David D. Allred received Alumni Professorship Award

Abstract: In this study, we have fabricated nanofuses from thin-film, arc-deposited carbon for use in permanent data storage. Thin-film carbon fuses have fewer fabrication barriers and retain the required resistivity and structural stability to act as a data-storage medium. Carbon thin films were characterized for their electrical, microstructural, and chemical bonding properties. Annealing these films in an argon environment at 400 °C reduced the resistivity from about 4 × 10–2 Ω cm as deposited to about 5 × 10–4 Ω cm, allowing a lower blowing voltage. Nanofuses with widths ranging from 200 to 60 nm were fabricated and tested. They blow with voltages between 2 and 5.5 V, and the nanofuses remain stable in both “1” and “0” states under a constantly applied read voltage of 1 V for over 90 h.

Abstract: Carbon nanotube (CNT)/polymer composite materials can be high strength, stiff, and lightweight, which makes them attractive for fabrication of micromechanical structures. Here we demonstrate a method whereby smooth, thin, high CNT concentration composite sheets can be fabricated and patterned on the microscale using a process of photolithography and plasma etching. Two types of CNT/polymer composite sheets were fabricated: one made from CNTs grown on patterned supported catalyst and one made from CNTs grown with floating catalyst; these had thicknesses of 6 µm and 26 µm respectively and a roughness of less than 60 nm.

Abstract: In this study, silicon-coated vertically aligned carbon nanotube (Si-VACNT) electrodes were used to examine the impact of encapsulation, which effectively reduced the surface area exposed to the electrolyte. This system is ideal for examining the influence of an electrolyte-blocking layer due to its well-defined geometry and high aspect ratio. The morphology, composition and electrochemical performance of electrodes cycled at different rates were characterized for a range of silicon loadings. Significant differences were observed in the morphology and composition of the electrodes. However, the electrochemical performance was similar, and capacity fading was still observed for the encapsulated electrodes. The impact of the encapsulation layer on lithium transport was examined. Two different transport directions and length scales are relevant–1) radial transport of Li in/out of each silicon-coated nanotube (∼50 nm diameter) and 2) lithium transport along the length of the nanotubes (∼100 μm height). Experimental results indicate that the height of the Si-VACNT electrodes does not limit Li transport, even though that height was orders of magnitude greater than the diameter of the tubes. These results have important implications for a variety of encapsulation strategies.

Abstract: The two microphone transfer function technique is used to measure sound transmission properties of porous screens or membranes in a plane wave tube. This paper will compare sound transmission of porous screens from several manufacturers. Measurements are made with two different plane wave tubes, one of diameter 10.2 cm to measure frequencies between 100 Hz and 2 kHz, and the other of diameter 1.3 cm to measure frequencies between 2 kHz and 16 kHz. Multiple methods of transmission loss measurement and analysis are presented. Special considerations are made to account for the intrinsic losses in the smaller diameter tube.

Abstract: An improved method for the metallization of DNA origami is examined in this work. DNA origami, a simple and robust method for creating a wide variety of nanostructured shapes and patterns, provides an enabling template for bottom-up fabrication of next-generation nanodevices. Selective metallization of these DNA templates is needed to make nanoelectronic devices. Here, we demonstrate a metallization process that uses gold nanorod seeds followed by anisotropic plating to provide improved morphology and greater control of the final metallized width of the structure. In our approach, gold nanorods are attached to an origami template to create a seed layer. Electroless gold deposition is then used to fill the gaps between seeds in order to create continuous, conductive nanowires. Importantly, growth during electroless deposition occurs preferentially in the length direction at a rate that is approximately 4 times the growth rate in the width direction, which enables fabrication of narrow, continuous wires. The electrical properties of 49 nanowires with widths ranging from 13 to 29 nm were characterized, and resistivity values as low as 8.9 × 10–7 Ω·m were measured. The anisotropic metallization process presented here represents important progress toward the creation of nanoelectronic devices by molecularly directed placement of functional components onto self-assembled biological templates.

Abstract: Sputtered amorphous carbon thin films were explored as corrosion resistant coatings on aluminum thin films to be incorporated into x-ray detector windows. The requirements for this application include high corrosion resistance, low intrinsic stress, high strains at failure, and high x-ray transmission. Low temperature sputtering was used because of its compatibility with the rest of the window fabrication process. Corrosion resistance was tested by exposure of carbon coated and uncoated Al thin films to humidity. Substrate curvature and bulge testing measurements were used to determine intrinsic stress and ultimate strain at failure. The composition and bonding of the carbon films were further characterized by electron energy loss spectroscopy, Raman spectroscopy, and carbon, hydrogen, and nitrogen elemental analyses. Samples had low compressive stress (down to.08 GPa), a high strain at failure (3%), and a low fraction of sp3 carbon–carbon bonds (less than 5%). The high breaking strain and excellent x-ray transmission of these sputtered carbon films indicate that they will work well as corrosion barriers in this application.