Open Access Nano Express

Nanoscale optical and electrical characterization of horizontally aligned single-walled carbon nanotubes

Raul D Rodriguez1*, Marius Toader2, Sascha Hermann3, Evgeniya Sheremet1, Susanne Müller1, Ovidiu D Gordan1, Haibo Yu4, Stefan E Schulz34, Michael Hietschold2 and Dietrich RT Zahn1

Author Affiliations

1 Semiconductor Physics, Chemnitz University of Technology, Chemnitz, D-09107, Germany

2 Solid Surfaces Analysis Group, Chemnitz University of Technology, Chemnitz, D-09107, Germany

3 Center for Microtechnologies (ZfM), Chemnitz University of Technology, Chemnitz, D-09107, Germany

4 Fraunhofer Institute for Electronic Nano Systems (ENAS), Chemnitz, 09126, Germany

For all author emails, please log on.

Nanoscale Research Letters 2012, 7:682  doi:10.1186/1556-276X-7-682

Published: 21 December 2012

Abstract

During the recent years, a significant amount of research has been performed on single-walled carbon nanotubes (SWCNTs) as a channel material in thin-film transistors (Pham et al. IEEE Trans Nanotechnol 11:44–50, 2012). This has prompted the application of advanced characterization techniques based on combined atomic force microscopy (AFM) and Raman spectroscopy studies (Mureau et al. Electrophoresis 29:2266–2271, 2008). In this context, we use confocal Raman microscopy and current sensing atomic force microscopy (CS-AFM) to study phonons and the electronic transport in semiconducting SWCNTs, which were aligned between palladium electrodes using dielectrophoresis (Kuzyk Electrophoresis 32:2307–2313, 2011). Raman imaging was performed in the region around the electrodes on the suspended CNTs using several laser excitation wavelengths. Analysis of the G+/G splitting in the Raman spectra (Sgobba and Guldi Chem Soc Rev 38:165–184, 2009) shows CNT diameters of 2.5 ± 0.3 nm. Neither surface modification nor increase in defect density or stress at the CNT-electrode contact could be detected, but rather a shift in G+ and G peak positions in regions with high CNT density between the electrodes. Simultaneous topographical and electrical characterization of the CNT transistor by CS-AFM confirms the presence of CNT bundles having a stable electrical contact with the transistor electrodes. For a similar load force, reproducible current–voltage (I/V) curves for the same CNT regions verify the stability of the electrical contact between the nanotube and the electrodes as well as the nanotube and the AFM tip over different experimental sessions using different AFM tips. Strong variations observed in the I/V response at different regions of the CNT transistor are discussed.

Keywords:
Single-walled carbon nanotubes; CNT transistor; Raman imaging; Current sensing AFM; Atomic force microscopy