Enhancement in electron transport and light emission efficiency of a Si nanocrystal light-emitting diode by a SiCN/SiC superlattice structure

We report an enhancement in light emission efficiency of Si nanocrystal (NC) light-emitting diodes (LEDs) by employing 5.5 periods of SiCN/SiC superlattices (SLs). SiCN and SiC layers in SiCN/SiC SLs were designed by considering the optical bandgap to induce the uniform electron sheet parallel to the SL planes. The electrical property of Si NC LED with SiCN/SiC SLs was improved. In addition, light output power and wall-plug efficiency of the Si NC LED with SiCN/SiC SLs were also enhanced by 50% and 40%, respectively. This was attributed to both the formation of two-dimensional electron gas, i.e., uniform electron sheet parallel to the SiCN/SiC SL planes due to the conduction band offset between the SiCN layer and SiC layer, and an enhanced electron transport into the Si NCs due to a lower tunneling barrier height. We show here that the use of the SiCN/SiC SL structure can be very useful in realizing a highly efficient Si NC LED.     

Erratum to “Prediction of fracture parameters of circumferential throughwall cracks in the interface between an elbow and a pipe under internal pressure”

Journal of Mechanical Science and Technology - There are two corrections to make to the original article. Firstly, Table 2 in the original article, was erroneously given. The Table 2 should read as...     

A device to measure the effects of strong magnetic fields on the image resolution of PET scanners

Very high resolution images can be achieved in small animal PET systems utilizing solid state silicon pad detectors. As these systems approach sub-millimeter resolutions, the range of the positron is becoming the dominant contribution to image blur. The size of the positron range effect depends on the initial positron energy and hence the radioactive tracer used. For higher energy positron emitters, such as and , which are gaining importance in small animal studies, the width of the annihilation point distribution dominates the spatial resolution. This positron range effect can be reduced by embedding the field of view of the PET scanner in a strong magnetic field. In order to confirm this effect experimentally, we developed a high resolution PET instrument based on silicon pad detectors that can operate in a 7 T magnetic field. In this paper, we describe the instrument and present initial results of a study of the effects of magnetic fields up to 7 T on PET image resolution for and point sources.     

A perturbation analysis on solid polymer surfaces

A linear stability model was formulated to analyze the perturbation of solid polymer surfaces. Surface energy and thermal stress were considered as the main variables. The surface tends to more unstable as the temperature increase. This is interpreted as the dominancy of the lattice vacancy diffusion over surface mass diffusion and the increase in thermal stress.     

Synthesis of polyaniline-gold/graphene oxide composite and microwave absorption characteristics of the composite films

This paper describes the synthesis of polyaniline-gold nanocomposite by an in situ polymerization of aniline hydrochloride with graphene oxide using hydrogen tetrachloroaurate as an oxidant. The synthesized nanocomposites were characterized by FT-IR and UV–vis spectroscopy, and their surface morphology was studied by scanning and transmission electron microscopy. Microwave absorption property of the composite films was studied at 2–12 GHz, and the effects of sample thickness on the microwave absorption were investigated. The electromagnetic interference shielding effectiveness of PANI-GNP has been enhanced due to the inclusion of GO.     

Printable and Rewritable Full Block Copolymer Structural Color

Structural colors (SCs) of photonic crystals (PCs) arise from selective constructive interference of incident light. Here, an ink‐jet printable and rewritable block copolymer (BCP) SC display is demonstrated, which can be quickly written and erased over 50 times with resolution nearly equivalent to that obtained with a commercial office ink‐jet printer. Moreover, the writing process employs an easily modified printer for position‐ and concentration‐controlled deposition of a single, colorless, water‐based ink containing a reversible crosslinking agent, ammonium persulfate. Deposition of the ink onto a self‐assembled BCP PC film comprising a 1D stack of alternating layers enables differential swelling of the written BCP film and produces a full‐colored SC display of characters and images. Furthermore, the information can be readily erased and the system can be reset by application of hydrogen bromide. Subsequently, new information can be rewritten, resulting in a chemically rewritable BCP SC display.     

In situ-grown hexagonal silicon nanocrystals in silicon carbide-based films

Silicon nanocrystals (Si-NCs) were grown in situ in carbide-based film using a plasma-enhanced chemical vapor deposition method. High-resolution transmission electron microscopy indicates that these nanocrystallites were embedded in an amorphous silicon carbide-based matrix. Electron diffraction pattern analyses revealed that the crystallites have a hexagonal-wurtzite silicon phase structure. The peak position of the photoluminescence can be controlled within a wavelength of 500 to 650 nm by adjusting the flow rate of the silane gas. We suggest that this phenomenon is attributed to the quantum confinement effect of hexagonal Si-NCs in silicon carbide-based film with a change in the sizes and emission states of the NCs.     

Dieless drawing steel wires using a dielectric heating method and modeling the process dynamics

Modern industries require the production of multi-functional, inorganic, micron-sized metal wires. This study suggests a novel method that could potentially offer a highly efficient dieless drawing technology for manufacturing thin stainless steel fibers. The method is based on a hot-working principle, using microwaves as the heat source and SiC as the susceptor. Experimental trials with a laboratory rig showed that the new system worked effectively for drawing the stainless steel wires and should be able to realize the diameter attenuation with a diameter reduction of up to 21%. The theoretical model describing the deformation behavior of the stainless steel wires in the working zone along with the constitutive equation of Bingham model modified with a power law and Zener–Hollomon parameter turned out to match very good with the actual results of the experiment. The coefficient of variation of the drawn wire diameter increased, as the draw ratio increased, which could be attributed to the occurrence of the narrow necking zone.     

Metamaterial-based electronically controlled transmission-line structure as a novel leaky-wave antenna with tunable radiation angle and beamwidth

A metamaterial-based electronically controlled transmission-line structure is presented and demonstrated as a novel leaky-wave (LW) antenna with tunable radiation angle and beamwidth functionalities. This structure is, in essence, a composite right/left-handed (CRLH) microstrip structure incorporating varactor diodes for fixed-frequency voltage-controlled operation. Angle scanning at a fixed frequency is achieved by modulating the capacitances of the structure by adjusting the (uniform) bias voltage applied to the varactors. Beamwidth tuning is obtained by making the structure nonuniform by application of a nonuniform bias voltage distribution of the varactors. A rigorous analysis based on an extension of the CRLH concept is proposed and the corresponding dispersion curves, obtained by equivalent-circuit formulas with LC parameters extracted from full-wave simulation, are shown. A 30-cell LW antenna structure, incorporating both series and shunt varactors for optimal impedance matching and maximal tuning range, is designed. This prototype exhibits continuous scanning capability from 50/spl deg/ to -49/spl deg/ by tuning the bias voltages from 0 to 21 V at 3.33 GHz. A maximum gain of 18 dBi at broadside is also achieved. In addition, it provides half-power beamwidth variation of up to 200% with comparison to the case of uniform biasing. The effect of intermodulation due to the nonlinearity of the varactors is shown to be negligible for antenna applications. The antenna is tested in a 10-Mb/s binary phase-shift keying transmission link and successful recovery of the baseband data is demonstrated.