Abstract:

To fabricate a photonic crystal with large and complete photonic bandgap, it often requires backfilling of high index inorganic materials into a 3D polymer template. However, the pore network may become disconnected before the template is completely filled in a conformal coating process, which, therefore, limits the achievable maximum bandgap in the 3D photonic crystals. Here, we demonstrate nearly complete filling of the holographically patterned, diamond-like polymer templates with titania sol−gel through the electrodeposition method. The deposition proceeded in two stages: a thin titania seed layer (~55 nm thick) was conformally coated on the surface of the polymer template at the early stage of electrodeposition, after which the deposition occurred preferentially from the template bottom layer at a rate of ~0.4 µm/min. After preannealing and a slow ramping rate to 500 °C to remove the polymer template, an inverse 3D anatase titania crystal was obtained without pattern collapse. The measurement of film reflectivity in the [111] direction before and after the deposition in comparison to the calculated photonic bandgap properties suggested that (1) the template was nearly completely filled by the electrodeposition process and (2) the photonic structure was well-preserved after the removal of the template.