Jungrae Park

Polyimide Surface Treatment by Atmospheric Pressure Plasma for Metal Adhesion

The surface of polyimide PI films before/after plasma surface treatment using a remote-type modified dielectric barrier discharge was investigated to improve the adhesion between the PI substrate and the metal thin film. Among the plasma treatments of the PI substrate surface using various gas mixtures, the surface treated with the N2/He/SF6/O2 plasma showed the lowest contact angle value due to the high CvO bondings formed on the PI surface, while that treated with N2/He/SF6 showed the highest contact angle value due to the high C–Fx chemical bondings on the PI surface. Specifically, when the O2 gas flow was varied from 0 to 2.0 slm in the N2 40 slm /He 1 slm /SF6 1.2 slm /O2 x slm gas composition, the lowest contact angle value of about 9.3° was obtained at an O2 gas flow of 0.9 slm. And it was due to the high content of oxygen radicals in the plasma, which leads to the formation of the highest CvO bondings on the PI surface. When the interfacial adhesion strength between the Ag film and PI substrate was measured after the treatment with N2 40 slm /He 1 slm /SF6 1.2 slm /O2 0.9 slm followed by the deposition of Ag, a peel strength of 111 gf/mm was observed, which is close to the adhesion strength between a metal and the PI treated by a low pressure plasma.

Magnetically driven spinning nanowires as effective materials for eradicating living cells

We present a method to inflame cells, in vitro, by applying an alternating current (ac) magnetic field to ferromagnetic nanowires (NWs) internalized by living cells. Nickel (Ni) NWs were internalized by human embryonic kidney cells (HEK-293). The application of ac magnetic field to the cells induced spinning of the cells via the motion of internalized NWs. This resulted in cell death by physically causing damage. A study of the response of cytokine to cells with spinning NWs shows increased interleukin-6 effects when compared with responses from non-spinning cells. The spinning effect of cells caused by the application of magnetic field can be used to target and inflame the cells. Such experiments suggest the possibility of inflaming cells for the treatment of cancer.

Radio frequency-mediated local thermotherapy for destruction of pancreatic tumors using Ni–Au core–shell nanowires

We present a novel method of radio frequency (RF)-mediated thermotherapy in tumors by remotely heating nickel (Ni)-gold (Au) core-shell nanowires (CSNWs). Ectopic pancreatic tumors were developed in nude mice to evaluate the thermotherapeutic effects on tumor progression. Tumor ablation was produced by RF-mediated thermotherapy via activation of the paramagnetic properties of the Ni-Au CSNWs. Histopathology demonstrated that heat generated by RF irradiation caused significant cellular death with pyknotic nuclei and nuclear fragmentation dispersed throughout the tumors. These preliminary results suggest that thermotherapy ablation induced via RF activation of nanowires provides a potential alternative therapy for cancer treatment.

Removal of Anodic Aluminum Oxide Barrier Layer on Silicon Substrate by using Cl2/BCl3 Neutral Beam Etching

The barrier layer of anodic aluminum oxide (AAO) formed on the silicon substrate was etched with Cl 2 /BCl 3 gas mixtures by a neutral beam and the results were compared with the AAO etched by an ion beam. The etch rate of AAO itself was increased with the increase of BCl 3 in Cl 2 /BCl 3 up to 60% in the gas mixture. And, the etching of AAO itself was related to the Cl radical density in the plasma and the formation of volatile BO x Cl y on the AAO surface for both the neutral beam etching and the ion beam etching. The AAO itself could be etched by both the neutral beam and the ion beam in all Cl 2 /BCl 3 gas mixtures. However, the barrier layer of the AAO located near the bottom of the AAO pore could not be etched using the ion beam etching due to the charging of the nanometer size AAO pore similar to the case of conventional reactive ion etching. Using the neutral beam etching, the barrier layer of AAO pore could be successfully etched with BCl 3 -rich BCl 3 /Cl 2 gas mixtures by removing the barrier layer without charging the AAO pore and by the forming volatile BO x Cl y .

Micro-capacitor with vertically grown silver nanowires and bismuth ferric oxide composite structures on silicon substrates:

We have designed and demonstrated a complementary metal-oxide-semiconductor compatible process for fabricating high capacitance micro-capacitors based on vertically grown silver nanowires on silicon substrates. Array of silver nanowires with high-aspect ratio were electrochemically grown in the pores of anodized aluminum oxide film, which was pre-formed through anodization of aluminum thin film deposited on titanium/silicon oxide/silicon substrates. High dielectric bismuth ferric oxide layer was electrodeposited to fill the gap between silver nanowires after anodized aluminum oxide film was removed. It was found that the micro-capacitor based on the silver nanowires/bismuth ferric oxide composite film possessed higher capacitance by approximately one order of magnitude from the COMSOL simulation results from the flat Ag thin-film capacitor and the silver nanowire capacitor.

Dynamic Microcontainers as Microvacuums for Collecting Nanomaterials After Clinical Treatments

We present a feasible method to collect ferromagnetic nanomaterials(FNMs) after clinical utilization by employing ferromagnetic microcontainers (MCs). The cubic MCs with dimensions of 200 micrometers have gold-coated nickel frames and were tethered such a way that they are able to remove FNMs from cells with the use of an external magnetic field. The study has been conducted in two parts: 1) enhancement of the motion of MCs in glass-based microfluidic channels filled with viscous fluids by magnetically-driven spinning MCs, i.e., “dynamic MCs”; 2)sweeping FNMs from the cells using magnetic attractive forces between FNMs and MCs through a “microvacuum”process. Our study shows that spinning MCs can transport better than nonspinning MCs through viscous fluids. We found that approximately 70% of FNMs internalized with human embryonic cells (HEK-293) were removed from the cells by the spinning MCs. Such in-vitro experiments suggest the possibility of resolving the issue of removing FNMs used for clinical treatments from human body after treatments.

Micro-convertor with remotely coupled DC power International Conference on Control, Automation and Systems (ICCAS 2014)

Microsystems are rapidly making their avenue into commercial applications. Power needs to be supplied to individual devices without requiring wires or physical tethering if the full potential of the micro-machines are to be realized. We develop direct DC power for micro-devices using remote radio-frequency (RF) generation as well as on-chip RF to DC micro-convertor. The micro-scale antennas will supply as much as 10 mW of DC power in an area less than 20mm × 20mm. Optical coupling may not be required because the RF energy can be penetrated into the system without significant loss of energy through media. Fabrication of working remotely powered micro-chips is being developed. This technology may realize power convertor for individual micro-robots, micro-probes as well as wireless power distribution to multi-chips and micro-scale energy storage devices such as batteries.