bluuebunny/crossref_metadata_2025 huggingface dataset:
Hydrodynamics of a Chemical-Mechanical Planarization Process
Authors: Sohn In-Sung , Moudgil Brij , Singh Rajiv , Park C.-W.
Published: April 2011

The flow of a slurry in a CMP process has been investigated. This wafer-scale model provides the three dimensional flow field of the slurry, the spatial distribution of the local shear rate imposed on the wafer surface, and the streamline patterns which reflect the transport characteristics of the slurry.
On the Pattern Dependency and Substrate Effects During Chemical-Mechanical Planarization for Ulsi Manufacturing
Authors: Tseng Wei-Tsu , Niu James Jong-Lin , Lin Chi-Fa
Published: April 2011

The change of surface profile during chemical-mechanical planarization (CMP) is monitored continuously in this study. The influences from pattemn dependency and substrate effects are discussed. Step height reduction rate is a function of pattern density and down force. The rate decreases with time until planarization is achieved. As the polish approaches the patterns underneath, the interaction between substrate effects and pattern dependency results in the resurgence of step height. The implication of this newly found phenomenon is discussed.
A Study of the Planarity by Sti Cmp Erosion Modeling
Authors: Kim K.H. , Hah S.R. , Han J.H. , Hong C.K. , Chung U.I. , Kang G.W.
Published: April 2011

In this work, we propose a new equation that predicts the planarity as a function of active pattern density, initial step height, selectivity between gapfilled oxide and silicon nitride and over CMP amounts. In order to achieve highly planarized STI surface, uniform active density, reduced initial step height, minimization of over CMP amounts and high selective slurry were required. Our new equation was applied to the 0.18um graded CPU devices’ STI CMP to enhance planarity and these parameters were evaluated quantitatively. It is concluded that the model suggested is useful in predicting CMP planarity
Low Temperature Formation of Ultra-Thin SiO2 Layers Using Direct Oxidation Method in a Catalytic Chemical Vapor Deposition System
Authors: Izumi A. , Sohara S. , Kudo M. , Matsumura H.
Published: April 2011

This paper reports a procedure for low-temperature formation of silicon dioxide (SiO2) using a catalytic chemical vapor deposition (Cat-CVD) system. The surface of Si(100) is oxidized at temperatures as low as 200°C and a few nm SiO2 films are formed. Electrical and structural properties of the layers are investigated. It is found that breakdown electric field, leakage current and the density of intermediate oxidation states is comparable with thermally oxidized sample.
Ultrathin Gate Oxides with Shallow Nitrogen Implants as Effective Barriers to Boron Diffusion
Authors: Ono Yoshi , Ma Yanjun , Hsu Sheng-Teng
Published: April 2011

Plasma immersion ion implantation (PIII) has been employed to controllably place nitrogen ions from an inductively coupled plasma into a thin furnace grown gate oxide 2.0nm thick with implant voltages from 25 to 500V. Control of the implant energy enables shallow implantation confining the nitrogen mainly within the oxide. Rapid thermal annealing is essential in repairing any damage to the implanted silicon dioxide and silicon while consolidating the bonding of nitrogen into the oxide film prior to gate polysilicon deposition. High frequency capacitance-voltage measurements of capacitors made with BF2+ implanted gates throughout a series of furnace anneals demonstrates the efficiency for blocking boron compared to non-nitrided oxides of similar thickness. Tddb measurements verify excellent reliability compared to a non-implanted oxide for both stress polarities.
Role of Silver Doping in the Improvement of Electrical Properties of (Ba,Sr)TiO3 Thin Films
Authors: Srivastava Anuranjan , Kumar D. , Singh Rajiv K. , Venkataraman Harish , Eisenstadt William R.
Published: April 2011

In this paper we report the fabrication and characterization of Ag/(Ba,Sr)TiO3 /LaNiO3/LaAlO3 capacitors. All the films, including the top (silver) and bottom (LaNiO3) electrodes, were deposited using a pulsed laser deposition technique. The electrical and dielectric properties of (Ba,Sr)TiO3 capacitors were found to improve significantly by means of silver doping. For example, the leakage current density of a Ag/Ag-doped-(Ba,Sr)TiO3 /LaNiO3/ capacitor was about an order of magnitude lower and dielectric constant was ∼40 % higher than that of a Ag/(Ba,Sr)TiO3 /LaNiO3/capacitor over a range of biases. The improvement in the electrical properties of (Ba,Sr)TiO3 films is believed to be caused by a double role of silver. The first one is associated with the reduced oxygen vacancies due to improved oxygenation of BST films in presence of silver and the second one is associated unpinning effect of domain walls again in presence of silver.
Quantitative Measurement of Reduction of Phosphorus Diffusion by Substitutional Carbon Incorporation
Authors: Carroll M. S. , Sturm J. C. , Chang C-L.
Published: April 2011

Complete suppression of transient enhanced boron diffusion (TED) and oxidation enhanced boron diffusion (OED) in silicon have been achieved using substitutional carbon to reduce the excess point defect concentration in the dopant region [1]. Recent efforts have focused on removing the carbon from the active regions of the device [2,3] to avoid device degradation due to electrically active carbon defects [4] and exploring remote carbon's effect on boron TED and OED, while using the boron diffusion to probe point defect concentrations.

In this paper we measure quantitatively the effect of remotely located carbon on phosphorus and boron diffusion above a buried SiGeC layer at 850°C in oxygen or nitrogen ambients. Remote carbon, located 1250 A below the phosphorus edge, is found to reduce the phosphorus diffusion enhancement factor due to OED from 8 to 2. The effect of the remotely located SiGeC buried layer on the excess interstitial concentration profile, which is responsible for the enhanced dopant diffusion, is probed by measuring boron and phosphorus diffusivites of in-situ doped boron and phosphorus layers above a buried SiGe(C) layer after oxidation or nitrogen anneals at 850°C. The enhanced boron diffusivity during oxidation is found to have a near linear dependence on depth ranging from 5–1.25. Finally, using x-ray diffraction and photoluminescence measurements of as-grown, buried, strained SiGe(C) structures and annealed SiGe(C) structures in oxygen or nitrogen ambient at 850°C the number of substitutional carbon atoms effectively consumed by oxidation is unambiguously correlated to the absolute number of injected interstitials using published values for the interstitial injection rate during oxidation [5].
Ultra-Low Energy Boron Implants in Crystalline Silicon: Atomic Transport Properties and Electrical Activation
Authors: Napolitani E. , Carnera A. , Privitera V. , Magna A. La , Schroer E. , Priolo F. , Mannino G. , Moffatt S.
Published: April 2011

We investigated the atomic transport properties and electrical activation of boron in crystalline epitaxial silicon after ultra-low energy ion implantation (0.25–1 keV) and rapid thermal annealing (750–1100 °C). A wide range of implant doses was investigated (3×1012-1×105/cm2). A fast Transient Enhanced Diffusion (TED) pulse is observed involving the tail of the implanted Boron, the profile displacement being dependent on the implant dose. The excess of interstitials able to promote enhanced diffusion of implanted boron occurs, provided the implant dose is high enough to generate a significant total number of point defects. The Boron diffusion following the fast initial TED pulse can be described by the equilibrium diffusion equations.

The electrical activation of ultra-shallow implants is hard to achieve, due to the high concentration of dopant and point defects confined in a very shallow layer that significantly contributes to the formation of clusters and complex defects. Provided a correct combination of annealing temperatures and times for these ultra-shallow implants is chosen, however, a sheet resistance 500 Δ/square with a junction depth below 0.1μm can be obtained, which has a noteworthy technological relevance for the future generations of semiconductor devices.
Comparison of Ultra-low-energy Ion Implantation of Boron and BF2
Authors: Park Jihwan , Hwang Hyunsang
Published: April 2011

We have compared the electrical characteristics and the depth profile of an ultrashallow junctions formed by boron implantation at 0.5 keV and BF2 implantation at 2.2 keV. The modeling of the boron profile was performed using the Monte Carlo method for an as-implanted profile and the computationally efficient method for transient-enhanced diffusion. A junction depth of BF2 is shallower than that of boron after annealing. HF dipping prior to rapid thermal annealing causes a significant loss of dopant and high sheet resistance. Considering the 0.1 νn metal-oxide-semiconductor field-effect-transistor (MOSFET) application, the optimizations of implantation and annealing conditions are necessary to satisfy the requirement ofjunction depth and sheet resistance.
Experimental Study of Self-Diffusion in Silicon Using Isotopically Enriched Structures
Authors: Ural Ant , Griffin Peter B. , Plummer James D.
Published: April 2011

Self-diffusion in silicon has been studied using epitaxially grown isotopically enriched structures under nonequilibrium concentrations of intrinsic point defects created by thermal oxidation and nitridation. Comparison of identical anneals for self, antimony, and phosphorus diffusion in silicon enables us to determine bounds on the fractional contributions of microscopic mechanisms for Si self-diffusion in the temperature range 800–1100°C. We obtain direct experimental evidence for a dual vacancy-interstitial mechanism of self-diffusion in silicon and show that the fractional contribution of each mechanism has a weak dependence on temperature.
Modeling The Evolution of Ellipsometric Data During The Thermally Induced Pt-Silicide Formation: Activation Energies and Prefactors
Authors: Ley L. , Stark T. , Hundhausen M. , Gruenleitner H.
Published: April 2011

The formation of Pt silicide (PtSi) by the thermally activated reaction of a 23 nm Pt layer on Si was monitored in situ by ellipsometry. Characteristic changes in the ellipsometric angles as a function of temperature signal the approach of two reaction fronts to the surface: one belonging to the Pt/Pt2Si and the other to the Pt2Si/PtSi interface. An analysis of the evolution of the ellipsometric angles as a function of temperature for different heating rates allows the accurate determination of the average activation energies of the two reactions. From a modeling of the optical data in terms of a specific reaction model further kinetic parameters such as the reaction rate constants and the actual distribution of activation energies have been deduced.
Real-time x-ray scattering study of sputter-deposited LaNiO3 thin films on Si substrates
Authors: Lee Hsin-Yi , Lee Chih-Hao , Liang Keng S. , Wu Tai-Bor
Published: April 2011

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

We have applied Atomic Number Contrast Scanning Transmission Electron Microscopy (Z-Contrast STEM) towards the study of colloidal CdSe semiconductor nanocrystals embedded in MEH-PPV polymer films.

For typical nanocrystal thicknesses, the image intensity is a monotonic function of thickness. Hence an atomic column-resolved image provides information both on the lateral shape of the nanocrystal, as well as the relative thickness of the individual columns.

We show that the Z-Contrast image of a single CdSe nanocrystal is consistent with the predicted 3-D model derived from considering HRTEM images of several nanocrystals in different orientations. We further discuss the possibility of measuring absolute thicknesses of atomic columns if the crystal structure is known.
Determination of Coherency Strain Fields Around Coherent Particles in Ni-Al Alloys by HREM and CBED
Authors: Calderon H. A. , Calzado L. , Kisielowski C. , Wang C. Y. , Kilaas R.
Published: April 2011

Quantitative evaluation of coherency strains around particles in the alloy Ni-12 at.% Al has been performed by means of high resolution electron microscopy (HREM) and convergent bean electron diffraction (CBED). Evaluation of the elastic strain fields around particles can give insight into the elastic interaction between particles during their coarsening mechanism and especially for the late stages where the elastic energy becomes particularly important. Typically, particles form spatial arrangements after long aging times. In the case of fcc-type structures, they align along the <001> soft elastic directions and form groups of many particles. HREM has been used to acquire images including the particle matrix interface. The selected zone axis is [001]. The quantitative analysis to determine the positions of the intensity maxima and the subsequent evaluation of the lattice parameters, is made by using the software Darip. Two different directions with respect to the particle matrix interface (parallel and perpendicular) are considered for the evaluation. These measurements are compared to determinations made by means of quantitative evaluation based on calibrated CBED patterns taken from similar regions of the samples.
On the Raman Spectrum of Nanobundles of Single Wall Carbon Nanotubes
Authors: Alvarez L. , Righi A. , Rols S. , Anglaret E. , Sauvajol J.L.
Published: April 2011

Raman scattering is used to study the structure and electronic properties of bundles of single wall carbon nanotubes. A relation between the tube diameter and the radial breathing mode frequency is derived by combining a description of the covalent bonds inside each nanotube via force constant model with a pair-potential approach to deal with the van der Waals interaction between nanotubes. In the framework of this approach a good agreement is evidenced between the diameter distribution derived from the A1g radial breathing mode frequencies and the one obtained from the analysis of the neutron diffraction spectrum. On the other hand, an investigation of the intermediate frequency range (600-1100 cm-1) of the Raman spectrum is reported. A dependence of the frequency of the modes with the excitation energy is clearly evidenced and assigned to a mode coupling.
Direct Observation of Intercalant and Catalyst Particle in Single Wall Carbon Nanotubes
Authors: Fan X. , Dickey E. C. , Eklund P. , Williams K. , Grigorian L. , Puretzky A , Geohegan D. , Buczko R. , Pantelides S. T. , Pennycook S. J.
Published: April 2011

The Z-contrast scanning transmission electron microscopy (STEM) imaging technique has been used to study dopant atoms and catalyst particles in single wall carbon nanotubes (SWNT). Iodine and bromine have been doped respectively in arc-grown SWNTs. We have directly observed the dopant sites and distributions. Both dopants appear to be incorporated linearly within the SWNT bundles. SWNT were also grown by pulsed laser ablation with mixed Ni and Co catalyst, and the size and distribution of catalytic particles was studied. By using Z-contrast imaging, we found that the size distribution of the catalyst particles varied over a large range, but even the smallest were larger than the diameter of an individual SWNT. Furthermore, electron energy loss spectroscopy (EELS) is used to determine the composition of individual nanocatalyst particles, and were found to consist of a uniform alloy of Co and Ni.
Electron Field Emission Characterization of Nanocrystalline Diamond Thin Film Cold Cathode Devices
Authors: Weiss B. L. , Badzian A. , Pilione L. , Badzian T. , Drawl W. , Morell G.
Published: April 2011

Electron field emission measurements have been performed on thin film cold cathode materials grown, on molybdenum, by a modified MPACVD diamond process. Specifically the modification is due to the addition of nitrogen and oxygen, in varying ratios, during the diamond growth phase. Characterization using Raman spectroscopy shows features at 1190, 1330 and 1550 cm−1. A simple triode device was fabricated for electron emission characterization. KAPTON® film is used as the insulating layer and a Mo mesh is used as the extraction gate electrode. The collector is an indium tin oxide (ITO) coated glass plate which is positively biased with respect to the gate electrode. Field emission characteristics have shown current measurements of greater than I microamp for fields of 40 V/micron. Gate currents are typically 1000 times greater than the emitted current. Issues currently being addressed include improvement in the total emitted current, current stability and device failure. We also present field emission measurements on diamond films grown by HFCVD.
Structure and Photoluminescence of Hydrogenated Amorphous Carbon Films Produced by Using Aromatic Hydrocarbon Source
Authors: Xu Jun , Ma Tianfu , Li Wei , Wang Li , Li Zhifeng , Chen Kunji
Published: April 2011

The organic carbon source –xylene(C6H6-C2H4), was used to fabricate a-C:H films in plasma enhanced chemical vapor deposition system. The structures and bonding configurations were characterized and compared with that of conventional methane-based samples by using Fourier Transform Infrared spectroscopy and Raman scattering technique. Strong room temperature luminescence in blue-green light range was found and the PL feature was quite different from that of methane-based a-C:H films.
Intrinsic Stress Measurements in CVD Diamond Films
Authors: Yu Jin , Kim J.G. , Sohn Y. C. , Lee Y. S.
Published: April 2011

Diamond films were grown over Si substrate at 1253K by the hot filament chemical vapor deposition method using CH4/H2 gas mixture, and intrinsic stresses in the film were deduced from the ex-situ curvature measurements. In order to account for the creep deformation of the Si substrate, an elastic/plastic stress and strain analysis were conducted. Results showed that intrinsic stresses were generally several times larger than the average film stresses and always positive increasing with the film thickness. For the film thickness larger than 10μm, stress relaxation by creep of the substrate became significant, and must be considered for the accurate assessment of the film stress in diamond. Later, an analysis based on the grain growth accounted for the development of intrinsic stresses reasonably well
Ultra-High Strain Response of Elastomeric Polymer Dielectrics
Authors: Kornbluh Roy , Pelrine Ronald , Joseph Jose , Pei Qibing , Chiba Seiki
Published: April 2011

The strain response of dielectric elastomers sandwiched between compliant electrodes was studied. These electroactive polymer artificial muscle (EPAM) materials show excellent overall performance and appear more attractive than many competing actuator technologies. Based on the available data, the actuation mechanism is due to the free charge interaction of the compliant electrodes, enhanced by the dielectric properties of the elastomer (Maxwell stress). Strains over 200%, actuation pressures up to 8 MPa, and energy densities up to 3.4 J/cm3have been demonstrated with silicone rubber and acrylic elastomers. Response time is rapid, and the potential efficiency is high. The fabrication of EPAM actuators can be simple and low cost. A wide range of small devices have been made, to demonstrate the potential of the technology and reveal more about performance and fabrication issues. These devices include bending beam actuators for scanners and clamps, diaphragm actuators for pumps and valves, stretched-film actuators for electro-optics, and bow actuators for muscle-like actuators for small robots and other micro machines.
On the Nature of Heterogeneity in Vacuum Deposited Polyaniline Films
Authors: Ivanov V. F. , Nekrasov A. A. , Cheberyako K. V. , Gribkova O. L. , Vannikov A. V.
Published: April 2011

Heterogeneity of polyaniline and other conductive polymers in intermediate oxidation states is fundamental problem of physics and chemistry of these ones. Usually only advanced methods may be used for immediate detection of the heterogeneity in the molecular scale range. For the first time we have observed the process of the heterogeneous net-like structure formation in macroscopic scale under the oxidation of the evaporated polyaniline films by aqueous HNO3. and other oxidative agents. Formation of heterogeneous structure is explained in terms of nonequilibrium thermodynamic and chemical kinetics.
Biochemical Synthesis and Unusual Conformational Switching of a Molecular Complex of Polyaniline and DNA
Authors: Nagarajan Ramaswamy , Tripathy Sukant K. , Kumar Jayant , Samuelson Lynne A. , Bruno Ferdinando F.
Published: April 2011

Polyaniline (Pani) is one of the most interesting conducting polymers because of its promising electrical properties and unique redox tunability. Recently a new template assisted, enzymatic synthetic approach has been developed which yields a water-soluble and conducting complex of polyaniline and the template used. The mild reaction conditions in this approach allow for the utilization of delicate biological systems as template materials, such as DNA. Here we report the extension of this enzymatic approach to the synthesis of Pani on a DNA matrix. DNA serves as a suitable template for complexation and formation of conducting polyaniline. The redox behavior of Pani induces reversible conformational change in the secondary structure of DNA. Circular dichroism results suggest that the secondary structure of the DNA may be reversibly switched through manipulation of the redox state of the polyaniline.
Modified Constitutive Equation of Superplasticity Including Grain Growth Rate
Authors: Miyazaki H. , Iseki T. , Yano T.
Published: April 2011

Superplastic behavior associated with grain growth in ceramics at high temperature is predicted by using a modified constitutive equation for superplasticity that incorporates the rate of grain growth. The equation reveals that there is an optimum deformation conditions – i.e., the strain rate and deformation temperature - so that ceramics have low flow stress when the grain growth is significant. The equation provides an explanation of increased flow stress for liquid-phase-sintered SiC in the slow-strain-rate region or higher-temperature region in which grain growth plays an important role.
Computer Simulation of Grain Boundary Character in a Superplastic Aluminum Alloy
Authors: McNelley T.R. , Peréz-Prado M.T.
Published: April 2011

High-angle grain boundaries are generally deemed necessary for superplasticity in metals. In polycrystalline materials the grain boundary character must be described in terms of a probability distribution rather than by a single parameter, and little has been reported on the relationship between this distribution and fine-grain superplasticity. For aluminum alloys that exhibit continuous recrystallization the results of computer-aided electron backscatter diffraction analysis have shown that bimodal grain boundary disorientation distributions are present in as-processed material and persist during subsequent annealing. Such distributions may be simulated by computer methods based on a model of the microstructure which assumes that deformation banding occurs during deformation processing. High-angle boundaries (≥30°) develop in association with deformation banding while boundaries of lower disorientation (<30°) develop by dislocation reaction within the bands. Improved understanding of the grain boundary types associated with various microstructural transformation mechanisms will aid the design of processes to produce superplastic microstructures.
Cavitation Behavior of Coarse-Grained Al-4.5Mg Alloy Exhibiting Superplastic-Like Elongation
Authors: Iwasaki H. , Mori T. , Hosokawa H. , Tagata T. , Mabuchi M. , Higashi K.
Published: April 2011

Cavitation behaviors related to ferrous primary crystals have been investigated at a temperature of 653 K and a strain rate of 10−3/s for Al-4.5%Mg-0.05%Fe and Al-4.5%Mg-0.2%Fe alloys which have a grain size of 50;Lm. The alloys constantly exhibited a large elongation-to-failure above 300% at the temperature of 653 K and strain rate of 10−3/s. Cavitation was increased by increasing the iron content. Most cavities were nucleated at the interface between the ferrous primary crystal and matrix and elongated parallel to the tensile direction. The experimental critical diameter of the primary crystal, above which cavity is nucleated, was 1.5 µm at the grain boundary and 0.5µm at grain interior, which were very close to double the critical diffusion length.
Intelligent Gels
Authors: Osada Yoshihito , Gong Jian Ping , Narita Tetsuharu
Published: April 2011

We reported an electro-driven chemomechanical hydrogel showing quick responses with worm-like motility. The principle of the motion is based on the molecular assembly reaction of cationic surfactant and negatively charged hydrogel. And direction of complexation accompanying gel contraction is controlled by changing the polarity of the applied electric field. Both thermodynamics and kinetics of surfactant binding and diffusion are investigated experimentally and theoretically. We also reported shape memory hydrogel by order-disorder transition of alkyl side chain, and some examples od friction of hydrogels showing that frictional behaviors of hydorgels do not conform to Amonton's law.