bluuebunny/crossref_metadata_2025 huggingface dataset:
Very Low Pressure Oxidation of Si and Ge Surfaces
Authors: Baikie Iain D.
Published: March 2011

Although the oxidation of Si(111) 7×7, Ge(111) 2×8 surfaces are relatively well understood very little work has been performed at sub monolayer coverage. We have utillsed a custom-built high resolution Kelvin probe to follow the changes in work function, and changes in band-bending and surface state occupancy via Surface Photovoltage Spectroscopy (SPV). The Kelvin probe Is an Ideal tool for such analysis due to Its extremely high surface sensitivity, equivalent to 4×1010 molecules/cm2, or 0.01% of the available sites.

We observe a very rapid initial adsorption phase, which has not been found by other surface probes, e.g., AES, EELS, etc, corresponding to the formation of an elementary dipole layer. During this phase the Increase In the effective electron affinity with oxygen uptake achieves a maximum of 1V at 0.3 monolayer (ML), on SI(111) at 300 K. We report, for the first time, SPV spectra of SI(111), at 100 K, indicating quenching of a band of surface states centered around the fermi-level, quenching Is completed at the max-Imum of the work function change.

The second adsorption phase, involving oxygen penetration through the surface layer and incorporation Into the lattice, commences at 0.25 ML for Si(111) at 300 K. a much earlier stage than previously reported. Further. we find evidence of a metastable SiO2 precursor at coverages below 1 ML. The dipole layer formation (and breakup) is shown to be very sensitive to both temperature and amount of surface Carbon contamination. The second phase also Involves a substantial reduction In band-bending to nearly flat bands at 2 ML, accounting for 20% of the work function change In the case of SI and almost 90% for Ge.
Unified Model for Ballistic Transport and Gas-Solid Reactions in Features
Authors: Cale T. S. , Raupp G. B. , Gandy T. H.
Published: March 2011

The three dimensional equations which govern free molecular or ballistic transport and heterogeneous gas-solid reactions in features on patterned wafers during low pressure processing are reviewed. The governing equations specific to long rectangular trenches are extended to include nonuniform molecular velocity distributions in the source volume above the wafer as well as surface diffusion of adsorbed species or intermediates. Introduction of reaction stoichiometries and kinetic expressions for general deposition and etch reactions completes the specification of the problem. Local generalized sticking factors arise in the process of nondimensionalizing the governing equations.
Metal-Organic Chemical Vapor Deposition of Aluminum from Trialkylamine Alanes
Authors: Gross M.E. , Dubois L.H. , Nuzzo R.G. , Cheung K.P.
Published: March 2011

Trialkylamine alanes are attractive precursors for the metal-organic chemical vapor deposition (MOCVD) of aluminum thin films in microelectronics applications. The weak Al-N interaction and the absence of Al-C bonds (which decompose by highly activated processes) make these compounds excellent alternatives to the most widely studied Al CVD precursor, triisobutyl aluminum (TIBA). Solid trimethylamine alane (TMAA) and liquid triethylamine alane (TEAA) have vapor pressures at room temperature of 1 and 0.5 torr, respectively. In addition, these compounds are stable, non-pyrophoric, and are easily prepared. We report parallel studies of Al CVD in a low pressure, cold wall reactor and in an ultrahigh vacuum chamber to understand both the surface chemistry and the growth morphology. These studies, in turn, are compared with the decomposition chemistry and MOCVD characteristics of TIBA.
Surface Reactions in the Decomposition of Zinc Alkyls on Si(100)-2×1 Surfaces
Authors: Rueter M.A. , Vohs J.M.
Published: March 2011

The adsorption and reaction of dimethylzinc and diethylzinc on Si(100)-2×l surfaces was studied using temperature programmed desorption and high resolution electron energy loss spectroscopy. These zinc alkyls were found to dissociate at temperatures less than 300 K to produce adsorbed alkyl species and deposit zinc on the surface. During temperature programmed desorption zinc metal desorbed at 530 K leaving only alkyl species on the surface at higher temperatures. Surface methyl groups were found to decompose to carbon and hydrogen or desorb as methyl radicals, while surface ethyl groups underwent a series of surface reactions which resulted in three separate ethylene desorption peaks. The results of this study provide new insight into the reactions of group II metal alkyls on silicon surfaces.
Blanket Tungsten Film Evaluation for Application to Submicron Contact Filling
Authors: Charneski Lawrence J. , Ha Chang L. , Matsuda Kenzo , Sakiyama Keizo
Published: March 2011

The ptanarization of metal interconnect Layers has recently been a subject of intensive development effort in semiconductor processing. Although layer thicknesses have not decreased In proportion, lateral dimensions have been reduced to the point that aspect ratios are too large for effective step coverage by conventional film deposition techniques. The most difficult structure to peanarize is submicron contact holes in thick dielectrics.

A dual-Layer CVD blanket tungsten film was shown to be viable for use as an interconnect material in submicron processes. A single-wafer reactor operating at a pressure of 80 Torr was used to deposit the film. The film exhibits superior properties in terms of its basic characteristics. The film completely fits submicron contacts to silicon, yet has a low surface roughness that would minimize concomitant photolithography and etching problems. Film adhesion is excellent, uniformity and reproducibility are >95%, depgsition rate is greater than 400 nm/mmn., stress is below 8×109 dynes/cm2, and resistivity is 11 μ-ohm-cm or less.
Excimer Laser-Induced Surface Activation of Aln for Electroless Metal Deposition
Authors: Esrom Hilmar
Published: March 2011

A new method for selective metal deposition on aluminum nitride (AIN) is presented. Excimer laser radiation is used for local decomposition of AIN in air. The degree of the surface modification depends on the fluence and number of pulses. A distinct wavelength dependence of the threshold fluence decomposition of AIN was found. The irradiated surface regions act as catalysts in conventional electroless metal plating baths. Structured metal coatings of various elements (Cu, Ni, Au, Pd, etc.) on AIN can thus be obtained in a simple way.
Chemistry of SiO2 Plasma Deposition
Authors: Smith Donald L. , Alimonda Andrew S. , Chuang Tzu-Chin
Published: March 2011

The chemistry of SiO2 deposition from N20-SiH4 plasma was studied by line-ofsight mass spectrometry coupled with film analysis. If rf power and N2O flow are sufficient, more than enough O atoms are available to convert all of the SiH4 to SiO2, and good electrical characteristics (IV and breakdown) are then obtained with or without He dilution. Gas-phase SimHn(OH)p species make a minor contribution to the deposition and may be the source of the OH in the film. Both [OH] and electron trapping are much larger than for thermal oxide, with or without He dilution.
Laser Studies of the Interaction of SiO with the Surface of a Thin Film
Authors: Ho Pauline , Buss Richard J. , Weber M. E.
Published: March 2011

The interaction of SiO radicals from a SiCl4/O2 plasma with the surface of a depositing thin film is studied with the IRIS (Imaging of Radicals Interacting with Surfaces) technique, which combines spatially-resolved laser-induced fluorescence with molecular beam methods. In contrast to previous results for SiH, SiO appears not to react at the surface of the depositing film, but desorbs with a cosine spatial distribution for a wide range of substrate temperatures. No evidence is observed for specular scattering of the molecules.
Electrical and Chemical Characterization of SiO2 Deposited by Electron Cyclotron Resonance - PECVD.
Authors: Andosca R.G. , Varhue W.J. , Titcomb S.
Published: March 2011

Thin films of silicon dioxide were deposited on (100) Si at low temperatures (room temperature to 375 °C). Oxygen was introduced into the resonance chamber while a dilute silane gas mixture (2% in helium) was fed to a gas ring supported 10 cm above the wafer. Index of refraction, deposition rates, etch rates (for buffered HF), dielectric constant, and oxide breakdown strength were determined as a function of substrate temperature and RF substrate bias. Hydrogen content and Si-O bonding were measured by FTIR spectroscopy. All properties are reported in terms relative to thermally grown oxide.

Film properties improved with increasing substrate temperature and RF substrate bias, sometimes equaling that of thermal oxide. Film quality was the highest for samples deposited at 375 °C, with an applied RF substrate bias.
Mechanism of Plasma-Enhanced Deposition of Silicon Dioxide from Teos/O2 Mixtures
Authors: Raupp Gregory B. , Cale Timothy S. , Peter H. , Hey W.
Published: March 2011

The deposition rate of silicon dioxide from TEOS/02 capacitively-coupled plasmas increases with increasing applied rf power, increasing total pressure and decreasing wafer temperature. These dependences can be explained by a mechanism in which deposition occurs through both an ionassisted and an oxygen atom initiated pathway. The ion-induced deposition rate increases with increasing rf power density and decreasing total pressure, and is independent of wafer temperature. Assuming a well-mixed plasma, and using literature values for reaction rate parameters and rate forms for oxygen plasma reactions, the rate of atom-induced deposition was found to be independent of temperature and TEOS concentration and directly proportional to oxygen atom concentration. The model suggests that the apparent negative activation energy for deposition results from competition between deposition and thermally-activated atomic oxygen surface recombination. The derived deposition rate form is consistent with an Eley-Rideal mechanism in which the rate determining step for film deposition is oxidative attack of adsorbed TEOS or TEOS fragments by a activated oxygen.
Diethylsilane as a Silicon Source for the Deposition of Silicon Nitride and Silicon Oxynitride Films by LPCVD
Authors: Hochberg Arthur K. , O'Meara David L.
Published: March 2011

A purified diethylsilane (DES), LTO-410TM, has been studied as a silicon precursor for the deposition of silicon nitride and silicon oxynitride films by LPCVD. In the temperature range from 650 to 725°C mixtures of DES and NH3 produce uniform, oxidation resistant silicon nitride layers. Auger and RBS analyses show that the carbon concentrations in the films are correlated with the DES partial pressures. The film refractive indices also correlate with the carbon levels in the films for a fixed deposition temperature. Mixtures of DES, NH3, and N2O deposit silicon oxynitride films in the temperature range from 650 to 700°C with compositions controlled by the NH3:N2O ratio for a fixed DES flow. These films have carbon levels below the minimum detectable limit of Auger and RBS analyses.
Modelling of Mechanisms Involved in Ceramic Synthesis by Laser Conversion of an Organosilazane Aerosol
Authors: Strutt Peter R. , Xiao Tongsan D. , Gonsalves Kenneth E. , Klemens Paul G.
Published: March 2011

A study has been made of basic mechanisms involved in a new process for the rapid synthesis of preceramic nanoparticle powders. In this process an aerosol, formed from an ultrasonically atomized liquid organosilazane monomer, (CH3SiHNH)n with n = 3 or 4, is injected into the beam of an industrial cw CO2 laser. One critical feature examined is the rapid condensation of molecular species from the laser plume, in a process involving 3-dimensional cross-linking. In accompanying studies, a model has been formulated to determine the laser plume temperature, the cooling rate of condensing species, and the particle diameter. These are obtained by analytical solution of heat conduction, momentum and mass conservation equations that consider heat loss, by gas conduction, radiation, evaporation, and convection.
Epitaxial Growth of Ferroelectric Pb(Mgl/3Nb2/3)03 Film by Sol-Gel Method
Authors: Okuwada Kumi , Nakamura Shin-Ichi , Imai Motomasa , Kakuno Keiichi
Published: March 2011

Ferroelectric thin films, which are Pb(Mgl/3Nb2/3)03 (PMN) and Pb(Mgl/3Nb2/3)03 - PbTiO3 (PMN-PT) in the perovskite phase, were obtained by the sol-gel method with metal alkoxides. The films had highly preferred orientation on substrates whose interplanar spacings are close to that for the perovskite structures in PMN and PMN-PT. Epitaxial growth process in PMN film was investigated.
Single Source Precursors for III-V OMCVD Growth and Pyrolysis Studies
Authors: Jones Richard A. , Cowley Alan H. , Ekerdt John G.
Published: March 2011

Compounds of the type (L2MEL'2)x, where M and E are the group III and V elements, respectively, and L and L' are ligands which may be thermally eliminated are being studied as single source precursors to III-V semiconductors. An array of these compounds have been synthesized with various III-V combinations, and hydride and alkyl ligands. Film growth was studied over the temperature range of 450-600 °C and at 10−4 Torr. Growth rates of 1 μm/hr are typical when the compounds are maintained at 125-140 °C. (Me2Ga(μ-t-Bu2As) [2 led to films which were polygrained with the grains oriented in the (111) direction and retained the 1:1 stoichiometry of the precursor. Films from [Me2Ga(μ-i-Pr2As)]3 did not retain the 1:1 stoichiometry and did not show the preference for (111)- oriented growth.
A Small Angle Neutron Scattering Investigation of the Kinetics of Phase Separation in an Fe-27.5 AT.% Cr-5.6 AT.% Ni Alloy
Authors: Epperson J. E. , Rainey V. S. , Windsor C. G. , Hawick K. A. , Chen Haydn
Published: March 2011

The small angle neutron scattering has been investigated in situ at 450° and 500°C for a polycrystalline, duplex Fe-27.5 at.% Cr - 5.6 at.% Ni steel. A broad diffuse maximum in the scattering function is the signature of the α' phase formation, and this maximum is superimposed on a strong, temperature-dependent component due mainly to critical magnetic scattering. The time dependence of the shift in the peak intensity position to lower scattering vectors and the increase in peak intensity obey power law scaling behavior. Furthermore, the structure function exhibits dynamical scaling, after about three hours annealing. It is suggested that this behavior could be utilized to predict the microstructure, and hence some of the properties, after significantly longer annealing times.
Short-Range-Ordering and Fe-Clustering in Au-Fe Alloys
Authors: Chou Chen-Chia , Chen F.-R. , Wayman C. M.
Published: March 2011

As an “archtypal” spin-glass system, the local atomic arrangement in Au-Fe alloys is still a controversial subject. In the present experiment, Au-Fe alloys with Fe content from 10.7 to 33% were studied as to microstructure evolution, through various transmission electron microscopic techniques. Information derived from aging experiments using real and reciprocal spaces appears to suggest the coexistence of short-range-order and Fe-clusters. At early stages of aging, lobe-like and/or rod-shaped strain contrast images, identified as clusters, were revealed after specimens were further cleaned by an ion-miller. The (1 1/2 0) special point diffuse reflections were prominent in the as-quenched condition and/or early stage aging, and the intensifies decrease gradually as aging proceeds. After a certain period, (1 1/2 0) diffuse reflections disappear but strain contrast images still remain similar. This suggests that the strain contrast images are not related to the (1 1/2 0) diffuse reflections. High resolution electron microscopy was also employed. The results are consistent with the arguments derived from aging experiments.
Small Angle Neutron Scattering Investigation of Paraffin Solid Solutions Undergoing Microphase Separation
Authors: Epperson J. E. , White J. W. , Wozniakt D. G.
Published: March 2011

We show that small angle neutron scattering can sensitively detect microphase separation in solid solutions of the C30H62:C36D74 mixed paraffins. By ramping the sample temperature at a constant rate of about 0.5°C per minute, information complementary to that from differential heat capacity measurements is obtained from the total small angle scattering signal and its first temperature derivative. Because neutron wavelengths in the range from 0.8 < λ (Å) < 14.0 are used, scattering functions over an extended range (0.005 < q (Å−1) < 0.35) are obtained at the Argonne pulsed neutron source in a single experiment. This is important inasmuch as there is significant scattering in the lowest q region accessible due to the presence of cracks and/or voids, in addition to that from the microphase separation. The specific interfacial area as a function of temperature is reported from time slicing experiments on the pure C36D74 compound. Weak superlattice reflections are identifiable in the scattering profiles of the mixed paraffins due to the microphase separation.
Time-Resolved Small-Angle X-ray Scattering Study of Reversion Kinetics of δ′ Precipitates in an Al - 12AT.% Li Alloy Utilizing Synchrotron Radiation
Authors: Chen Haydn , Yu M.S. , Okuda H. , Tanaka M. , Osamura K.
Published: March 2011

Structure change during the reversion process in an Al−12at.%Li alloy above the metastable δ′ solvus was investigated using a time-resolved small-angle x-ray scattering technique with synchrotron radiation. Results showed that the reversion process started after a short incubation time and that the growth of the stable δ phase began before completion of the δ′ dissolution. The radius of gyration of the second phase particles showed little change in the initial stage of reversion, then increased with time, suggesting the presence of diffuse interfaces between the dissolving δ′ particles and the matrix. It is suggested that the undissolved δ′ particles serve as the nuclei of the more stable δ precipitates, which continue to grow with their radii of gyration showing a parabolic power law in the early stage of growth followed by the familiar coarsening kinetics.
Crystallization Behavior of Sputter Deposited Amorphous NixZr100-x, Films
Authors: Winters Gillian E. , Unruh K.M. , Swann C.P.
Published: March 2011

Sputter deposited films of amorphous NixZr100-x, have been prepared over a wide and continuous range of compositions between x=20 and x=90 atomic percent Ni on liquid nitrogen cooled and room temperature substrates. These films have been characterized by xray and electron diffraction, transmission electron microscopy, and Rutherford backscattering spectrometry. The crystallization behavior of these films has been systematically studied by differential scanning calorimetry and compared with earlier measurements on amorphous liquid quenched alloys. Systematic differences were found between the thermal stability of amorphous alloys of the same nominal composition prepared at different substrate temperatures. Larger differences exist between vapor deposited amorphous films and liquid quenched ribbons.
Kinetics of NiSi Formation by Solid State Diffusion in Pt/NiCr/Si Via Growth of an Amorphous Cr-Rich Barrier Layer
Authors: Patnaik B.K. , Lee Ju Hyeon , Adams D. , Rozgonyi G.A. , Parikh N.R. , Swanson M.L. , Salih A.S.M. , Balducci P.
Published: March 2011

We have used Rutherford backscattering spectroscopy (RBS) to study the kinetics of NiSi growth during low temperature annealing of a Ni(Cr) layer on Si. During the silicide growth, a Cr-rich amorphous layer was formed between the silicide and the Ni(Cr) layers. This amorphous layer produces a slow and uniform silicide growth rate; the NiSi thickness was 60 nm after a 2h anneal at 475°C. After prolonged annealing, the amorphous layer recrystallized, causing very rapid silicide growth. When a thin (0.5 nm) layer of Pt was deposited between the Si and Ni(Cr) layers, the amorphous layer was thinner, the silicide growth rate was correspondingly greater and the rapid growth stage occurred earlier. The RBS data agreed qualitatively with transmission electron microscopy results for the growth of both the amorphous layer and the silicide.
Crystal Face Dependent Melting of a Polycrystalline Iron Surface During 30 PS Laser Pulses
Authors: Vaterlaus A. , Guarisco D. , Meier F.
Published: March 2011

The melting of a polycrystalline iron surface with short laser pulses induces a surface structure with an orientation and a morphology depending on the crystal face of the surface. Different crystal planes irradiated with the same laser pulses show different degrees of disorder. This points to a crystal face dependent surface melting temperature.
Kinetics of Relaxation at the Liquid-Glass Transition
Authors: Lewis Laurent J.
Published: March 2011

We use molecular-dynamics simulations to investigate relaxation processes near the liquid-glass transition for a realistic model of the metal-metalloid system Ni80P20. We find that relaxation proceeds in two stages, excluding phonons: fast (or conformational) relaxation, related to local rearrangements of atoms, and slow relaxation, connected with atomic transport, i.e. diffusion. These processes are usually referred to as β and α, respectively. Our simulations show that diffusion exists even in the glass state, where it proceeds mostly by jumps, in contrast to the liquid phase where it is continuous. This relaxation mechanism is well described by a stretched exponential (Kohlrausch) law, in accord with recent modecoupling theories for supercooled liquids. The fast relaxation regime, on the other hand, does not appear to be well described by the theory.
The Time Lag in Transient Nucleation
Authors: Wu David T.
Published: March 2011

The time lag in transient nucleation was originally introduced to characterize the temporal evolution of the nucleation current in the simplest possible way. Previous attempts to calculate the time lag have relied mainly on either the approximate solution of the continuous Fokker-Planck equation or the numerical solution of the discrete rate equations. It is shown that the exact time lag can be calculated using a different method which requires knowledge only of the initial and the steady-state cluster populations.
Energy Barrier for ‘Magic-Strain’ Transformations in Crystals with Fcc Lattices
Authors: Boyer L.L. , Kaxiras E. , Mehl M.J.
Published: March 2011

Energy barriers for ‘magic’ strains, large pure shear strains which transform a lattice into itself, are computed for aluminum and iridium, using the linearized-augmented-plane-wave method, and for silicon, using the plane wave pseudopotential approach. The barrier energies are found to be of the order of the thermal energy available at the melting temperature. Volume changes associated with the barriers are consistent with the fact that the metals decrease in density while silicon increases in density upon melting.
Anomalous Solid Phase Epitaxy Near the Compensation Point in Amorphous Silicon with Boron and Phosphorus Impurity Profiles
Authors: Jeon Young-Jin , Becker M. F. , Walserd R. M.
Published: March 2011

We made high precision cw laser interferometric measurements of the variations of the rate of solid phase epitaxial regrowth (SPER) of amorphous layers on (100) silicon implanted with both boron and phosphorus. Depth profiles of SPER were correlated with the implanted boron and phosphorus distributions measured by secondary ion mass spectroscopy (SIMS). The results showed that: (1) the minimum (SPER) rate did not occur at the depth where the implanted impurity concentrations were equal; (2) the maximum activation energy for SPER (∼2.9 eV; ≈0.18 eV greater than for SPER in intrinsic Si) occurred at the depth where the regrowth rate was a minimum; (3) the regrowth rates in the dual implanted sample were different from those of the samples doped only with phosphorus at the same net phosphorusc concentration; and (4) the rate at the depth where the impurity concentrations were equal was different from the intrinsic rate. Further interpretation of the results suggests that the SPER rate in the dual implanted samples is equal to the value for intrinsic silicon at a depth where the net ionized impurity concentration is compensated. The SPER rate was a minimum at a depth where the net ionized impurity concentration was slightly p type.
Amorphous-to-Crystalline Transformation and Metal Induced Crystallization Phenomena in a-Si:F and a-Si:D:H Thin Films
Authors: Edelman F. , Cytermann C. , Brener R. , Eizenberg M. , Weil R. , Beyer W.
Published: March 2011

The structural stability of silicon in the amorphous state has been studied by TE1 on in-situ heat treated non-supported layers of a-Si:F, a-Si:D:H and double-layers of a-Si:F/Pd and a-Si:D:H/Pd structures. The a-Si:F and a-Si:D:H films, 500-800A thick, were evaporated by plasma decomposition of a(SiH4+D2)-mixture and SiF2, at 200-260°C onto cleaved rock salt. Pd film was deposited on a-Si by electron beam evaporation at room temperature. The amorphous-to-crystalline transition for the a-Si was quantitatively described by the delay time, t0, before the onset of crystallization. This parameter was found to decrease exponentially with the temperature. Influence of the Pd on t0 (metal induced crystallization) is discussed. This is the first report on the influence of F on the metal/a-Si system. It is also the first time a direct method is used to determine the temperature dependence of the fundamental parameter-delay time preceding a-Si crystallization.
Changing Segregation Coefficients During Ion Beam Induced Epitaxy of Amorphous Si
Authors: Custer J. S. , Thompson Michael O. , Jacobson D. C. , Poate J. M.
Published: March 2011

Ion beam induced epitaxial crystallization of Au and Ag doped amorphous Si results in segregation and trapping of the impurity. Combining the measured interface velocity and impurity profiles in segregation simulations provides a measure of the segregation coefficient k during growth. To adequately match the experimental profiles, k must increase during the early stage of growth until saturating at a temperature dependent value. This segregation process cannot be explained within standard models where k depends on the inteface velocity (kinetic trapping) or the interface impurity concentration (thermodynamic solubility). Instead the data suggests that the number of trapping sites at the interface increases during the initial stages of ion beam induced growth. We present several possible mechanisms for this trapping increase and discuss their significance in ion beam and thermal epitaxy models.
Picosecond Time-Resolved Amorphization Velocities in Silicon
Authors: Macdonald C.A. , Homan B.E.
Published: March 2011

Transient time-resolved picosecond reflectivity measurements were performed on silicon melted by a 40 ps ultraviolet (308 nm) beam. These were compared to simulations of reflectivity versus amorphous and liquid layer depth and of amorphous interface velocity for various models including transition state theory and density limited growth, both with and without thermal activation.
Size Dependent Reactions of Boron and Carbon Cluster Ions
Authors: Hintz Paul A. , Ruatta Stephen A , Sowa Marianne B. , Anderson Scott L.
Published: March 2011

The results of boron cluster ion reactions with SiH4 and N2O are presented. For N2O reactions, significant size effects were observed in the branching between the BnO+ and BnN+ product channels. Carbon cluster ion reactions with D2 reveal the effect of structural isomers on cluster reactivity.
Arrested Solid-Solid Phase Transition in Semiconductor Nanocrystals
Authors: Haase M. , Alivisatos A. P.
Published: March 2011

CdS crystallites of 40 and 45 Å average diameter have been studied under hydrostatic high pressure by optical absorption. The optical absorption onset is observed to shift to higher energy with pressure according to

This is exactly the same shift with pressure as is observed in the bulk. The solid-solid phase transition from the zincblende to the NaCl phase is observed as an abrupt change in the intensity, intercept, and functional form of the absorption onset. The phase transition, which occurs at 27Kbar in bulk CdS, is shifted to 85 Kbar in nanocrystals stabilized with polyphosphate, and to 60 Kbar in nanocrystals surface derivatized with EDTA. It thus appears possible to control the relative stability of the crystalline phases of a nanocrystal by chemical manipulation of the surface.
An Assessment of Electronic Exchange in Phosphomolybdates
Authors: Singh David J. , Jansen Susan A. , Mazurek Harry , Crocco Guy
Published: March 2011

In the synthesis of polyacrylates, a necessary step involves the conversion of acroleins to acrylic acids- a process catalysed by Mo oxides. We have directed our work towards the elucidation of the electronic structure of the most stable structure of 12-heteromolybdate, ie. the α-keggin unit, using EPR spectroscopy, Cyclic Voltammetry, and molecular orbital calculations based on the extended Huckel theory. Metal ion substitution has been shown to have negligible effect on the electronic structure of the keggin unit thus rationalising previous arguments of structural rigidity. Electronic exchange has been shown to be facilitated through metal-metal interaction.
Synthesis, Characterization and Properties of Silver Aggregates
Authors: Licinio P. , Ferreira A. V. , de Albuquerque A. S. , Speziali N. L. , Rodrigues W. N.
Published: March 2011

Silver aggregates find their technological applications in electricity conducting cements and as catalysts in biomedical sciences. We have developped a method for synthesis of colloidal silver aggregates, based in redox reactions. Aggregate size and structure are strongly influenced by preparation physico-chemical conditions. We have investigated the pH influence over the growth mechanism through dynamic and static light scattering techniques. We introduce here an analysis of the sedimentation rate from which the aggregation regime can also be inferred.
Effect of Borohydride Addition Rate on Chemically Prepared Amorphous Fe–B Particles
Authors: Koch C. Bender , Mørup S. , Linderoth S.
Published: March 2011

Amorphous Fe-B alloys can be prepared by reacting aqueous solutions of Fe salts and NaBH4. In this work the effect of the addition rate of the NaBH4 solution to the FeSO4 solution on the precipitate is investigated. The chemical composition of the amorphous alloys formed varies between Fe79B21 and Fe68B32. The hyperfine parameters of the alloys, derived from Mössbauer spectra, show a decrease from 29 to 25 T of the magnetic hyperfine field and an increase from 0.19 to 0.28 mms−1 of the isomer shift with increasing NaBH4 addition rate. The results suggest that alloys with different structures but identical composition may be produced by chemical reduction.
Gas Jet Injection of Clusters into Liquids
Authors: Johnson Donald L. , Schmitt J. J. , Halpern B. L.
Published: March 2011

We discuss a novel approach to colloid synthesis in which high speed gas jets inject colloid forming species directly into liquids.
Soft-Landings, Hard Rebounds, and Fracture of Alkali-Halide Nanocrystals
Authors: Beck Rainer D. , St. John Pamela , Homer Margie L. , Whetten Robert L.
Published: March 2011

Collision phenomena involving the smallest solid objects and inert solid surfaces have been explored by the method of mass-selective time-of-flight and angular measurements of the surface-collision dynamics of ionized cluster beams. At lowest energy, both transient physisorption (soft-landing) and intact scattering have been observed. Impact of nanocrystalline sodium-fluoride clusters (NanFn-1+) against graphite at intermediate energy (0.2 - 1 eV per atom) leads efficiently to fracture-like processes. At higher energy, a featureless evaporative cascade dominates the fragment distribution. Energy- and angle-resolved scattering of mass-selected clusters from oriented graphite is shown to be a versatile method for investigation of cluster structure-energetics, cluster-surface interactions, and sticking phenomena.
Fabrication of Supported Catalytic Nickel Clusters of Controlled Size and Distribution Using Ionized Cluster Beam Deposition
Authors: Yoo M. C. , Kim K.
Published: March 2011

A novel technique for fabricating uniform, ultrafine metal clusters of controlled size and distribution is described. The technique employs conventional adiabatic expansion of an evaporated source material for controlled formation of the clusters, but additionally incorporates electron-impact ionization and acceleration for further control of the size and distribution of the deposited particles. The key control parameters investigated are the diameter of the adiabatic nozzle, the proportion and energy of the ionized particles in the cluster beam, the substrate temperature, and the deposition time. The use of electron irradiation and acceleration of the source beam has proven to be particularly effective in producing monodisperse clusters. Using this new approach, uniform Ni clusters as small as 10 Å were deposited on an amorphous carbon substrate. The size and structure of the deposited Ni clusters were analyzed using high-resolution TEM and STEM.
Studies of the Chemical Properties of Size Selected Metal Clusters: Kinetics and Saturation
Authors: Cox Donald M. , Brickman Robert O. , Creegan Kathleen , Kaldor Andrew
Published: March 2011

Our studies of small (n=2−40) gas phase transition metal clusters (cations, neutrals and anions) have revealed a number of size-dependent chemical and physical properties. This paper will discuss results involving activated dissociative molecular chemisorption of hydrogen (deuterium) and small alkanes on cationic, neutral and anionic platinum and gold clusters. For example, we have yet to find any size gold cluster anion to exhibit measurable reactivity towards di-deuterium, but reactivity is observed on small (n<15) gold cations and very small (n<9) neutral gold clusters. Methane or ethane chemisorption occurs most readily only on small Pt and Au cluster cations and least rapidly, if at all, on cluster anions. The larger Pt and Au clusters are found to be non-reactive towards the alkanes under our experimental conditions.

At the other extreme, at steady state, small clusters of Pt, Rh, Ni, Pd, V, Nb, and Ta are hydrogen “rich” exhibiting H/M stoichiometrics >> 1. These results are consistent with a limited data base on supported clsutes obtained via EXAFS measurements and have important implications for catalytic reactions involving hydrogen and light hydrocarbons.
Nanometer-Sized Microstructures
Authors: Gleiter H.
Published: March 2011

Materials with nanometer-sized microstructures are solids that contain such a high density of defects (point defects, dislocations, grain boundaries, interphase boundaries etc.) that the volume fraction of the defect cores becomes comparable to the residual, defect free volume. Since 1970, the interest of materials scientists focused on solids with nanometer-sized microstructures when it was recognized that specifically tailored nanometer-sized microstructures permit the generation of materials with new atomic and/or electronics structures. In the area of semiconductors, quantum well structures and superlattices consisting of thin coherent layers with different dopings or compositions have been studied extensively. In these structures quantum size effects prevail because the coherent boundaries structures between the layers act as electron confinements. Research activities aiming towards the synthesis of new atomic (and electronic) structures in metals, ceramics and semiconductors by means of three-dimensional nanometer-sized micro-structure were initiated by the proposal, to generate solids a large volume fraction of which consists of the cores of defects such as incoherent grain and/or interphase boundaries, such solids differ structurally and property-wise from crystals and glasses with the same chemical composition because the atomic arrangements formed in the cores of incoherent grain or interphase boundaries deviate from crystalline or glassy structures. Recent studies of nanometer-sized materials by x-ray/neutron diffraction, EXAFS, different spectroscopies as well as property measurements support this idea. The properties of materials with nanometer-sized microstructures are discussed on the basis of the knowledge available from the numerous studies that have been carried out in the last two decades about the structure and properties of grain and/or interphase boundaries.
Raman Scattering and Photoemission from Bi Clusters
Authors: Mitch M. G. , Chase S. J. , Yu R. Q. , Fortner J. , Lannin J. S.
Published: March 2011

Raman scattering measurements of Bi clusters formed on disordered C films at 110K exhibit a phase transformation from nanocrystalline rhombohedral structure to a suggested disordered phase. XPS measurements on this phase indicate core level shifts attributed to intrinsic, initial state effects on cluster electronic states.
Modelling Early Stages in the Formation of Cluster-Assembled Materials
Authors: Schön Christian , Salamon Peter
Published: March 2011

The formation of cluster-assembled materials using the sintering process is investigated. We present a model that describes the initial stages exactly using information derived from ab initio calculations of cluster behavior. Surface area, effective cross section and density of the cluster-assembled material, are calculated as functions of time for several implementations of the model.
Issues in the Processing of Bulk Nanocrystalline Ceramics for Structural Applications
Authors: Mayo M. J. , Çiftçioglu M.
Published: March 2011

TiO2 has been fabricated using a modified alkoxide hydrolysis route; the process yields about 50 g/day of nanocrystalline powder on a laboratory scale, which can be used to make large (1–10 g) samples. Pore size distributions show the powder is non-agglomerated, and TEM and BET analyses confirm the nanocrystalline size of the particles at about 20 nm. The powder is extremely reactive, sintering at about half the temperatures required of commercial powders. The chemically produced powder compacts to only 62% of the density that can be achieved by compacting a gas phase condensation (GPC)-produced TiO2. Nevertheless, the reactivity of this less dense compact is such that it reaches final densities comparable to that of the GPC TiO2. The difficulties in compacting and sintering large nanocrystalline samples are discussed. It is hoped that an understanding of these problems will lead to more intelligent densification of ultrafine powders so that full densification can be accomplished while retaining a nanocrystalline grain size.
Tensile Strength and Creep Resistance in Nanocrystalline Cu, Pd and Ag
Authors: Nieman G. W. , Weertman J. R. , Siegel R. W.
Published: March 2011

Measurements of tensile strength and creep resistance have been made on bulk samples of nanocrystalline Cu, Pd and Ag consolidated from powders by cold compaction. Samples of Cu-Cu2O have also been tested. Yield strength for samples with mean grain sizes of 5–80 nm and bulk densities on the order of 95% of theoretical density are increased 2–5 times over that measured in pure, annealed samples of the same composition with micrometer grain sizes. Ductility in the nanocrystalline Cu has exceeded 6% true strain, however, nanocrystalline Pd samples were much less ductile. Constant load creep tests performed at room temperature at stresses of >100 MPa indicate logarithmic creep. The mechanical properties results are interpreted to be due to grain size-related strengthening and processing flaw-related weakening.
Thermodynamics of Nano-Grain Boundaries
Authors: Fecht Hans J.
Published: March 2011

A universal, accurate and simple method is developed to describe the thermodynamic properties of disordered grain boundaries in nanocrystalline metals. Based on a free volume approach at negative pressure of the universal equation of state, the maximum free volume, bulk modulus, specific heat at constant pressure, thermal expansion coefficient, excess enthalpy, excess entropy and free energy of grain boundaries are derived from well-known thermodynamic relationships. Describing nanocrystalline metals as a bimodal material with a grain boundary component and a crystalline component, their thermodynamic properties can then be estimated by appropriate scaling of the boundary-to-volume ratio.
Carbon ARC Generation of C60
Authors: Haufler R. E. , Chai Y. , Chibante L. P. F. , Conceicao J. , Jin Changming , Wang Lai-Sheng , Maruyama Shigeo , Smalley R. E.
Published: March 2011

Generation of C60 at a rate of more than 10 grams per day has been accomplished by operation of a carbon arc in an atmosphere of helium. Optimum yield of 15% was found to occur near 100–200 torr, but yields greater than 3% were found throughout the range between 50 and 760 torr. A model is proposed to explain the observed behavior based on competition between annealing of graphitic sheets to curve so that they minimize dangling bonds, and further rapid growth of these sheets in the gas phase to form giant fullerenes. In agreement with predictions of this model, laser vaporization of graphite targets was found to produce macroscopic quantities of C60 only when performed in an oven above 1000 C.
Laser Annealing of Semiconductor Clusters: Trimethylamine Reactions with Positive and Negative Clusters
Authors: Maruyama S. , Anderson L. R. , Smalley R. E.
Published: March 2011

Reaction studies with trimethylamine on positively charged laser-annealed silicon clusters of 39, 43, and 48 atoms magnetically levitated in a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer reveal the same relative reaction pattern as previously observed for identical studies with ammonia and ethylene. The 39th cluster was found to be considerably less reactive than the other positive cluster sizes, and significantly, its negative ion is also relatively less reactive than the 43rd and 48th. The continued observation of this reactivity trend provides additional experimental evidence that the annealed clusters adopt well-organized structures, and that these crystal forms are similar for both charge states.
Spectrometric Characterization of Purified C60 and C70
Authors: Lykke Keith R. , Pellin Michael J. , Wurz Peter , Gruen Dieter M. , Hunt Jerry E. , Wasielewski Michael R.
Published: March 2011

C60 and C70 were synthesized and purified according to published procedures. Both nanosecond and picosecond laser desorption from coated substrates gave copious positive and negative ions. Mass spectra (TOF and FTMS) with excellent signal to noise, showing only the C60 and C70 mass peaks, have been observed. Well-resolved isotopic structure was seen in the FTMS spectra in agreement with the natural abundance of carbon. Laser desorption and multiphoton ionization/photodissociation of the neutral species, as well as electronic absorption, FTIR, and fluorescence spectra, have been obtained.
Diffraction Symmetry in Crystalline, Close-Packed C60
Authors: Fleming R. M. , Siegrist T. , Marsh P. M. , Hessen B. , Kortan A. R. , Murphy D. W. , Haddon R. C. , Tycko R. , Dabbagh G. , Mujsce A. M. , Kaplan M. L. , Zahurak S. M.
Published: March 2011

We have grown crystals of the carbon structure C60 by sublimation. In contrast to solution-grown crystals, the sublimed crystals have long range order with no evidence of solvent inclusions. Sublimed C60 forms three dimensional, faceted crystals with a close-packed, face-centered cubic unit cell. We have refined a crystal structure using the “soccer ball” model of the C60 molecule. The results indicate that the C60 molecule has the expected spherical shape, however the data are not sufficiently accurate to unambiguously determine atomic positions.
High Resolution Plan View Imaging of Clean and Au Deposited Si(111) surfaces
Authors: Ozawa S. , Tanaka Y. , Kobayashi K. , Yamamoto N. , Yagi K.
Published: March 2011

High resolution plan view images of clean and Au deposited Si(111) surfaces are presented. Corner holes and small holes between dimers of the DAS model of the 7×7 structure were clearly resolved. In the case of the Si(111)5×1-Au structure the 5 times period fringes did not show fine details.
Photoelectron Diffraction of Magnetic Ultrathin Films: Fe/Cu(001)
Authors: Tobin J. G. , Wagner M. K. , Guo X.-O. , Tong. S. Y.
Published: March 2011

The preliminary results of an ongoing investigation of Fe/Cu(001) are presented here. Energy dependent photoelectron diffraction, including the spin-dependent variant using the multiplet split Fe 3s state, is being used to investigate the nanoscale structures formed by near-monolayer deposits of Fe onto Cu(001). Core-level photoemission from the Fe3p and Fe3s states has been generated using synchrotron radiation as the tunable excitation source. Tentatively, a comparison of the experimental Fe3p cross section measurements with multiple scattering calculations indicates that the Fe is in a fourfold hollow site with a spacing of 3.6Å between it and the atom directly beneath it, in the third layer. This is consistent with an FCC structure. The possibility of utilizing spin-dleendent photoelectron diffraction to investigate magnetic ultrathin films will be demonstrated, using our preliminary spectra of the multiplet-split Fe3s of near-monolayer Fe/Cu(001).
X-Ray Reflectometry of Single- and Multi-Layer Thin Films
Authors: Parrish W. , Erickson C. , Huang T. C. , Hart M. , Gilles B. , Toraya H.
Published: March 2011

This paper describes the instrumentation and technique for the routine characterization of thin Films, multi-layers and substrates by grazing incidence X-ray reflectometry with a rotating anode and CuKα1, line source. Ge 220 channel monochromators with two reflections per channel were used with one CM placed before and the other after the specimen. In many applications the second CM could be replaced with a narrow receiving slit. The specimen holder was designed to make fine translations of the specimen for alignment, a base was designed to permit precise positioning of the diffractometer, and a high-speed Rigaku scintillation counter was used. The alignment and calibration are described and some typical data given to illustrate the capability of the method.
Substrate Dependent Texture and Heteroepitaxy for Group IIIA Nitride Films by the X-Ray Precession Method
Authors: Kistenmacher T. J. , Bryden W. A. , Wickenden D. K. , Ecelberger S. A.
Published: March 2011

The X-ray precession method has been utilized to study texture and heteroepitaxy for thin films of the Group IIIA nitrides deposited on a variety of amorphous and single-crystal substrates. Films of InN were synthesized by reactive rfmagnetron sputtering [employing an elemental target and N2 as the sputtering gas], while the GaN films were deposited by metalorganic chemical vapor deposition [utilizing (CH 3 ) 3Ga and NH3 as sources]. The quality of (00.1) textured films of InN on fused quartz and slightly off-axis (111) Si are taken as initial examples of the versatility of the X-ray precession method. The powder rings evolving from a lack of azimuthal coherence for InN films grown on quartz are contrasted with the scattering from weakly correlated (pseudo heteroepitaxial) domains for films grown on (111) Si. These latter scattering features are then compared with those from the true heteroepitaxial deposition of InN onto the (111) face of cubic ZrO2. And, finally, the scattering from the heteroepitaxial growth of InN and GaN on the (00.1) face of sapphire and some initial studies on the effect of nucleation layers on twinning in the GaN films are presented.
UHV Microscopy of the Reconstructed Au (001) Surface
Authors: Dunn D. N. , Marks L. D. , Zhang J. P.
Published: March 2011

We investigate the evolution of the microstructure of a reconstructed Au (001) single crystal surface using ultra high vacuum transmission electron microscopy (UHV-TEM). Bulk single crystal Au (001) surfaces were prepared via standard metallographic techniques and sputter anneal cycles. After a clean surface was obtained, the (001) surface was found to reconstruct into two nearly orthogonal domains of dimensions (5 × ∼ 20 ) along the <110> directions of the unreconstructed F.C.C. (001) surface. Transmission electron diffraction patterns (TED) and dark field microscopy are the two primary techniques used to determine the symmetry and dimensions of the reconstructed surface.