Formation of spherical-shaped GaN and InN quantum dots on curved SiN/Si surface.

This paper reports the formation of GaN and InN quantum dots (QDs) with symmetric spherical shapes, grown on SiN/Si(111). Spherical QDs are grown by modulating initial growth behavior via gallium and indium droplets functioning as nucleation sites for QDs. Field-emission scanning electron microscope (FE-SEM) images show that GaN and InN QDs are formed on curved SiN/Si(111) instead of on a flat surface similar to balls on a latex mattress. This is considerably different from the structural properties of In(Ga)As QDs grown on GaAs or InP. In addition, considering the shape of the other III-V semiconductor QDs, the QDs in this study are very close to the ideal shape of zero-dimensional nanostructures. Transmission-electron microscope images show the formation of symmetric GaN and InN QDs with a round shape, agreeing well with the FE-SEM results. Compared to other III-V semiconductor QDs, the unique structural properties of Si-based GaN and InN QDs are strongly related to the modulation in the initial nucleation characteristics due to the presence of droplets, the degree of lattice mismatch between GaN or InN and SiN/Si(111), and the melt-back etching phenomenon.

Development of Hybrid Surfaces with Tunable Wettability by Selective Surface Modifications.

Recent advances in micro/nano technology have driven artificial modifications of surface wettability by mimicking biological surfaces, such as superhydrophobic and water-harvesting surfaces. In this study, surface wettability of polycarbonate (PC) films was modified using various surface treatments: micropatterning using ultrasonic imprint lithography, fluorinate silane coating, and electron beam irradiation. To modify surface wettability selectively in a specified region, these three treatments were performed using profiled masks with the corresponding shapes. Various combinations of these treatments were investigated in terms of wettability changes, by measuring contact angle (CA). The semi-hydrophobic PC film (CA: 89.2°) was modified to create a super- hydrophobic state (CA: 155.9°) by virtue of the selective micropatterning and coating. The electron beam irradiation had an opposite effect, reducing the CA (48.2°), so that the irradiated region was modified to create a hydrophilic state. Two combinations of the proposed surface modifications made it possible to have a great difference in CA on a single surface (107.7°), and to have four different wetting states on a single surface. Various water-drop experiments proved that the developed hybrid surfaces were selectively wettable and showed water-collecting capability.

Detection and identification of breast cancer volatile organic compounds biomarkers using highly-sensitive single nanowire array on a chip.

A single nanowire array on a chip with different materials of Palladium, Polypyrrole and Zinc Oxide has been fabricated using electrochemical deposition method. The fabricated single nanowire array has been demonstrated for highly sensitive and specific diagnosis of breast cancer by detecting four volatile organic compound biomarkers: Heptanal, Acetophenone, Isopropyl Myristate and 2-Propanol. The demonstrated sensing limits for Heptanal, Acetophenone, Isopropyl Myristate and 2-propanol using individual Palladium, Polypyrrole and Zinc Oxide nanowires were 8.982 ppm, 798 ppb, 134 ppm, and 129.5 ppm, respectively, and the corresponding sensitivities of resistance change were in the range of 0.3%-5% which indicated excellent sensing performance of the single nanowires. The response time for Palladium, Polypyrrole and Zinc Oxide nanowires to achieve maximum conductance change was less than 200 seconds while also illustrating excellent signal repeatability. With the principal component analysis of the resistance change versus time in each detection period of the nanowire array, the smell prints for the four volatile organic compounds biomarkers of Breast Cancer are discriminated in the 3-D plots.

Integrating metal-oxide-decorated CNT networks with a CMOS readout in a gas sensor.

We have implemented a tin-oxide-decorated carbon nanotube (CNT) network gas sensor system on a single die. We have also demonstrated the deposition of metallic tin on the CNT network, its subsequent oxidation in air, and the improvement of the lifetime of the sensors. The fabricated array of CNT sensors contains 128 sensor cells for added redundancy and increased accuracy. The read-out integrated circuit (ROIC) was combined with coarse and fine time-to-digital converters to extend its resolution in a power-efficient way. The ROIC is fabricated using a 0.35 µm CMOS process, and the whole sensor system consumes 30 mA at 5 V. The sensor system was successfully tested in the detection of ammonia gas at elevated temperatures.

Biosensor system-on-a-chip including CMOS-based signal processing circuits and 64 carbon nanotube-based sensors for the detection of a neurotransmitter.

We developed a carbon nanotube (CNT)-based biosensor system-on-a-chip (SoC) for the detection of a neurotransmitter. Here, 64 CNT-based sensors were integrated with silicon-based signal processing circuits in a single chip, which was made possible by combining several technological breakthroughs such as efficient signal processing, uniform CNT networks, and biocompatible functionalization of CNT-based sensors. The chip was utilized to detect glutamate, a neurotransmitter, where ammonia, a byproduct of the enzymatic reaction of glutamate and glutamate oxidase on CNT-based sensors, modulated the conductance signals to the CNT-based sensors. This is a major technological advancement in the integration of CNT-based sensors with microelectronics, and this chip can be readily integrated with larger scale lab-on-a-chip (LoC) systems for various applications such as LoC systems for neural networks.