Seung-Oun Kang

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.

Single-electron transistors operating at room temperature, fabricated utilizing nanocrystals created by focused-ion beam

A focused-ion-beam (FIB) technique utilizing both lithographic and nanoparticle formation processes has been introduced to fabricate a single-electron transistor (SET) that can operate at room temperature. The results for the drain current as a function of the gate voltage at different source voltages at room temperature clearly show Coulomb oscillations indicative of Coulomb-blockade effects. These results indicate that SETs operating at room temperature, fabricated utilizing the FIB technique, hold promise for potential applications in ultra-high-density memory devices.

Conductivity and ion density of a plasma channel induced by a mildly relativistic electron beam from a gas-filled diode

Conductivity and ion density of a plasma channel induced by a mildly relativistic electron beam (300 kV, ∼2 kA, 10–50 ns) have been experimentally investigated under various gas pressures. Pressures of filling gas (air) in this experiment ranged from 10 mTorr to 100 mTorr. The net currents of the beam-induced plasma channel were measured by four Rogowski coils located along the propagating region, while the electron beam currents were measured by a Faraday cup. The inductive plasma currents observed at the above pressure regimes have been characterized by magnetic decay time. Plasma-channel conductivity and ion density induced by the beam are measured along the propagating axial positions under various gas pressures. The numerical result of the ion density is also obtained at the charge neutralization time when the ion density is just the same as the electron beam density, and the digitizing experimental data of the beam current Ib(t) and voltage Vd(t) have been used. As expected, in both numerical and ex...

Plasma propagation speed and electron temperature in surface-discharged alternating-current plasma display panels

The electron temperature and plasma density in coplanar alternating-current plasma display panels (AC-PDPs) have been experimentally investigated by a micro Langmuir probe and the high speed discharge images in this experiment. It is noted in this experiment that the electron temperature obtained from both the micro Langmuir probe and high speed ICCD camera decreases from 1.8 eV to 0.8 eV as the filling Ne gas pressure increases from 150 Torr to 400 Torr. It is noted that these electron temperatures are in good agreement with each other within 5% error limit. The plasma density at the lateral distance of 125 /spl mu/m away from the center of sustaining electrode gap has been found to be decreased from 3.7/spl times/10/sup 11/ cm/sup -3/ to 2.3/spl times/10/sup 11/ cm/sup -3/ at the Ne filling pressures ranged from 150 Torr to 350 Torr.

Computer-controlled fabrication of ultra-sharp tungsten tips

In order to monitor the end-point current during electrochemical etching, an analog to digital converter circuit aided by a personal computer has been setup. At the moment the lower part of the needle drops off during the etching process, a maximum current change across the reference resistor is detected by the PC interface card and the applied voltage is then cut off within a few milliseconds. Using these circuits to control the etching time, our experiment has been able to fabricate an ultra-sharp tip of ∼200 A radius with a higher reproduction rate and reliability than the conventional method.

Temperature effects on the energy spreads in liquid metal ion sources

The energy spread of charged particles during beam propagation is calculated for liquid-metal ion sources. After acceleration, the particles have different energies originating from Coulomb interactions among them, which are randomly located due to the statistical fluctuations caused by the emission-surface temperature. The energy spreads are obtained in terms of the total current and emitter temperature. In particular, the energy spread is proportional to the square root of the emission-surface temperature. The results agree remarkably well with previously reported experimental data for the liquid-gallium ion beam.

Liquid metal ion sources: The shape and size of the ion emitting area

Using the potential profile around the cone‐shaped protrusion at the end of the Taylor cone of the liquid metal ion sources, we investigate the shape and size of the ion emitting region and the ion formation mechanisms analytically. We find that the field evaporation is the main current‐generating mechanism. Contribution of the field ionization mechanism is around 0.01 μA, independent of the applied voltage. The ion emitting area is usually confined within a few tens of angstroms from the protrusion apex. The most important parameter that determines the emission current is found to be the apex angle of the protrusion cone. The apex angle near the ignition voltage is close to the Taylor angle. At this voltage, the ions are emitted from the very vicinity of the cone apex. Above the ignition voltage, a sharp protrusion cone develops of which the apex angle decreases as the applied voltage increases. In other words, sharpness of the cone apex is the measure of the field strength responsible for the field evap...

Room-temperature observation of the Coulomb blockade effects in Al two-terminal diodes fabricated using a focused ion-beam nanoparticle process

Al two-terminal diodes were fabricated on a basis of an artificial pattern formation method using focused ion-beam (FIB) techniques. The results of current–voltage and conductance–voltage measurements at room temperature showed the Coulomb staircase and the Coulomb blockade effects, respectively. The Coulomb blockade effects originate from the many nanoparticles created by the defects due to the Ga+ ion beam. These results indicate that Al two-terminal diodes fabricated by using the FIB system hold promise for potential applications in single-electron transistors operating at room temperature.

Shift of peak energy distribution in field-emitted charged particle beams

A theoretical model for energy spread and shift of peak energy distribution in a charged particle beam is developed. The beam may expand radially and axially as it propagates downstream. Charged particles placed randomly in the beam possess different potentials, which are converted to different kinetic energies as the beam propagates and expands. This randomness introduces energy spread in the beam. It is also shown that the shift of peak energy distribution in beam particles is proportional to the one‐third power of the beam current, which is the manifestation of random particle locations. The theoretical predictions of the energy‐distribution shift agree remarkably well with experimental data.

Electric field solutions between an emitter tip and a plane extractor in LMIS

The exact solution of Laplacian potential between a rod emitter and a plane extractor is obtained using the method of images. From the solution obtained in the polar coordinates whose origin is an emitter apex, the electric field strength and the angular distribution around the liquid metal surface are shown. The significance of this equation in predicting and verifying the equilibrium configuration and the characteristics of a field emission liquid metal ion source (LMIS) are discussed.