Overcoming obstacles for developing carbon nanotube-based devices

Abstract

Summary form only given. Carbon nanotubes (CNTs), one of the most popular nanoscale materials, have been investigated intensively over the last decade for many of their potential applications. These studies were largely based on theoretical and experimental results from limited numbers of prototype CNT-based devices including field effect transistors (FETs), electron field emitters, interconnects, sensors, probes, energy storage and energy conversion devices. However, the lack of techniques for controlled mass production of CNT-based nanodevices and the ability to accurately characterize their electronic and optical properties have been the primary obstacles for the realization of CNTs' promising technological applications. It is therefore well recognized by the CNT research community that optimization of nano-electronics such as CNT-FETs requires a comprehensive system of nanometrology. Such a system is critical for understanding the role of the local environment, device architecture and internal structure on CNT-FET performance. Oxygen and water vapor have been shown to impact both the CNT conduction channel and the CNT-electrode interface in significantly different ways. Alterations in carrier type such as p-type to n-type, unipolar to ambipolar and changes in contact resistance can all be correlated to oxygen-induced modulation of the Schottky barrier at the nanotube-electrode interface. Shifts in threshold voltage of CNT-FETs have been attributed to the doping of oxygen adsorbate on the bulk of the CNT. The choice of the electrode material, in terms of work function and oxidation state, can influence device resistance. Defects within the CNT itself can act both as electron/phonon scattering sites as well as bonding sites for various adsorbates. In this report, the author will provide an overview of on-going research of CNTs in her group and introduce several newly developed techniques aimed at mass producing CNT-based devices and accurately characterizing their properties. The electronic and optical characterization of the CNT nanodevices were carried out in a unique microenvironment probe system that was developed in her group, which reveals the impact of different adsorbate species and wavelengths of light on device performance. A recent effort of combining scanning electron microscopy, micro-Raman mapping, UHV probing and numeric simulation for studying the curvature of as-grown single-walled CNT in relation to their electronic properties will also be discussed.