Advanced methods in Glancing Angle Deposition to control thin film morphology, microstructure and texture

• Author / Creator

  LaForge, Joshua M

• Structuring of material on the nanoscale is enabling new functional materials and improving existing technologies. Glancing angle deposition (GLAD) is a physical vapor deposition technique that enables thin film fabrication with engineered columnar structures on the (10 to 100) nm scales. In this thesis, we have developed new methods for controlling the morphology, microstructure, and texture of as-deposited GLAD films and composite films formed by phase transformation of GLAD nanocolumn arrays during post-deposition annealing. These techniques are demonstrated by engineering the vapour flux motion in both Fe and ZnO nanorod deposition and FeS2 sulfur-annealing.

  Crystalline Fe nanorods with a tetrahedral apex can be grown under rapid continuous azimuthal rotation of the substrate during growth. Discontinuous azimuthal rotation with 3-fold symmetry that matches the nanocolumn's tetrahedral apex symmetry produces nanocolumns with in-plane morphological and crystal orientation. This method, called flux engineering, provides a general approach to induce biaxial crystal texture in faceted GLAD films. Similar effects were found for ZnO nanocolumns.

  Reliable production of photovoltaic-grade iron pyrite thin films has been challenging. Sulfur-annealing of bulk films often produces cracking or buckling. We used the flux-engineering processes developed for Fe to control the inter-column spacing of the precursor film. By precisely tuning the inter-column spacing of the precursor film we can produce iron pyrite films with increased crystallite sizes >100 nm with a uniform, crack-free, and facetted granular microstructure. Large crystallites may reduce carrier recombination at grain boundaries, which is attractive for photovoltaic cells. We assessed the viability of these films for photovoltaic applications with composition, electrical, and optical characterization. Notably, we found a 27 ps lifetime of photocarriers measured with ultrafast optical-pump/THz-probe and tested charge-separation characterization between the pyrite films and a conjugated polymer with absolute photoluminescence quenching measurements. These results provide the foundation for future improvements in pyrite processing for photovoltaic cells.

• Subjects / Keywords

  • Photovoltaic
  • Nanocolumn
  • Thin films
  • FeS2
  • Micro-structure
  • Morphology
  • Nanotechnology
  • Nanostructures
  • Glancing angle deposition
  • Nanorod
  • ZnO
  • Zinc oxide
  • Semiconductors
  • Crystal texture
  • Iron
  • Iron pyrite
  • Fe

• Graduation date

  Spring 2014

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3J097

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.