Yao-Chuan Tsai

Artificial Petal Effect on Nanofibrillar Parylene™ Surface

The hierarchical structure on a rose petal surface achieves a large contact angle with high contact angle hysteresis. Inspired by the petal effect, two types of artificial structures, fibril mesh and fibril microhills, were fabricated and compared with the rose petal surface. The fibril mesh, composed of Parylene™ nanofibrils and underneath capillary structures was fabricated using template-assisted deposition. The fibril microhills were formed by peeling the fibril mesh off. The contact angle and contact angle hysteresis on these two surfaces treated by various surface modifications for enhancing the hydrophobicity were measured. The fabricated surface showed similar wetting behavior to the rose petal which is hydrophobic and sticky to water droplets. The relation between the contact angle and the contact angle hysteresis on the various artificial surfaces and the rose petal were discussed. The qualitative estimations of the contact angle hysteresis for the various artificial surfaces were presented.

Rapid Dielectrophoresis Assembly of a Single Carbon Nanocoil on AFM Tip Apex

We assembled a single carbon nanocoil (CNC) on the tip apex of an atomic force microscope probe by utilizing dielectrophoresis in isopropyl alcohol (IPA). The total assembly process can be achieved within several seconds at room temperature by using a simple apparatus. Three-dimensional finite element simulations have been conducted to investigate the orientation and position of this assembly. Our experiment agrees well with the simulation. The results indicate that it is essential to filter the CNC/IPA suspension and manipulate the capillary meniscus for a single CNC to be vertically assembled on the tip apex. An inclined-edge electrode has, therefore, been suggested and found effectively confining the CNC/IPA suspension around the probe tip.

An electro-active nano-valve array for reusable drug delivery system

This paper presents a flexible and reusable drug delivery system controlled by a polypyrrole nano-valve array. Electro-active polymer working in aqueous medium has short response time and small power consumption. Polypyrrole is one of such electro-active polymers. Due to its stability, incorruptibility and micromachining compatibility, polypyrrole plays an important role in developing micro/nano-actuators. A novel method for depositing the polypyrrole is also demonstrated.

Self-cleaning Effects of Biomimetic Dry Adhesives

In this paper, we investigated the self-cleaning effects of biomimetic dry adhesives, which are made of e-beam photoresist and carbon nanotubes (CNT). Although the photoresist and the CNT are both intrinsically hydrophilic, superhydrophobic behavior was obtained when they were patterned or synthesized into nano-fibrils. The intrinsic hydrophilicity indicates that these materials possess sufficient surface energy for mimicking gecko foot-hairs as dry adhesives. The entrapped air between the nano-fibrils significantly decreases the contact area with small particles and enhanced the well-known lotus effects. Two methods are presented to facilitate this enforced hydrophobicity. First, nano-gaps on an e-beam photoresist surface are patterned with different contact area ratios. The experimental results show that it follows the theoretical prediction of hydrophobic behavior with the existence of nano-gaps. Second, carbon nanotubes are deposited with the assistance of water vapor on an oxidized silicon surface. Contact angle as large as 157 degree has been achieved on the oxide surface when the water vapor was optimized for the maximum density of CNT

Thermal Manipulation Utilizing Micro-cantilever Probe in Scanning Electron Microscopy

We present a novel design for a sensitive temperature micro-probe, situated at the tip of an atomic force microscopy cantilever. The temperature-sensing element utilizes a platinum resistance thermometer, which is well-known for its measurement reproducibility and chemical inertness. The probe is fabricated using conventional clean room techniques and then processed by focused ion beam milling and material deposition. The probe is able to be mounted to a movable platform inside a scanning electron microscope, enabling simultaneous characterization of a sample’s surface temperature and material topology. Furthermore, by reversing the detection mechanism of the platinum resistance thermometer, localized sample surface heating can be achieved, allowing small-scale sample manipulation and characterization. Such an ability to simultaneously characterize a material’s surface topology and temperature has not been previously reported in literature, and lends great practicality in the fields of materials research and integrated circuits diagnostics.