Nano‐Kirigami Structures and Branched Nanowires Fabricated by Focused Ion Beam‐Induced Milling, Bending, and Deposition

Abstract

stress or external forces. The external forces could include capillary force, [6] mechanical force, [7] thermal effects, [8] etc. Additionally, there are methods for the fabrication of 3D functional micro and nanostructures: gas-assisted focused electron beam-induced deposition (FEBID) and focused ion beam-induced deposition (FIBID), both of which use volatile organic and organometallic precursors. [9] Both FEBID and FIBID processes enable the direct-write fabrication of complex 3D nanostructures with feature dimensions below 50 nm, resulting in pore-free, nanometer-smooth high-fidelity structures with increasing choice of deposited materials via novel precursors. FEBID has recently evolved from a trial-anderror laboratory method to a predictable 3D nano-printing technology with unique advantages. [10] Kirigami, the art of cutting and folding a membrane to create versatile shapes, is an example of a transformational process allowing the creation of 3D structures from a 2D membrane. [11] Since the cutting of 2D patterns into a membrane at the nanoscale is well-established in recent years, nano-kirigami has offered new opportunities to explore the applications for 3D optical devices. [11,12] The 3D nano-kirigami and origami structures have promising optical and photonic functionality in giant optical chirality, [13] metasurfaces, [3,14,15] and plasmonics. [16] Commonly, the 2D substrates which are patterned for nanokirigami and origami are metal (e.g., Au), dielectric (e.g., Si 3 N 4 ), or bilayer (e.g Au on Si 3 N 4 ). Typically, these films are less than 100 nm thick and are free-standing, that is, not directly supported by a substrate. The techniques for introducing the precise cuts into these substrates include e-beam method [3,17] and focus ion beam (FIB) milling. [13,14,16] Recent e-beam lithography methods involve photoresist deposition, e-beam exposure, thin film deposition, etching, and removal of photoresist. With e-beam patterning methods, various resist nano-kirigami structures and multiscale metallic patterns can be fabricated with enhanced efficiency and precision to provide more choices of patterning solution for broader applications. [18,19] In contrast, FIB milling is more widely used because it allows for simple and direct writing (cutting) of the patterns on the 2D material. Because of their widespread commercial availability, the gallium FIB (Ga-FIB) is the routine FIB instrument for these 3D nanostructures hold the key to building custom devices with special and flexible functionalities. Ion beam-induced bending and folding are used for the fabrication of 3D nanostructures from prepared 2D nano-patterned membranes. Tensile and compressive stresses can be introduced within the layers of a thin membrane under ion beam irradiation to manipulate and control the formation of nano-kirigamis. Both localized and broader ion beam irradiation can be used to induce bending in the membrane with remarkable control of the bending angle and direction. In this work, an approach to fabricate nano-kirigamis with...

Broadband and high-efficiency polarization conversion with a nano-kirigami based metasurface

“…Nano-kirigami metasurfaces 1 , which are composed of polymorphic subwavelength artificial nanostructures based on versatile shape transformation methods, not only bring new degree of freedom to the traditional three-dimensional (3D) nanomanufacturing, but also exhibit extraordinary potentials in the field of reconfigurable holograms 2 , 3 , fractal-dependent optical vortices 4 , Fano-resonant metamaterials 5 – 7 , reversal of circular dichroism 8 , 9 , and so on. Particularly, nano-kirigami 1 , 10 , 11 could enable sophisticated shape changes from the two-dimensional (2D) precursors to 3D deformed nanostructures with vertical displacement, spatial bending, which provides a novel approach to manipulate the amplitude, phase, and polarization of electromagnetic waves in the microscale/nanoscale region. In this regard, the deformation of nano-kirigami structures have been induced by external stimuli such as pneumatic pressure 12 , mechanical compression 7 , 13 , electronic bias 14 , 15 , magnetic actuation 16 , and thermal expansion 17 .…”