This paper reports on new experimental findings and conclusions regarding the pulsed-laser-induced melting-and-solidification behavior of PECVD a-Si films. The experimental findings reveal that, within the partial-mel...
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This paper reports on new experimental findings and conclusions regarding the pulsed-laser-induced melting-and-solidification behavior of PECVD a-Si films. The experimental findings reveal that, within the partial-melting regime, these a-Si films can melt and solidify in ways that are distinct from, and more complex than, those encountered in microcrystalline-cluster-rich LPCVD a-Si films. Specifically (1) spatially dispersed and temporally stochastic nucleation of crystalline solids occurring relatively effectively at the moving liquid-amorphous interface, (2) very defective crystal growth that leads to the formation of fine-grained Si proceeding, at least initially after the nucleation, at a sufficiently rapidly moving crystal solidification front, and (3) the propensity for local preferential remelting of the defective regions and grain boundaries (while the beam is still on) are identified as being some of the fundamental factors that can participate and affect how these PECVD films melt and solidify.
The microstructure and mechanical properties of abalone shell were studied. It was found that fracture strength, αf, is 180 MPa, and fracture toughness, KIC, is 7 ± 3 MPa-m1/2; these values are comparable with o...
The microstructure and mechanical properties of abalone shell were studied. It was found that fracture strength, αf, is 180 MPa, and fracture toughness, KIC, is 7 ± 3 MPa-m1/2; these values are comparable with or better than most “high technology” ceramic materials. The microarchitecture of the nacre section of the red abalone shell is similar to a “brick and mortar” structure, where CaCO3 is the brick and organic matter is the mortar, constituting 95% and 5% of the microstructure by volume, respectively. This impressive combination of af and KIc values is attributed to the laminated structure of the shell with hard and thick (0.25±0.5 μm) CaCO3 and superplastic and thin (20–30 nm) organic components. Although there are several toughening mechanisms operating in the shell, fractographic studies identified sliding of CaCO3 layers and bridging by the organic layers to be the most effective ones. These phases also have a strong interface. The results of our experiments are discussed in the context of using abalone shell as a model for the design of synthetic laminates such as cermet (ceramic-metal) and cerpoly (ceramic-polymer) composites.
Dynamic behavior of particulate/porous energetic materials in a broad range of dynamic conditions (low velocity impact and explosively driven expansion of rings) is discussed. Samples of these materials were fabricate...
Dynamic behavior of particulate/porous energetic materials in a broad range of dynamic conditions (low velocity impact and explosively driven expansion of rings) is discussed. Samples of these materials were fabricated using Cold Isostatic Pressing and Hot Isostatic Pressing with and without vacuum encapsulation. The current interest in these materials is due to the combination of their high strength and output of energy under critical conditions of mechanical deformation. They may exhibit high compressive and tensile strength with the ability to undergo bulk distributed fracture resulting in small size reactive fragments. The mechanical properties of these materials and the fragment sizes produced by fracturing are highly sensitive to mesostructure. For example, the dynamic strength of Al-W composites with fine W particles is significantly larger than the strength of composites with coarse W particles at the same porosity. The morphology of W inclusions had a strong effect on the dynamic strength and fracture pattern. Experimental results are compared with numerical data.
High-efficiency polymer light-emitting diodes (LEDs) are often fabricated using multilayered structures with separate carrier transport and light emission layers. Recently, we reported on the synthesis and electrolumi...
High-efficiency polymer light-emitting diodes (LEDs) are often fabricated using multilayered structures with separate carrier transport and light emission layers. Recently, we reported on the synthesis and electroluminescence (EL) characteristics of poly(2,6-quinoline vinylene) (PQV) and its potential for use as an electron transport layer in poly(phenylene vinylene) (PPV) LEDs. To take advantage of the high emission efficiency of PPV and electron accepting ability of PQV, a copolymer of PPV and PQV, poly(phenylene vinylene-co-quinoline vinylene) (PPVQV) was synthesized via the precursor polymer route and converted to the conjugated form by thermal elimination. When used as the emissive layer with Indium-Tin Oxide (ITO) and aluminum as positive and negative electrodes respectively, PPVQV emitted blue light at an onset electric field of 1.05x 106 V/cm and emission efficiency of 0.08%. Improved efficiencies of the order of 0.15% were obtained when blends of copolymer with PPV were used in conjunction with PPV in a multi-layered structure. Along with copolymer chemical characterization data, results from EL studies on single and multi-layered devices are discussed. We also report on a simple and costeffective chemical deposition of silver for the negative electrode in polymer LEDs.
Sol-gel encapsulation has recently surfaced as a successful approach to biomolecule immobilization. Proteins, including enzymes, are trapped in the pores of the sol-gel derived glass while retaining their spectroscopi...
Sol-gel encapsulation has recently surfaced as a successful approach to biomolecule immobilization. Proteins, including enzymes, are trapped in the pores of the sol-gel derived glass while retaining their spectroscopic properties and biological activity. Our current work extends the unique capabilities of biomolecule-doped sol-gel materials to the detection of glutamate, the major excitatory neurotransmitter in the central nervous system. We are developing an in vivo fiber optic biosensor for glutamate along with methods to achieve continuous monitoring. In our research to date we have encapsulated GDH in a silica sol-gel film on the tip of an optical fiber. GDH catalyzes the oxidative deamination of glutamate to α-ketoglutarate and the simultaneous reduction of NAD+ to NADH. To quantify the glutamate concentration, we observe the rate of change of NADH fluorescence as a function of time. An important consideration for continuous in vivo monitoring is the incorporation of a selfsustaining NAD+ source. We have adopted a photochemical means of regenerating NAD+ from NADH, by irradiating thionine (3,7-diaminophenothiazin-5-ium) which we incorporate into the sol-gel sensor material. When excited with visible light (λabc∼ 596 nm), thionine undergoes a reaction with NADH resulting in a non-fluorescent form of thionine and NAD+. We have characterized the kinetics of this reaction in the sol-gel matrix, and have shown that the reaction results in regenerated co-factor that is usable by GDH for the oxidation of glutamate.
Layer-by-layer (LbL) assembly was used to deposit transparent, highly conductive thin films using aqueous solutions of nanotubes stabilized by deoxycholate (DOC) and poly(diallyl-dimethylammonium chloride) (PDDA). Thr...
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Layer-by-layer (LbL) assembly was used to deposit transparent, highly conductive thin films using aqueous solutions of nanotubes stabilized by deoxycholate (DOC) and poly(diallyl-dimethylammonium chloride) (PDDA). Three different types of carbon nanotubes (CNTs) were used: (1) multi-walled carbon nanotubes (MWNTs), (2) a mixture of single, di- and tri-walled nanotubes (XM grade) and (3) purified HiPCO single-walled carbon nanotubes (SWNTs). SWNTs produced the most transparent (> 85 %T across visible spectrum) and electrically conductive (˜ 150 S/cm) 20-bilayer films with 42 nm thickness. Moreover, optoelectronic performance of SWNT-based thin films was improved with heat treatment due to the removal of PDDA. A 20-bilayer SWNT LbL film achieved a conductivity of 369 S/cm with a 5 min exposure to 400 °C. This study demonstrates the ability of the LbL technique to produce highly transparent and conductive nanotube-based thin films, which may be useful for a variety of large area electronics applications.
Polysilsesquioxanes,-[RSi(O)1.5 ]x-, exhibit many properties that are potentially quite useful for industrial applications. These properties include high temperature stability (−600°C in O2); good adhesion and, l...
Polysilsesquioxanes,-[RSi(O)1.5 ]x-, exhibit many properties that are potentially quite useful for industrial applications. These properties include high temperature stability (−600°C in O2); good adhesion and, liquid crystal-like behavior for some derivatives. Moreover, [MeSi(O)l.5]x, polymethylsilsesquioxane has been used successfully as a precursor for the fabrication of carbon fiber/“black glass” (SiO2/SiC/C) composites and “black glass” fibers. Current methods of preparation depend on hydrolysis of RSiCl3 or RSi(OR)3. Unfortunately, this approach leads to several products that are difficult to purify because polysilsesquioxanes exhibit a great propensity for forming gels. We describe here a simple catalytic approach to the synthesis of polymethylsilsesquioxane copolymers of the type -[MeRSiO].3[MeSi(O)1.5].7- where R - H, OMe, OEt, OnPr and OnBu. The R - H copolymer is produced by catalytic redistribution of -[MeHSiO]xoligomers using dimethyltitanocene, Cp2TiMe2 as the catalyst precursor. Following catalytic redistribution, the resulting copolymer, -[MeHSiO].3[MeSi(O)1.5].7−, is reacted in situ with alcohols to produce -[Me(R’O)SiO].3[MeSi(0)1.5].7− (where R’ - Me, Et, nPr and nBu) which serve as masked forms of the polymethylsilsesquioxane. These new copolymers have been characterized by 1H, 13C and 29Si NMR TGA and DTA. The NMR studies allow us to assign structures for the copolymer. These new copolymers exhibit improved tractability. Their high temperature properties are all quite similar; although, the MeO-, EtO- and especially the nPrO- derivatives give much higher ceramic yields than expected.
We successfully engineered Si nano-columns with different cross-sectional geometries by e-beam evaporation with an angle between source and substrate. The Si nano-columns were grown as pillars with square, triangle an...
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This investigation studied the effects of Ho3+ and Er3+ on the luminescence of the blue emitting phosphor yttrium silicate, (Y1-mCem)2SiO5. Yttrium silicate has a large emission tail that extends into the red portion ...
This investigation studied the effects of Ho3+ and Er3+ on the luminescence of the blue emitting phosphor yttrium silicate, (Y1-mCem)2SiO5. Yttrium silicate has a large emission tail that extends into the red portion of the visual spectrum. To improve the chromaticity of this phosphor to give it a more saturated blue color, the emission intensity of the tail needs to be decreased. Photoluminscence and low-voltage cathodoluminescence measurements were performed on yttrium silicate phosphors with varying concentrations of Gd3+, Ho3+ and Er3+. It was found that when co-doping with Ho3+ and Er3+, the relative intensity of the emission tail was decreased, but so to was the overall luminescence intensity of this phosphor.
The lithium aluminum titanium phosphate (LATP)/Polyacrylonitrile (PAN) composite fiber-based membrane were prepared by electrospinning composite solution of LATP and PAN in N, N-dimethylformamide(DMF). The crystalliza...
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ISBN:
(纸本)9787122120199
The lithium aluminum titanium phosphate (LATP)/Polyacrylonitrile (PAN) composite fiber-based membrane were prepared by electrospinning composite solution of LATP and PAN in N, N-dimethylformamide(DMF). The crystallization phase of the LATP particles were characterized by X-ray diffraction(XRD). The electrolyte uptakes of the electrospun LATP/PAN composite fiber-based membranes were also evaluated. In addition, the electrochemical performance of the liquid electrolyte-soaked electrospun LATP/PAN composite fiber-based is also improved after the introduction of LATP particles.
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