CREST Center for Next Generation Multifunctional Composites - Supplemental Award

Overview. As the only rocky body in our solar system with a surface age comparable to the Earth, and with a similar size and composition, Venus presents a unique opportunity for understanding the Earth’s evolution.1 Unlike Earth, however, Venus lacks plate tectonics as a method to cycle volatile species and to lose heat, and the answer as to how Venus loses its heat in the absence of plate tectonics remains elusive. The development of an instrument to measure heat flow on the surface of Venus is key to discriminating between the classes of tectonic evolution models, and ultimately to determine the factors leading to the evolution of Earth-like planetary conditions.1 The operation of a heat-flux sensor on the Venus surface presents several unique challenges, since high sensitivity is required to detect geothermal flux levels, and the instrument must be capable of performing at the very high temperatures (~500 °C), pressures (~90 atm), and carbon dioxide (CO2) densities present at the surface.2 Previous work to develop skutterudite-based heat-flux sensors for Venus has been successful in achieving high sensitivity under high pressures up to ~300 °C, after which thermal expansion related stress was found to cause microcracking, in particular near to the metallization layer.2 Silicon nanowire (Si NW) based devices are under development at JPL as a possible alternative to these skutterudites, due to their high synthetic yield, low cost, and low reactivity with supercritical CO2. Based on previous experience, it is imperative to determine the microstructural stability of these nanowires, especially in the vicinity of metallization, when subjected to the high temperatures, high pressures, and supercritical CO2 densities present on the Venus surface. Proposed Work. The long-term goal of our JPL/UK/SUBR collaboration is to develop a working heat flux sensor with the required sensitivity and stability to measure geothermal flux on the Venus surface. Our objective in this application is to evaluate the microstructural stability of metallized silicon nanowires at conditions simulated to replicate the temperature, or pressure and gas environment, on the surface of Venus. Our rationale for undertaking this study is that a key step in developing a Si NW heat-flux sensor will be to understand the effect of the high stress environment imposed by the 500 °C, 90 atm, and supercritical densities of CO2, common to the Venus atmosphere, on the Si NW and its metal contacts.