Jonghan Song

Role of subnano-, nano- and submicron-surface features on osteoblast differentiation of bone marrow mesenchymal stem cells.

Subnano, nano and sub-micron surface features can selectively activate integrin receptors and induce osteoblast differentiation of bone marrow mesenchymal stem cells. Although it is widely accepted that nanoscale titanium surface roughness may promote differentiation of various osteoblast lineages, there has been no clear report on the threshold dimension of surface features and the optimized dimensions of surface features for triggering integrin activation and stem cell differentiation. This study systematically controlled titanium surface features from the sub-nano to sub-micron scales and investigated the corresponding effects on stem cell responses, such as integrin activation, cyclins, key transcriptional genes of osteoblast differentiation and osteoblastic phenotype genes. Surface features with sub-nano surface dimensions were insufficient to increase integrin activation compared to pure nanoscale titanium surface features. Although both pure nanoscale and nano-submicron hybrid scales of titanium surface features were sufficient for activating integrin-ligand proteins interactions through the α integrin subunits, only nano-submicron hybrid titanium surface features significantly accelerated subsequent osteoblast differentiation of primary mouse bone marrow stromal cells after 2 weeks. In addition, live cell analysis of human bone marrow mesenchymal stem cells on transparent titanium demonstrated rapid cytoskeletal re-organization on the nanoscale surface features, which ultimately induced higher expression of osteoblast phenotype genes after 3 weeks.

Analysis on migration and activation of live macrophages on transparent flat and nanostructured titanium.

The immunotoxicity of implanted nanostructured titanium is a paramount issue for vascular, dental and orthopedic applications. However, it has been unclear whether implanted surface nanostructures can inhibit or aggrevate inflammatory responses. Herein, macrophage activation, as evidence of migration, on transparent flat and nanostructured titanium correlated with pro-inflammatory protein synthesis and cytokine release. Through the real-time monitoring of initial cytoskeleton variations, this study identified that macrophage movement was restricted on nanostructured titanium compared to flat titanium surfaces. Furthermore, nanostructured titanium elicited secretion of fewer pro-inflammatory enzyme molecules and cytokines, as well as reduced nitric oxide production. All results collectively indicated that initial macrophage activation can be mitigated by nanoscale surface topography alone, without modification of surface chemistry or stiffness.

Photoresponse of Si detector based on n-ZnO/p-Si and n-ZnO/n-Si structures

Abstract The ZnO/Si photodiodes have been fabricated depositing n-ZnO films on n- and p-Si by rf sputtering method. All the n-ZnO/p-Si diodes show strong rectifying behavior characterized by the current–voltage ( I – V ) measurement under a dark condition while the n-ZnO/n-Si diodes showed weak rectifying behaviors. Photoelectric effects have been exhibited under an illuminated condition using a red light of 670 nm. High photocurrent or responsivities are obtained under a reverse bias when the crystalline quality of n-ZnO film is good enough to transmit the light into p-Si.

Structural characteristics of Y2O3 films grown on oxidized Si(111) surface

We investigated the characteristics of Y2O3 films grown on an oxidized Si(111) surface, using x-ray diffraction, Rutherford backscattering spectroscopy, and high-resolution transmission electron microscopy. The films grown on the oxidized Si show drastically improved crystallinity, compared with the film grown on clean Si surfaces: channeling minimum yield (Xmin) of 2.5% and full width at half maximum of rocking curve lower than 0.03°. The improvement of the crystallinity was due to the difference of the crystalline structure at the interface between the films grown on the oxidized and clean Si surfaces. Crystalline orientation of Y2O3 islands at the interfacial region was misaligned from the normal substrate direction. The misalignment decreased with increasing the substrate temperature. In particular, the ordering of the oxygen atom in the film grown on oxidized Si was improved compared to that of the Y atom, indicating that the crystallinity of the film is dominantly determined by the arrangement of th...

Defect versus nanocrystal luminescence emitted from room temperature and hot-implanted SiO2 layers

Abstract Silicon nanocrystals have been synthesized in SiO 2 matrix using Si ion implantation. Si ions were implanted into 300-nm-thick SiO 2 films grown on crystalline Si at energies of 30–55xa0keV, and with doses of 5×10 15 , 3×10 16 , and 1×10 17 xa0cm −2 . Implanted samples were subsequently annealed in an N 2 ambient at 500–1100°C during various periods. Photoluminescence spectra for the sample implanted with 1×10 17 xa0cm −2 at 55xa0keV show that red luminescence (750xa0nm) related to Si-nanocrystals clearly increases with annealing temperature and time in intensity, and that weak orange luminescence (600xa0nm) is observed after annealing at low temperatures of 500°C and 800°C. The luminescence around 600xa0nm becomes very intense when a thin SiO 2 sample is implanted at a substrate temperature of 400°C with an energy of 30xa0keV and a low dose of 5×10 15 xa0cm −2 . It vanishes after annealing at 800°C for 30xa0min. We conclude that this luminescence observed around 600xa0nm is caused by some radiative defects formed in Si-implanted SiO 2 .

The origin of photoluminescence in Ge-implanted SiO2 layers

Abstract Ge ions were implanted at 100xa0keV with 3×1016xa0cm−2 into a 300xa0 nm thick SiO2 layer on Si. Visible photoluminescence (PL) around 2.1xa0eV from an as-implanted sample is observed, and faded out by subsequent annealing at 900°C for 2xa0h. However, PL shows up again after annealing above 900°C at the same peak position. Compared with the as-implanted sample, significant increase of Ge–Ge bonds is measured in X-ray photoelectron spectroscopy, and the formation of Ge nanocrystals with a diameter of 5xa0nm are observed in transmission electron microscopy from the sample annealed at 1100°C. We conclude that the PL peak from the sample annealed above 900°C is caused by the quantum confinement effects from Ge nanocrystals, while the luminescence from the as-implanted sample is due to some radiative defects formed by Ge implantation.

Violet and orange luminescence from Ge-implanted SiO2 layers

Abstract Ge ions of 100 keV were implanted into a 120-nm thick SiO 2 layer at room temperature (RT), 300, and 500°C. The employed doses of Ge ion were 5×10 15 , 1×10 16 , 5×10 16 , and 1×10 17 cm −2 . Maximum intensity of sharp violet photoluminescence (PL) from the sample implanted at room temperature with a dose of 1×10 16 cm −2 is observed after the sample has been annealed at 500°C for 2 h. Broad orange luminescence is also shown in hot-implanted samples besides the violet. Both are known as defect-related luminescences. As observed by current-voltage (I–V) characteristics, the defect-related samples exhibit large leakage currents with electoluminescence (EL) at only reverse bias region while a nanocrystal-related sample obtained by an annealing at 1100°C for 4 h shows the leakages at both the reverse and the forward region. The carrier-transport and EL mechanisms are explained from the PL and I–V results.

Controlling the formation of luminescent Si nanocrystals in plasma- enhanced chemical vapor deposited silicon-rich silicon oxide through ion irradiation

The effect of ion irradiation on the formation of luminescent Si nanocrystals from silicon-rich silicon oxide (SRSO) films deposited by electron cyclotron resonance plasma-enhanced chemical vapor deposition (PECVD) whose Si content ranged from 33 to 50 at.u200a% is investigated. As-deposited SRSO films contained a high density of irregular-shaped Si nanocrystals. Irradiating these films with 380 keV Si at room temperature to a dose of 5.7×1015u2009cm−2 prior to anneal at 1000u200a°C is found to increase the luminescence intensity due to Si nanocrystals over the films. Based on the x-ray photoemission spectra and the dependence of the luminescence intensity on the irradiating ion dose, anneal time, and the silicon content of the film, we propose the destruction of pre-existing Si clusters by ion irradiation to be an important factor responsible for the observed enhancement of luminescence, and suggest that preanneal irradiation may be a viable method to control the formation of luminescent Si nanocrystals in PECVD-dep...

Visible photoluminescence in ion beam mixed SiO2/Si/SiO2 layers

Abstract Visible photoluminescence from silicon nanocrystals embedded in SiO2 matrix by ion beam mixing was investigated. Photoluminescence spectra of ion beam mixed SiO2/Si/SiO2 films excited by an Ar-laser (457.9 nm) showed more intense luminescence with a peak centered at 720 nm than that prepared by the conventional ion implantation method. The formation of nanocrystals in SiO2 matrix was confirmed by cross-sectional high resolution transmission electron microscopy. The red luminescence is attributed to the silicon nanocrystals produced by ion beam mixing.

Effect of Growth Mode on Eu-Incorporation and Luminescence of Eu-Doped GaN Epitaxial Film Grown by Plasma-Assisted Molecular Beam Epitaxy

The growth mode of europium (Eu)-doped GaN epitaxial films grown on a GaN template by rf plasma-assisted molecular beam epitaxy (PAMBE) was investigated with different III/V ratios under a constant Eu beam equivalent pressure ratio [PEu/(PEu+PGa)]. The reflection high-energy electron diffraction (RHEED) patterns and atomic force microscopy (AFM) images revealed the transition of the growth mode from three-dimensional (3D) to step-flow/two-dimensional (2D) by increasing the III/V ratio. When the films were grown in the 3D growth mode, Eu concentrations estimated by Rutherford backscattering spectrometry/channeling (RBS/channeling) were almost constant, although the III/V ratios varied. However, when the growth mode was transferred from 3D to step-flow/2D, precipitates on the surface abruptly increased while the Eu concentration abruptly decreased, indicating the abrupt degradation of Eu-incorporation in the film. Luminescence sites of Eu3+ were sensitive to the III/V ratio, and Eu atoms have different luminescence sites in both growth modes. Furthermore, luminescence efficiency abruptly increased when the growth mode was transferred from 3D to step-flow/2D.