Uniform Defect Research Articles

The director field distribution with the strongly pinned alignment in nematic structures at the polymer surface

We investigate orientational nematic liquid crystal structures that form at the polymer surface due to adsorption, their stability against the schlieren texture and features of point and linear singularities in them. We demonstrate that surface disclination lines, which also occur due to molecular adsorption, can lead to azimuthal anchoring of a bulk layer and make the singularities with the charge m = ±1 stable. We consider the director field distribution in a nematic layer as a result of the combination of two aligning factors, which are the linear disclination that tend to impose uniform planar ordering and point defects that impart the radial configuration to the director. With the use of the calculation, we analyse the energies of elastic distortions of the director field for the radial–planar, radial–homeotropic and radial–radial configurations, depending on the nematic layer thickness.

Enabling carbon nanofibers with significantly improved graphitization and homogeneous catalyst deposition for high performance electrocatalysts

ABSTRACT A facile and effective method is developed for the fabrication of ideal support and corresponding excellent catalysts. After spontaneous deposition of MnO2 onto electrospun carbon nanofibers (CNFs) in a solution of KMnO4 and subsequent thermal annealing, MnO-CNF hybrids with significantly enhanced graphitic structure and homogeneous surfaces defects are obtained. Further treatment with the solutions of H2PtCl6 and NaBH4 affords the resulting catalysts with codeposited Pt and MnO2 nanoparticles. To the best of our knowledge, it is the first time to simultaneously realize the combination of enhanced graphitization, uniform surface defects, and self N-doping of the carbon support materials. Compared to commercial Pt/XC72R and the counterparts without catalytic graphitization, Pt/MnO2-CNF exhibits significantly improved electrochemical active surface area, better CO tolerance for methanol electro-oxidation and excellent electrochemical durability.

Role of Al2O3 intermediate layer for improving the quality of polycrystalline-silicon film in inverted aluminum-induced layer exchange

A thin Al2O3 intermediate layer prepared by atomic layer deposition was introduced into inverted aluminum-induced layer exchange (inverted-ALILE) to form high-quality polycrystalline silicon (poly-Si) thin layer. It was demonstrated that the continuity and quality of poly-Si were obviously improved by the Al2O3 layer. The fraction of (100)-oriented crystals reached 93%, and the average grain size of 28μm with uniform surface morphology and low defect density were achieved at the optimal Al2O3 thickness of 4nm. It was also found that an a-AlOx layer always existed at the poly-Si/Al interface after inverted-ALILE process, which is independent on the original surface states. The results suggested that the thin poly-Si layer would be a promising epitaxial template for Si based thin film solar cells.

Covariant gradient continua applied to wave propagation within defective material

Riemann–Cartan geometry is used to model continuum with defects. In order to illustrate the differences induced by two possible definitions for the strain (spatial or material) in this framework, propagation of waves is studied for a simple example of infinite continuum with uniform and stationary defects density. Anisotropy and attenuation are caught by both models even if these effects are quite different. Furthermore, the spatial strain does not allow some polarizations, whereas the material one induces chirality and uniform breathing vibrations.

Stress-induced degradation of p- and n-type organic thin-film-transistors in the ON and OFF states

In this work we analyzed the effect of different stress configurations on p- and n-type organic thin-film-transistors, to emulate the various operating conditions in a real application. Devices showed the largest degradation when they are stressed in the ON condition, because of the uniform charge injection and defect generation in the whole channel area. Charge trapping kinetics and mobility degradation was also strongly dependent on the semiconductor type, suggesting a key-role of the semiconductor on the device reliability.

Strain- and defect-mediated thermal conductivity in silicon nanowires.

The unique thermal transport of insulating nanostructures is attributed to the convergence of material length scales with the mean free paths of quantized lattice vibrations known as phonons, enabling promising next-generation thermal transistors, thermal barriers, and thermoelectrics. Apart from size, strain and defects are also known to drastically affect heat transport when introduced in an otherwise undisturbed crystalline lattice. Here we report the first experimental measurements of the effect of both spatially uniform strain and point defects on thermal conductivity of an individual suspended nanowire using in situ Raman piezothermography. Our results show that whereas phononic transport in undoped Si nanowires with diameters in the range of 170-180 nm is largely unaffected by uniform elastic tensile strain, another means of disturbing a pristine lattice, namely, point defects introduced via ion bombardment, can reduce the thermal conductivity by over 70%. In addition to discerning surface- and core-governed pathways for controlling thermal transport in phonon-dominated insulators and semiconductors, we expect our novel approach to have broad applicability to a wide class of functional one- and two-dimensional nanomaterials.

Hydrothermal synthesis, characterizations and photoluminescence study of single crystalline hexagonal ZnO nanorods with three dimensional flowerlike microstructures

A simple, low-cost, and environmentally benign hydrothermal approach has been successfully developed to synthesize uniform, large-scale well-crystallized ZnO nanorods with different aspect ratios that were united together to form three dimensional (3D) flowerlike structures. The method involved direct growth of ZnO 3D microstructures using aqueous solution of Zn(CH3COO)2 as the precursor and NaOH to adjust the pH of resultant solution. Surfactants or templates were not used during the entire synthetic process. Moreover, the morphology evolution of the ZnO nanorods with reaction time suggests a recrystallization–dissolution–growth mechanism that continuously takes place for prolonged interval of time. The XRD pattern of the as-grown ZnO nanorods and relevant analyses confirm the well crystallized hexagonal structure of the ZnO microstructures and no evidence of any other impurity phases. SEM observations reveal that the ZnO product grew in the form of nanorods that were united together to form 3D flowerlike morphology. The high resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) shows that the ZnO nanorods were single crystalline and grew along the c-axis of the crystal plane. PL measurements of the as-synthesized nanorods exhibit excellent excitation features and strong band-edge UV luminescence even at room temperature. The uniform single crystalline, defect free, and high aspect ratio nanorods may find promising applications in optoelectronics and photo-catalysts. The growth habit of ZnO crystal is also illustrated. This method is suitable for large-scale production of ZnO microstructures and could be extended for syntheses of other metal oxides.

GLP-1 Responses Are Heritable and Blunted in Acquired Obesity With High Liver Fat and Insulin Resistance

OBJECTIVE Impaired incretin response represents an early and uniform defect in type 2 diabetes, but the contributions of genes and the environment are poorly characterized. RESEARCH DESIGN AND METHODS We studied 35 monozygotic (MZ) and 75 dizygotic (DZ) twin pairs (discordant and concordant for obesity) to determine the heritability of glucagon-like peptide 1 (GLP-1) responses to an oral glucose tolerance test (OGTT) and the influence of acquired obesity to GLP-1, glucose-dependent insulinotropic peptide (GIP), and peptide YY (PYY) during OGTT or meal test. RESULTS The heritability of GLP-1 area under the curve was 67% (95% CI 45-80). Cotwins from weight-concordant MZ and DZ pairs and weight-discordant MZ pairs but concordant for liver fat content demonstrated similar glucose, insulin, and incretin profiles after the OGTT and meal tests. In contrast, higher insulin responses and blunted 60-min GLP-1 responses during the OGTT were observed in the heavier as compared with leaner MZ cotwins discordant for BMI, liver fat, and insulin sensitivity. Blunted GLP-1 response to OGTT was observed in heavier as compared with leaner DZ cotwins discordant for obesity and insulin sensitivity. CONCLUSIONS Whereas the GLP-1 response to the OGTT is heritable, an acquired unhealthy pattern of obesity characterized by liver fat accumulation and insulin resistance is closely related to impaired GLP-1 response in young adults.

Low dislocation density AlGaN epilayers by epitaxial overgrowth of patterned templates

We present an epitaxial overgrowth process for reducing threading dislocations in AlxGa1−xN over the entire compositional range. This process avoids the use of UV-absorbing GaN layers and results in a spatially uniform defect reduction which eliminates the need for precise alignment of devices to low-defect areas of the wafer. Using the described overgrowth process, we demonstrate Al0.3Ga0.7N and Al0.6Ga0.4N epilayers with a dislocation density of 2×108cm−2 and 5×108cm−2 respectively, rendering them suitable as templates for deep-UV bottom-emitting LEDs and laser diodes. The process involves patterning of submicron-wide-stripes, less than 1μm in height, into an AlGaN/AlN/sapphire template and subsequent regrowth of a 5–10μm thick AlGaN epilayer. The sub-micron width of the mesa allows for bending of threading dislocations that would continue to thread vertically through wider mesas. Utilizing 1.3mm-thick sapphire substrates (3× thicker than commonly used), epilayer cracking from regrowth is eliminated and wafer bow over a 2-in. diameter substrate is reduced to less than 15μm. We observed a 7× increase in photoluminescence intensity from GaN–AlGaN multi-quantum well structures emitting at 340nm and a 15× increase in electroluminescence from laser diode heterostructures when grown on patterned Al0.3Ga0.7N templates.

On the scattering of longitudinal elastic waves from axisymmetric defects in coated pipes

Viscoelastic coatings are widely used to protect pipelines from their surrounding environment. These coatings are known to attenuate ultrasonic waves guided along the pipe walls, which may limit the range of a pulse/echo based inspection technique that seeks to detect defects in a pipeline. This article aims to investigate the attenuation of longitudinal modes in a coated pipe by comparing predicted and measured values for the reflection coefficient of an axisymmetric defect in a pipe coated with bitumen. This extends recent work undertaken by the authors for torsional modes, and also provides an independent investigation into the validity of those values proposed by the authors for the shear properties of bitumen, based on a comparison between prediction and experiment for torsional modes. Predictions are generated using a numerical mode matching approach for axially uniform defects, and a hybrid finite element based method for non-uniform defects. Values for the shear and longitudinal properties of bitumen are investigated and it is shown that the shear properties of the viscoelastic material play a dominant role in the propagation of longitudinal modes in a coated pipeline. Moreover, by using the shear values obtained from experiments on torsional modes, it is shown that good agreement between prediction and measurement for uniform and non-uniform defects may also be obtained for the longitudinal L(0,2) mode. This provides further validation for the shear bulk acoustic properties proposed for bitumen in the low ultrasonic frequency range, although in order to apply this methodology in general it is demonstrated that one must measure independently the reflection coefficient of both the torsional T(0,1) and the longitudinal L(0,2) mode before arriving at values for the shear properties of a viscoelastic material.

Nitrogen ion implanted InP based photo-switch

An Indium Phosphide-based device, switched by telecommunication wavelength laser pulses capable of operating at microwave frequencies up to 15 GHz has been designed and fabricated. Initial results confirm that using high energy nitrogen ion implantation to create EL-2 type trapping levels produces a photocarrier recombination time of a few picoseconds. The ion size and mass selected produces uniform bulk point defects in an In0.53Ga0.47As light absorbing region leading to high photocurrent mobility not exhibited in heavy ion irradiated samples resulting in a reduced peak pulse power requirement to switch the device.

Pten deletion causes mTorc1-dependent ectopic neuroblast differentiation without causing uniform migration defects

Neuronal precursors, generated throughout life in the subventricular zone, migrate through the rostral migratory stream to the olfactory bulb where they differentiate into interneurons. We found that the PI3K-Akt-mTorc1 pathway is selectively inactivated in migrating neuroblasts in the subventricular zone and rostral migratory stream, and activated when these cells reach the olfactory bulb. Postnatal deletion of Pten caused aberrant activation of the PI3K-Akt-mTorc1 pathway and an enlarged subventricular zone and rostral migratory stream. This expansion was caused by premature termination of migration and differentiation of neuroblasts and was rescued by inhibition of mTorc1. This phenotype is reminiscent of lamination defects caused by Pten deletion in developing brain that were previously described as defective migration. However, live imaging in acute slices showed that Pten deletion did not cause a uniform defect in the mechanics of directional neuroblast migration. Instead, a subpopulation of Pten-null neuroblasts showed minimal movement and altered morphology associated with differentiation, whereas the remainder showed unimpeded directional migration towards the olfactory bulb. Therefore, migration defects of Pten-null neurons might be secondary to ectopic differentiation.

Pten deletion causes mTorc1-dependent ectopic neuroblast differentiation without causing uniform migration defects

Neuronal precursors, generated throughout life in the subventricular zone, migrate through the rostral migratory stream to the olfactory bulb where they differentiate into interneurons. We found that the PI3K-Akt-mTorc1 pathway is selectively inactivated in migrating neuroblasts in the subventricular zone and rostral migratory stream, and activated when these cells reach the olfactory bulb. Postnatal deletion of Pten caused aberrant activation of the PI3K-Akt-mTorc1 pathway and an enlarged subventricular zone and rostral migratory stream. This expansion was caused by premature termination of migration and differentiation of neuroblasts and was rescued by inhibition of mTorc1. This phenotype is reminiscent of lamination defects caused by Pten deletion in developing brain that were previously described as defective migration. However, live imaging in acute slices showed that Pten deletion did not cause a uniform defect in the mechanics of directional neuroblast migration. Instead, a subpopulation of Pten-null neuroblasts showed minimal movement and altered morphology associated with differentiation, whereas the remainder showed unimpeded directional migration towards the olfactory bulb. Therefore, migration defects of Pten-null neurons might be secondary to ectopic differentiation.

High dispersion of Ru nanoparticles supported on carbon nanotubes synthesized by water-assisted chemical vapor deposition for cellobiose conversion

Abstract An easy and efficient method, water-assisted chemical vapor deposition (CVD), was developed to modify multi-walled carbon nanotubes (CNTs) during the CNT growth process. The as-synthesized CNTs with (-H 2 O) and without (-p) water assistance were explored as ruthenium (Ru) catalyst support for conversion of cellobiose. The Ru/CNTs-H 2 O catalyst shows much higher conversion of cellobiose (73.6%) and yield of sugar alcohols (39%) than those of Ru/CNTs-p catalyst (28.9% and 21.3%, respectively), which could be ascribed to the highly dispersed Ru nanoparticles due to the presence of oxygen-containing groups and uniform defects on the tube-walls introduced in the water-assisted CVD process.

Channel Strain Measurement in 32-nm-Node Complementary Metal–Oxide–Semiconductor Field-Effect Transistor by Raman Spectroscopy

We performed a strain analysis of a 32-nm-node microprocessing unit by Raman spectroscopy in conjunction with transmission electron microscopy. The channel surface was exposed by chemical etching and mechanical polishing for Raman spectroscopy. Some defects and Ge concentration variation were observed in embedded SiGe of a p-channel metal–oxide–semiconductor field-effect transistor (pMOSFET). Uniform defects lying at the same angle were observed in the source and drain regions of an n-channel MOSFET (nMOSFET). From the Raman measurement, the Raman peak from strained Si in the pMOSFET shifted toward a higher frequency at approximately 7.5 cm-1, which corresponds to -3.75 GPa (compressive) under the assumption of uniaxial stress along the channel direction. On the other hand, the Raman peak shift from strained Si in the nMOSFET was -1.7 cm-1 corresponding to 0.85 GPa (tensile) under the assumption of uniaxial stress. From the nanobeam diffraction measurements, the compressive strain at the channel edge was larger than that at the channel center in the pMOSFET. On the other hand, the tensile strain in the nMOSFET was induced uniformly in the channel region. We think that understanding and control of channel strain introduction are indispensable in the state-of-the-art complementary MOSFET technology.

Thermal ideality factor of hydrogenated amorphous silicon p-i-n solar cells

The performance of hydrogenated amorphous silicon (a-Si:H) p-i-n solar cells is limited, as they contain a relatively high concentration of defects. The dark current voltage (JV) characteristics at low forward voltages of these devices are dominated by recombination processes. The recombination rate depends on the concentration of active recombination centers and the recombination efficacy of each of these centers. The first factor causes the ideality factor of the devices to be non-integer and to vary with voltage. The temperature dependence of the dark current can be expressed by its activation energy. For microcrystalline silicon solar cells the activation energy varies with voltage with a so-called thermal ideality factor of 2. This value was derived for devices with a spatially uniform defect distribution and reflects the recombination efficacy. Here we present results of a thickness series of a-Si:H p-i-n solar cells. We have matched the experimental curves with computer simulations, and show that the voltage-dependent ideality factor curve can be used to extract information on the cross sections for electron and hole capture. Also, the activation energy is used as a measure for the mobility gap, resulting in a mobility gap for a-Si:H of 1.69 eV. We find a thermal ideality factor close to 2 for all samples. This is explained with a theoretical derivation, followed by a comparison between the internal electric field strength and the spatial variation of the defect density in the intrinsic layer. The thermal ideality factor is shown to be insensitive to the defect distribution and the recombination profile in the device. It is, therefore, an appropriate parameter to characterize a-Si:H p-i-n devices, providing direct insight on the recombination efficacy.

Dislocation structure and impact toughness of reactor pressure vessel steel 15Kh2NMFA upon ultrasonic treatment

The paper addresses the influence of high-temperature ultrasonic treatment on the structure and impact toughness of steel 15Kh2NMFA. The observed increase of impact toughness and decrease of ductile-brittle transition temperature for the steel upon ultrasonic treatment of various durations are due to the formation of a uniform defect structure.

Comprehensive model of how reality distortion and symptoms occur in schizophrenia: Could impairment in learning‐dependent predictive perception account for the manifestations of schizophrenia?

Conventional wisdom has not laid out a clear and uniform profile of schizophrenia as a unitary entity. One of the key first steps in elucidating the neurobiology of this entity would be to characterize the essential and common elements in the group of entities called schizophrenia. Kraepelin in his introduction notes 'the conviction seems to be more and more gaining ground that dementia praecox on the whole represents, a well characterized form of disease, and that we are justified in regarding the majority of the clinical pictures which are brought together here as the expression of a single morbid process, though outwardly they often diverge very far from one another'. But what is that single morbid process? We suggest that just as the uniform defect in all types of cancer is impaired regulation of cell proliferation, the primary defect in the group of entities called schizophrenia is persistent defective hierarchical temporal processing. This manifests in the form of chronic memory-prediction errors or deficits in learning-dependent predictive perception. These deficits account for the symptoms that present as reality distortion (delusions, thought disorder and hallucinations). This constellation of symptoms corresponds with the profile of most patients currently diagnosed as suffering from schizophrenia. In this paper we describe how these deficits can lead to the various symptoms of schizophrenia.

Modified Percolation Model for Polycrystalline High-$ \kappa$ Gate Stack With Grain Boundary Defects

We modify the existing oxide breakdown (BD) percolation model in this letter to account for the presence of microstructural weakest link grain boundary (GB) defects in polycrystalline high-κ (HK) gate stacks. The different rates of the stress-induced leakage current degradation and oxide trap generation at the bulk and GB regions need to be accounted for in modeling the statistical nature of BD in HK dielectric thin films. Simulated results reveal the dominance of GB-related failures and the origin of the non-Weibull stochastics inherent in polycrystalline HK stacks. We also point to the inability of conventional percolation models with an assumed uniform defect generation to describe the failure statistics of current HK gate stacks.

Effect of fluoroquinolones on the expression of matrix metalloproteinase in debrided cornea of rats

Matrix metalloproteinases (MMPs) are implicated in regenerative and healing processes in corneal injuries. Based upon reports that topical fluoroquinolones (FQs) may cause perforations during corneal healing by modulating MMPs, this study evaluated the comparative effects of commercially available FQs eye drops on the expression of MMP-2 and MMP-9 in the cornea after ethanol injury. Uniform corneal epithelial defects were created using 70% ethanol in the right eye of the rats (n = 6). The groups studied were (I) sham, (II) normal saline with benzalkonium chloride (NS-BKC), (III) norfloxacin 0.3%, (IV) ciprofloxacin 0.3%, (V) lomefloxacin 0.3%, (VI) sparfloxacin 0.3%, (VII) gatifloxacin 0.3%, and (VIII) moxifloxacin 0.5%. Each treatment was instilled six times/day up to 48 h and rats were sacrificed using excess of anesthesia. The corneas were excised to study the expression of MMP-2 and MMP-9 using gelatin zymography and real-time PCR. All the FQs significantly increased the expression of MMP-2 and MMP-9 as compared to the sham and NS-BKC-treated group. NS-BKC did not show a significant effect on MMPs expression compared to the sham group. Among the studied FQs, ciprofloxacin was observed to exhibit maximal induction of MMP-2 and MMP-9, whereas lomefloxacin exhibited an equivocal effect on both MMP-2 and MMP-9 expression. Findings of the present study demonstrate that topical application of FQs may induce the expression of MMP-2 and MMP-9 in debrided corneal epithelium and, therefore, may delay corneal wound healing. Thus, it can be concluded that selecting a FQ for ophthalmic use having minimal effect on MMPs may impact wound healing in injured or vulnerable cornea.