bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

AbstractExtrinsic 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

AbstractBaTiO3 (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

AbstractHigh 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

AbstractLithium 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

AbstractThe 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

AbstractA 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

ABSTRACTWe 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

ABSTRACTWhen 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

ABSTRACTMagnetic 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

ABSTRACTThe 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

ABSTRACTA 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

ABSTRACTIon 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

ABSTRACTThe 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

AbstractRapid 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

AbstractThe 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.
Ion Implantation Induced Interdiffusion in Quantum Wells for Optoelectronic Device Integration
Authors: Fu L. , Tan H. H. , Cohen M. I. , Jagadish C. , Dao L. V. , Gal M. , Li Na , Li Ning , Liu X. , Lu W. , Shen S. C. 
Published: April 2011

AbstractIon implantation induced intermixing of GaAs/AlGaAs and InGaAs/AlGaAs quantum wells was studied using low temperature photoluminescence. Large energy shifts were observed with proton implantation and subsequent rapid thermal annealing. Energy shifts were found to be linear as a function of dose for doses as high as ∼5×1016 cm−2. Proton implantation and subsequent rapid thermal annealing was used to tune the emission wavelength of InGaAs quantum well lasers as well as detection wavelength of GaAs/AlGaAs quantum well infrared photodetectors (QWIPs). Emission wavelength of lasers showed blue shift whereas detection wavelength of QWIPs was red shifted with intermixing.
A Bowtie Antenna Coupled Tunable Photon-Assisted Tunneling Double Quantum Well (DQW) THz Detector
Authors: Khodier Majid M. , Christodoulou Christos G. , Simmons Jerry A. 
Published: April 2011

AbstractThe integration of a bowtie antenna with a double electron layer tunneling transistor (DELTT) device for the purposes of THz detection is investigated in this paper. The concept of THz detection, based on photon-assisted tunneling (PAT) between the two electron layers in a double quantum well (DQW) heterostructure, will be explained. The detector is expected to have narrowband, electrically tunable, fast response, and the possibility to operate at relatively high temperatures. Since the active area of the detector is very small, which is necessary to achieve fast response, it is not efficient in collecting THz radiation. Therefore, a broadband bowtie antenna is integrated with the detector to efficiently collect the THz radiation. Characteristics of different bowtie antenna geometries at THz frequencies were studied. An equivalent circuit model of the THz detector was developed, for the first time, to estimate the impedance characteristics at THz frequencies. Such a model is crucial for achieving impedance matching between the DELTT and the antenna to increase the overall coupling efficiency.
Fast Room Temperature Detection of State of Circular Polarization of Terahertz Radiation
Authors: Ganichev Sergey D. , Ketterl Hermann , Prettl Wilhelm 
Published: April 2011

AbstractWe report on a room temperature detector which allows to determine and monitor the state of polarization of terahertz radiation with picosecond temporal resolution. The detector is based on the circular photogalvanic effect recently observed in GaAs/AlGaAs quantum wells. The circular photogalvanic effect yields in response to elliptically polarized radiation a current signal proportional to the degree of circular polarization. The peak current signal occurs in unbiased samples for circular polarization, vanishes at linear polarization and changes sign by switching the helicity from right-handed to left-handed. The detector consists of a (113)A MBE grown p-GaAs/AlGaAs multiple quantum well structure. The response has been measured in the wavelength range between 76 μm and 280 μm at normal incidence of the radiation on the sample.
Scatterometry for Lithography Process Control and Characterization in IC Manufacturing
Authors: Kostoulas Yiorgos , Raymond Christopher J. 
Published: April 2011

AbstractAs modern circuit architecture features steadily decrease in size, more accurate tools are needed to meaningfully measure critical dimensions (CD). As a general rule, a metrology tool should be able to measure 1/10 of the product tolerance. An emerging technology for high speed, high accuracy CD measurement is scatterometry. This paper describes scatterometrybased measurements of metal features of 350 nm with a space of 450 nm (pitch of 800nm) on top of a complicated layer stack and compares them with the results of an atomic force microscope (AFM). We also looked into lithography cell monitoring and trending by measuring CDs on 3 daily litho cell monitors over a period of 40 days. Our long term results show excellent agreement with those of a scanning electron microscope (CD-SEM).
Influence of Er and O doses in Er-related emission in Al0.70Ga0.30As:Er
Authors: Uekusa Shin-ichiro , Arai Tomoyuki 
Published: April 2011

AbstractEr ions with doses ranging from 1×1013 cm−2 to 1×1015 cm−2 were implanted into Al0.70Ga0.30As on GaAs substrates. at 800 °C. Photoluminescence (PL) intensity of Er-related emission around 1.54 μm was enhanced by co-implanted oxygen (O). The optimum dose of Er ion was 1×1014 cm−2 and O ion was 1×1015 cm−2, respectively. Furthermore, from the temperature dependence of the PL intensity of sample implanted with the optimum dose, we estimated the values of E1, E2, and E3, the activation energies in order to investigate the rapid thermal quenching of Er ion in Al0.70Ga0.30As. We found that PL intensity of Er-related emission, in addition to O dose, was enhanced approximately twenty two times at room temperature. And from the temperature dependence of the lifetime of the optimum dose of Er and O, the value 245meV of EA, the activation energy for the decrease of the lifetime, was nearly equal to the value 235meV of E3. Based on the result, the decrease of the lifetime confirms that the radiative efficiency is lower; therefore, we propose that rapid thermal quenching occurs at temperatures above 200 K due to the decrease of the radiative efficiency.
Intra-magnetoexciton transitions in semiconductor quantum wells
Authors: Barticevic Z. , Pacheco M. , Duque C. A. , Oliveira L. E. 
Published: April 2011

AbstractHighly sensitive optically detected resonance experiments have shown that magnetoexcitons in GaAs-(Ga,Al)As semiconductor quantum wells have discrete internal energy levels, with transition energies found in the far-infrared (terahertz) region. Here we are concerned with a theoretical study of the terahertz transitions of light-hole and heavy-hole confined magnetoexcitons in GaAs-(Ga,Al)As quantum wells, under a magnetic field applied in the growth direction of the semiconductor heterostructure. The various magnetoexciton states are obtained in the effective-mass approximation by expanding the corresponding exciton-envelope wave functions in terms of appropriate Gaussian functions. The electron and hole cyclotron resonances and intra-magnetoexciton transitions are theoretically studied by exciting the allowed electron, hole and internal magnetoexcitonic transitions with far-infrared radiation. Theoretical results are obtained for both the intra-magnetoexciton transition energies and oscillator strengths associated with excitations from 1s - like to 2s, 2p±, and 3p±- like magnetoexciton states, and from 2p- to 2s – like exciton states. Present results are in overall agreement with available optically detected resonance measurements and clarifies a number of queries in previous theoretical work.
Electron scattering in two-dimensional disordered heterostruetures
Authors: Gómez I. , Diez E. , Domínguez-Adame F. , Orellana P. 
Published: April 2011

AbstractThe main aim of this work is to study electron scattering in imperfect semiconductor heterostruetures. The source of unintentional disorder is the interface roughness at the heterojunctions occurring during growth. In order to achieve this goal we solve numerically the two–dimensional Ben Daniel–Duke equation for the electron scattering problem. Our model assumes open boundary conditions along the growth direction and periodic ones parallel to the heterojunctions. We then compute the reflection and transmission matrices that govern channel mixing due to interface roughness scattering. The knowledge of the mixing matrices allow us to calculate the transmission coefficient in any heterostruc-ture made of wide gap semiconductors. As an example, we compute the transmission coefficient in resonant tunneling devices based on double-barrier structures.