Andrew E Hollowell

Defect detection in foams and encapsulants using grating-based x-ray phase contrast imaging (Rising Researcher Presentation) (Conference Presentation)

Foams and encapsulants serve important roles in the protection of the components they surround. These low density materials may be used to provide shock protection, to protect against high voltage breakdown, or to minimize thermal fluctuations. Voids and gaps in the material, delaminations from a mating material, or non-uniformities in the encapsulating materials can lead to critical failures in the encapsulated component. Despite the important role these low density materials serve, traditional non-destructive inspection tools are limited in their ability to study this material set, especially in the presence of high density materials such as wires. The default approach has been destructive post-mortums where components are deconstructed after a failure and cause and effect are difficult to distinguish. X-ray phase contrast imaging has a longer history at synchrotrons, but this is not a realistic solution for non-destructive inspection. We have demonstrated grating-based x-ray phase contrast 3-D tomography in a laboratory environment with a conventional x-ray tube. Our large format grating fabrication capability enables imaging with large fields of view (10 cm2) at 28 keV for the successful non-destructive inspection of these low-density materials. We demonstrate that the complementary image modalities available with XPCI provide unique information and higher contrast for the inspection of defects in low density materials than conventional x-ray alone.

Flexible Solar Cells for Micro-Autonomous Systems Technology

Insensitivity to edge recombination is observed in GaAs-based InAs/InGaAs quantum dots-in-a-well (DWELL) solar cells by comparing their current-voltage (IV) plot to GaAs control samples. The edge recombination current component is extracted by analyzing devices of different areas and then compared to DWELL cells of comparable dimensions. The results demonstrate that GaAs-based solar cells incorporating a DWELL design are relatively insensitive to edge recombination by suppressing lateral diffusion of carriers in the intrinsic layer, and thus promising for applications that require small area devices such as concentration or flexible surfaces. Preliminary studies on the integration of these cells onto flexible surfaces such as Kapton and nanopaper are discussed including weight considerations for all the integrated materials.