Strain-induced fabrication of anisotropic nanopores by in-situ E-beam irradiation

Anisotropic nanopores are essential to regulate materials' anisotropic performance including thermal conductivity, ion blocking and so on. Nevertheless, fabricating anisotropic nanopores remains challenging because the formation mechanism is ambiguous, due to the lack of direct experimental evidence. Here, we reveal a unique strain-induced mechanism for the fabrication of anisotropic nanopores under electron beam irradiation. With the in-situ transmission electron microscopy (TEM) technique, an initial symmetric nanopore, with another nanopore nearby, is found to expand relatively uniformly in the first stage. When the spacing between two nanopores reaches to a critical point, however, the area near to the reference nanopore is stretched drastically by a strong driving force along the spacing direction, resulting in an obvious anisotropic morphology. The surrounding environment, spacing and relative position between two nanopores significantly influence the shape of eventually formed nanopores by controlling the strain's uniformity, action range and direction, respectively. Our work demonstrates a novel mechanism and visual evidence for the preparation of asymmetric nanopores in real time, with the hope of assisting in the controllable fabrication of desired nanostructures.