bluuebunny/crossref_metadata_2025 huggingface dataset:
Relation Between Microstructures and Constitutive Behavior of Advanced Tempered Martensitic Steels
Authors: Spätig Philippe , Schäublin Robin , Victoria Max
Published: April 2011

In an effort to better understand the plasticity of the tempered martensitic steels, the strain-hardening of two 7-9Cr steels is examined in terms of dislocation mechanics. It is shown that, over the temperature range investigated (173K-523K), the strain-hardening as a function of stress can be described by an equation taking account the dislocation storage and annihilation. The model of strain-hardening used in this study is based on the original Kocks description of the dislocation density evolution with plastic strain but the heterogeneous distribution of dislocations resulting from the lath boundaries and prior austenite grain boundaries is taking into account. The effect of stress and temperature on the storage and annihilation is discussed. The relation between the determined mean dislocation path associated to the heterogeneous lath dislocation structure and the transmission electron microscope observations performed on the two different steels is outlined.
Characterization of very low defect-density free-standing GaN Substrate Grown by Hydride-Vapor-Phase-Epitaxy.
Authors: Visconti P. , Reshchikov M. A. , Jones K. M. , Yun F. , Cingolani R. , Morkoç H. , Jasinski J. , Swider W. , Liliental-Weber Z. , Park S. S. , Lee K. Y.
Published: April 2011

Structural, electrical and optical properties of free-standing 200-μm thick GaN films grown by hydride vapor phase epitaxy (HVPE) have been investigated. After laser lift-off, the GaN substrates were mechanically polished on both Ga and N-sides and dry etched only on the Ga- side to obtain a smooth epi-ready surface. Hot H3PO4 chemical etching on both surfaces was used to reveal the defect sites, which appeared as hexagonal pits. The etched surfaces were then examined by atomic force microscopy. A few seconds of etching was sufficient to smooth the N- face surface and produce etch pits with a density of ≈ 1×107 cm−2. In contrast, a 50 minute etching was needed to delineate the defect sites on the Ga-face which led to a density as low as 5×105 cm−2. From plan-view and cross-sectional transmission electron microscopy (TEM) analysis, we have estimated that the dislocation density is less than about 5×106 cm−2 and ≈ 3×107 cm−2 for the Ga and N-faces respectively. The full-width at half-maximum (FWHM) of the symmetric (0002) X-ray diffraction rocking curve was 69 and 160 arcsec for the Ga and N-faces, respectively. That for the asymmetric (10 4) peak was 103 and 140 arcsec for Ga and N-faces, respectively. Hall measurements demonstrated very high mobility (1100 and 6800 cm2/V.s at 295 and 50 K, respectively) and very low concentration of donors (2.1×1016 cm−3) and acceptors (4.9×1015 cm−3). In the photoluminescence (PL) spectrum taken at 10 K, a rich excitonic structure has been observed with the highest peak attributed to the exciton bound to neutral shallow donor (BDE). The FWHM of the BDE peak was about 1.0 meV on the Ga face before and after hot chemical etching, whereas that on the N-face decreased from about 20 to 1.0 meV after chemical etching owing to the removal of the surface damage originated from the mechanical polishing.
Reduction of incorporation of B, Al, Ti and N in 4H-SiC epitaxial-layer grown by chemical vapor deposition at higher growth temperature
Authors: Kushibe Mitsuhiro , Masahara Koh , Kojima Kzutoshi , Ohno Tshiyuki , Ishida Yuki , Takahashi Tetsuo , Nishio Johji , Suzuki Takaya , Tanaka Tomoyuki , Yoshida Sadahumi , Arai Kazuo
Published: April 2011

The influence of growth conditions and susceptor purity on the residual contamination in undoped 4H-SiC epitaxial layer grown at higher temperature such as 1600 °C is investigated. Residual N concentration is found to increase with growth temperature. Growth temperature dependence of residual N concentration is stronger than that of Al or B. The effect of degradation of SiC coating layer on the purity of the epitaxial layer is studied. SiC coating layer is degraded after very few repetition of growth-run. SIMS measurement reveals that the concentration of N, Al, B, Ti and V in epitaxial layer increases with the deterioration of SiC coating layer. Therefore, serious consideration on the effect of contamination from the susceptor graphite is required. By using various grades of graphite as susceptor, the dependence of the purity of epitaxial layer on the susceptor purity is studied. High concentration (1017 to 1018 cm−3) of N is found in graphite. Contamination of all types of impurities such as p-type impurities, transition metal impurities and N in graphite is found to affect the purity of epitaxial layers.
Surface Photovoltage Spectroscopy of InGaN/GaN/AlGaN Multiple Quantum Well Light Emitting Diodes
Authors: Mishori B. , Muñoz Martin , Mourokh L. , Pollak Fred H. , DeBray J.P. , Ting S. , Ferguson I.
Published: April 2011

InGaN/GaN/AlGaN multiple quantum well light emitting diodes (MWQ LED's) with different levels of p-doping in the contact layer have been characterized using surface photovoltage spectroscopy (SPS). Due to the high sensitivity of the SPS technique to the electric field, there is a strong correlation between the p-doping level in the contact layer and the magnitude of the SPS signal originating from the MQW region. The experimental results are confirmed by a numerical simulation.
Photoluminescence and Excitation Spectra of Deep Defects in GaN
Authors: Reshchikov Michael A. , Molnar Richard J. , Morkoç Hadis
Published: April 2011

Deep defects responsible for broad bands in the red-to-green range of the photoluminescence (PL) spectrum of undoped and Si-doped GaN grown by molecular beam epitaxy (MBE) and hydride vapor phase epitaxy (HVPE) were studied by employing PL and PL excitation (PLE) methods. In HVPE grown samples, a red luminescence (RL) and a green luminescence (GL) bands were observed, respectively, at about 1.9 and 2.4 eV. Similar in positions but different in properties red and green bands (RL2 and GL2, respectively) dominated in the samples grown in Ga-rich conditions by MBE with radio frequency plasma as a nitrogen source (RF-MBE). A yellow luminescence (YL) with a maximum at about 2.2 eV dominated in the samples with ammonia used as a nitrogen source (NH3-MBE). It has been established from the variation of temperature, excitation intensity and excitation wavelength that the abovementioned five bands are related to different deep-level defects.
Defect investigation of GaN thin films etched by photo-electrochemical and hot wet etching by atomic force and transmission electron microscopy
Authors: Visconti P. , Jones K. M. , Reshchikov M. A. , Cingolani R. , Morkoç H. , Molnar R. J. , Smith D. J.
Published: April 2011

The availability of reliable and quick methods to investigate defects in GaN films is of great interest. Photo-electrochemical (PEC), and hot wet etching using both H3PO4 acid and molten KOH have been used to study structural defects in GaN layers grown by hydride vapor phase epitaxy and molecular beam epitaxy. The purpose of this work is to determine whether, and under what conditions, these different methods of investigation are consistent and to get to a more accurate estimation of the defect density. As-grown and etched surfaces were investigated by atomic force microscopy (AFM), and plan-view and cross-sectional transmission electron microscopy (TEM). Free-standing whisker-like features and hexagonal etch pits were formed on the etched sample surfaces by PEC and wet etching, respectively. Using plan-view AFM, we found the density of whiskers (8x108-1×109 cm−2) to be similar to the etch pit densities when etched in both H3PO4 and molten KOH under precise etching conditions. During the wet etching process, a careful balance must be struck to ensure that every defect is delineated, but not overetched to cause merging which would lead to an underestimation of the defect density. Additionally, TEM observations confirmed the dislocation densities obtained by etching, which increased our confidence in the consistency of the methods used.
Effects of Plasma Surface treatment on Ohmic Contact to n-GaN
Authors: Chor E.F. , Kang X. J.
Published: April 2011

We have investigated the effects of plasma surface treatment on ohmic contacts to n-type GaN. Prior to metal evaporation, n-GaN surface was etched either chemically using aqua-regia (control sample) or by means of inductively coupled Cl2/BCl3, N2 or Ar plasmas. The metal system adopted in our investigation was Ti/Al/Pd/Au. The as-deposited Ti/Al/Pd/Au contact on aqua-regia treated n-GaN exhibits an ohmic behavior with a specific contact resistance (ρc) of 2×10−4ωcm2. After annealing at 500°C for 5min, ρc is reduced by approximately 2 orders of magnitude to 5×10−6ωcm2. For Cl2/BCl3 and N2 plasma treated n-GaN surface, the as-deposited Ti/Al/Pd/Au contacts also yield ohmic behavior and ρc's are about 2×10−4 and 5×10−4 ωcm2 respectively. After annealing at 500°C for 5min, ρc's are reduced by about 3 orders of magnitude to around 5×10−7 and 8×10−7 ωcm2 respectively. On the other hand, the as-deposited Ti/Al/Pd/Au contact on Ar plasma treated n-GaN exhibits a non-ohmic behavior. After annealing at 500°C for 5min, ρc is about 5×10−7 ωcm2 and the lowest ρc of 7×10−8 ωcm2 is obtained after annealing at 700°C for 5min. The contacts on other surface treated n-GaN are found to degrade at 700°C annealing. By comparing the values of ρc for various surface treatments, particularly those after annealing, it is observed that plasma etching can be used beneficially in the formation of ohmic contacts – plasma surface treatment using Cl2/BCl3, N2 or Ar has resulted in an order of magnitude reduction in ρc compared to chemical surface treatment by aqua-regia.
Photoluminescence and Raman Spectra of Flux Processed Bulk Single Crystal GaN
Authors: Cho Chae Ryong , Park Sang Eon , Cho Yong Chan , Jeong Se-Young
Published: April 2011

Bulk wurtzite-GaN crystal was obtained with a size more than 3 mm along the length of the crystal and with a thickness 200 ∼ 300 µm at around 750°C and 100 bar for 24 hrs in the flux growth method. The structural and compositional property of the GaN bulk single crystal was also studied by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) techniques. Photoluminescence, cathodoluminescence and micro-Raman measurements at room temperature are investigated for bulk single crystals of wurtzite GaN. The cathodoluminescence peak of near band-to-band transition at 365.5 nm and the E2(high energy, 568 cm−1) and A1(LO, 737 cm−1) Raman phonon modes were obtained according to the different position of the (0001) surface of GaN grown by flux method. Sharp line shape for the strain-sensitive E2 (high) mode is considered to be due to the high crystalline quality of the crystal.
Design of Metal-Semiconductor-Metal Ultra-Violet Detector on Gallium Nitride
Authors: Gu Wenhua , Chua Soo Jin , Zhang Xin Hai
Published: April 2011

The design of Gallium Nitride based Metal-Semiconductor-Metal Ultra-Violet detector is discussed. We introduce a simulation model using Medici to describe the performances of such detectors. Structure parameters, such as the inter-digitated electrode dimension and the GaN layer thickness, are optimized for response current and time using this model. The simulation results can be explained by the variation of depletion region. We introduce the “effective electric field intensity” to describe the depletion region. The relationship between the “effective electric field intensity” and structure parameters are simulated and discussed.
Single domain structure of 2H-AlN films on Si(001) substrates
Authors: Jinschek Joerg , Lebedev Vadim , Kaiser Ute , Richter Wolfgang
Published: April 2011

Aluminum nitride (2H-AlN) films were grown by plasma-assisted molecular beam epitaxy (MBE) on Si(001). By conventional (CTEM) and high resolution transmission electron microscopy (HRTEM) investigations the influence of the off-axis angle of the substrate surface on the film structure was studied. Three types of Si(001) substrates were used: on-axis, ∼1°, and ∼5° off-axis. The 2H-AlN layer on an exact oriented Si(001) substrates consists of 3 AlN film domains: two main film domains, AlNI and AlNII, and a small domain AlNIII at substrate surface defects. Their c-axis orientations are parallel to the c-axis of the substrate: [0001]AlNI,II,III ∥ [001]Si. The a-axes of AlNI and AlNII rotated by 30° to each other: [11 20]AlNII∥[01 10]AlNII ∥ [1 1 0]Si. The orientation of AlNIII is [01 10]AlNIII ∥ [100]Si. In 2H-AlN films grown on off-axis Si(001) substrates (∼1° and ∼5°) the ratio between the AlNI and AlNII film domains changes dramatically as far as a single domain film structure consisting of mainly AlNI is reached. The AlN c-axes of all domains on the off-axis substrates are not parallel to the Si c-axis but tilted by the off-axis angle of the Si(001) substrate (∼1° respectively ∼5°), i.e. [0001]AlN is parallel to the Si(001) substrate surface orientation. Determination of the AlNI domain / Si(001) interface structure by HRTEM illuminates the origin of the preference of this domain in the 2H-AlN film by using off-axis Si(001) substrates. On the on-axis substrate a regular array of misfit dislocations causes a 5:4 fit between the (1 1 00)AlN and ( 1 1 0)Si lattice planes. The off-axis Si(001) leads to a rotation of the AlN lattice in respect of the Si lattice. An array of misfit dislocations with a 4:3 fit between (1 1 01)AlN and ( 1 1 1)Si lattice planes decreases the residual lattice misfit from -1.6% to -0.8%.
Material System for Packaging 500°C SiC Microsystems
Authors: Chen Liang-Yu , Okojie Robert S. , Neudeck Philip G. , Hunter Gary W. , T. Lin Shun-Tien
Published: April 2011

In order to establish a material system for packaging 500°C SiC microsystems, aluminum nitride (AlN) and aluminum oxide (Al2O3) were selected as packaging substrates, and gold (Au) thick-film materials were selected as substrate metallization material for electrical interconnection system (thick-film printed wires and thick-film metallization based wire-bond) and conductive die-attach interlayer. During a 1500-hour test in atmospheric oxygen with and without electrical bias, the electrical resistance of Au thick-film based interconnection system demonstrated low and stable electrical resistance at 500°C. The electrical interconnection system was also tested in extreme dynamic thermal environment. A silicon carbide (SiC) Schottky diode was attached to ceramic substrate using Au thick-film material as the conductive bonding layer and was successfully tested at 500°C in air for more than 1000 hours. In addition to the electrical test of die-attach in static thermal environments, nonlinear finite element analysis (FEA) was used for thermal mechanical evaluation and optimization of the die-attach in a wide temperature range.
A Dimple-Array Interconnect Technique for Power Semiconductor Devices
Authors: Wen Simon S. , Huff Daniel , Lu Guo-Quan
Published: April 2011

This paper describes a wireless-bond interconnect technique, termed Dimple-Array Interconnect (DAI) technique for packaging power devices. Electrical connections onto the devices are established by soldering arrays of dimples pre-formed on a metal sheet. Preliminary experimental and analytical results demonstrated potential advantages of this technique such as reduced parasitic noises, improved heat dissipation, as well as lowered processing complexity, compared to the conventional wire bonding technology in power module manufacturing. Thermomechanical analysis using thermal cycling test and FEM were also performed to evaluate the reliability characteristics of this interconnect technique for power devices.
An Investigation of Lead Free and Bromine Free Technologies for Medium Power Semiconductor Packaging
Authors: Adamson Philip , Dugdale Pamela
Published: April 2011

Over recent years there has been a growing interest in the removal or substitution of Lead, Bromine and other hazardous chemicals from electronic and electrical equipment. This relates primarily to products whose end of life disposal relies on the use of landfill sites or increasingly on recycling. The driving force for these changes come from both legislation such as that proposed by the European Union [1] and also from consumer awareness. The implications of the move towards more environmentally friendly electronics extend right down the level of discrete component packages including those produced in large numbers by the power semiconductor industry. In the present paper the technical challenges associated with the development of a lead and bromine free medium power packaging are discussed and the results of ongoing investigations are presented. The major challenges in this area relate not only to the substitution of key elements but also to ensuring compatibility with the higher reflow temperatures which may be associated with Pb-free surface mount processing. This raises particular issues with respect to the die attach material, which is often a high Pb soft solder; the encapsulation compounds which tend to rely on Bromine and Antimony compounds for their flame retardant properties; and the device plating which must be compatible with Pb-free board attach solders.
Adhesion Mechanisms of Silane Adhesion Promoters in Microelectronic Packaging
Authors: Jenkins Maura , Snodgrass Jeffrey , Chesterman Aaron , DeVries Gretchen , Dauskardt Reinhold H. , Bravman John C.
Published: April 2011

Silane adhesion promoters are seeing increasing use in microelectronic packaging applications. For example, they are currently used to adhere the passivating polymer overlayer to oxide. In this paper, we present detailed studies of silane adhesion promoters on the silicon oxide surface. Two common promoters (aminopropyltriethoxysilane and vinyltriethoxysilane) as well as non-functional silanes are investigated. It was found that without a functional end group, long carbon chain silanes can severely degrade adhesion, resulting in interfaces weaker than if no silane is used. Several spin coat solution formulations are used in depositing these films. The resulting surface coverage is examined and quantified using XPS, and the adhesion behavior of various promoter films is tested in sandwich structures using a fracture mechanics approach. Finally, spin-coat solution concentration, surface coverage, and interface fracture energy are compared for the amine functional promoter.
Dielectric Properties and Morphology of Ferroelectric Ceramic-Polymer Composite Films
Authors: Chiang C. K. , Popielarz R. , Sung L. P.
Published: April 2011

!Dielectric constant and morphology of BaTiO3-polymer composite films were studied as a function of the filler concentration. The morphology of the films was examined using laser scanning confocal microscopy, which is capable to measure small particle distributions in more details than conventional microscopy. The thin-slice images allowed us to visualize the micron-size particles and the polymer between them nondestructively. We have found that, although BaTiO3 particles appear to form clusters at low filler concentrations, the cluster formation does not affect the dielectric constant of the composites.
Aspects of Grain Size Strengthening in Polycrystals
Authors: Chandrasekaran Dilip , Pettersson Kjell
Published: April 2011

The strengthening effect of grain boundaries is well established and observed experimentally as the Hall-Petch relationship. In this paper different mechanisms proposed in the literature to explain the observed Hall-Petch effect are reviewed critically. The fundamental implications of the different approaches are discussed with reference to experimental data for two different classes of materials;

-Materials with locked dislocations, i.e. with a sharp yield point behaviour.

-Materials without locked dislocations, i.e. with a smooth yielding behaviour.

It is shown that a simple model (Bergström) can be used to understand the grain size strengthening in the latter class of materials while more work is needed to quantitatively understand the behaviour of materials showing a sharp yield point.
Dislocation patterning and conservative recovery in single slip
Authors: Veyssière Patrick , Grégori Fabienne
Published: April 2011

Prismatic loops generated by cross-slip are organised in staircase-like strings such that the beginning of a loop corresponds in the screw orientation with the end of its neighbour. Strings constitute nucleation sites for dislocation tangles thus offering an explanation for spontaneous patterning in single glide. A loop string can be partially and even totally eliminated by a single impacting dislocation. In dense walls, loop refinement can also take place conservatively by mutual annihilation of loops of opposite signs.
Microelectronics Process Engineering: A Non-Traditional Approach to MS&E
Authors: Allen E. , Gleixner S. , Young G. , Parent D. , Dessouky Y. , Vanasupa L.
Published: April 2011

Materials Science and Engineering straddles the fence between engineering and science. In order to produce more work-ready undergraduates, we offer a new interdisciplinary program to educate materials engineers with a particular emphasis on microelectronics-related manufacturing. The bachelor's level curriculum in Microelectronics Process Engineering (μProE)is interdisciplinary, drawing from materials, chemical, electrical and industrial engineering programs and tied together with courses, internships and projects which integrate thin film processing with manufacturing control methods. Our graduates are prepared for entry level engineering jobs that require knowledge and experience in microelectronics-type fabrication and statistics applications in manufacturing engineering. They also go on to graduate programs in materials science and engineering. The program objectives were defined using extensive input from industry and alumni. We market our program as part of workforce development for Silicon Valley and have won significant support from local industry as well as federal sources. We plan to offer a vertical slice of workforce development, from lower division engineering and community college activities to industry short courses. We also encourage all engineering majors to take electives in our program. All our course and program development efforts rely on clearly defined learning objectives.
Teaching General Chemistry Through Materials Science
Authors: Douglas Elliot P.
Published: April 2011

We have developed a new Materials Chemistry course for freshmen with the goal of improving retention in the engineering program. This Materials Chemistry course is fundamentally different from other introductory materials courses in that it does not cover the standard introductory materials curriculum (diffusion, strengthening mechanisms, eutectic phase diagrams, etc.). Rather, its goal is to teach engineering applications of fundamental chemistry concepts. This course consists of four basic units: atomic, molecular and supermolecular structures; chemical reactions; physical chemistry; and biological materials. Each of these units consists of topics designed to show how fundamental concepts in chemistry can be applied to engineering problems. For example, liquid crystal display technology is used to teach the concept of molecular shape. The course also contains a laboratory section. This paper will describe the detailed contents of the course and its relation to the engineering curriculum.
A Curriculum Resource for Materials Science and Engineering Education - Elementary School Through College
Authors: Jacobs James A , Mckenney Alfred E
Published: April 2011

This paper presents a new CD-ROM, (EMSET2, ISBN 0-13-030534-0) [1] which provides useful resources for courses in engineering and technology. A product of a fifteen-year effort, this CD contains hundreds of demonstrations and experiments which have been classroom tested and peer reviewed. These resources are available in the popular Adobe Acrobat PDF format, accessible thorough the Acrobat Reader, which is included. The contents are useful for such courses as materials science, materials technology, mechanics and strength of materials, as well as for pre-college level course and school visitations. Additional PDF-formatted resources on the CD-ROM include a short course on Microscopy of Fiber-Reinforced Polymer Composites, an Image Gallery showing materials, applications photos, photomicrographs of a wide range of materials, a structural models gallery, and related web site hyperlinks. There is also a section on how we made the PDFs. The manner in which the demonstrations and experiments are written provides useful tips on securing supplies and construction of devices. Topics include Structure, Testing & Evaluation, Metals, Polymers, Ceramics, Composites, Electronic & Optical Materials, as well as ideas for Materials Curriculum development.
Teaching Materials Characterization Techniques: An Interdisciplinary Approach to Develop Interactive Web-Based Multimedia Teaching/Learning Software
Authors: Prüßner Karin , Pingel Klaus , Dressel Horst-Peter , Becker Jens , Reiner Christof , Schlosser Marc , Christ Hans-Jürgen
Published: April 2011

In a first step of a larger project to develop software to teach materials characterization techniques, we have developed a module on scanning electron microscopy (SEM) to be used mainly in a Department of Mechanical Engineering. The goal is to use the unique capabilities of the computer to develop a platform-independent interactive web-based software package which can be used as a stand-alone application or as support in existing “traditional” classes and improve the quality of teaching. Commercial development tools like Macromedia Dreamweaver for HTML pages, Macromedia Flash and JBuilder to create animations and visualizations of basic concepts and simulations of microscope operations are used for improved teaching quality.
Low Temperature Preparation of High-Quality Pb(Zr,Ti)O3 Films by Metal Organic Chemical Vapor Deposition with High Reproducibility
Authors: Funakubo Hiroshi , Nagashima Kuniharu , Aratani Masanori , Tokita Kouji , Oikawa Takahiro , Ozeki Tomohiko , Asano Gouji , Saito Keisuke
Published: April 2011

Pb(Zr,Ti)O3 (PZT) is one of the most promising materials for ferroelectric random access memory (FeRAM) application. Among the various preparation methods, metalorganic chemical vapor deposition (MOCVD) has been recognized as a most important one to realize high density FeRAM because of its potential of high-step-coverage and large-area-uniformity of the film quality.

In the present study, pulsed-MOCVD was developed in which a mixture of the source gases was pulsed introduced into reaction chamber with interval. By using this deposition technique, simultaneous improvements of the crystallinity, surface smoothness, and electrical property of the film have been reached by comparing to the conventional continuous gas-supplied MOCVD. Moreover, this film had larger remanent polarization (Pr) and lower leakage current density. This is owing to reevaporation of excess Pb element from the film and increase of migration on the surface of substrate during the interval time.

This process is also very effective to decrease the deposition temperature of the film having high quality. In fact, the Pr and the leakage current density of polycrystalline Pb(Zr0.35Ti0.65)O3 film deposited at 415 °C were 41.4 μC/cm2 and on the order of 10−7 A/cm2 at 200 kV/cm. This Pr value was almost the same as that of the epitaxially grown film deposited at 415 °C with the same composition corrected for the orientation difference. This suggests that the polycrystalline PZT film prepared by pulsed-MOCVD had the epitaxial-grade ferroelectric properties even through the deposition temperature was as low as 415 °C. Moreover, large “process window” comparable to the process window at 580 °C, above 150 °C higher temperature and was widely used condition, was achieved even at 395°C by the optimization of the deposition condition.
Low-Temperature Crystallization of Pb(Zr0.4,Ti0.6)O3 Thin Films by Chemical Solution Deposition
Authors: Maki Kazunari , Soyama Nobuyuki , Nagamine Kaoru , Mori Satoru , Ogi Katsumi
Published: April 2011

We studied the crystallization of sol-gel derived Pb(Zr0.4Ti0.6)O3 [PZT(40/60)] thin films at 400 down to 390°C on Pt/SiO2/Si substrates by combination of diol-based solutions and modified film preparation processes. It was found that PZT films could be crystallized at 390°C and that PZT films crystallized at 400°C had microstructures with perovskite-single-phase columnar grains and good ferroelectric characteristics such as switched polarization (2 Pr) of 20 μC/cm2 and relative permittivity (εr) of 740. Next, we evaluated annealing temperature dependence of PZT(40/60) thin films crystallized at 390 to 435°C. The results indicated that (111)-orientation of perovskite phases became weaker, (100)-orientation of those became stronger, and the perovskite grain size increased with decreasing in annealing temperature.
Probing the Dead Layer in Barium Strontium Titanate Capacitors Made by Pulsed Laser Deposition
Authors: Sinnamon L. J. , Bowman R. M. , Gregg J. M.
Published: April 2011

Thin film capacitors with structures Au/Ba0.5Sr0.5TiO3/SrRuO3 were fabricated by pulsed laser deposition onto {001}-oriented MgO single crystal substrates. As part of an overall programme to investigate the so-called ‘dead-layer’ effect, polarisation loops were taken from the capacitors and analysed as a function of BST film thickness. Analysis was done within a Landau-Ginzburg-Devonshire (LGD) framework, and showed that for film thickness greater than ∼100nm, changes in the dielectric behaviour of the BST were dominated more by epitaxial mismatch strain, than by the conventional notion of the dead-layer.
Fabrication of V-Substituted (Bi,M)4Ti3O12 [M = Lanthanoids] Thin Films by Chemical Solution Deposition Method
Authors: Uchida H. , Yoshikawa H. , Okada I. , Matsuda H. , Iijima T. , Watanabe T. , Funakubo H.
Published: April 2011

Bismuth titanate (Bi4Ti3O12; BIT) -based ferroelectric materials are proposed from the view of the “Site-engineering”, where the Bi-site ions are substituted by lanthanoid ions (La3+ and Nd3+) and Ti-site ions by other ions with higher charge valence (V5+). In the present study, influences of vanadium (V) - substitution for (Bi,M)4Ti3O12 thin films [M = lanthanoid] on the ferroelectric properties are evaluated. V-substituted (Bi,M)4Ti3O12 films have been fabricated using a chemical solution deposition (CSD) technique on the (111)Pt/Ti/SiO2/(100)Si substrate. Remnant polarization of (Bi,La)4Ti3O12 and (Bi,Nd)4Ti3O12 films has been improved by the V-substitution independent of the coercive field. The processing temperature of BLT and BNT films could also be lowered by the V-substitution.
Crystallization Behavior and Ferroelectric Properties of YMnO3 Thin Films on Si (100) Substrates
Authors: Yoo Dong Chul , Lee Jeong Yong , Kim Ik Soo , Kim Yong Tae
Published: April 2011

YMnO3 thin films were sputtered on Si (100) substrates under different ambient conditions. After rapid thermal annealing process at 850 °C, the YMnO3 film deposited in Ar ambient had random orientations and the YMnO3 film deposited in Ar+O2 ambient was crystallized with distinct two layers, i.e., c-axis oriented layer in top region and random oriented layer in bottom region. Relations between the microstructure and the electrical properties of Pt/YMnO3/Si capacitor were investigated. Memory window and leakage current depended on the orientation of the YMnO3 thin films and the interfacial microstructure of the YMnO3/Si, respectively
Preparation and Characterization of a- and b-Axis-Oriented Epitaxially Grown Bi4Ti3O12-Based Thin Films on Rutile-Type Oxides
Authors: Watanabe Takayuki , Saito Keisuke , Osada Minoru , Funakubo Hiroshi
Published: April 2011

a- and b-axis-oriented epitaxial Bi4Ti3O12 films were prepared on (101)TiO2 substrates (rutile) at 600°C by metalorganic chemical vapor deposition (MOCVD). Subsequently, the same films were similarly prepared on (101)-oriented conductive materials with the same rutile structure and similar lattice parameters as TiO2, such as RuO2 and IrO2. Their perfect epitaxial growth was confirmed by several X-ray diffraction measurements. RuO2 and IrO2 were deposited on not only structurally equivalent (101)RuO2//(101)TiO2 and (101)IrO2//(101)TiO2 structures, but were also successfully deposited on the corundum (012)Al2O3 and (110)Al2O3 single crystals by the MOCVD and rf-sputtering method, respectively. A well-saturated P-E hysteresis with a remanent polarization above 20 μC/cm2 was observed for a- and b-axis-oriented Bi4Ti3O12-based materials, (Bi4−xNdx)(Ti3−yVy)O12 (BNTV), that were epitaxially grown on rutile-rutile and rutile-corundum stacking structures. These results should enable broader application of the bismuth layer-structured ferroelectrics.
Size Effects on Polarization in Epitaxial Ferroelectric Films and the Concept of Ferroelectric Tunnel Junctions Including First Results
Authors: Kohlstedt H. , Pertsev N. A. , Waser R.
Published: April 2011

Extrinsic and intrinsic size effects on the spontaneous polarization of epitaxial ferroelectric films are discussed. The extrinsic effect of electrostatic origin is attributed to the presence of nonferroelectric subsurface layers in the film. Theoretical studies of this depolarizing-field effect are reviewed. It is concluded that, for perovskite ferroelectrics sandwiched between electrodes with a perovskite structure, the depolarizing-field effect on the static properties should be negligible. The extrinsic size effect is also attributed to the thickness dependence of the film in-plane lattice strain Sm, which is due to the generation of misfit dislocations in the epitaxy. Variation of the film polarization with the misfit strain Sm is described by a nonlinear thermodynamic theory, which allows for the mechanical film/substrate interaction. The intrinsic effect of the film surfaces, which is associated with spatial correlations of the ferroelectric polarization, is simultaneously taken into account via the concept of extrapolation length δ. It is shown that, in films grown on compressive substrates (Sm < 0), the strain-induced increase of the mean polarization prevails over the negative intrinsic size effect (δ > 0). As a result, well below the transition temperature, ferroelectricity may be present even in nanometer-thick epitaxial layers. Motivated by this result, we propose the concept of ferroelectric tunnel junction. First results on tunnelling through ultrathin barriers of perovskite ferroelectrics are presented.
Crystallization of BaTiO3 Thin Films Prepared by Metalorganic Decomposition with Hydrothermal Treatment at 140°C
Authors: Wei Zhiqiang , Noda Minoru , Okuyama Masanori
Published: April 2011

BaTiO3 (BTO) thin films with perovskite structure have been prepared on Pt/Ti/SiO2/Si substrates using a combined process of a conventional MOD (metal organic decomposition) process and a hydrothermal treatment. The BTO thin films with polycrystalline structure are grown on Pt/Ti/SiO2/Si substrates at a processing temperature of 140°C. The structural development, stoichiometry, spectroscopic, and dielectric properties of the BTO thin films have been systematically investigated. X-ray diffraction patterns show that well-developed crystallites with a pure perovskite phase have been formed. ICP (Inductively coupled plasma) and XPS (x-ray photoelectron spectroscopy) results show that stoichiometric BTO thin films were obtained.
Ferroelectic BaTiO3 Thin Film Optical Waveguide Modulators
Authors: Petraru A. , Siegert M. , Schmid M. , Schubert J. , Buchal Ch.
Published: April 2011

High quality BaTiO3 epitaxial thin films on MgO substrates have been grown by pulsed laser deposition (PLD). Both c-axis and a-axis orientated BaTiO3 were studied. Mach-Zehnder (M-Z) optical waveguide modulators have been fabricated by ion beam etching. The BaTiO3 waveguide propagation losses are 1-2 dB/cm. Electro-optic modulation has been demonstrated with Vπ = 6.3 V at a wavelength of 633 nm and Vπ = 9.5 V at a wavelength of 1550 nm for the aaxis samples and with Vπ = 8 V at 633 nm wavelength and Vπ = 15 V at 1550 nm for the c-axis samples. Modelling of the modulators gave the Pockels coefficient r51 = 80 pm/V for the c-axis film and an effective Pockels coefficient reff =734pm/V for the a-axis films at 633nm wavelength.
Fabrication and Properties of Epitaxial Lithium Niobate Thin Films by Combustion Chemical Vapor Deposition (CCVD)
Authors: Jiang Yong Dong , McGee Jake , Polley Todd A. , Schwerzel Robert E. , Hunt Andrew T.
Published: April 2011

Lithium niobate has a wide variety of applications because of its excellent ferroelectric, piezoelectric and electrooptic properties. In this study, epitaxial lithium niobate thin films were deposited on c-sapphire (α-Al2O3) by the low-cost, open-atmosphere Combustion Chemical Vapor Deposition (CCVD) technique developed by MicroCoating Technologies, Inc. It was found that deposition temperature plays a critical role in determining the growth behavior and quality of the lithium niobate thin films. XRD measurements show that the lithium niobate films are epitaxial with two in-plane orientations (twin structure). A surface roughness (root mean square) of about 4 nm was obtained from the deposited film (about 200 nm thick), as measured by optical profilometry.
Local Polarization, Charge Compensation, and Chemical Interactions on Ferroelectric Surfaces: a Route Toward New Nanostructures
Authors: Bonnell Dawn A. , Kalinin Sergei V.
Published: April 2011

The local potential at domains on ferroelectric surfaces results from the interplay between atomic polarization and screening charge. The presence of mobile charge affects surface domain configuration, switching behavior, and surface chemical reactions. By measuring the temperature and time dependence of surface potential and piezo response with scanning probe microscopies, thermodynamic parameters associated with charge screening are determined. This is illustrated for the case of BaTiO3 (100) in air, for which the charge compensation mechanism is surface adsorption and enthalpy and entropy of adsorption are determined. The local electrostatic fields in the vicinity of the domains have a dominant effect on chemical reactivity. Photoreduction of a large variety of metals can be localized to domains with the appropriate surface charge. It has been demonstrated that proximal probe tips can be used to switch polarization direction locally. Combining the ability to ‘write’ domains of local polarization with domain specific reactivity of metals, vapors of small molecules, and organic compounds leads to a new approach to fabricating complex nanostructures.
Higher Order Nonlinear Dielectric Microscopy
Authors: Cho Yasuo , Ohara Koya
Published: April 2011

A higher order nonlinear dielectric microscopy technique with higher lateral and depth resolution than conventional nonlinear dielectric imaging is investigated. The proposed technique involves the measurement of higher order nonlinear dielectric constants, with a depth resolution of down to 1.5 nm. The technique is demonstrated to be very useful for observing surface layers of the order of unit cell thickness on ferroelectric materials.
Variable-Range Hopping in the Array of Magnetic Quantum Dots
Authors: Foygel M. , Morris R. D. , Petukhov A. G.
Published: April 2011

We analyzed the spin-dependent conductivity in the system of paramagnetic quantum dots embedded in semi-insulating matrix, which is due to bound magnetic polaron (BMP) inter-dot hopping. If such a system is characterized by wide distributions of the “bare” electron energies and BMP shifts, variable-range and variable-polaron-barrier hopping can be observed at low temperaturesT. It results in the giant magnetoresistance,ρ(H, T ) governed by a non-activation law, lnρ /α [T0(H)/T ]p, whereT0(H) drops with magnetic field,H. Depending on the conditions, parameters of the material, and the dimensionality of the system, the exponent 0.25 < p < 0.75. This type ofT -dependence has been observed in GaMnAs and MnGe magnetic semiconductors.
Spin Hall Effect in a Magnetic Field
Authors: Zhang Shufeng
Published: April 2011

When a spin-polarized current is injected into a non-magnetic semiconductor, a transverse electric field known as Hall voltage is generated. By using a macroscopic diffusion equation, we derive the Hall voltage in the presence of both spin current and magnetic field. Novel features such as oscillating Hall signals as a function of the magnetic field and geometrical dependence of Hall signals are predicted.
Inverse TMR Effect in Co0.9Fe0.1/SrTiO3/La0.7Sr0.3MnO3 Tunnel Junctions
Authors: Sugiyama M. , Asano H. , Matsui M. , Hayakawa J. , Kokado S. , Itou K. , Sakuma A. , Ichimura M.
Published: April 2011

Magnetic tunnel junctions of Co0.9Fe0.1/SrTiO3 (STO)/ La0.7Sr0.3MnO3 (LSMO) with a spin-valve structure having an antiferromagnetic MnIr layer have been fabricated by sputtering. Junction magnetoresistance (MR) behavior and its dependence on the bias voltage are examined for junctions with epitaxial STO barrier formed under different sputtering conditions. Spin dependent transport measurements show that these junctions exhibit spin-valve type MR loops with an inverse (positive) MR of the ratio of 14-22 % at 4.2 K. The inverse MR observed is asymmetric with respect to the bias voltage direction. Stoichiometric STO barrier, as characterized by Rutherford backscattering (RBS) analysis, is found to result in very large asymmetric bias dependence, while the junctions with nonstoichiometric STO barrier exhibit the symmetric bias dependence. Our results suggest that the nonstoichiometry of STO barrier modifies the electronic structures of electrode/barrier interfaces, and thereby reducing the asymmetry of bias voltage dependence of junction MR.
Electronic Structure and Magnetic Properties of Transition Metal Doped Silicon Carbide
Authors: Miao M. S. , Lambrecht Walter R. L.
Published: April 2011

The magnetic properties of cubic (3C) silicon carbide (SiC) doped by first row transition metals (TM) are studied within the local spin density functional approach using the linearized muffin-tin orbital (LMTO) method in the atomic sphere approximation (ASA). The magnetic properties are found to depend strongly on the doping site. For the preferred doping site (Si), Cr and Mn exhibit the most pronounced magnetic behavior with Cr favoring ferromagnetic coupling and Mn antiferromagnetic coupling.
Proposal of a Novel Spin Filter Realized in a Triple Barrier Resonant Tunnel Diode using Rashba Spin-Orbit Interaction
Authors: Koga Takaaki , Nitta Junsaku , Datta Supriyo , Takayanagi Hideaki
Published: April 2011

A spin rectifying diode, which utilizes Rashba spin-orbit coupling, is proposed using semiconducting triple barrier structures. This spin diode makes use of spin-dependent resonant tunneling levels that are formed in the triple barrier structures. We found that, for a certain emitter-collector bias voltage, it is possible to engineer the structure in such a way that a resonant l evel formed within the first quantum well matches that of the second quantum well only for a selected spin state, thus realizing an electronic spin rectifier. The calculated spin polarization of the transmitted current through the device, which is defined as I↑–I↓/(I↑+I↓), is found to be higher than 99.9%.
Ion Beam Deposited Gmr Materials
Authors: Lannon J. M. , Pace C.C. , Temple D. , McGuire G.E , Hebard A.F. , Ray M.
Published: April 2011

Ion beam sputter deposition (IBSD) techniques for deposition of giant magnetoresistance (GMR) films have been studied using an automated IBSD system designed and built in-house. We have studied the properties of Fe/Cr multilayers deposited using either Ar or Xe ions with the primary ion beam energy varying from 500 eV to 1100 eV. The films were characterized using transmission electron microscopy (TEM), atomic force microscopy (AFM), Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), secondary ion mass spectroscopy (SIMS), magnetization measurements, and magnetoresistance measurements. The maximum value of GMR obtained was 49% (measured at 10K). For the Cr spacer thickness layer chosen, this GMR ratio is larger than the values reported for polycrystalline Fe/Cr multilayers deposited by magnetron sputtering. In general, we have found that GMR ratios for the Fe/Cr multilayers increase with decreasing primary ion beam energy, and are greater for films deposited using Xe ions than for films deposited using Ar ions. We explain the observed effects on the basis of energy distributions of sputtered atoms and backscattered working gas atoms (neutrals). The energy distributions were calculated using TRIM (Transport of Ions in Matter) software based on the Monte Carlo method.
Magnetic Anisotropy of Strained La0.7Sr0.3MnO3 Thin Films Studied by MOKE
Authors: Koubaa M. , Haghiri-Gosnet A.M. , Lecoeur P. , Prellier W. , Mercey B.
Published: April 2011

The effects of the growth conditions and the lattice strains of pulsed laser deposited (PLD) La0.7Sr0.3MnO3 (LSMO) thin films upon the magnetic behavior have been studied using magneto-optical Kerr effect (MOKE) at room temperature. First, the structural quality of the films was investigated by XRD and the surface morphology was studied using AFM. It is shown that both surface morphology and crystallinity are optimized when the target-to-substrate distance and the oxygen pressure are chosen in agreement with a PD3 scaling law. Secondly, hysteresis loops have been recorded along the [100], [110] and [001] directions and the easy directions of magnetization have been determined for both stress states, i.e. tension on SrTiO3 and compression on LaAlO3. In tensile films, the whole plane is found to be easy, whereas, in compressive films, the easy axis should be an intermediate direction between the film's plane and its normal. Moreover, tensile films deposited under optimized growth conditions exhibit the largest anisotropy coefficient (K1eff = -6.9×105 erg/cm3).
Effect of rapid thermal annealing: red and blue shift in photoluminescence of GaNAs grown by RF plasma-assisted molecular beam epitaxy
Authors: Loke W. K. , Yoon S. F. , Ng T. K. , Wang S. Z. , Fan W. J.
Published: April 2011

Rapid thermal annealing (RTA) of 1000Å GaNAs films grown on (100) oriented GaAs substrate by radio frequency (RF) plasma assisted solid-source molecular beam epitaxy was studied by low-temperature photoluminescence (PL) and high-resolution x-ray diffraction (HRXRD). Samples with nitrogen content of 13 and 2.2% have shown an overall blueshift in energy of 67.7meV and an intermediate redshift of 42.2meV in the PL spectra when subjected to RTA at 525–850°C for 10min. It is also shown that the sample, which is annealed at temperature range of 700–750°C, has the highest photoluminescence efficiency (1.7–2.1 times increase in integrated PL intensity as compared to the as-grown sample). Reciprocal space mapping of the as-grown GaNAs samples obtained by using triple-crystal HRXRD shows the presence of interstitially incorporated of N atoms with no lattice relaxation in the direction parallel to the growth surface. These results have significant implication on the growth and post-growth treatment of nitride compound semiconductor materials for high performance optoelectronics devices.
Growth of High Nitrogen Content GaAsN by Metalorganic Chemical Vapor Deposition
Authors: Roberts J. C. , Moody B. F. , Barletta P. , Aumer M. E. , LeBoeuf S. F. , Luther J. M. , Bedair S. M.
Published: April 2011

The incorporation of a high percentage of nitrogen in the GaAs lattice has been the subject of recent interest to reduce the bandgap while maintaining the nearly lattice matched condition to GaAs. We will report on the metalorganic chemical vapor deposition (MOCVD) of GaAsN using trimethylgallium (TMG), tertiarybutylarsine (TBA) and dimethylhydrazine (DMHy) organometallic sources in a hydrogen-free carrier gas. A nitrogen concentration as high as ∼8% in GaAsN was achieved. The effect of nitrogen concentration on the structural, optical and surface properties of GaAsN films will be discussed.