Mechanistic Insights into the Synthesis of Nickel-Graphene Nanostructures for Gas Sensors.

Toxic gases are used in different types of industries and thus, present a potential health hazard. Therefore, highly sensitive gas sensing materials are essential for the safety of those operating in their environments. A process involving electrospinning polymer solutions impregnated with transition metal ions are developed to yield nanofibers that are annealed to form graphitic carbon / nickel nanoparticle-based fibers for gas sensing applications. The performance of these gas sensors is strongly related to the ability to control the material parameters of the active material. As the formation of these nanostructures, which nucleate within solid carbon scaffolds, have not been investigated, the growth mechanisms are look to understand in order to exert control over the resulting material. Evaluation of these growth mechanisms are conducted through a combination of thermogravimetric analysis with mass spectrometry (TGA-MS), x-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and x-ray photoelectron spectroscopy (XPS) and reveal nucleation of nickel at the onset of the polymer scaffold decomposition with subsequent growth processes, including surface diffusion, aggregation, coalescence and evaporation condensation, that are activated at different temperatures. Gas sensing experiments conducted on analyte gases demonstrate good sensitivity and response times, and significant potential for use in other energy and environmental applications.

Toward wide-angle microvision sensors.

Achieving computer vision on microscale devices is a challenge. On these platforms, the power and mass constraints are severe enough for even the most common computations (matrix manipulations, convolution, etc.) to be difficult. This paper proposes and analyzes a class of miniature vision sensors that can help overcome these constraints. These sensors reduce power requirements through template-based optical convolution, and they enable a wide field-of-view within a small form through a refractive optical design. We describe the tradeoffs between the field-of-view, volume, and mass of these sensors and we provide analytic tools to navigate the design space. We demonstrate milliscale prototypes for computer vision tasks such as locating edges, tracking targets, and detecting faces. Finally, we utilize photolithographic fabrication tools to further miniaturize the optical designs and demonstrate fiducial detection onboard a small autonomous air vehicle.