FIB Secondary Etching Method for Fabrication of Fine CNT Forest Metamaterials

Abstract

Anisotropic materials, like carbon nanotubes (CNTs), are the perfect substitutes to overcome the limitations of conventional metamaterials; however, the successful fabrication of CNT forest metamaterial structures is still very challenging. In this study, a new method utilizing a focused ion beam (FIB) with additional secondary etching is presented, which can obtain uniform and fine patterning of CNT forest nanostructures for metamaterials and ranging in sizes from hundreds of nanometers to several micrometers. The influence of the FIB processing parameters on the morphology of the catalyst surface and the growth of the CNT forest was investigated, including the removal of redeposited material, decreasing the average surface roughness (from 0.45 to 0.15 nm), and a decrease in the thickness of the Fe catalyst. The results showed that the combination of FIB patterning and secondary etching enabled the growth of highly aligned, high-density CNT forest metamaterials. The improvement in the quality of single-walled CNTs (SWNTs), defined by the very high G/D peak ratio intensity of 10.47, demonstrated successful fine patterning of CNT forest for the first time. With a FIB patterning depth of 10 nm and a secondary etching of 0.5 nm, a minimum size of 150 nm of CNT forest metamaterials was achieved. The development of the FIB secondary etching method enabled for the first time, the fabrication of SWNT forest metamaterials for the optical and infrared regime, for future applications, e.g., in superlenses, antennas, or thermal metamaterials. Electronic supplementary materialThe online version of this article (doi:10.1007/s40820-017-0145-5) contains supplementary material, which is available to authorized users.

Nanoscale Patterning of Carbon Nanotubes: Techniques, Applications, and Future

“…Reproduced under the terms of the CC BY 4.0 license. [ 235 ] Copyright 2017, The Authors, published by Springer Nature. f) SEM images of resist patterned via NIL, catalyst patterned via deposition through the resist, and subsequently grown nanoscale patterns of high aspect ratio CNT forests.…”

“…[234] Pander et al used a second FIB etching step applied evenly to the whole substrate to remove randomly redeposited catalyst particles from the first patterning FIB etching step. [235] This resulted in a decrease in the average roughness of the surface from ≈0.45 to ≈0.15 nm, and consequently higher density CNT forests down to 150 nm lateral resolution were synthesized (Figure 11d,e). Higher-quality SWCNTs were also produced as indicated by a reduction in the Dband of the Raman spectrum (Figure 11e).…”

Ultrafast Patterning Vertically Aligned Carbon Nanotube Forest on Al Foil and Si Substrate Using Chemical Vapor Deposition (CVD)

“…To incorporate CNTs into nanoelectromechanical systems, effective and controllable patterned synthesis of CNTs on specific substrates is crucial. A variety of methods have contributed to the preparation of CNT patterning and are still in use today, including shadow masking, photolithography, electron beam lithography, and soft lithography [20,21,22,23,24,25,26,27,28].…”

Localized growth of carbon nanotubes via lithographic fabrication of metallic deposits

“…Therefore, it is important to fabricate catalysts of controlled size and chemical composition at the desired spatial position in order to fabricate CNTs in well-defined configurations for building integrated systems for micro- and nanoelectronics. In this regard, classical methods like optical lithography (OL) [ 13 ] and electron beam lithography (EBL) [ 14 ], but also focused ion beam (FIB) processing [ 15 ], have been successfully applied to fabricate metallic templates for the localized growth of CNTs. However, all of these methods are lacking in either the final desired resolution or in flexibility of the targeted shapes.…”