Bandgap engineering of multi-walled carbon nanotubes via swift heavy ion irradiation for microelectronics—XAS and Raman study

Abstract

Microelectromechanical systems (MEMS) have witnessed rapid advancement over the past two decades, enabling the miniaturization and system on-chip integration of mechanical, electrical, and sensing components. In this context, carbon nanotubes (CNTs) have emerged as a promising 2D material for next-generation MEMS devices. In this study, the bandgap of CNTs is tuned via swift heavy ion (SHI) irradiation for enhanced electrical performance. SHI induced amorphization or strain in the CNT matrix shows defect creation or defect annealing depending on ion energy and fluence, directly correlated with Fermi level modulation and bandgap tuning. Raman spectroscopy is particularly valuable in quantifying Fermi level shifts by assessing changes in G-band and D-band intensities and peak positions of carbon-based materials. The disorder induced in CNTs under ion irradiation decreases from 1.23 to 1.12 for FeCNTs and increases from 0.64 to 1.25 for CoCNTs. X-Ray Absorption Spectroscopy and High-Resolution Transmission Electron Microscopy further correlate with Raman findings to study the changes in local electronic and morphological structures, respectively. High-Resolution X-Ray Diffraction also indicates the presence of irradiation-induced structural amorphization and loss of long-range order. The effect on spin and orbital magnetic moments due to irradiation is quantized via X-ray Magnetic Circular Dichroism Spectroscopy, discussing the ability to precisely tune magnetic properties of CNTs using ion beam irradiation. Thus, this study of bandgap tuning and controlled magnetism via SHI is suitable for MEMS and quantum-based applications.