Guangsup Cho

Measurement of Secondary Electron Emission Coefficient (γ) of MgO Protective Layer with Various Crystallinities

The secondary electron emission coefficient γ of a MgO protective layer with various crystallinities has been successfully measured by the γ-focused ion beam system with complete elimination of the charge accumulation problem by scanning-area adjustment techniques. It is found that the (111) surface has the highest γ from 0.14 to 0.26 in comparison with the other films with (200) and (220) crystallinities for operating Ne+ ions, while ranged from 0.03 to 0.24 for Ar+ ions, under operating ion energies from 50 eV to 500 eV throughout this experiment. These observations explain why the (111) crystallinity of the MgO protective layer plays an important role in lowering the firing voltages in AC plasma display panel compared to the films with other crystallinities.

Work function of MgO single crystals from ion-induced secondary electron emission coefficient

The work functions φω of MgO single crystals with its respective orientation (111), (200), and (220) have been investigated from their ion-induced secondary electron emission coefficient γ, respectively, using various ions with different ionization energies in a γ-focused ion beam system. The work function φω for MgO single crystal with (111) orientation has the lowest value, 4.22 eV, whereas it is 4.94 eV for (200) and the highest value is 5.07 eV for (220). These work functions of MgO single crystals can explain the nonzero values of the ion-induced secondary electron emission coefficient γ for Xe+ ions, whose ionization energy is 12.13 eV.

Secondary electron emission coefficient of a MgO single crystal

The secondary electron emission coefficient γ of different MgO single crystal has been measured by γ-focused ion beam system. It is found that the MgO single crystal with (111) orientation has the highest γ from 0.08 up to 0.21, while from 0.06 to 0.19 for (200) and from 0.05 to 0.15 for (220) orientation for operating Ne+ ions ranging from 50 to 300 eV throughout this experiment. It is also found that these observations can be explained by work functions, which are dependent on the crystal orientations of MgO.

Cold Plasma Jets Made of a Syringe Needle Covered With a Glass Tube

A syringe needle assembled with a glass tube has been used as a plasma jet device for biomedical applications. According to the various types of ground electrode installed at the glass tube, argon plasma from an atmospheric pressure discharge has been investigated with a dc-ac inverter of several tens of kilohertz. When the ground electrode is absent or floated, the length of the plasma jet is about 10 mm at an ignition voltage of about 3 kV, and it extends further to a few tens of millimeters as the voltage increases to 5 kV. If the ground electrode is inserted inside the end of the glass tube, all plasma current is sunk directly to the ground electrode so that the plasma plume cannot emit out of the glass tube. For the case of an external ground electrode which is similar to a dielectric barrier discharge, the ignition voltage is as low as 1 kV, and the plume length is easily adjustable to be 1-10 mm in the voltage range of 1-3 kV.

Capacitive coupled electrodeless discharge backlight driven by square pulses

Characteristic properties of backlight arraying electrodeless fluorescent lamps assembled with capacitive coupled electrode connector have been investigated in various frequencies with a switching inverter. In the backlight of a 17-in diagonal with 12 lamps driven by square pulses, the efficiency of 65/spl sim/70 lm/W and the luminance of 5000/spl sim/10 000 cd/m/sup 2/ have been achieved in the frequency range of 40/spl sim/80 kHz where the higher frequency provides the lower operating voltage in the range of 1.0/spl sim/2.0 kV.

Striations in a coplanar ac-plasma display panel

Striations observed in a coplanar or a wedge-shaped planar ac-type discharges are reported in this article. The observed data indicate that the striations are related to ion charge waves of the wall generated by the self-sustained perturbations that originate from the force balance between the ion and the electron wall-charge clouds accumulated on the dielectric layers over the metal electrodes.

Effects of Electrode Length on Capacitively Coupled External Electrode Fluorescent Lamps

The properties of capacitively coupled external electrode fluorescent lamps with the small outer diameter of 2.6 mm, driven by square pulses from a switching inverter, have been investigated for the electrode lengths of 1–5 cm. The brightness is saturated at an electrode length of over 3 cm, which is analyzed by charge-voltage Lissajous figures.

Electron plasma wave propagation in external-electrode fluorescent lamps

The optical propagation observed along the positive column of external electrode fluorescent lamps is shown to be an electron plasma wave propagating with the electron thermal speed of (kTe∕m)1∕2. When the luminance of the lamp is 10000–20000cd∕m2, the electron plasma temperature and the plasma density in the positive column are determined to be kTe∼1.26–2.12eV and no∼(1.28–1.69)×1017m−3, respectively.

Influence of the gas-flow Reynolds number on a plasma column in a glass tube

Atmospheric-plasma generation inside a glass tube is influenced by gas stream behavior as described by the Reynolds number (Rn). In experiments with He, Ne, and Ar, the plasma column length increases with an increase in the gas flow rate under laminar flow characterized by Rn   4000, the length of the plasma column is short in front of the electrode, eventually leading to a shutdown.

The spin-gap in high Tc superconductivity

We have investigated the spin-gap in high Tc superconductivity. We obtain the effective exchange integral in the presence of conduction in the ab-plane from the interaction Usd, where the electron–electron interaction is mediated by the localized spin flips. We choose the exchange interaction along the c-axis from the superexchange-type interaction, Usdc. We find the spin-gap from the conducting spin- ladder corresponding to the structure of high Tc superconductors.