bluuebunny/crossref_metadata_2025_split huggingface dataset:
Quantitative High-Resolution Electron Microscopy of Grain Boundaries in α-Al2O3
Authors: Höche T , Kenway P. R. , Kleebe H.-J. , Rühle M. 
Published: March 2011

AbstractDetailed structural characterization of a near Σ11 grain boundary in ultra-pure α-A12O3 bi-crystals was performed by means of high-resolution transmission electron microscopy (HRTEM). High-resolution imaging revealed a characteristic periodic pattern along the grain boundary. In addition to HRTEM studies, atomistic simulations based on an ionic model were used to calculate three-dimensional structure models that were compared with the experimentally obtained images of the grain boundary. The comparison between the simulated and experimental HRTEM images showed good agreement for the theoretically proposed grain-boundary structure with the lowest grain-boundary energy of 1.8 Jm−2.
Atomic Structure OF YΣ=5 (130) Symmetrical Tilt Boundary In Strontium Titanate
Authors: Ravikumar V. , Dravid Vinayak P. 
Published: March 2011

AbstractThe atomic structure of a pristine (undoped) boundary in strontium titanate has been investigated using transmission electron microscopy techniques. Results of electron diffraction studies indicate a pure tilt boundary with a common \001] tilt axis, and a tilt angle of 36.8°, which corresponds to a Σ-= 5 grain boundary in the Coincidence Site Lattice (CSL) notation. High Resolution Transmission Electron Microscopy (HRTEM) indicates a symmetric tilt grain boundary with a (130) type grain boundary plane. No cation non-stoichiometry or impurity segregants could be detected at the interface, within the limits of the Energy Dispersive X-ray microanalysis technique used. The grain boundary has a compact core, with negligible planenormal rigid body translation (RBT). An in-plane RBT of (1/2)d130 (˜ 0.62 A°) was identified from the high resolution electron micrographs. An empirical model of the relaxed atomic structure of the grain boundary is proposed.
Assessment Of GaInAs/GaInAsP Interdiffusion Profiles Obtained Using Stem-Edx And Hrem
Authors: Mallard R E , Long N J , Booker G R , Thrush E J , Scarrott K 
Published: March 2011

AbstractWe report on an investigation into the interfacial structure of undoped GaInAs/GaInAsP multiple quantum wells grown by metalorganic chemical vapour deposition (MOCVD), which exhibit a pronounced blue shift in luminescence output upon in-situ thermal annealing at 750°C. Using a recently developed composition mapping technique based on the scanning transmission electron microscope (STEM) in conjunction with energy dispersive X-ray (EDX) analysis, the constituent element concentration profiles across the interdiffused multilayer interfaces are measured with a spatial resolution of less than 2nm and a precision of better than 2–3%. The accuracy of the analysis is significantly improved by employing stoichiometric normalisation factors which compensate for systematic errors due to electron channelling. The results showed that the interdiffusion follows a highly non-linear path due to the relatively fast diffusion of the group V species compared to that of the group III species. This implies an increase in the coherency strain in the multilayer, a result which is supported by five-crystal Xray diffraction analysis of the layers. The samples have also been examined by high resolution electron microscopy (HREM) under chemically sensitive imaging conditions. The analysis of the interfacial chemical profile using HREM must be performed under analysis conditions for which a known and unique relationship between image contrast and composition occurs. This condition may not be satisfied in cases in which more than two chemical constituents interdiffuse and the diffusivities of these elements are not equal, as a range of similar lattice fringe motifs across the interface, representing different “diffusion paths”, could occur. The complementary nature of information provided by HREM and STEM provides a means of resolving this ambiguity.
Real-Time Viewing Of Dynamic Processes On Cdte Surfaces At Elevated Temperature
Authors: Smith David J. , Vogl R. , Lu Ping 
Published: March 2011

AbstractOnline video recording with a high-resolution electron microscope has been used to study real-time atomic events occurring at cadmium telluride surfaces over a range of temperatures from 27°C to 500°C. Using the profile imaging mode of observation, different types of surface activity have been documented on (001), (111) and (110) surfaces. For example, the (001) surfaces displayed reversible phase transformations between 2× 1 and 3×1 reconstructions at a transition temperature of about 200°C. The (111) surfaces exhibited sublimation by a ledge mechanism that depended upon the terminating surface: layer-by-layer removal invariably occurred for (110) surface terminations whereas bilayer removal was usually seen for terminations by (100) surfaces. Finally, the (110) surface rearranged by a hopping mechanism, but no substantial loss of material was observed.
Image Simulations of Ge Twin Boundaries.
Authors: Mckernan Stuart , Carter C. Barry 
Published: March 2011

AbstractGeneral high-angle tilt grain boundaries may be described by an arrangement of repeating structural units. Some grain-boundary defects may also be modeled by the incorporation of structural units of related boundary structures into the boundary. The simulation of these structures requires the use of prohibitively large unit cells. The possibility of modeling these boundaries by the superposition of image simulations of the individual structural units isinvestigated.
Low Energy Photoelectron Holography on Gaas
Authors: Denecke R. , Eckstein R. , Ley L. , Bocquet A. , Riley J. , Leckey R. 
Published: March 2011

AbstractFor GaAs (001) and (III) we have measured the photoelectron diffraction patterns at a kinetic energy of 86 eV. We applied an extended Fourier-transform algorithm to the (001) data to obtain real space images. The origin of structures in these images not representing atomic positions is investigated with the help of single scattering calculations
Imaging of Metal/Semiconductor Interface by Ballistic-Electron-Emission Microscopy (Beem)
Authors: Lee E. Y. , Turnew B. R. , Jimenez J. R. , Schowalter L. J. 
Published: March 2011

AbstractStudies in ballistic-electron-emission spectroscopy (BEES) have enabled precise energy measurements of Schottky barrier heights with excellent spatial resolution and, more recently, it was shown that even scattering at the metal/semiconductor interface affects the BEES spectrum [1]. Monte Carlo simulations have been done to predict the spatial resolution of ballistic-electron-emission microscopy (BEEM) [2]. In this paper, we will discuss the experimental spatial resolution of BEEM, and we will also give some of our BEES results for Au/Si and for Au/PtSi/Si. Our experimental BEEM studies indicate that, for Au/Si, hot electron transport is diffusive rather than ballistic, because the inelastic mean free path length (∼100 nm) is much larger than the elastic mean free path length (∼10 nm). This is in agreement with existing theories and with the literature on the internal photoemission method of studying the transport. Even in this diffusive regime, the spatial resolution of BEEM is still expected to be very good, being on the order of 10 nm [2]. Our preliminary work on PtSi shows that it has an attenuation length of 4 nm, which differs significantly from that of Au.
Rem and Rheed Studies of Pb Adsorption on Si(111)
Authors: Tanishiro Yasumasa , Fukuyama Masahiko , Yagi Katsumichi 
Published: March 2011

AbstractStructure changes of Si(111)-Pb surfaces due to deposition and heat treatment are studied by REM-RHEED. Surface structures observed are summarized as a phase diagram. Formation of an incommensurate layer(α) and a phase transition between incommensurate structures of α and α′ is described.
Atomic Structure of the (310) Twin in Niobium: Theoretical Predictions and Comparison with Experimental Observation
Authors: Campbell Geoffrey H. , Foiles S. M. , Rühle M. , King W. E. 
Published: March 2011

AbstractHigh - resolution transmission electron microscopy (HREM) has been used to characterize the atomic structure of the symmetric 36.9° tilt grain boundary with [001] tilt axes forming a twin about (310) in Nb. The projected structure was imaged along two different directions in the plane of the boundary and was compared to model structures through high - resolution image simulation. The atomic structure of this Σ5 boundary was predicted with atomistic simulations using interatomic potentials derived from the Embedded Atom Method (EAM), Finnis-Sinclair (FS), and the Model Generalized Pseudopotential Theory (MGPT). The EAM and FS predicted structures with translations of the adjacent crystals which break mirror symmetry. The MGPT predicted one stable structure with mirror symmetry. The atomic structure of the (310) twin in Nb was found by HREM to be mirror symmetric. These findings indicate that the angular dependent interactions modeled in the MGPT are important for determining the grain boundary structures of bcc transition metals.
Low Filament Temperature Deposition of a-Si:H by Catalytic Chemical Vapor Deposition
Authors: Brogueira P. , Grebner S. , Wang F. , schwarz R. , Chu V. , Conde J.P. 
Published: March 2011

Hydrogenated amorphous silicon, a-Si:H, is deposited from silane (SiH4) and hydrogen (H2) using a tungsten wire at low filament temperatures (Tfil = 1200°C) by catalytic chemical vapor deposition.The deposition rate increases monotonically with the depositions pressures and shows a maximum at an H2 : SiH4 flow ratio of unity. Vanishingly small deposition rates were observed for silane-only depositions and for H2-to-SiH4 flow ratios of 2.5 and above. The optoelectronic properties show complex dependence on substrate temperature (Tsub). Three intervals of Tsub with distinct optoelectronic were observed: as Tsub increases from 180 to 220°C, the optical bandgap, EgTauc increases from 1.9 to 2.4eV, the dark conductivity,σd, decreases from 10-10 to 10-15 Ω-1cm-1and the photoconductivity, σph, decreases from 10-5 to 10-10Ω-1cm-1 (region (i)). As Tsub increases from 220 to 250 °C, EgTauc decreases to 1.8eV and the photosensitivity, σph/σd decreases to ~ 1 due to an increase of both σd and σph (region (ii)). Throughout these two regions, the photoconductivity γ factor remains between 0.6 and 0.9 and the activation energy of the dark conductivity, Ea,σd, remains between 0.7 and 0.9eV. Above 250°C, the σph and σd remain approximately constant at 10-4 Ω-1cm-1 and γ decreases to below 0.5 and Ea,σd ~ 0.3eV.
Hydrogen Content of a-Si:H and a-Si:H,F as a Function of Chemical Annealing
Authors: Bullock J.N. , Rim K. , Wagner S. 
Published: March 2011

Chemical annealing, the periodic exposure of the growing amorphous silicon surface to H radicals, has evoked much interest because of its potential for modifying the film properties during the crucial process of sub-surface restructuring. We report the results of measurements of H content in chemically annealed a-Si:H and a-Si:H,F films.We prepared a-Si:H and a-Si:H,F in a dc-triode reactor from SiH4 and SiF4 plus H2, respectively. We chemically anneal with a H2 discharge by switching off the Si bearing gas and switching on the H2 flow after 7 s of deposition. We measure the H content with a differential pressure effusion apparatus. We also report the opto-electronic properties of these films, including the defect density after light-soaking.The key parameter of chemical annealing is the anneal duty cycle, which we specify as the fraction of the time that the H2 discharge is on. In the silane samples, we find that the H content is independent of chemical annealing. For the fluorinated samples we observe that the H content starts out at about 5 at.% without chemical annealing, rises to 10-15 at.% at 0.5 to 0.7 annealing duty cycle, and then decays to 6-7 at.% at 0.9 duty cycle. Although not fully understood, we offer evidence that these effects are due to the physics of the glow-discharge rather than surface reactions.
Mossbauer Spectroscopy Studies of Amorphous Metallic Solids
Authors: Chien C. L. 
Published: March 2011

ABSTRACTMössbauer spectroscopy as applied to the studies of amorphous metallic, and often magnetic solids will be discussed. The advantages of using this microscopic technique will be compared with others in terms of obtaining information on electronic, magnetic, hyperfine, structural and other properties. Examples of magnetic ordering structures, concentration dependence of ordering temperature, hyperfine field distribution, spin-wave excitations, crystallization behavior, quadrupole interaction, isomer shift, etc., as obtained by Mössbauer spectroscopy will be presented.
Defects in Metals–Detected by Spin Precession Methods
Authors: Wichert TH. , Recknagel E. 
Published: March 2011

ABSTRACTRecent advances in the study of point defects and small defect clusters by nuclear methods will be reviewed. Suitable radioactive atoms which fulfill the requirements of spin precession techniques are introduced into solids, where they are used as microscopic probes to investigate their immediate surrounding. Trapping, detrapping or annealing of defects is reflected by changes of the hyperfine interaction between the nuclear moments of the probe atoms and the electromagnetic fields of the defects. The interaction is extracted from a time differential spin precession pattern or–more obviously–from the Fourier transform of it, which can be regarded as the resonance spectrum of the involved frequencies. It allows a distinct recognition of different defects and comprises detailed information about their structural properties. Experimental data on interstitials, vacancies and clusters in metals will be quoted as illustrations for the scope of information, which can be achieved by hyperfine interaction studies.
Muons as Light Hydrogen Probes–Diffusion and Trapping
Authors: Richter D. 
Published: March 2011

ABSTRACTContributions of the muon spin rotation technique (μSR) to metal physics problems are surveyed. The similarity between the muon and the proton constitutes μSR as a new tool to investigate the physics of H–like interstitials on an atomic scale. Experiments on the lattice location and on local properties like the Knight shift as well as diffusion measurements are reviewed. In particular the extreme sensitivity of muons toward impurities and lattice defects is emphasized. Results on the trapping of muons by substitutional impurities or vacancies in the ppm range are displayed.
MÖssbauer Effect Study of the Absence of Fe Magnetism in Superconducting Sc2Fe3Si5 and Th7Fe3
Authors: Cashion J. D. , Shenoy G. K. , Niarchos D. , Viccaro P. J. , Falco Charles M. 
Published: March 2011

ABSTRACTThere are only a few Fe-based compounds which are superconducting since the depairing of Cooper pairs is unavoidable in the presence of an Fe moment. In Sc2Fe3Si5 and Th7Fe3, Mössbauer measurements on 57Fe show that there is no magnetism at the Fe site in either compound. The isomer shift values indicate the reason behind this identical magnetic behavior to be quite different in its electronic origin.
Proton NMR Spin-Lattice Relaxation Time Characterization of a-Si(H) Structure
Authors: Lowry M. E. , Barnes R. G. , Torgeson D. R. , Jeffrey F. R. 
Published: March 2011

ABSTRACTNMR data are presented for reactively sputtered amorphous silicon-hydrogen alloys (a-Si(H)). Measured differences in two of the samples are attributed to two distinct morphologies: a mixed phase (monohydride and dihydride) and a purely monohydride composition. Features of the mixed phase morphology have been modeled. Room temperature, 35 MHz spin-lattice relaxation times are presented for a series of monohydride samples prepared with systematically varied sputtering parameters. A correlation of proton T1 with the density of ESR states tentatively is suggested.
Proton NMR Studies of Amorphous Plasma-Deposited Films
Authors: Reimer Jeffrey A. , Vaughan Robert W. , Knights John C. 
Published: March 2011

ABSTRACTProton magnetic resonance data are presented for the hydrogen alloys of plasma-deposited amorphous boron, silicon, carbon, silicon carbide, and silicon nitride. Linewidth and lineshape analysis leads to the conclusion that hydrogen nuclei are clustered in a-Si/C:H, a-C:H, and a-Si/NiH. The a-Si/C:H and a-C:H data show that hydrogen exists in two phases. Modeling of linewidths in a-Si/C:H indicates that the two phases are heavily hydrogenated carbon clusters imbedded in a weakly hydrogenated silicon lattice. Evidence is also presented for the presence of motionally narrowed hydrogen spectra in a-B:H, a-Si/N:H and a-C:H. “B NMR spectra in a-B:H show no evidence of motional narrowing. It is suggested that the hydrogen nuclei giving rise to the motionally narrowed spectra are associated with disorder modes.
Tdpac-Studies of Electric Field Gradients in Amorphous Metallic Systems
Authors: Heubes P. , Korn D. , Schatz G. , Zibold G. 
Published: March 2011

ABSTRACTThe time differential perturbed γ-γ angular correlation technique (TDPAC) is applied to the amorphous metallic systems Ga, Bi, In50Au50 and In80Ag20. The electric field gradient tensor probed by 111Cd nuclei shows a broad probability distribution with a relative width of 0.4 – 0.5 for all systems, as suggested by a continuous random structural model.
Radiation Damage Studies of USn
Authors: Mcguire T. K. , Herber R. H. 
Published: March 2011

ABSTRACTUranium stannide, the most stable intermetallic compound in the Uranium/Sn system, has the Cu3Au(LI2 ) structure, and is paramagnetic to liquid He temperature. The magnetic susceptibility data are consistent with 5f band states rather than a localized electronic structure. Samples of this compound have been prepared both with depleted and 235U enriched, as well as 119Sn enriched starting material. Detailed 119mSn Mössbauer effect studies have been carried out over the temperature range 78≤T≤300 K on 60Co gamma ray irradiated, thermal neutron irradiated (depleted), and thermal neutron irradiated (enriched) samples, using the V 10 position of the Brookhaven HFR facility for the neutron irradiations (thermal/fast >3.6×102). The Mössbauer hyperfine parameters are: IS(78) = 2.45 mm/sec, Q.S.(78) 1.38 mm/sec for the unirradiated samples, consistent with the metallic nature of Sn in the USn3 structure. No anomalous charge states have been identified in the Mössbauer spectra of the gamma or neutron irradiated samples. The free-atom lattice temperature is ∼250 K for the unirradiated sample, and shows only minor changes with 60Co–γ radiation to a total dose of 1000 Megarad. Thermal neutron radiation (nvt ∼5×1016 ) of the depleted sample results in a lowering of the lattice temperature to ∼240 K. Two hours heating at 800°C are sufficient to anneal the radiation damage as judged by lattice dynamical data. A sample enriched to 99.94% 235U and irradiated to a fluence of ∼5×1015 slow neutrons/cm2 showed an increase in the freeatom lattice temperature to ∼275 K. A two hour anneal at 800°C restored this parameter to its original value. Resistivity data for these samples and their relationship to spin fluctuation temperatures will also be discussed.
Epr of Mn2+ in Ni(CH3COO)2 4H2O and K2 Ni(SO4)2 6H2O
Authors: Misra Sushil K. , Jalochowski M. 
Published: March 2011

ABSTRACTThe technique of electron paramagnetic resonance has been applied to study the magnetic properties of nickel acetate and nickel potassium tutton salt single crystals, using Mn2+ ion as probe. From the values of spin Hamiltonian parameters and linewidths at room, liquid nitrogen and liquid helium temperatures it is concluded that these crystals do not become magnetically ordered as the temperature is lowered to 3.2K, and thus the transition temperature, below which the crystal would order either ferromagnetically, or antiferromagnetically, for these crystals, should be below 3.2K.
Study of Internal Motion in Materials by Means of Direct Observation of Relaxation Resonances in NMR (NMRRR)
Authors: Van Gerven L. , Coppens P. , Van Hecke P. 
Published: March 2011

ABSTRACTA method, different from the classical ones, for studying internal motions - in particular reorientational and tunneling modulation of rotations - via NMR is described. Instead of looking for matching or resonance maxima in NMR T1−1 vs. T - curves [ where o (↗)≅ωo,with ρ the correlation rate and ωo: the Larmor frequency] we look for such maxima in NMR T1−1 vs. ωo - curves [where ω =↗o, with ω: the (tunneling)frequency]. These method, Nuclear Magnetic Resonance Relaxation Resonance (NMRRR), has marked advantages, which are discussed. A field cycling technique is presented. Typical results, for solid silane, are given.
Fully Planar Ion-Implanted 0.98 μm Strained Quantum Well Laser
Authors: Hobson W. S. , Pearton S. J. , Ren F. , Chu S. N. G. , Bylsma R. , Elliman R. G. 
Published: March 2011

ABSTRACTGaAs-InGaAs quantum well laser structures were fabricated using a 5 MeV O+ implant (∼1015 cm−2 dose) to disorder the quantum well for optical isolation upon post-implant annealing. End-of-range disorder is placed in the underlying substrate, and consisted of small dislocation loops. Electrical isolation was provided by a subsequent multiple energy (40-300 keV) O+ implant scheme. Masking for both implant steps was obtained using a lift-off Au deposition. This fully planar process is considerably simpler than the Si diffusion process for quantum well disordering that is commonly employed for 0.98 gim laser fabrication. A discussion will be given of the relative advantages and disadvantages of the two processes, with particular emphasis on reliability issues.
C-V and DLTS Investigations of GaAs/InGaAs/GaAs Strained Quantum Well Structures
Authors: Subramanian S. , Arora B. M. , Srivastava A. K. , Banerjee S. , Fernandes G. 
Published: March 2011

ABSTRACTIn this paper we report a modified Kroemer's analysis for the determination of the band offset (ΔEc) of single quantum well (SQW) structures from simple C-V measurements. The experimental carrier profile from an MOVPE grown pseudomorphic GaAs/InGaAs/GaAs strained SQW structure shows a sharp accumulation peak bounded by depletion regions on either side. The full width at half maximum of the accumulation peak is comparable to the width of the quantum well. The value of ΔEC obtained from C-V measurement is in good agreement with the values determined by simulation and photoluminescence measurements. DLTS measurements on our SQW samples do not show any peaks which is contrary to the published reports. We believe that it is necessary to carefully isolate the role of interface states, before assigning a DLTS peak to emission from the quantum well.
Low Temperature SiNx as a Sacrificial Layer in Novel Device Fabrication
Authors: Lothian J. R. , Ren F. , Pearton S. J. , Abernathy C. R. , Tseng B. , Hobson W. S. 
Published: March 2011

ABSTRACTIn this paper we will describe applications of a low temperature SiNx for the novel fabrication of lasers and FET's. Sidewall roughness which appears on dry etched semiconductor laser mesas is a common problem in laser fabrication. Protecting the sidewall with a low temperature PECVD SiNx can greatly reduce laser mesa roughness that occurs during dry etching of the mesa. Another application uses low temperature SiNx to extend the resolution of standard optical replication. Submicron gate fingers in field effect transistors can be fabricated by using this low-temperature SiNx deposition. By depositing SiNx on the photoresist gate pattern and etching back the SiNx leaving a sidewall, this will reduce the opening of gate features. Submicron gate length MESFETs have been demonstrated with this technique which showed comparable results to conventional submicron MESFETs fabricated with E-beam direct writing.