Chun-Ming Hsu

Ultrafast synthesis of continuous Au thin films from chloroauric acid solution using an atmospheric pressure plasma jet

Au can be easily formed by thermal calcination via the reduction of chloroauric acid. However, a conventional hot-plate or furnace calcination procedure often results in a piecewise and island-like film. In this study, the rapid synthesis of continuous Au thin films from spin-coated chloroauric acid precursor films is demonstrated by using an atmospheric pressure plasma jet (APPJ). The sheet resistance decreases from 2.175 to 0.997 Ω sq−1 as the APPJ processing time increases from 7 to 60 s. This ultrafast synthesis of continuous Au thin films is made possible by the synergistic effect of the highly energetic/reactive nitrogen species and the heat generated by APPJs.

Deposition of ZnO Thin Films by an Atmospheric Pressure Plasma Jet-Assisted Process: The Selection of Precursors

The deposition ZnO thin films using an atmospheric pressure plasmas jet (APPJ)-assisted process using different precursors is presented. In this process, nebulized salt solutions droplets or precursor vapor were injected into the downstream of the APPJ to perform deposition of ZnO thin films. Zinc chloride (ZC)-, zinc acetate (ZA)-, and zinc nitrate (ZN)-containing solution and zinc acetylacetonate (ZAA) were precursors tested. For all precursors tested, formation of ZnO was observed based on X-ray diffraction analysis. ZC, however, was the only precursor that yields smooth films, which yields average transmittance in the visible wavelength range well >70%. When ZN, ZA, and ZAA were used as the precursors, rather rough films were obtained due to the fact that these precursors decomposed and formed ZnO readily upon heating. A high rate of volume nucleation, therefore, occurs in the gas phase. The above observation serves as the guideline for the selection of precursors for APPJ-assisted thin-film deposition processes.

Numerical Simulation of Downstream Kinetics of an Atmospheric Pressure Nitrogen Plasma Jet Using Laminar, Modified Laminar, and Turbulent Models

We present numerical simulation of the nitrogen atmospheric pressure plasma jet (APPJ) using three fluid models—namely, laminar model, modified laminar model, and turbulent (k-ε) model—coupled with gas-phase reaction kinetics. The spatial profiles of the light emission intensities, gas temperature, and NO density predicted by the turbulent model show a better agreement with the experimental observations, compared with laminar and modified laminar models. We have demonstrated that the turbulent model shows more oxygen entrainment, more mixing with the ambient air, and a lower axial velocity at the downstream. These allow the turbulent model to more precisely capture the APPJ characteristics than the laminar and modified laminar models do.

Growth mechanism of ZNO thin films deposited by an atmospheric pressure plasma jet

The growth mechanism of ZnO thin films deposited by an atmospheric pressure plasma jet (APPJ) is study. The APPJ used is sustained by a pulsed power source with a repetitive frequency up to 25 kHz using N2 or O2 as plasma gases. Nebulized zinc chloride solution is used as the precursor and is sprayed into the downstream of the plasma jet to deposit thin films on Si wafers. X-ray diffraction spectra show that the crystalline structure changes with the operating parameters, namely plasma gas flow rate and the applied voltage, which influence the jet temperature and reactivity. It is found that upon exposure of the precursor to the plasma jet, sheet-like zinc hydroxide chloride (ZHC) are formed first, and is converted to zinc oxide if the jet temperature is high enough. Under relatively low temperature, the conversion of the precursor end at ZHC. The grain size of the films is greatly influenced by the nucleation and growth rate. High jet temperature leads to a larger number of the nuclei and results in smaller grain sizes and denser ZnO thin films. O2 plasma jets are also utilized. Preliminary studies show that the O2 plasma jet is able to convert the precursor to ZnO thin films under optimized conditions. Finally, the key parameters that influence the electrical and optical properties will be identified.

Downstream characterization of an oxygen atmospheric pressure plasma jet

The characterization of the downstream of an oxygen atmospheric pressure plasma jet (APPJ) is performed. This APPJ is sustained by pulsed power with a repetitive frequency up to 25 kHz. The reactivity of the plasma at different operating conditions is characterized using the intensities of O2 (759 nm) and O (777 nm) optical emission lines. The jet downstream temperature is measured by a thermocouple. It is shown that the intensity of O2 emission is not sensitive to the flow rate while it increases with the increase in the applied voltage. O emission is only observed at high flow rate. The temperature measurement shows that it slightly increases with the applied voltage. At the jet exit, the temperature monotonically increases with the flow rate while at 1 cm downstream of the jet, it shows an opposite trend. It is shown that the existence of an external surface at the downstream greatly influences the emission spectra adjacent to the surface. When the jet downstream is shielded with a glass tube, the O radical emission intensity increases by more than one order of magnitude. Preliminary studies show that the presence of the surface potentially enhances certain surface reactions. Such an enhancement leads to the increase of the O radical density, as suggested by the spatial-resolved optical emission spectra.

Diagnostic study of micro-discharges of inert gas under atmospheric pressure

Summary form only given. The characterization of microplasmas driven by DC and AC (50~1000 Hz) power supplies with a voltage up to 1000 V at atmospheric pressure is performed. Parallel planar aluminum electrodes with an inter-electrode gap 20~200 mm are patterned on a glass substrate by semiconductor fabrication processes. Pure argon and helium are used as the feedstock. Filamentary-like discharges are mostly observed in argon discharges and highly-nonuniform discharges result in locally high current densities, which lead to a severe damage of the electrode. In helium discharges, a corona-like discharge is observed when the plasma is ignited with the applied voltage slightly higher than the breakdown voltage. Under certain conditions, such discharges occupy the entire inter-electrode space. With the increase in the applied voltage, the transition to filamentary-like discharges is occurred. It is shown that the breakdown voltage increases with the gap, and the voltage is 100-200 V higher than that shown in the right branch of the Paschen curve. Oscillations of current and voltage waveforms at different frequencies are observed after the plasma is ignited. Preliminary studies show that the MHz-high frequency oscillation is associated with the external circuits due to the sudden voltage drop after the breakdown. The low frequency oscillation, few tens of kHz, is a result of the repetitive ignition and extinguishment of the discharge. No stable discharge is obtained. Such a behavior is seen in both DC-and AC-driven discharges. P-spice circuit simulation is performed to study the effects of the external circuitry on the discharge behavior. The I-V characteristics are simulated, and results qualitatively agree with the experimental measurements. The optical emission emanating from the plasma is monitored and the broadening of hydrogen emission lines is used to estimate the plasma characteristics, namely the electron density and neutral gas temperature. Finally, the potential using such a discharge in materials processing will be demonstrated.