Yao-Jhen Yang

Atmospheric pressure plasma jet annealed ZnO films for MgZnO/ZnO heterojunctions

Rf-sputtered ZnO films, annealed by atmospheric pressure plasma jet (APPJ), are characterized and used for MgZnO/ZnO heterostructures. The highly reactive N2 plasma generated by APPJ allows much shorter treatment time compared with conventional thermal anneals. The APPJ treatment can increase the crystallinity of ZnO films and release the compressive residue stresses, verified by XRD and UV‐Vis transmission measurements. In our previous studies, we demonstrate that thermal anneal is the critical step for the formation of two-dimensional electron gases in defective rf-sputtered MgZnO/ZnO heterostructures. This paper reports the experimental results that APPJ treatments can be used for the same purpose with a much shorter processing time. A thirty-second APPJ anneal on ZnO can be used to replace 400 ◦ C×30min furnace-anneal to promote the formation of 2DEGs in MgZnO/ZnO heterostructure. The ultra-short processing time is attributed to the synergy of plasma reactivity and temperature of APPJ. (Some figures may appear in colour only in the online journal)

Vapor-based tri-functional coatings†

The tri-functional coating synthesized via CVD copolymerization is comprised of distinguished anchoring sites of acetylene, maleimide, and ketone that can synergically undergo specific conjugation reactions to render surfaces with distinct biological functions, simultaneously. In addition, these tri-functional coatings can be fabricated in a micro-structured fashion on non-conventional surfaces.

Atmospheric-pressure-plasma-jet processed nanoporous TiO2 photoanodes and Pt counter-electrodes for dye-sensitized solar cells

We demonstrate the rapid fabrication of dye-sensitized solar cells (DSSCs) with both TiO2 photoanodes and Pt counter-electrodes processed using atmospheric pressure plasma jets (APPJs). The rapid conversion of PtCl62− to Pt for the counter-electrode of DSSCs is achieved using a 1 min 360 °C air-quenched N2 APPJ. The APPJ-processed Pt counter-electrode is then used together with an APPJ-calcined nanoporous TiO2 photoanode to make DSSCs that exhibit comparable efficiencies to those of cells fabricated using conventional furnace-calcination processes. APPJs can reduce the calcination durations from 30 min to 4 min for the nanoporous TiO2 photoanode and from 15 min to 1 min for the Pt counter electrode. The ultra-short processes of DSSCs are benefited from the synergistic effects of the energetic nitrogen molecules and the heat of APPJs.

A Foldable Microplasma-Generation Device on a Paper Substrate

We report the fabrication of a plasma-generating device on a paper substrate. This device was fabricated using a screen print process. Plasmas were ignited between two parallel electrodes with a plasma gap of 237 to 710 μm using a dc power source. We demonstrated that a stable helium plasma can be sustained when the substrate is flat, rolled, and folded along various orientations. When the plasma was ignited with a 0.2-μL salt solution droplet with 1.4, 4.6, and 7.8 ng of Li, Na, and K respectively applied to the discharge gap, clear metallic emission lines emanated from the plasma. Our result demonstrates that this paper-based plasma device can be used in analytical applications.

A Flexible Paper-Based Microdischarge Array Device for Maskless Patterning on Nonflat Surfaces

This letter presents a simple and economical paper-based device that is able to generate an array of stable Ar microdischarges. This is a dielectric-barrier-discharge device that exhibits filamentary-type features. The device is sustained by an ac voltage with a 550-V amplitude and 10-kHz frequency. Optical emission spectra show that Ar lines dominate the emission, with a trace amount of CH and C2 emissions. Despite slight damage, the electrode lifetime exceeds 20 min. Results demonstrate that this device is flexible and is able to achieve maskless patterning of hydrophilic patterns on flat and curved glass surfaces.

Ultra-low-cost and flexible paper-based microplasma generation devices for maskless patterning of poly(ethylene oxide)-like films.

This work presents the use of an ultra-low-cost and flexible paper-based microplasma array to perform maskless patterning of poly(ethylene oxide)-like (PEO-like) thin films with a feature size down to submillimeter scale. In this process, the liquid precursor was directly applied to the paper substrate, gradually vaporized, and dissociated in the microplasma cavity, which leads to plasma polymerization. The FTIR and XPS spectra of the deposited film confirm the PEO-like structures. The protein adsorption test using the absorption of fluorescence-labeled fibrinogen conjugates on the treated surface shows the deposited films possessed the antifouling property with decent pattern transfer fidelity defined by the geometry of the microplasma array.

A Low-Cost and Flexible Microplasma Generation Device to Create Hydrophobic/Hydrophilic Contrast on Nonflat Surfaces

This letter presents a low-cost (<;0.25 USD per device), easy-to-fabricated, and flexible microplasma generation device (MGD), and the use of this device to perform surface patterning. This dielectric-barrier-discharge-type MGD is made of double-side copper clad laminates and the electrode patterns were fabricated by a printed circuit board fabrication-based method, which allows the patterning without lithographic processes with good feature transfer fidelity. The MGD was utilized to create hydrophilic/hydrophobic contrast by a maskless patterning process, either creating hydrophobic patterns on hydrophilic surfaces or hydrophilic pattern on hydrophobic surfaces with sub-millimeter spatial resolution. In the former case, the hydrophobic fluorocarbon polymer (FCP) patterns were deposited on glass using c-C4F8 and He plasmas. In the latter case, hydrophilic patterns were created on a FCP-coated glass substrate using the MGD operated in ambient air. We also demonstrated that the flexibility of the device enabled non-flat surface patterning.

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.