Jung Ho Je

Effects of strain energy on the preferred orientation of TiN thin films

The effects of strain energy on the preferred orientation of TiN thin films were investigated. In the TiN film deposited by plasma‐enhanced chemical‐vapor deposition with a power of 50 W, the overall energy of the film mainly depended on the surface energy because its strain energy was relatively small. The preferred orientation of the film corresponded to the plane with the lowest surface energy, i.e., (200). However, in the TiN film deposited by rf sputtering with a power of 200 W, the overall energy of the film was largely controlled by strain energy due to its large strain energy, and its growth orientation corresponded to the plane with the lowest strain energy, i.e., (111). Furthermore, the preferred orientation of the TiN film was changed from (200) to (111) with the film thickness. It is considered that this phenomenon is due to the increase of strain energy with its thickness.

Electrochemistry: building on bubbles in metal electrodeposition.

In the electrodeposition of metals, a widely used industrial technique, bubbles of gas generated near the cathode can adversely affect the quality of the metal coating. Here we use phase-contrast radiology with synchrotron radiation to witness directly and in real time the accumulation of zinc on hydrogen bubbles. This process explains the origin of the bubble-shaped defects that are common in electrodeposited coatings.

Heteroepitaxial growth behavior of Mn-doped ZnO thin films on Al2O3 (0001) by pulsed laser deposition

Heteroepitaxial growth behavior of Mn-doped ZnO thin films (Zn1−xMnxO) on Al2O3 (0001) substrates by pulsed laser deposition was investigated particularly as a function of Mn content (0.00⩽x⩽0.35) using synchrotron x-ray scattering and atomic force microscopy. The undoped ZnO film was grown epitaxially with a 30° rotation of ZnO basal planes with respect to the Al2O3 substrate while having a small amount of grains with another epitaxial relationship, i.e., the hexagon-on-hexagon growth. A small amount of Mn doping (x=0.05) not only greatly improved the atomic alignment both in the in-plane and in the out-of-plane directions, but also led to a singly oriented film by totally suppressing the hexagon-on-hexagon growth. With further incorporation of Mn into ZnO beyond that content, the epitaxial nature again deteriorated. The superior epitaxial growth of the film with an optimum Mn content is attributed to the formation of much larger grains in it. In addition, our Mn-doped ZnO thin films showed a paramagneti...

Patterning droplets with durotaxis

Numerous cell types have shown a remarkable ability to detect and move along gradients in stiffness of an underlying substrate—a process known as durotaxis. The mechanisms underlying durotaxis are still unresolved, but generally believed to involve active sensing and locomotion. Here, we show that simple liquid droplets also undergo durotaxis. By modulating substrate stiffness, we obtain fine control of droplet position on soft, flat substrates. Unlike other control mechanisms, droplet durotaxis works without imposing chemical, thermal, electrical, or topographical gradients. We show that droplet durotaxis can be used to create large-scale droplet patterns and is potentially useful for many applications, such as microfluidics, thermal control, and microfabrication.

A Stretchable Nanowire UV–Vis–NIR Photodetector with High Performance

A simple direct-writing technique can be used to fabricate a stretchable UV-vis-NIR nanowire photodetector (NWPD) consisting of PbS quantum dot (QD)-poly(3-hexylthiopehene) (P3HT) hybrid NWs. The hybrid NWPD shows superior sensitivity and response speed in the UV-vis to NIR range. The stretchable UV-vis-NIR NWPD shows a nearly identical photoresponse under extreme (up to 100%) and repeated (up to 100 cycles) stretching conditions.

Synchrotron radiation in radiology: radiology techniques based on synchrotron sources

The characteristics of synchrotron X-ray sources—quite different from those of conventional sources—are exploited by several new imaging techniques. These techniques expand the capabilities of conventional radiology and find interesting application in special cases. We briefly review the basic principle, applications and limitations of the most important of them: monochromatic mammography, two-wavelength digital subtraction angiography, phase-contrast/edge-enhancement imaging, diffraction-enhanced imaging and microtomography.

The topographic effect of zinc oxide nanoflowers on osteoblast growth and osseointegration.

Cell-material interactions are one of the most important factors to be considered for the applications of biomaterials to tissue engineering fi elds. Cellular responses are dependent on the bio-interphases with various topologies such as nanopits, nanorods, nanogrates, and nanotubes, etc. [ 1–3 ] Cells interact with specifi c binding motifs in adhesion proteins via cell surface receptors, such as integrins with non-covalently associated α and β chains. There have been extensive research efforts to investigate the topographic effect of biomaterials with various microand nano-structures on cell-material interactions. The fabrication of nanostructures on biomaterials improves their biocompatibility more effectively with well-defi ned morphologies than the conventional chemical or physicochemical surface treatments. [ 4 , 5 ] It was reported that aligned groove patterns led to an increase in endothelial cell and osteoblast adhesions. [ 2 ] In the same way, nanostructures were fabricated and assessed with human foreskin fi broblasts. The results showed that these architectures were advantageous to cause the discreet contact guidance for fi lopodia extension. [ 4 ] Despite wide investigations on the interactions between cells and nanoscale topographic surfaces of biomaterials, the effect of nanofl ower structure on cell adhesion, proliferation, and growth has not been reported yet. ZnO nanostructures have been widely studied for various electronic applications due to their unique piezoelectric, semiconducting, and catalytic properties with a high electron mobility and a wide band-gap. [ 6 ] Recently, they have been also exploited for biomedical applications such as implantable biomedical nanosensors, and restorative and prosthodontic applications in dentistry. [ 7 , 8 ] The biodegradability, biocompatibility, and biosafety of ZnO nano-structures were reported in cellular levels elsewhere. [ 9 , 10 ] Furthermore, the topographic effect and the cytotoxicity of ZnO nanorods were extensively studied to control the cell adhesion and macrophage responses for tissue engineering applications. [ 11 , 12 ] In this work, we investigated the topographic effect of ZnO nanofl owers on MC3T3-E1 osteoblast

Visualization of asymmetric wetting ridges on soft solids with X-ray microscopy

One of the most questionable issues in wetting is the force balance that includes the vertical component of liquid surface tension. On soft solids, the vertical component leads to a microscopic protrusion of the contact line, that is, a ‘wetting ridge’. The wetting principle determining the tip geometry of the ridge is at the heart of the issues over the past half century. Here we reveal a universal wetting principle from the ridge tips directly visualized with high spatio-temporal resolution of X-ray microscopy. We find that the cusp of the ridge is bent with an asymmetric tip, whose geometry is invariant during ridge growth or by surface softness. This singular asymmetry is deduced by linking the macroscopic and microscopic contact angles to Young and Neuman laws, respectively. Our finding shows that this dual-scale approach would be contributable to a general framework in elastowetting, and give hints to issues in cell-substrate interaction and elasto-capillary problems.

Three-Dimensional Writing of Conducting Polymer Nanowire Arrays by Meniscus-Guided Polymerization

Accurate and versatile three-dimensional writing of individually controlled conducting polymer nanodevices forming dense arrays is demonstrated by guiding a monomer meniscus in pulling a micropipette during oxidative polymerization. We specifically demonstrate well-defined dense arrays of various freestanding nano-components with controlled radius down to similar to 50 nm: straight wires, nanowires with variable radius, branches, and bridges.

Structural evolution of ZnO/sapphire(001) heteroepitaxy studied by real time synchrotron x-ray scattering

The structural evolution during heteroepitaxial growth of ZnO/sapphire(001) by radio-frequency magnetron sputtering has been studied using real-time synchrotron x-ray scattering. The two-dimensional (2D) ZnO(002) layers grown in the initial stage are highly strained and well aligned to the substrate having a mosaic distribution of 0.01° full width at half maximum (FWHM), in sharp contrast to the reported transition 2D layers grown by molecular-beam epitaxy. With increasing film thickness, the lattice strain is relieved and the poorly aligned (1.25° FWHM) three-dimensional (3D) islands are nucleated on the 2D layers. We attribute the 2D–3D transition to the release of the strain energy stored in the film due to the film/substrate lattice mismatch.