David D. Allred received Alumni Professorship Award

High-aspect-ratio metallic microstructures have a variety of potential applications in sensing and actuation. However, fabrication remains a challenge. We have fabricated nickel microstructures with over 20:1 aspect ratios by electroplating patterned carbon-coated carbon-nanotube forests using a nickel chloride bath. Pulse plating allows nickel ions to diffuse into the interior of the forest during off portions of the cycle. Done properly, this solves the problem of the formation of an external crust, which otherwise blocks nickel deposition in the interior of the structures. Thus, densities of 86 ± 3% of bulk Ni for the composite structures are achieved. Cantilever structures do not yield under load, but break. Measurements of the material properties of this composite material indicate an elastic modulus of ~42 GPa and a strength of 400 MPa. We demonstrate the utility of this method with an external field magnetic actuator consisting of a proof mass and two flexures. We achieved 1-mN actuation forces. [2014-0274]

The utility of unmanned micro underwater vehicles (MUVs) is paramount for exploring confined spaces, but their spatial agility is often impaired when maneuvers require burst-propulsion. Herein we develop high-aspect ratio (150:1), multiwalled carbon nanotube microarray membranes (CNT-MMs) for propulsive, MUV thrust generation by the decomposition of hydrogen peroxide (H₂O₂). The CNT-MMs are grown via chemical vapor deposition with diamond shaped pores (nominal diagonal dimensions of 4.5 × 9.0 μm) and subsequently decorated with urchin-like, platinum (Pt) nanoparticles via a facile, electroless, chemical deposition process. The Pt-CNT-MMs display robust, high catalytic ability with an effective activation energy of 26.96 kJ mol^–1 capable of producing a thrust of 0.209 ± 0.049 N from 50% [w/w] H₂O₂ decomposition within a compact reaction chamber of eight Pt-CNT-MMs in series.

Carbon nanotubes (CNTs) can be grown in dense lithographically patterned forests to form framework structures that can be filled in via chemical vapor deposition to form solid structures. These solid structures can then be used in microelectromechanical systems (MEMS) applications. Initial testing with these structures suggests that when these frameworks are filled with carbon, the resulting material exhibits favorable properties for use in compliant MEMS. To better understand this material's properties, we conducted tests to measure its Young's modulus, failure stress, and stress relaxation in the direction perpendicular to the CNT growth, as well as the modulus and stress in the direction parallel to the CNTs. To determine the properties in the transverse direction, we applied vertical loads to the tips of simple cantilever beam samples, and recorded the force and deflection until failure. The results showed failure strain up to 2.48%. Cantilever samples prepared from the same pattern were also used to measure the stress relaxation of the material. The first test for each sample showed an average force relaxation of 3.72%, while successive tests only produced 1.23% after 24 h. To determine the properties in the direction parallel to the CNTs, we prepared simple rectangular beams and subjected them to 3-point bending tests. The average strain calculated in the parallel direction was 8.17%.

We describe the direct, conformal, atomic layer deposition (ALD) of silica onto carbon nanotubes (CNTs) in the microfabrication of thinlayer chromatography (TLC) plates. As before, these plates were prepared with zig-zag hedge and channel microstructures, with high aspect ratio, porous hedges. After ALD, scanning electron microscopy (SEM) showed an increase in the radius of the CNTs of 8–40 nm. X-ray photoelectron spectroscopy (XPS) showed that the plates were composed almost entirely of silicon and oxygen, without contamination of metals or other elements that might compromise chromatographic performance, e.g., aluminum. Time-of-flight secondary ion mass spectrometry confirmed the extremely low level of aluminum in the plates. The final TLC layer thickness was ca. 50 μm. Separations of a test mixture of dyes from CAMAG (Muttenz, Switzerland) on an uncoated silica plate under traditional, normal phase conditions gave efficiencies of 40,000–140,000 plates m⁻¹ with migration distances ranging from 2 to 36 mm. A separation of two fluorescent dyes, eosin Y disodium salt and sulforhodamine B, on an amino silane-coated plate gave efficiencies of ca. 170,000 and 200,000 plates m⁻¹, with hR_F values of 76 and 88, respectively. Run times on these new plates were much faster than on conventional TLC plates.