There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

First-principles calculations have evolved from mere aids in explaining and supporting experiments to powerful tools for predicting new materials and their properties. In the first part of this review we describe the state-of-the-art computational methodology for calculating the structure and energetics of point defects and impurities in semiconductors. We will pay particular attention to computational aspects which are unique to defects or impurities, such as how to deal with charge states and how to describe and interpret transition levels. In the second part of the review we will illustrate these capabilities with examples for defects and impurities in nitride semiconductors. Point defects have traditionally been considered to play a major role in wide-band-gap semiconductors, and first-principles calculations have been particularly helpful in elucidating the issues. Specifically, calculations have shown that the unintentional n-type conductivity that has often been observed in as-grown GaN cannot be a...

First-principles calculations for defects and impurities: Applications to III-nitrides

Gallium nitride (GaN) and its allied binaries InN and AIN as well as their ternary compounds have gained an unprecedented attention due to their wide-ranging applications encompassing green, blue, violet, and ultraviolet (UV) emitters and detectors (in photon ranges inaccessible by other semiconductors) and high-power amplifiers. However, even the best of the three binaries, GaN, contains many structural and point defects caused to a large extent by lattice and stacking mismatch with substrates. These defects notably affect the electrical and optical properties of the host material and can seriously degrade the performance and reliability of devices made based on these nitride semiconductors. Even though GaN broke the long-standing paradigm that high density of dislocations precludes acceptable device performance, point defects have taken the center stage as they exacerbate efforts to increase the efficiency of emitters, increase laser operation lifetime, and lead to anomalies in electronic devices. The p...

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Luminescence properties of defects in GaN

Titanium dioxide (TiO2 ) nanocrystals are prepared by a hydrolysis process of tetrabutyl titanate. Nanocrystal samples with various sizes of 6.8-27.9 nm are obtained after annealing from 100 to 650 °C. The crystal structures and the average particle sizes are examined using x-ray diffraction. Raman scattering was employed to investigate the evolution of the anatase phase in the nanocrystals during annealing. Phonon confinement and non-stoichiometry effects are responsible for the blueshift and broadening of the lowest-frequency Eg Raman mode. The influence of interfacial vibrations on the Raman linewidth is also discussed.

https://iopscience.iop.org/article/10.1088/0022-3727/33/8/305/pdf

Raman scattering study on anatase TiO2 nanocrystals

https://hal.archives-ouvertes.fr/hal-00120432/document

Raman Spectroscopy of Nanomaterials: How Spectra Relate to Disorder, Particle Size and Mechanical Properties

Low-frequency Raman spectra have been measured to clarify the relationship between low frequency modes and the incommensurate modulation in Pb doped Bi2Sr2CaCu2O8. The lines corresponding to the folded acoustic modes arising from the incommensu­rate modulation change in frequency rather abruptly at around nominal Pb composi­tion of 13%. This result is interpreted in terms of the change in the period of the modulation with the Pb doping.

Low-Frequency Raman Spectra of (BiPb)2Sr2CaCu2O8

Microwave Oscillations from P-N Junction in Germanium

Seven cases of septic arthritis of the hip joint in infancy and childhood were examined from March 1999 to September 2001. Arthrotomy was performed on all patients after diagnosis had been established by joint aspiration. One patient on whom arthrotomy was performed 21 days from onset had fair results with radiological evidence of the developmental disorder of the femoral head. One patient on whom arthrotomy was performed only 2 days from onset had fair results with radiological evidence of the developmental disorder and subluxation of the femoral head because of recurrence on two occasions.We recommend immediate diagnostic joint aspiration for all cases with suspected septic arthritis of the hip joint, and emergency arthrotomy should be performed as soon as septic arthritis is diagnosed.

Treatment of Septic Arthritis of the Hip Joint in Infancy and Childhood.

Forty-five patients who had surgery to repair a full thickness rotator cuff tear (45 shoulders) were followed for an average of 35.5 months (range, 6 to 72). Thirty were men and 15 women. The average age of the patients was 56 years (range, 31 to 67 years). After anterior acromioplasty, tendon to bone repair was accomplished in 37 shoulders, tendon to tendon repair in three, and repair with Teflon felt in five. It was necessary to transfer the subscapularis in three shoulders and to advance supraspinatus in one shoulder. Generally patients were placed in abduction braces to hold the shoulder in 60° to 90° flexion and abduction after the operation. Patients received passive ROM (range of motion) exercises to the shoulder for the initial 4 to 6 weeks. This therapy was followed by active assisted ROM and finally by active ROM as strength was regained. Using JOA score, excellent or good results were achieved in 93% of the patients with small or medium tears (5cm≥, N=29). However, excellent or good results were achieved in 70% of large or massive tears (5cm<, N=16).

Surgical Management of Full Thickness Rotator Cuff Tears

We succeeded in continuous growth of SiC single crystal by CPD (Chemical Particle Deposition) method with the spray dried ultra-fine particle precursor powder. By the introduction of the spray dried spherical powder, we could clarify the mechanism of SiC single crystal growth by CPD method, through the observation of the deformation and the transformation of the spherical precursor powder into the epitaxial SiC grown layer on the seed crystal surface. The SiC layer grown by this method showed promising crystal quality indicated by the rocking curve with FWHM of 70~80 arcsec. Introduction At ICSCRM2001, we presented a novel method to grow the SiC single crystals from pulverized precursor powder made of SiO2 and C(graphite) nano-particles, named CPD (Chemical Particle Deposition) method. This method is considered to be a quasi-melt growth which was suggested by the observed flow pattern on the growing surface of Acheson crystal [1]. At ECSCRM2002, we discussed the chemical reaction and growth kinetics of crystal growth in CPD method under the condition of intermittent supply of precursor powder [2]. In CPD method, the precursor powder made of SiO2 and C nano-particles is deduced to react on the seed surface as follows: SiO2 + 3C → Si + C + 2CO → SiC + 2CO. (1) The intermediate state will be the fluid material which includes stoichiometric amount of free Si and C atoms along with liberated CO gas molecules. The precursor powder is to be liquefied or gasified at the moment of carbothermal reduction and diffuse over the seed surface to form epitaxial SiC single crystal layer. The density of this fluid at the moment of reaction must be as high as the solid precursor material. In such fluid, the interaction between Si and C atoms must be very active and will result in the self-organizing crystal growth of SiC single crystal with the equilibrium growth condition. In other words, quasi-melt growth of SiC single crystal will be realized by CPD method. Another advantage of this method is to grow the longer crystal compared with the modified Lely method keeping the growth condition constant if we succeed in continuous supply of precursor powder. In CPD method, the size of the precursor powder should be as small as possible, ideally in same order with its starting materials of fumed silica and carbon black, both less than100nm. However, such small size particles tend to coalesce to form larger particles and adhere to the wall of powder feeding equipment, disturbing smooth and constant transportation. In the establishment of the stable powder feeding system for Materials Science Forum Online: 2004-06-15 ISSN: 1662-9752, Vols. 457-460, pp 131-134 doi:10.4028/www.scientific.net/MSF.457-460.131 © 2004 Trans Tech Publications Ltd, Switzerland All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications Ltd, www.scientific.net. (Semanticscholar.org-11/03/20,15:23:09) industrial production of SiC single crystal, the suitable granulation of the precursor material is essential, in the same way as the many cases in the other powder utilizing technologies. The hollow spherical particles made by spray drying, typical granulating technology, were suitable for handling but its size was the order of 20~50μm in diameter, and it was a question whether SiC single crystal of excellent quality could be grown by feeding such a large precursor powder in CPD method. In the present work, using the spray dried hollow spherical precursor powder in stead of the former pulverized random figure precursor powder, we have succeeded in the epitaxial growth of SiC single crystal and have confirmed the fundamental mechanisms of crystal growth in CPD method , through the observation on the deformation and the transformation of spherical precursor powder into SiC single crystal. Experimental The ultra-fine particle precursor for SiC single crystal growth by CPD method was prepared by mixing SiO2 (fumed silica: 380m 2 /g) and C (carbon black: 240m 2 /g) of approximately 1 to 3 molar ratio, through ball-milling of their aqueous slurry with no surface-active agents, more than 24 hours. After the ball-milling, the precursor slurry was granulated and dried by the spray dryer equipped with rotating disc atomizer. The spray dried precursor powder had the hollow spherical structure of 20~50μm in diameter (Fig.1). Before filling into the hopper of the powder feeding equipment, we put the precursor powder in the vacuum chamber and replaced the air remaining in the hollow core with the Ar gas. The continuous growth of SiC single crystal by the continuous feeding of the spray dried powder was performed in the open electrothermal furnace with Ar gas ambient of 1 atm pressure. Prior to the heating process , the reactor in the furnace was evacuated to 10 Pascal or less, then filled up to atmospheric pressure with Ar gas. The temperature of the seed crystal was represented by that of the reactor wall near it measured by the optical pyrometer. In the every experiments, we heated up the reactor to the growing temperature of 2300~2400 ̊C at the rate Fig.1. The spray dried precursor powder. of 20~30 ̊C/min and hold the temperature for 20~30 minutes, feeding the spray dried precursor powder onto the seed crystal surface. In the ordinary growing experiments, we started to feed the precursor powder at 2300 ̊C and continued to the same temperature in the cooling down phase. In the experiments to observe the deformation and the transformation of the precursor powder on the seed crystal surface, powder feeding was continued to 2000 ̊C after turning off the heater current, in order to slow down the reaction. Typical flow rate of the precursor powder and Ar carrier Fig.2. The experimental apparatus. gas were 2~3 g/min. and 5 l/min respectively. 132 Silicon Carbide and Related Materials 2003

Shin-ichi Nakashima

Papers

Low-Frequency Raman Spectra of (BiPb)2Sr2CaCu2O8

Microwave Oscillations from P-N Junction in Germanium

Treatment of Septic Arthritis of the Hip Joint in Infancy and Childhood.

Surgical Management of Full Thickness Rotator Cuff Tears

Continuous Growth of SiC Single Crystal by the Spray Dried Powder Made of Ultra-Fine Particle Precursors