bluuebunny/crossref_metadata_2025 huggingface dataset:
Anisotropic Charge Transport in Organic Single Crystals Based on Dipolar Molecules
Authors: Fraboni Beatrice , Di Pietro Riccardo , Castaldini Antonio , Cavallini Anna , Fraleoni Alessandro , Setti Leonardo , Mencarelli Ivan , Femoni Cristina
Published: April 2011

We studied the anisotropic charge transport properties of solution-grown organic single crystals based on a dipolar molecule 4HCB (4-hydroxy-cyanobenzene) by electrical transport measurements, current-voltage and space charge limited current (SCLC), and by X-ray diffraction analyses.

Optical excitation differently affects the flow of charge carriers along the two main planar crystal axis, altering the charge transport anisotropy induced by the molecular π-orbitals stacking. We attribute this behaviour to the presence of an intrinsic molecular dipole and to its different orientation within the crystal lattice. The anisotropy of transport along the three crystallographic directions has been assessed by electrical characterization and correlated to the crystal molecular packing as determined by X-ray analyses.
Synthesis of Fullerene by Spark Plasma Sintering and Thermomechanical Transformation of Fullerene Into Diamond on Fe-C Composites
Authors: Robles-Hernández Francisco C. , Calderon H. A.
Published: April 2011

In this work, results are presented regarding the characterization of nanostructured Fe matrix composites reinforced with fullerene. The fullerene is a mix of 15 wt.%C60, 5 wt.%C70 and 80 wt.% soot that is the product of the primary synthesis of C60. The composite has been produced by means of mechanical alloying and sintered by Spark Plasma Sintering (SPS). The characterization methods include XRD, SEM and TEM. The C60 and C70 withstand mechanical alloying, SPS, and thermomechanical processing and act as a control agent during mechanical alloying. The results show that the mechanically alloyed and SPS product is a nanostructured composite. A larger amount of C60 is found in the sintered composite than in the original fullerene mix, which is attributed to an in-situ synthesis of C60 during the SPS process. The synthesis of C60 is presumably assisted by the catalytic nature of Fe and the electric field generated during the SPS process. In order to study the effect of high temperature, high strain, high heating and cooling rates on C60, the composite is subjected to a thermomechanical processing; demonstrating that some of the C60 resists the above described environment and some of it partially transforms into diamond.
Atomic-Resolution Chemical Analysis at 100 Kv in the Scanning Transmission Electron Microscope
Authors: Browning N. D. , Chisholm M. F. , Pennycook S. J.
Published: April 2011

In a 100 kV VG HB501 UX dedicated scanning transmission electron microscope, the 2.2 Å probe size allows the atomic structure to be observed with compositional sensitivity in the Z-contrast image. As this image requires only the high-angle scattering, it can be used to position the probe for simultaneous electron energy loss spectroscopy. Energy loss signals in the core loss region of the spectrum (>300 eV) are sufficiently localized that the spatial resolution is limited only by the probe. The electronic structure of the material at the interface can thus be determined on the same scale as the changes in composition, and atomic structure can be observed in the image, allowing the structure and chemical bonding at interfaces and boundaries to be characterized at the atomic level.
Nanoanalytical Characterization of Granular Ag-Fe Films with Giant Magnetoresistance
Authors: Liu J. , Li Z. G. , Wan H. , Tsoukatos A. , Hadjipanayis G. C.
Published: April 2011

Dedicated scanning transmission electron microscopy and associated techniques were used to extract microstructural and compositional information about granular Ag-Fe magnetic films produced by sputtering. Nanometer-resolution compositional analysis by energy dispersive X-ray spectroscopy (EDS), showed that Ag-Fe granular films consist of two separate phases. It has been found that nanometer size Fe particles are separated by small as well as large Ag particles. Nanodiffraction patterns showed that a large proportion of small Ag particles have an icosahedral shape and that the Fe particles are highly disordered. The nanostructure of the Ag-Fe system and its relation to the giant magnetoresistance of granular films are discussed.
Scanning Tunneling Microscopy (Stm) and Scanning Force Microscopy (Sfm) of Liquid Crystals and Polymers
Authors: Jandt K. D. , Mcmaster T. J. , Mcdonnell D. G. , Blackmore J. M. , Miles M. J.
Published: April 2011

Recent progress in the field of liquid crystal materials and oriented polymers studied by nearfield scanned probe microscopies (SPM) is presented here. The investigations were focused on scanning tunneling microscopy (STM) results of antiferroelectric liquid crystalline molecules observed at different elevated temperatures corresponding to different bulk mesophases of the material, and on surface morphological studies of a liquid crystalline polymer by scanning force microscopy (SFM). In the field of oriented thermoplastic polymers, SFM images of the morphology and molecular packing in the outermost surface of poly(butene-1) films are presented.
Surface Morphology of Diamond Thin Films Using Photoinduced Scanning Tunneling Microscopy
Authors: Carroll D.L. , Mercer T. , Liang Y. , Dinardo N.J. , Bonnell D. A.
Published: April 2011

Photo-induced conduction in thin insulating films of diamond was used to obtain STM images indicative of film morphology. UV light was used to generate carriers in the conduction band of diamond films grown on Si (111). Tunneling currents could only be established when the tunnel junction was illuminated. Without the light, no current was measured even with the tip in contact with the surface. Two types of films were studied. A CVD grown diamond film with nitrogen impurities and a diamond-like film grown by laser ablation of graphite. Topological detail was compared to that obtained with an AFM. The correspondence between AFM and photoinduced STM images suggests that the STM images are indicative of film morphology.
Imaging The Atomic-Scale Structure of Molybdenum and Vanadium Oxides by Scanning Tunneling Microscopy
Authors: Rohrer Gregory S. , Lu Weier , Smith Richard L.
Published: April 2011

Single crystals of Na0.003V2O5 and Mo18O52 were grown by chemical vapor transport and cleaved surfaces were imaged in ultrahigh vacuum using scanning tunneling microscopy (STM). Because the Mo18O52 (100) and Na0.003V2O5 (010) surfaces of these layered materials have a bulk terminated structure, the atomic-scale contrast in constant current images can be directly compared to components of the bulk structure. Among the structural features identified in the STM images are the surface/crystallographic shear plane intersections, the different MoOx coordination polyhedra on the Mo18O52 (100) surface, and the VO5 square pyramids that make up the Na0.003V2O5 (010) surface. In each of these cases, it was found that the atoms closest to the tip dominate the image contrast.
Characterization of InP/GaInAs Nanometer Sized Columns Produced by Aerosol Deposition and Plasma Etching
Authors: Maximov I. , Deppert K. , Montelius L. , Samuelson L. , Gray S. , Johansson M. , Hansson H.-C. , Wiedensohler A.
Published: April 2011

We present a technique for the fabrication of InP nano-columns and GaInAs/InP quantum-dots based on the use of sintered aerosol Ag particles as a mask in an electron cyclotron resonance etching process. The sintered particles have much more regular shapes than the unsintered ones used in previous studies and are more resistant to the etching environment, which results in the formation of more regular and reproducible structures. For example, we have been able to produce columns 100 nm in height which have an average diameter of 24 nm and a density of 109 cm−2.We have investigated the shape of the etched columns as a function of the Ag particles’ size, and characterized their electrical and optical properties using a combination of scanning electron microscopy, scanning tunneling microscopy, atomic force microscopy, and photoluminescence.
Incoherent Imaging by Z-Contrast Stem: Towards 1Å Resolution
Authors: Pennycook S. J. , Jesson D. E. , Mcgibbon A. J.
Published: April 2011

By averaging phase correlations between scattered electrons a high angle detector in the scanning transmission electron microscope (STEM) can provide an incoherent, Z-contrast image at atomic resolution. Phase coherence is effectively destroyed through a combination of detector geometry (transverse incoherence) and phonon scattering (longitudinal incoherence). Besides having a higher intrinsic resolution, incoherent imaging offers the possibility of robust reconstruction to higher resolutions, provided that some lower frequency information is present in the image. This should have value for complex materials and regions of complex atomic arrangements such as grain boundaries. Direct resolution of the GaAs sublattice with a 300kV is demonstrated.
Epitaxial Growth of Two-Dimensional Dichalcogenides and Modification of Their Surfaces with Scanning Probe Microscopes
Authors: Parkinson Bruce A.
Published: April 2011

Methods for epitaxial growth of two dimensional materials are described. The lack of interlayer bonding in these materials allows for epitaxial growth with large lattice mismatches. Growth of MoSe2 on MoS2 (a 5% mismatch) or on SnS2 (10% mismatch) can be demonstrated. Scanning tunneling microscopy (STM) revealed remarkable structures in the epilayer as a result of the large mismatches. A technique using the STM or atomic force microscope (AFM) to selectively remove single molecular layers from the surface of layered materials is also described. The combination of these two technologies may result in the ability to produce nanoscale devices exhibiting quantum size effects.
Comparison between SiO2 Films and Nitridated Oxides in N2O Ambient in Terms of Bulk/Interface Trapping Properties
Authors: Papadas Constantin , Mortini Patrick
Published: April 2011

The necessity of employing nitridation process in advanced technologies will be underlined. The different technological alternatives for preparing oxinitride layers will be traced back, followed by a review of the methods currently available for assessing the degradation features of the Si/SiO2 system. Furthermore, comparison between pure SiO2 layers and nitridated films in N2O ambient will be conducted in terms of bulk/interface trapping properties and the obtained physical degradation data will be correlated with classical reliability results. Large emphasis will be given on the trapping properties of tunnel oxides used in non—volatile memory arrays and different technological alternatives will be exploited (i.e. Rapid Thermal Nitridation, Furnace Nitridation). In addition, a similar analysis will be carried out for gate oxides. Finally, some guidelines concerning the optimum selection of the furnace nitridation conditions will be given.
Microstructural Characterization of Copper Thin Films on Metallic Underlayers
Authors: Zielinski E. M. , Vinci R. P. , Bravman J. C.
Published: April 2011

Grain size distribution and texture of thin films of sputtered copper were characterized as a function of underlayer choice, deposition temperature and annealing temperature. For Cu deposited on Ta at room temperature and annealed at 100, 150, 200 and 250 °C, abnormal growth of the (100) orientation was observed for annealing temperatures above 150 °C, resulting in a bimodal grain size distribution. This orientation was also seen to grow abnormally for films deposited and annealed under identical conditions, but with a W underlayer. (100) growth for this case was observed at annealing temperatures as low as 100 °C. Abnormal grain growth was suppressed for Cu deposited on Ta at 150 °C and annealed to 250 °C. A bimodal grain size distribution was observed in a similar sample deposited on W under identical conditions, however, the abnormally growing orientation for this case was observed to be the (111) orientation, not the (100) orientation.
Dislocation Climb in the Electron Wind
Authors: Suo Z.
Published: April 2011

When a current flows in a conductor, the electron wind causes atoms to diffuse. This paper considers the consequences of such diffusion along dislocation cores. A dislocation climbing in a crystal is viewed as a non-equilibrium thermodynamic system to define the force that drives selfdiffusion along the core. Not only is a dislocation a mass-transport pipe, it also climbs and generates more dislocations—all in the electron wind. A prismatic loop moves like a rigid disk, as atoms electro-migrate along the core from one edge of the loop to the other. Each loop is therefore a mass carrier responding to an electric current. Interstitial and vacancy loops can be simultaneously generated and subsequently climb in the opposite directions. The process transports mass in single crystal or bamboo-like interconnects at moderate temperatures.
Critical Review of 1-Particle Models in Electromigration Resistance Change Modeling
Authors: Niehof J. , Graaff H.C. de , Mouthaan A.J. , Verwey J.F.
Published: April 2011

An investigation is made into the capability of one-particle models in modeling electromigration-induced resistance changes. Analytically obtained solutions to the model equations are used to gain more insight into the vacancy distribution as a result of the applied boundary conditions. These solutions are then used to determine the resistance change modeling capabilities of three types of one-particle models.
The Edge Delamination Test: Measuring the Critical Adhesion Energy of Thin-Film Coatings, Part II: Mode Mixity & Application
Authors: Shaffer Edward O. , Sikorski Scott A. , McGarry Frederick J.
Published: April 2011

The edge delamination test (EDT) is being developed to measure the critical energy required to cause a thin film, under biaxial tensile stress, to debond from a rigid substrate[1]. The test uses circular features etched through biaxially stressed films adhered to a rigid substrate. If the stress is large enough, a stable debond ring grows radially about the feature. We use a finite element analysis to model the test, solving for the applied strain energy release rate as a function of crack length, feature hole radius and other geometrical parameters. The model identifies both mode I and mode II components of the strain energy release rate, and agrees with previous analytical solutions for the total debond energy. However, the model predicts, with a very refined mesh at the crack tip, the fracture process is pure mode I. To explore this result, critical strain energy release rates from the EDT and the island blister test (IBT) are compared. This agreement supports the model prediction that the failure process in the EDT is modeI peeling.
Water Adsorption at Polymer/Silicon Wafer Interfaces
Authors: Wu Wen-Li , Kent Michael S.
Published: April 2011

Neutron reflectivity (NR) was applied to measure the concentration of water at the buried interfaces between polymer and silicon single crystal wafers. In the polyimide samplesexcess water was discovered within 30 Å of the silicon/polymer interface,where the water concentration reached 17% (by volume) for the samples without a couplingagent and 12% for the ones with coupling agent. Beyond the interface, the water concentration was measured at 2-3%, which is typical of bulk polyimide. Excess water was alsofound at the silicon/epoxy interface; more than 30% water was found within 150Å of the interface in the samples with their interface precoated with a coupling agent.The equilibrium moisture content in bulk epoxy used in this study is about 6%. The aboveresults demonstrate conclusively the unique power of NR in determining water concentration near a buried interface, and provide the first quantitative evidence for a water concentration profile which peaks in the interface region.
Long-Term Study on the Optical Performance of Ion Implanted PMMA Under the Influence of Different Media
Authors: Kallweit R. , Roll U. , Kuppe J. , Strack H.
Published: April 2011

To be able to implement light-sensitive properties of ionimplanted PMMA in optical devices, it is first necessary to investigate the optical stability of the implanted layers. For this purpose, PMMA samples were implanted with nitrogen using doses from 7×1013/cm 2 to 5×1015/cm2 as well as energies from 100 keV to 380 keV. Subsequently these samples were exposed to dry media such as H2, 02, CO2, N2, Ar as well as to dry and humid atmosphere. In a further investigation, the optical stability was examined under the influence of different wavelength ranges. The changes resulting in these layers were ascertained over various periods (maximum of 5 years) by ellipsometric measurement of the refractive indices and, in parallel, the chemical modification of the surface was examined by means of XPS. If any changes were caused by the media, they consisted basically in a decrease of the index values and of the original concentrations on CH— and COH—groups generated by the bombardment— i.e. in a recombination of molecular chains. In correlation to the chemical modification of the surface, the refractive index partly changed drastically.
Adhesion Measurements of Thin Films by Several Methods
Authors: Kinbara Akira , Banno Tatsuya , Kondo Ichiharu , Takenaka Osamu
Published: April 2011

Adhesion of thin films to solid substrates has been measured by various methods. In addition to the traditional and the conventional methods, a novel method has been proposed. The adhesion is expressed by various units depending on the measuring method. Obtained values by typical or well known methods such as scratch, peel and pull method are expressed in terms of N, N/m and N/m2, respectively. Relation among these quantities was discussed. The interface structure between the films and the substrates was investigated by TEM, ED, EDS, etc. and was related to the adhesion. Particular attention was paid to the ion bombardment effect of the substrate on the adhesion.
Epitaxial Relationships of the a-Axis Oriented YBa2Cu3O7-x Thin Films on the PrBa2Cu3O7-xTx Buffered SrTiO3(100) by two Step PLD
Authors: Sung Gun Yong , Suh Jeong Dae , Nahm Sahn
Published: April 2011

An a-axis oriented YBa2Cu3O7-x (YBCO) thin film exhibiting zero resistance at 83 K and critical current density of 7.9x103 A/cm2 at 62 K was obtained on an 180 nm - thick PrBa2Cu3 O7-xx(PBCO) buffered SrTiO3(100) substrate by two step pulsed laser deposition (PLD). The volume fraction of a-axis orientation and the crystallinity(Xmin) of the 150 nm-thick YBCO thin films were increased with increasing the thickness of PBCO buffer layer, which was varied friom 0 nm to 180 nm. It is concluded that the thickness of PBCO buffer layer is one of the important parameters to control the structural and superconducting properties of the a-axis oriented YBCO thin films using the PBCO buffer layers.
Epitaxial LaNiO3Interlayers for Ferroelectric Memory Structures
Authors: Klein J. D. , Yen A. , Clauson S. L.
Published: April 2011

LaNiO3 thin films were utilized as metallic contact layers in ferroelectric capacitors. The LaNiO3 films were probably epitaxial when deposited atop (100) LaAlO3 substrates. They exhibited metallic resistivity over a wide range of temperature and oxygen partial pressure. Subsequent deposition of PZT and LaNiO3 thin films atop LaNiO3/LaAlO3 allowed realization of parallel-plate ferroelectric capacitor structures. The suitability of such devices for nonvolatile memory applications was surveyed through pulsed voltage testing. The observed 1-second remanent polarization exceeded 18 μC/cm2. Long-term memory was demonstrated for up to sixteen hours. No decrease in remanent polarization was apparent after more than 109 switching cycles.
Thin Gate Oxide using a New RTO/-N Clusterable Reactor
Authors: Walk H. , Deutschmann L. , Martin F. , Masurel C. , Bauer A.
Published: April 2011

We present recent results obtained in thin gate oxides. These oxides are grown in a new clusterable RTP-system for 200mm diameter wafers. The main innovations of the reactor are dealing with the chamber geometry, gas distribution, double pyrometry and dedicated circular lamp array in order to insure an optimized light flow onto the wafer. Analytical and electrical data are given according to several oxidant and nitridant ratios (O2, N2O), The influence of different process parameters such as temperature, reaction time, N-content are discussed.
Temperature Measurement of Metallized Silicon Wafers by Infrared Transmission Using Single- and Double-Pass Geometries
Authors: Cullen C.W. , Sturm J.C.
Published: April 2011

The infrared transmission technique for the measurement of silicon wafer temperature has been extended to metallized wafers. For wafers with partial metal coverage, a single-pass method has been demonstrated from 200°C to 550°C. For wafers with blanket metal coverage, a novel double-pass infrared transmission technique is presented.
Silicon-Carbon Random Alloy Epitaxy on Silicon by Rapid Thermal Chemical Vapor Deposition
Authors: Mi J. , Letourneau P. , Ganière J.-D. , Gamhanou M. , Dutoit M. , Dubois C. , Dupuy J. C.
Published: April 2011

We have grown dilute Si-C epitaxial layers on Si (100) substrates at 800°C with a RTCVD process using SiH4 and C3H8. C atoms can be kinetically stabilized in interstitial sites in the Si lattice at relatively high temperatures if process parameters, such as growth rate and C/Si flux ratio, are optimized.
Recrystallization of Amorphous Silicon Using Rapid Thermal Processing, Laser Annealing and Furnace Heating
Authors: Viatella J. , Singi R.K. , Thiakur R.P.S. , Sandhu G. , Harkness S.D.
Published: April 2011

Recrystallization of amorphous silicon has been investigated using conventional furnace annealing, incoherent light-based rapid thermal annealing (RTA) and pulsed laser annealing using excimner laser (wavelength=248 nm, energy density = 0.1−0.6 J/cm2) at a pulse width of approximately 20 nanoseconds. The effects of annealing methods are characterized for grain growth and crystallized orientation using transmission electron microscopy (TEM) and X-ray diffraction analysis. The various recrystallization methods are compared based on the structural properties of the resulting film and optimized thermal budgets for each heating mechanism are discussed.
A Comparison of In-Situ Vapor/Gas Phase Cleaning with Conventional RCA based Wet Cleaning
Authors: Grant John M.
Published: April 2011

A comparison study of the effectiveness of in-situ vapor/gas phase cleaning versus conventional wet RCA based cleaning has been performed. The effectiveness of the cleans were compared using Surface Photo-Voltage (SPV) measurements of the quality of a 70Å gate dielectric. Dielectrics grown in oxygen by Rapid Thermal Oxidation (RTO) were measured using SPV. The vapor/gas phase cleaning processes studied have three steps corresponding to the baths in a conventional RCA-based clean. A clean using O2 was used to clean the organic contaminants normally cleaned in the SC-1 bath, a C12 based step corresponded to the SC-2 solution, and an HF/alcohol etch was used to remove the oxide normally etched using buffered HF. It was seen that temperature control of the cleaning chamber walls is necessary to insure reproducible processes and reasonable pump down times. Measurements by SPV indicate that dielectrics grown after vapor-gas phase cleaning have lower interface trap densities than oxides grown after an RCA-based clean.
Shallow-Junction Formation by Rapid Thermal Diffusion into Silicon from Doped Spin-on Glass Films
Authors: Ventura L. , Slaoui A. , Hartiti B. , Muller J. C. , Stuck R. , Siffert P.
Published: April 2011

Here we investigate the possibility to use rapid thermal annealed spin-on doped glass (SOG) films as a doping source as well as a surface passivation layer. The dilution of the SOG liquid source with methanol allows to control the oxide film thickness and the dopant concentration. The results show that the combination of spin-on film (after dilution) and RTP can produce shallow lightly doped emitters. Junction depths less than 0.2 µm and surface concentrations in the range 1−20 × 1019 cm−3 are obtained. Sheet resistances lower than 150 Ω/□ are easily reached. Moreover, the minority-carrier diffusion length is improved due to the gettering effect induced by phosphorus diffusion. The use of the remaining SOG oxide film as a passivation layer makes this technique favourable for some application.
Modelling of Temperature Distribution of Semiconductors During Rapid Thermal Processing
Authors: Tillmann Andreas
Published: April 2011

The modelling of temperature distribution on semiconductor wafers in common RTP-equipment is described. The incident intensity distribution on the wafer is calculated using raytracing. Based on this distribution the temperature distribution on the wafer is determined solving the two-dimensional heat conduction equation. If the dependence of a considered material property on the process temperature is known, the calculated temperature distribution can be convened to a distribution of this parameter.

The distinctive feature of the described algorithms is the two-dimensional treatment of the distributions using a grid of ring segments, each with equal area. This grid is identical to the usual circular test patterns of multipoint measurement equipment. This is convenient since the evaluation of temperature uniformity in RTP equipment is done mostly by mapping an appropriate temperature dependent material property. All calculated distributions can be presented by contour plots as well as 3-D plots. This results in a very suitable method to compare simulated and experimental wafer maps.

The agreement between simulated and experimental temperature distributions is shown.
Ab Initio Study of Pd Carbonyls and CO/Pd(110)
Authors: Ramprasad R. , Glassford K. M. , Adams J. B.
Published: April 2011

We have performed ab initio studies to understand the electronic and geometric aspects of the Pd-CO bond in small carbonyl clusters and the CO covered (2 × 1)p2mg superstructure of the Pd(110) surface. We have used the standard quantum chemistry package Gaussian to study the former system and an LDA formalism using ab initio pseudopotentials and a plane wave basis to study the latter. The latter results are preliminary; we intend to study thicker slabs in the future.
Aerosol Coating of Silica Fibers with Nanoparticles
Authors: Fotou George P. , Scott Steven J. , Pratsinis Sotiris E.
Published: April 2011

Ultrafine silica fibers were coated with nanosized particles by an aerosol process. The fibers were introduced in a diffusion flame reactor where silica particle formation took place by oxidation of SiCl4. Coagulation of particles with fibers resulted in fractal-like structures on the latter, enhancing the specific surface area of the product fibers. Ferrocene used as an additive at a mole fraction of 6.6 × 10−5 in the flame promoted the surface area enhancement. A sol-gel coating technique was also used to produce particle coated fibers.
Carbon Fiber Composite Molecular Sieves for Gas Separation
Authors: Jagtoyen M. , Derbyshire F. , Brubaker N. , Fel Y. Q. , Kimber G. , Matheny M. , Burchell T.
Published: April 2011

Introduction

Carbon fibers are produced commercially from rayon, phenolics, polyacrylonitrile (PAN), or pitch. The last are further divided into fibers produced from isotropic pitch precursors, and those derived from pitch that has been pretreated to introduce a high concentration of carbonaceous mesophase. Over the past few decades, interest in research and manufacturing carbon fibers has overwhelmingly centered on producing fibers with high tensile strength and high modulus for lightweight, high performance composites, where polymers, metals, and carbon can form the continuous matrix. The fibers most commonly used in advanced materials are produced from PAN or mesophase pitch. Graphitized mesophase pitch fibers tend to have higher modulus and lower tensile strength than the PAN-based equivalents. They have advantages in applications requiring high stiffness, high electrical and thermal conductivity, low thermal expansion, and high temperature oxidation resistance, while PAN fibers are employed where high strength is required.
New Inorganic/Organic Copolymers (Ormocer®s) for
Dental Applications
Authors: Wolter Herbert , Storch Werner , Ott Heidrun
Published: April 2011

Urethane- and thioether (meth)acrylate alkoxysilanes have been used, as
sol-gel precursors, for the preparation of a special family of
inorganic/organic copolymers (ORMOCER®s). The basic silane type
offers the following structural and synthetic possibilities for modifying
the properties of the resulting copolymers: variation of the number of
alkoxy groups, combination with other, different, sol-gel precursors,
variation of the number of attached (meth)acrylate groups (1– 5), and
variation within the molecular segment (kind, structure and length)
connecting the inorganic with the organic polymer structure. To achieve the
additional organic polymer structure in the cured copolymer the use of
different radically induced polymerization approaches (UV-, visible light-,
thermal-and redox induced) is possible. Taking the incorporation of fillers
into account, the Young's modulus of these copolymers is adjustable in a
range of 1–17000 MPa, and the thermal expansion coefficient in a range of
17–250·10-6·K-1 (5 - 50 °C). Other advantages are
the low shrinkage (1 - 2,8 vol.-%), the high flexural strength (up to 160
MPa), and the high abrasion resistance. This new copolymer type seems to
have significant potential for medical applications, especially as dental
filling material to replace the currently used controversial amalgam
fillings.
Organic-Silica Hybrid Materials Consisting of the Double
Four-Ring Silicate Structure as a Building Block
Authors: Hasegawa Isao , Ishida Masanori , Motojima Seijl , Satokawa Shigeo
Published: April 2011

Copolymerization of the cubic octameric silicate anion
(Si8O208-) with dimethyldichlorosilane in 2, 2-dimethoxypropane has
yielded organic-silica hybrid materials consisting of the S13O20 structure
as a building block. The hybrid materials have shown high surface area by
calcination in air. The reaction conditions have been optimized to produce
the materials with higher specific surface area. As a result, the hybrid
materials with BET surface area of 406 m2 g-1 have
been obtained.
Sol-Gel Lithium Silicate Electrolyte Thin Films
Authors: Mouchon E. , Klein L. C. , Picard V. , Greenblatt M.
Published: April 2011

For more than a decade, the sol-gel process has been used to prepare lithium
silicate gels that have potential applications as solid electrolytes in
lithium batteries and electrochromic windows. The interest in these
Li2O-SiC2 materials is their fast and stable ionic
conductivity from room temperature up to 350°C. Typically these materials
have been prepared with 15 mole % Li2O in bulk samples, but
rarely in thin films. This work was undertaken to prepare chemically stable
lithium silicate thin films with up to 30 mole % Li2O. Lithium
nitrate was used as the lithium precursor. Solutions were evaluated for
gelling time and homogeneity. Thin films were made by dip coating. After
heat treatment at 200, 250 and 300°C, films were characterized for surface
quality, thickness and microstructure using electron microscopy, x-ray
diffraction analysis and profilometry. Transparency was investigated in the
visible range (350–800 nm).
Photochemistry Channels of Merocyanine Encapsulated in Sol-Gel
Glasses
Authors: Mahloudji A. M. , Meuret L. B. , Lin C. T.
Published: April 2011

Photophysical properties of l-Docosyl-4-(4-hydroxystyryl)pyridiniurn bromide
(SB), a merocyanine dye in solution and encapsulated in sol-gel derived
glass are investigated at 298 and 77 K. In solution, the absorption spectra
of SB display an equilibrium between the quinolinium and benzoid forms. The
equilibrium can be shifted to either quinolinium or benzoid form under an
acidic or basic condition, respectively. The emission spectra of SB, on the
other hand, give not only the quinolinium and benzoid forms but also the
quinoid form which emits at 500 nm. The existence of excited state quinoid
form of SB is also evident in the excitation spectrum while the emission at
500 nm is monitored. Both in solution and in xerogel, the quinoid form of SB
is shown to be photochemically unstable as compared to the benzoid form. It
is proposed that the photoexcited quinolinium form of SB is a proton
dissociative species which transforms readily to become the quinoid form.
The results indicate that photochemistry channels of SB are originated from
the quinoid form. Moreover, the benzoid form of SB (photochemically stable)
exhibits large hyperpolarizability due to its charge-transfer
characteristic, and is a desired molecular form for nonlinear optical (NLO)
applications. The material processing techniques for stabilizing the benzoid
form of SB in optically transparent sol-gel glasses are illustrated for the
first time.
Mixed-Metal Bismuth-Titanium Species. Chemical Routes to
Bi4Ti3O12
Authors: Papiernik Renee , Hubert-Pfalzgraf Liliane G. , Parola S. , Jagner S. , Soares-Carvalho F. , Thomas P. , Mercurio J.P.
Published: April 2011

Several routes to mixed-metal Bi-Ti species have been investigated. The
inertness of bismuth alkoxides Bi(OR)3 (R = Et, iPr) toward their
titanium analogs could be overcome by controlled microhydrolysis of Bi
alkoxides. The first mixed-metal species based on bismuth,
BiTi2O(OiPr)9, has thus been isolated and
structurally characterized.

Coatings of Bi4Ti3O12 have been deposited
on silicon wafers by using the gels derived from Ti and Bi
2-methoxyethoxides solutions.
Fast Solution Precursor Synthesis of the 2223 Phase: the Role of
Lead in the Reaction Pathway
Authors: Miao H. , Primo V. , Ibáñez R. , Sapiña F. , Beltrán A. , Beltrán Uibcm D.
Published: April 2011

Valuable mechanistic information, about the reaction pathway in the
formation of the 2223 phase, has been obtained by the use of a solution
synthesis route. The presence of lead in the starting mixture has remarkable
effects on the nature and stability of the different intermediates: i) the
grain size and morphology of Bi2CuO4 is severely
changed, ii) calcium carbonate is partially decomposed to yield the calcium
plumbate, iii) the 2201 phase results stabilized against the formation of
the collapsed phase
Bi17Sr16Cu7O49-δ, iv) the
melting point of the intermediate 2212 is lowered by about 10 °C. All these
effects, due to lead substitution, contribute to promote the formation of
the 2223 phase, controlling also the morphology and properties of the final
product.
Near-Net-Shape Forming of Celsian Ceramics from Ion-Exchanged
Zeolite Precursors
Authors: Hoghooghi Bahar , Mckittrick Joanna , Butler Chad , Helsel Eugene , Lopez Olivia
Published: April 2011

A technique has been developed for the synthesis and near-net-shape forming
of celsian glass-ceramics. This technique involves ion exchange of zeolite
precursor powders, heat treatment of the powders to temperatures between
800–90°C to form a glassy phase during which the samples are formed under
low stresses (<20 MPa). Upon further heat treatment to about 1000°C,
crystallization occurs and the amorphous formed body is transformed to the
celsian ceramic phase. Using this technique, and through the addition of
monoclinic seed particles as well as a mineralizer, monoclinic celsian was
produced at temperatures as low as 1000°C at heat treatment times of less
than one hour. This forming technique also resulted in a significant
reduction in the porosity of the ceramic bodies compared to free-sintered
samples.
Structural and Optical Aspects of Sol-Gel Optical
Composites
Authors: Li Xiaochun , King Terence A.
Published: April 2011

Sol-gel derived optical composites have been prepared by both the
in-situ polymerisation and ORMOSIL methods and
characterised by FT-Raman and near infrared (NIR) spectroscopies regarding
their chemical structures, optical properties and molecular interactions. A
model based on intermolecular and intramolecular hydrogen bondings has been
proposed to interpret the observed spectral results.
Induction of Bidimensionality in CU-TI
Perovskttes
Authors: Palacín M.R. , Fuertes A. , Casañ-Pastor N. , Gómez-Romero P.
Published: April 2011

The synteses and structure of the three-dimensional perovskite LajCuTiOg are
described. In this oxide Cu and Ti atoms are disordered among octahedral
sites. The introduction of oxygen vacancies by an adequate cation
substitution leads to the induction of bidimensionality as well as an
ordered arrangement of cations and oxygen vacancies as found in the layered
oxides
Ln2Ba2Cu2Ti2O11
(Ln=La,Nd,Eu).
Silica Porous Glasses With Silicon Impregnations
Authors: Roizin Yakov O. , Korlyakov Andrey B. , Gevelyuk Sergey A.
Published: April 2011

Quantum-size silicon enriched regions were formed in silica porous glasses
obtained by three different technologies. Processing in the spark discharge
and carbon reduction of silicon dioxide in the solid phase were performed
for this purpose. All fabricated specimens have been investigated in
relation to their electrical and photoluminescence (PL) properties. A
pronounced increase of visible luminescence and single-type changes in the
a.c. conductivity were registered in all cases.
Novel Inorganic Hydrogels Based on The Polymerization of
Cyanometalate Transition Metal Complexes With
[PdCl4]2-: A New Approach To Ceramic And Alloy
Precursors
Authors: Bocarsly Andrew B. , Kumar Gireesh , Heibel Marija
Published: April 2011

The reaction of a wide variety of cyanometalate complexes of the general
form [M(CN)x]n- (where M= a transition metal ion) with
square planar [PdCl4]2- in aqueous solution leads to
the formation of linear polymers. Polymerization occurs via substitution of
chloride ligands on the Pd(II) centers, by the nitrogen end of the cyanide
ligand to generate extended bridging cyanide structures. Upon generation at
room temperature polymer solutions of this type under go a sol-gel
transition to generate robust hydrogels having water content in excess of
95%. In the case of the cyanocobaltate/tetrachloropalladate gel, pyrolysis
at 900°C produces ferromagnetic Pd/Co metallic alloys having novel
morphological character. Materials formed with a hydrogel having a 2:1 Pd to
Co stoichiometry are found to be “sponge-like”. When placed in water, the
metallic matrix swells becoming pliable and holding up to seven equivalents
of water per metal site. The conductivity and magnetic properties of this
material are maintained in the swollen state. Sintering of the Pd/Co
hydrogel in air generates the layered oxide, PbCoO2 having a
delafossite structure.
Preparation of π-vi Semiconductor Nanocrystallites in a Glass
Matrix Using Chalcogenizing Agent: Application to cdse
Authors: Marc J.L. , Gramer W. , Pradel A. , Ribes M. , Richard T. , Allegre J. , Lefebvre P.
Published: April 2011

A new route for preparing CdX (X = S, Se, Te, S+Se) nanocrystallites
dispersed in a sodium borosilicate glass matrix from a hydrogel is proposed.
Chalcogenizing complexing molecules - for instance a mixture of
NH4SCN + H2SeO3 - introduced in the
starting solution allowed an in situ crystallite
preparation concomitant to gel densification. Prevention of crystallite
oxidation is thus obtained. Moreover, coalescence is minimized because of
the low gel-glass transition temperature. Low temperature absorption spectra
have been interpreted in terms of exciton and electron-hole confinements,
accounting for both an intrinsic broadening of energy states inside each
nanocrystal and a Gaussian size distribution. Crystallite sizes and size
dispersion can be adjusted by changing the initial Cd concentration. The
crystallinity of the nanoparticles without change in dispersion is strongly
improved by thermal treatment above the Tg of the glass
matrix.
A New Type of a Sol-Gel-Derived Inorganic-Organic
Nanocomposite
Authors: Kasemann Reiner , Schmidt Helmut K. , Wintrich Elisabeth
Published: April 2011

A new type of sol-gel-based transparent inorganic-organic nano composites
has been developed by increasing the inorganic phase dimension to values
just below the point, where scattering can be neglected. For this purpose,
nanosized boehmite particles ≤ 50 nm are homogeneously incorporated in a sol
based on tetraethoxysilane and an epoxysilane. The nano-scale boehmite
particles act as catalysts for the polymerization of the epoxy silane to
polyethylene oxide, as proved by 13C NMR, and are linked to the
matrix by Si-O-Al bridges, as proven by 27Al-NMR spectroscopy.
The synthesized sols can be applied by standard coating techniques on
transparent polymers and are cured thermally. The mechanical properties
(scratch resistance, hardness) have been substantially improved compared to
systems with molecular dimensions of the inorganic phase. The effect is
attributed to the special structure of flexibly suspended nano-scale
boehmite particles in an inorganic-organic network by a tailored
interface.
Fullerene-Based Catalysts for Methane Activation
Authors: Wu Hui-Jung , Hirschon Albert S. , Malhotra Ripudaman , Wilson Robert B.
Published: April 2011

We investigated fullerene based catalysts for the conversion of methane into higher hydrocarbons. Fullerene soot, CO2 activated soot, and extracted soot as well as a Norit-A carbon were examined as catalysts for methane activation. The soot was found to easily activate the C-H bond of methane, allowing methane conversion at lower temperatures (lower by 250°C) than found under purely thermal conditions. Furthermore, soot catalysis appears to produce a minimal amount of aromatic hydrocarbons. Extracted soot was found to have a lower selectivity for C2 hydrocarbons than the non-extracted soot, and the CO2 activation of the soot did not appear to dramatically alter the catalytic activity.
Structural and Electronic Studies of C60 Films Deposited Using a New Technique of Neutral Cluster Beam Deposition
Authors: Ren Zhong-Min , Ying Zhi-Feng , Xiong Xia-Xing , He Mao-Qi , Du Yuan-Cheng , Li Yu-Fen , Li Fu-Ming
Published: April 2011

C50 films, are deposited on Si(111) substrates using neutral cluster beams of fullerenes generated from a crucible with a special nozzle. X-ray diffraction (XRD) have been used to investigate the structural properties of C50 films, which indicate highly textural films as close-packed structure with strong (110) XRD assignment and 400Å for correlation length. Raman spectrum indicates the existence of stable C60 films. X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) measurements are carried out to analyze the electronic properties of the films. The resistivity to contamination of C50 film deposited here is better than that deposited by MBE. Different kinds of oxygen contamination on the surfaces of C50 films and HDPG are detected by the results of O 1s XPS analyses.
High-Density Production of Carbon Nanotubes in Contact Arc-Discharge at Low Helium Pressure
Authors: Zhou Dan , Wang Su , Seraphin Supapan , Withers James C.
Published: April 2011

We report here on the structural properties of carbon nanotubes prepared by contact arc-discharge at low helium pressure of 100 torr. In contrast to the conventional arcdischarge, the contact discharge reduces the gap between the electrodes to a minimum value while still maintaining a plasma. The resulting carbonaceous deposit on the cathode surface, with the contact discharge operating under 100 torr helium atmosphere, contains the columnar structures with high density carbon nanotubes. These columnar structures are several millimeters in length, much longer than those generated under the conventional arc-discharge. These experimental results reveal that reducing the gap adds greater stability to the arc-discharge and establishes conditions that favor high-density nanotube growth under a low helium pressure.
Residual Stress and Raman Spectra of Laser Deposited Highly Tetrahedral-Coordinated Amorphous Carbon Films
Authors: Friedmann T. A. , Siegal M. P. , Tallant D. R. , Simpson R. L. , Dominguez F.
Published: April 2011

We are studying carbon thin films by using a pulsed excimer laser to ablate pyrolytic graphite targets to form highly tetrahedral coordinated amorphous carbon (at-C) films. These films have been grown on room temperature p-type Si (100) substrates without the intentional incorporation of hydrogen. In order to understand and optimize the growth of at-C films, parametric studies of the growth parameters have been performed. We have also introduced various background gases (H2, N2 and Ar) and varied the background gas pressure during deposition. The residual compressive stress levels in the films have been measured and correlated to changes in the Raman spectra of the at-C band near 1565 cm−1. The residual compressive stress falls with gas pressure, indicating a decreasing atomic sp3-bonded carbon fraction. We find that reactive gases such as hydrogen and nitrogen significantly alter the Raman spectra at higher pressures. These effects are due to a combination of chemical incorporation of nitrogen and hydrogen into the film as well as collisional cooling of the ablation plume. In contrast, films grown in non-reactive Ar background gases show much less dramatic changes in the Raman spectra at similar pressures.
Studying the Technology of Renaissance Bronzes
Authors: Bewer Francesca G.
Published: April 2011

Late fifteenth- and sixteenth-century freestanding bronze statuary presents evidence that the artists drew from both Experimentation sad divrcse, technological traditions prevalent at the time. The indirect lost wax casting technique was refined for the manufacture of statuettes by the end of the sixteenth century in the Florentine workshop of the Flemish sculptor Giambologna. Combining art historical and scientific analysis with an understanding of materials and techniques provides an integrated method of study which helps art historians and conservators to clarify the manufacturing process of these works. This can serve to construct a broad historical picture of techniques in different workshops and regions and to date and authenticate particular bronzes. X-radiography is the most informative tool for identifying technological features in this kind of work. Surface examination, analyses of the metal (by x-ray fluorescence spectroscopy and atomic absorption spectrometry) and refractory molding materials (by polarized light microscopy and microprobe analysis) complement this information.
Lattice Properties of Ge and GaAs Strained-Layers on Si
Authors: Eryigit Resul , Sui Zhifeng , Herman Irving P.
Published: April 2011

A phenomenological lattice dynamics model has been developed that describes how strain affects phonon frequencies and elastic constants in Group IV and III-V semiconductor thin films and strained layers. Using this model, the phonon dispersion relations for strained-layer heterostructures of Ge and GaAs on Si have been obtained in the quasiharmonic approximation. This model uses available experimental data and can predict the effect of arbitrary strains on thin films.
A Numerical Study of Stress Controlled Surface Diffusion During Epitaxial Film Growth
Authors: Chiu Cheng-Hsin , Gao Huajian
Published: April 2011

A two-dimensional numerical simulation is performed to model the morphological evolution of a strained film growing heteroepitaxially on a substrate under simultaneous action of vapor deposition and surface diffusion. To facilitate numerical implementation, a continuum boundary layer model is proposed to account for the influence of film/substrate interface on the film growth pattern. Discussions are focused on the Stranski-Krastanow growth mode, although our model is capable of explaining Frank-van der Merwe and Volmer-Weber growth modes as well. Both first-order perturbation and numerical results are developed to demonstrate that the film surface tends to remain flat during the initial stage of growth and that surface roughening occurs once the film thickness exceeds a critical value, in consistency with experimentally observed patterns of S-K growth. Numerical results further show that, depending on the deposition rate, the surface evolution could lead to a steady state morphology, unstable cusp formation, or growing islands with flattened valleys.