Change of the microstructure has also been investigated to further improve the performance. In 2002, Guerra (Nanoptek Corporation) discovered that high localized strain could be induced in semiconductor films formed on micro to nano-structured templates, and that this strain shifted the bandgap of the semiconductor, in the case of titanium dioxide, into the visible blue.U.S. Patent No. 7,485,799: Stress-induced bandgap-shifted semiconductor photoelectrolytic/photocatalytic/photovoltaic surface and method for making same; John M. Guerra, February 2009. It was further found (Thulin and Guerra, 2008) that the strain also favorably shifted the band-edges to overlay the hydrogen evolution potential, and further still that the strain improved hole mobility, for lower charge recombination rate and high quantum efficiency._{2}$ band structures |journal=Physical Review B |volume=77 |issue=19 |pages=195112 |doi=10.1103/PhysRevB.77.195112}} Chandekar developed a low-cost scalable manufacturing process to produce both the nano-structured template and the strained titanium dioxide coating.U.S. Patent No.8,673,399: Bandgap-shifted semiconductor surface and method for making same, and apparatus for using same; John M. Guerra, Lukas M. Thulin, Amol N. Chandekar; March 18, 2014; assigned to Nanoptek Corp. Other morphological investigations include nanowire arrays or porous nanocrystalline photoelectrochemical cells.
