bluuebunny/crossref_metadata_2025 huggingface dataset:
Nonvolatile resistive switching characteristics of HfO2 with Cu doping
Authors: Guan Weihua , Long Shibing , Liu Ming , Wang Wei
Published: April 2011

In this work, resistive switching characteristics of hafnium oxide (HfO2) with Cu doping prepared by electron beam evaporation are investigated for nonvolatile memory applications. The top metal electrode/ hafnium oxide doped with Cu/n+ Si structure shows two distinct resistance states (high-resistance and low-resistance) in DC sweep mode. By applying a proper bias, resistance switching from one state to the other state can be achieved. Though the ratio of high/low resistance is less than an order, the switching behavior is very stable and uniform with nearly 100% device yield. No data loss is found upon continuous readout for more than 104 s. The role of the intentionally introduced Cu impurities in the resistive switching behavior is investigated. HfO2 films with Cu doping are promising to be used in the nonvolatile resistive switching memory devices.
Temperature Dependence of Electrical Properties of NiO Thin Films for Resistive Random Access Memory
Authors: Suzuki Ryota , Suda Jun , Kimoto Tsunenobu
Published: April 2011

Temperature dependence of electrical properties in NiO thin films for ReRAM applications has been investigated. I-V measurements have been carried out in the temperature range from 100K to 523K. The resistance in the high resistance state (HRS) is almost independent of temperature below 250K, whereas it decreases with an activation energy of 300 meV above 250K. Hopping conduction and band conduction may be dominant in the low- and high-temperature range, respectively. Admittance spectroscopy on the NiO/n+-Si structure¡¡reveals the existence of a high density of traps, which may contribute to the conduction in HRS. In the low resistance state (LRS), however, the resistance slightly increased in the whole temperature range and the trend is similar to that of metallic Ni film, indicating the metallic Ni defects is related to the conduction in LRS. The Pt/NiO/Pt structure demonstrated stable resistance switching even at temperature as high as 250°C or higher. Since other competitive nonvolatile memories will face severe difficulty in high-temperature operation, the present ReRAM shows promise for high-temperature application.
Large-domain Organic Crystalline Films for Field-effect Transistors
Authors: Tominari Y. , Uno M. , Yamagishi M. , Suzuki Y. , Wakamiya A. , Yamaguchi S. , Takeya J.
Published: April 2011

We report a method to fabricate thin films of large-domain organic semiconductor single crystals dispersed over the whole surface of centimeter-scale substrates for field-effect transistors. Growing less than 500-nm thick film-like organic crystals of sub-millimeter sizes densely in a furnace independently of substrates by physical vapor transport, the collection of the single crystals is mechanically attached to the surface of gate dielectric layers. The organic transistors made of large-domain benzo-annulated pentathienoacene crystals exhibited pronounced transistor performances with mobility values of ∼ 0.2-2 cm2/Vs, which is as high as devices of one-piece crystals. The result demonstrates that the above technique provides a method to apply high performance of organic single crystal transistors to real circuitry devices on large-area substrates.
Effect of Polymer Gate Dielectric Surface Viscoelasticity on Pentacene Thin-Film Transistor Performance
Authors: Kim Choongik , Facchetti Antonio , Marks Tobin J.
Published: April 2011

Pentacene is one of the most studied semiconductor for organic thin-film transistors (OTFTs), and enhanced understanding of pentacene-based TFTs has significantly advanced the organic electronics. We report here the crucial effect of the polymer gate dielectric glass transition temperature (Tg) on pentacene film growth mode, microstructure, and the resulting TFT performance. Nanoscopically-confined thin polymer films are known to exhibit reduced glass-transition temperatures versus the corresponding bulk values, and we demonstrate here that pentacene films grown on polymer gate dielectrics at temperatures well below their bulk Tg exhibit morphological/microstructural transitions and OTFT performance discontinuities at well-defined growth temperatures [defined as the surface Tg, or Tg(s)] characteristic of the underlying polymer structure and independent of the film thickness. The results argue that realistic OTFT response must take into account this fundamental polymer property, and that TFT measurements represent a new probe of polymer surface thermal properties.
Thermoelectric Power Changes of Low Strength Steel Induced by Hydrogen Embrittlement Tests
Authors: Mohamed-Noriega N. , López Cuéllar E. , de la Cruz A. Martinez
Published: April 2011

This work reports the thermoelectric characterization of a hydrogen embrittlement (HE) of low strength steel. Two sets of tests are performed in an electrochemical cell of H2SO4, with and without applied stress, lasting from 2 to 94 hours. Thermoelectric power (TEP) measurements are matched with ductility measurements (%RA and %EL) of samples tested in tension, as well as with microhardness measurements. Results indicate that TEP is sensitive to HE of low strength steels; the maximum variation of TEP is of ∼80nV/°C for samples tested without stress.
Application of High Spatial Resolution Electron Diffraction Techniques to the Study of Local Properties of Crystalline Solids
Authors: Steeds J W , Duan X F , Midgley P A , Spellward P , Vincent R
Published: April 2011

The addition of a Gatan imaging parallel electron-energy loss spectrometer (IPEELS) to a Hitachi HF 2000 cold field emission TEM has allowed us to produce high quality energy-filtered coherent electron diffraction patterns and electron holograms from a wide variety of materials. In this paper we review the recent achievements and make an assessment of the use of coherent electron diffraction in solving problems at high spatial resolution in materials science.
Atomic Resolution Electronic Structure Using Spatially Resolved Electron Energy Loss Spectroscopy
Authors: Batson P.E.
Published: April 2011

Electronic structure in small areas is obtainable by inspection of near edge fine structure of core excitations. We can accomplish this today with near atomic resolution, using EELS at high energy. At IBM, we have obtained results using a sub-0.2nm probe at 120KeV with enough current to allow 200meV resolution studies at the Si L2,3 edge. It is especially crucial for Si-based structures that this allows us to obtain Z-contrast dark field images of the Si lattice at an acceleration voltage that is low enough to minimize radiation damage, but with a high enough current to allow good quality spectra to be obtained. A review of instrumental requirements, spectral interpretation, and applications to Si-Ge alloys is presented.
Quantitative X-Ray Microanalysis for the Study of Nanometer-Scale Phases in the Aem
Authors: Anderson Ian M. , Bentley Jim , Carter C. Barry
Published: April 2011

Secondary excitation can be a large source of inaccuracy in quantitative X-ray microanalysis of inhomogeneous specimens in the AEM. The size of the secondary excitation component in the measured X-ray spectrum is sensitive to the geometry of the thin foil specimen. Secondary excitation has been examined in a self-supporting disc specimen of composition NiO-20 wt.% TiO2 which has been partially masked by a gold slot washer. The ratio of the intensities of the characteristic Kα peaks of Ti and Ni in X-ray spectra from a periclase-structured phase, of nominal composition NiO, has been measured to be NTi / NNi ≈ 0.005. There is no apparent Ti L2,3 signal in the corresponding electron energy-loss spectrum. The secondary excitation contribution to the characteristic Ti K≈a-peak from all sources can therefore be no larger than 0.5%. It should be possible to reduce this modest level of secondary excitation still further with a better masking arrangement.
Determination of the Number of Molecules Bonded to a CdSe Nanocrystallite Surface
Authors: Majetich Sara , Newbury Jennifer , Newbury Dale
Published: April 2011

Electron excited energy dispersive X-ray spectrometry (EDS) was used to determine the atomic species present in 35 Å diameter CdSe nanocrystallites. Both theoretical modeling and experimental calibration with standard materials were used to relate the relative X-ray intensities to the atomic fractions present in the sample. The EDS results were normalized to those found by elemental analysis, which also detects light elements. With different surface models, and the atomic fractions found by EDS, the number of surface groups per nanocrystallite was determined.
Eels Imaging of Biological Materials
Authors: Leapman R.D. , Sun S. , Hunt J.A. , Andrews S.B.
Published: April 2011

Parallel-detection electron energy loss spectroscopy (EELS) in the scanning transmission electron microscope provides a very sensitive means of detecting specific elements in biological systems. By analyzing EELS spectrum-image data recorded from rapidly-frozen and cryosectioned tissue it is possible to map quantitatively the distribution of the biologically important element, calcium, which is typically present at concentrations of only a few parts per million in cellular structures some tens of nanometers in diameter. A significant improvement (factor of four) in calcium detectability has been demonstrated for EELS compared with energy-dispersive x-ray spectroscopy. The spectrum-imaging technique has also been applied to map water distributions in hydrated biological specimens by utilizing the valence electron excitations.
Visualizing Langmuir-Blodgett Films with the Atomic Force Microscope
Authors: Viswanathan Ravi , Schwartz D.K. , Madsen L.L. , Zasadzinski J.A.
Published: April 2011

The Atomic Force Microscope (AFM) has created exciting new possibilities for imaging thin organic films under ambient conditions at length scales ranging from tens of microns to the sub - molecular scale. We present images of thin organic films prepared by the Langmuir-Blodgett (LB) technique that demonstrate the possibilities of the AFM.
Structural and Magnetic Properties of Epitaxially Grown Fcc Fe/Cu(100) and Fe/CaF2/Si(111)
Authors: Scheinfein M.R. , Healy S.D. , Heim K.R. , Yang Z.J. , Drucker J.S. , Hembree G.G.
Published: April 2011

We have used nanometer spatial resolution secondary electron and Auger electron imaging in an ultra-high vacuum scanning transmission electron microscope to characterize microstructure in ultrathin films of Fe/Cu(100) grown at room temperature and Fe/CaF2/Si(111) grown at room temperature and 150 C. Thin film microstructure was correlated in situ with magnetic properties by using the surface magneto-optic Kerr effect.
Atomic Scale Characterization of (NH4)2Sx-Treated GaAs (100) Surface
Authors: Yokoi Naoki , Andoh Hiroya , Takai Mikio
Published: April 2011

The geometric structure of GaAs (100) surfaces, treated in a (NH4)2Sx solution and annealed in N2 environment, has been studied in an atomic scale using high-resolution Rutherford backscattering (RBS), X-ray photoemission spectroscopy (XPS) and scanning tunneling microscopy (STM). RBS analysis using medium energy ion scattering (MEIS) could provide the thickness of the sulfur layer on the GaAs surface of about 1.5 monolayers. RBS channeling spectra indicated that the disorder of atoms in the surface region of S-terminated samples was smaller than that of untreated one. XPS spectra showed that S atoms on the surface bonded only As atoms. STM observation revealed that S atoms had a periodicity of 4 Å corresponding to that of Ga or As atoms in the (100) plane.
Size-effect Stabilization of the Low-T Ferroelectric Phase in Nanocrystalline WO3
Authors: Bi Xiang-Xin , Lee W. T. , Wang Kai-An , Collins D. F. , Bandow S. , Eklund P. C.
Published: April 2011

Using a CO2 laser to drive the pyrolysis of W(CO)6 and O2, we have synthesized nanocrystalline WO3-x particles. These nanopowders are found to exhibit a narrow size distribution with an average particle size produced in the range 5 to 10 nm, depending on the experimental conditions. Typical production rates are ∼ 2 g/h. Results from a Raman scattering study on WO3 nanopowder samples annealed in O2 indicate that a smaller particle size appears to stabilize the low-T ferroelectric phase ( < -40 °C) at room temperature.
Strength-Flaw Relationship of Corroded Pristine Silica Studied by Atomic Force Microscopy
Authors: Zhong Qian , Inniss Daryl , Kurkjian Charles R.
Published: April 2011

Glass strength is controlled by microscopic surface flaws. Attempts to quantify the strengthflaw relationship for corroded silica fibers have been unfruitful, principally because of the difficulty in identifying the nanometer-sized, strength-controlling flaws on a uniformly corroded surface. In this paper, studies on corrosion of pristine silica optical fibers by HF vapor are presented. The HF-treated fibers exhibit strength degradation and contain well-defined, spatially-resolved surface flaws, which are characterized with an atomic force microscope. Excellent strength agreement is obtained for all chemically corroded fibers when the flaws are modeled as partially embedded hemispheres (i.e., blunt flaws). The implication of these results to the corrosion and fatigue process of silica glasses is discussed, since all previous analyses have assumed the strength-controlling flaws to be sharp.
3-D Imaging of Crystals at Atomic Resolution
Authors: O'keefe M.A. , Downing K.H. , Wenk H-R. , Meisheng Hu
Published: April 2011

Electron crystallography has now been used to investigate the structures of inorganic materials in three dimensions. As a test of the method, amplitudes and phases of structure factors were obtained experimentally from high resolution images of staurolite taken in a number of different projections. From images in five orientations, a three-dimensional Coulomb potential map was constructed with a resolution of better than 1.4Å. The map clearly resolves all the cations (Al,Si,Fe) in the structure, and all of the oxygen atoms. This method promises great potential for structure determinations of small domains in heterogeneous crystals which are inaccessible to x-ray analysis. Three-dimensional structure determinations should be possible on small domains only approximately 10 unit cells wide, and may resolve site occupancies in addition to atom positions. Given a microscope stage with a suitable range of tilt and enough mechanical stability, the method could also be applied to small crystalline particles larger than about 50Å to 100Å. In addition, it may be possible to apply the method to derive the two-dimensional structure of periodic defects.
Analysis of Interface Dynamics in Solid-State Phase Transformations by In Situ Hot-Stage High-Resolution Transmission Electron Microscopy
Authors: Howe James M. , Benson W. E. , Garg A. , Chang Y.-C.
Published: April 2011

In situ hot-stage high-resolution transmission electron microscopy (HRTEM) provides unique capabilities for quantifying the dynamics of interfaces at the atomic level. Such information is critical for understanding the theory of interfaces and solid-state phase transformations. This paper provides a brief description of particular requirements for performing in situ hot-stage HRTEM, summarizes different types of in situ HRTEM investigations and illustrates the use of this technique to obtain quantitative data on the atomic mechanisms and kinetics of interface motion in precipitation, crystallization and martensitic reactions. Some limitations of in situ hot-stage HRTEM and future prospects of this technique are also discussed.
Chip Surface Damage Induced by Internal Stress of Lead–ON–Chip (Loc) Packages
Authors: Amagai Masazumi , Kawasaki Eiji
Published: April 2011

In lead–on–chip (LOC) packaging technology, the lead fingers are attached directly to the surface of the chip using a double–side adhesive tape. This method of chip attachment naturally concerns with regards to stress on the polyimide coated chip surface. Device failure related to fracture in the passivation layers and the Al–Si metal has been observed in temperature cycle tests. The dominant issue is polyimide cracking due to mechanical stress caused by internal stress of LOC packages. To investigate the effect of polyimide characterization, devices were fabricated with different polyimides. The degree of polyimide cracking was determined with scanning electron microscope (SEM) technique. The polyimides were characterized with chemicals, tensile measurement tester, thermal analyzer, fourier transform infrared spectroscope (FTIR), computer simulation and various package-level reliability tests. The results of the characterization and an explanation of the primary factors affecting chip surface damage are presented in this paper.
X-Ray Strain Measurements in Fine-Line Patterned AL-CU Films
Authors: Marcus M. A. , Flood W.F. , Cirelli R. A. , Kistler R. C. , Ciampa N. A. , Mansfield W. M. , Barr D. L. , Volkert C.A. , Steiner K. G.
Published: April 2011

In order to better understand the mechanics of metallization structures having very fine features, we performed in-situ, temperature-dependent X-ray strain measurements on Al-Cu films patterned into gratings with linewidths of 0.2-0.8μm, with and without a dielectric covering In comparison with earlier work on coarser structures, we find larger strains and less hysteresis, indicating an increased yield stress. The stress in unpassivated lines is almost independent of the linewidth. The slope of the stress/temperature curves for passivated lines increases with decreasing linewidth, so that the compressive stress at 500°C reaches 900MPa for the narrowest lines. The tensile stress at RT is smaller for the narrower lines, suggesting that these lines may not stress-void as much as wider ones. The significance of these results for stress voiding and electromigration will be discussed.
Thermally Induced Stresses in Passivated Thin Films and Patterned Lines of AlSiCu
Authors: Burges U. , Helneder H. , KÖrner H. , Schroeder H. , Schilling W.
Published: April 2011

A bending beam technique was used to measure the mechanical stresses in AlSi(l%)Cu(0.5%) blanket films as well as in patterned lines (aspect ratio: 0.8) - unpassivated and passivated with SiNx - during thermal cycling from –170°C or room temperature to 450°C.

Main results are:

a) No significant differences in unpassivated and passivated blanket films with thickness ranging from 0.2 µm to 3.2 µm.

b) In unpassivated patterned lines of 0.8 µm thickness the stresses across the lines are very small, while parallel to the lines they show nearly elastic behaviour, except at high temperatures.

c) In passivated patterned lines the stresses are much higher than in blanket films, very similar parallel and across the line and nearly elastic. The stress relaxation is small compared with blanket films and depends strongly on the temperature.
Line-Width Dependence of Stress in Passivated Al Lines During Thermal Cycling
Authors: Chidambarrao D. , Rodbell K. P. , Thouless M. D. , DeHaven P. W.
Published: April 2011

We have obtained theoretical stress-temperature curves for passivated Al lines undergoing thermal cycling. A finite element plane-strain cross-sectional analysis with a time-dependent constitutive property for Al, based on equations for discreteobstacle controlled plasticity, was performed. The parameters for this Al constitutive relation were obtained by fitting with experimentally obtained stress-temperature curves for Al blanket films on silicon. Theoretical results agree well with the x-ray diffraction experimental data of Besser et al.1 Using a time-dependent property for Al helps match the data better than a time-independent property. Theoretical stress-temperature curves were also obtained for the longitudinal, transverse, and normal stress components in aluminum lines for line-widths ranging from 0.5 to 10 µm. The hysteresis of the stress-temperature curve of Al gets less as the line-width gets smaller. All stress components in the Al line change substantially with linewidth for the same oxide thickness.
Electromigration Failure of Narrow Al Alloy Conductors Containing Stress - Voids
Authors: Oates A. S. , Lloyd J. R.
Published: April 2011

Electromigration and stress - induced voiding are two of the most important metallization failure mechanisms for integrated circuits. These mechanisms are not independent since stress voiding may affect electromigration. In this paper we examine the impact of stress voiding on electromigration failure of narrow Al alloy stripes, and show that the major effects of stress voiding are significant reductions in failure times, and a non-Arrenhius temperature dependence of the lifetime. We propose a model to explain these effects based on the formation of flux divergences at pre-existing voids due to stress gradients.
Segregation of Copper in Dilute Aluminum - Copper Alloys for Interconnects
Authors: Smith D.A. , Small M.B. , Garratt-Reed A.J.
Published: April 2011

It is well known that the resistance to electromigration of aluminum-based interconnects is enhanced by alloying with copper. The mechanism is thought to involve the segregation of copper to the grain boundaries. The copper concentration at grain boundaries has been measured in well annealed alloys, with the compositions A1-0.5wt% Cu and AI-2wt%Cu using a VG HB5 STEM. The grain structure was stabilized by an anneal at 673K for one hour and the grain boundaries were loaded with copper by an anneal for 90 hours at 503K. It was found that the copper concentration varied from boundary to boundary. With the assumption that the copper was concentrated in a single layer the saturation concentration of copper was found to be in the range 0.025 to 0.25. This corresponds to an enhancement of the copper concentration relative to that in the grain interiors by a factor in the range between 3 and 30. The higher value approaches the copper concentration which would correspond to a monolayer of theta phase. Extensive surface segregation, amounting to a monolayer equivalent was also detected.
Passivation Design / Electromigration Performance Correlations in Layered Aluminum Metallizations
Authors: Graas Carole D. , Ting Larry L.
Published: April 2011

The study presented in this paper establishes correlations between key passivation morphological characteristics and metal electromigration performance. This was done by using test structures including extrusion monitors which provided narrow gaps along both sides of the test stripes. The parameters studied were: (1) the nature of the gap filling (oxide process and step coverage), (2) local oxide planarization, and (3) oxide thickness above the leads tested. Failure analysis was conducted by SEM cross-sections of cracked passivation areas. We observed that in the case of aluminum metallizations capped by a thin anti-reflective coating (ARC) layer, failure occurred in all cases by aluminum extrusion from the top corners of the leads, and at 45 degree angles into the passivation. Ultimately, the lifetime was dependent on oxide thickness above the test leads rather than gap-filling characteristics.
Epitaxial Relationships and Electrical Properties of SrTiO3 Films on Various Thin -Fluoride/Si Structures
Authors: Moon B. K. , Ishiwara H.
Published: April 2011

Crystalline strontium titanate (SrTiO3:STO) films were grown on Si(111) and Si(100) substrates using thin SrF2 and CaF2 buffer layers by two-step growth method. In all cases, fluoride buffer layers were effective in growing STO films on Si substrates, which is probably due to that fluoride buffer layers have excellent crystallinity and they can prevent formation of amorphous SiO2 layers on Si substrates at the initial stage of the STO deposition. It was found from X-ray diffraction and pole-figure measurements that (110)-oriented STO crystallites with three different positions to the substrate were grown on Si(111) substrates for both SrF2 and CaF2 buffer layers. In constrast, (100)-oriented STO films with 12-fold symmetry were grown on a SrF2/Si(100), and mixed (110)- and (100)-oriented STO crystallites were grown on a CaF2/Si(100) structure. It was concluded from these results that better crystallinity of STO films can be obtained on the SrF2 buffer layer in case of Si(111) and on the CaF2 buffer layer in case of Si(100). It was also found from I-V and C-V analyses that the STO films have good insulating and dielectric characteristics. For a SrTiO3 film on SrF2/Si(111) structure, the best values of breakdown field (at l.μA/cm2), resistivity (at IMV/cm) and dielectric constant were 2.3MV/cm, 8.2 × 1012 Ωcm and 72, respectively.
Molecular Layer Epitaxy of Perovskite-Based Oxides by Laser MBE
Authors: Yoshimoto M. , Maeda T. , Gonda S. , Shimozono K. , Koinuma H. , Ishiyama O. , Shinohara M.
Published: April 2011

Molecular layer epitaxy and the topmost surface structure in laser MBE of perovskite and other related oxides were investigated by in situ RHEED, in situ angle-resolved XPS (ARXPS) and ex situ co-axial ISS (CAICISS) analyses. Two-dimensional epitaxial growths of SrTiO3 (001) and BaCuO2(001) on SrTiO3(001) substrate were achieved by optimizing the growth conditions. Periodicities of RHEED oscillation corresponded well to the growth of a repeating unit cell (molecular layer). ARXPS and CAICISS spectra revealed that (Sr-0) atomic plane came at the top of SrTiO3(001) film growing on SrTiO3 (001) substrate with (Ti-O) atomic plane on the top. This indicates the structural conversion of the topmost atomic layer from TiO2 to SrO occurred during the SrTiO3 homoepitaxial growth.
The Influence of Processing Parameters on the Development of Biaxially Aligned Zirconia Thin Films Deposited by Ion Beam Assisted Deposition
Authors: Sonnenberg Neville , Ressler Kevin G. , Mcintyre Paul C. , Cima Michael J.
Published: April 2011

Deposition of high quality superconducting thin films requires lattice-matched single crystal substrates. This greatly reduces the number of candidate materials to a few expensive substrates that are only available in small sizes. Inexpensive, low-dielectric constant amorphous or polycrystalline substrates would greatly enhance the feasibility of superconducting devices such as HTSC multichip modules. Deposition of HTSC films on aligned dielectric layers allows the use of amorphous and polycrystalline substrates in these structures. Biaxially aligned zirconia thin films have been deposited using ion beam assisted deposition (IBAD) on pyrex, quartz, and Hastelloy substrates. Deposition rate, substrate temperature, ion beam energy, and other processing parameters control the orientation of films deposited by ion beam assisted deposition. Biaxially aligned (200) oriented zirconia has been deposited by IBAD on all three substrates without active substrate heating. Biaxial alignment was not observed in films deposited at 400°C. Increased ion beam energy promotes polycrystalline nucleation at lower temperatures, which is important to the development of biaxial alignment. Other faster growing orientations begin to dominate as the temperature is increased. These results are consistent with a growth and extinction model.
Examination of Particles and Outgrowths on the Surface of Epitaxial Yba2Cu3O7 Thin Films
Authors: Norton M. Grant , Biggers Rand R. , Maartense I. , Moser E. K. , Brown Jeff L.
Published: April 2011

The surface morphology of Yba2Cu3O7 thin films formed on (001)-oriented LaAlO3 substrates by pulsed-laser deposition has been examined using electron and scanning probe microscopies. The observed surface features can be divided into two types: particles formed as a result of material (often molten) ejected from the target and outgrowths formed as a result of nucleation and growth processes on the substrate and/or the film surface. Where both types of surface feature occur on a particular film the outgrowths are always more numerous. The density of outgrowths is strongly related to the deposition parameters and, as a consequence, with the film growth mechanism.
MBE Growth of CoO and Fe3O4 films and CoO/Fe3O4 multilayers
Authors: Wolf R. M. , Veirman A. E. M. De , Sluis P. Van der , Zaag P. J. van der , Stegge J. B. F. aan de
Published: April 2011

The growth of CoO and Fe3O4 single crystalline layers has been studied. CoO and Fe3O4 can be grown under similar growth conditions in a small pressure window. (001) oriented CoO/Fe3O4 multilayers were grown on MgO and MgAl2O4 substrates. On MgO substrates coherent heteroepitaxial growth was observed in the multilayers resulting in high crystalline quality multilayer structures with 0.018° FWHM of the multilayer rocking curve. The mean interface roughness is 4Å as determined by low angle X-ray reflection measurements and HRTEM observations.
Growth of Epitaxial KNbO3 Thin Films
Authors: Graettinger Thomas M. , Morris P. A. , Roshko A. , Kingon A. I. , Auciello O. , Lichtenwalner D. J. , Chow A. F.
Published: April 2011

KNbO3 possesses high nonlinear optical coefficients making it a promising material for frequency conversion of infrared light into the visible wavelength range using integrated optical devices. While epitaxial thin films of KNbO3 have previously been grown using ion beam sputtering, defects (i.e. grain boundaries, domains, surface roughness) in these films resulted in high optical losses and no measurable in-plane birefringence. Previous films were grown on MgO substrates, which have a >4% lattice mismatch with KNbO3. In the work reported here, we have grown films on MgO, MgA12O4, NdGaO3, and KTaO3 to investigate the role of lattice mismatch on the resulting film quality. Films have also been grown with and without oxygen ion assistance. The orientations, morphologies, and defects in the films were examined using x-ray diffraction and AFM to determine their relationships to the growth conditions and substrate lattice mismatch.
Epitaxial Growth of (110) KnbO3 Films on (100) MgO Substrates via Sol-Gel Processing
Authors: Derderian Garo J. , Barrie James D. , Aitchison Kenneth A. , Mecartney Martha L.
Published: April 2011

Epitaxial, single phase (110) KnbO3 films were grown on (100) MgO substrates using a sol-gel process employing ethoxide precursors in methanol. The degree of epitaxy was dependent on both the annealing temperature and the amount of potassium in the film. Excess potassium in the sol-gel solution (K/Nb = 1.2) was necessary to produce single phase films. An amorphous or polycrystalline MgO interfacial layer was observed in some films, postulated to have developed after nucleation of KnbO3 and due to a highly defective surface layer.
The MBE Growth and Optical Quality of BaTiO3 and SrTiO3Thin Films on MgO
Authors: McKee R. A. , Walker F. J. , Specht E. D. , Alexander K. B.
Published: April 2011

High quality epitaxial BaTiO3 and SrTiO3 have been grown on MgO, stabilized at a one unit cell height, and grown to film thicknesses of 0.5 - 0.7 μm. These relatively thick films remain adherent when thermally cycled between growth temperatures and room temperature, are crack free with high optical quality, and have both in-plane and out-of-plane X-ray rocking curves of 0.3–0.5°. These films have been grown using molecular beam epitaxy (MBE) methods starting with the TiO2 layer of the perovskite structure. The TiO2-Iayer/MgO interface uniquely satisfies electrostatic requirements for perovskite heteroepitaxy and provides the template structure that leads to the high quality films that are obtained. Wavelength dependence of optical loss has been characterized between 475 nm and 705 nm with loss coefficients < 1dB/cm being obtained at the He-Ne wavelength.
The Influence of RTA Heating Rate on the TiSi2 and Si - TiSi2 Interface Roughness
Authors: Lagana A. A. M. , Valente M. C. , Pedrine A. G. , Filho J. C. de Souza , Stuart J. W. , Santiago-Avilés J. J.
Published: April 2011

In TiSi2 metallized devices, the second distribution of leakage current (I>lμA) is caused by the Si/TiSi2 interface roughness. In this work, 40gm thick Ti films are sputtered onto Si waters. RTA was done in N2 atmosphere. Heating rates of 0, 0.5, 1, 5, and 100°C S−-1 are examined. Samples are characterized by AFM, RBS, XRD and laser light scattering methods. The parameters related to roughness are heating rate sensitivity and oxygen contamination which decreases the roughness on the interface.
Rapid Thermal Oxidation for Passivation of Porous Silicon
Authors: BÁrsony I. , Klappe J.G.E. , Vázsonyi É. , Lohner T. , Fried M.
Published: April 2011

Chemical and mechanical stability of porous silicon layers (PSL) is the prerequisite of any active (luminescent) or passive (e.g. porous substrate) integrated applications. In this work X-ray diffraction (XRD) was used to analyze quantitatively the strain distribution obtained in different morphology PSL that were prepared on (100) p and p+Si substrates. Tetragonal lattice constant distortion can be as high as 1.4% in highly porous “as-prepared” samples. Incoherent optical heating RTO is governed by the absorption in the oxidized specimen. PSL show vertical inhomogeneity according to interpretation of spectroscopic ellipsometry (SE) data. Oxygen incorporation during RTO is controlled by specific surface (in p+ proportional, in p inversely proportional with porosity), while the developing compressive stress depends on pore size, and decreases with porosity in both morphologies.
Decomposition of CO2 to Carbon Using Oxygen-Deficient Zn(II)-Bearing Ferrite
Authors: Tabata M. , Kato H. , Tsuji M. , Tamaura Y.
Published: April 2011

Oxygen-deficient Zn(II)-bearing ferrites (ZnxFe3-xO4-δ, 0≤×≤l, δ>0) have been synthesized and studied for their reactivity in the decomposition of CO2 to carbon at 300 °C. They were prepared by reducing Zn(II)-bearing ferrites with H2 gas at 300 °C. The oxygen-deficient Zn(II)-bearing ferrites consisted of a single phase of a spinel-type structure which was oxygendeficient compared with their stoichiometric compositions. Their lattice constants were larger than those of the corresponding stoichiometric spinels. Decomposition of CO2 to carbon proceeded accompanied by an oxidation of the oxygen-deficient Zn(II)-bearing ferrite. The amount of carbon deposited on the ferrite decreased when Zn content in Zn(II)-bearing ferrite increased. The decrease in the amount of carbon deposited is due to changes in the electron conductivity according to the Zn content in Zn(II)-bearing ferrite. These changes contribute to their reactivity for decomposition of CO2 to carbon.
Methanation of CO2 on Ni(II)-Bearing Ferrite (NixFe3-xO4-δ; x=0.39, δ>0) in Flow System
Authors: Kato H. , Tabata M. , Tsuji M. , Tamaura Y.
Published: April 2011

The methanation of CO2 has been studied by using reduced Ni(II)-bearing ferrite (NixFe3-xO4-δ; x=0.39, δ=0.1∼0.2) in an H2/CO2 mixed gas flow system. A yield of 31% and a high selectivity of 89% were obtained in the methanation for 6h using the H2-reduced Ni(II)-bearing ferrite. The X-ray diffractometry showed that the reduced Ni(II)-bearing ferrite during the methanation retained the spinel-type structure whose lattice constant increased from 0.8375 to 0.8379 nm. The chemical analysis corroborated an increase in the mole ratio of Fe2+/Fetotal in the Ni(II)-bearing ferrite. These results suggest that oxygen-deficient sites were formed in the spinel structure of the reduced Ni(II)-bearing ferrite. It has been found from the analysis using the Langmuir isotherm for dissociative adsorption that CO2 is adsorbed onto oxygen-deficient sites to be decomposed to an elemental carbon and two oxygen-deficient ions. The methanation of CO2 is considered to proceed owing to the oxygen deficient sites. It is considered that the methanation consists of three elementary reaction steps: 1) Formation of oxygen-deficient sites by H2-reduction, 2) Reduction of CO2 to carbon and Incorporation of two oxygen ions of the CO2 into the oxygen-deficient sites, and 3) Hydrogenation of the deposited carbon to CH4.
Surface Characterization of Carbon-Bearing Magnetite (CBM) and Carbon-Bearing Ni(II)-Ferrite (CBNF)
Authors: Sano T. , Akanuma K. , Tsuji M. , Tamaura Y.
Published: April 2011

Oxygen-deficient magnetite (ODM; Fe3O4-δ, δ>0) synthesized by reduction of magnetite with H2 at 300°C decomposed CO2 to carbon with an efficiency of nearly 100% at 300°C. In this reaction, two oxygen ions of the CO2 were incorporated into the spinel structure of ODM and carbon was deposited on the surface of ODM with zero valence to form visible particles. The particles of carbon separated from ODM were studied by Raman, energy-dispersive X-ray and wave-dispersive X-ray spectroscopies. The carbon which had been deposited on the ODM was found to be a mixture of graphite and amorphous carbon in at least two levels of crystallization. X-ray photoelectron spectroscopy and X-ray diffraction patterns of the carbon-bearing magnetite (CBM) showed no indication of carbide (Fe3C) or metallic iron (α-Fe) phase formation. In the C 1s XPS spectra of the CBM, no peaks were observed which could be assigned to CO2 or CO. X-ray diffractometry, chemical analysis and TG-MS measurement showed that the carbon-bearing Ni(II)-ferrite (CBNF) (Ni(II)/Fetotal = 0.15) synthesized by the carbon deposition reaction from CO2 with the H2-reduced Ni(II)-ferrite was represented by (Ni0.28Fe2.72O4.00)1-δ (Ni2+06.9Fe2+2.31O3.00)δCτ (δ= 0.27, τ= 0.17). The carbon of the CBNF gave the CIOlayer-like oxide containing some Ni2+ ions.
Recycled Rubber in Cement Composites
Authors: Raghavan D. , Tratt K. , Wool R. P.
Published: April 2011

Disposal of 200 million waste tires in the US each year has become a major problem. An environmentally sound innovative technology of recycling rubber in cement matrix was examined. Using silane coupling agent the rubber was bonded to the hydrating cement making a lighter composite, which absorbed more energy than ordinary Portland cement. The bonding information was obtained by peel strength analysis. SEM was used to understand the mode of fracture in pure cement paste, cement bonded rubber composite and rubber filled cement paste. It was found that cracks propagate through the rubber particle in rubber bonded cement composite while in unbonded rubber cement mix, the cracks propagate around the interface. The density and shrinkage measurements are also discussed.
Recycling of Plastic and Rubber Tire Waste in Asphalt Pavements
Authors: Morrison Geoffrey R. , Lee Nolan K. , Hesp Simon A.M.
Published: April 2011

This paper discusses some important issues related to the use of recycled thermoplastics and rubber tire waste in asphalt binders for hot-mix pavements. Both high temperature rheological and low temperature fracture studies are presented on recycled polyethylene, devulcanized and crumb rubber-modified asphalt binders. The results are compared to unmodified and commercially available modified binders. This research is especially timely in light of the U.S. Intermodal Surface Transportation Efficiency Act of 1991, Section 1038 which, starting in 1995, will force state and local governments to use significant amounts of recycled rubber tire or plastic waste in federally funded highway projects.

High temperature rheological measurements of the loss modulus, loss tangent and complex modulus show a significant improvement when only small quantities of crumb rubber, devulcanized crumb rubber or waste polyethylene are added to the asphalt binders.

The low temperature fracture performance of the modified asphalts is greatly influenced by the interfacial strength between the dispersed and continuous phase. The fracture toughness increases dramatically, only when low molecular weight polymers are grafted in-situ onto the rubber and polymer dispersed phases in order to strengthen the interface. This points to a crack-pinning mechanism as being responsible for the dramatic increase in fracture toughness that is observed in this work. Single phase, devulcanized crumb rubber-asphalt systems perform quite poorly at low temperatures.
Fundamentals of Particle Flocculation and Removal From Water
Authors: Spicer Patrick T. , Pratsinis Sotiris E.
Published: April 2011

The flocculation of polystyrene particles with aluminum sulfate or alum (Al2 (SO4)3) by turbulent shear was studied as a function of the applied shear rates (63–129 s−1) and flocculant concentrations (11 and 32 mg/L) in a stirred tank. Increasing the shear rate increased the floc growth rate but decreased the maximum attainable floc size. Increasing the concentration of alum increased the floc growth rate and the maximum floc size. A steady state between floc growth and breakage was attained after which the floc size distribution no longer changed. The normalized steady state size distributions allowed evaluation of the relative contributions of shear rate and flocculant concentration to the performance of the process.
Structural Development In Silica Systems
Authors: Dokter W.H. , Beden T.P.M. , van Garderen H.F. , van Santen R.A.
Published: April 2011

Results obtained with small angle neutron and X-ray scattering will be
presented of systems with various silica concentrations. Silica gels with
low silica concentration exhibit uniform mass fractal behaviour and after
prolonged aging, dual mass fractal behaviour. A zeolite (silicalite)
synthesis precursor gel with a high silica concentration was also
investigated and was found to exhibit surface fractal behaviour. A model is
presented, explaining the occurrence of dual fractality after prolonged
aging. The change-over from mass fractal behaviour to surface fractal
behaviour is explained, supported by scattering spectra calculated from
simulated aggregate structures.
Formation, Structure, and Material Properties From the Reaction
Product of M(OCHMe2)4 (M=Ti, Zr) And
HOAc
Authors: Alam Todd M. , Boyle Timothy J. , Buchheit Catherine D. , Schwartz Robert W. , Ziller Joseph W.
Published: April 2011

In attempt to ultimately control the characteristics of the PZT films, we
have decided to investigate some of the basic chemistry associated with
these solutions. Frequently, these solutions have been generated from Group
IV metal alkoxides in acetic acid (HOAc). Therefore, studies of the
simple reactivity between
M(OCHMe2)4 (M = Ti, Zr) and HOAc have been
undertaken. These reactions were monitored by 1H, 13C,
17O NMR, FT-IR, TGA/DTA, and single crystal X‐ray studies.
Films were produced from spin‐coat deposition of crystalline material (from
the titanium reaction) in toluene and aged solutions as well.
Titania-Alumina Composites
Authors: Luo Shengcheng , Gui Unli'n , Fu Xianzhi , Tang Youqi
Published: April 2011

Titania-alumina composites were carried out by various methods. The
composite prepared by mixed gelation method showed the merits of both
γ-Al2O3 and TiO2 (anatase), and it
behaved much better than the γ-Al2O3 alone as the
carrier of HDS catalyst or H2S adsorbent. Another representative composite
was prepared by sol-gel method. The hydroxide of aluminium alkoxide was
peptised directly with TiCl4 to form
TiO2-Al2O3 composite sol, and then the
composite membrane without support was obtained. The sizes of primary
particles were around 5nm as characterised by TEM.
Nano-Crystalline Powders and Suspensions Generated Using A
Flow-Through Hydrothermal Process, Part II: Applications
Authors: Darab John G. , Buehler M. F. , Linehan J. C. , Matson D. W.
Published: April 2011

Ultra-fine, nano-crystalline six-line ferrihydrite
(5Fe2O3-9H2O) and cubic zirconia (ZrÜ2)
powders have been produced using the Rapid Thermal Decomposition of
precursors in Solution (RTDS) technology. Nano-crystalline RTDS six-line
ferrihydrite powder used as an in situ precursor for
first-stage direct coal liquefaction catalysts increased the liquefied
products from Blind Canyon Seam coal by 22% absolute over thermal background
at 350°C. Initial sintering studies performed on nano-crystalline RTDS
ZrO2 powder have also been presented and compared to
predictions made from theories derived for micro-crystalline powders.
Engineering of Porosity in Amorphous Materials. Plasma Oxidation
of Hydrocarbon Templates in Polysilsesquioxanes*
Authors: Loy Douglas A. , Buss Richard J. , Assink Roger A. , Shea Kenneth J. , Oviatt Henry
Published: April 2011

Arylene- and alkylene-bridged polysilsesquioxanes were prepared by sol-gel
processing of bis(triethoxysilyl)-arylene monomers 1-4, and alkylene
monomers 5-9. The arylene polysilsesquioxanes were porous materials with
surface areas as high as 830 m2/g (BET). Treatment with an
inductively coupled oxygen plasma resulted in the near quantitative removal
of the arylene bridging groups and a coarsening of the pore structure. Solid
state 29Si NMR was used to confirm the conversion of the
sesquioxane silicons (T) to silica (Q). The alkylene-bridged
polysilsesquioxanes were non-porous. Oxygen plasma treatment afforded silica
gels with mesoporosity. The porosity in the silica gels appears to arise
entirely from the oxidation of the alkylene spacers.
The Reactivity of C60 in Fuming Sulfuric and Chlorosulfonic Acids
Authors: Miller G.P. , Buretea M.A. , Swirczewski J.W. , McConnachie J.M.
Published: April 2011

C60 is sultonated in fuming sulfuric acid and chlorinated in chlorosulfonic acid. Both reactions involve initial oxidation of C60 followed by in situ trapping of electrophilic C60 cation.
Fi-Stm Study of Fullerenes
Authors: Hashizume Tomihiro , Sakurai T.
Published: April 2011

Adsorption of C60, C70, C60(x)C70(1-x) and Sc2C84 on the Cu(111)1×1 and Ag(l11)1×1 surfaces has been investigated by field ion-scanning tunneling microscopy (FI-STM). On the Cu(111) and Ag(111) surfaces, the fullerene molecules are mobile on the terrace at room temperature and segregate to the steps to form linear chains then two-dimensional islands with a close-packed configuration. Upon monolayer adsorption, highly ordered 4×4 commensurate phases form in the case of the C60, C70 and C60(x)C70(1−x) adsorption on the Cu(111) surface, while close-packed hexagonal multiple phases, with nearest-neighbour distance equal to that of the bulk phase, form in the case of the C60 and Sc2C84 adsorption on the Ag(111) surface. These observations imply the competition between the adsorbate-adsorbate and adsorbate-substrate interactions. The intramolecular structures observed in the STM images of the C60 and C70 molecules in the Cu(111)-4×4 phases are analyzed to determine the adsorption geometry and are interpreted as the local density of the states of the C60 and C70 molecules.
Electrical Properties of C60 and Its Partially Decomposed Thin Films Fabricated by Vacuum Evaporation and Ion Plating Methods
Authors: Asakawa T. , Sasaki M. , Yoshimoto M. , Gonda S. , Shiraishi T. , Koinuma H.
Published: April 2011

Thin films were prepared, from C60 powders by vacuum evaporation and rf-plasma excited ion plating methods. The film structures ranged from fcc-polycrystal C60film to amorphous C60 film and to amorphous carbon films containing varying amounts of C60 molecules depending on the preparation method and conditions. Electrical conductivity of these films was found so sensitive to air that highly reproducible data were obtained only when the measurement was done by in-situ high vacuum conditions. The Co films deposited at 120°C on fused silica substrates by vacuum evaporation were amorphous and they had conductivities three orders of magnitude lower than those of fcc-polycrystal C60 films deposited on cleaved NaCl(100) substrates under the same conditions. The conductivities of both amorphous and fcc-polycrystal C60 films decreased drastically when these films were exposed to air. Partially decomposed C60 ion-plating films showed conductivities close to those of the air-exposed amorphous and fcc-polycrystal C60 films.