Optical and electrical properties of undoped and doped Ge nanocrystals

ABSTRACT: Size-dependent photoluminescence characteristics from Ge nanocrystals embedded in different oxide matrices have been studied to demonstrate the light emission in the visible wavelength from quantum-confined charge carriers. On the other hand, the energy transfer mechanism between Er ions and Ge nanocrystals has been exploited to exhibit the emission in the optical fiber communication wavelength range. A broad visible electroluminescence, attributed to electron hole recombination of injected carriers in Ge nanocrystals, has been achieved. Nonvolatile flash-memory devices using Ge nanocrystal floating gates with different tunneling oxides including SiO2, Al2O3, HfO2, and variable oxide thickness [VARIOT] tunnel barrier have been fabricated. An improved charge storage characteristic with enhanced retention time has been achieved for the devices using VARIOT oxide floating gate.     

Fault Diagnosis of Dynamically Loaded Bearing with Localized Defect Based on Defect-Induced Excitation

Journal of Failure Analysis and Prevention - The defect-induced excitations causing the bearing to vibrate have significant contribution in vibration generated from rolling element bearings....     

Triptycene‐based fluorescent polymers with pendant alkyl chains: interaction with fullerenes and morphology of thin films

We report unique triptycene‐based alternating copolymers bearing long alkyl chains as pendants. Syntheses utilized 2,6‐diethynyltriptycene and appropriate alkyloxyarene monomers polymerized via Sonogashira cross‐coupling reaction to yield triptycene‐based poly(phenylene ethynylene)s. Resulting polymers are soluble in organic solvents and were characterized using various techniques. Experimental results suggest the polymers are thermally stable and fluorescent. The fluorescence emission is quenched in the presence of fullerenes (C₆₀ and C₇₀) suggesting strong host–guest interactions. The magnitude of the binding constant between the polymers and these fullerenes was determined to be of the order of 10⁵ mol L^?1. The effects of chain length on the morphology and wettability of the polymers on silicon substrates were studied using atomic force microscopy. Three distinct dewetting patterns, i.e. spherical domains, fractal structures and ring structures, were observed with variation in the pendant chain length. This ability to control the thin‐film morphology of the polymers may have potential technological applications, which include but are not limited to sensors, fluorescent coatings and organic electronics. © 2018 Society of Chemical Industry     

Turbine missile — a critical review

The turbine missile problem has been critically reviewed. A probabilistic approach to the problem seems to be most reasonable. However, United States Nuclear Regulatory Commission's guidelines on this subject may not be adequate. In this paper, some of the critical parameters in the turbine missile problem have been identified and their probabilistic characteristics have been discussed. Separation of high and low trajectory missiles in damage potential evaluation appears to be inappropriate. Definitions of targets from the engineer's point of view have also been suggested. In estimating the occurrence rate of external missiles the statistical approach using the Duane growth rate model seems to be more appealing than the systems reliability approach. However, the observed samples and durations may not be adequate for the Duane growth rate model. A probabilistic methodology to estimate the damage potential of turbine missiles is also developed considering various sources of uncertainty. The methodology is clarified with the help of an example. If the uncertainties in the contributing parameters are considered appropriately, the crude conservatism that has been introduced into the damage potential evaluation can be reduced with confidence.     

An innovative electro-corrosion recess creation technique for improved microelectrode fabrication

A new and simple electrochemical (corrosion) method for recess creation for the fabrication of metal and metal-metal oxide microelectrodes has been developed. Controlled recess was created in low melting point alloy (LMA)-filled micropipettes using slightly acidic 1-3 M ZnCl2 as the electro-corrosion solution. The current was applied from a 3 V DC source. The recess length in the LMA-filled micropipette can be manipulated as needed for a specific microelectrode by varying the electro-corrosion time. The present method is expected to make microelectrode fabrication a less tedious process. Dissolved oxygen, oxidation-reduction potential and pH microelectrodes have been made using the present method and the microelectrode characteristics were found to be in conformity with those reported by other researchers.     

Performance of a constructed wetland with a sulfur/limestone denitrification section for wastewater nitrogen removal

The effectiveness of a nonvegetated lab-scale subsurface flow constructed wetland for wastewater treatment had been evaluated with the feed ammonium concentration of approximately 20-40 mg of NH4(+)-N L(-1) and a hydraulic retention time of approximately 10 d. The present system had a nitrification zone plus a sulfur/limestone (S/L) autotrophic denitrification zone followed by an anaerobic polishing zone and was operated with and without aeration. The wetland had only 80% organics removal and no net nitrogen removal when there was no artificial aeration. However, almost 100% organics removal and approximately 81-90% total inorganic nitrogen (TIN = NH4(+)-N + NO2(-0-N + NO3(-)-N) removal were achieved when the oxic zone of the system was aerated with compressed air. S/L autotrophic denitrification contributed 21-49% of total NO3(-)-N removal across the whole wetland and 50-95% across the S/L column. TIN and NH4(+)-N in the effluent were always < 5.5 and < 0.7 mg L(-1), respectively, when the feed had NH4(+)-N < or = 35 mg L(-1). Sulfate removal of approximately 53-69% was achieved in the anaerobic polishing zone. The position of the S/L column was changed (1.78, 2.24, and 2.69 m from the inlet), and no remarkable difference in nitrogen removal was observed. However, without the S/L column, TIN removal decreased to approximately 74%, and the effluent NO3(-)-N increased about two times (9.13 mg of N L(-1)). The present study has demonstrated the possible use of S/L autotrophic denitrification for nitrate removal in a constructed wetland.     

Iron nanoparticles coated with amphiphilic polysiloxane graft copolymers: dispersibility and contaminant treatability

Amphiphilic polysiloxane graft copolymers (APGCs) were used as a delivery vehicle for nanoscale zerovalent iron (NZVI). The APGCs were designed to enable adsorption onto NZVI surfaces via carboxylic acid anchoring groups and polyethylene glycol (PEG) grafts were used to provide dispersibility in water. Degradation studies were conducted with trichloroethylene (TCE) as the model contaminant. TCE degradation rate with APGC-coated NZVI (CNZVI) was determined to be higher as compared to bare NZVI. The surface normalized degradation rate constants, k(SA) (Lm(2-) h(-1)), for TCE removal by CNZVI and bare NZVI ranged from 0.008 to 0.0760 to 007-0.016, respectively. Shelf life studies conducted over 12 months to access colloidal stability and 6 months to access TCE degradation indicated that colloidal stability and chemical reactivity of CNZVI remained more or less unchanged. The sedimentation characteristics of CNZVI under different ionic strength conditions (0-10 mM) did not change significantly. The steric nature of particle stabilization is expected to improve aquifer injection efficiency of the coated NZVI for groundwater remediation.     

What Remains Unexplained about the Properties of Halide Perovskites?

The notion that halide perovskite crystals (ABX₃, where X is a halide) exhibit unique structural and optoelectronic behavior deserves serious scrutiny. After decades of steady and half a decade of intense research, the question which attributes of these materials are unusual, is discussed, with an emphasis on the identification of the most important remaining issues. The goal is to stimulate discussion rather than to merely present a community consensus.     

Reduced residual DC voltages in LCDs by using fluorinated polyimides

Abstract— The effect of a fluorinated alignment layer in reducing image retention in liquid‐crystal displays has been quantified. In our experiments, image retention is characterized by measuring the residual DC (RDC) value, which for both planar cells and vertical‐alignment cells are shown to be very small for a fluorinated alignment layer. The lowered dielectric constant of a fluorinated alignment layer is shown to be correlated with RDC improvement. A result of this work is the demonstration that fluorinated alignment layers have great potential to be used in low‐refresh‐rate LCDs for reducing power consumption.