Appl Phys A (2011) 102: 401–406 DOI 10.1007/s00339-010-6069-2 Demetalization of single-walled carbon nanotube thin films with microwave irradiation Lu Wang · Yao Xiong · Ziran Wu · Binh Duong · Supapan Seraphin · Hao Xin · Liwei Chen Received: 1 April 2010 / Accepted: 28 September 2010 / Published online: 16 October 2010 © Springer-Verlag 2010 Abstract The microwave irradiation effects on purified HiPCO and CoMoCat single-walled carbon nanotube (SWNT) thin films are investigated. The surface conduc- tivities of the SWNT films are extracted from the measured THz transmission coefficients to provide a direct indication of the metallic content in the films. The observed drastic conductivity decrease indicates a significant metallic con- tent reduction after the microwave irradiation. Two different laser excitations are applied for Raman spectroscopy to re- veal the response of different nanotube species. The Raman spectra of both HiPCO and CoMoCat thin films confirm the decrease of metallic carbon nanotubes. The observed microwave-induced effects may potentially lead to a con- venient scheme for demetalization of single-walled carbon nanotube mixtures. L. Wang · Z. Wu · H. Xin ( ) Department of Electrical and Computer Engineering, University of Arizona, Tucson, AZ 85721, USA e-mail: hxin@ece.arizona.edu Fax: +1-520-6218076 L. Wang · Z. Wu · H. Xin Department of Physics, University of Arizona, Tucson, AZ 85721, USA Y. Xiong Department of Chemistry and Biochemistry, Ohio University, Athens, OH 45701, USA B. Duong · S. Seraphin Department of Materials Science and Engineering, University of Arizona, Tucson, AZ 85721, USA L. Chen ( ) Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Science, Suzhou, Jiangsu 215125, P.R. China e-mail: lwchen2008@sinano.ac.cn Fax: +86-512-62603079 1 Introduction Carbon nanotubes (CNTs) possess unique thermal, mechan- ical and electrical properties [1, 2]. Various applications of CNTs have been proposed, such as field emission dis- plays [3], microscope tips [4], fuel cells [5], and nanoelec- tronics [6]. The extremely small diameter and high carrier mobility of CNTs suggest great potential in nano-electronic devices such as CNT field effect transistors (FET) [6], nano- antennas [7], and nano-interconnects [8], etc. However, most of the applications preferably require nanotubes to be ei- ther purely semiconducting, or purely metallic. The hetero- geneity of as-synthesized single-walled carbon nanotubes (SWNTs), which are always mixtures of both metallic and semiconducting species, has therefore become one of the biggest obstacles for CNTs to enter nano-scale integrated circuits. Thus far, several methods for separation of metal- lic and semiconducting SWNTs have been reported, based on their differences in electric conductivity, chemical reac- tivity, dielectric response, affinity with surfactants, and den- sity [9–14]. Nevertheless, none of the methods are complete solutions for applications in nano-electronics. For exam- ple, the reported selective electrical destruction method [11] by applying a dc current is fairly reliable but it is a serial process that requires microelectrode fabrication and sequen- tial manipulation of each individual device, thus has limited throughput. To simplify the selective electrical destruction scheme, electromagnetic waves can be considered as an alternative to dc excitation so that the electrode fabrication and CNT- electrode contacts are no longer necessary. For example, when a microwave signal impinges on SWNTs, currents are induced in the tubes. If simply approximating a nan- otube as an infinitely long solid cylinder with a conduc- tivity σ , the induced current is proportional to σ and the