bluuebunny/crossref_metadata_2025 huggingface dataset:
Nucleation and Growth of Sputter Deposited Zno:Al Thin Films on Soda-Lime Glass Substrates
Authors: Rieth L. W. , Holloway P. H. , Lambers E.
Published: April 2011

Degenerately doped thin films of zinc oxide are useful in a variety of applications, including front transparent contacts to Cu(In,Ga)Se2 thin film solar cells and flat panel displays. To gauge the influence of the interface on the performance of sputter deposited ZnO:AI transparent electrodes, the structure and electrical properties of the interfacial region has been investigated during nucleation and growth of the thin films. RF magnetron sputter deposited films with thicknesses ranging from ∼20 to 1580 Å were characterized using Atomic Force Microscopy (AFM), Auger Electron Spectroscopy (AES), Hall measurements, and four point probe. AES spectra of the films with thickness between ∼20 and 60 Å exhibited clear Si (1619eV) peaks suggesting the thin films were discontinuous islands on the substrate. AFM micrographs indicated a distribution of hillocks on the surface which agrees with AES results, and suggest a Volmer-Webber nucleation and growth mechanism. Hall measurements indicated that the films had electron carrier concentrations on the order of 1019 to 1020/cm−3, mobilities of <10cm2V.s, and resistivities on the order of 10−2 to10−3Ω-cm depending on the film thickness. The possible impact of these results on solar cell performance is discussed.
Exotic Doping for Zno Thin Films: Possibility of Monolithic Optical Integrated Circuit
Authors: Fujimura Norifumi , Shimura Tamaki , Wakano Toshifumi , Ashida Atsushi , Ito Taichiro
Published: April 2011

We propose the application of ZnO:X (X = Li, Mg, N, In, Al, Mn, Gd, Yb etc.) films for a monolithic Optical Integrated Circuit (OIC). Since ZnO exhibits excellent piezoelectric effect and has also electro-optic and nonlinear optic effects and the thin films are easily obtained, it has been studied as one of the important thin film wave guide materials especially for an acoustooptic device[1]. In terms of electro-optic and nonlinear optic effects, however, LiNbO3 or LiTaO3 is superior to ZnO. The most important issue of thin film waveguide using such ferroelectrics is optical losses at the film/substrate interface and the film surface, because the process window to control the surface morphology is very narrow due to their high deposition temperature. Since ZnO can be grown at extremely low temperature, the roughness at the surface and the interface is expected to be minimized. This is the absolute requirement especially for waveguide using a blue or ultraviolet laser. Recently, lasing at the wavelength of ultraviolet, ferroelectric and antiferromagnetic behaviors of ZnO doped with various exotic elements (exotic doping) have been reported. This paper discusses the OIC application of ZnO thin films doped with exotic elements.
Pulsed Laser Deposition of Superconductor/Ferromagnetic YBa2Cu3Oy/SrTiO3/La2/3Sr1/3MnO3 Heterostructures
Authors: Trtík V. , Sánchez F. , Ferrater C. , Varela M. , Fábrega L. , Rubi R. , Fontcuberta J.
Published: April 2011

YBa2Cu3Oy/SrTiO3/La2/3Sr1/3MnO3 heterostructures have been deposited on LaAlO3(001) and SrTiO3(001) substrates by pulsed laser deposition. First, the influence of deposition conditions on crystallinity and morphology of single LSMO films was examined. Results were used for preparation of heterostructures in tri-layer and cross-strip geometry. Cross-strip geometry was defined by direct shadow mask patterning. Different characterization techniques have been used to determine and correlate the heterostructure properties. A complete analysis of the crystal structure has been carried out with a four-circle difractometer. Morphology has been studied by scanning electron microscopy and atomic force microscopy in order to determine surface roughness and droplet density. Basic electrical properties of films have been determined.
Influence of Post-Deposition Annealing on Lattice Strain, Electrical Transport and Magnetic Properties in Epitaxial La0.8Ca0.2MnO3 CMR Films
Authors: Nath T. K. , Rao R. A. , Lavric D. , Eom C. B.
Published: April 2011

The effect of annealing on 3-dimensional lattice strain, crystallographic domain structure, magnetic and electrical properties of both 250 Å and 4000 Å thick epitaxial La0.8Ca0.2MnO3 (LCMO(x=0.2)) thin films grown on (001) LaAlO3 substrates have been studied. While short annealing time (∼2hrs. at 950 °C in oxygen of 1 atm. pressure) leads to anomalous increase of the peak temperature (Tp) and Curie temperature (Tc) above room temperature and that of the bulk material, longer annealing time (∼10 hrs.) restores the Tp and Tc to almost the same values as that of the as-grown films. Furthermore, as the annealing time is increased, the lattice strain relaxes with film's lattice parameter approaching the bulk value. In-plane and out-of-plane lattice parameters and strain states of the as-grown and annealed films were measured directly using normal and grazing incidence x-ray diffraction. A clear correlation is observed between Tp and perovskite unit cell volume for both the films. Tp is found to increase with the decrease of perovskite unit cell volume. This is attributed to the enhancement of overlap between Mn d orbitals and oxygen p orbitals leading to increased bandwidth and conductivity. Crystalline quality of the films as determined by the full width at half maximum (FWHM) of the x-ray rocking curves, improves with the annealing time. This work highlights the importance of controlling the 3-dimensional lattice strain for optimizing the properties of CMR films.
Investigating the Relationship Between Atomic Structure and Carrier Depletion at [001] tilt Grain Boundaries in Ybco
Authors: Browning N. D. , Buban J. P.
Published: April 2011

Recent theoretical analyses [1] have suggested that the origin of the reduced Jc at grain boundaries in high-Tc superconductors may be band bending, which results in the depletion of mobile charge carriers at the boundaries. For this to occur in these p-type superconductors there must, by definition, be a high density of localized donor states in the boundary plane. Here we report a “structural unit” analysis of [0011 tilt grain boundaries in YBa2Cu 3O7-δ (YBCO) that indicates there may be a simple structural origin for such localized donor states.
Response of Semiconductors and Fullerenes to Ultrashort and Ultra-Intense Laser Pulses
Authors: Dumitrica Traian , Torralva Ben , Allen Roland E.
Published: April 2011

We report new theoretical studies of the electronic and structural response of materials to fast intense laser pulses, with durations ∼ 10–100 feintoseconds and intensities up to ∼10 terawatts/cm2. The results provide still stronger evidence that GaAs undergoes a true nonthermal phase transition as the intensity is varied at constant pulse duration. For C60, there are also different regimes of behavior as a function of pulse intensity. At low intensity, various optically-active modes are observed. At high intensity, the breathing moode is by far the most dominant. At still higher intensities, there is photofragmentation, with the evolution of dinmers and other products. These results were all obtained in simulation-. using tight-binding electron-ion dyanamics (TED).
Predicting Nonlinear Optical Properties of Delocalized Charge States in Polyenylic Chromophores and Dendrimers
Authors: Dirk C. , Spangler C. , Madrigal L. , Elandaloussi E. H.
Published: April 2011

Over the past several years there has been continuing interest in the design of highly conjugated monomers, oligomers and polymers for a variety of photonics applications dependent on a nonlinear response to intense laser radiation. Materials design criteria for these various applications depend on accurate structure-property relationships, and while these relationships can best be determined experimentally, computational approaches that can accurately predict trends in series are extremely useful in establishing target molecules having the desired photonic properties. We have recently reviewed the relationship between incorporation of polaronic or bipolaronic charge states in oligomeric or polymeric conjugation sequences' and enhanced third-order optical nonlinearity, particularly for finite-length polyenes. In this presentation we will focus on how these charge states can be stabilized by electron-donating substituents in dithienylpolyenes, and in model dendrimers based on bis(diphenylamino)stilbene repeat units, and illustrate why these criteria are important for the design of new optical limiting chromophores.
Theoretical Investigation of the Second and Third Order Nonlinear Optical Properties of Some Fused Heterocyclic Aromatic Compounds
Authors: Bader Mamoun M.
Published: April 2011

We report herein the results of coupled perturbed Hartree-Fock (CPHF) ab initio extended basis set calculations on the geometric structures, dipole moments, static first-order (α), second-order (β), and third-order polarizabilities (λ) of a series of fused heterocyclic aromatic compounds based on quinoline. The effects of the presence/absence of the heteroatom as well as the introduction of other substituents at various positions in the ring system on these molecular properties are described. The effect of the presence of N-oxide is also examined. Suggestions for the design of heterocyclic systems with enhanced polarizabilities are made.
Controlled Phase Formation by Using a Diffusion Barrier - The Fe-Si REACTION
Authors: Theron C.C. , Falepin A. , Degroote S. , Dekoster J. , Vantomme A. , Langouche G. , De Waal H.S. , Pretorius R.
Published: April 2011

By analogy to reactive deposition epitaxy and titanium interlayer mediated epitaxy experiments, an attempt has been made to constrain the supply of reactants to the reaction interface in the solid phase reaction between Fe and Si. The goal being to change the normal phase formation sequence by using a suitable diffusion barrier, so that β-FeSi2 forms directly. Both Fe-V and Fe-Zr diffusion barriers were used to constrain the supply of the two reactants during Fe-silicide formation. Measurements with these barriers, show first phase formation of β-FeSi2, but direct formation of 3-FeSi2 as first phase has not been observed. In the case of the Fe-V diffusion barrier it was shown that the use of the diffusion barrier resulted in smoother layers of β-FeSi2 than could be formed by direct reaction of Fe on Si. In the case of the Fe-Zr barrier it is found that the barrier fails structurally at high temperatures. While it does prohibit Fe diffusion at low annealing temperatures, significant Si diffusion occurs prior to ε-FeSi formation.
Effects of Ge on The Nucleation and Growth of Si1−xGex
Authors: Yamaguchi S. , Park S. K. , Sugii N. , Nakagawa K. , Miyao M.
Published: April 2011

Nucleation and growth properties of Si1-xGex (0≦x≦0.3) have been investigated by using ellipsometric spectroscopy. The incubation time and the crystallization time significantly decrease with increasing x; the estimated incubation time (and crystallization time) in Si0.7Ge0.3 is about 1/100 of that in Si. During the incubation time, the increase of the crystallinity has been observed which corresponds to the nucleation of crystal seeds. From the behavior of the crystallinity during the incubation and the crystallization time, we estimated the activation energy of the nucleation and the crystallization. Both energies monotonically decrease with increasing x. The saturated crystallinity after crystallization decreases with increasing x. It has been found that the effect of Ge reduces the crystallinity of Si1-xGex while significantly enhancing the crystallization.
Effects of Boron Doping on the Grain Growth Behaviour of γ/γ Nickel-Aluminium Alloy
Authors: Chiu Y.L. , Ngan A.H.W.
Published: April 2011

Effects of 0.5 at. % boron doping on Ni85Al γ/γ superalloys were investigated for the first time, yielding a number of observations not previously observed in the literature. First, the grain growth kinetics of both the doped and undoped alloys were found to disobey the simple Nielsen law d = Ctn but instead follow an equation of the type d = C ln(t) + C0. The constants C and C0 were found to be respectively 10.2 and 23.2 for the boron-free alloy, and 6.2 and 14.2 for the boron-doped alloy, i.e., the grain growth rate was retarded significantly upon boron doping. Such a retarding effect is thought to be due to the formation of a boron-nickel cosegregated zone observed at the grain boundaries of the doped alloy; the width of the zone, in μm's, is two to three orders of magnitude larger than the boron induced disordered layer found in nickel rich Ni3Al compounds doped with boron. Other associated effects of the cosegregated zone include a sharp increase in toughness, much better slip transmission across grains and reduced workhardening rates. Another intriguing point is that the γ precipitates were found to segregate to the grain boundaries in the boron-free alloy after cold rolling, but no such segregation of γ precipitates has been observed in the boron-doped alloy. The different deformation microstructures and the retarded grain growth rates upon boron doping will be discussed.
Crystallization of Al-Gd-La-Ni Metallic Glasses
Authors: Croat T.K. , Gangopadhyay A.K. , Kelton K.F.
Published: April 2011

The crystallization kinetics of Al-Gd-La-Ni metallic glasses to nanostructured phases are analyzed using differential scanning calorimetry and transmission electron microscopy. In a narrow alloy composition range near Al88Gd6La2Ni4, TEM reveals an amorphous phase separation that occurs upon annealing at low temperatures prior to crystallization. Al-enriched regions, typically 40 nm in diameter, bounded by rare-earth rich regions, are visible. Upon crystallization, α-Al forms preferentially at the interface between these phase separated regions. The relevance of this crystallization sequence to previous work in Al-RE-TM glasses and to the evolution of nanoscale microstructures common in the crystallization of other metallic glasses are discussed.
Patterned ZnS Thin-Film Growth using KrCl Excimer Lamp on the Zn Nuclei
Authors: Toda M. , Lizuka H. , Murahara M.
Published: April 2011

Patterned Zn nuclei were formed by exposure with a single shot of an ArF excimer laser through a patterned photo mask onto a Si substrate which adsorbed DMZ (dimethylezinc). A ZnS thin film was then grown only onto the patterned Zn nuclei by KrCl excimer lamp irradiation of the substrate which was sealed in the chamber along with DMZ and H2S.
Ion Irradiation Induced Crosslinking Effects on Mechanical Properties of Photoresist Films
Authors: Garcia I. T. S. , Samios D. , Zawislaka F. C. , Jornada J. A. H. Da , Foerster C. E. , Serbena F. C. , Lepienski C. M.
Published: April 2011

We investigate the crosslinking process in ion irradiated AZ 1350J™ photoresist. The films were deposited on clean silicon wafers and irradiated with 380 keV He ions in the fluence range of 1013 to 1016 He.cm-2, corresponding to average deposited energy densities from 0.02 to 20 eV. Å-3.respectively. Nanoindentation, Raman spectroscopy as well as gel content and density measurements have been used to determine mechanical and structural properties of the irradiated films. The results show that the irradiation induces crosslinking of the polymeric chains but also produces carbonization of the films. For deposited energy densities up to 2 eV.Å-3. the crosslinking process is predominant and is mainly responsible for the increase of hardness and Young's modulus by respectively 5 and 2 times in relation to the values of the pristine film and for the gel content of 90%. For deposited energy densities larger than 2 eV.Å-3, the photoresist film is progressively transformed into an amorphous carbon layer as is shown by the Raman results, and also by the increase of the density at a deposited energy of 20 eV.Å-3.
Application of Cluster Ion Beam Smoothing to SiC and YBCO Surfaces
Authors: Fathy D. , Holland O. W. , Liu R. , Wosik J. , Chu W. K
Published: April 2011

Optimization of the surface topography, especially in high-temperature superconductors (HTS) and silicon carbide is crucial for device processing. Surface smoothing in these materials was investigated using Gas Cluster Ion Beams (GCIB) capable of delivering cluster ions of ≥ 2000 Ar atoms with energies of up to 30keV. Examination of the surface topography after cluster-ion irradiation was done using cross-sectional transmission electron microscopy (TEM) and atomic force microscopy (AFM). The results indicate that typical as-deposited YBCO films on MgO substrates have an average roughness of the order of 40 nm, and interpeak distance between 300–600 nm. Application of GCIB to the surface planarization reduces the roughness to only 10 nm. Also power handling and microwave surface resistance of the YBCO film and its relationship to surface smoothness are reported. Similar observations using bulk SiC are discussed.
Ion Beam Induced Growth Structure of Fluorite Type Oxide Films for Biaxially Textured HYSC Coated Conductors
Authors: Iijima Y. , Kimura M. , Saitoh T.
Published: April 2011

Biaxially aligned film growth by dual-ion-beam sputtering methods were studied for fluorite type (Zr0.85Y0.15O1.93(YSZ), Hf0.74Yb0.26O1.87, CeO2), pyrochlore type (Zr2Sm2O7), and rare-earth C type (Y2O3, Sm2O3) oxides on polycrystalline Ni-based alloy substrates. Cubetextured (all axes aligned with a <100> axis substrate normal) films were obtained for fluorite and pyrochlore ones by low energy (<300 eV) ion bombardment at low temperatures (< 300 °C). Besides, cube textured Y2O3 films were obtained in far narrower conditions with a quite low energy (150 eV)-ion bombardment at the temperature of 300 °C. The assisting ion energy dependence was discussed in connection with lattice energies for these oxide crystals.
Quantitative Rheed Analysis of Biaxially-Textured Polycrystalline MgO Films on Amorphous Substrates Grown by Ion Beam-Assisted Deposition
Authors: Brewer R. T. , Hartman J. W. , Atwater Harry A.
Published: April 2011

We have developed a computer simulation based on analytic calculation of reflection high energy electron diffraction (RHEED) patterns in the kinematic approximation for mosaic polycrystalline films for given values of electron beam incidence angle, polycrystalline texture, in-plane orientation distribution, and grain size. Although RHEED is most appropriately modeled using dynamical scattering theory, the computational efficiency of the kinematic approximation has enabled the development of a model suitable for real time measurement of crystallographic texture and in-plane orientation distributions for biaxially-textured films grown by ion beam-assisted deposition (IBAD). Using the simulation, we can quantitatively determine how RHEED spot shapes and relative intensities depend on the crystallographic texture and in-plane orientation distribution of polycrystalline films. RHEED patterns taken at 25 keV with incidence angle in the range 1–5 degrees from 10 nm thick, nominally [100]-textured MgO films grown on amorphous Si3N4 by IBAD were analyzed by comparing experimental RHEED phi rocking curves with those predicted by the simulation. For some films, an additional 200 nm thermally-grown MgO homoepitaxial layer was grown on top of the IBAD MgO layer. The model enables a quantitative correlation between biaxial texture and RHEED measurements. RHEED results are compared to X-ray rocking curve film analysis.
Specimen Current Imaging of Delamination in Ceramic Films on Metal Substrates in the SEM
Authors: Rangarajan S. , King A.H.
Published: April 2011

Plasma spraying of yttria-stabilized zirconia on stainless steel substrates generates rapidly solidified thin film discs called splats. Constraint due to adhesion at their interface generates sufficient stresses during cooling from the splat melting to generate extensive cracking. Stress relief by cracking always accompanied by delamination of the thin films at the edges of cracked segments. It is shown here that images obtained in the SEM through amplification of the specimen current signal generate the right contrast for delineating regions of edge delamination in the cracked segments of a splat. Image analysis using this contrast provides a quantitative measure of the extent of delamination at the interface. Greater delamination in the splats formed on cooler substrates. Correlation also indicates complimentary nature of stress relief by delamination and cracking. A detailed analysis including data from solidification and cooling and cracking statistics will give a measure of the adhesion strength at the interface. This technique is a quick method for measuring delamination of microscopic degree in thin insulating films on conducting substrates.
Energy-Loss Filtered Imaging of Segregation-Induced Interface Broadening in SiGe/Si p-Channel MOSFET Device Structures
Authors: Norris D.J. , Cullis A.G. , Grasby T.J. , Parker E.H.C.
Published: April 2011

SiGe/Si p-channel heteroepitaxial MOSFET test structures have been fabricated using solid-source molecular beam epitaxy. High-resolution transmission electron microscopy and energy-loss filtered imaging have been used to quantitatively determine the nanoscale Ge distributions across the SiGe alloy channel. The Ge profile at the edges of the alloy channel were found to be asymmetrical due to the effect of Ge segregation, with an exponential-like distribution directed toward the surface. The results agree well with the predictions of segregation theory and indicate that the concentration of Ge in the extended distribution lay in the range 10%-1% over a distance of several nanometers from the body of the channel. Secondary ion mass spectrometry measurements upon the same samples were insensitive to this short range extended Ge distribution.
Interface Structure and Zn Diffusion in the CdTe/ZnTe/Si System Grown by MBE
Authors: Tsen S.-C. Y. , Smith David J. , Crozier P. A. , Rujirawat S. , Brill G. , Sivananthan S.
Published: April 2011

Two CdTe/ZnTe/Si samples were grown on Si (211) and Si(111) substrates by molecular beam epitaxy for use as lattice-matched substrates for HgCdTe growth. An As precursor was used before growing ZnTe. In order to understand the interface structure, the Zn diffusion problem and any effect due to As passivation, high resolution bright-field images, dark-field images and energy-dispersive X-ray spectra were studied. Fourier-filtered images have revealed details of the atomic arrangements and the dislocation defects at the interface. Local lattice parameters such as (111) d-spacings at different distances from the interface were measured to determine the Zn concentration based on Vegard's law. The Zn concentration profiles were consistent with measurements from energy-dispersive X-ray spectroscopy. The As-passivated interface showed vacancy-type defects.
High-Resolution Scanning Electron Microscopy and Microanalysis of Supported Metal Catalysts
Authors: Liu Jingyue
Published: April 2011

The use of a high-brightness field emission gun and novel secondary electron detection systems makes it possible to acquire nanometer-resolution surface images of bulk materials, even at low electron beam voltages. The advantages of low-voltage SEM include enhanced surface sensitivity, reduced sample charging on non-conducting materials, and significantly reduced electron range and interaction volume. High-resolution images formed by collecting the backscattered electron signal can give information about the size and spatial distribution of metal nanoparticles in supported catalysts. Low-voltage XEDS can provide compositional information of bulk samples with enhanced surface sensitivity and significantly improved spatial resolution. High-resolution SEM techniques enhance our ability to detect and, subsequently, analyze the composition of nanoparticles in supported metal catalysts. Applications of high-resolution SEM imaging and microanalysis techniques to the study of industrial supported catalysts are discussed.
Atomic Scale Analysis of Cubic Zirconia Grain Boundaries
Authors: Dickey E.C. , Fan X. , Yong M. , Sinnott S.B. , Pennycook S.J.
Published: April 2011

The core structures of two symmetric tilt [001” grain boundaries in yttria- stabilized cubic zirconia are determined by Z-contrast imaging microscopy. In particular, near-σ=13 (510) and σ=5 (310) boundaries are studied. Both grain boundaries are found to be composed of periodic arrays of basic grain-boundary structural units, whose atomic structures are determined from the Z-contrast images. While both grain boundaries maintain mirror symmetry across the boundary plane, the 36° boundary is found to have a more compact structural unit than the 24° boundary. Partially filled cation columns in the 24° boundary are believed to prevent cation crowding in the boundary core. The derived grain boundary structural models are the first developed for ionic crystals having the fluorite structure
Electronic Effects on Grain Boundary Structure in Bcc Metals
Authors: Campbell Geoffrey H. , King Wayne E. , Belak James , Moriarty John A. , Foiles Stephen M.
Published: April 2011

The dominant factor in determining the atomic structure of grain boundaries is the crystal structure of the material, e.g. FCC vs. BCC. However, for a given crystal structure, the structure of grain boundaries can be influenced by electronic effects unique to the element comprising the crystal. Understanding and modeling the influence of electronic structure on defect structures is a key ingredient for successful atomistic simulations of materials with more complicated crystal structures than FCC. We have found that grain boundary structure is a critical test for interatomic potentials. To that end, we have fabricated the nominally identical Σ5 (310)/[001] symmetric tilt grain boundary in three different BCC metals (Nb, Mo, and Ta) by diffusion bonding precisely oriented single crystals. The structure of these boundaries have been determined by high resolution transmission electron microscopy. The boundaries have been found to have different atomic structures. The structures of these boundaries have been modeled with atomistic simulations using inter-atomic potentials incorporating angularly dependent d–state interactions, as obtained from Model Generalized Pseudopotential Theory. We report here new experimental and theoretical results for Ta
Effects of ‘As Deposited’ and Alloying Temperatures on the Distribution of Cu in 0.5%Cu-Al Films
Authors: Smith P. L. , Gazda J.
Published: April 2011

The Al-0.5wt%Cu alloys in Ti-TiN/Al/Ti-TiN metal interconnects were investigated using blanket and patterned films deposited on SiO2. Distribution of Cu and Ti within the Al films was determined using Resistivity (Rs), X-ray Diffraction (XRD), Rutherford Backscatter Spectroscopy (RBS), and Secondary Ion Mass Spectroscopy (SIMS). The location of Cu, Ti, Al and their intermetallics were studied in a CM300 field emission gun (FEG) TEM using Energy Filtered Transmission Electron Microscopy (EFTEM) with a Gatan Imaging Filter (GIF). No significant differences were observed with Rs or XRD textural analysis. Elemental distribution analysis from RBS and SIMS revealed relatively higher concentrations Cu at the Al/Ti-TiN barrier interface. This was attributed to sputtering bias during the start of the Al deposition and the subsequent snow plowing of Cu during the growth of the TiAl3 intermetallic. TEM imaging and elemental analysis showed that Cu is completely dissolved into solution at deposition temperatures ≥ 300°C. At temperatures ≤ 250°C some (Al2Cu) precipitates were observed on grain boundaries. Continued thermal cycling does not effectively change the elemental distribution. Therefore, it can be concluded that the solid solubility of 0.5wt%Cu in Al was not reached at these low temperatures or during the subsequent thermal cycling
Deposition and Annealing Studies of Diamond-Like Carbon Grown by Molecular Beam Deposition
Authors: Goetzberger Oliver , Kojima Nobuaki , Khan Aurangzeb , Yamaguchi Masafumi
Published: April 2011

Studies on the electrical conductivity of molecular beam deposited carbon films after annealing of the carbon films have been carried out. Detailed temperature dependence of conductivity on the as-deposited and on annealed samples has been investigated. The results were interpreted in terms of a model which includes a variable range hopping and strongly scattering metallic components. A correlation between annealing behavior of the electrical conductivity and the results of x-ray photoelectron spectroscopy and Raman spectroscopy is presented.
Photoconductivity and Photoluminescence of Amorphous Carbon Nitride a-CNx Films Prepared by the Layer-by-Layer Method
Authors: Katsuno T. , Nitta S. , Habuchi H. , Iwasaki T. , Itoh T. , Nonomura S.
Published: April 2011

Amorphous carbon nitride films a-CNx, which made in our laboratory, show high photosensitivity Ps that is a ratio of photoconductivity σp and dark-electrical conductivity σd Maximum Ps of a-CNx is about 5×106 which is about 50 times larger than that of hydrogenated amorphous silicon a-Si:H.

We have succeeded to observe photoconductivity spectra where photoconductivity starts nearly at 2 eV and saturates at 3 eV. Then σp increase again at 3.7 eV up to 6.2 eV. The dependence of σp on excitation energy and intensity is observed. Photoluminescence spectrum is also obtained which have a spectrum from infrared of 0.8 eV up to ultraviolet of 3.5 eV. Using these data together with photothermal deflection spectra, we have presented a refined model of the electronic density of states for LLa-CNx.
Mechanical and Chemical Properties of CBxNy and CSixNy Thin Films Grown by N*-Plasma Assisted Pulsed Laser Deposition
Authors: Thärigen T. , Riede V. , Lippold G. , Hartmann E. , Hesse R. , Streubel P. , Lorenz D. , Grau P. , Lorenz M.
Published: April 2011

Carbon silicon nitride (CSixNy), and carbon boron nitride (CBxNy) thin films have been grown by pulsed laser deposition (PLD) of various carbon (silicon/boron) (nitride) targets using an additional nitrogen RF plasma source on [100] oriented silicon substrates without additional heating. The CSixNy and CBxNy thin films were amorphous and showed nano hardness up to 23 GPa compared to 14 GPa for silicon and maximum nitrogen content of 30 at%. The maximum nanohardness was achieved for 10% Si and 10% B content in the films. The lower hardness of this films compared to the nanohardness of 30-50 GPa of DLC films indicates a lower amount of covalent carbon-nitrogen bonding in the films. However, in contrast to DLC films, the CSixNy and CBxNy films can be grown to thickness above 3 μm due to lower internal compressive stress. XPS of CSixNy and CBxNy film surfaces shows clear correlation of binding energy and intensity of N ls, C ls, and Si 2p peaks to composition of the PLD-targets and to nitrogen flow through plasma source, indicating soft changes of binding structure due to variation of PLD parameters. The results demonstrate the capability of the plasma assisted PLD process to deposit hard amorphous CSixNy, and CBxNy thin films with adjustable properties.
Atomic Transformations and Quantum Transport in Carbon Nanotubes
Authors: Bernholc J. , Nardelli M. Buongiorno , Fattebert J.-L. , Orlikowski D. , Roland C. , Rosef F. , Zhao Q.
Published: April 2011

High strain conditions can lead to a variety of atomic transformations in nanotubes, which usually occur via successive bond rotations. The energetic barrier for the rotation is dramatically lowered by strain, and ab initio results for its strain dependence are presented. While very high strain rates must lead to tube breakage, (n,m) nanotubes with n, m < 14 can display plastic flow under suitable conditions. This occurs through the formation of a 5-7-7-5 defect, which then splits into two 5-7 pairs. The index of the tube changes between the 5-7 pairs, potentially leading to metal-semiconductor junctions. The high strain conditions can be imposed on the tube via, e.g., AFM tip manipulations, and we show that such procedures can lead to intratube device formation.

The defects and the index changes occurring during the mechanical transformations also affect the electrical properties of nanotubes. We have computed the quantum conductances of strained defective and deformed tubes using the tight binding method. The results show that the defect density and the contacts play key roles in reducing the conductance at the Fermi energy. We also explored the role of bending in changing the electrical properties and found that mechanical deformations affect differently the transport properties of achiral and chiral nanotubes. Our results are in good agreement with recent experimental data.
Novel Silica-Sol Mediated Synthesis of Nanoporous Carbons
Authors: Hyeon Taeghwan , Han Sangjin , Sohn Kwonnam
Published: April 2011

New preparative methods for the synthesis of nanoporous carbons using silica particles as templates will be presented. Gellation of resorcinol and formaldehyde in the presence of silica sol particles generated RF gel-silica nanocomposite. Carbonization followed by HF etching of silica templates generated nanoporous carbons with pore size ranging 10 ∼ 100 nm. When silica particles stabilized with surfactant were used as templates, uniform ∼ 10 nm pore-sized carbons have been formed. These nanoporous carbons exhibited excellent adsorption capacity for dyes.
Smart Polymer Composite Thermistor
Authors: Strümpler Ralf , Glatz-Reichenbach Joachim
Published: April 2011

An industrially important class of passively smart materials is electrically nonlinear polymer composites. The transition of conducting composites from low to high resistivity can be utilized for current limitation. Due to Joule losses the material is heated by a fault or short-circuit current. With increasing temperature the polymer matrix expands and the current paths over the conducting filler particles are interrupted. Within milliseconds, the material responds to the fault current by an increase in resistivity up to eight orders of magnitude. Due to the strong nonlinear resistivity - temperature relation, a narrow hot-zone is formed even for long samples. The length of the hot-zone limits the maximum switching voltage. By adding a second filler material of varistor- type, however, the maximum voltage can be considerably increased. When a hot spot is formed in one of the current paths over the conducting particles, a small voltage increase allows already a commutation of the current to neighboring varistor particles. Consequently, the current can still flow to a certain degree and allows to heat also the rest of the material around its path. This leads finally to a very broad hot area, which can resist much higher voltages. By the development of a smart material with two strong non-linearities, a dramatic improvement has been achieved for the application of thermistor composites in current limitation.
Fast Proton Conductors from Inorganic-Organic Composites: I. Amorphous Phosphate-Nafion and Silicophosphate-PMA/PWA Hybrids
Authors: Park Yong-Il , Kim Jae-Dong , Nagai Masayuki
Published: April 2011

A drastic increase of electrical conductivity was observed in the composite of amorphous phosphate and ion-exchange resins (Nafion) as phosphorus concentration increased. Incorporation of amorphous phosphate into Nafion caused a large increase of conductivity to about 4×10−1S/cm at 23°C. However, the fabricated composite showed very low chemical stability.

A high proton conductivity was also observed in a new inorganic-organic hybrids through incorporating PMA(molibdo-phosphoric acid)/PWA(tungsto-phosphoric acid) as a proton source in amorphous silicophosphate gel structure. Obtained gels were homogeneous and chemically stable. Resulting proton conductivity is very high (up to 5.5×10−3S/cm) compared to those of silicophosphate gels.
Fast Proton Conductors from Inorganic-Organic Composites: II. Amorphous Phosphate-PTFE and ZrP-PTFE Composites
Authors: Park Yong-Il , Kim Jae-Dong , Nagai Masayuki
Published: April 2011

A high proton-conductivity was observed in the composite of amorphous phosphate and polytetafluoroethylene (PTFE). Incorporation of amorphous phosphate into PTFE emulsion caused a large increase of conductivity to about 4×10−2S/cm at 23°C. However, the conductivity decreased with increasing heat-treatment temperature, and the fabricated composite showed very low chemical stability.

As a chemically stable composite, PTFE-based composite was also synthesized from α- or γ-zirconium phosphate crystalline powders dispersed in partially polymerized PTFE particles. By addition of zirconium phosphate powders, the proton conductivity jumped up to 2.2×10−3S/cm from 10−13S/cm of PTFE.
Dynamics of Pyroelectricity of a Copolymer of Vinylidene Fluoride with Trifluoroethylene
Authors: Takahashi Y. , Taniwaki J. , Furukawa T.
Published: April 2011

The pyroelectric response of a copolymer of vinylidene fluoride with trifluoroethylene was measured as a function of time by applying a laser pulse to give an abrupt increase in temperature. The response curve shows several processes: the thickness extensional mode TEM, the length extensional mode LEM and the heat transfer to the environment. By fitting a theoretical curve for the TEM mode, the pyroelectric primary and secondary effects are separated. The primary effect is found to be small at room temperature. Additional gradual response shows that there exists a surface layer which has smaller polarization than in the bulk.

The temperature dependence of the pyroelectric response curve shows that the primary effect increases with temperature. It dominates the response at just below the ferroelectric-paraelectric transition temperature.
Some Aspects of Plastic Flow in Silicon Nitride
Authors: Rouxel T. , Rabier J. , Testu S. , Milhet X.
Published: April 2011

The different scales of plastic flow in silicon nitride were investigated either by indentation experiments and compression under hydrostatic pressure in the 20-850°C temperature range, and by stress relaxation and creep above 1350°C. [0001], 1/3<11-20> and 1/3<11-23> dislocations were evidenced by Transmission Electron Microscopy (TEM) in the low temperature range. Cross-slip events in {10-10} prismatic planes were observed at temperature as low as 20°C by Atomic Force Microscopy (AFM) on micro-hardness indents. By increasing the temperature, the deviation plane becomes {11-20} prismatic planes. The easiest slip system is by far the [0001]{10-10} system. Above 1350°C, the creep strain could be fitted by the sum of a transient component, εt=ε∞[1-exp-(t/τc)bc], where τc reflects the duration of the transient creep stage, and bc is between 0 and 1, and a stationary component, εs=εst =Aσnt, where σ is the stress and n is the stress exponent. The increase of ε∞ with temperature is interpreted on the basis of the formation of liquid intergranulary phases above 1400°C by progressive melting of some of the grains. A creep exponent of 1.8 was determined. A single value could hardly be given to the activation energy since an S-shape curve was observed in the In εs versus l/T plot, as for most glasses over large temperature ranges. The stress relaxation kinetics was found to follow the Kohlrausch-Williams-Watt expression: σ/σo=exp [-(t/τr)br], where br ranges between 0 (solid state) and I (liquid state) and τr is a characteristic relaxation time constant. As in the case of glasses, τr decreases rapidly whereas br increases from about 0.2 to 0.7 as the temperature increases from 1400 to 1650°C. But again, it is very difficult to get a single value for the activation energy from the In τr versus 1/T plot.
Newtonian Flow in Bulk Amorphous Alloys
Authors: Wadsworth J. , Nieh T.G.
Published: April 2011

Bulk amorphous alloys have many unique properties, e.g., superior strength and hardness, excellent corrosion resistance, reduced sliding friction and improved wear resistance, and easy formability in a viscous state. These properties, and particularly easy formability, are expected to lead to applications in the fields of near-net-shape fabrication of structural components. Whereas large tensile ductility has generally been observed in the supercooled liquid region in metallic glasses, the exact deformation mechanism, and in particular whether such alloys deform by Newtonian viscous flow, remains a controversial issue. In this paper, existing data are analyzed and an interpretation for the apparent controversy is offered. In addition, new results obtained from an amorphous alloy (composition: Zr–10Al–5Ti–17.9Cu–14.6Ni, in at. %) are presented. Structural evolution during plastic deformation is particularly characterized. It is suggested that the appearance of non-Newtonian behavior is a result of the concurrent crystallization of the amorphous structure during deformation.
High-Resolution EBSD Analysis of Severely Deformed Submicron Grained Aluminum Alloys
Authors: Prangnell P. B. , Bowen J. R. , Gholinia A. , Markushev M. V.
Published: April 2011

There is currently much interest in the use of severe plastic deformation techniques for the production of submicron grained Al-alloys. Because of their small grain sizes, previous investigations have relied on the TEM to study the grain structures after processing. However, the TEM is not that well suited to obtaining statistically significant data on the misorientations of the boundaries present in the deformed state. Recent improvements in the resolution of SEMEBSD systems means that this powerful technique can now be used to quantitatively analyse severely deformed structures more reliably than was previously possible. Results using this method have shown that the deformation structure is very sensitive to the strain path, material, and processing conditions. With a constant strain path fibrous grain structures tend to be formed and homogeneous submicron grain structures can only be produced at very high plastic strains, of greater than ten. Materials deformed with cyclic strain paths are more isotropic, but generally have bimodal grain structures and contain a lower density of high angle boundaries and only bands of submicron grains.
Cavitation in a Uniaxially deformed Superplastic Al-Mg Alloy
Authors: Bae D. H. , Ghosh A. K.
Published: April 2011

Cavitation caused by superplastic straining of a fine-grained Al-Mg-Mn-Cu alloy under uniaxial tension has been systematically evaluated. Tensile tests were conducted in the strain-rate range of 10−4s−1 to 10−2s−1 and in the temperature range of 450°C to 550°C. Measurements of the number and size of cavities were made by image analysis through optical microscopy on tested specimens. With increasing imposed strain, the cavity population density increases. Cavity growth has been found to be primarily due to the plastic deformation of the matrix. These results are characterized by the total volume fraction of cavities which is found to increase exponentially with strain. However, the dependencies of cavity volume fraction on strain-rate and temperature are not straightforward and the notion of just a few large cavities controlling the total cavity volume is not always true. Attempts to explain these complex dependencies have been carried out based on the concepts of debonding between the matrix and non-deformable particles, the continuous nucleation of new cavities, and plasticity-based cavity growth for large cavities.
Superplasticity and Joining of Zirconia-Based Ceramics
Authors: Gutierrez-Mora F. , Dominguez-Rodriguez A. , Jimenez-Melendo M. , Chaim R. , Ravi G. B. , Routbort J. L.
Published: April 2011

Steady-state creep and joining of alumina/zirconia composites containing alumina volume fractions of 20, 60, and 85% have been investigated between 1250 and 1350°C. Superplasticity of these compounds is controlled by grain-boundary sliding and the creep rate is a function of alumina volume fraction, not grain size. Using the principles of superplasticity, pieces of the composite have been joined by applying the stress required to achieve 5 to 10% strain to form a strong interface at temperatures as low as 1200°C
Temperature Dependence of High Field Characteristics in PMN-PT-BT Ceramics Containing Chemical Additives
Authors: Cho Yong S. , Yoon Chang H. , Pilgrim Steven M. , Bridger Keith
Published: April 2011

A chemical additive method was used to modify the composition and resultant properties of a commercially available 0.96(0.9lPb(Mg1/3Nb2/3)O3 - 0.09PbTiO3) - 0.04 BaTiO3 (PMN-PT-BT) ceramic. Without an additional ball-mixing process, several combinations of minor additives such as Fe, Ba, Sr, Zn and Ti were incorporated by the chemical method. Weak- and high-field characteristics including dielectric properties, induced strain and polarization, and associated hystereses were evaluated for the samples sintered at 1200°C for 4 hrs. All properties were found to depend on the chemical additives and temperature. Especially, the temperature dependence of high-field characteristics revealed different behavior from that reported for conventionally-prepared samples. For example, the samples containing 0.5 wt% SrO, 0.5 wt% ZnO, and 0.5wt% TiO2 did not exhibit a transition to piezoelectric behavior at the temperature expected from the dielectric measurements. Overall, the coating process has been successfully used to modify, and in some cases, enhance the high-field characteristics of PMN-based ceramics for electromechanical uses.
The Effect of Hafnium and Thermal Cycling on the Transformation Temperatures of NiTi-Based Shape Memory Alloys
Authors: Thoma Paul E. , Boehm John J.
Published: April 2011

The effect of thermal cycling on the austenite to martensite (A→M) and martensite to austenite (M→A) transformation temperatures (TTs) of Ni49.8Ti50.2 and Ni49.8Ti40.2Hf10 shape memory alloys is investigated. Test specimens are from arc melted buttons homogenized at 900°C for 100 hours. Results show that the A→M and M→A TTs for the alloys decrease with increasing number of thermal cycles through the phase transformations. The A→M TT of the NiTiHf alloy stabilizes more quickly than the A→M TT of the NiTi alloy when cycled. However, the M→A TT of the binary NiTi alloy stabilizes more quickly than the M→A TT of the NiTiHf alloy when cycled.
Development of High Frequency Terfenol-D Transducer Material
Authors: Lindgen E. A. , Poret J. C. , Whalen J. J. , Rosen M. , Wun-Fogle M. , Restorff J. B. , Clark A.E.
Published: April 2011

The objective of this research and development program is to develop production methods to obtain thin strips of oriented crystalline Terfenol-D and to develop multi-layered driver rods for transducers that will operate over a broad spectrum into the MHz frequency range. To reach this goal, special methods must be used to minimize the amount of mechanical processing, such as machining, as the material is both brittle and expensive. A modified rapid solidification method has been developed to process Terfenol-D to obtain the desired geometric configuration of long thin strips. Currently, sections that are 500 mm long, 2 mm wide and 0.1 mm thick can be produced. In addition, this method enables the crystallographic orientation of the strips of Terfenol-D to be controlled to obtain the preferred orientation that will maximize the magnetostrictive displacement of the material. Magnetostrictive measurements have shown that the samples prepared by this approach have a 62 percent improved magnetostrictive performance when compared to non-oriented Terfenol-D. The ribbons have been consolidated into transducer driver rods. The magnetostrictive performance of the driver rods has been measured to be 60 percent of the as prepared ribbons. The reduction in performance is attributed primarily to the geometric placement of the ribbons inside the driver rods.