Focused-ion-beam-introduced stress as a driving force for three-dimensional micro/nano-assembly

Abstract

<p>Focused ion beam (FIB) with keV Ga⁺ has been observed to be able to introduce nanoscale localized tensile stress in materials including Si₃N₄, SiO₂, crystal-Si, poly-Si, Al, and Au. Such stress is employed as a driving force to assemble free-standing two-dimensional (2D) nano-film patterns to three-dimensional (3D) structures. Continuous bending from 0° to 90° of the 2D patterns is demonstrated. A strained-bilayer-system model is proposed to qualitatively describe the bending angle. Fabrications of a 3D cubic frame as well as helices are achieved by the FIB stress induced deformation (FIB-SID) technology with proper stress-introducing strategy. To prove the power of FIB-SID, we fabricate stereo metamaterials composed of “standing” 3D split ring resonators (SRR), demonstrating considerable optical absorption in IR regime. Theoretical and experimental results manifest that the metamaterial device has reflection minimum at 5.3 µm. On this basis, we develop a programmable quasi-parallel FIB fabrication method for 3D nanostructure (taking the 3D SRRs structure as an example) which has advantages of much higher efficiency, great consistency and considerable throughput. The revealed flexibility and controllability of this technology make it promising in constructing diverse forms of 3D micro/nano-structures for micro/nano-electromechanical systems.<br></p>