Molecular dynamic study for nanopatterning using atomic force microscopy

The atomic force microscopy (AFM)-based nanolithographic technique is currently used to directly machine material surfaces and fabricate nanocomponents for microelectromechanical systems (MEMS) devices. In the current study, three-dimensional molecular dynamic (MD) simulations with potentials based on the Morse function were performed to evaluate the effect of crystallographic factors and process variables on the nanodeformation characteristics of the nanolithography processing of monocrystalline copper. Moreover, the effects of process variables (tool shape, cutting speed, and ploughing depth) on the nanostructural pattern are investigated. The simulation results revealed that the crystal orientation and ploughing direction had a significant influence on varying the forces (cutting force, thrust force, and width-direction force); the nature of the nanodeformation ahead of the tool; and the surface quality of the machined material.     

Degradation behavior of Ni-YSZ anode-supported solid oxide fuel cell (SOFC) as a function of H2S concentration

This study investigated the effect of H₂S concentration (5, 10 and 50 ppm) on the degradation and performance of Ni-YSZ anode supported solid oxide fuel cells. When supplied with hydrogen fuel containing H₂S, the cell voltage dropped rapidly, and with increasing H₂S concentration, voltage drop % increased (due to higher sulfur coverage on the Ni surface) and saturated more rapidly. A high concentration (50 ppm) of H₂S led to an additional, slow rate voltage loss. In all cases, cell performance did not completely recover even after being supplied with H₂S-free hydrogen fuel, because of the incomplete desorption of sulfur from the Ni surface. After the performance tests, nickel sulfides were detected on the Ni surface by Raman spectra, which were produced by the reaction of the remaining adsorbed sulfur with Ni during the cooling process. This indicates that the formation of nickel sulfides was not responsible for the secondary voltage drop. SEM/EDS analyses combined with FIB revealed that the reason for the additional 2^nd drop was Ni oxidation; at a high sulfur coverage ratio (50 ppm), the outer layer of the Ni particle was oxidized by oxygen ions transported from the electrolyte. This indicates that H₂S concentration as well as current density is a critical factor for Ni oxidation, and gives rise to the second voltage drop (irreversible cell degradation). The present work showed that the degradation behavior and phenomenon can differ significantly depending on the concentration of H₂S, i.e., permanent changes may or may not occur on the anode (such as Ni oxidation) depending upon H₂S concentration.     

A control system for uniform bead in fillet arc welding on tack welds

Positioning a workpiece accurately and preventing weld distortion, tack welding is often adopted before main welding in the construction of welded structures. However, this tack weld deteriorates the final weld bead profile, so that the grinding process is usually performed for a uniform weld bead profile. In this study, a control system for uniform weld bead is proposed for the fillet arc welding on tack welds. The system consists of GMA welding machine, torch manipulator, laser vision sensor for measuring the tack weld size and the database for optimal welding conditions. Experiments have been performed for constructing the database and for evaluating the control capability of the system. It has been shown that the system has the capability to smooth the bead at the high level of quality.     

Picture-Based Address Power Saving Method for High Resolution Plasma Display Panel (PDP)

A picture-based high-speed address recovery technique for AC (adaptive control) plasma display panels (PDPs) is proposed. By removing the ground (GND) switching operation, the recovery speed can be increased and the switching loss due to the GND switch is reduced. The proposed method can perform load-adaptive operations by controlling the voltage level of the energy recovery capacitor, which prevents the increase of inefficient power consumption caused by circuit loss during the recovery operation. Thus, the technique shows the minimum address power consumption according to various displayed images, which is different from previous methods operating in fixed mode regardless of images. Test results with a 50-in HD single-scan PDP (resolution=1366 times 768) show that a recovery time of less than 350 ns is successfully accomplished and about 54% of the maximum power consumption can be reduced, by tracing the minimum power consumption curves.     

Dual wavelength OLEDs with blue and yellow emission peaks

New organic light emitting diodes (OLEDs) with dual peak emission spectra were fabricated and their electrical and optical characteristics were investigated. In the experiments, the blue emission materials GDI602 and GDI602 were doped with GDI691(2%)[GDI602∶GDI691(2%)] and the yellow emission material Alq3 was doped with Rubrene(10%)[Alq3∶Rubrene(10%)]. Under an applied voltage of 10 V, the OLED with the GDI602/Alq3∶Rubrene(10%) emission layer had a luminance of 325 Cd/m² and a power efficiency of 0.7 lm/W, whereas the OLED with the GDI602∶GDI691(2%)/Alq3∶Rubrene(10%) emission layer had a luminance of 500 Cd/m² and a power efficiency of 0.94 lm/W. The dual peak wavelengths of the OLEDs were fixed but the relative intensities of the peak wavelengths varied according to the applied voltage. The OLED with the GDI602/Alq3∶Rubrene(10%) emission layer showed a somewhat reddish-white emission with a Commission Internationale de L'Eclairage(CIE) coordinate of (0.33, 0.32) at 9 V. In contrast, the OLED with the GDI602: GDI691(2%)/Alq3∶Rubrene(10%) emission layer showed an almost pure white emission with a CIE coordinate of (0.32, 0.33) at 6 V; furthermore, the color changed to blue as the applied voltage was increased.     

Magnetic-coupled high power factor converter with low line currentharmonic distortions for power factor correction and fast outputresponse

A new magnetic-coupled high power factor converter (MCHPFC) with a single switch/single stage is proposed. The proposed converter gives good power factor correction, low current harmonic distortions, and tight output voltage regulation. The prototype shows that the IEC555-2 requirements are met satisfactorily with nearly unity power factor. A proposed MCHPFC is particularly suited for low-power-level power supply applications     

Effects of the composition of sputtering target on the stability of InGaZnO thin film transistor

In this study, we investigated the electrical characteristics and the stability of amorphous indium gallium zinc oxide (a-IGZO) thin film transistors (TFTs) from the viewpoint of active layer composition. Active layers of TFTs were deposited by r.f. sputtering. Two kinds of sputtering targets, which have different compositional ratios of In:Ga:Zn, were used to make variations in the active layer composition. All the fabricated IGZO TFTs showed more excellent characteristics than conventional amorphous silicon TFTs. However, in accordance with the Ga content, IGZO TFTs showed somewhat different electrical characteristics in values such as the threshold voltage and the field effect mobility. The device stability was also dependent on the Ga content, but had trade-off relation with the electrical characteristics.     

The current injection method for AC plasma display panel (PDP) sustainer

A new concept of energy recovery for a plasma display panel (PDP) is proposed. Different from conventional LC resonant sustaining drivers, the current built up before inverting the polarity of the panel electrodes is utilized to change the panel polarity together with energy previously charged in panel capacitance. This operation provides zero-voltage switching of switches and reduction of electromagnetic interference by rejecting the surge current when the sustain switches are turned on. The buildup current helps to reduce the transition time of the panel polarity and may produce more stable light waveforms. This method is suitable for a PDP sustaining driver requiring stable light emission characteristic while it maintains low circuit loss like the series-resonant-type energy recovery circuit which is known to be a very effective method.     

Optimization of excitation frequency and guided wave mode in acoustic wavenumber spectroscopy for shallow wall-thinning defect detection

In plate-like structures, wall-thinning defects resulting from corrosion may not be accompanied by any indication of damage on the surface. Thus, inspections are required to ensure that wall-thinning defects are within allowable limits. However, conventional ultrasonic techniques require physical contact to the structure. Alternatively, acoustic wavenumber spectroscopy (AWS) may be used for detecting, locating, and characterizing defects. This paper describes the performance of AWS in the estimation of a wall-thinning defect size in thinplate structures using finite element analysis (FEA). Through a series of FEAs, the structure’s steady-state response to a single-tone ultrasonic excitation is simulated, and the wall-thinning defect-size effect on the wavenumber-estimation accuracy is investigated. In general, the A0 guided wave mode is widely used to visualize defects because of the nature of the wave speed variation in relation to the plate thickness. However, it is not appropriate for the detection of relatively shallow wall-thinning defects, because the rate of change in wave speed with the thickness decreases with increasing plate thickness. To overcome this limitation, we propose a method to optimize excitation frequency and effective guided wave mode instead of utilizing the A0 mode. The results can be used to determine the size of shallow wall-thinning defects in plate-like structures.