bluuebunny/crossref_metadata_2025_split huggingface dataset:
Reciprocal Space X-Ray Mapping and Transmission Electron Microscopic Studies of Coincided δ-Inas and As-Cluster Superlattices in Gaas Films Grown by Molecular-Beam Epitaxy at Low Temperature
Authors: Chaldyshev V. V. , Bert N. A. , Faleev N. N. , Musikhin Yu. G. , Kunitsyn A. E. , Preobrazhenskii V. V. , Putyato M. A. , Semyagin B. R. , Werner P. , Takeda Y. 
Published: April 2011

AbstractInAs/GaAs superlattices with thin (0.5–1 monolayer) δ-InAs insertions were grown by molecular beam epitaxy at low (150–200°C) temperature. The as-grown samples contained up to 1020 cm−3 arsenic antisite defects. Transmission electron microscopic study revealed no extended defect and showed that the real thickness of δ-InAs insertions is 3–4 monolayers. This thickness seems to be due to short-range roughness of the growth surface. Low diffuse scattering and extended interference picture were observed for such superlattices by x-ray diffraction study. Superlattices of two-dimensional cluster sheets were produced by annealing of the δ-InAs/GaAs superlattices at 500–600°C. Precipitation of excess arsenic at InAs δ-layers was found to be accompanied by enhanced In-Ga intermixing, roughening the InAs δ-layers, and smoothing the x-ray interference picture. No evidence for any self-ordering in the system of nanoscale As clusters was revealed using x-ray mapping in reciprocal space.
Growth Phenomena of Quantum Dot Structures in the Ingaas System Investigated by Tem Techniques
Authors: Werner P. 
Published: April 2011

AbstractThe contribution is mainly focused on the formation and properties of InGaAs islands (quantum dots, QD) in a GaAs matrix, viz. a system showing properties similar to those of other materials systems. Depending on the growth techniques applied (MBE or MOCVD), the islands/dots differ in size, shape, chemical composition, and lattice strain. These parameters influence strongly the optical properties of QD structures, which might consist of single layers or complex 3-dimensional arrays. To reveal the correlation between the morphology/structure and the optical behavior of such systems different analytical methods are available, more effective in some combined applications. The present paper is mainly focused on the possibilities and limitations of transmission electron microscopy (TEM) to analyze the lattice structure of QDs down to the nm-range. Such TEM investigations imply a general problem: to deconvolute separately information on the QD size, shape (e.g., pyramidal or spherical islands), strain and composition. TEM imaging techniques used for such structural analyses will be described, including conventional diffraction contrast and high-resolution electron microscopy, respective examples of which will be presented. For the chemical analysis energy sensitive techniques (e.g., energy filtered images) are appropriate methods. Applications and limitations of such investigations will be discussed.
X-Ray and Tem Studies of Short-Range Order in Al1−xInxAs Thin Films
Authors: Kulik Joseph , Forrest Rebecca , Li Jianhua , Golding Terry , Moss Simon C. , Bai Jianming 
Published: April 2011

AbstractX-ray scattering and transmission electron microscopy (TEM) have been used to study short-range order in Al1−xlnxAs thin films grown by molecular beam epitaxy. Two samples grown on (001) InP at temperatures of 370°C and 400°C are characterized. The first exhibits simultaneous triple-period-A and CuPt-A short-range order with a rather short correlation range of about 2.4 nm normal to the (111) planes. Within these (individual) planes the concentration, however, is uniform over a considerably greater distance – about 6 to 9 nm – leading to a highly anisotropic scattering. This observation of triple-period short-range ordering in a sample that exhibits 2×1 surface reconstruction during growth is unexpected. We also report on the first observation of the coexistence of triple-period-A and CuPt-B short-range order. The diffuse scattering exhibits significant intensity anomalies that we attribute to atomic displacements associated with the short-range order. The second sample exhibits CuPt-B short-range ordering with scattering that is significantly streaked, suggestive of lamellar-shaped ordered domains. This sample also exhibits intensity anomalies that must be associated with atomic displacements. The first sample contains a high density of twin lamellae, while both samples contain high densities of stacking faults leading to additional narrow streaking along symmetry-allowed 〈111〉 directions. These growth faults most likely arise from the relatively low growth temperatures.
Epitaxial Growth of CuAu–Ordered CuInSe2 Structural Polytypes by Migration Enhanced Epitaxy
Authors: Stanbery B. J. , Chang C.-H. , Kim S. , Kincal S. , Lippold G. , Ahrenkiel S. P. , Li L. , Anderson T. J. , Al-Jassim M. M. 
Published: April 2011

AbstractMigration-Enhanced Epitaxy (MEE) has been successfully employed to grow epitaxial films of the ternary compound CuInSe2 on (001) GaAs that are ordered in a CuAu crystallographic structure rather than the compound's equilibrium chalcopyrite structure. Evidence for this structural polytype is provided by XRD, TEM–TED, and Raman scattering data. Film growth under the conditions employed for this study occurs in a Stranski-Krastanov mode. The effects of growth system parameters and overall stoichiometry on 3–D island formation are described, including our observation that ordering of those islands into quasiperiodic self-assembled arrays occurs only in the case of nonstoichiometric copper excess.
Morphological and Compositional Instabilities of Strained and Unstrained Alloy Layers
Authors: Glas F. , Patriarche G. 
Published: April 2011

AbstractWe study several aspects of the instability of epitaxial layers with respect to composition modulations and surface non-planarities. After recalling previous experimental and theoretical results, we first give a detailed calculation of the elastic energy of a lattice-matched layer where both these phenomena occur. As in the lattice-mismatched case, the elastic strain fields of the modulation and the undulation interact, but the critical temperature under which composition modulations become favorable remains the same as in the planar layers. However, when a composition modulation is present, the system is unstable to a specific class of surface undulations. We then discuss TEM experiments investigating systematically the morphological instability in superlattices containing either tensile or compressive layers. Growth on surfaces variously disoriented with respect to (001) allows us to study two debated points: Does the instability develop by bunching of steps already present on the substrate or through nucleation of new steps? What is the nature of the asymmetry between tensile and compressive layers? We show that in the compressive layers, the surface non-planarity develops by bunching of a large fraction of the original substrate steps, whereas for layers under tension facets appear.
Growth and Characterization of Inas Quantum Dots on Silicon
Authors: Hansen L. , Ankudinov A. , Bensing F. , Wagner J. , Ade G. , Hinze P. , Wagner V. , Geurts J. , Waag A. 
Published: April 2011

AbstractUp to 1011 cm−2 InAs quantum dots (QD) can be grown on Silicon(001) by molecular beam epitaxy. This very new material system is on the one hand interesting with regard to the integration of optoelectronics with silicon technology on the other hand it offers new insight into the formation of QDs. We report on RHEED, TEM and Raman studies about (in-) coherence of the QDs and on an according to our knowledge so far unknown dewetting transition in this material system. The results are being discussed on the basis of a thermodynamic model, assuming a liquid-like behavior of a strained adlayer.
Profiling Composition Variations in Composition-Modulated GaP/InP Short-Period Superlattices Using Resonance Raman Scattering
Authors: Cheong H. M. , Zhang Yong , Norman A. G. , Perkins J. D. , Mascarenhas A. , Cheng K. Y. , Hsieh K. C. 
Published: April 2011

AbstractWe use resonance Raman scattering (RRS) and electroreflection (ER) measurements to profile the the composition and strain variations in laterally composition-modulated (CM) GaP/InP short-period superlattices (SPS's). The ER spectra of a GaP2.2/InP2.0 SPS give the fundamental band-gap energy at 1.69±0.05eV, which is about 210 meV lower than the band gap energy of a GaInP random alloy with the same overall composition. The RRS measurements reveal strong dependences of the phonon spectrum on the polarization and the excitation energy. In RRS spectra measured with the polarization of both excitation and scattered photons along the composition modulation direction, the GaP-like longitudinal optical (LO) phonon redshifts by 4.0±0.5 cm−1 near the resonance with the fundamental energy gap. On the other hand, when the polarizations are orthogonal to the composition modulation, the LO phonons redshift as much as 16 cm−1 at low excitation energies. A comparison of the experimental data with a model calculation gives the average In composition in the In-rich region as 0.70±0.02, and the average Ga composition in the Ga-rich region as 0.68±0.02. Our result also indicates that there are small volumes (less than 1% volume fraction) with very high In mole fraction.
Self-Organized Composition Modulation In Omvpe Ga1−xInxAsySb1−y/GaSb Epitaxial Heterostructures
Authors: Chen Y-C. , Bucklen V. , Rajan K. , Wang C. A. , Charache G. W. , Nichols G. , Freeman M. , Sander P. 
Published: April 2011

AbstractMicrostructures of lattice-matched Ga1−xInxAsySb1−y grown by organometallic vapor phase epitaxy (OMVPE) on (100) 6°→ (111)B GaSb substrates have been examined in detail by transmission electron microscopy. A three-dimensional self-organized composition modulation (SOCM) microstructure was found with an orientation inclined 10 degrees to the surface orientation when viewed in (011) cross-section. The periodicity of the SOCM increased from ˜13 nm to 20 nm, as x increased from 0.1 to 0.2 while the orientation of the SOCM remained the same. The fact that the orientation was not sensitive to the component composition indicated that substrate misorientation plays a major role in deciding this SOCM orientation. This may open fabrication opportunities for three-dimensional natural superlattices by engineering on the substrate misorientation.
Novel Stm Probe Assisted Site-Control of Quantum Dots With Nanometer Precision
Authors: Nakamura Hitoshi , Kohmoto Shigeru , Ishikawa Tomonori , Asakawa Kiyoshi 
Published: April 2011

AbstractWe propose a novel site-control technique for strained quantum dots (QDs) based on nano-lithography using an STM integrated into a UHV STM/MBE multi-chamber system. A nano-scale deposit was formed on a GaAs surface by applying voltage between the GaAs surface and the tungsten tip of the STM. Since the deposit acted as a nano-mask, the subsequent GaAs growth formed a nano-hole just above the deposit. Subsequent InAs supply produced a QD on the hole site, and no QD was observed in any undesirable regions. We also observed the QD formation processes involved in the technique, based on step-by-step STM observations of the QD formation process. The observation directly revealed an InAs wetting layer formation with 1-ML thickness on the GaAs terraces followed by the QD formation in the Stranski-Krastanow growth mode.
Optical Characterization and Process Control of Top Surface Imaging
Authors: Luo Ying-Ying , Stauffer Craig , Ygartua Carlos , Chu Dinh , Hayzelden Clive 
Published: April 2011

AbstractThe use of selectively silylated resists to facilitate top surface imaging offers the potential for nanoscale lithography using both deep ultra violet (DUV) illumination and electron beam techniques. In this process, an exposure-generated crosslinking prevents silicon incorporation from silylating agents. In the non-crosslinked regions, a silylation agent reacts with OH groups in the resist to form silicon-oxygen bonds. During subsequent dry development in an oxygen plasma, the incorporated silicon attracts oxygen to form silicon dioxide, protecting the resist underneath. The adjacent un-silylated resist erodes (develops) anisotropically 25–100 times faster than the silylation-protected resist. The key to this process is the chemical formation of a silylated region at the top of the resist. A challenge associated with the silylation process, however, is lateral swelling of the silylated layer, which can lead to difficult dimensional control. The amount of swelling depends on the amount of incorporated silicon. Therefore, the uniformity and repeatability of the silylation process must be controlled. This paper will describe how spectroscopic ellipsometry has been used to characterize and monitor the resist silylation process in a non-destructive manner. The simultaneous characterization of the thicknesses and optical properties of a series of silylated resists will be presented. Optical metrology of the thickness of the silylated resists will be correlated with SEM cross-sectional analyses, and process uniformity will be quantified using 49-site wafer maps.
Extending the Possibilities of Near-Field Scanning Optical Microscopy for Simultaneous Topographical and Chemical Force Imaging
Authors: Nagy N. , Goh M. C. 
Published: April 2011

AbstractThe Near-field Scanning Optical Microscope (NSOM) is an innovative new form of surface microscopy, which can be used to obtain local spectroscopic information about surfaces, enabling the characterization of nanometer-sized regions. The most important component of this instrument is the scanning probe tip. In this paper, we discuss the production of a novel fiber optic probe that can be used in local spectroscopy with an NSOM, but also for
simultaneous imaging of topography and chemical forces. The probe consists of a bent, tapered silicon dioxide optical fiber. We have determined the rates of selective wet chemical etching of germanium dioxide doped pure silica optical fibers and used this information to optimize the probe etching process. A systematic approach for the development and testing of such probes is presented. The performance of the optical probes was characterized using surfaces prepared by the technique of microcontact printing. Phase and friction images of these surfaces were obtained using both standard atomic force microscopy tips and the optical fiber probe. The new optical probe was capable of distinguishing between different chemical regions on the patterned surface.
Effects of Interface Roughness and Embedded Nanostructures on Device Properties
Authors: Ting D. Z.-Y. , Mcgill T. C. , Chen N. Y. , Wang J. N. , Li R. G. , Wang Y. Q. , Ge W. K. , Schulman J. N. 
Published: April 2011

AbstractWe give an overview of the open-boundary planar supercell stack method (OPSSM), as a means for treating 3D quantum transport in mesoscopic tunnel structures. The flexibility of the method allows us to examine a variety of physical phenomena relevant to quantum transport. In this work we focus on the effects of interface roughness and embedded nanostructures in tunnel devices. Four representative applications of OPSSM are discussed: (1) interface roughness in double barrier resonant tunneling structures, (2) self-organized InAs quantum dot insertions in GaAs/AlAs double barrier structures, (3) tunneling characteristics of ultra-thin oxides with interface roughness, and, (4) embedded quantum wire model of dielectric breakdown. These examples demonstrate scattering and localization effects under different biasing conditions.
Cluster Model Study of the Incorporation Process of Excess Arsenic into Interstitial Positions of the GaAs Lattice
Authors: Marek T. , Kunsági-Máté S. , Strunk H. P. 
Published: April 2011

AbstractWe study an As2 molecule approaching a planar, non-reconstructed, As terminated GaAs(001) surface by using a suitable cluster and quantum mechanical ab-initio calculation methods. During our calculations the As2 molecule is always oriented perpendicularly to the surface and its bonding length may vary. We find a metastable position below the growing surface which facilitates the incorporation of the leading As atom into an interstitial position of the crystal during growth. We give a first model for this incorporation process.
Step Bunching during SiGe Growth on Vicinal Si(111) Surfaces
Authors: Hibino H. , Ogino T. 
Published: April 2011

AbstractWe investigate step bunching during SiGe growth on vicinal Si(111) surfaces. Step bunching occurs irrespective of the misorientation angle and direction of the vicinal surface, the growth temperature, and the Ge concentration. At 550°C, the average number of the steps in the bunch increases with the Ge concentration. After growth of 10-nm-thick SiGe layers, twodimensional islands are formed on the terraces, which indicates that the terrace width has already been saturated. Therefore, the terrace width is mainly determined by the diffusion length of the adatom. The average number of steps in the bunch increases with the Ge concentration because the diffusion length increases with the Ge concentration. The diffusion length also increases with the temperature. So the higher the temperature is, the larger the step bunch becomes.
Anisotropic Organic/Inorganic Resists: A Novel Concept for Electron Proximity Effect Reduction
Authors: Merhari Lhadi , Li Henry H. , Gonsalves Kenneth E. 
Published: April 2011

AbstractElectron projection lithography is considered to be one of the best candidates for sub-100 nm production circuits. One of the major problems that hinders its development is not related to machine fabrication issues but to electron proximity effects which stem from fundamental electron-polymer interactions. During the past two decades, efforts to reduce the electron proximity effects have essentially focused on the optimization of the resist exposure by means of dose modulation correction programs. We propose a novel approach where the structure of the resist can be tailored so that controlled anisotropy is introduced to laterally constrain the electron scattering. This novel approach does not require the use of high-voltage electron beams nor the processing of a large amount of data, which is a significant economic advantage. Some concepts for the synthesis of these anisotropic resists are discussed and the preliminary example of iron oxide nanorods aligned in poly(methylmethacrylate) (PMMA) is studied.
On the Influence of Applied Fields on Spinel Formation
Authors: Korte C. , Farrer J. K. , Ravishankar N. , Michael J. R. , Schmalzried H. , Carter C. B. 
Published: April 2011

ABSTRACTInterfaces play an important role in determining the effect of electric fields on the mechanism of the formation of spinel by solid-state reaction. The reaction occurs by the movement of phase boundaries but the rate of this movement can be affected by grain boundaries in the reactants or in the reaction product. Only by understanding these relationships will it be possible to engineer their behavior. As a particular example of such a study, Mgln2O4 can be formed by the reaction between single-crystal MgO substrate and a thin film of In2O3with or without an applied electric field. High-resolution backscattered electron (BSE) imaging and electron backscattered diffraction (EBSD) in a scanning electron microscope (SEM) has been used to obtain complementary chemical and crystallographic information.
Adhesion Properties of Cellulose Films
Authors: Zhang Xiujuan , Young Raymond. A. 
Published: April 2011

ABSTRACTThe adhesion properties were evaluated for untreated and modified cellulose (cellophane) films. Several functional groups were introduced on the film surfaces by plasma based treatments. All the films were characterized by atomic force microscopy (AFM) and scanning electron microscopy (SEM). AFM was employed to study the adhesion properties using both standard silicon nitride tips as well as self-assembled monolayer (SAM) modified gold coated tips containing a variety of specific functional groups. The acetone extracted cellulose films, which are rich in –OH groups, were used as substrates. The adhesion force detected with –COOH terminated AFM tips (∼ 34.8 nN) was much larger than that with –CH3 terminated AFM tips (∼16.7 nN), which was attributed to the hydrogen bonding between –COOH and –OH functional groups. The adhesion force of –NH2 terminated AFM tips on the acetone extracted cellulose film was higher at 42.92 nN. However, after surface modification of the cellulose films with argon and oxygen based plasma treatments, the adhesion force were decreased to 17.4 and 19.4 nN respectively as a result of greatly enhanced surface roughness. Hydrazine plasma treatment also was used to introduce –NH2 groups on the film surfaces, and the strongest adhesion behavior was observed with AFM tips terminated with -COOH groups on the aminated film due to acid-base interaction. The argon and oxygen plasma treatment greatly increased the surface roughness, resulting in poor adhesion properties. Both surface roughness and chemical modification of the cellophane films affected the adhesion properties as measured by AFM force curves.
Observations of Interaction Between Magnetic Domain Wall and Grain Boundaries in Fe-3wt%Si Alloy by Kerr Microscopy
Authors: Kawahara K. , Yagyu Y. , Tsurekawa S. , Watanabe T. 
Published: April 2011

ABSTRACTMagnetic domain structures in Fe-3wt%Si alloy have been observed by a Kerr microscopy to understand the interaction between the magnetic domain wall and grain boundaries. It was found that the domain structures in the vicinity of the grain boundary depend on the misorientation angle; the high angle random boundary disturbs the magnetic domain structure more than the low angle boundary. In addition to the misorientation angle, magnetic domain structures were affected by the inclination of the grain boundary plane. Moreover, dynamic observations of rearrangement of the magnetic domain structure during magnetization revealed that grain boundaries could act as the sink and/or the source for magnetic domains.
Integranular Fracture: The Effect of Grain Boundary Orientation and Crack Growth Directions
Authors: Kysar Jeffrey W. 
Published: April 2011

ABSTRACTIntergranular fracture is a common failure mechanism for which many issues remain to be resolved. In this study we investigate intergranular fracture behavior of specially oriented symmetric tilt bicrystals of aluminum as well as the fracture behavior of a crack along the interface of a copper-sapphire bicrystal. We begin by describing briefly the structure of a symmetric tilt grain boundary which leads to a discussion of the types of issues related to intergranular fracture that can be addressed with symmetric tilt grain boundaries. We then discuss in detail one of these issues, that of the directional dependence of fracture, and present results of finite element simulations of a copper-sapphire bicrystal specimen that exhibits the directional dependence of fracture. The simulations account for the single crystal nature of the constituents and use a cohesive-zone model, for which the grain boundary energy can be varied, to simulate the fracture process along the interface. The directional dependence of fracture emerges from the simulations for a broad range of parameters in the constitutive models of both the single crystal constituents as well as the interfacial cohesive-zone.
Creep in Polycrystalline Aluminum
Authors: Briant C. L. , Davidson D. L. 
Published: April 2011

ABSTRACTThis paper presents a study of creep in polycrystalline aluminum. The sample was deformed in a scanning electron microscope and local strain was measured by analyzing micrographs taken during the test. EBSP was used to examine grain curvature and recrystallization The results showed that tensile strain developed during the test. The strain was not constant but varied both spatially and with time. Significant grain boundary migration occurred during the test, and near a triple point a grain with a completely new orientation was formed.