the addition of about I at.% of Mg into the solution improves significantly the structural quality of crystals reducing dislocation density at least by 3 orders of magnitude comparing to the crystals grown without an intentional doping. As it was estimated by selective wet etching and transmission electron microscopy the dislocation densities in the Mg-doped GaN is as low as 10 cm-1. The introduction of Mg also lowers the optical absorption coefficients for energies below fundamental edge by 2 to 3 orders of magnitude what is explained by disappearance of defect related states in the gap.

The procedures for preparation of atomically flat epi-ready (000 1 ) surfaces without subsurface damage will be described. It will be shown that high quality homoepitaxial layers growing by monoatomic steps are possible on these substrates.
Doping of Aigan Alloys
Authors: Walle Chris G. Van de , Stampfl C. , Neugebauer J. , McCluskey M. D. , Johnson N. M.
Published: April 2011

Nitride-based device structures for electronic and optoelectronic applications usually incorporate layers of AlxGal-xN, and n- and p-type doping of these alloys is typically required. Experimental results indicate that doping efficiencies in AlxGal-xN are lower than in GaN. We address the cause of these doping difficulties, based on results from first-principles density-functional-pseudopotential calculations. For n-type doping we will discuss doping with oxygen, the most common unintentional donor, and with silicon. For oxygen, a DX transition occurs which converts the shallow donor into a negatively charged deep level. We present experimental evidence that oxygen is a DX center in AlxGal-xN for x>∼0.3. For p-type doping, we find that compensation by nitrogen vacancies becomes increasingly important as the Al content is increased. We also find that the ionization energy of the Mg acceptor increases with alloy composition x. To address the limitations on p-type doping we have performed a comprehensive investigation of alternative acceptor impurities; none of the candidates exhibits characteristics that surpass those of Mg in all respects.
Structural Study of GaN(As,P) Layers Grown on (0001) GaN by Gas Source Molecular Beam Epitaxy
Authors: Seong Tae-Yeon , Bae In-Tae , Zhao Y. , Tub C.W.
Published: April 2011

Transmission electron microscope (TEM) and transmission electron diffraction (TED) examination has been performed to investigate microstructural properties of gas source molecular beam epitaxial GaN(As,P) layers grown on (0001) GaN/sapphire at temperatures in the range 500–760 °C. As for the GaNAs, we report the observation of ordering with a space group P3ml in the layer grown at 730 °C. The layers grown at temperatures below 600 °C are polycrystalline, whist the 730°C GaNAs layer has epitaxial relation to the GaN substrate. It is also shown that the GaNAs layers experience a structural change from a zinc-blende phase to a wurtzite phase, as the growth temperature increases. As for the GaNP, it is shown that the layers grown at temperatures ≤ 600 °C experience phase separation resulting in a mixture of GaN-rich and GaP-rich GaNP with zinc-blende structure. However, the layers grown at temperatures ≥ 730 °C are found to be binary zinc-blende GaN(P) single crystalline materials. The layers grown at temperatures ≥ 730 °C consist of two types of micro-domains, i.e., GaN(P)1 and GaN(P)11; the former having twin relation to the latter.
Pressure Dependence of Optical Transitions in InGaN/GaN Multiple Quantum Wells
Authors: Shan W. , Ager J.W. , Walukiewicz W. , Haller E.E. , McCluskey M.D. , Johnson N.M. , Bour D.P.
Published: April 2011

The effect of hydrostatic pressure on optical transitions in InGaN/GaN multiple quantum wells (MQWs) has been studied. Photoluminescence (PL) and photomodulated transmission (PT) measurements were performed under applied pressure to examine the pressure dependence of optical transitions associated with confined states in MQWs. The PL emission from the MQWs was found to shift linearly to higher energy with applied pressure but exhibit a significantly weaker pressure dependence compared to epilayer samples with similar bandgap energies. Similar pressure coefficients obtained by PT measurements rule out the possibility of PL resulting from deep localized states. We show that the difference in the compressibility of InGaN and of GaN induces a tensile strain in the compressively strained InGaN well layers that partially compensates the applied hydrostatic pressure. This mechanical effect is the primary factor for the smaller pressure dependence of the optical transitions in the InGaN/GaN MQWs. At pressure above 100 kbar, the PL signal in MQWs samples is quenched, indicating that the carriers involved in the radiative recombination processes in the well layers originate primarily from the adjacent GaN layers.
Cubic InGaN Grown by Mocvd
Authors: Li J.B. , Yang Hui , Zheng L.X. , Xu D.P. , Wang Y.T.
Published: April 2011

We report on the growth of high-quality cubic phase InGaN on GaAs by MOCVD. The cubic InGaN layers are grown on cubic GaN buffer layers on GaAs (001) substrates. The surface morphology of the films are mirror-like. The cubic nature of the InGaN films is obtained by X-ray diffraction (XRD) measurements. The InGaN layers show strong photoluminescence (PL) at room temperature. Neither emission peak from wurtzite GaN nor yellow luminescence is observed in our films. The highest In content as determined by XRD is about 17% with an PL emission wavelength of 450 nm. The FWHM of the cubic InGaN PL peak are 153 meV and 216 meV for 427 nm and 450 nm emissions, respectively. It is found that the In compositions determined from XRD are not in agreement with those estimated from PL measurements. The reasons for this disagreement are discussed.
Nitridation of GaAs (001)-2x4 Surface Studied by Auger-Electron Spectroscopy
Authors: Aksenov Igor , Nakada Yoshinobu , Okumura Hajime
Published: April 2011

Auger electron spectroscopy (AES) was used to investigate the processes taking place during the initial stages of nitridation of GaAs (001) surface. The analysis of the AES results combined with that of RHEED show that the processes taking place during nitridation greatly differ depending on the nitridation temperature. At low temperatures (≤ 200°C) nitridation is hindered by kinetic restrictions on atomic migration, whereas at high temperatures (≥ 500°C) the process of nitridation takes place simultaneously with the etching of the surface. However, for intermediate temperatures (300°C ∼ 400°C) the results indicate that a complete monolayer of N atoms may be formed on the substrate during the initial stage of nitridation. The post-nitridation annealing of the samples nitrided at the intermediate temperatures results in the formation of a crystalline GaN layer, the line shape of the AES signals from which is identical to that for a GaN reference sample.
Piezoelectric Level Splitting in GaInN/GaN Quantum Wells
Authors: Wetzel C. , Takeuchi T. , Amano H. , Akasaki I.
Published: April 2011

Identification of the electronic band structure in AlInGaN heterostructures is the key issue in high performance light emitter and switching devices. In device-typical GaInN/GaN multiple quantum well samples in a large set of variable composition a clear correspondence of transitions in photo- and electroreflection, as well as photoluminescence is found. The effective band offset across the GaN/GaInN/GaN piezoelectric heterointerface is identified and electric fields from 0.23 - 0.90 MV/cm are directly derived. In the bias voltage dependence a level splitting within the well is observed accompanied by the quantum confined Stark effect. We furthermore find direct correspondence of luminescence bands with reflectance features. This indicates the dominating role of piezoelectric fields in the bandstructure of such typical strained layers.
Epitaxial Growth and Structural Characterization of Single Crystalline ZnGeN2
Authors: Zhu L.D. , Maruska P.H. , Norris P.E. , Yip P.W. , Bouthillette L.O.
Published: April 2011

A new nitride semiconductor, single crystalline ZnGeN2 has been successfully grown by MOCVD for the first time. The epitaxial ZnGeN2 is found to be of hexagonal wurtzite lattice without ordering of the zinc and germanium atoms in the pseudomorphic Group III sublattice. Lattice constants of the ZnGeN2 are a = 3.186 ± 0.007 A, c = 5.174 ± 0.012 A, which gives c/a = 1.624.
Homo- and Hetero-Epitaxial Gallium Nitride Grown by Molecular Beam Epitaxy
Authors: Foxon C.T. , Cheng T.S. , Korakakis D. , Novikov S.V. , Campion R.P. , Grzegory I. , Porowski S. , Albrecht M. , Strunk H.P.
Published: April 2011

Various methods have been used to initiate growth by Molecular Beam Epitaxy (MBE) of GaN on sapphire, or other substrates, but there is always a problem with morphology and with a high defect density which results in the formation of a sub-grain boundary structure. We show that by using, homo-epitaxial growth on properly prepared bulk GaN substrates, combined with high temperature growth, we obtain a significant improvement in surface morphology. Growth at sufficiently high temperature leads to a rapid smoothing of the surface and to almost atomically flat surfaces over relatively large areas. Multi-Quantum Well structures grown on such GaN epitaxial films are dislocation free with abrupt interfaces.
Epitaxial Lateral Overgrowth of GaN with Chloride-Based Growth Chemistries in Both Hydride and Metalorganic Vapor Phase Epitaxy
Authors: Zhang R. , Zhang L. , Hansen D.M. , Boleslawski Marek P. , Chen K.L. , Lu D.Q. , Shen B. , Zheng Y.D. , Kuech T.F.
Published: April 2011

Epitaxial lateral overgrowth (ELO) of GaN on SiO2-masked (0001) GaN substrates has been investigated by using chloride-based growth chemistries via hydride vapor phase epitaxy (HVPE) and metal organic vapor phase epitaxy (MOVPE). Diethyl gallium chloride, (C2H5)2GaCl, was used in as the MOVPE Ga precursor. The lateral and vertical growth rates as well as the overgrowth morphology of ELO GaN structures are dependent on growth temperature, V/III ratio and the in-plane orientation of the mask opening. A high growth temperature and low V/III ratio increase the lateral growth rate and produce ELO structures with a planar surface to the GaN prisms. High-quality coalesced and planar ELO GaN has been fabricated by both growth chemistries. The use of the diethyl gallium chloride source allows for the benefits of HVPE growth to be realized within the MOVPE growth environment.
GaN P-N Structures Fabricated by Mg ION Implantation
Authors: Kalinina E.V. , Solov'ev V.A. , Zubrilov A.S. , Dmitriev V.A. , Kovarsky A.P.
Published: April 2011

In this paper we report on the first GaN p-n diodes fabricated by Mg ion implantation doping of n-type GaN epitaxial layers. Ion implantation was performed at room temperature. Implantation dose ranged from 1013 to 2 × 1016 cm2. After implantation samples were annealed for 10-15 s at a wide temperature interval from 600°C to 1200°C in flowing N2 to form p-type layers. Secondary ion mass spectroscopy, scanning electron microscopy with electron beam induced current and back scattered electron modes as well as current-voltage and capacitance-voltage measurements were used to study structural and electrical characteristics of the Mg implanted p-n structures.
Minimum Surface Formation Energy for Three-Dimensional Intergranular Fracture
Authors: Holm E. A. , McGovney G. N.
Published: April 2011

The minimum expended energy for fracture is the free energy required to form two new surfaces. For intergranular fracture, the minimum surface formation energy is complicated by the rough fracture surface, with area greater than the specimen cross-section. We utilize network optimization algorithms (max-flow/min-cut) to determine the minimum surface formation energies and surfaces for intergranular fracture in 3D polycrystals. For equiaxed grains and uniform boundary strength, the minimum energy fracture area is independent of grain size and is 45% larger than the specimen cross-section, and intergranular fracture will occur when surface energy is less than 1.6 times the grain boundary energy. The 3D fracture area is larger than projected from 2D systems. In systems with microcracked boundaries, the fracture surface deviates to preferentially include microcracked boundaries, creating interlocking grain configurations. Two-dimensional percolation of microcracks occurs at about 80% microcracked boundaries.
Dislocation Emission from a Thin-Film-Covered Crack
Authors: Zhang Tong-Yi , Qian Cai-Fu , Wang Tianhong , Tong Pin
Published: April 2011

The present work investigates the effects of a passive film formed during stress corrosion cracking on ductile/brittle fracture behavior, considering the interaction of a dislocation with a thin- film-covered crack under an applied remote load. The dislocation emission from the thin-film- covered crack tip is analyzed, on the basis of the two-dimensional Rice-Thomson model, for screw and edge dislocations. The results show that the nominally critical stress intensity factor for dislocation emission is related to the thin film thickness, the properties of the film and the loading conditions. For a given loading mode and a given crack length, there exists a critical value of the film thickness at which the film does not influence the dislocation emission. When the film thickness is smaller than the critical value, a harder thin film makes the dislocation emission easier and a softer film makes the dislocation emission more difficult. The opposite is also true if the film thickness is larger than the critical value.
Growth, Microstructural and Ferroelectric Properties of PZT Films Prepared by Pulsed Laser Deposition Method
Authors: Kumar Ashok , Alam M.R. , Shamsuzzoha M.
Published: April 2011

Pb(ZrxTi1−xO3 (lead zirconate titanate or PZT) ferroelectric thin film capacitors are of considerable interest for the realization of memory devices such as nonvolatile random access memories (NVRAMs). The PZT capacitors were prepared on platinized silicon Pt/(100)Si using conducting oxide LaxSrl.xCOO (lanthanum strontium cobalt oxide or LSCO) as electrodes. The PZT and LSCO thin films were deposited by the KrF excimer laser ablation technique. The optimum preparation conditions such as oxygen pressure, laser energy influence and substrate temperature were investigated. The PZT and LSCO films grown on Pt/(100)Si are polycrystalline. The crystallographic properties of the films were determined using X-ray diffractometer (XRD) method. The cross-sectional transmission electron microscope showed very smooth interface among different layers of films. The electrical characterizations of the films including hysteresis loop, fatigue, and retention properties were determined by the RT66A Standardized Ferroelectric Test System.
Effect of Stoichiometry on the Ferroelectric Properties of (Pb1−xLax)TiO3 Thin Films
Authors: Lin I-Nan , Lin Cheng-Hsiung , Hsu Yen-Hua , Teng Han-Fang , Cheng Hsiu-Fung
Published: April 2011

The (Pb1−xLax)TiO3, (PLT) thin films possessing good ferroelectric properties were successfully obtained by using metal-organic-decomposition (MOD) process, followed by furnace post-annealing at 600-700°C (60 min) or rapid thermal annealing (RTA) at 600-700°C (60 s). Excess Pb-species incorporated in precursors for compensating for the Pb-loss during MOD process results in pronounced modification on thin film's electrical properties. The leakage current is reduced from JL= 1 × 10−3 A/cm2 to 1 × 10−4 A/cm2 (at 400 kV/cm) and the remanent polarization is increased from Pr= 8.3 µ C/cm2 to 12.6 µC/cm2, when 10 mol% excess-Pb is added. On the other hand, larger La-content in PLT films results in more pronounced Pb-loss and induces larger leakage current, which significantly degrades the ferroelectric properties of the films. The best properties obtained for PLT films prepared by the MOD process are: Pr= 12.6 µC/cm2, Ec = 80 kV/cm and JL= 10−5 A/cm2 (at 400 kV/cm).
Properties and Orientation of Antiferroelectric Lead Zirconate Thin Films Grown by MOCVD
Authors: Chen Nan , Bai G. R. , Auciello O. , Koritala R. E. , Lanagan M. T.
Published: April 2011

Single-phase polycrystalline PbZrO3 (PZ) thin films, 3000-6000 A thick, have been grown by metal-organic chemical vapor deposition (MOCVD) on (111)Pt/Ti/SiO2/Si substrates at ≍525°C. X-ray diffraction analysis indicated that the PZ films grown on (111)Pt/Ti/SiO2/Si (Pt/Tgi/Si) showed preferred pseudocubic (110) orientation. In contrast, PZ films grown on 150 A thick PbTiO3 (PT) template layers exhibited a pseudocubic (100) preferred orientation, and PZ films deposited on TiO2 template layers consisted of randomly oriented grains. The PZ films grown on Pt/Ti/Si with or without templates exhibited dielectric constants of 120-200 and loss tangents of 0.01-0.0. The PZ films with (110) orientation exhibited an electric-field-inducedtransformation from the antiferroelectric phase to the ferroelectric phase with a polarization of ≍34 µC/cm2, and the energy that was stored during switching was 7.1 J/cm3. The field needed to excite the ferroelectric state and that needed to revert to the antiferroelectric state were 50 and 250 kV/cm, respectively. Relationships between the MOCVD processing and the film microstructure and properties are discussed.
Heteroepitaxial Growth of PZT Film on (100)Ir/(100)YSZ/(100)Si Substrate Structure Prepared by Reactive Sputtering
Authors: Horita Susumu , Horii Sadayoshi
Published: April 2011

A heteroepitaxial (001)Pb(ZrxTi1−x)O3(PZT) film was grown on the (100)Ir/(100)YSZ/Si structure with a cube-on-cube relationship by using reactive sputtering. The X-ray diffraction patterns of this sample showed that the double domain crystal layer of the (110) IrO2 was formed between the Ir and PZT films. According to reflection high energy electron diffraction observation and X-ray photoelectron spectroscopy measurements, it was found that the initial epitaxial growth of the PZT film occurred on the Ir film. The polarization-electric field hysteresis loop of the 285-nm-thick epitaxial PZT film with the top electrode of IrO2 showed a saturated square shape at the ac amplitude of 3V, and the remanent polarization 2Pr and the coercive field 2Ec were 80 µC/cm 2 and 100 kV/cm, respectively. The 2Pr's were not reduced up to the switching cycles of 5 × 1010 with ± 5V bipolar pulse.
Effect of Annealing Treatment on PZT Thin Fiilm Properties Using Oxygen 18 Depth Profiling Technique
Authors: Ayguavives F. , Ea-Kim B. , Agius B. , Vickridge I. , Kingon A. I.
Published: April 2011

Lead zirconate titanate (PZT) thin films have been deposited in a reactive argon/oxygen gas mixture from a metallic target of nominal composition Pb1.1(Zr0.4Ti0.6)O3 by rf magnetron sputtering on Si substrates and RuO2/SiO2/Si structures. During plasma deposition, in situ Optical Emission Spectroscopy (OES) measurements clearly show a correlation between the evolution of characteristic atomic emission line intensities and the thin film composition determined by simultaneous Rutherford Backscattering Spectroscopy (RBS) and Nuclear Reaction Analysis (NRA). As a result, the cathode surface state can be monitored by OES to ensure a good compositional transferability from the target to the film and reproducibility of thin film properties for given values of deposition parameters. Electrical properties and crystallization have been optimized with a 90 nm PZT thin film grown on RuO2 electrodes. These PZT films, annealed with a very modest thermal budget (550°C) are fatigue-free and show very low leakage currents (J=2.10−8 A/cm2 at 1 V). The use of a metallic target allows us to control the oxygen incorporation in the PZT thin film and also, using 18O as a tracer, to study the oxygen vacancy migration which plays a key role in fatigue, leakage current, and electrical degradation/breakdown in PZT thin films.
Suppression of Size Effects in Ferroelectric Films
Authors: Desu Seshu B.
Published: April 2011

It is widely reported that the dielectric permittivity of ferroelectric films decreases with decreasing film thickness, and understanding and controlling these size effects are very important for charge storage application of these films. By combining phenomenological theory with careful experimental work, we have shown that the form of the boundary condition for the polarization plays a decisive role in the manifestation of size effects in ferroelectric films. We have taken two extreme boundary conditions to prove our point. For the case normal electrodes, it is assumed that the boundary condition for the component of polarization vector at the ferroelectric/electrode interface is P = 0. This case corresponds to the presence of a strong edge field, resulting in “freezing out” of the ferroelectric polarization at the interface and thus exhibiting severe size effects. However, if one utilizes conductive oxide electrodes that are ferroelectric in nature the polarization would not vanish at the ferroelectric/electrode interface and therefore the size effects are largely suppressed. To prove our point and to eliminate grain size, stress, and compositional effects, epitaxial SrTiO3 thin films with stoichiometric composition on SrTiO3 single crystal substrates were investigated. In fact, the experimental data also indicates that the use of ferroelectric electrodes indeed suppress the size effects.
Antiferroelectric to Paraelectric Phase Transition in Lead Zirconate Thin Films
Authors: Fanning D.M. , Robinson I.K. , Tani T. , Payne D. A.
Published: April 2011

Lead zirconate, PbZrO3, is antiferroelectric at room temperature and has a first-order phase transition to the paraelectric state at 230°C in bulk crystals. At room temperature, the antiferroelectric Pb displacements along [110] directions produce a superstructure at the (h+¼ k+¼, 1) positions (referenced to pseudo-tetragonal unit cell). The Pb displacements occur perpendicular to the shorter c axis. In this study, the behavior of thin films was compared to the bulk. Films of lead zirconate were deposited onto electroded silicon wafers via the sol gel method. By varying the deposition conditions of the Pt substrate, films with both {111} and {100} preferred orientation were grown. The crystalline film consisted of columnar grains which were not completely aligned with each other, but had a random orientation with respect to the film's perpendicular axis. Measurements of superstructure peak intensities vs. temperature show that the thin films exhibit a much more gradual phase transition to the paraelectric state compared to the bulk. Furthermore, comparison of a and c vs. temperature show this effect, as well as a strain of about 0.5% in c. In the {100} oriented films, we found that the c-axis was oriented perpendicular to the film's surface, meaning they should be classified as (001).
Synchrotron X-Ray Scattering of (Ba0.5Sr0.5)TiO3 Thin Films Epitaxially Grown on MgO(100)
Authors: Kim Sang S. , Je Jung H.
Published: April 2011

((Ba0.5Sr 0.5)TiO3 thin films of two different thicknesses (∼ 250 Å and ∼ 1330 Å) epitaxially prepared on MgO(100) using pulsed laser deposition were studied by synchrotron x-ray scattering measurements. The film initially grew on MgO(100) with a cube-on-cube relationship, maintaining it during further growth. As the film grew, the surface of the film became rougher significantly, but the interface between the film and the substrate did not change so much. In the early stage, the film was highly strained in a tetragonal structure with the longer axis parallel to the surface normal direction. As the growth proceeded further, it was mostly relaxed to a cubic structure with the lattice parameter of the bulk value and the mosaic distribution improved significantly in both the in-plane and the out-of-plane directions. The thinner film showed only one domain limited mainly by the film thickness, but the thicker film exhibited three domains along the surface normal direction.
Preparation and Characterization of Bi2VO5.5 Films by MOD Method
Authors: Tokumitsu E , Takahashi Y. , Ishiwara H.
Published: April 2011

We report the preparation and characterization of Bi2VO5.5(BVO) films grown on SrTiO3, Pt/SiO2/Si, and n-Si(100) substrates by the MOD technique. Since a dielectric constant of BVO is much lower than that of PZT or SBT, BVO is one of the promising candidates for metal-ferroelectric-semiconductor field-effect transistors (MFSFETs). It is found by X-ray diffraction (XRD) measurements that highly (001)-oriented BVO films were obtained and that the crystalline quality was improved with increasing the annealing temperature. The full width at half maximum (FWHM) in the X-ray rocking curve measurements for BVO films on SrTiO3, Pt/SiO2/Si, and n-Si(100) substrates are 0.60, 1.00, and 5.10, respectively. Electrical properties were measured with Pt top electrodes and the typical relative dielectric constant determined by the C-V characteristics is 60-80.
Characterization of Pb(ScTa)1−xTixO3 (x<0.3) Thin Films Grown on LaNiO3 Coated Si by MOCVD
Authors: Lin C. H. , Kuo H. C. , Stillman G. E. , Chen Haydn
Published: April 2011

Highly (100) textured pseudo-cubic Pb(ScTa)1−xTixO3 (x=0-0.3) (PSTT) thin films were grown by metal-organic chemical vapor deposition (MOCVD) on LaNiO3 (LNO) electrode buffered Si substrates at 650 °C. The microstructure and chemical uniformity were studied using X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM) and nanoprobe X-ray energy dispersive spectroscopy (EDS). The temperature dependence of dielectric properties and P-E behavior were measured. A shift of Curie temperature of these PST-based thin films due to Ti addition was demonstrated, Furthermore, the pyroelectric properties of these thin films were estimated.