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Stress dependence on N/Ga ratio in GaN epitaxial films grownon ZnO substrates
Tsutomu Minegishi,Takuma Suzuki,Chihiro Harada,Hiroki Goto,Meoung-Whan Cho,Takafumi Yao 한국물리학회 2004 Current Applied Physics Vol.4 No.6
GaN films were grown on ZnO substrate under various beam equivalent pressure ratios by plasma-assisted molecular beamepitaxy (P-MBE). We theoretically calculated the thermal stress caused by the dierence of thermal expansion coecients betweenGaN and ZnO. The changes of stress and critical thickness were evaluated by measurement of XRD for HT GaN and LT GaNbuer grown under Ga-rich and N-rich conditions. From this study, we observed that GaN grown under Ga-rich condition causesGaN lm to under compressive-stress, while GaN grown under N-rich condition was tensile-stressed. Consequently, interdiusionhas no eect on the variation of the critical thickness.
T. Minegishi,Z. Vashaei,G. Fujimoto,H. Suzuki,K. Sumitani,M. Cho,M. Suemitsu,O. Sakata,S. Tokairin,T. Yao,Y. Narita 한국물리학회 2006 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.49 No.3
We studied ZnO growth on 3C-SiC(001)/Si(001) templates. In-situ reflection high- energy electron diffraction (RHEED) observations implied that ZnO grown on 3C-SiC(001) had a critical thickness (50 nm). From a structural characterization by using X-ray diffraction, we revealed that ZnO films thinner than the critical thickness grown on 3C-SiC(001) had a [10-11] orientation with 4-fold in-plane symmetry. On the other hand, ZnO films thicker than the critical thickness consisted of [10-11] and [0001] orientations. Also, the portion of [0001] oriented ZnO increased with the layer thickness. Possible interface configurations of ZnO(10-11)/3C-SiC(001) and ZnO(0001)/ZnO(10-11) are suggested.
Lateral arrays of vertical ZnO nanowalls on a periodically polarity-inverted ZnO template
Lee, Sang Hyun,Minegishi, Tsutomu,Ha, Jun-Seok,Park, Jin-sub,Lee, Hyo-Jong,Lee, Hyun Jung,Shiku, Hitoshi,Matsue, Tomokazu,Hong, Soon-Ku,Jeon, Heonsu,Yao, Takafumi IOP Pub 2009 Nanotechnology Vol.20 No.23
<P>Well aligned ZnO nanowall arrays with submicron pitch were grown on a periodically polarity-inverted ZnO template using a carbothermal reduction process. Under the conditions of a highly dense Au catalyst for increasing nucleation sites, ZnO nanowalls with a thickness of 126 ± 10 nm, an average height of 3.4 µm, and a length of about 10 mm were formed on the template. The nanowalls were only grown on a Zn-polar surface due to a different growth mode with an O-polar surface. The results of x-ray diffraction and photoluminescence (PL) measurements revealed a single crystalline, vertical alignment on the template, and a large surface to volume ratio of the ZnO nanowalls.</P>
Growth mechanism of ZnO low-temperature homoepitaxy
S. H. Park,T. Minegishi,H. J. Lee,D. C. Oh,H. J. Ko,J. H. Chang,T. Yao 호서대학교 공업기술연구소 2010 공업기술연구 논문집 Vol.29 No.1
The authors report on the growth mechanism of ZnO films at the low growth temperature of 500 oCusinghomoepitaxy,whosetemperatureisunavailabletoobtainhigh-qualityZnOfilmsinheteroepitaxy. One typical set of ZnO films were grown on (0001) ZnO substrates by molecular-beam epitaxy: a standard structure without buffer and two buffered structures with high-temperature (HT) homobuffer and low-temperature (LT) homobuffer. As a result, the LT homobuffered structure had the outstanding material properties: the surface roughness is 0.9 nm, the full width at half maximum of x-ray rocking curve is 13 arcsec, and the emission linewdith of donor-bound excitons is 2.4 meV. In terms of the theoretical interpretation of the experimentally obtained electron mobilities, it was found that the LT homobuffered structure less suffers from the dislocation scattering and the ionized-impurity scattering, compared to the HT homobuffered structure. It is proposed that in the ZnO low-temperature homoepitaxy, the LT homobuffer plays a key role in suppressing the outdiffusion of contaminants and inducing the complete termination of dislocations in the homointerface, which result in the formation of smooth wetting layer on the homointerface.
Review : Prenatal diagnosis of cardiac defect
( Mamoru Tanaka ),( Kei Miyakoshi ),( Kazuhiro Minegishi ),( Yasunori Yoshimura ) 대한산부인과학회 2010 Journal of Womens Medicine Vol.3 No.1
Fetal cardiac malformations are the most common congenital malformations with an incidence of 8:1000 among live births. Furthermore, 10% of neonatal deaths and up to 50% of infant deaths were attributed to congenital anomalies. In 2006 the International Society of Ultrasound in Obstetrics and Gynecology (ISUOG) published practice guidelines for the sonographic screening of congenital heart disease (CHD) at some time between 18 and 22 weeks` gestation. Two levels for screening low-risk fetuses for heart anomalies are recommended. Firstly, a basic scan should be performed by analyzing a four-chamber view of the fetal heart. Secondly, an extended-basic scan further examines the size and relationships of both arterial outflow tracts. Obstetricians, midwives, and perinatalogists are able to evaluate a thorough examination of the four-chamber view, both arterial outflow tracts, three vessels and trachea view, and an assessment of pulmonary venous return. These anatomical features are usually evaluated using transverse views, although sagittal scanning planes are also used as necessary. Color Doppler ultrasonography is an important component of the fetal echocardiogram. Occasionally, advanced techniques such as Velocity Vector Imaging (VVI) may be required to evaluate fetal cardiac function using measurements of ventricular ejection fraction, stroke volume, and ventricular strain parameters. An accurate prenatal diagnosis of cardiac defects, especially ductal dependent anomaly, is extremely important for healthcare professionals who will be counseling parents about the nature, severity, clinical management and prognosis of their unborn child.