Free-standing polyimide nanotips on substrates for preparation of hollow TiO₂ nanotips

We report a facile method to fabricate free-standing polyimide (PI) nanotips on substrates by using plasma treatment with oxygen gas. The PI nanotips were prepared from the self-organization of unetchable materials deposited on a PI film during the plasma treatment. This approach provides a single-step process for the preparation of polymer nanotips in a large area (>inch scale). Furthermore, a selective patterning of the PI nanotips in a specific area was achieved by using a shadow mask. Due to excellent thermal resistance of PI, the PI nanotips maintained structural integrity at high temperature (∼ 300 °C). To demonstrate potential application of PI nanotips as a template for hollow nanostructures, hollow TiO₂ nanotips were prepared after atomic layer deposition of TiO₂ followed by the burning of PI layer.