Imaging Electronic Structure of Carbon Nanotubes by Voltage-Contrast Scanning Electron Microscopy

We introduce voltage-contrast scanning electron microscopy(VC-SEM)for visual characterization of the electronic properties of single-walled carbon nanotubes.VC-SEM involves tuning the electronic band structure and imaging the potential profi le along the length of the nanotube.The resultant secondary electron contrast allows to distinguish between metallic and semiconducting carbon nanotubes and to follow the switching of semiconducting nanotube devices,as confi rmed by in situ electrical transport measurements.We demonstrate that high-density arrays of individual nanotube devices can be rapidly and simultaneously characterized.A leakage current model in combination with fi nite element simulations of the device electrostatics is presented in order to explain the observed contrast evolution of the nanotube and surface electrodes.This work serves to fi ll a void in electronic characterization of molecular device architectures.

Principles of carbon nanotube dielectrophoresis

Dielectrophoresis(DEP)describes the motion of suspended objects when exposed to an inhomogeneous electric field.It has been successful as a method for parallel and site-selective assembling of nanotubes from a dispersion into a sophisticated device architecture.Researchers have conducted extensive works to understand the DEP of nanotubes in aqueous ionic surfactant solutions.However,only recently,DEP was applied to polymer-wrapped single-walled carbon nanotubes(SWCNTs)in organic solvents due to the availability of ultra-pure SWCNT content.In this paper,the focus is on the difference between the DEP in aqueous and organic solutions.It starts with an introduction into the DEP of carbon nanotubes(CNT-DEP)to provide a comprehensive,in-depth theoretical background before discussing in detail the experimental procedures and conditions.For academic interests,this work focuses on the CNT-DEP deposition scheme,discusses the importance of the electrical double layer,and employs finite element simulations to optimize CNT-DEP deposition condition with respect to the experimental observation.An important outcome is an understanding of why DEP in organic solvents allows for the deposition and alignment of SWCNTs in low-frequency and even static electric fields,and why the response of semiconducting SWCNTs(s-SWCNTs)is strongly enhanced in non-conducting,weakly polarizable media.Strategies to further improve CNT-DEP for s-SWCNT-relevant applications are given as well.Overall,this work should serve as a practical guideline to select the appropriate setting for effective CNT DEPs.

Erratum to: Principles of carbon nanotube dielectrophoresis

The article"Principles of carbon nanotube dielectrophoresis" written by Wenshan Li,Frank Hennrich,Benjamin S.Flavel,Simone Dehm,Manfred Kappes,and Ralph Krupke,was erroneously originally published electronically on the publisher internet portal(currently SpringerLink)without Open Access.