bluuebunny/crossref_metadata_2025 huggingface dataset:
Ftir Studies of Water and Ammonia Decomposition on Silicon Surfaces
Authors: Dillon A.C. , Gupta P. , Robinson M.B. , Bracker A.S. , George S.M.
Published: March 2011

Fourier transform infrared (FTIR) transmission spectroscopy. was used to monitor the decomposition of H2O (D2O) and NH3(ND3) on silicon surfaces. Experiments were performed in-situ in an ultra-high vacuum (UHV) chamber using high surface area poroussilicon samples. The FTIR spectra revealed that H2O dissociates upon adsorption at 300K to form SiH and SiNH2 surface species. NH3 also issociates upon adsorption at 300 K to form SiH and SiOH2 species. Silicon samples with saturation exposures of H2O and NH3 were progressively annealed from 300 K to 860 K. The FTIR spectra of an H2O-saturated silicon surface revealed that the SiOH species decomposed to form a silicon oxide species and additional surface hydrogen between 460 K and 580 K. Likewise, the SiNH2 species decomposed between 540 K and 660 K to produce silicon nitride and additional surface hydrogen. In both cases, the Sill surface species decreased as H2 desorption from the silicon surface was observed above 700 K.
High Pressure Oxidation of Strained Si1−xGe Alloys
Authors: Caragianis Christine , Paine David C. , Roberts Carson B. , Crisman Everett
Published: March 2011

Thermal passivation of Si1−x Gex using high pressure (10,000 psi) oxidation was studied. Alloys of Si1−xGex (with x=5.4, 11.6, and 17 at. %) approximately 200 nm thick were oxidized using two processes: (i) dry oxygen at 10,000 psi at a temperature of 550°C and (ii) conventional, 1 atm steam at 800°C. The wet oxidation conditions were chosen to produce an oxide thickness comparable (=100 nm for xGe=11.6 at. %) to that obtained during high pressure oxidation at 550°C. Auger sputter depth profiling (AES), X-ray photoelectron spectroscopy (XPS), and cross-sectional transmission electron microscopy (TEM) were used to characterize the as-grown oxides. XPS studies reveal that high pressure oxides formed from all three of the alloys of Si1−xGex have greatly enhanced incorporation of Ge compared to those grown to a similar thickness under wet atmospheric conditions. We report that a significant benefit of this increase in Ge incorporation is the minimization of Ge enrichment near the oxide/Si1−xGex interface. Cross-sectional TEM images reveal a 30 nm thick Ge-rich band at the wet oxide/alloy interface and a dramatically thinner band (<5 nm) present at the oxide/alloy interface produced by high pressure oxidation. For the atmospheric oxidation samples, interfacial misfit dislocations were observed at the alloy/substrate interface indicating that the film relaxed during oxidation. In contrast, the high pressure samples showed no interfacial defects after oxidation.
Open Circuit Repair Using Thermal Exchange Deposition of Copper
Authors: Gutfeld R. J. Von , Vigliotti D. R.
Published: March 2011

We describe a two step method that uses thermally driven exchange plating to repair open copper circuits with local heating produced by ac Joule losses. The first step utilizes a non-acid copper sulfate solution to grow copper dendrites across the open circuit. This electrical “bridge” is then strengthened using additional plate-up in acid copper sulfate.
Kinetics of Localized Laser-Photochemical Deposition
Authors: Ward Timothy L. , Kodas Toivo T. , Jackson Robert L
Published: March 2011

Highly localized metal deposits can be produced at low temperature by direct writing using a focused laser beam to induce photodissociation of gaseous organometallic precursors. The deposition rate and localization of the deposit are influenced by the kinetics of photochemical reaction and transport of reactants and products. Two-dimensional finite-element computations were performed to determine the effect of deposition parameters, such as laser power, precursor concentration, system pressure, and sticking coefficient, on deposition rates and deposit profiles resulting from single-photon gas-phase dissociation of organometallic precursors. The effect of various gas-phase transport regimes and the conditions and importance of reactant depletion have been investigated. Numerical results have also been compared to theoretical and experimental results from the literature.
In Situ Diagnostics Of Epitaxial Growth Using Reflectance-Difference
Authors: Samuelson Lars , JÖnsson Jan , Paulsson Gert
Published: March 2011

Optical in situ methods are becoming of increasing importance for studies of the mechanisms of growth and for real-time control of surface processes involved in epitaxial growth. We present data from studies, using the reflectance-difference (RD) method, of different processes related to epitaxial growth of GaAs (001) from arsine (AsH3) and from triethylgallium (TEG). RD studies make it possible to follow how the near-equilibrium, Ga-rich, configuration of the GaAs (001) surface changes with temperature and we show how the transformation to this state can be followed from As-saturated as well as from Ga-saturated surfaces. From the initial slope of the RD-transient, corresponding to the AsH3 reaction with a Ga-stabilized surface, the temperature dependence of the catalytic effect of this surface on the decomposition of arsine is measured. Of special significance for an atomic layer epitaxial process (ALE) is the demonstration of a self-limiting reaction of TEG. This process can be followed as the surface modifies itself from a state obtained by exposure to excess TEG to the near-equilibrium Ga-terminated reconstruction. Finally, we demonstrate how pulsing sequences for the realization of ALE can be followed and controlled in real time using RD as a diagnostic tool.
The LPCVD of Silicon Nitride Films from Alkylazidosilanes
Authors: Roberts David A. , Hochberg Arthur K. , O'Meara David L. , Rusnak Felicia , Hockenhull Herman
Published: March 2011

The series of azidosilanes, SiEtn(N3)4-n where n = 1,2,3 and Si(t-butyl)(N3)3 were evaluated for the LPCVD of silicon nitride thin films. Both SiEt(N3)3 and Si(t-butyl)(N3)3 gave deposition rates of approximately 100 Å/min at temperatures of 450–500°C but films appear to be porous and air sensitive. Film properties improved as deposition temperatures were increased to 600°C. The polyazides must be handled with extreme caution. An unexplained detonation of one sample of SiEt(N3)3 occurred during the course of this study.
The Deposition of Borophosphosilicate Glass Films by LPCVD Using 2,4,6,8 Tetramethylcyclotetrasiloxane
Authors: O'Meara David L. , Hochberg Arthur K.
Published: March 2011

Borophosphosilicate glass (BPSG) films used in integrated circuit processing are grown from combinations of toxic and pyrophoric silane, diborane, and phosphine at atmospheric and reduced pressures. A safe, alternative chemical system has been developed with liquid source replacements for each dangerous gas. 2,4,6,8 tetramethylcyclotetrasiloxane (TMCTS) and oxygen are used as the silicon oxide sources, and trimethylphosphite (TMP) and trimethylborate (TMB) are the phosphorous and boron sources, respectively. Films grown in a hot wall LPCVD reactor with standard diffusion boats have thickness uniformities of ± 2 % and doping uniformities < ± 5 %.
Kinetics of the Icosahedral -to- Approximant Transformation in Al-Cu-Fe
Authors: Hayzelden Clive , Spaepen Frans
Published: March 2011

The kinetics of an icosahedral to approximant phase transformation were investigated in cast alloys in the composition range Al(63.65)Cu(20–25)Fe(12–15). Perfect icosahedral crystals are stable in the temperature range below the peritectic melting temperature and above approximately 700°C, below which they transform to a textured polycrystalline mixture of small microcrystals of an icosahedral approximant. The transformation is isocompositional and does not appear to occur by nucleation and growth. The kinetics of the transformation under continuous cooling and isothermal conditions were investigated using conventional and high resolution electron microscopy. The transformation is reversible, takes place over a range of compositions, temperatures and times and results in distinctive strain contrast in the electron microscope.
Composition Dependence of Solid-State Amorphization Kinetics
Authors: Boyer W. S. L. , Atzmon M.
Published: March 2011

Solid-state amorphization rates have been measured for amorphous Ni1-cMc in contact with the crystalline terminal phase M, (M=Hf or Zr). The interdiffusion coefficient Dis found to depend on the composition of the amorphous phase, with higher Ni content resulting in a higher Dover the composition range Ni67Hf33 to Ni47Hf53. The common tangent composition at which the amorphous alloy is in metastable equilibrium with the terminal crystalline phase is found to be greater than 70 at.% Hf, which is considerably higher than previously reported values. This discrepancy is explained in terms of the interdiffusion coefficient's variation with composition.
The Annealing Induced Solid State Transformation of Quenched Beta Cr-Ti
Authors: Sinkler W. , Luzzi D. E.
Published: March 2011

Microstructural changes in the bcc-based water-quenched alloy β Cr40Ti60 have been investigated as a function of annealing time at 873 K. The as-quenched structure has been found to contain a non-ideal form of the ω structure, which has been detected and characterized on the basis of diffuse scattering to which it gives rise in electron diffraction patterns. Annealing at 873 K results initially in platelet precipitates of the metastable β″ phase, which is found to posses a bulk body centered tetragonal structure in which chemical ordering has been detected via electron diffraction and high resolution microscopy. After several hours of annealing at 873 K the equilibrium phases α-Ti and the C15 Laves phase Cr2Ti form as spherical polycrystalline aggregates. No evidence is found of reported annealing-induced amorphization [1]. It is suggested that amorphization cannot occur in this alloy via thermal activation, and that the reported findings may have resulted from impure specimens.
Kinetics of Glass Formation by Solidification and Melting
Authors: Fecht Hans J.
Published: March 2011

A scenario has been developed combining the glass transition (liquid to glass) with the crystal-to glass transition. If the “melting” point of a crystalline solid solution is reduced to the ideal glass transition temperature a triple point is predicted between crystal, liquid and glass. Based on extrapolations of measured specific heat data of undercooled liquid glass-forming Au- Pb-Sb alloys the excess entropy is found to vanish close to the glass transition. On the other hand, the amorphization reaction of crystalline Fe2Er-hydrides is characterized by a lambda-type anomaly in the specific heat. The logarithmic temperature-dependence of the specific heat results from local fluctuations in the crystalline phase, rather than thermally activated lattice defects. These results suggest that glass formation from the liquid as well as the crystalline state is characterized by an underlying instability.
Melting Velocity Measurements in Silicon
Authors: Homan B.E. , Macdonald C.A.
Published: March 2011

Melting velocities in silicon were measured on a picosecond time scale by employing pump-probe and self-reflectivity measurements. The pump laser was a 40 picosecond XeCl excimer (308 am) and the probe a dye laser at 600 am. Samples were phosphorous doped silicon wafers. Average melt-in velocities as high as 800 m/s were observed. Best fit to the data was achieved with an asymmetric transient state theory model.
Rapid-Quenching Investigation of the Nb-Pd-Ge System
Authors: Krill C. E. , Johnson W. L.
Published: March 2011

The structure of rapidly quenched Nb100-x-yPdxGey alloys has been investigated using x-ray diffraction. Niobium concentrations were varied between 100 and 45 at.% the remainder at each Nb concentration was composed of Pd and up to y = 15 at.% Ge. Germanium was found to suppress the nucleation rate of the fcc α-NbPd phase relative to that of the bcc α-Nb phase, thereby extending the single-phase bcc solubility range by ≈ 2 at.% Nb. High Ge content (y > 6) also induced quenching of the amorphous phase. These results can be understood from the standpoint of classical nucleation theory and from a consideration of the polymorphic phase diagram of Nb-Pd. The two approaches are consistent with Ge addition depressing the To line of the fcc phase more rapidly than it depresses the To line of the bcc phase.
Interface Stability During Rapid Directional Solidification
Authors: Hoglund David E. , Aziz Michael J.
Published: March 2011

At the solidification velocities observed during pulsed laser annealing, the planar interface between solid and liquid is stabilized by capillarity and nonequilibrium effects such as solute trapping. We used Rutherford backscattering and electron microscopy to determine the nonequilibrium partition coefficient and critical concentration for breakdown of the planar interface as a function of interface velocity for Sn-implanted silicon. This allows us to test the applicability of the Mullins- Sekerka stability theory to interfaces not in local equilibrium and to test the Coriell-Sekerka and other theories for oscillatory instabilities.
Solute Trapping of Ge in Al
Authors: Smith Patrick M. , West Jeffrey A. , Aziz Michael J.
Published: March 2011

Partitioning during rapid solidification of dilute Al-Ge alloys has been investigated. Implanted thin films of Al have been pulsed-laser melted to obtain solidification at velocities in the range of 0.01 m/s to 3.3 m/s, as measured by the transient conductance technique. Previous and subsequent Rutherford Backscattering depth profiling of the Ge solute in the Al alloys has been used to determine the nonequilibrium partition coefficient k. A significant degree of lateral film growth during solidification confines determination of k to the placing of an upper bound of 0.22 on k for solidification velocities in this range. We place a lower limit of 10m/s on the “diffusive velocity,” which locates the transition from solute paritioning to solute trapping in the Continuous Growth Model.
Calculation and Simulation of Interdiffusion Coefficients and Ordering Kinetics in Binary Alloys.
Authors: Atzmon M.
Published: March 2011

Rate equations for thermally activated atomic exchange were used to calculate chemical diffusion coefficients for an initially disordered simple-cubic lattice and for a body-centered lattice with equilibrium long-range order. The results show that the chemical enhancement as a function of the enthalpy of mixing saturates, in contrast with results of conventional mean-field theories. Simulations in a disordered alloy agree with the calculations. The existence of longrange order is shown to increase the apparent activation energy for diffusion. The present theory is also shown to provide a simple method of calculating ordering kinetics and equilibrium longrange order, and good agreement with previous experiments and simulations is achieved.
Molecular Dynamics Study of the Elastic Response of Crystalline, Amorphous and Chemically Disordered NiZr2
Authors: Massobrio Carlo , Rosato Vittorio , Willaime Francois
Published: March 2011

We calculate the shear elastic constants of the alloy NiZr2 by molecular dynamics simulations in the crystalline and amorphous phases as well as upon introduction of antisite defects in the crystal at T=300K. For S (long range order parameter) equal to 0.5, the system is amorphous and C' is larger than the same quantity relative to the crystal whereas C44 and C66 are smaller.
A Comparison of Semiconductor Models for the Study of Liquid Phase Epitaxy
Authors: Cook Stephen J. , Clancy Paulette
Published: March 2011

The phase behavior of silicon is studied using the Modified Embedded Atom Method (MEAM) proposed by Baskes, Nelson and Wright. We find this model to quantitatively reproduce aspects of both the solid and liquid phases with an accuracy comparable to the widely-used Stillinger-Weber (SW) potential, thus providing an opportunity to examine the consistency of results obtained previously using the SW model. Although the models are very different, they both produce solid-liquid interfaces on both silicon (100) and (111) which have very similar morphologies. We find that the MEAM predicts the melting point of silicon to be 1445K, or 14% lower than the experimental value. The model also predicts the heat of melting to be 34.9 kJ/mol, 45% lower than the experimental value of 50.6 kJ/mol, and a liquid density which is 5.4% larger than that of the solid at the melting point, which is the density ratio found by experiment. The liquid density is found to be too low with respect to experiment. We also suggest a correction which might be applied to the MEAM model to improve its description of the liquid phase.
Asymmetric Membrane Formation in the Heterogeneous Polymerization of Methyl Methacrylate
Authors: Mikos Antonios G. , Kiparissides Costas
Published: March 2011

A mathematical model is presented to describe the fundamental phenomena occurring in the vicinity of the interface between a polymerizing medium and a non-solvent. The model combines the principles of polymerization kinetics, mass transfer and polymer solution thermodynamics and is applied to the polymerization of methyl methacrylate with water. Numerical simulations indicate the development of large interface velocities and the formation of a dense polymer skin at very low monomer conversions in agreement with experimental observations.
Epitaxy and Nucleation in Cu and Ag Doped Amorphous Si
Authors: Custer J. S. , Thompson Michael O. , Eaglesham D. J. , Jacobson D. C. , Poate J. M. , Liefting J. R. , Saris F. W.
Published: March 2011

The competition between solid phase epitaxy and random nucleation during thermal annealing of amorphous Si implanted with the fast diffusers Cu and Ag has been studied. For low concentrations of these impurities, solid phase epitaxy proceeds with small deviations from the intrinsic rate and with the impurity remaining in the shrinking amorphous layer. At a critical metal concentration in the amorphous layer of ∼ 0.12 at.% rapid random nucleation occurs, halting epitaxy and transforming the remaining amorphous material to polycrystalline Si via grain growth. The nucleation rate is at least 8 orders of magnitude greater than the intrinsic homogeneous rate. At higher Cu concentrations nucleation is observed below the temperature needed for epitaxy (400°C). This nucleation, clearly caused by the presence of Cu or Ag in the layer, may be induced by the impurities exceeding the absolute stability concentration and starting to phase separate, leading to enhanced crystal Si nucleation in the metal rich regions.
Defects, Entropy, and Melting of Amorphous Silicon
Authors: Roorda Sjoerd , Sinke Wim C.
Published: March 2011

Structural relaxation of amorphous Si (a-Si) is thought to be fully controlled by annihilation of point defects quenched in during preparation. The density of defects in unrelaxed a-Si is estimated from a wide variety of published experimental data to amount to several atomic %. The enthalpic and entropic contributions of these defects to the excess Gibbs free energy difference of a-Si over c-Si is estimated. The variation in free energy due to defects may lead to afurther melting temperature depression of 40 - 200 K for unrelaxed a-Si in addition to the 200 K depression already present between c-Si and relaxed a-Si.
Neutral Mass-Selected Lead Cluster Beams
Authors: Abshagen M. , Träger F. , Kowalski J. , Meyberg M. , zu Putlitz G. , Slaby J.
Published: March 2011

Experiments 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

The 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

Reflection 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

The 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

Electronic 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

A 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

Over 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

The 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

This 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

We 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

This 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

Nanocrystalline 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

It 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

We 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

An 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

Open 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

The 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

The 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

Thin 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

A 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

Reflection 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

We 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

The 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

We 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

An 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

Using 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.
Mirror Electron Microscope-Low Energy Electron Diffraction for Studies of Surface Ordering and Melting
Authors: Unertl W. N. , Shern C. S.
Published: March 2011

Mirror Electron Microscopy – Low Energy Electron Diffraction (MEMLEED) combines a LEED with MEM in a single simple instrument for studies of surface processes such as phase transitions and premelting under ultra-high vacuum (uhv) conditions. In MEMLEED, 5–20 keV primary electrons are decelerated by an electrostatic mirror-objective lens in which the sample is the mirror element. In the MEN mode, electrons are reflected just above the surface, reaccelerated through the objective lens and imaged. Contrast is due to variations in both surface potential and topography. Current uhv instruments have lateral resolution of about 1 μm. In the LEED mode, 0-100 eV electrons strike the sample at near normal incidence. Diffracted electrons are accelerated through the objective lens. Beam spacings in the imaged diffraction pattern are proportional to k11 and beams do not move as the incident energy is varied. MEMLEED has intrinsically higher transfer width and is less sensitive to magnetic fields near the sample than conventional LEED. Design considerations for uhv instruments are discussed. Applications to the study of order-disorder transitions, premelting phenomena, and to measurements of changes in surface potential are described.
Double Axis X-Ray Diffractometry Analysis of the Homoepitaxial Interface Between Substrate and Buffer Layer
Authors: Green G. Stephan , Tanner Brian K. , Kightley Philip
Published: March 2011

High resolution double axis X-ray diffractometry has been undertaken on InGaAs/AlGaAs strained layer epitaxial systems on (001) GaAs substrates. A clear set of fringes has been identified which arises due to the presence of an imperfect layer at the interface between the GaAs substrate and the undoped GaAs epitaxial buffer layer. The period corresponds to the Pendellosung period for the whole epitaxial layer stack. These fringes have very low contrast and are not present in all specimens studied. Detailed simulations have been undertaken assuming a thin interfacial layer of GaAs with a different lattice parameter to the substrate. The system is equivalent to a Bragg case X-ray interferometer. Fringe amplitude is found to vary linearly with interface layer thickness and increases with mismatch of this layer. A good match between experiment and simulation was obtained for a 1 nm layer mismatched by 3000 ppm. The presence of such a layer, probably GaCxAsl-x has been confirmed by transmission electron microscopy. We show that highly sh'rained layers of this thickness between layers over 1 micron in thickness can lead to splitting of high intensity layer peaks, giving rise to possible misinterpretation of data.
Characterization of GaAs/Si Interface Structure by X-Ray Diffraction
Authors: Specht E. D. , Ice G. E. , Peters C. J. , Sparks C. J. , Lucas N. , Zhu X.-M. , Moret R. , Morkoc H.
Published: March 2011

By measuring the intensity profiles along the crystal truncation rods of a Si(001) substrate, we obtain the depth sensitivity necessary for x-ray diffraction measurements of the structure of its interface with a thick GaAs overlayer which is epitaxial to, but not in registry with the substrate. By comparing the diffraction with a model based on a grid of misfit dislocations, we find that the atoms at the interface have a root mean square displacement of 1.09±0.1Å from this ideal structure, and that the interface has a roughness of 2.9±1 Å. The diffraction indicates an anomalously small strain perpendicular to the interface in the GaAs near the interface.
X-Ray Reflectivity Study of Single- and Bicrystals of Gold
Authors: Fitzsimmons M. R. , Burkel E. , Peisl J.
Published: March 2011

X-ray reflectivity techniques have been used to characterize the surfaces of 0.4µm thick Au films epitaxially grown on single-crystals of NaCl. Measurements of both the specular and non-specular reflectivity suggest that the Au surface is very rough. The nonspecular reflectivity provides valuable information about the correlation of the heights at different points on the surface. The first in situ reflectivity study of the formation and destruction of a grain boundary shows direct evidence for the existence of diffuse scattering from the grain boundary. Measurements of several [0011 twist grain boundaries suggest that the roughness and texture of an interface depends upon the geometrical orientation of the surrounding substrates.
X-Ray Reflectometry from Semiconductor Surfaces and Interfaces
Authors: Tanner Brian K , Miles Simon J , Bowen D Keith , Hart Linda , Loxley Neil
Published: March 2011

X-ray reflectance measurements at grazing incidence provide non-destructively a measure of the thickness of thin layers, the electron density as a function of depth, and interface and surface roughness. We show that the effect of roughness at a buried interface is only to reduce the visibility of the interference fringes, whereas roughness at the top surface leads also to an overall increase in the rate of fall of intensity with angle (or energy). These two contributions can then be readily distinguished.

Most work has been performed in monochromatic angular dispersive mode. We present here a preliminary study of the application of the high-energy, fixed-angle, energy dispersive mode for the study of thin epitaxial layers, Langmuir-Blodgett films, surface damage on silicon chemi-sol polished wafers and ion implanted silicon and aluminium. Data has been analysed using the theory of Parratt, which we have adapted for use in the energy dispersive method.
X-Ray Reflectivity Measurements of Surface Roughness Using Energy Dispersive Detection
Authors: Chason E. , Warwick D. T.
Published: March 2011

We describe a new technique for measuring X-ray reflectivity using energy dispersive X-ray detection. The benefits of this method are the use of a fixed scattering angle and parallel detection of all energies simultaneously. These advantages make the technique more compatible with growth chambers and useable with laboratory X-ray sources. We find excellent agreement between the calculated Fresnel reflectivity and the reflectivity obtained from a smooth Ge (001) surface. Reflectivities obtained during 500 eV Xe ion bombardment of Ge surfaces demonstrate the sensitivity of the technique to be better than 1 Å.