Solvent Remodeling in Single-Chain Amphiphilic Heteropolymer Systems

Through molecular dynamics simulations, we demonstrate how single-chain nanoparticles (SCNPs) assembled via transient linkages in water can remodel in organic solvent. Methacrylate-based random heteropolymers (RHPs) have shown promise in an assortment of applications that harness their bio-inspired properties. While their molecular behavior has been broadly characterized in water, many newer applications include the use of organic solvent rather than bio-mimetic conditions in which the polymer assemblies, typically driven by the hydrophobic effect, are less well understood. Here, we examine a specific RHP system which forms compact globular morphologies in highly polar and non-polar environments while adopting extended conformations in solvents of intermediate polarity. We also demonstrate the pivotal role of electrostatic interactions between charge groups in low dielectric mediums. Finally, we compare high temperature anneal cycles to room temperature equilibrations to illuminate activation barriers to remodeling upon environmental changes.

Identification of Pink-Coloured CVD Synthetic Diamonds from Huzhou Sino-C Semiconductor Co. in China

In recent years, increasing numbers of pink-coloured CVD synthetic diamonds have appeared on the market. One of the major sources is Huzhou SinoC Semiconductor Science and Technology Co., Ltd., Zhejiang province of China. In this article, seven pink-coloured CVD-grown diamonds produced in the last two years by Huzhou have been investigated and identified, including their gemological and spectroscopic characteristics. In DiamondView, they fluoresced orange–red, with an obscure striated growth structure, which is common for CVD synthetics. The mid-IR absorption spectra of these samples showed some single nitrogen and hydrogen-related features (1130, 1344, 3123, 3323 cm−1), which indicated that the diamonds were type Ib and were CVD-grown diamonds. The H1a defect annealed out at approximately 1400 °C, whereas the 3107 cm−1 defect was produced by annealing above 1700 or 1800 °C. This implied that the samples had undergone two separate heat treatments: first, a high-temperature anneal (possibly an HPHT treatment to reduce any brown colour), which would have produced the 3107 cm−1 defects and a small number of A centres, followed by irradiation, followed by annealing above 800 °C to make the vacancies mobile. The UV–Vis–NIR absorption spectra showed distinct NV-related features (575 and 637 nm), the main reason for the pink colour. Photoluminescence spectra obtained at liquid nitrogen temperature recorded radiation-related emissions (388.9, 503.5 nm), a strong N-V centre, H3 and H2 defects, and many unassigned emissions. These pink CVD products can be separated from natural and treated pink-coloured diamonds by a combination of optical spectroscopic properties, such as fluorescence colour, and absorption features in the infrared and UV–Vis regions.

Enhancement of Minority Carrier Lifetime in Ultra-High Voltage 4H-SiC PiN Diodes by Carbon-Film Annealing

A novel process is developed for minority carrier lifetime enhancement in ultra-high 4H-SiC PiN diodes. It comprises two separate processes. Firstly, the ultra-thick epitaxial grown drift layer (200μm) covered with a protective thin carbon film is subject to a 1500°C high-temperature anneal process in Ar atmosphere for 2 hours. Secondly, a surface passivation process is adopted to reduce the surface recombination rate. μ-PCD tests show that after high-temperature anneal, the thick drift layer shows a minority carrier lifetime increase to about 1.6 μs. PiN diodes based on the novel process are fabricated and their electric characteristics are measured. Results show a low specific on-resistance of 16.3 mΩ·cm2 at 25°C and 14 mΩ·cm2 at 125 °C. Compared with simulation results, it is shown that its effective minority carrier lifetime increase to about 5μs .Our study demonstrates that the developed novel process is effective in minority carrier lifetime enhancement in ultra-voltage 4H-SiC PiN diodes.

Ion Beam Synthesis of Doped Nanocrystals of Si1-xGex Alloys Embedded in SiO2

ABSTRACTAs an extension of our previous proving that ion beam synthesis is an efficient route to form doped silicon nanocrystals (nc’s) [1, 2], we show here that ion beam synthesis, by co-implantion of the dopant and of the constituents of the alloy, followed by a single high temperature anneal, is also a convenient way to grow more complex structures, such as As doped nc’s of Si1-xGex alloys.Rutherford backscattering spectrometry (RBS) is used to measure the impurity profiles and evaluate the average concentration of the various species (Si, Ge, As). The formation of the nc’s is evidenced by TEM observation and further confirmed by Raman and XRD analysis, which also allow us to estimate the Ge content of the nc’s.The incorporation of As inside the Si1-xGex nc’s is attested by the presence of the characteristic Ge-As related line in the Raman spectra of the As-doped samples, and strengthened by the increased conductivity of MOS structure including such doped nc’s inside the dielectric film.

Machinability of an Experimental Graphitised Carbon Steel

The machinability of an experimental medium-carbon steel with a composition designed to promote rapid graphitisation during a high temperature anneal has been studied. The goal has been to explore alternative routes to a competitive free-cutting composition enabling less expensive steelmaking, manufacturing and recycling. Three starting microstructures prior to annealing have been considered; martensite, bainite and ferrite/pearlite. The microstructures and graphite dispersions formed have been characterised by optical and electron microscopy and the performance of the steel during machining compared with commercial free-cutting steel grades. A bench-top drill rig and metallographic techniques were used to evaluate relative machinability parameters, including surface roughness, tool wear and chip morphology. Thus it proved possible to rank the experimental steel graphitised from the three starting microstructural conditions and also against the commercial free-cutting steels.

Thin PSG Process for 4H-SiC MOSFET

The use of phosphorous as a passivating agent for the SiO2/4H-SiC interface increases the field effect channel mobility of 4H-SiC MOSFET to twice the value, 30-40cm2/V-s, that is obtained with a high temperature anneal in nitric oxide (NO). A solid SiP2O7planar diffusion source is used to produce P2O5for the passivation of the interface. Incorporation of phosphorous into SiO2leads to formation of phosphosilicate glass (PSG) which is known to be a polar material causes device instability. With a new modified thin phosphorous (P) passivation process, as described in this abstract, we can improve the stability of MOSFETs significantly with mobility around 75cm2/V.s.

Investigation of Trenched and High Temperature Annealed 4H-SiC

This study focuses on the effects of a high temperature anneal after dry etching of trenches (post-trench anneal, PTA) on 4Hsilicon carbide (4H-SiC). We aim at the optimum 4H-SiC post-trench treatment with respect to the fabrication and the operation of a trenched gate metal oxide semiconductor field effect transistor (Trench-MOSFET). PTA significantly reduces micro-trenches, also called sub-trenches [, in the corners of the bottom of the trench. This is highly beneficial in case the etched trench sidewall is used as the channel of a Trench-MOSFET. However, PTA is also shown to cause a slight enlargement of the trench width along with a considerable increase of the substrate surface roughness. In addition, X-ray photoelectron spectroscopy (XPS) depth profiles indicate an increased carbon atom concentration at the 4H-SiC surface after the high temperature PTA. The non-stoichiometric surface composition affects the quasi-static capacitance-voltage (QSCV) behavior of MOS structures using a deposited gate oxide (GOX). We assume that a sacrificial oxidation directly after the PTA could restore a stoichiometric 4H-SiC surface.

Study of the Effect of Oxygen Annealing on YBCO Platelet Aggregates Synthesized by a Biomimetic Method

The effect of different oxygen annealing treatments on the structural and electrical properties of samples of the high temperature superconductor YBa2Cu3O7δ(YBCO) synthesized by a biomimetic method has been studied. By oxygen annealing, the oxygen deficiency resulting from the synthesis in air can be adequately compensated. A two-stage annealing process including a high temperature step results in a sharper superconducting transition and higher critical current density of the YBCO than annealing only at low temperature, due to the additional elimination of carbon residues from the biopolymer additive. To avoid the formation of impurity phases resulting from decomposition of the YBCO during the high-temperature anneal, careful pre-treatment by rinsing the as-synthesized YBCO with distilled water to remove residual NaCl is necessary.