UC Irvine

Metals were first refined over 10,000 years ago, and have been crucial components in all aspects of society ever since. From the steel structural supports in buildings to the microscopicwires in cell phones, there are countless ways to shape and mold metals for any purpose. In this dissertation, I will be focusing on shaping metals on the nanometer scale to build sensors small enough to detect gaseous molecules in air. The first device consists of a single platinum nanowire for the detection of ethylene. With cylindrical dimensions on the order of 100s of nanometers, this device is sensitive enough that molecules adsorbing onto the nanowires’ surface are capable of producing a measurable resistance change. By applying a current through the nanowire, this device can be heated to elevated temperatures to measure how this response changes. The resulting sensor relies on principles of adsorption and surface scattering, which can be applied to a wide variety of metal-adsorbate systems for future sensing purposes. This device was also able to reversibly detect down to single-ppm concentrations of ethylene, making it an ideal candidate for measuring the ripening of produce. The second device discussed in this paper is a single nanoribbon made of palladium. This device is much easier to fabricate than previously described nanowires, and while retaining a nanoscale height, it is orders of magnitudes wider. Previous studies have shown that size is a critical factor in assessing the performance of palladium-based sensors and that nanowires are typically the fastest architecture for hydrogen sensing. By applying a catalytically active surface layer of platinum, however, this device defies this rationale and outperforms other nanowire systems. Resulting platinum-coated palladium nanowires are sensitive towards hydrogen gas, and upon exposure produce a rapid resistance change. The effect of this platinum layer has been explored across several different loadings, with an optimal coating observed between 0.5 and 1.5 ML of platinum coverage. We can also tune the sensitivity and response/recovery rates of this device by altering the amount of platinum doping.