Abstract This study aimed to model and investigate the distribution characteristics of NO and O3 produced by a Compact Air Plasma Jet device using 0D and 2D fluid models. The 0D global model was employed to calculate densities in the plasma volume before constructing the 2D model for the distribution of densities via boundary conditions. As the feeding gas flow rate increased from 3 to 11 slm, the NO and O3 densities predicted by the 0D model decreased from 10 ppm to 1 ppm and from approximately 12 ppm to 1 ppm. In comparison with the gas detector measurements, the NO densities exhibited the same values and trends with respect to the number of pulses and flow rate, but O3 concentrations from the 0D model simulations were higher than those measured by the gas detector. With a 20 ms simulation time, NO concentrations decreased along the axial length, whereas O3 concentrations increased. Additionally, O3 concentrations from both models were higher than the measurements from the gas detector, which did not align with the experimental results. The incorporation of dominant humidity reaction sets improved the alignment between the modeling results and specific experimental observations. The model equipped with these additional humidity reaction sets can be effectively employed to predict the NO and O3 density generated by the Compact Air Plasma Jet device.

Plasma immersion ion implantation was carried out to create the wrinkle patterns on polydimethylsiloxane (PDMS). We demonstrated that the wrinkles were formed spontaneously without the application of the external agents and the wrinkle morphology as well as the geometry were dependent on the ion species and the high voltage pulse frequency. The PDMS was irradiated with hydrogen ions or argon ions in the plasma generated using radio frequency. The pulsed negative bias voltage was fixed at − 5 kV whereas the pulse frequency was varied to observe its influence on the wrinkles. Hydrogen irradiation resulted in the parallel patterns while random patterns were revealed after argon irradiation. The different wrinkle morphology could be attributed to the difference in energy loss processes of the ions; i.e., nuclear stopping and electronic stopping. The amplitude and wavelength of wrinkles increased almost linearly with the pulse frequency. This could be described in terms of the cross-linking and the thermal stress induced in the PDMS after irradiated with different pulse frequency. X-ray photoelectron spectroscopy analysis exhibited that ion irradiation transformed the surface of PDMS into silica-like with abundant oxygen functional groups that accommodated the formation of wrinkles in the PDMS. The polar component of surface energy of PDMS increased drastically after the irradiation due to the presence of oxygen functional groups, changing the PDMS surface to a more hydrophilic state. The polar component of surface energy scaled with the pulse frequency.

MeV-ion microbeam using the capillary technique was home-developed based on the 1.7-MV tandem accelerator and beamline at Chiang Mai University. The system consisted of the capillary itself, a capillary holder, a holder swing mechanism, and a system support frame with a micrometer for vertical micro-adjustment. The glass capillaries had various sizes in a range of 10 – hundreds μm in the exit inner diameter. In this study, the capillary ion-microbeam was applied in elemental concentration distribution mapping of plant leaves using particle induced X-ray emission (PIXE) analysis. The interests were focused on difference in the elemental concentrations distributed between the leaf vein and lamina of local longan leaves which were sprayed by chemical fertilizer and pesticide and leaves of Peperomia pellucida, a herb, which was cultured by dissolved supplement solution of various nutrients. 1D and 2D maps of detected elements from the longan and herb leaves across vein and lamina were generated respectively, showing redistributions of the elements between vein and lamina due to the human activities. Details of the mapping results are reported and discussed.

Particle inertial focusing is a passive phenomenon at which a particle is acted upon by interaction with fluid and a channel wall, causing it to align at a certain distance from the channel wall called the equilibrium position as all transverse forces balance. In this work, numerical simulations using the finite element method were conducted in order to evaluate the forces acting on a spherical particle under Poiseuille flow in a 2D microchannel. Various fluid and particle parameters investigated include fluid density, viscosity, mean flow velocity, particle and channel dimensions. The calculated particle’s equilibrium position in relation to each individual parameter is found to be proportional to the square of mean fluid velocity and fluid density, and the cube of particle size while inversely proportional to channel half-width and the square of fluid viscosity.

Single cell analysis is a measurement or detection of individual cell properties and responses. The method is of significance due to stimulated responses of any individual cell are different depending on their morphology and functionality. Therefore, detected properties from a group of cells cannot be used to represent that of the individual cell. Since cells can move freely in a microfluidic system, a trap must be added to the system to fix the cell position at the detection region for long period observation and assay. One of the most popular used cell trap in the biomedical field is a microwell array. A sensitive technique for measuring single cell properties is an impedance measurement, in which small change in electrical properties of the cell and the surrounding medium between excitation and pick-up electrodes is recorded. However, the microwell placed between two electrodes acts as an electrical insulator to reduce the signal passing through the system. This paper focuses on the effect of microwell geometry parameters generated from the design of experiments (DOE) software on detected signals using finite element simulation software. The study found that the microwell wall thickness affects the detected current signal most significantly and the optimized geometry that minimally reduces measured current signal was 20 µm height, 5 µm well thickness, and 16 µm gap size.

Free surface synthetic schlieren (FS-SS) is a liquid surface topography visualization technique relying on apparent dot pattern displacement due to liquid surface deformation. It has gained attention in the fluid visualization field due to its relatively simple and inexpensive setup. One of the most powerful features of the FS-SS technique is the 3D topography of deformed liquid surface, in which submillimeter scale changes can be readily observed in great detail. The visualization of liquid meniscus at the solid interface is proposed in this study to calculate surface tension by equating the surface tension force with weight of light, floating object with circular geometry. It was found that surface tensions of liquids are much greater than anticipated, suggesting that the effect of buoyant force of displaced liquid due to deformed interface cannot be neglected. When the buoyant force is included, the calculated surface tension of liquids are within 10% of the reference values.

In performing microfluidic electrophoresis, sample loading must be prioritized since the shape of the initial sample plug injected into the separation channel immensely influences the electrophoretic separation efficiency. Non-zero pressure gradient due to different liquid level in finite size reservoirs is generated as a result of continuous electroosmotic flow (EOF) pumping, resulting in undesired parabolic pressure profile both in the same and opposite direction of sample propagation. This issue could be alleviated by fabricating larger reservoirs which can maintain the liquid level due to gradual volume changing as time elapses. This work presents experimental and numerical study on effect of 3.5 – 8.0 mm reservoir size on Rhodamine B plug flow generation from pinched injection sample loading method in cross design microfluidic device. COMSOL Multiphysics AC/DC module was used in calculating electric field distribution from desired applied voltages. The shapes of the injected sample plugs in the beginning of separation step were studied by varying the time of injection step. The experimental result shows that long-tailed sample plug and pressure profiles were generated when the injection time is 2 minutes or more. For the 8 mm diameter reservoirs, the flow profile illustrates pure EOF plug flow when the injection time does not exceed 1.5 minutes. This implies pressure gradient is virtually disappeared. The result of this study will be later applied for protein transferrin electrophoretic separation.

Over the last few years, study of microfluidic flow cytometry using electrical signals has developed at a fast pace. There are several electrical detection congurations but differential impedance sensing offers a greater advantage due to its capability of cancelling common noise from the detected signal, resulting in improved signal to noise ratio. This paper presents the simulation of a differential impedance sensor by employing the finite element method to gain an insight and to find the proper range of the working excitation frequency for the detection system. A polystyrene microbead was used as a model particle flowing past the detection area that had non-contact excitation and two pickup coplanar electrodes in which an excitation electrode was positioned between the two pickup electrodes. The modeling results showed that for a 2 μm PDMS separation layer, the range of optimal excitation frequency was about 100 - 1000 Hz when DI water was a background medium. The bead size to microchannel height ratio was found to affect the sensitivity of detection, in which the closer the height ratio was to the unity ratio, the more current was detected. The results of the simulation study will be used in fabricating an actual device for microfluidic particle cytometry applications.

The ripple tank is a popular water wave phenomena demonstration tool for secondary school students. The projected wave images are observed in bright - dark patterns on a screen. This tool, however, falls short in presenting the amplitude of the waves which is another important parameter in explaining the wave phenomena. The free surface synthetic schlieren (FS-SS) method presents an immense technical tool for solving this problem. FS-SS is an optical method based on light refraction in determining the surface gradient field from the motion of a random dot pattern when the water surface is perturbed. The surface height of the wave is constructed using the inverse gradient operation on the displacement gradient field of the random dot pattern. In this work, Wave propagation, reflection, diffraction, and interference pattern surface construction were performed to visualize wave phenomena in 3D.

Schlieren photography is a technique used to capture air movement based on differences in fluid density. Air with higher temperature has lower density than the surrounding air with lower temperature, leading to different values of refractive index. This work aimed to determine optimized conditions for schlieren photography to capture air movements in several situations. Schlieren photography was set up by using a single off-axis parabolic mirror with a 14.1cm diameter and a focal length of 131.2 cm. The air movement was captured in hi-speed mode with a Nikon V1 at 400 frames per second with a resolution of 640 × 240 pixels. The camera was set at ISO 400 at f/5.6 and used with a 70 − 300 mm zoom lens. Optimized conditions include percentage of light blocked by a knife edge, distance of test area to the mirror, illuminance of the light source, and ambient temperature.

Electrical cell lysis is one of the most efficient techniques in cell analysis in extracting intracellular components for further use or examination. Cells are exposed to high electric field strength that can rupture cell membrane due to nano-size pores creation. Thanks to microfabrication technology, electrodes can be materialized in close proximity to each other leading to high electric field strength with low applied voltage. In this study, two microfluidic systems were designed: straight and tapered systems. The straight channel was chosen due to the ease of fabrication, while the tapered channel was picked since it intensifies electric field strength in the tapered area. Finite element method was used to simulate electric field distribution inside the microfluidic systems and transmembrane potential (TMP) across cell membrane. In the experiment, green algae Carteria sp. which contains large amount of lipid was used in performing microfluidic electrical cell lysis. For 30 nm thick gold planar electrodes with 110 μm spacing fabrication, the simulated TMPs produced in both microfluidic systems exceed 0.2 V which is a threshold potential for pore generation in cell membranes when applying 34 Vp–p, 1000 Hz AC voltage. Only Carteria sp. cells were successfully lysed in straight microfluidic system after being exposed to high electric field strength for several minutes. Although electric field in the tapered region was higher than that of the straight microfluidic system, the cells were rushed out of the tapered region due to electrohydrodynamic effects.

One of a few disadvantage properties of polymethylsiloxane (PDMS) is its hydrophobicity which can hinder its fluidic applications. Oxygen plasma treatment on PDMS surfaces is a conventional method in rendering them hydrophilic, however hydrophobicity returns within days after treatment. This study proposes oxygen ion implantation at the micrometer scale inside PDMS structures to ensure lasting hydrophilicity. The PDMS slabs were treated with 20 keV oxygen ion with 1 x 10(15) ions/cm(2) fluence and inductively coupled oxygen plasma generated at a power of 28 W and frequency of 13.56 MHz. The chemical composition of the treated PDMS surface was monitored by X-ray photoelectron spectroscopy (XPS) and it was found that oxygen concentration remain high after three days of oxygen plasma treatment on the PDMS. Although the surface oxygen concentration in the oxygen ion implanted PDMS was not as high as that oxygen plasma treated PDMS, the oxygen concentration level was remained higher than that of the untreated PDMS surface for four weeks.

This study was aimed at understanding elemental concentration distribution in local longan leaf for how the plant was affected by the environment or agricultural operation. The analysis applied the MeV-microbeam particle induced X-ray emission (PIXE) mapping technique using a home-developed tapered glass capillary microbeam system at Chiang Mai University. The microbeam was 2-MeV proton beam in 130 µm in diameter. The studying interest was in the difference in the elemental concentrations distributed between the leaf midrib and lamina areas. The micro proton beam analyzed the leaf sample across the leaf midrib edge to the leaf lamina area for total 9 data requisition spots. The resulting data were colored to form a 1D-map of the elemental concentration distribution. Seven dominant elements, Al, S, Cl, K, Ca, Sc and Fe, were identified, the first six of which were found having higher concentrations in the midrib area than in the lamina area, while the Fe concentration was in an opposite trend to that of the others.

Developing high technologies but in economic manners is necessary and also feasible for developing countries. At Chiang Mai University, Thailand, we have developed MeV-ion microbeam technology based on a 1.7-MV Tandetron tandem accelerator with our limited resources in a cost-effective manner. Instead of using expensive and technically complex electrostatic or magnetic quadrupole focusing lens systems, we have developed cheap MeV-ion microbeams using programmed L-shaped blade aperture and capillary techniques for MeV ion beam lithography or writing and mapping. The programmed L-shaped blade micro-aperture system consists of a pair of L-shaped movable aperture pieces which are controlled by computer to cut off the ion beam for controlling the beam size down to the micrometer order. The capillary technique utilizes our home-fabricated tapered glass capillaries to realize microbeams. Either system can be installed inside the endstation of the MeV ion beam line of the accelerator. Both systems have been applied to MeV-ion beam lithography or writing of micro-patterns for microfluidics applications to fabricate lab-on-chip devices. The capillary technique is being developed for MeV-ion beam mapping of biological samples. The paper reports details of the techniques and introduces some applications.

Al2O3-TiC (AlTiC) burnish head is widely used in hard disk drive manufacturing process to smoothen magnetic media surface produced from metal deposition process. Vertical etched wall of air bearing surface burnish head is ideal fabrication target since it provides fly height stability. Commonly used fluorine-based plasma etchant leads to an incline etched AlTiC wall due to redeposition of AlF3 etch byproduct. This paper proposed the chlorine-based etching to improve etched wall profile due to etch byproduct volatility. A vapor pressure-temperature plot of potential etch byproducts in etching process was created to help design etching conditions that result in volatile etch byproducts. The BCl3/Cl2/Ar combinations were varied to obtain optimized etched wall profile, etch rate, and, etch selectivity between AlTiC and NiCr hard mask. It was found that 60sccm BCl3: 60sccm Cl2: 80sccm Ar with 20°C platen temperature and 5mTorr processing pressure provided etched wall angle of 79° with 152nm/min etch rate and 4.1:1 AlTiC:NiCr etch selectivity.

Etched steep wall is very difficult to achieve by fluorine-based Reactive Ion Etching (RIE) process on Air Bearing Surface (ABS) made of alumina titanium carbide (Al2O3-TiC or AlTiC). The ideal wall angle of a fly height target for read/write slider head would be perfectly vertical, however the fabricated patterns normally ends up in slope etched wall of AlTiC. Also, shallow etched ABS walls cause great variation in fly height between inner and outer radii of recording disk when performing data reading or writing. It is necessary to develop etching method that results in steep and clean etched wall of AlTiC substrate. In this study, the effect of photoresist mask angle prior to RIE process on degree of slope etched wall was explored. The goal was to have the etched angle steeper than 40° and re-deposition free etched wall. Sloped wall variation in photoresist was accomplished using optical proximity correction (OPC) mask. Due to technical difficulty in photoresist patterning, the angles of patterned photoresist achieved were between 30°–65° and 70°–90°. It was found that with photoresist's angles between 30°–65°, the etched wall angles of AlTiC were less than 40° and no re-deposition of by-product was observed. With the resist's angle between 70°–90°, the etched wall angles exceed 40° but the built-up byproduct deposition was observed. It is suggested that the photoresist's angles of 65°–70°could provide desired etched angle and clean etched wall. Further development of photoresist patterning technique is required to produce photoresist wall angles of 65°–70°.

Silicon-based thermoelectric device fabricated using standard semiconductor manufacturing technique is a promising technology that could lead to a mass production of clean energy. The vertical wall fabrication on Si substrates is typically achieved by high cost plasma etching and involved hazardous gases. The proper wet etching condition offers an economically alternative method in obtaining vertical wall on the Si substrate. Experimental trials were conducted by design of experiments (DOE) technique to find an anisotropic wet etching condition that achieves vertical etched wall on (100) Si wafer. Three considered factors assigned to the DOE were NaOH concentration, solution temperature, and IPA addition. The response aimed for this study was not only targeting at 90° wall but also providing highest etch rate. The experimental results showed that in order to get the 90° wall, the best etching condition achieved was using 45% wt of NaOH concentration, 40°C solution temperature, and without IPA added. This condition gave an etch rate of 97.11 nm/min with surface roughness (Ra) of 10.58 nm.

The experimental trials were conducted by design of experiments (DOE) technique to find an anisotropic wet etching condition that achieves 90° wall angle on silicon (100) orientation wafer. Three considered factors assigned to the DOE were NaOH concentration, solution temperature, and stirring speed. The response aimed for this study was not only targeting at 90° wall but also providing highest etch rate. The experimental results showed that in order to fabricate the 90° wall angle, the best etching condition using was 30% wt NaOH concentration, 80°C solution temperature, and 300 rpm stirring speed. This condition gave an etch rate of 1245 nm/min with surface roughness (Ra) of 701.48 nm.

For soft lithography, the conventional negative tone resists, such as SU-8, that are used to create the mold have a number of drawbacks. PMMA, which is normally used as a positive tone resist, can be used as a negative resist by using high-fluence irradiation conditions. In this report, we outline optimization of the irradiation conditions for PMMA thin films using 2MeV H+ ions to exploit their ability to work as a negative tone resist at ion fluences above 1.0×1015ionscm−2. The main aim was to induce cross-linking while maintaining the exposed regions free of blisters and maintaining short irradiation times. We found that by using a two-step process with a low-flux irradiation, followed by a high-flux irradiation, the exposure time could be shortened by ∼50%. We also found that ion fluences greater than 5.0×1015ionscm−2 minimized the distortion in stitched regions.

Several recent reports have indicated that a tapered glass capillary tube with a tip size on the order of micrometers has a focusing effect on transmitted ion beams. In relation to our particular area of interest, this could be a simple and cheap way to generate a focused ion beam for ion beam lithography and beam-in-air analysis and irradiation applications. Here, details of the method and the equipment used to produce a tapered glass microcapillary tube will be described. The equipment, which is simply called a “glass microcapillary puller”, is made using an induction heater. This method ensures that the glass tube, which is inserted inside and along the central axis of the solenoid, is heated uniformly in all directions. The heating temperature is adjusted by a power control, with a maximum temperature of approximately 2,000C. The pulling tension is varied over a wide range by using different weights. Application of the tapered glass microcapillary for 2 MeV H+ ion beam lithography is also demonstrated.