Jianzhong Zhu

Mitigation of tensile failure in released nanoporous metal microstructures via thermal treatment

The authors have developed a method to fabricate released microstructures of nanoporous Au (np-Au) by dealloying a Au–Ag alloy film patterned over a sacrificial Al layer. Doubly clamped bridges fail during dealloying owing to large tensile stresses induced during the dealloying process. Thermal treatments of released microstructures prior to dealloying generate sufficient compressive stress to induce plastic buckling. This buckling compensates the tensile stresses generated during the dealloying process, thus mitigating fracture of the np-Au.

Bio-Inspired Robotic Cownose Ray Propelled by Electroactive Polymer Pectoral Fin

The cownose ray (Rhinoptera bonasus) demonstrates excellent swimming capabilities; generating highly efficient thrust via flapping of dorsally flattened pectoral fins. In this paper, we present a bio-inspired and free swimming robot that mimics the swimming behavior of the cownose ray. The robot has two artificial pectoral fins to generate thrust through a twisted flapping motion. Each artificial pectoral fin consists of one ionic polymer-metal composite (IPMC) as artificial muscle in the leading edge and a passive PDMS membrane in the trailing edge. By applying voltage signal to the IPMC, the passive PDMS membrane follows the bending of IPMC with a phase delay, which leads to a twist angle on the fin. The characterization results have shown that the pectoral fin was able to generate up to 40% tip deflection and 10° twist angle with less than 1 Watt power consumption. A bio-inspired rigid body was designed using Computerized Axial Tomography (CT Scan) data of the cownose ray body and printed using a 3-dimensional printer. A light and compact on-board control unit with a lithium ion polymer battery has been developed for the free swimming robot. Experimental results have shown that the robot swam at 0.034 BL/S.Copyright

Three-phase contact force equilibrium of liquid drops at hydrophilic and superhydrophobic surfaces

Hydrophilic and superhydrophobic surfaces were obtained by modifying a dendritic Au surface with carboxyl- or methyl-terminated self-assembled monolayers, respectively. The hydrophilic surface generates capillary forces which induce water flow through the grooves defined by the dendritic structure, resulting in a halo structure; the superhydrophobic surface on the other hand completely repels water drops. The contrasting behaviors exhibited by the two surfaces with nominally identical morphology but different surface chemistry are explained semi-quantitatively in terms of the equilibrium of surface forces developing at the three-phase (air-solid-water) contact lines.

Wetting Phenomenon in Nanoporous Gold Films

We have fabricated nanoporous gold (np-Au) films on silicon wafers by dealloying films formed by simultaneous sputter deposition of gold and silver. We report an interesting wetting phenomenon observed after placing a droplet of liquid on the np-Au film surface. As a droplet was dispensed onto the surface, wetting equilibrium was quickly reached and a wetting halo appeared with its perimeter equidistant from the perimeter of the droplet. Non-porous gold control samples did not display such behavior. This phenomenon was systematically studied by dispensing liquid droplets with different surface tensions and then measuring the width of the wetting halo. It was observed that halo width increased with surface tension. Experiments were extended to observe the effects of film thickness and porosity on the halo width. The width increased as film thickness increased. The relationship between the width and porosity was inconclusive due to large data scatter

Thermo-Mechanical and Size-Dependent Behavior of Freestanding AuAg and Nanoporous-Au Beams

Nanoporous gold (np-Au), produced by selectively removing silver from an AuAg alloy, has recently gained considerable attention from the scientific community. Biocompatibility, chemical inertness, increased surface area, relatively low elastic modulus, and ease of synthesis make np-Au an important candidate for biomedical, catalytic, and MEMS applications. Np-Au films also offer substantial ground for theoretical and empirical research, including mechanical characterization, fracture mechanics, and porosity evolution. Even though a significant effort has been directed towards exploring blanket np-Au films (i.e., foils, strips), to our knowledge no work has been done on fabricating or investigating freestanding np-Au structures (i.e., micro-beams, cantilevers). Recently we have developed techniques to create freestanding clamped np-Au beams with widths from 5 to 40 microns and lengths from 20 to 500 microns. The percentage yield was more than 97% for 2880 beams on a 2-inch wafer. A critical step in the fabrication process, necessary to prevent tensile failure of the beams during dealloying, is a thermal heat treatment prior to dealloying. The study of thermal treatment of beams at temperatures between 100°C and 600°C prior to dealloying revealed three distinct beam behavior regimes, namely quasi-elastic buckling, plastic buckling, and material interdiffusion. This paper will present the preliminary results from thermal treatment experiments particularly focusing on how beam dimensions affect percentage yield and beam fracture.