C. O. Kim

Ultraviolet laser treatment of multiwall carbon nanotubes grown at low temperature

Simple laser irradiation of well-aligned multiwall carbon nanotubes (MWCNTs) was performed to intentionally modify structural defects and to ablate possible contamination of the MWCNTs. Scanning electron microscopy and transmission electron microscopy confirmed the clear presence of the MWCNTs with open tips. A Raman spectra exhibited a decrease in an intensity ratio (ID/IG) of 1352 cm−1 (D band) over 1583 cm−1 (G band) peaks by significantly reducing the amorphous carbon phases of D band peaks. The structural improvement in the MWCNTs after optimum laser exposure resulted in a reduction of the turn-on voltage from 1.0 to 0.6 V/μm and an increase in the emission current.

Ferromagnetic quantum dots formed by external laser irradiation

We present an efficient method for the formation of cobalt ferromagnetic quantum dots (FMQDs) by exposing a Nd: YAG laser (wavelength=355 nm) on ferromagnetic thin films grown on Si substrates. Primary emphasis is placed on the simple and direct fabrication of the FMQDs without performing any micro- or nanopattering process. Scanned laser irradiation of low power causes localized segregation of ultrathin as-deposited films by the laser-induced heat, resulting in the fabrication of FMQDs. Observations by scanning electron microscope and atomic force microscope clearly confirm highly uniform controllable nanoscale FMQDs in our case. The average size and density of the FMQDs were about 10 nm and 2×1011/cm2, respectively. Magnetic characteristics of the FMQDs were also measured by a superconducting quantum interference device at 5 K.

Efficient characterization of ultrathin AlOx insulating barriers in magnetic tunnel junctions fabricated by masked rf plasma oxidation technique

AlOx insulating barriers in magnetic tunnel junctions were prepared by a masked rf plasma oxidation process to reduce direct ion-bombardment effect on the barrier. In our method, the root-mean-square value of 2.1 A in the barrier and the magnetic resistance ratio up to 32% were observed. In addition, the surface plasmon resonance spectroscopy (SPRS) measurement was performed to efficiently determine optimum oxidation time, dielectric properties, and oxidation states inside thin barrier. The SPRS results revealed that the dielectric value and thickness of the optimum barrier were found to be 1.3576+i1.4488 and 16.3 A, respectively, with a thickness confirmation by a high resolving transmission electron microscope measurement.

Enhanced performance of CoFe/AlOx/CoFe magnetic tunnel junctions prepared by an off-axis rf remote plasma oxidation method

A new off-axis rf remote oxidation technique for the insulating barrier was carried out to enhance performance of CoFe/AlOx/CoFe magnetic tunneling junctions. The rf remote plasma method was designed to reduce self-bias voltage effect on the barrier during the rf oxidation process and to increase atomic oxygen concentration at high power operation, compared with a conventional rf plasma oxidation method. In addition, the off-axis geometry was chosen to give rise to high uniformity of the insulating layer. Experimentally observed root mean square of the barrier was decreased from 5 A to 1.5 A in our method. Electrical breakdown voltage and magnetoresistance of our MTJ devices increased from 0.8 V up to 1.4 V and from 20.2% up to 33.6%, respectively, correlated with the improved structural information of the barrier.

Laser-induced surface cleaning of molybdenum field emitter arrays for enhanced electron emission

Visible laser irradiation on molybdenum field emission arrays (Mo–FEAs) was performed as one efficient cleaning method in order to etch off any unnecessary oxidation layers on the FEA surface. Scanning electron microscopy and high-resolution transmission electron microscopy showed clear removal of ultrathin MoO oxide layers at the emitter edge through a photoinduced thermal process. A sharp surface morphology of the emitter tips was also observed due to the crystallization or thermalmigration effect during the laser exposure. The structural enhancement of the FEA was strongly confirmed by a remarkable increase of 40% in the emission current after laser exposure.

Influence of grain size on the electronic and the magnetic properties of La0.7Ca0.3MnO3−δ

Polycrystalline La0.7Ca0.3MnO3−δ (LCMO), prepared by a solid-state reaction, was annealed at different temperatures TA. The variation of TA was responsible for observed changes in the physical properties, including a shift in the metal-insulator transition temperature, which is explained by variation in the oxygen content. At low temperatures the magnetization of LCMO samples was also observed to be dependent on TA. A reduction of the grain boundaries leads to enhancement of both the magnetization and the sensitivity for low-field magnetoresistance. By using Mn L3-edge x-ray absorption, it was also found that the Mn3+∕Mn4+ ratio increases with the grain size, and that the oxygen content in LCMO is governed by the grain boundaries.

Microstructure and electrical transport property of Fe/Cu nanoscale multilayered materials

The microstructures and electrical conductivity (σ) at room temperature of Fe/Cu multilayered material, which was prepared by the electron-beam physical-vapor-deposition technique, were investigated to understand the dependence of σ on the bilayer thickness (Λ=dFe+dCu) and the sublayer thickness ratio (χ=dFe/Λ), where d is the sublayer thickness. Satellite peaks in the x-ray diffraction spectra were observed, indicating a layered structure in the multilayered material. The specimen was polycrystalline, and the in-plane grain size is independent of the sublayer thickness. σ at a fixed χ increases with increasing Λ, and keeps nearly constant when Λ is larger than 30 nm. σ at a fixed Λ decreases linearly with increasing χ. The size dependence of σ is explained using a model that takes into account scattering by the sublayer interfaces and the grain boundaries. The scattering at interfaces and grain boundaries is thought to be the dominant mechanism for the size dependence of σ on Λ when dFe is smaller and la...

A new rf plasma oxidation method for the insulating AlOx barrier in magnetic tunneling junctions

Abstract An rf remote plasma oxidation technique to form an insulating barrier was carried out to enhance properties of CoFe/AlO x /CoFe magnetic tunneling junctions. The rf remote plasma method was found to reduce self-bias effect on the barrier during the rf oxidation process and to increase atomic oxygen concentration in a plasma state. Experimentally observed rms roughness of the barrier in our magnetic tunnel junction was decreased from 5 to 1.5 A. In addition, electrical breakdown voltage and magnetoresistance of our magnetic tunnel junction devices were increased from 0.8 V up to 1.2 V and from 7% up to 30%, respectively.

P‐45: Performance of in‐situ Laser Vacuum Sealing and Annealing on the Panel for the Application of Field Emission Displays

In-situ laser sealing and annealing treatments have been performed inside a high vacuum chamber for efficient completion process of field emission displays. A high power Nd:YAG continuous wave (λ = 1,064nm) laser was mainly used as an irradiation source was used as a source. In a packaging scheme, the most vital part of the panel was kept at temperature below 300°C to shorten the entire panel process. Experimental work exhibits efficiently local hitting of frit by the laser to stitch both cathode and anode plate during the short time. In addition, laser treatment on electrophoretically deposited phosphors has been carried out as one of efficient post-annealing methods in order to improve the brightness of the phosphor coated on indium-tin oxide-coated glasses. For the annealing process, two basic parameters, such as laser power and treatment time were examined inside the same vacuum chamber. The experimental results presented useful laser-annealing time and enhanced improvement of about 10% in the brightness after the laser irradiation on the phosphor. The improvement in the brightness was thought due to the surface cleaning effect on the phosphor surface.

The Dependence of the Flux Pinning Effects on the Au Mole Fraction in Y1Ba2Cu3–3xAu3xO7–δ Superconductors

Measurements of the dependences of the magnetization relaxation and the magnetization hysteresis on the Au mole fraction in Y 1 Ba 2 Cu 3-3x Au 3x O 7-δ superconductors have been performed to investigate the flux pinning effects. As the Au mole fraction increases, the density of the Y 1 Ba 2 Cu 3-3x Au 3x O 7-δ superconductor becomes larger due to its decreased porosity. The zero-field-cooled and the field-cooled measurements show that the critical temperatures are independent of the Au mole fraction but that the Meissner effects increase slightly with increasing Au mole fraction. The values obtained for the flux pinning potential and for the width of the magnetization decrease with increasing Au mole fraction except the Au mole fraction of 0.01. These results indicate that the flux pinning effects are decreased by substituting Au into Y 1 Ba 2 Cu 3-3x Au 3x O 7-δ superconductors.