bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermoplastics Modified with Nanoscale Inorganic Macromers
Authors: Haddad Timothy S. , Mather Patrick T. , Jeont Hong G. , Romo-Uribe Angel , Farrist Amy R. , Lichtenhant Joseph D.
Published: April 2011

We have taken a unique approach to the synthesis and study of hybrid organic/inorganic materials. Our method involves synthesizing nano-size inorganic P1R7Si8O12 clusters which contain seven inert “R” groups for solubility and only one functional “P” group for polymerization. This strategy permits the synthesis of melt processable, linear hybrid polymers containing pendent inorganic clusters and allows us to study the effect these clusters have on chain motions and polymer properties. The synthesis of norbomenyl-based polyhedral oligomeric silsesquioxane (POSS) macromers, their ring opening metathesis copolymerizations with varying amounts of norbornene, and analysis of the effect of the pendent POSS group is presented. The mechanical relaxation behavior and microstructure of norbornyl-POSS hybrid copolymers have been examined for their dependencies on the mole fraction of POSS-norbornyl monomer, as well as for potential sensitivity to the seven inert “R” groups present in each POSS macromer. POSS copolymerization is observed to enhance the α-relaxation temperature, Tα, in proportion to the mole fraction of POSS-norbornyl comonomer. Interestingly, however, the magnitude of this dependence is larger for POSS-norbornyl comonomer possessing cyclohexyl groups (CyPOSS) than for cyclopentyl groups (CpPOSS). While POSS copolymerization yields only slight enhancement of the tensile storage modulus measured near room temperature, at temperatures lower than a strong mechanical relaxation (β-relaxation near T = -75 °C), there is a significant POSS-reinforcement of the storage modulus.
Transmission Electron Microscopy of Semiconductor Based Products
Authors: Mardinly John , Susnitzky David W.
Published: April 2011

The demand for increasingly higher performance semiconductor products has stimulated the semiconductor industry to respond by producing devices with increasingly complex circuitry, more transistors in less space, more layers of metal, dielectric and interconnects, more interfaces, and a manufacturing process with nearly 1,000 steps. As all device features are shrunk in the quest for higher performance, the role of Transmission Electron Microscopy as a characterization tool takes on a continually increasing importance over older, lower-resolution characterization tools, such as SEM. The Ångstrom scale imaging resolution and nanometer scale chemical analysis and diffraction resolution provided by modem TEM's are particularly well suited for solving materials problems encountered during research, development, production engineering, reliability testing, and failure analysis. A critical enabling technology for the application of TEM to semiconductor based products as the feature size shrinks below a quarter micron is advances in specimen preparation. The traditional 1,000Å thick specimen will be unsatisfactory in a growing number of applications. It can be shown using a simple geometrical model, that the thickness of TEM specimens must shrink as the square root of the feature size reduction. Moreover, the center-targeting of these specimens must improve so that the centertargeting error shrinks linearly with the feature size reduction. To meet these challenges, control of the specimen preparation process will require a new generation of polishing and ion milling tools that make use of high resolution imaging to control the ion milling process. In addition, as the TEM specimen thickness shrinks, the thickness of surface amorphization produced must also be reduced. Gallium focused ion beam systems can produce hundreds of Ångstroms of amorphised surface silicon, an amount which can consume an entire thin specimen. This limitation to FIB milling requires a method of removal of amorphised material that leaves no artifact in the remaining material.
Microstructural Changes in W-Polycide Gates Capped with A Thin Polysilicon Layer
Authors: Kima Y. O. , Bevk J. , Furtsch M. , Georgiou G. E. , Mansfield W. , Masaitis R. , Opila R. , Silverman P. J.
Published: April 2011

We find that sheet resistance of tungsten polycide can be reduced up to 40% by depositing thin polysilicon layers on the top of the films. Transmission electron microscopy shows no significant differences in the crystal structure, grain size, or dislocation density inside the films by adding a polysilicon cap, but it clearly shows roughening of the top interface. Auger depth profiling shows substantial reduction of the Si/W ratio in the capped films. Both results imply that the excess Si segregates to both polysilicon interfaces, effectively lowering the Si/W ratio and resulting in a low sheet resistance.
Electron Microscopy on GaAs Based Devices
Authors: Etienne P. , Magis M. , Cassette S. , Delage S. , Galtier P.
Published: April 2011

We present a methodology suitable for SEM and TEM analysis on Heterojunction Bipolar Transistors (HBT) developed for microwave applications. The Focused Ion Beam (FIB) technique has been investigated for SEM observations. It is found that best results are obtained when the active areas are micromachined from the back side and at a low incidence angle. The help of backscattered electron imaging for metallurgical assessment is emphasized on that kind of devices. A combination of both precision dimpling and FIB micromachining is found to be a good solution for the achievement of TEM slabs with an acceptable thickness. Finally we present the design of a dual beam system which uses Ar+ or Ga+ ions for highest TEM slab quality built into a SEM for an accurate localization and monitoring of the milling process. The respective advantages and limitations of this method are stressed in term of precision of localization of device features, surface roughness, contamination and slab thickness. The possibility to apply this technique on 0.1 µm silicon based technology will be discussed.
Microstructure Analysis of Barium Strontium Titanate Thin Film
Authors: Chen Wei , Hooker Joe , Monarch Kathy , Fejes Peter , Chu Peir
Published: April 2011

Microstructures of Barium Strontium Titanate (Ba, Sr)TiO3 [BST] thin film play an important role in determining the electrical properties of BST. In particular, it is found that the grain size distribution as a function of deposition conditions correlates with the dielectric constant of BST film. Traditionally, Transmission Electron Microscopy (TEM) provides an accurate method for determining microstructures such as interface structure between BST and electrodes and BST grain size distribution. However, TEM analysis relies heavily upon successful sample preparation, and film adhesion for BST proves to be a difficult problem to overcome for successful sample preparation. With the state of the art Scanning Electron Microscope (SEM) and Atomic Force Microscopy (AFM), useful information can be obtained for BST and electrode microstructures requiring little or no sample preparation. A good correlation among TEM, SEM and AFM techniques is achieved which allows useful information of BST grain size distribution to he obtained via SEM and AFM analyses. Power spectral density (PSD) analysis of contrast enhanced AFM images proves to be an efficient method for estimating BST grain size distribution.
Reduction of the Damage Induced in an Fib-Fabricated X-Tem Specimen
Authors: Kato N. I. , Tsujimoto K. , Miura N.
Published: April 2011

In focused ion beam (FIB) fabrication of cross-sectional transmission electron microscopy (X-TEM) specimens, highly accelerated ion beams sometimes cause serious damage. The damage can be induced in both the specimen surface and in the side walls. We used X-TEM observations to investigate the side-wall damage induced by FIB fabrication in crystalline silicon. The damaged layer was found to be about 20 nm thick in the case of 30-keV FIB etching. We tried to reduce the damage by several methods, such as gas-assisted etching (GAE) with iodine, broad argon ion milling and wet etching. The damaged layer was 19 nm for GAE and 12 nm for argon ion milling with a beam current of 70 mA and the tilt angle between the beam and the specimen of 15 degrees. Wet etching using a mixture of nitric and hydrofluoric acid removes most of the damaged layer.
Evaluation of Single Semiconductor Defects Using Multiple Microanalysis Techniques
Authors: Kinney P. D. , Uritsky Y. , Principae E. L. , Savoy R. , Mowat I. , McCaig L.
Published: April 2011

New analytical techniques are being employed to meet the stringent requirements for controlling defects in semiconductor manufacturing. While SEM/EDX continues to be an effective tool for root-cause analysis of particles and defects on the wafer surface, increasingly it is necessary to employ multiple techniques in analysis of a single defect to obtain sufficient information to resolve the problem. Until recently, this approach was impractical because the defects were too difficult to locate in standard analytical tools, especially on unpatterned wafers. But with the newly developed Mark-Assisted Defect Analysis (MADA) technique, the positioning problem has been eliminated, and it is a simple matter to employ multiple techniques on the same defect. In this paper we present results for defects analyzed by SEM/EDX, TOFSIMS, μ-ESCA, and AUGER, highlighting how these techniques compliment each other. Particular emphasis is given to the issue of the analytical technique changing the sample chemistry and influencing the results of subsequent analysis techniques.
Crystallographic Analysis of Cvd Films by Using X-Ray Polychromatic Radiation
Authors: Lavelle B. , Brissonneau L. , Baggot E. , Vahlas C.
Published: April 2011

The Energy Dispersive X-ray Diffiractometry (EDXD) technique was tested for in-situ crystallographic characterization of nickel films processed by chemical vapor deposition (CVD). The diffracted beam at low Bragg angle was analyzed in energy by a solid state detector. A nickel reference sample was used to face the problems of EDXD background signal and uncertainty of sample location. The relative accuracy on lattice parameters measurements is 1.5.10−3, to be compared to 0.5.10−3 for classical (monochromatic) X-Ray diffraction. Texture measurements yields results in agreement with those obtained from recent texture goniometer. Finally, an estimation of the thickness was obtained from the intensity of nickel fluorescence peak. In view of the obtained results, EDXD appears to be a promising technique for in-situ studies. Although less powerful compared to the synchrotron facility, it is more flexible and can be applied at lower cost.
Interfacial Effects in Multilayers
Authors: Barbee Troy W.
Published: April 2011

Interfacial structure and the atomic interactions between atoms at interfaces in multilayers or nano-laminates have significant impact on the physical properties of these materials. A technique for the experimental evaluation of interfacial structure and interfacial structure effects is presented and compared to experiment. In this paper the impact of interfacial structure on the performance of x-ray, soft x-ray and extreme ultra-violet multilayer optic structures is emphasized. The paper is concluded with summary of these results and an assessment of their implications relative to multilayer development and the study of buried interfaces in solids in general.
X-Ray Fluorescence Microtomography on a SiC Nuclear Fuel Shell
Authors: Naghedolfeizi; M. , Chung J.-S. , Ice G. E. , Yun W. B. , Cai Z. , Lai B.
Published: April 2011

TRISO fuel particles contain a small kernel of nuclear fuel encapsulated by alternating layers of C and a barrier layer of SiC. The TRISO fuel particle is used in an advanced nuclear fuel where the SiC shell provides the primary barrier for radioactive elements in the kernel. The performance of this barrier is key to containment. We have used x-ray fluorescence microtomography to measure the trace element distribution in a SiC shell. Prior to our measurements the nuclear fuel and C layers were leached from the particle. The shell was then encapsulated by kapton tape to simplify handling. The shell was mounted on a glass fiber and measurements were made with an ∼1 x3 ωm2 x-ray probe on beamline 2-ID at the APS. The distribution of trace elements in the SIC shell was reconstructed after correcting the data for artifacts arising from absorption and scattering off the kapton tape. The observed trace elements are distributed in small <1ωm regions through the SiC shell. The trace elements can be attributed to radiation enhanced diffusion of elements in the kernel or to trace elements introduced during fabrication. X-ray fluorescence microtomography is an ideal tool for this work because it is a penetrating nondestructive probe sensitive to trace elements in a low Z matrix and because it provides a picture of the elemental distribution in the shell.
Characterization of Silver Binding in Cryptomelane by X-ray Absorption Spectroscopy
Authors: Ravikumar R. , Fuerstenau D. W. , Waychunas G. A.
Published: April 2011

Using silver K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy, two different samples of silver-containing manganese oxide were analyzed in the fluorescence mode. For the first sample, silver ions from solution were sorbed onto one synthetic manganese oxide phase, namely cryptomelane (KxMn8O16, where l<x<2). The second sample was a silvermanganese oxide from Colorado. From the EXAFS analysis, silver was found to occupy two different sites in the synthetic sample. The natural samples from Colorado also exhibited a very similar coordination distances as the synthetic samples. In the low temperature spectrum of the synthetic sample at 10 K, the Ag-O peak was found to be missing and the amplitude of the Ag- Ag peak was approximately three times larger than the corresponding room temperature sample.
Contrast Mechanism in Superscrew Dislocation Images on Synchrotron Back-Reflection Topographs
Authors: Huang X. R. , Dudley M. , Vetter W. M. , Huang W. , Wang S. , Carter C. H.
Published: April 2011

The topographic contrast of superscrew dislocations in 6H-SiC crystals has been studied by synchrotron white-beam x-ray topography in the Bragg reflection geometry. The diffraction images of these dislocations are simulated using a ray-tracing method. Systematical simulations, which coincide with the dislocation images taken by back-and grazing-reflection topography, clearly reveal the kinematic diffraction mechanisms of the superscrew dislocation, and illustrate that synchrotron reflection topography is capable of providing accurate descriptions of the strain fields, the Burgers vector magnitudes, and the senses of these dislocations. In addition, our experiments and simulations demonstrate straightforwardly the relation between the topographic contrast and the lattice distortions, and therefore the general mechanisms underlying contrast formation of defect images in synchrotron reflection topographs are provided.
Strain and Shape in Self-Assembled Quantum Dots Studied by X-Ray Grazing Incidence Diffraction
Authors: Kegel I. , Metzger T. H. , Peisl J. , Fratzl P. , Lorke A. , Kotthaus J. P. , Garcia J. M. , Petroff P. M.
Published: April 2011

We have developed a method to determine the relationship between strain and lateral size of coherent self-organized quantum dots. In our approach, X-ray grazing incidence diffraction is used to collect information on strain and shape effects in the vicinity of a prominent surface reflection. We demonstrate that for highly strained nano-scale islands it is possible to separate strain-induced and form factor-induced scattering without comparing different reflections. Experimental data from InAs on GaAs(100) quantum dots is discussed with respect to this model. Reciprocal space mapping around the (220) surface reflection shows a linear relationship between relaxation from the substrate lattice parameter and the outer perimeter of the dot. In addition, the functional form of the gradient of relaxation is found to be nonmonotonous and rapidly increasing towards the tip of the dot.
Structure and Magnetotransport Properties of La2/3Ca1/3MnO3 Thin Films Prepared by Pulsed Laser Deposition
Authors: Lebedev O.I. , van Tendeloo G. , Amelinckx S. , Leibold B. , Habermeier H.-U. , Phillipp F.
Published: April 2011

La1-xCaxMnO3-δ (LCMO) thin films are grown by pulsed laser deposition on a (100) SrTiO3 substrate at temperatures between 530°C and 890°C. The magnetotransport properties show a high negative magnetoresistance and a shift of the maximum of the R(T) curve as function of temperature. The Curie temperature changes with deposition temperature and film quality in the range of 100-220K. The film quality is characterised by X-ray diffraction and transmission electron microscopy (TEM); film and target compositions were verified by atomic emission spectroscopy. The local structure of the film depends on the growth conditions and substrate temperature. TEM reveals a slight distortion of the film leading to a breakdown of the symmetry from orthorhombic to monoclinic. At the highest growth temperatures, a well defined interface is observed within the LCMO film, parallel to the substrate surface; this interface divides the film into two lamellae with a different microstructure. The lamella close to the substrate is perfectly coherent with the substrate, suggesting that it is strained as a result of the lattice parameter mismatch; the upper lamella shows a typical domain structure with unusual translation interfaces characterised by a displacement vector of the type 1/2 [010]m and 1/2[001]m when referred to the monoclinic lattice.
Pulsed Laser Deposition of High Coercivity Barium Ferrite Films
Authors: Song W. D. , Lu Y.F. , Wang J.P. , Zeng X.T. , Lu L. , Low T.S.
Published: April 2011

Barium ferrite films with high coercivity (>2000 Oe) have been prepared on single crystal sapphire substrates by laser in-situ deposition. The structures of these films were characterized by x-ray diffractometry. X-ray diffraction pattern shows a preferential c-axis orientation normal to the film plane at a high deposition temperature and a random orientation at a lower deposition temperature. The magnetic properties of the films were analysed by a Vibrating Sample Magnetometer (VSM) and surface morphology was analysed by an Atomic Force Microscope (AFM).
Deposition and Characterization of Carbon Nitride Films by Laser Processed Methods
Authors: Kumar Ashok , Alexandrescu R. , George Michael A.
Published: April 2011

Laser assisted methods such as laser physical vapor deposition (LPVD) and laser induced chemical vapor deposition (LCVD) have been utilized to grow carbon nitride (CNx) films on various substrates. It has been shown that the both techniques produce good quality thin films of CNx. In LPVD, a laser beam (λ= 248 nm) has been used to ablate the pyrolytic graphite target in nitrogen atmosphere, where as CO2 laser was to irradiate carbon-nitrogen containing mixtures such as C2H2/N2O/NH3 in LCVD method. A comparative analysis will be presented in terms of structural properties of CNx films prepared by both techniques.
Microscopic Diffusion Mechanism of Iron in FeAl Revisited by New Methods
Authors: Vogl G. , Sepiol B. , Czihak C. , Rüffer R. , Weinkamer R. , Fratzl P. , Fähnle M. , Meyer B.
Published: April 2011

The elementary diffusion jump of Fe atoms in the ordered intermetallic alloy FeAl is studied in a coordinated effort of atomistic experimental techniques, Monte Carlo simulation and abinitio electron theory. The experiment demands that the elementary diffusion jump is a jump into an antistructure site on the Al sublattice which is occupied for a much shorter time than the sites on the Fe sublattice. The diffusion path can be followed by Monte Carlo simulations which can perfectly explain the experiments. Since ab-initio theory yields a very low concentration of Al vacancies it is suggested that correlated jumps of two atoms prevent the creation of a fully developed Al vacancy.
Kinetics and Mechanisms of Intermetallic Growth by Surface Interdiffusion
Authors: Kaganovskii Yu.S. , Paritskaya L.N. , Bogdanov V.V.
Published: April 2011

Kinetics of growth and lateral spreading of an intermetallic layer along a free surface during surface interdiffusion in binary systems have been studied both theoretically and experimentally. By comparison of experimental data on intermetallic growth kinetics with the proposed theory, the surface diffusion constants have been calculated for intermetallics Cd21Ni5 and Cu5Zn8, and mechanisms of surface diffusion have been discussed.
Determination of Ionic Diffusion Mechanisms in Solids
Authors: Corish John
Published: April 2011

The experimental and atomistic simulation methodologies by which microscopic diffusion mechanisms can be determined in solids are described. Measurement of the Haven Ratio requires evaluation of the diffusion coefficient and of the ionic conductivity for the species in pure and doped specimens and is, in practice, limited to simpler materials. Atomistic simulations using lattice statics, molecular dynamics and Monte Carlo techniques can yield very detailed information on the pathways followed by migrating ions and are being utilised more extensively for this purpose. Examples of such experimental and simulation studies are discussed.
Oxygen Ion and Proton Transport in Mixed Metal Oxides
Authors: Islam M. Saiful
Published: April 2011

Computational techniques are now well established tools in the study of structural properties and transport mechanisms in solid state ionic materials. This paper will highlight recent developments of such methods, with a strong emphasis on their use in the elucidation of ion diffusion mechanisms or pathways at the atomic level. In particular, contemporary work will be illustrated by accounts of calculations on oxygen ion and proton conduction in LaMO3 perovskite-type oxides, which find use in various electrochemical applications. We have used atomistic simulation, molecular dynamics (MD) and ab initio techniques to provide fresh insight as to their defect and ion diffusion properties.
Mobility of Self-Interstitials in FCC and BCC Metals
Authors: Osetsky Yu.N. , Serra A. , Priego V. , Gao F. , Bacon D.J.
Published: April 2011

Diffusion of self-interstitial atoms (SIAs) has been studied in bcc-Fe and fcc-Cu using molecular dynamics and interatomic potentials of different types. The Fe potentials describe SIA configurations of different stability. The temperature dependence of the SIA diffusion mechanisms is qualitatively similar for both potentials. At high temperature the diffusion is three-dimensional via the <110> dumbbell mechanism. The contribution of one-dimensional mechanism via the <111> crowdion increases when temperature decreases. At low temperature (<300K) the diffusion mechanism depends on the stable configuration of the SIA.

In fcc-Cu all the potentials reproduce the same stable configuration, namely the <100> dumbbell. The migration mechanism is mainly a three-dimensional random walk via this dumbbell with small contributions from the <110> crowdion at high temperature and a two-dimensional caging mechanism at low temperature.
Surface Interaction of Inflammatory Species with Titanium and Titanium Oxide
Authors: Suzuki R. , Hirata G. , McKittrick J. , Frangos J.A.
Published: April 2011

Titanium has been successfully used for decades in dental and orthopedic implants, but the mechanism for this metal's biocompatible properties have not been determined. Our hypothesis is that this biocompatibility involves interaction between the surface layer of titanium dioxide on the metal implant and reactive oxygen mediators of the inflammatory response. The affect of different titanium surface oxide layers on the reactive oxygen mediators produced during the inflammatory response has never been examined. Peroxynitrite is a highly reactive and unstable compound produced in vivo by the reaction of nitric oxide with superoxide. We investigated if titanium oxides affect the stability of peroxynitrite by promoting its breakdown. Peroxynitrite levels can be measured by its absorbance at 302 nm. At pH= 13.2, we found a 100% increase in the rate of degradation of peroxynitrite in the presence of titanium particles. Peroxynitrite is capable of nitrating 4-hydroxyphenolacetic acid (4-HPA). The nitrated form of 4-HPA can be measured by its absorbance at 432nm. 3-morpholinosydnonimine (SIN-1), a nitric oxide donor, has been shown to produce superoxide during its breakdown resulting in the formation of peroxynitrite. At physiological pH (7.4), a solution of 0.5mM 4-HPA was exposed to 5mM SIN- 1 on passivated titanium surfaces. There was a decrease of 58% nitrated 4-HPA in the solution exposed to passivated titanium compared to controls. Unpassivated titanium surfaces resulted in only a 10% decrease of nitrated 4-HPA while titanium treated with hydrogen peroxide resulted in a 70% decrease in nitrated 4-HPA concentrations compared to controls. Zirconium and palladium were also tested. These experiments suggest that titanium is capable of enhancing the breakdown of the inflammatory compound peroxynitrite which may account for the metal's biocompatible properties.
Crosslinking Characteristics of an Injectable Poly(Propylene Fumarate)/ β-Tricalcium Phosphate Paste and Mechanical Properties of the Crosslinked Composite for Use as a Biodegradable Bone Cement
Authors: Peter S.J. , Kim P. , Yasko A.W. , Yaszemski M.J. , Mikos A.G.
Published: April 2011

We investigated the crosslinking characteristics of an injectable composite paste of poly(propylene fumarate) (PPF), N-vinyl pyrrolidinone (N-VP), benzoyl peroxide (BP), sodium chloride (NaCl), and β-tricalcium phosphate (β-TCP). We examined the effects of PPF molecular weight, N-VP/PPF ratio, BP/PPF ratio, and NaCl weight percent on the crosslinking temperature, heat release upon crosslinking, gel point, and the composite compressive strength and modulus. The maximum crosslinking temperature did not vary widely between formulations, with the absolute values falling between 38 and 48 °C, and was much lower than that of 94°C for poly(methyl methacrylate) bone cement controls tested under the same conditions. The total heat released upon crosslinking was decreased by an increase in PPF molecular weight and a decrease in N-VP/PPF ratio. The gel point was effected strongly by the PPF molecular weight, with a decrease in PPF molecular weight leading to a more rapid gel point. An increase in initiator concentration had the same effect to a lesser degree. The time frame for curing was varied from 1 -121 minutes, allowing the composite to be tailored to specific applications. The compressive strength and compressive modulus values increased with decreasing N-VP/PPF, increasing NaCl content, and increasing BP/PPF ratio. For all formulations, the compressive strength values fell between 1 and 12 MPa, and the compressive modulus values fell between 23 and 265 MPa. These data suggest that injectable PPF/β-TCP pastes can be prepared with handling characteristics appropriate for clinical orthopaedic applications and that the mechanical properties of the cured composites are suitable for trabecular bone replacement.
Tailoring of the Nitrogen Profile in Thin Gate Oxides Using Substrate Nitridation by Nitric Oxide
Authors: Halimaoui A. , Henrisey E. , Hernandez C. , Martins J. , Paoli M. , Regache M. , Vallier L. , Bensahel D. , Blanchard B. , Rouchon D. , Martin F.
Published: April 2011

Direct nitridation of the silicon substrate using gaseous NO at 550–700°C, 10 mbar is studied using physical (SIMS, TEM, XPS) and electrical characterisations. The nitrogen profile can be tailored for the fabrication of thin nitrided oxides as in the case of implanted nitrogen. Degradation of the I(V) characteristics has been evidenced when the nitrogen amount increases.
Crystalline Structure Around the Single Vacancy in Silicon: Formation Volume and Stress Effects
Authors: Antonellip A. , Kaxiras Efthimios , Chadi D. J.
Published: April 2011

The crystalline structure surrounding a single neutral vacancy in silicon is investigated through extensive first-principles total-energy calculations. The results indicate the existence of two distinct distortions of the lattice around the vacancy with essentially the same formation energies at zero pressure, but, however, with different formation volumes. The effect of hydrostatic and biaxial stresses on the relative concentration of each distortion is discussed, suggesting experimental ways to investigate the crystalline structure around the single vacancy and its role as a mediator of atomic diffusion in silicon.
New Tight-Binding Method for Simulation of Defect Configurations, Creation and Diffusion Mechanisms in Solids: Application to Silicon
Authors: Khakimov Zokirkhon M.
Published: April 2011

This paper presents the self-consistent tight-binding method of new generation which, unlike other tight-binding methods, allows one to calculate structural energies of multiatomic systems (molecules, clusters, defects in solids) and their spectroscopic energies in the framework of the same computational scheme and with comparable accuracy. Reliability of the method is illustrated considering defect state problems in crystalline and amorphous silicon (electronenhanced- atomic diffusion, metastable defect creation, defects with effective-negative correlation energies, etc.) and comparing obtained results with ab initio calculations and experimental data.
Electrical Active Defects in the Band-Gap Induced by Ge-Preamorphization of Si-Substrates
Authors: Boussaid F. , Olivie F. , Benzohra M. , Alquier D. , Claverie A. , Martinez A.
Published: April 2011

Ultra-shallow p+ -n junctions have been obtained from Ge+ -preamorphized and crystalline <100> silicon substrates. B+ and BF2+ dopants have been used. Boron was implanted at low energy 3 keV / 1015 cm−2 while an equivalent energy of 15 keV / 1015 cm−2 was chosen for BF2+. Rapid Thermal Annealing (RTA) for 15 s at 950 °C was then used for dopant electrical activation and implantation damage removal. Electrically active defects in these samples were characterized using Deep Level Transient Spectroscopy (DLTS) and isothermal transient capacitance (ΔC(t, T)). Two electron traps were detected in the upper half of the band gap at Ec – 0.20 eV and Ec – 0.45 eV, respectively. These traps are shown to be induced by the Ge+ preamorphization stage. Dopant implantation along with RTA result in the formation of a depth distributed energy continuum for B+ and BF2+ implants. Each continuum has been ascribed to annealing residual defects. Low energy B+ implantation is seen to induce twice as many defects as BF2+, implantation. From isothermal transient capacitance (ΔC(t, T)), reliable damage concentration profiles have been obtained, revealing that preamorphization induces not only defects in the regrown silicon layer but also a relatively high concentration of electrically active defects up to 3.5 μm into the bulk.
Erbium Doped Si/Sige Waveguide Diodes: Optical And Electrical Characterization
Authors: Neufeld E. , Luigart A. , Sticht A. , Brunner K. , Abstreiter G.
Published: April 2011

We have fabricated erbium- and oxygen-doped Si/SiGe waveguide diodes showing the characteristic 1.54 µm electroluminescence (EL) from incorporated Er+3, ions. All samples were grown by molecular beam epitaxy (MBE). The EL from the polished end facet of the waveguide was measured with a confocal microscope revealing a spatially narrow emission. Additional annealing was not necessary to improve the luminescence characteristics. Only a weak temperature dependence is found for the EL intensity between 4K and room temperature.
Measurements of Confined Energy Levels and Coulomb Charging Effect in Self-Assembled Ge Quantum Dots by Admittance Spectroscopy
Authors: Zhang S. K. , Jiang Z. M. , Zhu H. J. , Lu F.
Published: April 2011

We perform measurements of the discrete quantum energy levels and Coulomb charging of self-assembled Ge quantum dots imbedded in Si barriers by using the admittance spectroscopy technique that was originally developed to measure the defect levels of bulk materials and the band offsets of heterojunctions. By varying the bias voltage, the population of carriers in the dot changes and the Coulomb charging effect could be clearly seen from the step-like change of the activation energy for hole emission in the admittance spectra. Up to five holes charged in a Ge dot with a lateral dimension of 13nm is observed. The energy levels of ground state and first excited state are determined. The advantages of this method are the relatively high measuring temperature, large signal to noise ratio, and its simple and straightforward use and interpretation. The requirement on the uniformity of the dot size distribution of the sample is quite tolerant.
Real-Time Observation of Ti Silicide Epitaxial Islands Growth with the Photoelectron Emission Microscopy
Authors: Yang W. , Ade H. , Nemanich R. J.
Published: April 2011

The formation of nanoscale Ti silicide islands was observed by Photo-electron emission microscopy (PEEM). The islands were prepared by deposition of an ultrathin Ti (3–12ML) on Si(001) at room temperature and at an elevated temperature of 950°C. The island formation was initiated by in situ annealing to 1150° C. It was observed that initially Ti silicide islands form while longer annealing indicates some islands move and coalesce with other islands. Most of the islands are similar in size and have relatively uniform separation. Also, it was shown that for continued Ti deposition at a temperature of 950°C, the density of islands did not increase. However, islands grew together when their perimeter lines touch each other. The results are described in terms of island growth processes of coalescence and ripening.
Low-Energy Plasma Enhanced Chemical Vapor Deposition
Authors: Rosenblad Carsten , Graf Thomas , Dommann Alex , Von känel Hans
Published: April 2011

We discuss a new method for plasma enhanced chemical vapor deposition, applied to the epitaxial growth of Si and of Si-Ge heterostructures. Growth rates up to 5 nm/s become possible at substrate temperatures below 600°C, by utilizing very intense but low energy plasmas to crack the reactive gases, SiH4 and GeH4, and to speed up the surface kinetics. The method is applied to the synthesis of step-graded Si-Ge buffer layers, exhibiting the well known cross-hatched surface morphology.
Characteristics of Surface-Channel Strained Si1-yCyn-MOSFETS
Authors: Rim K. , Mitchell T. O. , Hoyt J. L. , Fountain G. , Gibbons J. F.
Published: April 2011

The first demonstration of n-MOSFETs fabricated using strained Si1-yCy surface channels is reported. Tensile-strained Si1-yCy layers with substitutional carbon contents up to 0.8 atomic percent were epitaxially grown on <100> Si substrates by rapid thermal chemical vapor deposition, using silane and methylsilane as the silicon and carbon precursors. n-MOSFETS were fabricated using standard MOS processing with reduced thermal exposure to minimize the possibility of strain relaxation. A remote plasma CVD oxide was employed to form the gate oxide. The Si1-yCy devices exhibit electrical characteristics that are typical for Si n-MOSFETs, with good turn-on and subthreshold characteristics. MOS capacitance-voltage analysis demonstrates comparable oxide interface qualities for the Si1-yCy and Si control devices. No carbon-related leakage current is observed in source and drain diode junctions. Characterization of the MOSFET electron inversion layer mobility at room temperature shows comparable mobilities, within the sensitivity of the measurement, for the Si1-yCy and Si control devices. This is in contrast to the mobility enhancement observed in n-MOSFETs fabricated using tensile- strained Si grown on relaxed Si1-xGex layers. At low temperatures, the inversion layer mobility of Si1-yCy devices is lower than that of the Si controls, and appears to be affected by Coulomb and possibly random alloy scattering.
Quantitative Experimental Determination of The Effect of Dislocation - Dislocation Interactions on Strain Relaxation in Lattice Mismatched Heterostructures
Authors: Stach E. A. , Hull R. , Tromp R. M. , ROSS F. M. , Reuter M. C. , Bean J. C.
Published: April 2011

We present real time observations of the interaction of dislocations in heteroepitaxial strained layers using a specially modified ultrahigh vacuum transmission electron microscope equipped with in-situ deposition capabilities. These observations have led to delineation of the regime of epilayer thickness and composition where dislocation interactions result in blocking of the propagating threading segment. It is found that both the blocking probability as well as the magnitude of the dislocation interaction force are strongly dependent on the Burgers vectors of the dislocations involved, with the greatest effects observed when the Burgers vectors of the two dislocations are parallel with respect to each other. Frame-by-frame analysis of the motion of the dislocation threading segment during interaction is used to extract the magnitude of the interaction stresses as a function of both the level of heteroepitaxial strain and the dislocation geometry. Finally, by continuing growth following observations of blocking during annealing, we find that blocked dislocations are likely to remain in that configuration until substantial additional heteroepitaxial stresses are incorporated into the layer. These results have direct relevance to the successful integration of strained layer heterostructures into electronic device applications. This is because blocked threading segments result in the introduction of undesired band gap states, enhance impurity diffusion, modify surface morphology and act to limit the dislocation density reductions achievable in graded buffer structures.
Thermal Reliability of Pt/Ti/Pt/Au Schottky Contact on InP with a GalnP Schottky Barrier Enhancement Layer
Authors: Kuo H. C. , Lin C. H. , Moser B. G. , Hsia H. , Tang Z. , Chen H. , Feng M. , Stillman G. E.
Published: April 2011

We present the studies of the thermal stability of various metal including Au, Ti, Pt, Pd and Pt/Ti/Pt/Au Schottky contacts on strained Ga0.2In0.8P/InP semiconductors. Auger electron spectroscopy (AES) analysis and cross-sectional TEM of the thermally annealed Schottky diode were performed to investigate the failure mechanism. For Pt/Ti/Pt/Au schottky contacts on strained GalnP/InP, no significant change was found for samples annealed up to 350°C. However, a drastic degradation of the barrier height and the ideality factor was observed in samples annealed at 400°C, which may be caused by the interdiffusion and penetration of metals into the semiconductor. Finally InGaAs/InP doped channel heterojunction FET's (DC-HFET's) with a GaInP Schottky barrier enhancement layer (SBEL) were grown and fabricated. The 0.25 μm gate-length devices showed excellent DC and RF performance, with anfi of 117 GHz and an fmax of 168 GHz.
Fermi-Level Effect and Junction Carrier Concentration Effect on Boron Distribution in GexSil−x/Si Heterostructures
Authors: Chen CHang-Ho , Gösele Ulrich M. , Tan Teh Y.
Published: April 2011

Dopant segregation mechanism in general involves the chemical effect, the Fermi-level effect, and the effect of the junction carrier concentrations. Satisfactory fits of available B distribution profiles in GexSil−x/Si heterostructures have been obtained using such a model, but with the chemical effect not important. The Fermi-level effect determines the difference in the ionized B solubilities in GexSil−x and Si. The singly-positively charged crystal self-interstitials I+ governs the boron diffusion process. The junction carrier concentration affects the concentration of I+ and solubility of B in the region and hence controls B diffusion across the heterojunction.
A Mechanism for the Removal Of Dislocations in SOI Compliant Substrate Systems
Authors: Kukta R. V. , Freund L. B.
Published: April 2011

It is demonstrated that the time required for strain transference during the postgrowth anneal of a SOI compliant substrate system is much too long to explain the observed reduction in dislocation density in the resulting microstructure. A mechanism by which misfit dislocation segments are drawn out of the system through viscous dissipation in the bonding layer is proposed and demonstrated to be consistent with observation. The mechanism is mtodeled in the context of elastic dislocation theory and linear viscoelasticity.
Optical Absorption in ZnSe-GaAs Heterovalent Quantum Structures
Authors: Funato Mitsuru , Fujita Shizuo , Fujita Shigeo
Published: April 2011

ZnSe-GaAs(001) heterovalent quantum structures, multiple quantum wells (MQWs), were fabricated. Since the band offsets in this heterovalent heterostructure are controllable, different offsets can artificially be put at both sides of the GaAs wells, which may lead to modification of the electronic properties of the MQWs. This hypothesis was examined by the optical absorption measurement. Consequently, by changing the valence band offset at the GaAs-on-ZnSe interface from 0.6 to 1.1 eV, while keeping that at ZnSe-on- GaAs constant at 0.6 eV, the absorption edge energies of the MQWs shifted from 1.43 to 1.37 eV. This indicates the presence of an internal electric field and the capability of controlling the electronic properties of heterovalent MQWs with the completely same structural parameters. The numerical analyses of the Poisson and Schrddinger equations well explain the trend of this experimental result.
Finite Temperature Quasicontinuum Methods
Authors: Shenoy Vivek , Shenoy Vijay , Phillips Rob
Published: April 2011

In this paper we extend the quasi-continuum method to study equilibrium properties of defects at finite temperatures. We present a derivation of an effective energy function to perform Monte Carlo simulations in a mixed atomistic and continuum setting. It is shown that the free energy minimization technique can be easily incorporated into the quasi-continuum frame work, permitting a reduction of the full set of atomistic degrees of freedom even in the finite temperature setting. The validity of the proposed methods is demonstrated by computing the thermal expansion and the temperature dependence of the elastic moduli for Cu. We also employ the quasi-continuum free energy minimization method to study the finite temperarure structure of a dislocation core in Al.
Effect of Non-Glide Components of the Stress Tensor on Deformation Behavior of Bcc Transition Metals
Authors: Ito K. , Vitek V.
Published: April 2011

In this paper we demonstrate by atomic computer simulation that the non-Schmid slip behavior in bcc metals is a direct consequence of the non-planar core structure of 1/2<111> screw dislocations and their response to the applied stress tensor. The analysis has been carried out in detail for tantalum using the Finnis-Sinclair type central force many-body potentials. Two distinct non-Schmid effects have been discerned. The first is twinning-antitwinning slip asymmetry on {112} planes. This is an intrinsic property of the bcc structure and depends on the sense of the applied glide stress. The second non-Schmid effect is extrinsic and is controlled by the non-glide shear stresses perpendicular to the total Burgers vector on {110} planes into which the stress-free core of screw dislocations spread.
Noncrucial Role of the Defects in the Splitting for Hydrogen Implanted Silicon With High Boron Concentration
Authors: Popov V.P. , Stas V.F. , Antonova I.V.
Published: April 2011

The present work deals with the investigation of the electrical and structural properties of heavily boron-doped silicon irradiated by hydrogen. Blistering and splitting processes are enhanced with an increase in boron concentration in the crystal. The measured values of perpendicular strain are over 0.7% which corresponds to a gas overpressure of 0.5 GPa. Processes which lead to blistering and splitting is better described in the frame of a gas pressure model than a model of local stress caused by the defects.
Optical Properties of Laser-Modified Diamond Surfaces
Authors: Khomich A.V. , Polyakov V.I. , Pimenov S.M. , Kononenko V.V. , Konov V.I. , Gloor S. , Lüthy W. , Weber H.P.
Published: April 2011

Results are reported on laser-induced surface modification of 150-400 µm thick free-standing diamond films with excimer lasers under different irradiation regimes, including laser polishing at a grazing beam incidence or ablative etching of the films at the normal beam incidence. Properties of the laser-graphitized layer at the diamond surface were studied with optical spectroscopy techniques in the process of oxidative removal of the layer with increasing temperature of oxidation in ambient air. The optical properties and oxidation stability of the laser-modified surface layer were found to change through its thickness from the surface to the diamond interface, depending on the laser ablation regime.
Self-Compression and Diamond Nucleation In Irradiated Carbon Onions - A Theoretical Model
Authors: Zaiser M.
Published: April 2011

The nucleation of small diamond crystals during irradiation of spherical graphitic particles (’bucky onions’) is discussed. A mechanism for irradiation-induced self-compression of such ’onions’ is proposed. It is demonstrated that this may yield pressures which are sufficiently high for diamond formation. The theoretical results are in good agreement with experimental findings.
Behaviour of CS and I In Zirconia Based Fuel
Authors: Degueldre C. , Pouchon M. , Doebli M. , Ledergerber G.
Published: April 2011

A zirconia based ceramic is foreseen as an inert matrix fuel for burning excess plutonium in light water nuclear reactors. For reactor safety reasons the behaviour of volatile fission products such as cesium and iodine must be studied since a retention of fission products is favourable for licensing the studied inert matrix fuel. In this study, implantation of Cs and I was performed into polycrystalline (Zr0.85, Y0.15)O1.925 samples. The implantation depth was selected on the basis of the ability to observe by Rutherford backscattering spectroscopy (RBS) the behaviour of Cs and I after treatment. With a 1 MeV incident energy, the ions are implanted at a depth of 200 nm as predicted by TRIM. After implantations full quantification of I and Cs concentration profiles was performed by RBS. The implantation profiles are measured as a function of sample temperature during stepwise heating programs. It is interesting to observe retention of Cs and I at relatively high temperature (e.g. for 2 h, below 900 K for Cs and below 1400 K for I). This behaviour is likely to be due to the size and interactions of these species in the zirconia solid solution.
Ion Irradiation Effects for Two Pyrochlore Compositions: Gd2Ti2O7and Gd2Zr207
Authors: Wang S. X. , Wang L. M. , Ewing R. C. , Govindan Kutty K. V.
Published: April 2011

Pyrochlore is an important nuclear waste form phase for actinide immobilization. Two synthetic pyrochlores, Gd2Ti2O7and Gd2Zr2O7were irradiated at various temperatures (25 K to 1073 K) by different ion species (1.5 MeV Xe+, 1.0 MeV Kr+, and 0.6 MeV Ar+). The titanate pyrochlore amorphized at relatively low doses (0.5 ∼ 0.6 dpa). Temperature dependence of the amorphization dose for titanate pyrochlore was measured, and the critical temperatures for amorphization were 1300 K, 1100 K and 950 K by 1.5 MeV Xe+, 1.0 MeV Kr+and 0.6 MeV Ar+, respectively. The higher critical temperature for the heavier ion irradiation is consistent with an amorphization mechanism by which the heavier ion produces a larger cascade. The zirconate pyrochlore, Gd2Zr2O7, showed a strong amorphization “resistance”. Gd2Zr2O7did not become amorphous under 1.0 MeV Kr+and 1.5 MeV Xe+irradiation. After prolonged irradiation (up to 7 dpa) even at a temperature of 25 K, no amorphization was observed. The irradiated zirconate pyrochlore showed abundant dislocations as observed by TEM. The pyrochlore structure of Gd2Zr2O7transformed to the fluorite structure after irradiation. The diffraction patterns of irradiated Gd2Zr2O7showed the existence of short-range ordering of cations. The large difference between these two pyrochlores emphasizes the strong effect of chemical composition on radiation-induced amorphization.