bluuebunny/crossref_metadata_2025 huggingface dataset:
Layered Inorganic-Organic Nanocomposites: Application to Photofunctional Materials and Conversion to Inorganic Microporous Materials
Authors: Kuroda Kazuyuki , Ogawa Makoto , Yanagisawa Tsuneo , Kato Chuzo
Published: March 2011

Layered inorganic-organic nanocomposites can be prepared by intercalation of organic compounds into various two dimensional inorganic compounds, such as clay minerals and layered polysilicates. Two different roles of organic guest species are described in the application of intercalation compounds to development of functional materials. The first case shows that organic substances with peculiar photochemical properties can be incorporated in the nanometer—scaled interlayer spaces. Luminescence behavior and photochemical hole burning (PHB) of layered inorganic—organic nanocomposites are investigated from the viewpoint of host-guest interactions. The luminescence maxima of intercalated Ru(bpy)32+ incorporated into fluor—tetrasilicic mica cointercalated with poly(vinylpyrrolidone) shifted gradually oward blue with the decrease in the loading of Ru(bpy)32+ Ru(bpy)32+ was effectively isolated to suppress self quenching due to aggregation even at its high concentration loading. 1,4-Dihydroxyanthraquinone which is known to show a PHB reaction was intercalated into a tetramethylammonium pillared clay mineral and persistent spectral zero—phonon hole was observed at liquid helium temperatures. In spite of the high concentration of 1,4-dihydroxyanthraquinone, a narrow hole was obtained with no distinct decrease in burning efficiency if compared with those doped in ordinary polar polymers or organic glasses. In the second case, intercalation of organic substances into a layered polysilicate induces the change of the layered structure to form a three—dimensional silicate network by condensation of silanol groups in adjacent layers. This phenomenon indicates that novel microporous materials with controlled pore sizes can be prepared through inorganic-organic nanocomposites.
Structure, Mechanical Properties, and Oxidation Behavior of Nanolayered MoSi2/SiC Coatings
Authors: Hirvonen J-P. , Lappalainen R , Kattelus H. , Likonen J. , Suni I. , Kung H. , Jervis T.R. , Nastasi M.
Published: March 2011

The structure, hardness and elastic properties, and oxidation behavior of a nanolayered MoSi2/SiC structure were examined. DC magnetron and rf diode sputtering were used to deposit MoSi2 and SiC, respectively. The total number of sublayers of each kind was 90. The nominal thickness of the MoSi2 sublayers was 10 and that of the SiC 3 nm. The microstructure of the as-deposited samples was amorphous whereas annealing at 500 °C for I h resulted in the transformation of MoSi2 into C40 type hexagonal structure as determined using cross-section transmission electron microscopy (TEM). However, silicon carbide still remained amorphous. Hardness and Young's modulus were determined by using a nanoindentation technique. Hardness of 11.6 and 20.8 GPa were obtained for the asdeposited and annealed structure, respectively. Corresponding Young's moduli were 220 and 290 GPa, which yield values of 232 and 332 GPa for Young's moduli of amorphous and crystalline MoSi2. Oxidation tests were carried out in wet oxidation conditions at 400 and 500 °C. The degree of oxidation was determined by measuring oxygen concentration on the surface using a nuclear reaction 16O(d,p) 17O at a deuterium energy of 950 keV. The MoSi2/SiC coating gave good protection against oxidation for unalloyed steel. As compared to a single MoSi2 coating a slightly higher degree of oxidation and a significantly different mechanism of oxidation was observed. This was also supported by secondary ion mass spectroscopy (SIMS) measurements. Cracking of the coating caused by a thermal mismatch and transformation stresses was worse in the case of the single MoSi2 layer than in the case of the composite coating. Thus cracking of the coating can be significantly reduced by using a nanolayered structure.
Jet Vapor Deposition of Nanostructure Composite Materials
Authors: Zhang J.-Z. , Golz J.W. , Johnson D.L. , Mcavoy D.T. , Halpern B.L. , Schmitt J.J.
Published: March 2011

We describe the use of Jet Vapor Deposition for efficient synthesis of nanoscale multilayer films, ceramic-organic films, cluster embedded films, and colloids.
Anisotropic Electron Transport in Cu/Al Multilayers
Authors: Fadnis A. N. , Baxter David V.
Published: March 2011

We have measured the anisotropy of the electron diffusivity in a series of Cu/Al multilayers. The Samples were made by magnetron sputtering and characterized by X-Ray diffraction. The low temperature transverse magnetoresistance of each sample was measured for two different orientations of the magnetic field—parallel and perpendicular to the plane of the sample film. The Weak Localization(WL) contribution to the magnetoresistance is sensitive to the component of the electron diffusivity in a plane perpendicular to the magnetic field. We use this fact to calculate the ratio of different components of the diffusivity from the observed dependence of magnetoresistance on the orientation of magnetic field. For our samples, the ratio of the in and out of plane components of the diffusivity, (Dxy/Dz), is seen to range between 1 and 2.2, and the anisotropy is largest for the sample with the highest conductivity.
Raman and X-Ray Scattering From Dense Semiconductor-Dielectric Nanocomposites
Authors: Yang W.H. , Huber T.E. , Lubin J.A. , Walrafen G.E. , Huber C.A.
Published: March 2011

Raman scattering measurements have been performed on semiconductor-insulator nanocomposites in which the semiconducting phase occupies a significant (30%) volume fraction. The composites have been synthesized by high pressure injection of the conducting melt into the nanochannels of commercially available insulating matrices. The optical phonon spectra of GaSb- and Te-SiO2 composites exhibit shifts, broadenings, and asymmetries when compared to those of the semiconducting bulk. These are interpreted in terms of strains and phonon confinement in the microcrystalline semiconducting phase. Xray diffraction measurements allow us to correlate the effects of crystallite size and strains on the optical modes of the composites.
Synthesis, Processing and Phase Evolution of TiN/TiB2 Composites From Polymeric Precursors
Authors: Nowakowski M. , Su K. , Sneddon L. , Bonnell D.
Published: March 2011

A high yield synthetic route to TiN/TiB2 nanocomposites based upon polymeric precursors has been developed. The phase evolution and microstructural development have been characterized and related to preliminary measurements of properties, i.e. hardness. The observations indicate the existence of TiN-TiB2, TiN-BN, and TiB2-BN subsolidus compatibilities.
Template Synthesis and Optical Properties of Small Metal Particle Composite Materials: Effects of Particle Shape and Orientation On Plasmon Resonance Maxima.
Authors: Foss Colby A. , Hornyak Gabor L. , Stockert Jon A. , Martin Charles R.
Published: March 2011

An electrochemical method for the preparation of nanoscopic gold particles which allows for the control of particle size, shape and orientation is described. The UV/visible/near-IR spectra of Au/alumina and Au/polyethylene composites are described and shown to be in accord with the predictions of Maxwell-Garnett theory. The applications of such composites to surface enhanced spectroscopy are also discussed.
Connected Cadmium Selenide Nanocrystallite Networks
Authors: Majetich Sara A. , Carter Adriaan C. , Mccullough Richard D.
Published: March 2011

The optical properties of semiconductor nanocrystallites, or small quantum dots, are well understood, but little is known about nanocrystallite networks. Here we report preliminary results on a glassy network of CdSe nanocrystallites connected by molecular bridges. This network has been analyzed by transmission electron microscopy (TEM) and small angle X-ray scattering to determine its structure, and to see if long range order is present. The effect of nanocrystallite interactions on electron-hole recombination is inferred from characterization by UV-VIS absorption and photoluminescence.
Sinter-Forging of Nanocrystalline TiO2
Authors: HÖfler H.J. , Averback R.S.
Published: March 2011

Sinter-forging experiments were performed on cylindrical samples of n-TiO2 at various stresses and temperatures and with varying initial densities. The results are described on the basis of a constitutive law similar to creep deformation of dense bodies. The activation enthalpy measured is consisted with a grain boundary diffusion limited process, whereas the stress exponent found excludes simple diffusional creep. Furthermore, a threshold stress was found to exist. The results are discussed in terms of existing models and it is shown that the threshold stress can be explained in terms of the creation of additional surface area due to grain boundary sliding.
Sialon Ceramics Sintered with Yttria and Rare Earth Oxides
Authors: EkstrÖm Thommy
Published: March 2011

Dense single-phase α-, β- and O′-sialon cermics or mixed sialon ceramics without a glassy grain-boundary phase can be prepared at high temperatures and pressures, and these materials are well suited for high-temperature use, but they are usually brittle. Additional quantities of oxides of group IIIB metals in the periodic table are often added as sintering aids to achieve pressureless sintering and thereby to allow more complicated shapes to be manufactured directly and at lower costs. The most common additive is yttria, but the rare earth oxides are also of interest. All these oxides will promote the growth of elongated β crystals in the microstructure, and the fracture toughness will be improved considerably. Low-cost oxides like Nd2O3, La2O3or CeO2may replace Y2O3without significantly impairing the mechanical properties at room temperature. The expensive rare-earth oxides like Sm2O3, Dy2O3or Yb2O3have been found to be as good additives as yttria, or even better, but improvements in mechanical properties are generally small and do not justify the use of these additives in large-scale production. The residual intergranular glassy phase usually found in the microstructure of metal-oxide-doped sialons will deteriorate the properties at very high temperatures, and this type of material is best suited for use at operation temperatures below 900-1000°C.
The Influence of Microstructure on the Mechanical Behavior of Silicon Nitride Ceramics
Authors: Becher P. F. , Lin H. T. , Hwang S. L. , Hoffmann M. J. , Chen I-Wei
Published: March 2011

The introduction of elongated silicon nitride grains during densification in the presence of a liquid phase can impart considerable improvement to the fracture toughness. This toughening is not universally attained but depends on the activation of intergranular rather than transgranular fracture. This is reminiscent of the requirement of interfacial debonding in whiskerreinforced ceramics. In fact, additional observations such as bridging in the crack wake by elongated grains and pullout of some of these grains further suggest that the crack wake mechanisms that contribute to the toughening of whisker-reinforced ceramics can also operate in silicon nitrides containing elongated grains. Various investigators have found that, consistent with crack wake mechanisms, the fracture toughness of silicon nitrides increases with increase in the diameter of the larger elongated grains. However, little is known about the effects of the grain boundary phase(s) and their properties on the interfacial debonding/intergranular fracture in such silicon nitrides. This is critical as observations show that crack propagation in some systems exhibiting larger elongated grains occurs transgranularly and no toughening occurs.
Synthesis of Si3N4 Powder by Thermal Decomposition of SI(NH)2
Authors: Ampuero Silvia , Bowen Paul , Ring Terry A.
Published: March 2011

A fine white α-Si3N4 powder has been produced by the thermal decomposition of the coprecipitation product of the reaction between SiC14 and NH3. The Cl content, due to a reaction between Si(NH)2 and the NH4Cl by-product during the thermal treatment of the coprecipitate, has been reduced by using an isothermal step at ≈ 250°C in the heat treatment cycle.
Spectroscopic Characterization of the Nitridation Process of Polymeric Precursors to SI-M-N-O Systems (M=Ti, Zr, Al)
Authors: Babonneau F. , Soraru G. D.
Published: March 2011

A commercial polycarbosilane was modified with various metallic alkoxides to get mixed ceramic precursors in the Si-M-C-O systems (M=Ti, Zr Al). Pyrolysis under ammonia leads to the formation of various ceramic materials depending on the nature of M : Si3N4/TiN, Si3N4/ZrO2 or β′-SiAlON phases.

The polymer-to-ceramics conversion have been studied by MAS-NMR (29 Si, 27Al) and X-ray absorption (Ti K-edge). This paper will show how these two complementary spectroscopic techniques can be used to follow the nitridation process by probing local environments of different elements. In addition, it will be pointed out how X-ray absorption can be a powerful tool for the detection of the crystallization of nitride cubic phases.
Tape Casting of Silicon Nitride
Authors: Kim Young-Wook , Lee June-Gunn
Published: March 2011

Tape casting behavior of submicron silicon nitride powder(UBE SN–E1O) with Al2O3and Y2O3as sintering additives was studied. It was found that Hypermer KD1(polymeric dispersant) is effective dispersant for submicron silicon nitride in organic solvent system.

Optimization of the rheological properties of the slurries allows the homogeneous green tapes with green densities of 45–50% theoretical. The cast tapes could be sintered to closed porosity with densities of higher than 96% theoretical.
Rheological Behavior of Silicon Nitride Whiskers
Authors: Toro Patricio , Wittke Oscar
Published: March 2011

Si3N4 whiskers are found through SEM analysis of powder obtained by carbothermal reduction of calcined Chilean rice husks. X-ray and FTIR analysis showed that the ceramic material was mainly α-Si3N4. A stable aqueous suspension with 30 or 40 wt% Si3N4 was obtained at pH = 8.5. A maximum viscosity at pH = 4.0 and low rpm was also observed and this rheological behavior is consistent with the zeta potential data. An irregular flow behavior near pH 4.0 shows a decrease in viscosity that is related to active impurities as detected by potentiometric titrations.

These rheological studies conducted allowed production of a Si3N4 green ceramic body measuring 170 × 25 × 5 mm formed by slip casting. The optimal aqueous suspension of powder contained the following: 17.0 g Si3N4, 1.0 g Cu2O, 1.3 g bentonite, and 20.0 g water.
Strength Optimization Through Powder Modification
Authors: Pasto Arvid E. , Avella F. , Natansohn S. , Rourke W. J.
Published: March 2011

The effect of oxygen content of silicon nitride powders on the properties of resulting ceramics was studied by physically and chemically treating the powder to modify its surface oxygen content. These powders were compounded with yttria and hot-pressed into dense ceramics. Strength and oxidation resistance of these ceramics were measured and correlated with the powder and ceramic compositions as well as the resulting intergranular phases. Results showed that the phases varied with slight differences in the initial powder oxygen content as predicted, and that strength could be correlated to initial oxygen concentration. Best results were obtained when the oxygen content was increased by thermal oxidation. A Taguchi Methods experimental study designed to optimize the thermal treatment resulted in silicon nitride ceramics with strength improvements of 22 and 37% at ambient temperature and 1370°C, respectively. Oxidation resistance was also improved.
Intergranular Microstructure and Oxidation Behaviour of Si3N4 Ceramics Formed with Y2O3, Al2O3 AND ZrO2
Authors: Falk L.K.L. , EngstrÖm E.U. , Rundgren K.
Published: March 2011

Analytical electron microscopy, X-ray diffractometry and secondary ion mass spectrometry (SIMS) have been used to characterize the intergranular microstructure of nitrided pressureless sintered (NPS) Si3N4 ceramics and the phase transformations which occur in the intergranular regions during oxidation. The phase transformations, which take place after crystallisation of the residual intergranular glass, are caused by an inward transport of oxygen and result in the development of sub-scalar phase gradients. Cubic Y2O3 stablized ZrO2 partitions from the oxynitride liquid phase sintering medium when a small amount of ZrO2(+ 3 mol% Y2O3) is added together with the Y2O3 and Al2O3 sintering additives. The latter material has a reduced oxidation resistance, presumeably due to the high oxygen conductivity of the cubic ZrO2 structure.
Partial Devitrification of Sintered Silicon Nitride During Static Fatigue Testing
Authors: Braue W. , Quinn G. D.
Published: March 2011

The static fatigue behavior of sintered Y2O3/A12O3-fluxed Si3N4 in air is controlled by slow crack growth or creep fracture. Partial devitrification of the amorphous grain boundary phase at 1000°C and 1100°C improves the static fatigue resistance with specimens surviving up to 1500 hrs. during stress rupture experiments. In this study the early stages of partial devitrification during static fatigue testing at 1000°C are investigated by conventional and analytical transmission electron microscopy with emphasis on nucleation and growth of δ-Y2Si2O7 and X1-Y2SiO5 and possible constraints from different stress states. The results show that the stress state does not affect the nature of the secondary phase assemblage. However, the amount of crystallization is higher within the tensile region of the flexural specimens than in areas which experienced compressive stresses.
Role of Sintering Parameters on Microstructure Development and Mechanical Properties of Sinter/hip Silicon Nitride
Authors: Kühne Arnd , Oberacker Rainer , Grathwohl Georg
Published: March 2011

Sinter/HIP consolidation with systematic variation of all relevant process parameters was performed for low additive (Y2O3-A12O3) silicon nitride material. With SEM-investigations as well as bending and creep tests the relevance of process parameters on microstructure development and mechanical properties was studied.
Deformation and Toughness of α-Silicon Nitride Single Crystals
Authors: Suematsu H. , Petrovic J. J. , Mitchell T. E.
Published: March 2011

Vickers and Knoop indentation methods were used to determine the deformation behavior and fracture toughness of single crystal α-Si3N4at room temperature. The tests were performed on (0001), (1100) and (1120) faces; both hardness and toughness values were found to be independent of orientation within statistical variations. Thus, the mechanical properties of silicon nitride are essentially isotropic at room temperature.

Single crystals of α-Si3N4were also compressed at 1760 and 1820°C at a strain rate of The sample tested at 1760°C showed yielding at a stress of 200MPa but it fractured before indicating a significant amount of plastic deformation. On the other hand, the sample compressed at 1820°C deformed to a strain of 2.7% at a stress of 4OMPa before fracturing. A significant density of dislocations was observed by transmission electron microscopy. From conventional g.b analysis, the Burgers vector of the dislocations was determined to be 1/3<1120>. From the line direction of the dislocations, the primary slip system of α-Si3N4is determined to be {1101}<1120>.
Damage Resistance of In Situ Reinforced Silicon Nitride
Authors: Li Chien-Wei , Gasdaska Charles J. , Goldacker Jeffrey , Lui Siu-Ching
Published: March 2011

The room temperature fracture behavior for in situ reinforced (ISR) silicon nitride is correlated to its microstructure and R-curve behavior. The relation of strength to fracture origin suggests that stable growth of the intrinsic flaw precedes catastrophic fracture. Grainbridging that generates a rising bridging stress behind the crack-tip has been proposed as the cause for stable crack growth, which in turn reduces the strength dependency on initial flaw size. As a result of strong bridging by the acicular β-Si3N4 grains, ISR Si3N4 is characterized for high Weibull modulus. At elevated temperatures, the material's tensile creep rupture behavior follows the Monkman-Grant type plot. A tensile creep rate of -10−9s−1 at 1260°C/250 MPa, 1300°C/180 MPa, and 1350°C/90 MPa has been recorded. This relatively strong creep resistance is related to the sliding-resistance of the acicular grains and the properties of the amorphous film between the grains in ISR Si3N4.
Oxidation Behaviour of Zirconia-Sialon Composites
Authors: Cheng Yibing , Thompson Derek P.
Published: March 2011

In yttria densified ZrO2-sialon composites, an increase in β′:O′-sialon ratio results in a structural change in the zirconia phase because an increasing amount of nitrogen dissolves in the zirconia structure as the overall composition becomes increasingly nitrogen rich. Both ZrN and nitrogen-containing zirconia (N-ZrO2) are observed in the β′-ZrO2 composite and these phases show a poor oxidation performance above 600°C. However, the introduction of small amounts of O′ phase into the β′-ZrO2 composite has provided an effective oxygen-rich barrier to reduce the diffusion rate of nitrogen in zirconia and therefore O′-β′-ZrO2 composites showed superior oxidation resistance compared with β′-ZrO2 materials at temperatures between 600 and 1200°C.
Factors Affecting the Extensional Flow of Crowded Suspensions for the Manufacture of thin Wall Ceramic Bodies
Authors: Greener James , Evans Julian R.G.
Published: March 2011

Procedures for the manufacture of thin wall ceramic components from particulate suspensions using plastic forming methods which employ extensional flows are described. These include vacuum forming, blow moulding and film blowing. In order to understand how to select materials and to adjust the composition of such suspensions, the factors which control suspension rheology are identified. The measurement of extensional viscosity of ceramic suspensions is reported and compared with shear flow measurements.
Characterization of Monodisperse Aqueous Latex Dispersions Prepared with N-Isopropylacrylamide
Authors: Kiminta D. , Costello B. , Lenon S. , Luckham P.F.
Published: March 2011

Poly-N-isopropylacrylamide (poly-NIPAM) is a water soluble nonionic polymer that exhibits a lower consolute solution temperature (LCST) of about 31°C. This paper describes the preparation and characterization of a monodisperse, hydrophilic polymer latex of poly-NIPAM, crosslinked by N,N'-methylenebisacrylamide. The presence of these crosslinking moieties will prevent dissolution of the particles at low temperatures; rather the particles will be swollen with solvent such that a microgel is formed. The swelling and rheological behaviour of the latex has been studied. The results show that at high temperatures the particles are ˜ 30 nm whilst at 25°C, the particles were ˜ 130 nm in diameter. This four fold increase in the particle diameter correspond to a ˜ sixty fold increase in volume. The rheological properties, both continuous and oscillatory shear, of these systems have also been studied and is strongly temperature dependant, reflecting the changes in phase volume of the NIPAM latex.
Rheology of YBa2Cu3O7−x Precursors
Authors: Green Timothy M. , Akinc Mufit
Published: March 2011

Nitrate and acetate precursors to Ba2Cu3O7−x (123) are prepared using a molten salt technique. The viscosity and shear stress of the paste are controlled by evaporation of water from the paste. The pastes contain ˜20 - 80 volume percent solids. Rheometry over strain rates of 0 - 200 sec−1 shows both systems are shear-thinning. Both systems are thixotropic. The nitrate system may be described by a two-stage Bingham Plastic model, the acetate by a Hershel-Bulkley model. The existence of more than one region of flow behavior suggests that there are at least two mechanisms which contribute to flow. In the low strain rate region, flow resistance is due to the existence of flocs in the colloidal assembly. At higher strain rates, flow is probably controlled by interlaminar drag interactions. Precursors produced by both methods have been used to form fibers of YBa2Cu3O7−x, by ram extrusion.
Theoretical and Empiriical Modeling of the Rheology of Fresh Cement Pastes
Authors: Karam Gebran N.
Published: March 2011

The most important property of cements and concretes after strength is the workability, which is controlled by the rheological characteristics of the mix. Theoretical modeling having proved complicated and in some cases mathematically untractable, cement specialists have concentrated on empirical based models for the last two decades. The major theoretical contributions to date on the properties of colloidal and concentrated suspensions are summarized and a general framework for theoretical modeling of cement viscosity is established. The empirical modeling and the experimental investigation of the rheological properties of fresh cements are reviewed and discussed. A semi-empirical model is proposed and its validity tested in the interpretation of some published experimental results.
The Interaction of Polymer Dispersions with Portland Cement Paste
Authors: Su Z. , Bijen J.M.J.M. , Fraaij A.L.A.
Published: March 2011

Research has been done on the interaction of two types of polymer dispersions, a styrene acrylate (SA) and a polyvinylidene chloride (PVDLC), with portland cement by means of a COULTER particle size analyzer and a filtration technique. It was found that over 50% of the polymer SA particles were adsorbed onto the cement surface, the others did not adhere to cement grains and remained dispersed in the mixing water. However, the polymer dispersion PVDLC caused a quick flocculation and coagulation of cement grains and stiffening of the paste. Hardly any free polymer particles of this polymer were found in the liquid phase.
Constitutive Behavior of Semi-Solid Metal Alloy Slurries
Authors: Kumar Pratyush , Martin Christophe L. , Brown Stuart
Published: March 2011

The constitutive flow behavior of semi-solid metal alloy slurries has been modeled using an internal variable framework. The formulation represents the primary flow response of these materials: history dependence (thizotvopy), steady state shear rate thinning (pseudoplasticity) and constant internal structure shear rate thickening (dilatancy). The flow response at any given structure has been decoupled from structure-dependent response in carefully controlled rapid transient experiments done on a computer-controlled, high temperature, Couette geometry rheomneter. The data for Sn-15wt%Pb correlates well with the model.
Interaction Between Colloidal Particles in A.C. Electric Fields in the Relaxation Region of Double Layers
Authors: Hu Yue , Fraden Seth , Glass J. L. , Wenner L. E.
Published: March 2011

When an electric field is applied to a colloidal suspension of micronsize particles, the particles are attracted to each other in the direction of the external field. They line up to form chains and columns across the gap of the electrodes and therefore drastically change the rheological properties of the suspension. These electrorheological phenomena have been studied extensively by recent computer simulation work [1,2], and it is generally accepted that the interactions between the induced electric dipole moments of the particles are responsible for their alignment in the external fields. To avoid net migrations of particles in electric fields of small inhomogeneity, alternating fields are generally used in experiments.
Crystallization in Suspensions of “Hard” Colloidal Spheres
Authors: Ackerson Bruce J.
Published: March 2011

Extended Abstract

Submicron diameter polymethylmethacrylate (PMMA) particles suspended in a solvent mixture of tetralin and decalin have been observed to undergo a crystal to liquid phase transformation as a function of particle volume fraction[1]. This thermodynamic phase transformation and other measurements of the crystal structure [2], sedimentation rates [1], and response of particle microstructure to shear flow [3] suggest hard sphere behavior for the interparticle interactions.
Orientational Ordering of Rigid Rod Polymers in Shear Flow
Authors: Vugmeister B.E. , Wang C. , Ou-Yang H.D.
Published: March 2011

We present the results of experimental and theoretical study of the orientational ordering of rigid rod like polymers in the presence of shear flow. Shear induced birefringence was measured to determine the dependence of orientational order parameter S=<3cos2θ−l>/2 on the shear rate at different values of the volume fraction. Experimental results are discussed in terms of an approximate solution of the rotational diffusion equation in the presence of shear flow based on the construction of the effective interaction energy.
Direct Holographic Processing Using Laser Chemistry
Authors: Gilgen H. H. , Podlesnik D. , Chen C. J. , Osgood R. M.
Published: March 2011

By using two interfering laser beams to initiate localized chemical reactions at an interface, very high resolution, maskless microfabrication can be done over relatively large substrate areas. The resulting deposited or etched patterns can be used in a variety of electrooptical and electronic applications. In addition, this type of fabrication, which can be monitored in real time, provides insight into many new interfacial phenomena.
Plasma-Initiated Laser Deposition of Polycrystalline and Monocrystalline Silicon Films
Authors: Gee J. M. , Hargis P. J. , Carr M. J. , Tallant D. R. , Light R. W.
Published: March 2011

In this paper we report a new method of silicon deposition using the interaction between the radiation from a pulsed-ultraviolet excimer laser and the plasma species produced in a glow discharge in silane (SiH4). Examination of the deposited film by laser Raman spectroscopy and by transmission electron microscopy revealed that the morphology ranged from polycrystalline silicon at laser fluences of 0.13–0.17 J/cm2 to epitaxial silicon at fluences of 0.4–0.6 J/cm2 . Growth rates of 100 nm/min for polycrystalline silicon and 30 nm/min for monocrystalline silicon were achieved.
Localized Photoprocesses at Semiconductor-Electrolyte Interfaces Using a Programmable Laser Spot Scanner
Authors: Kavassalis C. A. , Longendorfer D. H. , Lelievre R. A. , Rauh R. D.
Published: March 2011

A highly focused laser can be used to perform spatially selective photoelectrochemistry at semiconductor-electrolyte interfaces. These processes may be used for imaging (etching, deposition, etc.) or for nondestructive mapping of semiconductor properties from photoelectric response. A programmable laser scanner is described which can be used for both. An example of imaging is given for photoelectrochemical etching of pits in CdSe electrodes, which may be applied to archival data storage. Nondestructive evaluation is shown for a CdS crystal, in which the lateral distribution of subband gap photovoltage response is related to surface states incurred by polishing damage.
Excimer-Laser-Initiated, Dry Etching of Single Crystal GaAs
Authors: Brewer P. , Halle S. , Osgood R. M.
Published: March 2011

Gas-phase UV-initiated (193 nm) photodissociations of methyl (CH3) and trifluoromethyl (CF3) containing compounds have been investigated for the dry etching of single crystal GaAs substrates. Etching rates of greater than 1 μ/min. have been observed. Etching rates and surface profiles will be discussed in terms of crystal orientation, reactive etching fragments, and laser-surface interactions. Products of the etching reactions have been examined by UV absorption, mass spectrometry and laser-induced fluorescence techniques. Applications to large scale and micron dimension etching processes will be briefly discussed.
Laser-Induced Chemical Etching of Solids: Promises and Challenges
Authors: Chuang T. J.
Published: March 2011

Recent studies have shown the potential of laser-induced chemical etching to become a powerful technique for processing electronic materials. In this paper, the unique strengths and limitations of the laser chemical approach are examined. Some photon-enhanced reaction mechanisms, in particular silicon-halogen reactions, are discussed to illustrate the many facets of the electronically, vibrationally and thermally activated surface processes. It is suggested that the field-assisted diffusion mechanism proposed by Winters, Coburn and Chuang may also be applicable to some photon-induced etching reactions. In addition, the salient features of the laser and the plasma-assisted etching methods are compared. The challenges to resolve certain fundamental and practical difficulties involved in developing the laser technique for processing technology are also outlined.
Laser-Induced Deposition of Silicon Films and Cars Diagnostics
Authors: Hanabusa M. , Kikuchi H.
Published: March 2011

Various laser-based deposition methods for preparation of silicon films have been reviewed briefly with emphasis on laser chemical vapor deposition (CVD). The main body of this paper is concerned with CO2laser CVD of silane. This is interesting because the observed dependence of deposition rates on laser wavelengths indicates that gas-phase reactions are involved in deposition processes and therefore we can apply a powerful new diagnostic means, coherent anti-Stokes Raman spectroscopy (CARS), to examine gas-phase dynamics. From N2CARS thermometry the CO2laser beams were found to raise the temperature of the gas containing silane, when they were tuned to absorption lines of SiH4. Silane CARS spectra were characterized by a complicated profile with double peaks. We interpreted the shape of the spectra as arising from excitation of rotational levels following gas-phase reactions. Applying this interpretation, we can judge how SiH4molecules are disturbed differently according to CO2laser wavelengths and a distance from a substrate.
Real-Time Diagnosis of Etching and Deposition Processes by Spectroscopic Ellipsometry
Authors: Aspnes D. E. , Chang R. P. H.
Published: March 2011

Recent advances in instrumentation and data analysis have made spectroscopic ellipsometry a routine analytic tool with submonolayer sensitivity for monitoring and controlling cleaning, etching, deposition, or other processes that take place in relatively high-pressure or reactive environments. We discuss representative applications in chemical etching, plasma processing, and MOCVD to illustrate analytical procedures and to indicate other potential uses of the technique. The possibility of extracting surface information already carried in the polarization state of the processing laser beam is also discussed.
Mechanism of Laser-Assisted Evaporation of II-VI Semiconductors
Authors: Cheung J. T.
Published: March 2011

The evaporation mechanism of CdTe, HgTe and HgO.7CdO.3Te under high power laser irradiation was investigated using mass spectroscopy. Results were compared to thermal evaporation. Thermal evaporation yields Te molecules and Cd(Hg) atoms. In the case of HgTe and Hgo.7Cdo.3Te, the evaporation is noncongruent. Evaporation induced by the irradiation of 1.06 μm Nd:YAG laser pulses evolves atomic Hg, Cd and Te congruently. The dissociative and congruent nature of this process makes it a very attractive technique for depositing thin films.
Ion Dynamics in Low Frequency RF Plasmas
Authors: Gottscho Richard A. , Flamm Daniel L. , Burton Randolph H. , Donnelly Vincent M.
Published: March 2011

We describe the use of time-resolved laser-induced fluorescence (TRLIF) and plasma-induced emission (PIE) spectroscopy in studying the dynamics of ion transport, formation, and loss in low frequency RF plasmas, used in plasma etching and deposition. N2+ and Cl2+ ions formed in N2, Cl2, and N2/Cl2 discharges were monitored as a function of both position between the electrodes and magnitude of the applied rf potential. In the discharge center, TRLIF was used to measure ground state ionic lifetimes. In N2/Cl2 mixtures, N2+ was found to charge exchange rapidly with Cl2 and Cl to form Cl2+ and Cl+. In the electrode sheaths, the ion response to the applied potential was evident from periodic depletion of the ion concentration as a result of acceleration by the field. From the spatial variation in the ion concentration time dependence, we deduce that the sheaths expand and contract with the same period as the applied potential.
Recent Advances in Laser-Enhanced Plating
Authors: Von Gutfeld R. J. , Gelchinski M. H. , Vigliotti D. R. , Romankiw L. T.
Published: March 2011

A summary of the recent work on laser-enhanced gold plating is presented. The purpose of the study has been to obtain rapid maskless plating on thick metal samples. Results will be described on the plating rates for a variety of laser and electrical parameters. The most recent work on a laser-jet plating system will be discussed. With this system, rates of up to 30 μm/s have been achieved on 8 mil thick Be-Cu samples.
Pyrolytic Laser Activation Of Cds Thin Film Photoconductors
Authors: Kitai A. H. , Wolga G. J.
Published: March 2011

CdS and CdS:Ag thin films, deposited at room temperature, were irradiated using an argon-ion laser, causing them to become photoconductive in the path of the laser beam. Physical deformation of the thin films is reported, and the optical and electrical properties of the photoconductive devices thus fabricated are described. We suggest this as a means to fabricate small area, patterned photoconductors with the benefit of maskless, low temperature processing.
Primary and Secondary Ion Deposition of Epitaxial Semiconductor Films From Laser-Induced Plasmas
Authors: Lubben D. , Barneti S.A. , Suzuki K. , Greene J.E.
Published: March 2011

Primary and secondary ion deposition of epitaxial semiconductor films from laser-induced plasmas is reported Laser plasmas were generated by focusing 15 ns, 107 to 108 W/cm2 pulses of 5 eV photons from a KrF excimer laser onto Ge and Si wafer targets. Time-of-flight, current-voltage, and film thickness measurements at secondary (i.e., ion) targets indicated that the ions were emitted, with an average energy of ∼40 eV, in a distribution which was strongly peaked in the normal direction. Primary ion deposition was performed by placing substrates on an ion target/substrate heater biased to give additional ion acceleration as required. Secondary deposition was achieved by biasing the ion target, in this case a wafer of the same material as the laser target, sufficiently negative to sputter target material onto a third electrode. Epitaxial Si on (100) Si and Ge on (100) Si and (100) GaAs were obtained by both methods. Hall effect measurements on heteroepitaxial Ge grown at 1 μm/hr on GaAs substrates by primary deposition showed thatfthe films were p-type with hole concentrations of ∼1018 cm−3 and mobilities of ∼150 cm2/V-sec.
A Model for the Laser-Induced Chemical Vapor Deposition of Hydrogenated Amorphous Silicon
Authors: Meunier M. , Flint J.H. , Adler D. , Haggerty J.S.
Published: March 2011

We propose a model for laser-induced chemical vapor deposition in which the growth of hydrogenated amorphous silicon (a-Si:H) thin films is rate-controlled by the gas phase homogeneous thermal dissociation of SiH4 The gas temperature is determined by a steady-state balance between energy absorbed from the laser and energy lost by thermal conduction.The film properties are primarily controlled by the substrate temperature.
On the Origin of Iabmella-Like Inhmog Ities in Owupled Laser-Semiccnducior Interacticns
Authors: Sipe J.E. , Youn Jeff F. , Van Driel H.M.
Published: March 2011

Near the threshold for laser-induced melting of semiconductors like Si and Ge, the resulting surface morphology is characterized by spatial inhcaogeneities. For cw illumination, several authors have observed the formation of randan, microscopic lamellae interspersed with molten regions, for incident fluences between threshold and approximately twice threshold.We demonstrate experimentally that such lamellae also form under pulsed conditions for 20nsec, 1.06μ pulses incident on Ge.Theoretically, we consider the simpler case of cw illumination on a bulk sample: We show that, although in principle it should be possible to form uniform melt layers of arbitrarily small thickness, for melt depths less than the skin depth of the radiation in the liquid any spatial modulation of the liquid-solid interface leads to instabilities in the coupled laser-material system.These instabilities would result in runaway inhamogeneous heat flow and hence to the formation of lamellae.Three distinct types of instabilities are identified for melt-front penetrations of less than ∼l000Å in Ge.
Laser Direct Write Technologies as Tools for Gate-Array Development*
Authors: Silversmith D. J. , Ehrlich D. J. , Tsao J. Y. , Mountain R. W. , Sedlacek J. H. C.
Published: March 2011

Using CMOS, poly-Si gate, single-level metal, gate-array chips, techniques have been developed to reconfigure the interconnect metallization on individual circuits without degradation of device or circuit performance. These techniques involve a laser-assisted capillary wet-etch process for highly selective removal of Al-alloy interconnects and laser CVD of doped poly-Si links. This technique may be useful for prototyping, testing and optimization of gate-array and standard-cell designs and layouts.
Uv Laser-Initiated Deposition of Al2O3 Films: The Effect of Surface Irradiation
Authors: Deutsch T. F. , Silversmith D. J. , Mountain R. W.
Published: March 2011

The effects of 193 and 248 nm UV surface irradiation on the properties of Al2O3 films produced by UV laser-initiated deposition have been investigated using ellipsometry and electrical measurements. The UV irradiated region shows a higher refractive index than the unirradiated regions, indicating that densification has occurred. Energy fluences as low as 1 mJ/cm2, too low to cause significant transient heating, produce measurable effects. The results suggest that UV irradiation may be used to obtain lower deposition temperatures in a variety of deposition systems.
Interfacial Effect in Water-Infiltrated Nanoporous Media
Authors: Chen Zhongshan , Jiang Fangxing , Li J. C. M.
Published: March 2011

Water infiltrated nanoporous glasses have a damping peak at about 1 Hz (4.6 nm pore size) and 6 Hz (8.8 nm pore size) at room temperature; their relaxation strengths are consistent with the damping mechanism in which water flows from the regions of compression to those of tension. However, the damping peaks disappear when water content is below 60% for the 4.6 urn pore size glass and 40% for the 8.8 urn pore size glass. These water contents correspond to about a 0.85 and 1.0 urn thick interfacial water layer on the internal surfaces of the nanoporous glasses. The adsorbed layer contributes only to the damping background. Finally, dependencies of relaxation time on sample thickness, bulk modulus and viscosity agree well with the predictions of the model.
Esm Method and Laplace Transform of Klafter-Bluken Equation for Det Analysis in Polyker Blend Like Naterials.
Authors: Pekcan önder
Published: March 2011

Fluorescence decay curves from particles composed of poly(vinyl acetate) (PVAc) and naphthalene (N) labelled poly (2-ethylhexyl methacrylate) (PEHMA) were analyzed for Direct Energy Transfer (DET) from N to anthracene by the exponential series method(ESM). An averaged apparent dimension of d=2.0 were observed. The Laplace transformed Klafter-Blumen(KB) equation for the lifetime distribution was used to interpret these dimensions. Additional fluorescence experiments were carried out on Polymer films composed of the same material above. Exposure of the films to a pentane solution of 9-anthrylmethyl pivalete (AMP) transferred the AMP molecules exclusively to the PEHMA phase of the material. ESM analysis together with transformed KB equation showed that PEHMA thread has a unique dimension of 1.3 in PVAc matrix of this polymer film.
A New Mechanism for Lubrication in Liquid Crystals
Authors: Bruinsma Robijn F. , Safinya Cyrus R.
Published: March 2011

Recent synchrotron X-ray scattering studies on the thermotropic liquid crystal lubricant 8CB under shear flow have shown that for high shear rates the smectic layers are oriented perpendicular to the orientation assumed by conventional solid layered lubricants. This result invalidates existing theories of the lubrication mechanism of these materials. We show that the new orientation is the result of flow deformation of thermal fluctuations. This same mechanism is found to create a “normal stress” lift-force which we propose as the new lubrication mechanism.
The Influence of Local Magnetization on Transport in Cd0.91Mn0.09Te:In
Authors: Molnar S. Von , Penney T. , Terry I. , Becla P.
Published: March 2011

We describe the influence of local magnetization on electron localization and transport properties on the insulating side of the metal insulator transition in the dilute magnetic persistent photoconductor Cd0.091Mn0.09Te:ln. Measurements of both the temperature dependence of the transport properties, and also the dielectric constant, are reported for just one sample in which the carrier concentration n was varied by photodoping. From these results we are able to extract the carrier concentration dependence of the localization length and the permitivity of the electrons. We also report onl a new transport effect which occurs at ultra low temperatures and/or carrier concentrations very close to the metal insulator transition. We find that this mechanism is totally magnetic in origin and are able to explain it in terms of the well devewloped ideas of magnetic polarons in magnetic semiconductors.
Phasie Transitions in Confined Molecularly-Thin Films
Authors: Cushman John H. , Diestler D. J. , Schoin M. K.
Published: March 2011

Phase changes in Lennard-Jones (IJ) and Stockmayer fluids confined between two parallel fcc (100) planes of rigidly fixed IJ atoms are studied by means of mixed isostress-isostrain canonical and isostrain grand-canonical Monte Carlo methods, and a microcanonical ensemble molecular dynamics technique. A nonequilibrium continuum thermodynamic derivation of the constitutive laws for the basic slit-pore model is developed and an equilibrium statistical thermodynamics anolog is reviewed. Independent constitutive parameters are chosen from the list T, μ, Ēv or their thermodynamic duals μ, N, Tij where T is absolute temperature, μ is the chemical potential, Ēv is the infinitesimal strain tensor, N is the particle number, μ is the entropy and Tij is the Piola stress tensor.

Relaxation in monolayer films is studied via mean square displacement of an atom. The vicinal atoms are found to diffuse anomolously slow in accordance with a power-law relation.
Biomimetic Process for Preparing Magnetite Fibers
Authors: Lawton Carl W. , Shields Christopher S.
Published: March 2011

Two different biomimetic strategies were utilized in the formation of magnetite fibers. The first strategy utilized natural (Sphaerotilus natans sheaths) or synthetic (hollow fibers) matrices for magnetite formation. The second strategy made use of an iron-hydroxide intermediate that was subsequently chemically converted to magnetite within the biomimetic matrix. The formation of magnetite was determined by both visual and x-ray diffraction analysis. This process has advantages over conventional routes because of the expense and handling problems associated with the production of ceramic whiskers and fibers. The magnetite formed by this process may prove to have unique properties due to its unusual fiber structure.