bluuebunny/crossref_metadata_2025 huggingface dataset:
Structural Studies of Silver/Permalloy and Copper/Permalloy GMR Spin Valve Multilayers
Authors: Geng H. , Zhu W. , Heckman J.W. , Loloee R. , Pratt W.P. , Bass J. , Crimp M.A.
Published: April 2011

Giant magnetoresistance (GMR) spin valves of the form Ag/Py/Ag/Py/FeMn and Cu/FeMn/Py/Cu/Py have been studied using conventional and high-resolution electron microscopy complemented with fast Fourier transform (FFT) diffractogram analysis. Cross-sectional TEM thin foil samples were prepared in order to characterize the layer structures and interfaces. In the Ag/Py system, we have examined a simple spin valve, part of which was grown on the Nb contact and part directly on the Si substrate. The spin valve displays a polycrystalline structure when grown on the Nb contact. In contrast, when grown directly on the Si substrate, the first Ag layer of the spin valve grew as a continuous epitaxial single crystal while the rest of the layers were polycrystalline. Two Cu/Py spin valves, grown on Nb, with 30 nm and 3 nm thick Py layers have been investigated. TEM images reveal good contrast between the Nb contacts and the spin valves, but weak contrast between the individual spin valve layers. Both spin valves displayed columnar, polycrystalline grain structures. HRTEM analysis indicates some non-equilibrium structures exist in the spin valve layers.
Modeling of Substrate Bias Effect on the Compositional Variations in Sputter-Deposited TiB2+x Diffusion Barrier Thin Films
Authors: Sinder M. , Sade G. , Pelleg J.
Published: April 2011

Sputter-deposited titanium boride diffusion barrier layers have been found to be boron enriched when r.f substrate bias was applied. In the present experiments titanium boride was deposited by co-sputtering from Ti and B pure targets in Ar discharge and the voltage of r.f. self-bias was in the range of 100 – 250 V. Films deposited were found by Auger electron spectroscopy to be B enriched with increasing bias voltage at constant Ti and B sputtering rates. A model of the sputter-deposition conditions was developed to predict the composition and the thickness of the growing film. The model explains the experimental results indicating that B enrichment is mainly a result of differential resputtering of the components from the growing film by energetic Ar ions captured from the r.f discharge.
Computational Modelling of Ring-Shaped Magnetic Domains
Authors: Gal'tsev A.F. , Pokazan'ev V.G. , Yalishev Y.I.
Published: April 2011

A theoretical research of static stability of peculiar localized domain structures (LDS) in a thin magnetic film with the perpendicular anisotropy is presented. The model describes a system consisting of cylindrical magnetic domain (CMD) and several concentric ring-shaped domains. Such structures arise under influence of the external low frequency (100–1000 Hz) magnetic field applied perpendicular to the film plane and were observed experimentally in 1992. Non-linear singular integro-differential equation for a magnetization distribution is provided by a minimization condition for the system's complete energy local density. Energy dependencies on geometry parameters are calculated numerically. The conditions of magnetostatic stabilization of the simplest CMD-ring system, as well as some of its dynamical properties, are discussed in detail on this basis.
Localized Surface Instabilities of Stressed Solids
Authors: Colin J. , Grilhé J. , Junqua N.
Published: April 2011

Localized instabilities formation on the free surface of solids has been studied when sources of non-homogeneous stress such as dislocations or precipitates are present in the bulk. This formalism of localized perturbations has been used to describe the butterfly transformation of cubic precipitates in superalloys and the contraction of rectangular specimens under stress.
Abrasion Damage to Lightguide Fiber Surfaces
Authors: Kurkjian C. R. , Matthewson M. J. , Chaudhri M. M.
Published: April 2011

The two general types of strength-reducing defects most commonly found in lightguide fibers are those due to chemical interactions of refractory particles with the hot glass and those due to mechanical damage resulting from indentation or scratching. In this paper we review some work on the mechanical damage in silica lightguide fibers and some of the approaches which have been taken to simplify the study of such damage. We are reminded that the indentation and scratching behavior of silica glass is not simple and that in all probability there are a variety of different types of flaws which may have different fatigue and aging behavior, and therefore result in different lifetimes. It is therefore suggested that either the actual proof test level flaws, or at least a wide variety of synthetic flaws, must be studied in order to develop sufficient background and experience to confidently predict fiber lifetimes.
High Speed Strength Testing of Optical Fiber
Authors: Glaesemann G. S. , Clark D. A. , Hanson T. A. , Wissuchek D. J.
Published: April 2011

Optical fiber models for mechanical reliability require that the initial strength and crack growth parameters be measured. High speed testing allows one to investigate and model common high-speed processing events during fiber processing such as proof testing, coloring and cabling. In this study stressing rates ranging from 7×10−6 GPa/s to 1.5 TPa/s were accomplished using a universal testing machine, belt slide and pneumatic piston. When plotted in typical dynamic fatigue fashion the data shows curvature at the faster stressing rates. The presence of region II type crack growth is suggested as a possible explanation for this curvature. A multi-region crack growth model is used to extract crack growth parameters that are used to make comparisons with crack velocity results on bulk glass.
Theoretical Investigation of Metal Coating Deposition on Optical Fibers by Freezing Technique. The Model of the Process
Authors: Biriukov A. S. , Bogatyrjov V. A. , Lebedev V. F. , Khitun A. G.
Published: April 2011

Metal-coated fibers are irreplaceable in a multiplicity of uses owing to high hermeticity of the coating and its chemical and thermal stability. At present, the most widespread technique for the metal coating application onto a fiber is a so-called freezing technique, which consists in pulling a silica fiber through a layer of a metal's melt directly in the fiber drawing process. If the fiber temperature is lower than the metal melting point, a certain amount of the melt is frozen on the fiber surface in the form of coating. For this to occur, it is necessary that the duration of the fiber-melt contact did not exceed the time during which the fiber heats up to the metal's melting point; otherwise, the frozen metal will melt again. Because silica glass is poorly wetted with a majority of liquid metals, the coating in the latter case is likely to become discontinuous.
Reliability of Linbo. Based Integrated Optical Waveguide Devices for Fiber Communication Systems
Authors: Nagata Hirotoshi , Mitsugi Naoki , Higuma Kaoru , Ichikawa Junichiro , Sakamoto Toshihiro , Fujino Tetsuya , Shinriki Takashi
Published: April 2011

Increasing demands for LiNbO3 (LN) optical waveguide devices installed into submarine and terrestrial fiber communication systems necessitate that high quality and long-term reliability (over 20 years) be established. In addition to general requirements for reliability in electrooptical devices, the LN devices need to assure of the dc-drift phenomena in the optical output signal. The dc-drift is caused by the complex electrical nature of constituent device materials; i.e. LN substrates and SiO2 buffer layers on LN. Results of theoretical and experimental investigations of the suppression of dc-drift are applied to the design of practical LN devices, and the devices have been in service for 4 years, as of this moment, without any failure. Here, problems on the dc-drift are discussed from the viewpoints of device reliability and actual fabrication processes.
Pyroelectric and Piezoelectric Properties of Gan-Based Materials
Authors: Shur M. S. , Bykhovski A. D. , Gaska R.
Published: April 2011

We review pyroelectric and piezoelectric properties of GaN-based materials. Pyroelectric effects in GaN have been studied in two different regimes: (i) uniform sample heating regime and (ii) under applied temperature gradient along the sample. The modeling results show that the pyroelectric coefficient, Pv, in GaN (for c-axis along the contacts) can reach 7x105 V/m-K (compared to Pv = 5x105 V/m-K for the best-known high temperature pyroelectric/piezoelectric material LiTaO3). This points to a high potential of GaN-based sensors for high temperature pyroelectronics. Piezoelectric effects strongly affect the performance of electronic and light-emitting devices based on III-N materials. Piezoelectrically induced charge in heterostructures can be as large as 3 to 4x1013 cm-2. Hence, strong lattice polarization effects provide unique possibilities for utilizing GaN-based materials in high temperature piezoelectronics and for their applications in pyroelectric detectors.
Luminescence from Erbium-Doped Gallium Nitride Thin Films
Authors: Zavadat J. M. , Thaik Myo , Hòmmerich U. , MacKenzie J. D. , Abernathy C. R. , Ren F. , Shen H. , Pamulapati J. , Jiang H. , Lin J. , Wilsont R.G.
Published: April 2011

The III-V nitride semiconductors appear to be excellent host materials for optical device applications involving thin films doped with rare earth atoms. In particular, GaN epilayers doped with Er ions have shown a highly reduced thermal quenching of the Er luminescence intensity from cryogenic to elevated temperatures. The remarkable thermal stability of the light emission may be due to the large energy bandgap of the material, as well as to the optical inactivity of material defects in the GaN film. In this paper we present recent developments concerning the luminescence characteristics of Er-doped GaN thins films. We have used two methods for doping GaN films with Er ions, ion implantation and in-situ incorporation during gas source metal-organic molecular beam epitaxy (MOMBE). Bandedge (at ∼ 0.34 μm) and infrared (at ∼ 1.54 μm) photoluminescence (PL) spectra have been measured for both types of Er-doped GaN films. Considerably different emission spectra have been observed depending upon the incorporation method and the heat treatment procedure. In situ Er-doped GaN layers have been processed into hybrid light emitting devices and emission spectra at 1.54 Pm have been measured.
Composition Dependence of the Band Gap Energy of InxGal-xN Layers on GaN (x≤0.15) Grown by Metal-Organic Chemical Vapor Deposition
Authors: Wagner J. , Ramakrishnan A. , Behr D. , Maier M. , Herres N. , Kunzer M. , Obloh H. , Bachem K.-H.
Published: April 2011

We report on the composition dependence of the band gap energy of strained hexagonal InGal-,N layers on GaN with x≤0.15, grown by metal-organic chemical vapor deposition on sapphire substrates. The composition of the (InGa)N was determined by secondary ion mass spectroscopy. High-resolution X-ray diffraction measurements confirmed that the (InGa)N layers with typical thicknesses of 30 nm are pseudomorphically strained to the in-plane lattice parameter of the underlying GaN. Room-temperature photoreflection spectroscopy and spectroscopic ellipsometry were used to determine the (InGa)N band gap energy. The composition dependence of the band gap energy of the strained (InGa)N layers was found to be given by EG(x)=3.43-3.28.x (eV) for x≤0.15. When correcting for the strain induced shift of the fundamental energy gap, a bowing parameter of 3.2 eV was obtained for the composition dependence of the gap energy of unstrained (InGa)N.
Domain Structure of Thick GaN Layers Grown by Hydride Vapor Phase Epitaxy
Authors: Paskova T. , Svedberg E.B. , Madsen L.D. , Yakimova R. , Ivanov I.G. , Henry A. , Monemar B.
Published: April 2011

The crystal structure and surface morphology of hydride vapour phase epitaxy grown thick (12-105 μm) GaN layers have been investigated as a function of growth rate using several structure sensitive techniques like atomic force microscopy (AFM), x-ray diffraction (XRD) in ω-2Θ and ω-rocking curve measurements as well as low temperature photoluminescence (PL). PL and XRD measurements reveal rather narrow lines: full width at half maximum (FWHM) values of the strongest donor-bound exciton line are in the range from 6.0 to1.8 meV and ω-2Θ FWHM values are between 80 and 23 arcsec indicating good structural quality of the films. The ω-rocking curves show a single peak for the thinnest films with a FWIM of 250 arcsec and multiple peaks with FWHIM of about 250-350 arcsec in thicker films indicating the formation of several high-quality domains when increasing either thickness or growth rate. Optical microscopy and AFM images reveal a domain type of morphology and also show an appearance of spiral hillocks in layers grown at growth rates exceeding a critical value. We interpret these results as dominating 2D multilayer growth at low growth rates, and competing 2D multilayer and spiral growth mechanisms at high growth rates.
Extended Defects in GaN: a Theoretical Study
Authors: Eisner J. , Frauenheim Th. , Haugk M. , Gutierrez R. , Jones R. , Heggie M. I.
Published: April 2011

We present density-functional theory studies for a variety of surfaces and extended defects in GaN. According to previous theoretical studies {1010} type surfaces are electrically inactive. They play an important role in GaN since similar configurations occur at open-core screw dislocations and nanopipes as well as at the core of threading edge dislocations. Domain boundaries are found to consist of four-fold coordinated atoms and are also found to be electrically inactive. Thus, except for full-core screw dislocations which possess heavily strained bonds all investigated extended defects do not induce deep states into the band-gap. However, electrically active impurities in particular gallium vacancies and oxygen related defect complexes are found to be trapped at the stress field of the extended defects.
Statistical Analysis of Local Composition and Luminescence in InGaN Grown by Molecular Beam Epitaxy
Authors: Einfeldt S. , Böttcher T. , Hommel D. , Selke H. , Ryder P. L. , Bertram F. , Riemann T. , Rudloff D. , Christen J.
Published: April 2011

InGaN layers grown by molecular beam epitaxy are investigated in terms of their compositional homogeneity using transmission electron microscopy and cathodoluminescence spectroscopy performed with high spatial resolution. Strong fluctuations of the indium content were found in bulk-like layers, which could be partially reduced by modulating the indium flux during growth, i. e. by nominally growing a short period GaN/InGaN superlattice. For indium compositions above x ≠ 0.1 this approach fails. Strained InGaN in quantum wells exhibits lateral fluctuations on an atomic scale and on a scale of several hundred nanometers. The results are discussed in view of the origin of inhomogeneous indium incorporation.
Disordering of InGaN/GaN Superlattices After High-Pressure Annealing
Authors: McCluskey M.D. , Romano L.T. , Krusor B.S. , Hofstetter D. , Bour D.P. , Kneissl M. , Johnson N.M. , Suski T. , Jun J.
Published: April 2011

Interdiffusion of In and Ga is observed in InGaN multiple-quantum-well superlattices for annealing temperatures of 1250 to 1400°C. Hydrostatic pressures of up to 15 kbar were applied during the annealing treatments to prevent decomposition of the InGaN and GaN. In as-grown material, x-ray diffraction spectra show InGaN superlattice peaks up to the fourth order. After annealing at 1400°C for 15 min, only the zero-order InGaN peak is observed, a result of compositional disordering of the superlattice. Composition profiles from secondary ion mass spectrometry indicate significant diffusion of Mg from the p-type GaN layer into the quantum well region. This Mg diffusion may lead to an enhancement of superlattice disordering. For annealing temperatures between 1250 and 1300°C, a blue shift of the InGaN spontaneous emission peak is observed, consistent with interdiffusion of In and Ga in the quantum-well region.
Enhanced GaN Decomposition at Movpe Pressures
Authors: Koleske D.D. , Wickenden A.E. , Henry R.L. , Twigg M.E. , Culbertson J.C. , Gorman R.J.
Published: April 2011

GaN decomposition was studied above 800°C in flowing H2 and N2 for pressures ranging from 10 to 700 torr. From careful weighings of the GaN film on sapphire before and after annealing, the rates for GaN decomposition, Ga surface accumulation, and Ga desorption were obtained. An enhancement in the GaN decomposition rate was observed in H2 pressures greater than 100 torr. Even with this enhanced GaN decomposition, the Ga desorption rate is nearly constant at higher pressures. As a result, Ga droplets accumulate on the surface. For N2 pressures ranging from 76 to 400 torr no net enhancement in the GaN decomposition rate is observed and the GaN decomposition rate is reduced compared to identical annealing conditions in H2. This suggests that HI- is acting chemically to reduce the barrier for GaN decomposition. This may occur through a surface mediated dissociation of H2 followed by the formation of more mobile and volatile hydrogenated N and Ga species. The significance of this study for GaN growth is that by increasing the GaN decomposition, the Ga atoms diffuse farther and subsequently re-incorporate into the growing lattice, increasing the GaN crystal quality. Connections between the enhanced GaN decomposition rate and the coalescing of nucleation layer during the ramp to high temperature and the consequences for the high temperature growth are discussed.
Relaxation Phenomena in GaN/ AlN/ 6H-SiC Heterostructures
Authors: Edwards N.V. , Batchelor A.D. , Buyanova I.A. , Madsen L.D. , Bremser M.D. , Davis R.F. , Aspnes D.E. , Monemar B.
Published: April 2011

We have developed a method to modulate the strain state (normally > 4 kbar, tensile) of moderately thick (∼2 μm) GaN based structures grown on 6H-SiC to a range 0 to -2 kbar of compressive stresses by introducing a strain-mediating layer (SML) above the standard high-temperature AlN buffer layer. The strain characteristics of subsequently deposited nitride layers can be modulated by changing the growth parameters of the SML layer. This is achieved by in-situ techiniques during crystal growth without degrading the optical and structural properties of the deposited layers.
Optical and Structural Properties of Er3+-Doped GaN Grown by MBE
Authors: Birkhahn R. H. , Hudgins R. , Lee D. S. , Lee B.K. , Steckl A. J. , Saleh A. , Wilson R. G. , Zavada J. M.
Published: April 2011

We report the morphological and compositional characteristics of Er-doped GaN grown by MBE on Si(111) substrates and their effect on optical properties. The GaN was grown by molecular beam epitaxy using solid sources (for Ga and Er) and a plasma gas source for N2. The films emit by photoexcitation in the visible and near infrared wavelengths from the Er atomic levels. The morphology of the GaN:Er films was examined by AFM. Composition was determined by SIMS depth profiling that revealed a large Er concentration at 4.5 × 1021 atoms/cm3 accompanied by a high oxygen impurity concentration.
Characteristic Temperature Estimation for GaN-Based Lasers
Authors: Honda T. , Kawanishi H. , Sakaguchi T. , Koyama F. , Iga K.
Published: April 2011

We have estimated the characteristic temperature T0 of GaN-based vertical-cavity surface-emitting lasers. The density matrix theory including intraband relaxation broadening has been taken into account. The estimated T0 is about 300 K, which suggests a good temperature characteristic in GaN-based lasers.
Focused ION Beam Etching of GaN
Authors: Flierl C. , White I.H. , Kuball M. , Heard P.J. , Allen G.C. , Marinelli C. , Rorison J.M. , Penty R.V. , Chen Y. , Wang S.Y.
Published: April 2011

We have investigated the use of focused ion beam (FIB) etching for the fabrication of GaN-based devices. Although work has shown that conventional reactive ion etching (RME) is in most cases appropriate for the GaN device fabrication, the direct write facility of FIB etching - a well-established technique for optical mask repair and for IC failure analysis and repair - without the requirement for depositing an etch mask is invaluable. A gallium ion beam of about 20nm diameter was used to sputter GaN material. The etching rate depends linearly on the ion dose per area with a slope of 3.5 × 10-4 μm3/pC. At a current of 3nA, for example, this corresponds to an etch rate of 1.05μm3/s. Good etching qualities have been achieved with a side wall roughness significantly below 0.1μm. Changes in the roughness of the etched surface plane stay below 8nm.
Monitoring and Controlling of Strain During Mocvd of AlGaN for UV Optoelectronics
Authors: Han Jung , Crawford M. H. , Shul R. J. , Hearne S. J. , Chason E. , Figiel J. J. , Banas M.
Published: April 2011

The grown-in tensile strain, due to a lattice mismatch between AlGaN and GaN, is responsible for the observed cracking that seriously limits the feasibility of nitride-based ultraviolet (UV) emitters. We report in-situ monitoring of strain/stress during MOCVD of AIGaN based on a wafer-curvature measurement technique. The strain/stress measurement confirms the presence of tensile strain during growth of AlGaN pseudomorphically on a thick GaN layer. Further growth leads to the onset of stress relief through crack generation. We find that the growth of AlGaN directly on low-temperature (LT) GaN or AIN buffer layers results in a reduced and possibly controllable strain.
Normal and Inverted Algan/Gan Based Piezoelectric Field effect Transistors Grown by Plasma Induced Molecular Beam Epitaxy
Authors: Murphy M. J. , Foutz B. E. , Chu K. , Wu H. , Yeo W. , Schaff W. J. , Ambacher O. , Eastman L. F. , Eustis T. J. , Dimitrov R. , Stutzmann M. , Rieger W.
Published: April 2011

High quality Ga-face and N-face AlGaN/GaN based heterostructures have been grown by plasma induced molecular beam epitaxy. By using Ga-face material we are able to fabricate conventional heterojunction field effect transistors. Because the N-face material confines electrons at a different heterojunction, the resulting transistors are called inverted. The Ga-face structures use a high temperature AIN nucleation layer to establish the polarity. Structures from these materials, relying only on polarization induced interface charge effects to create the two-dimensional electron gases, are used to confirm the polarity of the material as well as test the electrical properties of the layers. The resulting sheet concentrations of the two dimensional electron gases agree very well with the piezoelectric theory for this materials system. Hall mobilities of the two-dimensional gases for the N-face structures are as high as 1150 cm2/Vs and 3440 cm2/Vs for 300 K and 77 K respectively, while the Ga-face structures yield room temperature mobilities of 1190 cm2/Vs. Both structures were then fabricated into transistors and characterized. The inverted transistors, which were fabricated from the N-face material, yielded a maximum transconductance of 130 mS/mm and a current density of 905 mA/mm. Microwave measurements gave an ft of 7 GHz and an fmax of 12 GHz for a gate length of 1 μm. The normal transistors, fabricated from the Ga-face material, produced a maximum transconductance of 247 mS/mm and a current density of 938 mA/mm. Microwave measurements gave an ft of 50 GHz and an fmax of 97 GHz for a gate length of 0.25 μm. This shows that using plasma induced molecular beam epitaxy N-face and Ga(A1)-face AlGaN/GaN heterostructures can be grown with structural and electrical properties very suitable for high power field effect transistors.
Molecular Dynamics Simulations of Nanoindentation of Silicon Nitride
Authors: Walsh Phillip , Omeltchenko Andrey , Kikuchi Hideaki , Kalia Rajiv K. , Nakano Aiichiro , Vashishta Priya
Published: April 2011

This is a report of work in progress on 10 million atom Molecular Dynamics (MD) simulations of nanoindentation of crystalline and amorphous silicon nitride (Si3N4). Nanoindentation is used to determine mechanical properties of extremely thin films such as hardness and elastic moduli. We report load-displacement curves for several Si3N4 configurations using an idealized non-deformable indenter and analyze the local stress distributions in the vicinity of the indenter tip. Preliminary results for surface adhesion using Si3N4 for both tip and substrate are also reported.
Studies of Crack Pattern in Two Dimensional Media as Resulting From Ion Beam like or Freezing Destruction
Authors: Ausloos M. , Vandewalle N. , D‘Hulst R.
Published: April 2011

We have numerically studied various models for crack formation in the slow dynamical regime. Two different aspects are presented herein: (i) sputtering with reconstruction and (ii) internal destruction of a porous medium through the invasion of a secondary phase.
Deposition of Pb(Zr, Ti)O3-Films on High-Grade Steel Hastelloy and Modification by Ion Implantation
Authors: Klarmann R. , Biegel W. , Wörz B. , Hemberger J. , Stritzker B.
Published: April 2011

Pulsed Laser Deposition (PLD) was used to deposit Pb(Zr,Ti)O3 thin films on high-grade steel Hastelloy. This material is suitable as substrate and electrode material as well. The deposited films were characterized with respect to their structural (XRD, RBS), topological (AFM) and their ferroelectric properties (P(E) hysteresis, retain and fatigue) which were found to be excellent. The ferroelectric properties in general, are sensitive to structural modifications and chemical doping and could therefore be influenced by ion implantation. Several species of ions (Ca+, O+) show different influence on the ferroelectric behavior and on the structural defects of the films. A subsequent annealing process can partially restore these modifications. The implanted Ca+ films were characterized by dielectric spectroscopy dependend on frequency and temperature to get information about ferroelectric domains.
Composition Dependence of Dielectric Anomaly in Strontium Bismuth Tantalate Thin Films
Authors: Takemura Koichi , Noguchi Takehiro , Hase Takashi , Kimura Hidekazu , Miyasaka Yoichi
Published: April 2011

Effects of off-stoichiometry and Nb substitution on the dielectric anomaly and ferroelectric properties have been investigated for SrBi2Ta2O9(SBT) thin films. Local atomic environment for the stoichiometric and off-stoichiometric SBT films has been also measured. The features of the dielectric anomaly, the Curie temperature (Tc), and the temperature dependence of the spontaneous polarization (Ps) are independent of the film thickness, and are governed by the nature of the crystal. For the stoichiometric Sr content SBT films, the grain size increases and the temperature dependence of the remanent polarization (Pr) decreases with increasing thickness. For the films with Sr/Bi/Ta = 0.8/2/2 and 0.8/2.2/2, Sr deficient local structure was observed, and such lattice structure probably leads to higher Tc than the stoichiometric crystal. Nb substitution for Ta also raises Tc, and makes the dielectric anomaly sharper. The phase transition associated with the dielectric anomaly for these films is thought to be first-order.
Studies of Electrical Polarization Fatigue in SrBi2Ta2O9 Thin Films
Authors: Lee K. M. , Thomas D. , Kim S. H. , Maria J. P. , Kingon A. I. , Jang H. M.
Published: April 2011

The polarization suppression and electrical properties directly associated with the electrical polarization fatigue in SrBi2Ta2O9system were systematically investigated using Pt/SBT/Pt capacitors. Three general observations were made after 109 switching cycles: (i) ∼95% of the remanent polarization was conserved, (ii) both high and zero bias field capacitance decreased, and (iii) leakage current density increased from approximately 10−7 to 10−5 A/cm2at ∼30kV/cm2. In addition, the “knee” field, at which the leakage abruptly increases, assumed smaller values with cumulative switching cycles. Temperature dependent leakage data was collected for both as-deposited and field-cycled samples. Based on these results, we propose the possibilities of enhanced concentration of charge carriers or additional reductions in interfacial conduction barriers. Motion of oxygen vacancies to less-shallow energy levels near electrode/ferroelectric interface may allow this mechanism to occur.
Synthesis and Dielectric Properties of SrBi2Nb2O9 Layered Perovskite by Sol-Gel Processing
Authors: Wu Y. , Ohuchi F. S. , Cao G. Z.
Published: April 2011

Ferroelectric layered perovskite strontium bismuth niobium oxide SrBi2Nb2O9(SBN) ceramics and films were made by sol-gel processing. A multiple step hydrolysis-condensation process was applied to the synthesis of the SBN sol by using inorganic salts as precursors with citric acid as a complexing agent. Single phase polycrystalline SBN was obtained after heat-treatment at 650°C. It was found that the dielectric constants of SBN ceramics were dependent on heat-treatment. SEM, XPS, TGA/DTA and XRD analyses indicated that bismuth-deficiency may contribute to the relatively low dielectric constants. While a prolonged firing time at high temperatures may lead to a lattice expansion resulting in a significant decrease of the dielectric constant. C-oriented SBN films were obtained by dip-coating onto SrTiO3 substrates and the films are dense and crack-free with a thickness of 900 nm.
Studies of Metallic Species Incorporation During Growth of SrBi2Ta2O9 Films on YBa2Cu3O7−x Substrates Using Mass Spectroscopy of Recoiled Ions
Authors: Dhote A.M. , Krauss A.R. , Auciello O. , Im J. , Gruen D.M. , Ramesh R. , Pai S.P. , Venkatesan T.
Published: April 2011

The incorporation of metallic species (Bi, Sr and Ta) during the growth of layered perovskite SrBi2Ta2O9 (SBT) on a-axis oriented YBa2Cu3O7−x (YBCO) conducting oxide substrates has been investigated using in situ low energy mass spectroscopy of recoiled ions (MSRI). This technique is capable of providing monolayer-specific surface information relevant to the growth of single and multi-component thin films and layered heterostructures. The data show a temperature dependence of metallic species incorporation during co-deposition of Sr, Bi and Ta on YBCO surfaces. At high temperatures (400 < T ≤ 700°C), negligible incorporation of Bi is observed as compared to Ta and Sr. At low temperatures (≤ 400°C), there is a substantial incorporation of Bi, Sr and Ta on the surface of YBCO, and the MSRI signal intensities for Sr, Bi and Ta are nearly independent of substrate temperature. According to thermodynamic calculations, the presence of Ba and Y on the YBCO surface inhibit the incorporation of Bi due to competition for oxygen required to establish bonding of metallic species to the surface. This may be the explanation for the observed Bi deficiency in films grown on YBCO surfaces at temperatures > 400°C. SBT films grown at temperatures ≤ 400°C and annealed in oxygen or air at 800°C exhibit a polycrystalline structure with partial a-axis orientation.
Low Temperature MOCVD of Thin Film PZT
Authors: Chen Ing-Shin , Roeder Jeffery F.
Published: April 2011

Incorporation of ferroelectric thin films into integrated microelectronics requires deposition temperatures compatible with back-end processing. Pb(Zr,Ti)O3 (PZT) thin films have been deposited at low temperatures by a thermal chemical vapor deposition process using flash-vaporized metalorganic precursors. Deposition temperatures, A-site to B-site ratios in the precursor solution, and bottom electrodes have been surveyed. Stoichiometric perovskite films with (Zr/Ti) ratios ranging from 20/80 to 50/50 were obtained. Films deposited at temperatures below 500°C possess very fine grain structures. Capacitor structures were fabricated by depositing top electrodes using electron-beam evaporation, followed in some cases by a post-electrode anneal at 650°C. Remanent polarizations greater than 20 μC/cm2 were observed on films deposited on Pt at temperatures as low as 475°C. Perovskite films were obtained on Ir electrodes at temperatures as low as 450°C, with remanent polarization greater than 10μC/cm2 in the as-deposited condition.
Correlation Between Large Electrostrictive Strain and Relaxor Behavior with Structural Changes Induced in P(VDF-TrFE) Copolymer by Electron Irradiation
Authors: Bharti Vivek , Ye Yaohong , Xu T.-B. , Zhang Q. M.
Published: April 2011

The effect of high energy electron irradiation is investigated on poly(vinylidene fluoridetrifluoroethylene), P(VDF-TrFE), copolymers in the broad range of irradiation doses and temperature. It was found that after a suitable electron irradiation condition, ferroelectric polymer materials show exceptionally high electrostrictive response (> 4%), high dielectric constant (>60) with low dielectric loss over a broad temperature range. In addition, the material after irradiation exhibits many features resembling those of a relaxor ferroelectric, suggesting that the electron irradiation breaks up the coherent polarization domain in a normal ferroelectric material into micro-polar regions that transform the material into a relaxor ferroelectric. These distinct features make this material very attractive for a broad range of applications. In this paper we will review the experimental results on various characteristics of material properties including the dielectric and electrostrictive strain response induced at different temperatures under different electron irradiation conditions and their relation with structural changes observed by X-ray and DSC.
Target Crystallography and the Growth of Pb(Mg1/3Nb2/3)O3 (PMN) Thin Films
Authors: Corbett M.H. , Catalan G. , Gregg J.M. , Bowman R.M.
Published: April 2011

Lead magnesium niobate thin films have been grown on {100} MgO substrates using pulsed laser deposition (PLD). Several series of films were made using targets of varying perovskite and PbO content. The conditions necessary to produce almost 100% perovskite Pb(Mg1/3Nb2/3)O3 (PMN) films were most sensitive to the growth temperature rather than the starting target crystallography. The electrical properties were determined by fabricating planar thin film capacitor structures and monitoring capacitance and dielectric loss as a function of temperature. Our best capacitors yielded a loss of 0.1 at 1 kHz over a wide temperature range.
Electrical Properties of PZT Thin Film Capacitors with Novel Pt-Ir Based Electrode Barriers for Nonvolatile Memories
Authors: Desu Chandra S. , Vedula Ramakrishna , Lee Kwang B. , Desu Seshu B.
Published: April 2011

A new electrode barrier structure based on noble metals Pt and Ir alloys and their oxides was proposed for the integration of PZT capacitors into high density nonvolatile memories. The proposed PtIrOx/PtIr/PtIrOx structure with Pt rich compositions (∼90%) is an excellent conducting electrode for the ferroelectric capacitor and a very good diffusion barrier for species like oxygen and Si. These structures are thermally stable up to the PZT processing temperatures of 650°C. PZT deposited on these electrodes crystallized predominantly in pervoskite phase. The test capacitors showed well saturated hysteresis loops with Pr and Ec of 21.3 µC/cm2 and 43 kV/cm, respectively. An extremely low polarization fatigue of 3% after 1× 1011 repetitions and leakage currents close to those on Pt were observed.
Glass Transition in Sub-nanometer Confinement
Authors: Huwe A. , Kremer F. , Arndt M. , Behrens P. , Schwieger W. , Ihlein G. , Akdogan Ö. , Schüth F.
Published: April 2011

Broadband dielectric spectroscopy (10−2 Hz - 109Hz) is employed to study the molecular dynamics of low-molecular-weight glassforming liquids being confined to nanopores. For the H-bond forming liquid propylene glycol being confined to (uncoated and silanized) nanopores (pore size: 2.5 nm, 5.0 nm and 7.5 nm) a molecular dynamics is observed which is comparable to that of the bulk liquid. Due to surface effects in uncoated nanopores the relaxation time distribution is broadened on the long term side and the mean relaxation rate is decreased by about half a decade. This effect can be counterbalanced by lubricating the inner surfaces of the pores resulting in a relaxation rate which is slightly faster compared to the bulk liquid. For the H-bonded liquid ethylene glycol (EG) embedded in zeolites of different pore size and topology one observes a sharp transition from a single-molecule dynamics to that of a liquid depending on the coordination number of the confined molecules. While EG in silicalite (showing a single molecule relaxation) has four neighboring molecules, EG in zeolite beta or AIPO4-5 has a coordination number of five and behaves like a bulk liquid.
Confinement Effects on The Local Motion in Nanocomposites
Authors: Anastasiadis S. H. , Karatasos K. , Vlachos G. , Manias E. , Giannelis E. P.
Published: April 2011

The local segmental dynamics of polymers confined within the 15–20 Å interlayer spacing of nanocomposites consisting of poly(methyl phenyl siloxane) intercalated within organically modified silicates, has been investigated utilizing Dielectric Relaxation Spectroscopy. The effect of confinement on the local reorientational dynamics is evident by the observation of a relaxation mode, which is much faster than the segmental α-relaxation of the bulk polymer and exhibits much weaker temperature dependence. This is attributed to the restrictions placed by the interlayer spacing on the cooperative volume required for the ax-relaxation.
Molecular Dynamics of Alkanes in Faujasite Zeolites
Authors: Clark L. A. , Ye G. T. , Gupta A. , Hall L. L. , Snurr R. Q.
Published: April 2011

Molecular dynamics simulations of C1 through C14 n-alkanes have been used to elucidate diffusion mechanisms in siliceous faujasite zeolites. Additional simulations of the bulk liquids were conducted to compare the liquid and adsorbed phases. Macroscopic quantities, such as heats of adsorption, diffusivities, and activation energies, were calculated and compare well with experimental values. In addition, the simulations provide detailed information about the mechanisms of alkane diffusion in the confined pores of faujasite.
Thin Conducting Polymer Films: Effect of Thickness on Wetting Behavior of Polyaniline Ultra Thin Films
Authors: Li J. , Hill T. H. , Gregory R. V. , Perahial D.
Published: April 2011

Wetting properties and surface structure of polyaniline (PANI) thin films were studied as a function of the polymer thickness, using AFM and neutron reflectivity. Increasing the oxidation state as well as polymer thickness was found to increase the tendency of the polymer to form polycrystalline films. Three main regions with characteristic behavior were observed: ultra thin films of the order of several molecular layers, an intermediate thickness film of several molecular layers to ∼150nm, and films thicker than 150nm. In the ultra thin region the polymer formed nano-scale spherical domains. In the intermediate one, the films tend to be continuous and amorphous. In the thick films, crystallinity was observed.
Experimental Chemical Kinetics of an A+B→0 System Showing Non-Classical Effects of Initial Reactant Distribution
Authors: Monson Eric , Kopelman Raoul
Published: April 2011

We demonstrate here the implementation of an experimental system suitable for the study of the diffusion-limited A+B→0, non-classical reaction behavior. Using a combination of a fluorescent calcium indicator and a calcium ion which is initially “caged”, a pulse of near-UV light initiates the reaction which is followed as product formation vs. time. Sensitive dependence on the initial reactant distribution is observed through patterns in the uncaging UV light profile. The reaction progress passes through two non-classical time regimes, one due to roughness originating from laser speckles, followed by one exhibiting the three-dimensional Zeldovich rate of (1/ρA − 1/ρA0) ˜ t3/4, with features matching Monte Carlo simulations on this initial distribution.
Effect of Dimensionality and Anisotropy on the Holstein Polaron
Authors: Lindenberg Katja , Romero A. H. , Brown D. W.
Published: April 2011

We apply weak-coupling perturbation theory and strong-coupling perturbation theory to the Holstein molecular crystal model in order to elucidate the effects of anisotropy on polaron properties in D dimensions. The ground state energy is considered as a primary criterion through which to study the effects of anisotropy on the self-trapping transition, with particular attention given to shifting of the self-trapping line and the adiabatic critical point. The effects of dimensionality and anisotropy on electron-phonon correlations and polaronic mass enhancement are studied, with particular attention given to the polaron radius and the characteristics of quasi-l-D and quasi-2-D structures. Perturbative results are confirmed by selected comparisons with variational calculations and quantum Monte Carlo data.
Sliding Friction by Atomic Force Microscopy
Authors: Pasquier V. , Drake J. M.
Published: April 2011

Lateral Force Microscopy offers the possibility of exploring tribological properties of interfaces atthe nanoscale. Our research focused on some crucial conditions that must be fuffilled to obtainquantitative and reliable LFM friction measurements. We have characterized the mechanical andvibrational properties of the cantilever. Precise force calibration were made based on ourknowledge of the intrinsic coupling modes of the cantilever. We report measurements of the slidingfriction between two silica surfaces. The load dependence of the friction force was analyzedassuming different models for the contact, from Hertzian to Amontons law.
In SITU Spectroscopic Diagnostics of the Influence of Chamber Wall Polymer on Oxide Etch Rate
Authors: Lee Szetsen , Tien Yu-Chung , Hsu Chin-Fa
Published: April 2011

The drift of PECVD TEOS etch rate has been observed during MERIE oxide etch for damascene process. Etch rate typically fluctuates between 5300 Å/min. and 6000 Å/min. depending on chamber condition. Studies using fluorocarbon based chemistry show high TEOS etch rate when chamber wall is heavily coated with polymer deposition. Low etch rate appears when chamber has less deposition. Hysteresis behavior has been observed in TEOS etch rate and emission intensity trends ofF and CFx (x = 1 ∼ 3). From the correlation between etch rate and emission intensity, a model is proposed to explain the impact of chamber wall polymer deposition on TEOS etch rate. It clearly shows that F is directly responsible for the etch of TEOS. Comparing to F, CFx plasma chemistry has a closer link in chamber wall polymer formation, but less contribution in the etch of TEOS.
Plasma-Induced Stabilization of Pmma Surfaces for Enhanced Adhesion of Plasma-Deposited Coatings
Authors: Klemberg-Sapieha J. E. , Martinu L. , Yamasaki N. L. S. , Lantman C. W.
Published: April 2011

Adhesion of plasma-deposited optical and protective coatings, such as amorphous hydrogenated silicon nitride, SiN1.3, on polymethyl-methacrylate (PMMA) substrates has been found to be limited by a cohesive failure inside the PMMA bulk. Using direct exposure to a low pressure plasma in helium or to vacuum ultraviolet radiation generated from H2 plasma for an extended period of time, we succeeded to obtain excellent adhesion even under a humidity test at elevated temperature. We found, using a multitechnique approach, that such improved adhesion is achieved by forming a crosslinked, mechanically stabilized layer in the interfacial region, which possesses a physical thickness of 50 to 100 nm.
Analysis of Vibrational Properties of Thin Films Using in-Situ Infrared Ellipsometry: Applications to Polymerlike Amorphous Carbon Films
Authors: Heitz T. , Drevillon B. , Godet C. , Bouree J. E. , Clerc C.
Published: April 2011

An original method is developed to investigate vibrational properties of thin films using infrared (IR) ellipsometry. The procedure is based on in-situ measurements as a function of deposition time. Out of absorption bands, the IR refractive index can be determined and related both to film density and oscillator strengths of electronic transitions. Thanks to band decomposition performed for a given film at different thicknesses, line frequency, band width and intensity of each vibration can be precisely determined, even in case of band overlapping or low IR oscillator strengths. As an illustration, C-H bonding of 1000 Å-thick plasmadeposited polymerlike hydrogenated carbon (PLC) films has been studied. Analysis of the interface between highly saturated PLC films and crystalline silicon reveals the formation of a 20 Å interlayer. Bulk analysis evidences weak vibrations located at 1405 and 1440 cm−1 which had not been observed so far and which are related to π bonds. By combining elastic recoil detection measurements and IR analysis, effective charges of sp3 CHn groups have been calculated. For methyl and methylene groups, these charges are similar to those of hydrocarbon compounds. As far as the sp3 CHn group is concerned, a strong decrease of the effective charge versus film density is evidenced and attributed to the formation of distorted weakly hydrogenated regions induced by ion bombardment.
Infrared-Sensitive Photovoltaic Devices for Thermophotovoltaic Applications
Authors: Fatemi Navid S. , Wilt David M. , Hoffman Richard W. , Weizer Victor G.
Published: April 2011

One of the critical components in a thermophotovoltaic (TPV) system is the infrared-sensitive photovoltaic (PV) semiconductor device that converts the emitted radiation to electricity. Currently, several semiconductor material systems are under development by various workers in the field. The most common are InGaAs/InP, GaSb, and InGaSbAs/GaSb. These devices normally have electronic energy bandgap values in the range of 0.50-0.74 eV. In addition, the design and structure of these devices fall into two distinct formats: conventional planar and monolithic interconnected module (MIM). The conventional planar devices normally have one semiconductor junction and are high-current/low-voltage devices. In a MIM, small area PV cells are connected in series monolithically, on a semi-insulating substrate. This results in the formation of a single high-voltage/low-current module. Electrical and optical performance results for MIMs with electronic energy bandgaps of 0.60 and 0.74 eV will be presented.
Synthesis of Thin Film Battery Components by the Spray Decomposition Technique
Authors: Weil K.S. , Kumta P.N. , Harris J. D. , Hepp A. F.
Published: April 2011

Thin film LiCoO2 anodes and SnO2 cathodes on the order of 1-10 µtm thick have been synthesized using a spray decomposition technique, employing a lithium-nickel nitrate/methanol solution and tin ethylhexanoate/methanol solution, respectively. Preliminary electrochemical test results on the films indicate that the LiCoO2 anodes in general display a relatively high open circuit voltage (OCV) of ∼4.10-4.25V, good specific capacity on the order of 120 mAh/g, and acceptable cycle-ability, with a 16-25% decay in operating voltage after 50 cycles. The SnO2 films display excellent performance characteristics, upon an expected initial drop in capacity, with an OCV of 1.00-1.10V, specific capacity of ∼600 mAh/g, and virtually no decay in operating voltage after 50 cycles. The solid-state electrolyte, lithium phosphate, was prepared in thin film form by a similar spray processing technique. Additionally, it has been demonstrated that spray decomposition can be used to sequentially deposit the anode, electrolyte, and cathode film layers to form a layered thin film battery (TFB), although electrochemical testing of this thin film device has not yet been conducted.