bluuebunny/crossref_metadata_2025_split huggingface dataset:
Real-time x-ray scattering study of sputter-deposited LaNiO3 thin films on Si substrates
Authors: Lee Hsin-Yi , Lee Chih-Hao , Liang Keng S. , Wu Tai-Bor 
Published: April 2011

ABSTRACTReal-time x-ray reflectivity and diffraction measurements under in-situ sputtering deposition conditions were performed to study the crystallization behavior of LaNiO3thin films on Si substrate. We found that an amorphous layer of 60 Å was grown in the first 6 min of the deposition and subsequently a polycrystalline overlayer was developed as observed from the in-situ x-ray reflectivity curves and diffraction patterns. Polycrystalline columnar textures of (110) and (100) were grown on the top of this amorphous film. By comparing the integrated intensities of two Bragg peaks in the plane normal of x-ray diffraction, it was found that the ability of (100)-texturization enhanced with increasing film thickness over a certain critical value.
In-Situ Real-Time Depth Profiling by Elastic Recoil Detection and Its Application to Ion Nitriding of Stainless Steel
Authors: Kruse O. , Parascandola S. , Groetzschel R. , Moeller W. 
Published: April 2011

ABSTRACTA dual beam experiment has been set up combining real-time depth profiling and low energy ion implantation in order to study the kinetics of ion nitriding. The choice of low energy ion implantation allows precise and independent control of the important ion nitriding parameters ion energy, ion current density, temperature and residual gas composition. Real-time depth profiling is achieved by Elastic Recoil Detection (ERD) using an angle resolving ionization chamber telescope detector. A large solid angle (5.4 msr) allows a fast data acquisition and hence real-time depth profiling with a time resolution of about 30 s combined with a depth resolution of about 10 nm. The capabilities of the setup and its limitations will be discussed. Measurements revealing the role of mechanisms relevant for the nitrogen transport during ion nitriding of stainless steel i.e. diffusion, sputtering, adsorption of oxygen from the residual gas will be presented.
The Identification of the Metallic Glass State
Authors: Spaepen Frans 
Published: April 2011

AbstractDavid Turnbull has been the most prominent figure in the identification of the metallic glass state. This paper reviews his many contributions: the free volume model for transport in simple liquids, the demonstration of a substantial crystal nucleation barrier in liquid metals, the prediction of the universality of the glass transition, the formulation of criteria for glass formation, the first demonstration of the characteristic glass transition phenomena in a metallic glass, and important contributions to the study of the structure and physical properties.
Nucleation and Glass Formation
Authors: Uhlmann D. R. , Weinberg M. C. 
Published: April 2011

AbstractThe role of nucleation kinetics in affecting glass formation behavior is discussed. Also considered are measurements of homogeneous crystal nucleation in a variety of liquids. For a number of oxide glass-forming liquids, available data indicate pre-exponential factors which are larger than those predicted from classical nucleation theory by factors of 1017 to 1049. Possible sources of this discrepancy are discussed.
Photocurrent Spectroscopy of InAs/GaAs Self-Assembled Quantum Dots: Observation of a Permanent Dipole Moment
Authors: Fry P.W. , Itskevich I.E. , Mowbray D.J. , Skolnick M.S. , Barker J.A. , O'Reilly E.P. , Wilson L.R. , Larkin I.A. , Maksym P.A. , Hopkinson M. , Al-Khafaji M. , David J.P.R. , Cullis A.G. , Hill G. , Clark J.C. 
Published: April 2011

ABSTRACTPhotocurrent spectroscopy of InAs/GaAs self-assembled quantum dots, studied as a function of applied electric field, is used to probe the nature of the confined electronic states. A field asymmetry of the quantum confined Stark effect is observed, consistent with the dots possessing a permanent dipole moment. The sign of this dipole indicates that for zero field the hole wavefunction lies above that of the electron, in disagreement with the predictions of all recent calculations. Comparison with a theoretical model demonstrates that the experimentally determined alignment of the electron and hole can only be explained if the dots contain a nonzero and non-uniform Ga content. The role of two different carrier escape mechanisms, tunneling and thermal excitation, is studied.
Charge Separation Between Strain Coupled Quantum Dots in a Self-Assembled InAs Quantum Dot Structure
Authors: Schoenfeld W. V. , Lundstrom T. , Petroff P. M. 
Published: April 2011

ABSTRACTWe present an InAs QDs structure designed to separate and store photo-generated electron-hole pairs. Charge separation in the structure is demonstrated using power dependent photoluminescence and biased photoluminescence. Preliminary data from time resolved photoluminescence suggest storage times in the device in the μsec range.
Charge Generation and Transport in CdSe Semiconductor Quantum Dot Solids
Authors: Leatherdale C. A. , Morgan N.Y. , Kagan C. R. , Empedocles S. A. , Bawendi M. G. , Kastner M. A. 
Published: April 2011

ABSTRACTWe demonstrate photoconductivity and conductivity in three-dimensional close-packed solids of colloidal CdSe quantum dots. We observe quantum dot size and surface passivation dependent photoconductivity that can be qualitatively understood by considering the energy required in order to overcome the Coulomb energy of the initial electron-hole pair. Our results suggest that surface ligands that promote initial separation of the electron and hole reduce the electric field required for the onset of the photocurrent. The dark conductance is much smaller than the photoconductance. Hysteretic behaviour and extremely long-lived current transients are observed in the dark current that are suggestive of Coulomb-glass behaviour.
Interfacial Electron Transfer in MoS2 Nanoclusters
Authors: Parsapour F. , Kelley D.F. 
Published: April 2011

ABSTRACTThe dynamics of photoinduced electron transfer between 3.0 nm diameter MoS2 nanoclusters and adsorbed electron acceptors have been studied using static and time resolved optical spectroscopy. Two types of electron acceptors are adsorbed on these nanoclusters: 2,2'-bipyridine and 4,4',5,5'-tetramethyl-2,2'-bipyridine. The results reported here focus on the interpretation of the strongly non-exponential electron transfer kinetics. Electron/hole recombination kinetics have previously been analyzed in terms of a simple distributed kinetics model, and this model is extended to include the case of interfacial electron transfer.
Microstructure and Nonstoichiometry of Barium Strontium Titanate thin films for dram Applications
Authors: Stemmer S. , Streiffer S. K. , Browning N. D. , Kingon A. I. 
Published: April 2011

AbstractIn this paper we investigate the microstructural accommodation of nonstoichiometry in (BaxSr1-x)Ti1+yO3+Z thin films grown by chemical vapor deposition. Films with three different (Ba+Sr)/Ti ratios of 49/51 (y=0.04 in the notation of the formula above), of 48/52 (y = 0.08) and of 46.5/53.5 (y=0.15), were studied. High-resolution electron microscopy is used to study the microstructure of the BST films. High-spatial resolution electron energy-loss spectroscopy (EELS) is used to reveal changes in chemistry and local atomic environment both at grain boundaries and within grains as a function of titanium excess. We find an amorphous phase at the grain boundaries and grain boundary segregation of excess titanium in the samples with y=0.15. In addition, EELS is also used to show that excess titanium is being partially accommodated in the grain interior. Implications for the film electrical and dielectric properties are outlined.
Investigation of Growth Evolution in c-Axis SrBi2Nb2O9 Epitaxial Thin Films
Authors: Lettieri J. , Zurbuchen M. A. , Brown G. W. , Jia Y. , Tian W. , Pan X. Q. , Hawley M. E. , Schlom D. G. 
Published: April 2011

Abstract(001)-oriented epitaxial SrBi2Nb2O9 thin films have been grown by pulsed laser deposition on (001) SrTiO3 and (001) LaAlO3—Sr2AlTaO6 substrates at optimized growth conditions. 4-circle x-ray diffraction, Rutherford backscattering spectrometry, and transmission electron microscopy reveal highly oriented epitaxial films. Atomic force microscopy indicates spiral growth for films grown on SrTiO3 and layer-by-layer growth for films grown on LaAlO3—Sr2AlTaO6.
First Principles Calculation of the Hot Electron Lifetime in Simple and Noble Metals
Authors: Campillo I. , Rubio A. , Pitarke J. M. , Echenique P. M. 
Published: April 2011

ABSTRACTFirst-principles calculations of the inelastic lifetime of low-energy electrons in Al. Cu and Au are reported. Quasiparticle damping rates are evaluated from the knowledge of the electron self-energy, which we compute within the GW approximation. Inelastic lifetimes are then obtained along various directions of the electron wave vector, with full inclusion of the band structure of the solid. Average lifetimes are also reported, as a function of the electron energy. In Al splitting of the band structure over the Fermi level yields electron lifetimes that are smaller than those of electrons in a free-electron gas. In Cu and Au, a major contribution from d electrons participating in the screening of electron-electron interactions yields electron lifetimes which are well above those of electrons in a free-electron gas with the electron density equal to that of valence (4s1 and 6s1 respectively) electrons.
Optical Properties of Cu-(110) Surface
Authors: Monachesi Patrizia , Palummo Maurizia , Sole Rodolfo Del , Ahuja Rajeev , Eriksson Olle 
Published: April 2011

ABSTRACTWe present the first ab initio calculations of the optical properties of the (110) clean surface of Cu for which the Anisotropic Surface Reflectivity (RAS) has been recently measured. This technique exploits the anisotropy of the reflectivity along the directions [110], [001] on the surface. Calculations are performed with a Full Potential Linear Muffin Tin Orbital method, within LDA, in the slab geometry. The comparison of our calculated Surface Dielectric Anisotropy (SDA) ω[1110] – [001] with the one obtained from the RAS spectrum is almost satisfactory for a slab of 11 atomic layers.
Process and Mechanism of CoSi2/Si Solid Phase Epitaxy by Multilayer Reaction
Authors: Li Bing-Zong , Qu Xin-Ping , Ru Guo-Ping , Wang Ning , Chu Paul 
Published: April 2011

AbstractA multilayer structure of Co/a-Si/Ti/Si(100) together with Co/Ti/Si(100) is applied to investigate the process and mechanism of CoSi2 epitaxial growth on a Si(100) substrate. The experimental results show that by adding an amorphous Si layer with a certain thickness, the epitaxial quality of CoSi2 is significantly improved. A multi-element amorphous layer is formed by a solid state amorphization reaction at the initial stage of the multilayer reaction. This layer acts as a diffusion barrier, which controls the atomic interdiffusion of Co and Si and limits the supply of Co atoms. It has a vital effect on the multilayer reaction kinetics, and the epitaxial growth of CoSi2 on Si. The kinetics of the CoSi2 growth process from multilayer reactions is investigated.
Nanoscale Sn Inclusions in Al – Structure and Melting-Solidification Properties
Authors: Johnson E. , Bahl C.R.H. , Touboltsev V.S. , Johansen A. 
Published: April 2011

AbstractAl-Sn surface alloys with 2-3 at.% Sn have been made by ion implantation of Sn in Al. The microstructure of the alloys consists of dense distributions of nanoscale Sn inclusions embedded in the Al matrix. For implantations carried out at 425 K the inclusions have sizes in the range from about 2 to 15 nm. The structure of the inclusions is tetragonal - the white Sn structure – with lattice parameters of a = 0.583 nm and c = 0.318 nm respectively, i.e. identical to the lattice parameters of bulk Sn. The inclusions grow in preferred alignment with the matrix and the most commonly observed orientation relationships is given by (100)Sn ||(111)Al and [010]Sn || [211]Al. The shape of the inclusions is partly faceted and partly rounded with larger flat facets on the {100}Sn/{111}Al interfaces. Melting and solidification of the inclusions, which have been studied by in-situ transmission electron microscopy (TEM) and Rutherford backscattering spectrometry (RBS) in combination with channeling, shows a distinct hysteresis. Melting of the inclusions which is associated with a distinct premelting, takes place in the range from about 430 K to 485 K, i.e. significantly below the bulk melting point of 505 K. The premelting is size dependent and the smallest inclusions melt at the lowest temperatures. Solidification requires a substantial undercooling and takes place from around 400 K with a much weaker size dependence.
Grain Growth in Nanocrystalline Nickel
Authors: Hibbard G.D. , Erb U. , Aust K.T. , Palumbo G. 
Published: April 2011

AbstractIn this study, the effect of grain size distribution on the thermal stability of electrodeposited nanocrystalline nickel was investigated by pre-annealing material such that a limited amount of abnormal grain growth was introduced. This work was done in an effort to understand the previously reported, unexpected effect, of increasing thermal stability with decreasing grain size seen in some nanocrystalline systems. Pre-annealing produced a range of grain size distributions in materials with relatively unchanged crystallographic texture and total solute content. Subsequent thermal analysis of the pre-annealed samples by differential scanning calorimetry showed that the activation energy of further grain growth was unchanged from the as-deposited nanocrystalline nickel.
Phase Field Approach to Transformations Involving Concurrent Nucleation and Growth
Authors: Simmons J.P. , Shen C. , Wang Y. 
Published: April 2011

AbstractA model is developed that is capable of simulating simultaneous nucleation, growth, and coarsening. Growth and coarsening are simulated with a 2-D Phase Field model and nucleation is simulated by a stochastic algorithm. The actual nucleation events are simulated by placing ordered particles in the matrix, according to the local supersaturation, with the mean rate of introduction matching that of the nucleation rate. The nucleation rates are input parameters that could, for example, be supplied by experiment or atomistic modeling. Isothermal results for this model under conditions approaching constant nucleation show excellent agreement with the Johnson-Mehl- Avrami-Kolmogorov (JMAK) theory of isothermal transformations involving nucleation and growth. Because the Phase Field simulation is interrupted in order to put particles in, problems can arise due to the mismatch of the assumed diffusion field about the nucleating particles and that would be obtained as a result of growth. This can lead to numerical instabilities as the simulation parameters are adjusted to approach the site saturation extreme as well as underestimating the transformation rate by a small transient time. Preliminary step quench results showed the method to be stable enough to simulate non-isothermal transformations with a series of step quench operations.
Effects of Transient Diffusion on Ipvd Feature Scale Evolution
Authors: Kim G. -S. , Hansen U. P. , Rodgers S. T. , Jensen K. F 
Published: April 2011

AbstractWe present a simulation study of the long range diffusion behavior of impinging atoms during ionized physical vapor deposition conditions with focus on grazing angles of incidence and kinetic energies in the range of 35 eV to 50 eV. Two different types of long range diffusion processes are observed and investigated: (1) diffusion of atoms ultimately adsorbing and (2) diffusion of atoms that eventually desorb. The simulations reveal that the second case is particularly pronounced for grazing angles and high kinetic energies, since the adsorption probability is very low under those conditions. In a further step, information about diffusion lengths is incorporated into a previously developed level set profile simulator to predict thin film topologies. These feature scale simulations show that long-range diffusion diminishes “macroscopic” grooving.
Surface Smoothing upon Deposition of Nanoparticles on Single Crystalline Substrates
Authors: Zimmermann C. G. , Liu C. P. , Yeadon M. , Nordlund K. , Gibson J. M. , Averback R. S. , Herr U. , Samwer K. 
Published: April 2011

AbstractSurfaces with artificial roughness were generated by deposition of nanoparticles on single crystalline substrates. Nanoparticles with an average size ≈ 15 nm were produced by inert gas condensation and deposited in situ on the substrate mounted inside a modified ultra high vacuum (UHV) transmission electron microscope (TEM). We have investigated the smoothing behavior on annealing based on the difference in surface energies between cluster and substrate and their heat of mixing. The cluster substrate combination Co/Cu(100) was chosen as a model system in which the cluster has a significantly higher surface energy than the substrate. Upon deposition at 600 K, the clusters do not remain on the surface, but rather burrow into the substrate. This is confirmed by a detailed strain analysis of the particles. Nanoparticles in the system Ge/Si(100) in contrast have a lower surface energy than the substrate and are completely miscible. The particles assume the substrate orientation around 700 K. At 900 K coherent islands form which are arranged in clusters of 4 in the form of a square. The reason for this previously unobserved pattern is not yet understood.
Ion Beam Processing of Carbon Nitride Thin Films
Authors: Wu Richard L.C. , Lanter William C. , Wrbranek John , Kosel Peter B. , Dejoseph Charles A. 
Published: April 2011

AbstractAmorphous carbon nitride films have been deposited by two different methods: (1) direct ion beam deposition from a gas mixture of CH4/N2; and (2) nitrogen ion beam sputtering of a graphite target. The chemical composition, deposition rate, chemical bond and optical properties of the as-deposited films were studied as a function of the process parameters. In the first technique, ions (CH3+, N2+, N+, NH4+, NH3+, NH2+, HCN+, CN+ and N2H2+) were directly impacted onto the substrate surface. The effects of RF power, CH4/N2 gas ratio, total gas flow, pressure, and ion energy on the film properties and deposition rates were studied. In the second technique, a flux of energetic nitrogen ions (N2+, N+), generated by N2 and N2/Ar plasmas, were used to directly sputter a graphite target. In this case, the effects of RF power, gas mixture (N2, N2/Ar), and ion energy on the film characteristics and deposition rates were determined. The properties of the films generated by the two alternative techniques were also compared.
Field Emission from Carbon Films Deposited by Controlled-Low-Energy Beams and CVD Sources
Authors: Lowndes Douglas H. , Merkulov Vladimir I. , Baylor L. R. , Jellison G. E. , Poker D. B. , Kim S. , Sohn M. H. , Paik N. W. 
Published: April 2011

AbstractThe principal interests in this work are energetic-beam control of carbon-film properties and the roles of doping and surface morphology in field emission. Carbon films with variable sp3-bonding fraction were deposited on n-type Si substrates by ArF (193 nm) pulsed-laser ablation (PLA) of a pyrolytic graphite target, and by direct metal ion beam deposition (DMIBD) using a primary Cs+ beam to generate the secondary C- deposition beam. The PLA films are undoped while the DMIBD films are doped with Cs. The kinetic energy (KE) of the incident C atoms/ions was controlled and varied over the range from ∼25 eV to ∼175 eV. Earlier studies have shown that C films' sp3-bonding fraction and diamond-like properties can be maximized by using KE values near 90 eV. The films' surface morphology, sp3–bonding fraction, and Cs-content were determined as a function of KE using atomic force microscopy, TEM/EELS, Rutherford backscattering and nuclear reaction measurements, respectively. Field emission (FE) from these very smooth undoped and Cs-containing films is compared with the FE from two types of deliberately nanostructured carbon films, namely hot-filament chemical vapor deposition (HF-CVD) carbon and carbon nanotubes grown by plasma-enhanced CVD. Electron field emission (FE) characteristics were measured using ∼25-μm, ∼5-μm and ∼1-μm diameter probes that were scanned with ∼75 nm resolution in the x-, y-, and z-directions in a vacuum chamber (∼5 × 10-7 torr base pressure) equipped with a video camera for viewing. The hydrogen-free and very smooth a-D or a-C films (with high or low sp3 content, and with or without ∼1% Cs doping) produced by PLD and DMIBD are not good field emitters. Conditioning accompanied by arcing was required to obtain emission, so that their subsequent FE is characteristic of the arc-produced damage site. However, deliberate surface texturing can eliminate the need for conditioning, apparently by geometrical enhancement of the local electric field. But the most promising approach for producing macroscopically flat FE cathodes is to use materials that are highly nanostructured, either by the deposition process (e.g. HF-CVD carbon) or intrinsically (e.g. carbon nanotubes). HF-CVD films were found to combine a number of desirable properties for FE displays and vacuum microelectronics, including the absence of conditioning, low turn-on fields, high emission site density, and apparent stability and durability during limited long-term testing. Preliminary FE measurements revealed that vertically aligned carbon nanotubes are equally promising.
In Situ Study of Zirconia Stabilization by Anion Exchange (N for O) Using High-Temperature, Controlled Atmosphere Electron Diffraction
Authors: Sharma Renu , Schweda Eberhard , Naedele Dirk 
Published: April 2011

AbstractStabilization of zirconia by anion exchange (N for O) is a novel idea. A number of oxy-nitrides with flourite-related (cubic) structure have been reported to form at high temperatures (1100°C). We have used a TEM equipped with environmental cell and Gatan Imaging Filter (GIF) to study the nitridation behavior of zirconia. The in situ observations reveal the formation of a cubic structure at ≈800°C when the Zr(OH) 4×H2O precursor was heated in ≈2 torr of NH3. The presence of N in the lattice is confirmed by electron energyloss spectroscopy.
Nanocrystal Thickness Information From Z-STEM: 3-D Imaging in One Shot
Authors: Kadavanich A.V. , Kippeny T. , Erwin M. , Rosenthal S. J. , Pennycook S. J. 
Published: April 2011

AbstractWe have applied Atomic Number Contrast Scanning Transmission Electron Microscopy (Z-Contrast STEM) towards the study of colloidal CdSe semiconductor nanocrystals embedded in MEH-PPV polymer films.For typical nanocrystal thicknesses, the image intensity is a monotonic function of thickness. Hence an atomic column-resolved image provides information both on the lateral shape of the nanocrystal, as well as the relative thickness of the individual columns.We show that the Z-Contrast image of a single CdSe nanocrystal is consistent with the predicted 3-D model derived from considering HRTEM images of several nanocrystals in different orientations. We further discuss the possibility of measuring absolute thicknesses of atomic columns if the crystal structure is known.