FIB Secondary Etching Method for Fabrication of Fine CNT Forest Metamaterials

Adam Pander,Akimitsu Hatta,Hiroshi Furuta

doi:10.1007/s40820-017-0145-5

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.

Highlights

Carbon nanotubes (CNTs) possess extraordinary electrical, physical and optical properties [1,2,3,4,5] due to their unique structure, such as the anisotropic electrical conductivity of horizontally aligned CNTs [2] and the anisotropic optical absorption of vertically aligned CNTs [3]
The results showed that the combination of focused ion beam (FIB) patterning and secondary etching enabled the growth of highly aligned, highdensity CNT forest metamaterials
The extraordinary properties of CNT forests were recently used for the fabrication of metamaterials and nonlinear photonic devices in the form of multi-walled CNT (MWNT) arrays [6,7,8], slits cut in the CNT films [9], or spray-coated CNT films on ceramic metamaterials [10, 11]; none of these examples utilized the unique properties of a CNT forest

Summary

Introduction

Carbon nanotubes (CNTs) possess extraordinary electrical, physical and optical properties [1,2,3,4,5] due to their unique structure, such as the anisotropic electrical conductivity of horizontally aligned CNTs [2] and the anisotropic optical absorption of vertically aligned CNTs [3]. To fully utilize the properties of a CNT forest with the high alignment, density, and the CNT forest structure, a different method of patterning is required. The patterning of predeposited catalyst at the nanoscale, which would enable uniform, vertically aligned SWNT forest growth on various shapes of nanosize structures, is still challenging and is yet to be achieved [17, 19,20,21]. High-quality CNT structures with various shapes were achieved by utilizing different fabrication methods. A focused ion beam (FIB) and electron beam (EB) were used for the patterning of catalyst nanodots and enabled the fabrication of arrays of individual MWNTs [6, 8, 27]

Objectives

Results

Conclusion