Direct assembly of nanowires by electron beam-induced dielectrophoresis.

Controllable self-assembly is an important tool to investigate interactions between nanoscale objects. Here we present an assembly strategy based on 3D aligned silicon nanowires. By illuminating the tips of nanowires locally by a focused electron beam, an attractive dielectrophoretic force can be induced, leading to elastic deformations and sticking between adjacent nanowires. The whole process is performed feasibly inside a vacuum environment free from capillary or hydrodynamic forces. Assembly mechanisms are discussed for nanowires in both one and two layers, and various ordered organizations are presented. With the help of moisture treatment, a hierarchical assembly can also be achieved. Notably, an unsynchronized assembly is observed in two layers of nanowires. This study helps with a better understanding of nanoscale sticking phenomena and electrostatic actuations in nanoelectromechanical systems, besides, it also provides possibilities to probe quantum effects like Casimir forces and phonon heat transport in a vacuum gap.