Brown University researchers in partnership with Korean scientists have identified unique properties in nanoscale folds and wrinkles.

According to the findings, wrinkles formed on ultrathin films have hidden long waves that can be stretched even when the film is in a compressed state. The researchers have also found that several hundreds of closed nanochannels that resemble ultra-small pipes are created below the surface during the formation of folds on such films.

Researchers at Brown University and in Korea used focused ion beams to extract a cross-section of compressed gold nanofilm. When tips of regular, neighboring folds touched, nanopipes were created beneath the surface. Credit: Kyung-Suk Kim lab, Brown University

Wrinkles, which are forerunners of normal folds, are formed when a thin film is clasped on a soft base, and further compression of the sheet will result in the formation of folds due to the tight spacing of wrinkles. Manufacturers show interest on these folds, as they can accommodate large surface area in a limited space.

The researchers placed 20-80 nm thick sheets of gold nanogranular film on a rubbery substrate that is widely utilized in the microelectronics industry. They then compressed the sheet to form wrinkles and studied their properties. In earlier investigations, they observed primary wrinkles having short periodicities, which represent the distance between valleys or peaks of individual wrinkles. Now, they have found another type of wrinkle having a periodicity longer than that of the primary wrinkles, resembling a hidden long wave.