BYU Physics and Astronomy

As micro and nanotechnology continue to advice into products, durability, reliability and robustness become important factors. One application where micro technology needs such qualities is X-ray windows. X-ray windows consist of free standing thin film membranes made from low Z elements. An ideal X-ray window is thin enough to allow for soft X-ray transmission and yet is strong enough to maintain a vacuum. X-ray windows are used to analyze samples in microscopes and hand held devices for mining and other applications. These membranes in hand held devices need to be able to withstand impacts due to dropping or jarring of the device. Shock test studies have been performed on electronics and membranes related to biological system, but literature showing the robustness of free standing membranes is not ready found. In this study free standing thin film membranes’ ability to withstand repeated shocks created by using a bar contact pendulum shock apparatus is investigated. A comparison of shock resistance of X-ray window membrane materials specifically silicon nitride and beryllium will be presented.

An issue that often impacts x-ray and electron analysis of transmission electron microscopy (TEM) samples is the presence of high-Z atoms in the sample substrate. In many cases, it is also desirable that the chosen substrate be resistant to chemicals and various processing methods. We present an improved TEM grid made by carbon-infiltrated carbon nanotube templated microfabrication (CNT-M). These grids provide a significant advantage in analytical TEM applications due to the absence of high-Z atoms and the improved chemical resistivity which allows for a wider range of sample preparation and processing techniques. We have refined the CNT-M process by developing a method for preventing delamination of highly carbon-infiltrated CNT-M structures from the growth substrate. We further present a scalable method for suspending thin films (<30 nm) across large gaps (>100 um) between CNT-M defined features. Several membranes were deposited on the grids including amorphous carbon, boron carbide, silicon dioxide, and alumina. These results are of significance to CNT-M MEMS design and production.

The objective of this study was to test the mechanical durability of a polyurethane/organoclay nanocomposite modified with perfluoroalkyl methacrylic copolymer in conditions that replicate extended rain impact. Samples were impacted with 1.4 mm droplets at a velocity of 24 m/s and a flow rate of 0.78 gpm for a period of 5 hours by an axial full cone nozzle. The cases of the spray nozzle being placed vertically above a sample as well as at a 40° angle were examined. After the spray period, samples were heated at 100° C to allow saturated liquid to evaporate from the surface. Contact angle and sliding of the superhydrophobic surfaces were measured before and after the spray period. A decrease in performance for both samples was observed, with the vertically sprayed sample seeing greater degradation. SEM images of superhydrophobic samples before and after spray impact revealed large amounts of circular indentations on the surfaces caused by the impacting droplets which, along with leaching of the fluoroacrylic copolymer, was likely the cause of the decrease in performance.

We have fabricated nanoscale tellurium fuses using electron beam lithography for long term data storage applications. The tellurium fuses contain a narrow resistive region(250 nm to 10 micron). Application of a sufficiently high voltage accross the tellurium fuse causes resistive heating of the narrow region. After a sufficient temperature is reached, the tellurium melts and begins to flow until a gap is formed in the material. After the gap is formed there is no longer a path for electric current flow, causing a large permanent change in the resistance of the device. We have measured teh resistance change following gap formation and have experimentally determined the effect of voltage on the resulting gap size. Finite element simulations have been used to estimate the effect of applied voltage on the temperature of the fuses.