Woo-Hee Kim

Gene polymorphisms of endothelial nitric oxide synthase and angiotensin-converting enzyme in patients with asthma.

Background: Nitric oxide, including that produced by endothelial constitutive nitric oxide synthase (ecNOS), may regulate vascular and airway tone in the lungs and may influence various aspects of airway homeostasis. Angiotensin‐converting enzyme (ACE) is expressed at high levels in the lungs and plays a role in the metabolism of angiotensin II, bradykinin, and substance P, all of which are potentially involved in the pathogenesis of asthma. An insertion‐deletion polymorphism of the ACE gene has been shown to be associated with enzyme activity levels of ACE. To examine the possible involvement of the ecNOS and/or ACE genes as the genetic basis of bronchial asthma, we investigated whether there was any association between bronchial asthma and polymorphisms of the ecNOS and/or ACE genes.

Atomic Layer Deposition of Ni Thin Films and Application to Area-Selective Deposition

Downlo Atomic Layer Deposition of Ni Thin Films and Application to Area-Selective Deposition Woo-Hee Kim, Han-Bo-Ram Lee, Kwang Heo, Young Kuk Lee, Taek-Mo Chung, Chang Gyoun Kim, Seunghun Hong, Jong Heo, and Hyungjun Kim* Department of Material Science and Engineering, Pohang University of Science and Technology, Pohang 790-784, Korea School of Electrical and Electronic Engineering, Yonsei University, Seoul 120-749, Korea Department of Physics and Astronomy and Interdisciplinary Program in Nano-Science and Technology, Seoul National University, Seoul 151-747, Korea Advanced Materials Division, Korea Research Institute of Chemical Technology, Daejeon 305-600, Korea

Flat band voltage (VFB) modulation by controlling compositional depth profile in La2O3/HfO2 nanolaminate gate oxide

We investigated the flat band voltage (VFB) modulation by insertion of lanthanum oxide (La2O3) into hafnium oxide (HfO2) gate dielectrics. The properties of La2O3/HfO2 nanolaminates were precisely modulated by controlling the position of La2O3 layer at bottom, middle, or top using atomic layer deposition. When the La2O3 layer was positioned closer to the interface (bottom), the reduction in VFB shift was more effective than the other two cases (middle and top). From our experimental results, we propose that the main mechanism of VFB modulation using La2O3 layer is dipole moment formation at an interfacial layer between high k gate dielectric and Si substrate.

The effects of La substitution on ferroelectric domain structure and multiferroic properties of epitaxially grown BiFeO3 thin films

We report the influence of La substitution in epitaxial BiFeO3 thin films prepared by pulsed layer deposition on a Nb-doped SrTiO3 substrate, focusing on ferroelectric domain structure, leakage current, and multiferroic properties. Enhanced ferroelectric remanent polarization and reduced leakage current density were established via La substitution in the BiFeO3 film. Based on leakage conduction mechanism and piezoelectric force microscopy studies, this is indicative of reduced trap densities and increased domain energy. Besides that, the ferromagnetic properties were improved by the La doping as well. The possible mechanisms for the enhancement of electrical and multiferroic characteristics are extensively discussed.

Current degradation mechanism of single wall carbon nanotube emitters during field emission

Electron emission current degradation is often observed from printed single wall carbon nanotube emitters during field emission process. After a highly imposed emission, structural deformation of emitters from thin crystalline nanotube bundle to thick amorphous-type carbon fiber was observed. This deformation seems to relate to the current degradation, deteriorating the efficiency of field emission either by increasing the resistance of emitters or by decreasing the field enhancement factor of emitter tips. Two possible mechanisms of structural deformation are internal structural transformation by Joule heating under excessively imposed emission current and continuous adsorption of carbon particles on actively working emitters.

Plasma-Enhanced Atomic Layer Deposition of Ni

Ni plasma enhanced atomic layer deposition (PE-ALD) using bis(dimethylamino-2-methyl-2-butoxo)nickel [Ni(dmamb)2] as a precursor and NH3 or H2 plasma as a reactant was comparatively investigated. PE-ALD Ni using NH3 plasma showed higher growth rate, lower resistivity, and lower C content than that using H2 plasma. PE-ALD Ni films were analyzed by X-ray photoelectron spectroscopy (XPS), scanning transmission electron microscopy (STEM), and electron energy loss spectroscopy (EELS). The results showed that the reaction chemistry of ALD using NH3 plasma was clearly different with that using H2, probably due to the effects of NHx radicals.

Confinement of Ferroelectric Domain-Wall Motion at Artificially Formed Conducting-Nanofilaments in Epitaxial BiFeO3 Thin Films

We report confinement of ferroelectric domain-wall motion at conducting-nanofilament wall in epitaxial BiFeO3 thin film on Nb-doped SrTiO3 substrate. The BiFeO3 film exhibited well-defined ferroelectric response and unipolar resistive switching behavior. We artificially formed conducting-nanofilaments in the BiFeO3 via conducting atomic force microscope techniques. The conducting-nanofilament wall, which does not possess any ferroelectric polarization, is then able to block domain propagation. Consequently, we demonstrate that the domain-wall motion is effectively confined within the conducting-nanofilament wall during polarization switching. This significant new insight potentially gives an opportunity for the artificial manipulation of nanoscale ferroelectric domain.

Electron emission from carbon nanotube-dispersed MgO layer

A simple secondary-electron-emission (SEE)-based source was fabricated using a carbon-nanotube-dispersed MgO precursor solution. This emission source exhibits a high SEE gain as over 103. In addition, the self-sustaining current was observed even after turning off the primary electron beam, then the emission current could be modulated by a small electric field variation (1.2–2V∕μm). The electron energy spectrum of the self-sustaining emission indicates that the major character of the emission is attributed to the field-enhanced SEE rather than direct field emission.

Flatband voltage control in p-metal gate metal-oxide-semiconductor field effect transistor by insertion of TiO2 layer

Titanium oxide (TiO2) layer was used to control the flatband voltage (VFB) of p-type metal-oxide-semiconductor field effect transistors. TiO2 was deposited by plasma enhanced atomic layer deposition (PE-ALD) on hafnium oxide (HfO2) gate dielectrics. Comparative studies between TiO2 and Al2O3 as capping layer have shown that improved device properties with lower capacitance equivalent thickness (CET), interface state density (Dit), and flatband voltage (VFB) shift were achieved by PE-ALD TiO2 capping layer.

Triangular ferroelectric domains of highly (111)-oriented NaNbO3 thin film on a glass substrate

Highly (111)-oriented polycrystalline NaNbO3 (NNO) thin films were deposited on Pt/Ta/glass substrates by pulsed laser deposition. To obtain a well-crystallized Pt bottom electrode on glass substrates, Ta buffer layers were employed between Pt bottom electrodes and glass substrates. The NNO thin film exhibited good ferroelectricity with high remanent polarization (2Pr ≈ 46 µC/cm2) and leakage current density (∼2 × 10−6 A/cm2 at 500 kV/cm). Based on a piezoelectric force microscope study, it is demonstrated that the NNO thin film with triangular grains has ferroelectric domain wall energy slightly less than PbTiO3 thin films.