S.J. Noh

Optical quenching of NiO∕Ni coated ZnO nanowires

Low temperature photoluminescence (PL) measurements were carried out to investigate optical transition characteristics of ZnO nanowires, Ni nanodot, and NiO coated ZnO nanowires (NWs). PL emission spectra show emission peaks of distinctive bound exciton to neutral donor (DX0) and to acceptor (AX0) transition. The authors found that the optical quenching was drastic with increasing temperature and the activation energies are unusually small. The major PL emission peak for ZnO NW was switched from DX0 to AX0 for Ni–ZnO nanodot NWs. This is due to the reason that diffused hydrogen atoms into ZnO NWs during thermal annealing played as acceptors.

Oxygen plasma effects on sol-gel-derived lead-zirconate-titanate thin films

We studied effects of oxygen plasma treatment on the ferroelectric Pb(Zrx,Ti1−x)O3 (PZT) films prepared by a sol-gel method. Electrical characteristics of the films were found to be improved considerably by exposure to the O2 plasma, with enhanced remanent polarization and decreased leakage current densities. Chemical bonding analysis by means of x-ray photoelectron spectroscopy in the Pb 4f region indicated that the intensity from the perovskite PZT phase increased considerably after the O2 plasma treatment, giving rise to the improved performances of the PZT films.

Oxygen-plasma effects of a La0.7Ca0.3MnO3−δ single crystal

A La0.7Ca0.3MnO3−δ single crystal was oxygen-plasma treated at 200 °C. Our electrical and magnetic measurements indicate that the oxygen-plasma treatment can be an effective low temperature method of oxygen stoichiometry modification of colossal magnetoresistance manganites. The oxygen plasma is also shown to introduce structural defects, whose effects are prominent near the Curie temperature (Tc), giving rise to anomalies in the resistivity and magnetic behaviors.

Low-temperature processing of sol–gel-derived lead–zirconate–titanate thin films by oxygen-plasma treatment

Abstract Ferroelectric thin films of sol–gel-derived Pb(Zr x , Ti 1− x )O 3 (lead–zirconate–titanate, PZT) were obtained by the low-temperature processing employing oxygen-plasma treatment. The as-coated PZT films were annealed in oxygen ambience at 450 °C, followed by oxygen-plasma treatment at 200 °C, which gave rise to the ferroelectric hysteresis. Annealing of the as-coated PZT films followed by oxygen-plasma teratment at 200 °C gave rise to the ferroelectric hysteresis.

Fabrication of a large LCD backlight unit with red, green, and blue LED lamps

Abstract A backlight unit for a 42‐inch LCD TV was manufactured with red, green, and blue LED lamps. The luminous and light extraction efficiencies of the LED lamps were increased by improving their light reflection structures and thermal properties. The blue, green, and red LED lamps showed different luminous efficiencies as a function of the input current. Compared to the conventional red LED lamp, however, the developed red LED lamp showed very high luminous efficiency in a low drive current. Taking these luminous efficiencies into account, the fabricated backlight unit showed high energy efficiency, low power consumption, and a wide color gamut.

Nonlinear optical transitions of GaAs∕AlGaAs asymmetric double-well structures

A thin AlGaAs barrier (2.5nm) inserted into a GaAs∕AlGaAs single heterojunction formed a square and a wedge-shaped triangular quantum well in the conduction band. In such a structure, the valence band does not have tunnel-coupled energy levels. Hence, the photogenerated valence holes tend to move to the GaAs flatband region. This asymmetric quantum structure showed intense nonlinear photoluminescence emission behavior with external excitation power and magnetic field. Increasing the external laser power simply caused the number of photogenerated holes to increase near the interface close to the quantum well, which then recombined with the conduction band electrons. External magnetic fields resulted in an increased Coulomb attraction which generated dynamic movement of valence holes. The migration of unbound holes to the interface region from the GaAs flatband area produced highly nonlinear optical transitions in magnetic fields.

Structural defects in LiCoO2 studied by L7i nuclear magnetic relaxation

Microscopic environments and dynamics in LiCoO2 systems were probed by L7i nuclear magnetic relaxation measurements with regard to the structural defects as revealed by x-ray diffraction and electron spin resonance measurements. Thus, the structural defects of differing degrees, associated with Li vacancies, were well accounted for in the temperature-dependent spin-lattice relaxation rate analysis, and in the structural and dynamical inhomogeneity as derived from the relaxation patterns.

Electrical Fatigues in Oxygen Plasma-Treated Sol-Gel-Derived Lead-Zirconate-Titanate Films.

Effects of O2-plasma on the electrical fatigue characteristics in ferroelectric [Pb(Zrx, Ti1-x)O3] (PZT) films prepared by a sol-gel method were investigated. Before and after oxygen plasma treatment, the switched remanent polarization decreased to 59% and 76% of the initial value, respectively, when electrical stress was applied by 108 switching cycles. Thus, oxygen plasma treatment is shown to be a simple and effective method of reducing electrical fatigues in PZT thin films.

Hydrogen Permeation in Cold-Rolled High-Mn Twinning-Induced Plasticity Steels

AbstractHydrogen permeation is investigated in cold-rolled Fe-0.6C-18Mn-(1.5Al) alloys. The hydrogen mobility is lower in cold-rolled alloys compared with annealed alloys. Al-containing alloy shows less deceleration of hydrogen mobility compared with the Al-free alloy. This is attributed to the reduced formation of mechanical twins and dislocations. Mechanical twins trap hydrogen strongly but are vulnerable to crack initiation; suppression of these is thought to be a major favorable influence of Al on hydrogen-induced mechanical degradation.