Surface-polarization-induced formation of amorphous foliaceous SiO ₂ helical nanobelts

Amorphous foliaceous SiO₂ helical nanobelts with equidistant alternating bright and dark stripes are synthesized using thermal evaporation. A very thin polar crystalline layer spontaneously formed on the nanobelt surface stabilizes the twist and the internal shear stress imbalance induces the periodic reconstruction. The periodic bright and dark stripes disappear slowly with growth time because the polar crystalline SiO₂ layers are covered slowly by an amorphous layer. The polar surface-driven mechanism, which can adequately explain the appearance and disappearance of the periodic fringes, is verified theoretically. © 2009 American Institute of Physics.