Principles of carbon nanotube dielectrophoresis

摘要

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.