bluuebunny/crossref_metadata_2025_split huggingface dataset:
Neutral Mass-Selected Lead Cluster Beams
Authors: Abshagen M. , Träger F. , Kowalski J. , Meyberg M. , zu Putlitz G. , Slaby J. 
Published: March 2011

ABSTRACTExperiments are described which illustrate that resonant neutralization of mass-selected cluster ions provides a universal method to produce neutral mass-selected metal cluster beams. Specifically, lead cluster ions, Pbn+ with n d 12, were neutralized by charge exchange reactions in atomic sodium and other target materials. Absolute charge exchange cross sections are on the order of 40 Å2 and up to 30% of the incident ions were neutralized. Possible fragmentation of the clusters associated with neutralization was investigated by translational spectroscopy. No indication of fragmentation was found for resonant electron transfer with atomic Na as target gas.. Thus, neutral metal cluster beams with ultra-narrow size distribution are produced. Deposition of such size-selected metal clusters on substrates opens new perspectives in materials science.
Manipulation of Metal Cluster Size Distributions with Laser Light
Authors: Hoheisel W. , Träger F. , Schulte U. , Vollmer M. 
Published: March 2011

ABSTRACTThe size and size distribution of small metal particles on surfaces can be manipulated with laser light. This has become possible by use of a nonthermal desorption process based on surface plasmon excitation in the particles. Most importantly, a considerable narrowing of a given size distribution on a surface can be achieved. Recent experiments on the desorption mechanism and the size manipulation are summarized.
High Sensitivity Spectroscopy of Supported Clusters
Authors: Parks Joel H. , McDonald Stephen A. 
Published: March 2011

ABSTRACTReflection spectroscopy techniques have been developed with a sensitivity of detecting a change in surface reflectivity of ∼1 part in 106. This has provided the opportunity to measure spectra of ∼1010isolated clusters with an average cluster size as small as 〈N〉=10 atoms. This paper will describe the application of these techniques to the study of alkali clusters emphasizing the size and shape dependence of cluster spectra as well as measurement of surface kinetics determining cluster growth and desorption.
Energetics of Icosahedrally Twinned Rare Gas and Aluminum Clusters
Authors: Boyer L. L. , Pederson M. R. , Jackson K. A. , Broughton J. Q. 
Published: March 2011

ABSTRACTThe factors which promote stability of icosahedrally twinned clusters are discussed. Results for the statics and dynamics of Lennard-Jones clusters are summarized, with special focus on the unusual vibrational properties of Icosahedrally twinned clusters. In addition, we present results from density-functional -based electronic structure calculations on for 13– and 55– atom aluminum clusters with icosahedral and octahedral symmetries.
Physics of Charged Mgn (n≤7) and Mixed MgnKy (x+y≤4) Clusters
Authors: Khanna S. N. , Reuse F. , de Coulon V. , Buttet J. 
Published: March 2011

ABSTRACTElectronic structure calculations on neutral and charged Mgn (n≤7) clusters and KnMgm mixed clusters have been carried out within a linear combination of atomic orbitals molecular orbital approach. The exchange correlaton effects have been treated via local spin density functional and non-local pseudopotentials have been used to replace the core. Our studies on charged Mgn clusters focus on the electron affinity and atomic binding in anionic clusters and the stability and observability of doubly ionized clusters. In KnMgm clusters, we have considered the evolution of the electronic spectrum and the variation of the binding energy with size and composition.
Computer Analysis of the Eaton ICB Source
Authors: Turner D. E. , Shanks H. R. 
Published: March 2011

ABSTRACTA computer simulation that includes the space charge of electrons and ions has been done for the Eaton ionized cluster beam source in order to better understand how the potential fields affect film deposition. It is found that the space charge effects dominate the dynamics of the ionized clusters, painting a picture that differs radically from what the Laplace fields predict.
Electronic Structure Calculations of Ti doped CeFe2
Authors: Khowash P. K. 
Published: March 2011

ABSTRACTOver the past years, theoretical and experimental investigations have shown that Ce plays an important role in determining the electronic and magnetic properties in CeFe2- Recent experiments indicate that Ce carries a small moment in contrast to the earlier notion of its being non-magnetic. It is also been found that various additives to the intermetallic CeFe2 alloy behave differently when substituted at the Fe site. The magnetization in some cases remains nearly the same whereas in other cases drops off drastically. We report here the effect of Ti impurity substituted at the Fe site in CeFe2.
Molecular Dynamics Simulations of the Impact of Energetic Cu Clusters on Cu and Ni Substrates
Authors: Hsieh Horngming , Averback R.S. 
Published: March 2011

ABSTRACTThe interaction between energetic clusters of atoms and solid surfaces has been investigated by molecular-dynamics computer simulation. In this model, the impact of Cu clusters containing 4, 13 or 92 atoms and energies of 326 eV with Cu or Ni substrates is investigated. Either embedded-atom-method (EAM) potentials or a combination of Moliere and EAM potentials were employed for the calculations. The simulations reveal that different physical processes occur depending on cluster size and energy, and the cohesive properties of the substrate.
Clusters and Cluster Assembly of Interfaces
Authors: Waddill G. D. , Ohno T. R. , Weaver J. H. 
Published: March 2011

ABSTRACTThis paper discusses the formation of metal clusters on Xe buffer layers and the deposition of those clusters on GaAs, silica, and Bi2Sr2CaCu2O8 when the Xe is desorbed. These clusters contain hundreds to thousands of atoms, and their interactions with the substrate is different from that encountered when atoms are deposited directly. Since cluster assembly alters the reaction pathway at the surface, novel structures with unique chemical and physical properties can be stabilized.
Fractal Aggregation of Magnetic Particles
Authors: Bucher J. P. , Rizzo N. D. , Louderback J. G. , Bloomfield L. A. 
Published: March 2011

ABSTRACTWe present an experimental model where magnetic balls in a box are used to simulate aggregation of small ferromagnetic particles a few nm in diameter. The aggregation can be characterized by a fractal dimension that increases as the magnetic moment of the particles decreases. The magnetization of the system of balls has been measured in an external magnetic field and compared for different values of the magnetic moments.
Nanocrystalline Structures of A13Fe Intermetallic Produced by Ball-Milling
Authors: Morris Maria A. , Morris David A. 
Published: March 2011

ABSTRACTThis study explores the influence of the ball-milling process on A3Fe compound formation starting from three compositions of mixed elemental powders. It has been found that nanocrystalline structures of A3Fe can directly form by ball-milling of powders with composition Al-20%Fe and Al-25%Fe whilst for the composition Al-12.5%Fe the compound only forms after annealing the milled powders.
Sintering and Deformation of Nanocrystalline Ceramics
Authors: Hahn H. , Averback R. S. , Hofler H. J. , Logas J. 
Published: March 2011

ABSTRACTNanocrystalline ceramics have been produced by the method of inert gas condensation of ultra-small particles and in situ consolidation. Sintering characteristics and microstructural parameter such as grain size, porosity and pore size distributions have been investigated by a variety of techniques, including: X-ray diffraction, gravimetry, nitrogen adsorption, scanning electron microscopy and small angle neutron scattering. In pure TiO2, the sintering temperatures are drastically lowered compared to conventional ceramics, however, extensive grain growth occurs before full densification is achieved. High density, nanocrystalline ceramics can be prepared by pressure assisted sintering, doping and additions of second phases. High temperature microhardness and creep deformation in compression were measured and it was found that creep processes occur at lower temperatures than in ceramics with larger grain sizes. Nanocrystalline TiO2 with densities > 99 % can be deformed plastically without fracture at temperatures below half the melting point. The total strains exceed 0.6 at strain rates as high as 10−3 s−1. The stress exponent of the strain rate, n, is approximately 3 and the grain size dependence is G-q with q in the range of 1 – 1.5. It is concluded that the creep deformation occurs by an interface reaction controlled mechanism.
C60 Buckminsterfullerene
Authors: Kroto H. W. 
Published: March 2011

ABSTRACTIt has taken almost exactly five years to prove that the buckminsterfullerene structure, originally proposed to account for the unexpected stability of the C60 molecule in cluster beam experiments, is actually correct. That an easily-produced, stable compound of pure carbon, the most studied of all the elements, could have been under our noses since time immemorial and have eluded detection for so long seems almost unbelievable. Although the existence of this molecule appears to have boundless prospects for the development of new materials with exciting and novel applications it is worth noting that it was serendipitously discovered during basic science programmes aimed at understanding the nature of processes in space rather than an applied programme aimed at understanding the intrinsic properties of carbon.
Laser Deposition, Vibrational Spectroscopy, NMR Spectroscopy and Stm Imaging of C60 and C70
Authors: Meijer G. , Bethune D. S. , Tang W. C. , Rosen H. J. , Johnson R. D. , Wilson R. J. , Chambliss D. D. , Golden W. G. , Seki H. , De Vries M. S. , Brown C. A. , Salem J. R. , Hunziker H. E. , Wendt H. R. 
Published: March 2011

ABSTRACTWe recently demonstrated that C60 and C70, as well as other fullerenes, can be deposited and accumulated on surfaces using laser ablation of graphite in an Inert gas atmosphere. After learning of the work of Krätschmer et al. indicating the presence of C60 in carbon soot, we showed that samples consisting almost exclusively of C60 and C70 can be sublimed from such soot. Vibrational Raman spectra of C60 and C70 were obtained from these samples. The C60 spectrum Is consistent with the calculated spectrum of Buckmlnsterfullerene, and the strongest three lines can be assigned on the basis of frequency and polarization. The NMR spectrum of dissolved C60 was then obtained, and found to consist of a single resonance, establishing the icosahedral symmetry of this molecule. STM images of the C60 molecules on a Au(111) crystal face show that these clusters form hexagonal arrays with an intercluster spacing of 11.0 Å and are mobile at ambient temperature. Distinctly taller species evident in the arrays are believed to be C70 clusters. Vibrational Raman and infrared spectra have also been obtained for separated C60 and C70.
C60 Research at the University of California at Berkeley
Authors: Heath J. R. , Hawkins J. M. , Alivisatos P. A. , Saykally R. J. , Lewis T. A. , Loren S. D. , Meyer A. , Shibato Y. , Tolbert S. , Shang J. 
Published: March 2011

ABSTRACTAn extremely simple and inexpensive apparatus for preparation of the C60 and C70 fullerenes is described. An efficient separatory technique is described which implements a phenylglycine based HFLC column for preparation of high purity (99.99%) C60 and C70 samples. Treatment of C60 with osmium tetroxide and pyridine gives the osmate ester (2:1 adduct) and establishes that oxygen functionality can be added to C60 without disrupting the carbon framework. Raman spectroscopy of high purity C60 indicates that several lines previously not assigned to C60 (D.S.Bethune, G.Meijer, W.C.Tang, and H.J.Rosen, Chem.Phys.Lett.174, 219(1990)) are attributable to C60.
Improvement of a Porous Material Mechanical Property by Hot Isostatic Process
Authors: Takata Atsushi , Ishizaki Kozo , Okada Shojiro 
Published: March 2011

AbstractOpen porous materials of higher strength and higher porosity were produced by a hot isostatic process (HIP). A grinding wheel of fused alumina grain with powdered frit for bridge is discussed as an example. The samples were directly heated to a normal sintering temperature under HIPping conditions. The HIPped products were characterized by higher bending strength in spite of having more open porosity than the normally sintered ones.
Characterization of Porous Cellular Materials Fabricated by Chemical Vapor Deposition
Authors: Sherman Andrew J. , Williams Brian E. , Delarosa Mark J. , Laferla Raffaele 
Published: March 2011

AbstractThe flexibility of chemical vapor deposition (CVD) permits the fabrication of a large number of materials in various geometric forms, one of which is the porous cellular structure. CVD fabrication of such a structure begins with the pyrolysis of a resin-impregnated thermosetting foam to obtain a reticulated carbon foam skeleton. The foam ligaments can then be coated with a variety of materials (metals, oxides, nitrides, carbides, borides, silicides, etc.), either singly or as hybrid, layered, alloyed, or graded structures. During this process, 10 to 1000 microns of the desired material(s) are deposited onto the foam ligaments by a variation of CVD known as chemical vapor infiltration (CVI). The thermomechanical properties of the resultant structure are dominated by the properties of the deposit, becoming independent of the carbon properties at very small material loadings. With precise control over the variables available, it is possible to obtain the simultaneous optimization of stiffness, strength, thermal conductivity, overall weight, and environmental resistance. This paper discusses the fabrication and properties of various CVD foam materials investigated to date.
The Mechanical Behavior of Microcellular Foams
Authors: Ozkul M. H. , Mark J. E. , Aubert J. H. 
Published: March 2011

AbstractThe mechanical behavior of microcellular open-cell foams prepared by a thermally induced phase separation process are investigated. The foams studied were prepared from isotactic polystyrene, polyacrylonitrile, and poly(4-methyl-1-pentene) (rigid foams), and polyurethane and Lycra (elastomeric foams). Their densities were in the range 0.04–0.27 g/cm3. Conventional polystyrene foams were used for comparison. The moduli and collapse stresses of these foams were measured in compression and compared with the current constitutive laws which relate mechanical properties to densities. A reinforcement technique based on the in-situ precipitation of silica was used to improve the mechanical properties.
Inhomogeneity and Microstructure in e-Beam Evaporated ZrO2 Films
Authors: Bellotto M. , Cremnonesi C. , Parmigiani F. , Scagliotti M. , Beretta S. 
Published: March 2011

ABSTRACTThin films of zirconium dioxide are deposited by e-beam evaporation on optically polished borosilicate crown glass. Two different oxygen partial pressures in the chamber are used. The optical properties of the films are characterized by ellipsometry. The influence of oxygen stoichiometry on the composition and microstructure of the material is investigated by polycrystalline X-ray diffraction for different film thicknesses. The films are found to be inhomogeneous, and a composition gradient (i.e. amorphous ⇔ tetragonal ⇔ monoclinic) is observed from the substrate to the surface. The oxygen partial pressure influences the growth of the films.
Improved Kematical X-Ray Rocking Cjrve Analyses
Authors: Kim H. M. , Wie C. R. 
Published: March 2011

ABSTRACTA new boundary condition is used in the kinematical x-ray diffraction model analysis of rocking curves. The boundary condition is the dynamical reflection amplitude instead of the previously used dynamical intensity for the substrate. It is shown that this boundary condition properly accounts for the angular shift effect in the Bragg peak profile of very thin epitaxial layers and in the 0th-order superlattice peak. We present experimental and simulated rocking curves for various samples. The simulation was performed by using the dynamical diffraction theory, the kinematical model with the new amplitude boundary condition, and the kinematical model with the old intensity boundary condition. We also analyzed the strained resonant tunneling device structure and single strained quantum well samples by x-ray interference technique. Our x-ray interference results showed a good agreement with the nominal values for both experimental and simulated rocking curves.
In-Situ Observations of High Temperature Surface Processes on α-Alumina Bulk Crystals
Authors: Wang Z. L. , Bentley J. 
Published: March 2011

ABSTRACTReflection electron microscopy (REM) was applied to image in-situ the dynamic changes of atomic-height steps on the surfaces of a-alumina bulk crystals heated to high temperatures. Atomic diffusion, desorption and adsorption processes on cleaved a-alumina (012) surfaces were directly observed at temperatures of 1470 to 1670 K. The surface started to show visible structural changes at 1470–1520 K. The main surface process appears to be atomic desorption, which creates large, flat vacancy-type terraces on the surface.
Microstructure of Epitaxial Al(111)/Si(111) Films Studied by Synchrotron Grazing Incidence X-Ray Diffraction
Authors: Hung H. H. , Liang K. S. , Lee C. H. , Lu T.-M. 
Published: March 2011

ABSTRACTWe report the results of our x-ray diffraction studies on epitaxial Al(lll)/Si(lll) films prepared by the partially ionized beam deposition technique. Significant changes were observed in intensity profiles for samples before and after annealing. In the in-plane radial scan of Al(220) peak, the shift of Bragg peak is shown due to misfit strain. A weak satellite is also observed which indicates a semicoherent interfacial structure of the annealed film with misfit dislocations. A possible picture of misfit-induced incommensurate structure of Al films is discussed.
Structure Determination of the Nisi2 (111) Surface Using Medium Energy Ion Scattering with Monolayer Resolution
Authors: Vrijmoeth J. , Zagwijn P. M. , Frenken J. W. M. , Van Der Veen J. F. 
Published: March 2011

ABSTRACTThe surface structure of epitaxial Nisi2 films grown on Si(111) has been determined using a new method. The backscattering signals from subsequent Ni layers in the Nisi2 (111) surface are resolved.The topology of the Nisi2(111) surface is concluded to be bulklike, i.e., it is terminated by a Si – Ni – Si triple layer.
Development of Cation-Dependent Layer to Layer Intermolecular Correlations in 5-Bilayer Arachidic Acid Multilayers
Authors: Fischetti Robert F. , Xu Songtao , Blasie J. Kent 
Published: March 2011

ABSTRACTWe have recorded two-dimensional X-ray diffraction patterns from fivebilayer Langmuir-Blodgett multilayer films. The films were deposited on alkylated glass substrates from monolayers of arachidic acid which were spread on barium or cadmium cation containing subphases: the pH was systematically varied from 4 to 9. The diffraction patterns were recorded using doubly-focusing X-ray optics and a two-dimensional position sensitive detector.Generalized Patterson function analysis of the meridional X-ray diffraction I (qxy = 0, qz), which arises from the profile structure of the multilayer, indicated that the bilayer to bilayer correlations improved with increasing pH value (i.e., with incorporation of divalent metal cations into the film). Experimentally determined electron density profiles have previously shown that the average in-plane density of the down-stroke monolayers was greater than that of the the up-stroke monolayers, in agreement with the observed transfer ratios.We observed Bragg rods at several qxy-values only for multilayers for which the subphase was of intermediate to high pH. The intensity and degree of sampling of the Bragg rods along qz increased with increasing pH value. At the highest pH values, the in-plane intermolecular correlation lengths were ∼600 Å and the bilayer to bilayer intermolecular correlation lengths were ∼165 Å or ∼2 1/2 bilayers. This indicates that for the fatty-acid salts the monolayers of low average in-plane density are “patched” with separated domains which have been deposited epitaxially on the underlying monolayers of high average inplane density.
Characterization of (Al,Ga)As/GaAs Multilayer Structures by X-Ray Interference
Authors: Goorsky M. S. , Kuech T. F. 
Published: March 2011

ABSTRACTAn experimental study of x-ray interference effects from GaAs/AlxGa1−xAs multilayer structures was conducted. The presence of a GaAs layer, whose thickness ranged from 50 Å to 10 μm, between two Al0.30Ga0.70As layers was found to significantly affect the x-ray rocking curves from these structures. We determined both the thickness and the composition of the AlxGa1−xAs layers and the thickness of the GaAs layers by comparing the rocking curves to simulated ones using a dynamical x-ray diffraction model. A sensitivity analysis showed that the thickness predicted for the GaAs buried layer was precise to within 90 Å for a ≃ 2000 Å GaAs layer and that the barrier layer Al content and thickness could be determined to within 1% and 80 Å, respectively for ≃ 5000Å layers. This analysis also showed that, within experimental resolution limits, the structure determined from comparing simulated and experimental rocking curves was unique. Both the limits of this technique in determining interfacial grading and applications to specific device structures and other materials systems are discussed.
Surface Analysis During the Growth of Ge and GexSi1−x Alloys on Si by Reflection Electron Energy Loss Spectrometry
Authors: Ahn Channing C. , Nikzad Shouleh , Atwater Harry A. 
Published: March 2011

ABSTRACTUsing a conventional 30 keV reflection high energy electron diffraction gun on a custom built molecular beam epitaxy system together with an energy loss analyser, we have combined in situ measurements of inelastically scattered electrons from Si L2,3 (99 eV) and Ge L2,3 (1217 eV) core losses with reflection electron diffraction data in order to study the initial stages of Ge heteroepitaxy on Si (001). Diffraction data indicate Stranski-Krastanov growth mode and indicate islanding for Ge thicknesses greater than 0.3 nm. The normalized core loss intensities from electron energy loss data are consistent with a simple model based on grazing incidence electron scattering from the growing Ge film.Additional experiments designed to determine the surface composition sensitivity from Si K (1840 eV) and Ge L2,3 ionization cross-sections reveal that accurate values of composition for a dilute GexSi1−x alloy (x=0.02) can be obtained from raw data when compared with Rutherford Backscattering and Transmission Electron Microscopy/X-ray microanalysis measurements.