Soon Ku Hong

Nanostructural analysis of trabecular bone

The mechanical properties of bone are dictated by the size, shape and organization of the mineral and matrix phases at multiple levels of hierarchy. While much is known about structure–function relations at the macroscopic level, less is known at the nanoscale, especially for trabecular bone. In this study, high resolution transmission electron microscopy (HRTEM) was carried out to analyze shape and orientation of apatite crystals in murine femoral trabecular bone. The distribution and orientation of mineral apatites in trabecular bone were different from lamellar bone and the c-axis of the tablet-like mineral apatite crystals in trabecular bone was arranged with no preferred orientation. The difference in the orientation distribution of apatite crystals of trabecular bone in the present study compared with that of lamellar bone found in the literature can be attributed to the more complex local stress state in trabecular bone. Apatite crystals were also found to be multi-crystalline, not single crystalline, from dark field image analysis. From the observations of this study, it is suggested that Wolff’s law can be applicable to the nanostructural orientation and distribution of apatite crystals in trabecular bone. It was also found that small round crystalline particles observed adjacent to collagen fibrils were similar in size and shape to the apatite crystals in biomimetically nucleated synthetic amorphous calcium phosphate, which suggests that they are bone mineral apatite nuclei.

Study on MgO buffer in ZnO layers grown by plasma-assisted molecular beam epitaxy on Al2O3(0001)

Abstract We have investigated effects of MgO buffer layers and its annealing on the structural quality of ZnO layers grown on Al 2 O 3 (0001) by plasma assisted molecular beam epitaxy (P-MBE). It was found that surface morphology and crystalline quality of ZnO layers were improved by employing thin MgO buffer layers. Furthermore, annealing of the MgO buffer at high temperatures enhanced the surface migration of adatoms, leading to the formation of larger terraces and smoother surface morphology. We speculate that the relaxation of strain in the MgO buffer contributes to lowering of the surface energy. The dislocation density of ZnO layers was also reduced from 5.3×10 9 cm −2 to 1.9×10 9 cm −2 by annealing a low temperature (LT) MgO buffer.

Effects of two-step growth by employing Zn-rich and O-rich growth conditions on properties of (112¯0) ZnO films grown by plasma-assisted molecular beam epitaxy on sapphire

The authors report properties of a-plane ZnO films on r-plane sapphire substrates by plasma-assisted molecular beam epitaxy in which two-step growth is employed. They show that the two-step growth is effective in improving structural and optical properties of a-plane ZnO films. Here, the two-step growth is preceded by growing the first layer under Zn-rich (O-rich) conditions and growing the second layer under O-rich (Zn-rich) conditions. All the grown samples show striated anisotropic morphology. The samples with the first, thin, O-rich layer plus the second, thick, Zn-rich layer show smaller root-mean-square (rms) roughness than those with the first, thin, Zn-rich layer plus the second, thick, O-rich layer. The sample with the 20-nm-thick first layer grown under O-rich condition shows the smallest rms roughness of 1.06nm, which is a smaller rms value than that of the sample grown under the single-step, stoichiometric condition. This sample shows the highest intensity of DX0 emission at 3.392eV and small ...

Effect of Various Crucibles for High Quality AIN Crystal Growth on SiC Seed by PVT Method

Aluminum nitride (AlN) bulk crystals, approximately 50.8mm in diameter and up to 5mm thickness, were grown by a physical vapor transport (PVT) method in a tantalum crucible. To investigate the effect of crucible materials, various crucible materials, a graphite and TaC-coated graphite and tantalum crucible were used for the AlN growth. XRD pattern of AlN crystal grown on SiC seed in the Ta-crucible exhibited only (00l) peaks, indicating that AlN single crystal was successfully grown on SiC seed. The interface structure between AlN and SiC crystals was observed by a high resolution TEM.

The Effect of Modified Crucible Design and Seed Attachment on SiC Crystal Grown by PVT

The present research was focused to investigate the effect of internal crucible design that influenced the 4H-SiC crystal growth onto a 6H-SiC seed by PVT method. The crucible design was modified to produce a uniform radial temperature gradient in the growth cell. The seed attachment was also modified with a use of polycrystalline SiC plate. The crystal quality of 4H-SiC single crystals grown in modified crucible and grown with modified seed attachment was revealed to be better than that of crystal grown in conventional crucible. The full width at half maximum (FWHM) values of grown SiC crystals in the conventional crucible, the modified seed attachment and the modified crucible were 285 arcsec, 134 arcsec and 128 arcsec, respectively. The micropipe density (MPD) of grown SiC crystals in the conventional crucible, the modified seed attachment and the modified crucible were 101ea/cm^2, 81ea/cm^2 and 42ea/cm^2, respectively.

SiC Single Crystal Growth on Dual Seed with Different Surface Properties

SiC crystal ingots were grown on 6H-SiC dual-seed crystal with different surface properties by a PVT (Physical Vapor Transport) technique. And then SiC crystal wafers sliced from the SiC ingots were systematically investigated in order to find out the dependence of surface properties for seed on the polytype formation. While n-type SiC crystals exhibiting the 4H polytype were grown on seed crystal having high root-mean-square (rms) value, 6H-SiC crystals were grown on seed having lower rms value. However, 6H polytype was maintained on on-axis and off-axis seeds during the entire growth period. The crystal quality of 6H-SiC single crystals grown on on-axis seed were revealed to be slightly better than that of 6H-SiC crystal grown on off-axis seed.

Magnetic and Magnetotransport Properties of Annealed Amorphous Ge 1-x Mn x Semiconductor Thin Films

Amorphous Ge_1-xMn_x thin films grown by low temperature vapor deposition were annealed and their electrical and magnetic properties have been studied. Amorphous Ge_1-xMn_x thin films were annealed at 300°C, 400°C, 500°C, 600°C and 700°C for 3 minutes in high vacuum chamber. X-ray diffraction and TEM analyses reveal that as-grown Ge_1-xMn_x thin films are amorphous, and fine crystalline phases are precipitated when annealed. The fine crystalline precipitates appear at the lower temperature as the Mn concentration of amorphous Ge_1-xMn_x thin films increases. As-grown amorphous Ge_1-xMn_x thin films have p-type majority carriers and the type of majority carriers is not changed after annealing, but the electrical resistivity increases with annealing temperature. Magnetization characteristics show that the as-grown amorphous Ge_1-xMn_x thin films are ferromagnetic and the Curie temperatures are around 130K. Curie temperature and saturation magnetization of annealed Ge_1-xMn_x thin films increase with annealing temperature. There are different mechanisms to understand increasing of Curie temperature that is related with annealing temperature. Firstly, interaction between Mn spins might be changed by annealing effect. Secondly, magnetization behavior and X-ray analysis imply that the formation of ferromagnetic Ge₃Mn₅ phase causes the change of magnetic and electrical properties of annealed Ge_1-xMn_x thin films.