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Abstract
Coaxial nanotubes, composed of silicon nitride outer wall and silica inner wall, were prepared via a two-step process, firstly synthesizing three-layer silicon nitride–silica–In nanocables and then removing the indium core from nanocables via heating in vacuum. The nanotubes are amorphous and typically have round cross-sections. The outer diameters of nanotubes range from 100 to 300 nm. Photoluminescence measurement show that the nanotubes exhibit a weak ultraviolet emission at 379 nm and a strong visible light emission centered at 622 nm with a shoulder at 578 nm.
... Furthermore, a variety of nanomaterials including CdSe nanorods, 114 Ge nanorods, 115 In 2 S 3 nanorods, 116 Bi 2 S 3 nanorods, 117 silicon nitride nanotubes, 118 and titania nanotubes 89 have been filled into silica nanotubes to prepare composite functional nanotubes for applications in various areas such as biosensing, chemical sensors, photocatalysis, selective recognition and separation. The design of silica nanotube-based nanofiltration systems was developed by El-Safty and co-workers 119 where mesoporous silica nanotubes hybrid membranes were found to be suitable for separation of biomolecules and were used as highly efficient ultrafine filtration systems for noble metal nanoparticles and semiconductor nanocrystals. ...
Silica (SiO2) is one of the most frequently used inorganic materials. This review covers the research progress in the synthesis of one-dimensional silicananotubes as well as the newest aspects of silicananotubes in applications where their structural attributes are exploited. The synthetic methods for well-defined silicananotubes and a variety of specific silicananotubes including hollow silicananotubes, mesoporous silicananotubes, chiral or helical silicananotubes are summarized. One-dimensional tubular silica nanomaterials display structures that differ from those of other kinds of nanostructured silica materials and provide unique features such as very uniform diameter, open at both ends. In addition, sol–gel process and silane chemistry offer the reliable and robust surface modification or functionalization of silicananotubes. Attractively, end functionalization of silicananotubes may be able to control drug release, resulting in their wide applications in controlled drug and gene delivery; also their distinctive inner and outer surfaces can be differentially functionalized making silicananotubes ideal multifunctional nanostructure candidates for biomedical applications in various areas such as biosensing, bioseparation and biocatalysis.
Three types of composite nanotube heterostructures (two double-layered and one triple-layered structure) are synthesized by simple heat treatment, forming SiC–SiO2, C–SiO2, and C–SiC–SiO2 composite coaxial nanotubes. These multilayered composite nanotubes consist of several components with different electrical properties, for example, metal, semiconductor, and insulator components. In particular, C–SiC–SiO2 triple-layered nanotubes with metallic, semiconducting, and insulating layers are synthesized for the first time. These multilayered nanotubes can be expected to find applications in nanoscale heterostructure electronic and optical devices.
Belt-shaped Si3N4 whiskers have been synthesized by a carbothermal reduction and nitridation method. The whiskers had an average width of 800 nm, width-to-thickness ratios of 4–6, and a length in the range of several tens of microns to hundreds of microns. Photoluminescence (PL) spectrum of the whiskers showed a strong blue emission peak at 410 nm, and PL lifetime measurement exhibited a rapid decay within a few nanoseconds. The growth of the whiskers was supposed to be dominated by a vapor–solid (VS) mechanism.
Top-emitting yellow light polymer light-emitting diodes (PLEDs) were fabricated on the FR4 board for future application in optical interconnects. A 100μm thick glass plate with sputtered Ag films on the back side for light reflection was bonded to the board for smooth surface. The PLED had a structure of indium tin oxide /poly(3,4-ethylenedioxythiophene)poly(styrenesulfonate)/phenyl substituted polypa raphenylene-vinylene/Ba/Ag and reached the brightness of 4528cd/m2 with a corresponding current efficiency of 7cd/A. A small AC signal imposed onto a DC bias was employed to characterize the electroluminescence delay time and hole mobility in the PDY-132 super yellow films.
The quest for materials with molecular scale properties that can satisfy the demands of the 21st century has led to the development of one dimensional nanostructures, ODNS. Nearly, every class of traditional material has an ODNS counterpart. ODNS has a profound impact in nanoelectronics, nanodevices and systems, nanocomposite materials, alternative energy resources and national security. The interface of nanoscience and technology with biological and therapeutic sciences is expected to radically improve the ability to provide efficient treatments in otherwise impossible situations. Ironically, the huge investment in the past few years across the globe is yet to bring the real benefit of nanotechnology in day to day life. While scientists and engineers are working towards this goal, concerns about the possible harmful effects of the high aspect ratio materials are increasing every day. Following is an effort to assimilate most of the aforementioned aspects including the entire gamut of ODNS, i.e., elements, ceramics, polymers and composites, with a brief discussion on CNT and toxicology. The focus of this article is mainly on the science behind the synthesis and properties of the ODNS rather than the device fabrication. However, a few challenges in the field of device fabrication are mentioned in appropriate contexts. Possible mechanisms of the ODNS evolution from various methods, such as vapor liquid solid (VLS), template based and electrochemically induced growth, have been discussed in detail. Electron microscopy analysis has received special focus in determining the unique structural features. The article concludes by discussing current research related to environment and toxicology effects and current challenges in this rapidly evolving field.
Highly efficient top-emitting organic light-emitting devices (TOLEDs) using a Fe3O4 modified Ag anode have been demonstrated. The tris-(8-hydroxyquinoline) aluminum-based TOLEDs exhibit a very low turn-on voltage of 2.5V and a high current efficiency of 8.1cd/A. The improved properties for the TOLEDs is mainly due to the enhanced hole injection by introducing the anodic buffer. The mechanism of this enhanced hole injection is studied by the X-ray and ultra-violet photoemission spectroscopy, which demonstrated that the dipole layer is formed at the anode/organic interface and the hole-injection barrier is therefore reduced after introducing the thin Fe3O4 film between the Ag anode and the hole-transport layer.
We have developed transparent organic light-emitting devices (TOLEDs) with CsCl capping layers deposited on top of semitransparent Ca/Ag cathodes. The CsCl layer was deposited by the thermal evaporation method which does not result in any damage to the underlying organic layers. The transmittance was enhanced by depositing the CsCl layer on the Ca/Ag cathode. The current efficiency measured at the cathode side increased by the enhanced transmittance of the cathode, whereas the anode-side current efficiency was determined by the reflectance of the cathode. In a TOLED with semitransparent Ca/Ag/CsCl layer, the microcavity effect was not profound so that the electroluminescence spectrum was not seriously changed by the CsCl capping layer.
Study objective:
Although men may influence women's reproductive choices, little is known about men's knowledge regarding gynecologic matters (eg, sex, anatomy, and contraception). This study aimed to evaluate the level of gynecologic knowledge among college students, particularly to investigate the differences in knowledge between men and women.
Design, setting, participants:
We administered a survey to assess knowledge of sex, contraception, and female anatomy to college students at a Midwestern university during the spring 2010 semester.
Interventions and main outcome measures:
The survey included demographic and behavioral questions, 9 general gynecology knowledge items, and 11 female anatomy items. A total gynecology score was generated by summing the correct responses to 20 items.
Results:
The 236 respondents included 98 men and 138 women (aged 18-36 years). Women scored higher than men on 19 of 20 individual items, with mean total scores of 13.4 vs 10.1 (P < .01). There was a trend for gynecologic knowledge to be higher among those who reported having had been STI tested (P = .13), and whose parents had discussed anatomy with them (P = .07). In multivariable modeling, being male was associated with lower mean knowledge scores, whereas increasing age and having a parent who discussed anatomy were associated with greater knowledge scores, even while controlling for having a gynecologist parent, multiple sexual partners, and prior STI testing.
Conclusions:
College men have lower gynecologic knowledge than women. Increasing age and having a parent who discussed anatomy with them served as predictors of higher knowledge scores. Because men influence women's reproductive choices, efforts to increase men's knowledge are needed.
We developed an approach to realize blue, green and red emission from top-emitting white organic light-emitting diodes (OLEDs) through depositing exterior tunable optical films on top of the OLEDs. Three primary colors for full color display including blue, green and red emission are achieved by controlling the wavelength-dependent transmittance of the multilayer optical films overlaid on the emissive layer. The advantage of such a device configuration is that the emissive color of the OLEDs can be tuned via the exterior optical films which do not affect the electrical characteristics of the device. This may provide a way to realize full color display by using white top-emitting OLEDs.
The authors’ endeavors in recent years to synthesize novel inorganic semiconducting nanowires, to analyze their atomic structures using state-of-the-art electron microscopy facilities and techniques, and to evaluate electrical properties are highlighted. Along with a general survey of nanostructures prepared and thoroughly characterized in the laboratory, particular emphasis is placed on analysis of non-standard nanowires in the Si-ZnS and B-C-N inorganic systems. Si-ZnS biaxial nanowire heterojunctions are found to be n-type semiconductors, due primarily to a lower resistance Si-path. Fractal-like B-C-N nanofibers display high-resistivity I-V curves arising from enrichment of the nanostructure periphery by the insulating BN-rich phase, as revealed by spatially-resolved chemical mapping during energy-filtering electron microscopy.
Gallium-doped silicon nitride nanowires sheathed with amorphous silicon oxynitride have been prepared on silicon substrates using GaN as the source of Ga. Ga plays important roles not only in the formation of silicon nitride nanowires but also their oxidation, forming the sheath of silicon oxynitride. The as-grown nanowires are of significance in facilitating complementary metal-oxide semiconductor-based nanodevice manufacturing. The photoluminescence spectra of the nanowires at 10K and 300 K are also investigated. (c) 2005 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Thermally stimulated exoelectron emission method is applied to amorphous silicon nitride (α-Si3N4) thin insulating films in the temperature region (300–550) K for energy spectroscopy of electronic states. The measured spectrum of electron (hole) traps is in good agreement with the known data obtained by other methods. The experimental data are interpreted on the basis of the model of electron-hole recombination in the two-center Auger process. © 2002 American Institute of Physics.
White electroluminescence (EL) was observed from hydrogenated amorphous-SiNx-based light-emitting device. Silicon nitride thin films were deposited on the indium-tin-oxide (ITO)-coated glass substrate by plasma enhanced chemical vapor deposition method with a mixture of Ar-diluted 5% SiH4 and pure N2 gases, in the ratio 2 to 1. Measured x value of the film is 0.56, and the corresponding photoluminescence of a-SiN0.56:H thin film exhibited a red-infrared spectrum, centered at 630 nm. The layer structure of the EL device is ITO/a-SiN0.56:H (80 nm)/Al, with light emitting from the ITO layer, recognizable by the naked eye in the dark, under the 14 V forward bias conditions. White EL spectra from ∼400 to 750 nm, with a central peak at 560 nm, were observed in the hydrogenated amorphous silicon nitride EL device. A carrier transport mechanism was suggested, and the EL was attributed to the recombination of carriers through the luminescent states. © 2002 American Institute of Physics.
We investigated photoluminescence (PL) from one-dimensional photonic band gap structures. The photonic crystals, a Fabry–Perot
(FP) resonator and a coupled-microcavity (CMC) structure, were fabricated by using alternating hydrogenated amorphous-silicon-nitride
and hydrogenated amorphous-silicon-oxide layers. It was observed that these structures strongly modify the PL spectra from
optically active amorphous-silicon-nitride thin films. Narrow-band and wide-band PL spectra were achieved in the FP microcavity
and the CMC structure, respectively. The angle dependence of PL peak of the FP resonator was also investigated. We also observed
that the spontaneous emission increased drastically at the coupled-cavity band edge of the CMC structure due to extremely
low group velocity and long photon lifetime. The measurements agree well with the transfer-matrix method results and the prediction
of the tight-binding approximation.
Hollow nanotubes comprised of In2O3 and Ga2O3 have been successfully synthesized for the first time via sol–gel chemistry and porous alumina templating thereby providing a new morphology for these important semiconductor oxides. The nanotubes are characterized by SEM, XRD and XPS, and the length (typically tens of microns) and outside and inside diameter (of the order of 100 nm) can be varied by selecting the template dimensions and sol immersion time. This new morphology with a large surface area may be important in applications ranging from gas sensors to optoelectronic nanodevices.
Monodisperse hollow nanocylinders consisting of crystalline titania particles have been directly prepared in a porous alumina membrane by a deposition technique using an aqueous solution system of titanium tetrafluoride.
Planar microcavities based on amorphous silicon-nitride Fabry–Perot (F–P) structures have been grown by plasma-enhanced-chemical-vapor deposition (PECVD). Tunable narrow emission bands, directionality of the radiation pattern and a resonant enhancement of the luminescence intensity have been demonstrated. The results, which are promising for thin film light emitting devices, could be explained in terms of a weak coupling regime between photons and electronic excitations, where a spatial redistribution of the spontaneous emission (SE) occurs.
A method to prepare silicon nitride nanoscale rods using carbon nanotube as a template has been presented in this letter. The products of the reaction of carbon nanotubes with a mixture of Si and SiO2 powder in nitrogen atmosphere are β-Si3N4, α-Si3N4, and Si2N2O nanorods. The sizes of the nanorods are 4–40 nm in diameter and up to several microns in length. The formation mechanism of the nanorods has also been discussed. © 1997 American Institute of Physics.
The geometric and electronic structure and the optical, vibrational, and magnetic properties of paramagnetic point defects in Si3N4 have been studied by means of ab initio quantum-chemical methods. Using cluster models and gradient-corrected density functional theory or configuration interaction (CI) wave functions, we have studied the N(3)equivalent to Si-. and Si-2=N-. paramagnetic point defects, also known as K-0 and N-0 centers, respectively. The computed ground-state properties, in particular the hyperfine coupling constants of N(3)equivalent to Si-. and Si-2=N-.. the vibrational spectra of the corresponding hydrogenated centers, N(3)equivalent to Si-H and Si-2=N-H, and the valence density of states are correctly described, showing the adequacy of the cluster models used for the study of point defects in silicon nitride. The optical transitions associated with N and K centers have been computed by means of CI calculations. The results are compared with those of the analogous defects in SiO2, the nonbridging oxygen and the E' center, respectively. [S0163-1829(99)12741-3].
Well-aligned silica nanotubes with lengths up to 0.9-1.0 mm have been prepared via a vapor-liquid-solid process. The nanotubes are either partially filled with indium or hollow (see Figure). The thermal expansion behavior of a liquid indium column inside a silica nanotube, a prospective novel inorganic nanotube-based nanothermometer, is analyzed in a transmission electron microscope.
A novel approach using unoxidized porous Si (UPS) as an isolation material for mixed-signal integrated circuit applications is presented. Very thick PS can be locally fabricated without severe stress problems. Relative dielectric constants of PS are adjustable from 3 to 9 by changing porosity from 78% to 24%. PS with more than 51% porosity has low loss tangent (<0.001) at 20 GHz demonstrating the superior dielectric material for RF ranges. PS trench inserted between two signal pads is shown to provide effective suppression of crosstalk through substrates. On-chip inductors built on porous Si regions have a Qmax of 29 at 7 GHz and a resonant frequency that is higher than 20 GHz. Superb and controllable dielectric properties as well as mechanical integrity of porous Si have clearly demonstrated its promising role among various RF isolation materials for mixed-signal integrated circuits and system-on-chip.
The energy levels of defect states in nanometer‐sized amorphous silicon nitride solids were systematically studied in terms of ultraviolet emission spectra. Six emission bands were observed, corresponding to 3.2, 2.8, 2.7, 2.4, 2.3, and 2.0 eV, respectively. With increasing the heat‐treated temperature from room temperature to 1000 °C in low vacuum, these emission bands became high. For the specimen heated at 1000 °C, a new emission band of 3.0 eV appeared. The appearance of these emission bands is closely related to the formation of the energy levels of the defect states in the energy gap. The origin of these emission bands are discussed in detail.
InS nanowires uniformly sheathed with amorphous SiO <sub>2</sub> were synthesized via a physical vapor deposition process. InS nanowires were 20–100 nm in diameter, and the SiO <sub>2</sub> sheaths were 5–20 nm in thickness. Single-crystalline InS cores displayed orthorhombic structure and their longitudinal directions were preferentially aligned in the [100] orientation. Pure SiO <sub>2</sub> nanotubes of typically round cross sections were also obtained by removing InS cores from the prepared nanocables via thermal evaporation. Photoluminescence measurements on these SiO <sub>2</sub> nanotubes demonstrated strong visible-light emission peaked at 570 nm. © 2003 American Institute of Physics.
We report macroscopic synthesis of silica nanotubes by the sol–gel template method. A large number of silica nanotubes with small diameters (30–50 nm) were produced and were shaped into flakes successfully. Strong photoluminescence (PL) was observed in both as-grown and annealed nanotube flakes. The PL spectra have maxima at 2.55 and 2.30 eV for the as-grown and annealed samples, respectively; the PL intensity of annealed nanotubes is much higher than that of as-grown nanotubes. The strong emission may be due to the Si–OH complex located on both the inner and outer surfaces of the nanotubes. The nanotube flakes we prepared may have potential applications in future integrated optical devices. © 2002 American Institute of Physics.
The energy levels of defect states in amorphous silicon nitride have been calculated and the results are used to identify the nature of trap states responsible for charge trapping during transport and the charge storage leading to memory action. We argue that the Si dangling bond is the memory trap in chemical vapor deposited memory devices and is also the center in plasma‐deposited nitride responsible for hopping at low electric fields and for charge‐trapping instabilities in amorphous silicon‐silicon nitride thin‐film transistors.
We present a novel method to synthesize high-density silicon nitride nanowires directly from the silicon substrates via a catalytic reaction under ammonia or hydrogen flow at 1200 °C. Gallium, gallium nitride, and iron nanoparticles deposited on the silicon substrate were used as catalysts. Gallium nitride can act as a nitrogen source under hydrogen flow. The average diameter of the nanowires is 40 nm and their length is about 300 μm. The silicon nitride nanowires consist of a defect-free single-crystalline α-phase crystal grown with various growth directions.
Si3N4 nanowires and SiO2 amorphous nanowires with diameters of 10–70 and 10–300 nm, respectively, have been synthesized by heating Si powders or Si/SiO2 mixtures with or without metal catalyst at 1200°C at ambient pressure. It is found that the reactant gases (N2, Ar and NH3) affect the yields and morphologies of the products, and the metal catalysts are not necessary in growth of the Si3N4 and SiO2 nanowires. High resolution electron microscopy (HREM) and electron energy loss spectrum (EELS) reveal that the Si3N4 nanowire is a single crystal covered by an amorphous SiO2 layer. The growth mechanism is assumed to be a vapor–solid (VS) process.
Since the discovery of carbon nanotubes in 1991 (ref. 1), there have been significant research efforts to synthesize nanometre-scale tubular forms of various solids. The formation of tubular nanostructure generally requires a layered or anisotropic crystal structure. There are reports of nanotubes made from silica, alumina, silicon and metals that do not have a layered crystal structure; they are synthesized by using carbon nanotubes and porous membranes as templates, or by thin-film rolling. These nanotubes, however, are either amorphous, polycrystalline or exist only in ultrahigh vacuum. The growth of single-crystal semiconductor hollow nanotubes would be advantageous in potential nanoscale electronics, optoelectronics and biochemical-sensing applications. Here we report an 'epitaxial casting' approach for the synthesis of single-crystal GaN nanotubes with inner diameters of 30-200 nm and wall thicknesses of 5-50 nm. Hexagonal ZnO nanowires were used as templates for the epitaxial overgrowth of thin GaN layers in a chemical vapour deposition system. The ZnO nanowire templates were subsequently removed by thermal reduction and evaporation, resulting in ordered arrays of GaN nanotubes on the substrates. This templating process should be applicable to many other semiconductor systems.
In this study, we evaluated the potential apoptosis effects of baicalein on human promyelocytic leukemia HL-60 cells in vitro. Apoptosis induction, cell viability, morphology and caspase-3 activity were then performed to determine by flow cytometric assay, DNA gel electrophoresis, anti-ADP-ribose stain and determination of caspase-3 activity. There is a significant difference in cell death of HL-60 cells that was detected between baicalein-treated and untreated groups. Furthermore, there was a further significant increase in apoptosis induction when cells were treated with baicalein compared to without baicalein treated groups. Flow cytometric assays and DNA fragmentation gel electrophoresis also confirmed baicalein induced apoptosis in HL-60 cells. Baicalein also promoted caspase-3 activity then leading to cleavage of poly-ADP-ribose polymerase finally leading to DNA fragmentation occurrence. Furthermore, the baicalein-induced apoptosis was markedly blocked by the broad-spectrum caspase inhibitor, z-VAD-fmk. Taken together, these results suggest that treatment of human leukemia HL-60 cells with baicalein induced apoptosis through activation of caspase-3 activity.