Real-Time Electrical Characterization of Dielectrophoretic Assembly of Multi-Walled Carbon Nanotubes
- PDF / 1,907,827 Bytes
- 7 Pages / 612 x 792 pts (letter) Page_size
- 78 Downloads / 145 Views
1057-II17-03
Real-Time Electrical Characterization of Dielectrophoretic Assembly of Multi-Walled Carbon Nanotubes Libao An, and Craig Friedrich Multi-Scale Technologies Institute, Michigan Technological University, Houghton, MI, 49931 ABSTRACT This paper reports on a real-time monitoring method for the assembly of a small number of multi-walled carbon nanotubes (MWNTs) by dielectrophoresis (DEP). A time-varying impedance model of the electrode gap was developed to evaluate the number of carbon nanotubes (CNTs) which span the gap by measuring the simultaneous variation of gap impedance during the DEP process. Sudden decreases of gap impedance signals were detected during the DEP assembly of MWNTs corresponding to assembly of single or multiple tubes across the gap. The method reduces the requirement of scanning electron microscopy (SEM) inspection and could help automate DEP assembly of CNTs. INTRODUCTION Due to their excellent properties carbon nanotubes (CNTs) have been under intense study as a promising material for a variety of potential applications in nanoelectronics [1-5]. There is a need to align and deposit single or multiple CNTs between electronic conductors [6-8]. Among the present manipulation methods, dielectrophoresis (DEP) has attracted much research [9-17]. However, confirming the DEP assembly results by scanning electron microscopy (SEM) is tedious and time-consuming. Our experiments show that gap impedance measurement is a feasible way to monitor DEP assembly of metallic CNTs. Suehiro and co-workers used impedance measurement to quantitatively estimate the number of CNTs which were trapped by DEP [18], but they dealt with a very large number of CNTs. Their monitoring time lasted for up to several hours and their impedance or conductance signals changed continuously with time. The number of CNTs trapped by DEP was not quantitatively identified in their method. Our paper addresses the monitoring of the DEP deposition of a small number (1-3) of multi-walled carbon nanotubes (MWNTs). The goal was to develop a real-time monitoring method for DEP assembly that is simultaneous with CNT deposition. Time-varying impedance measurements of the electrode gap during CNT deposition was performed to determine the number of CNTs spanning the gap. A HP 4284A precision LCR meter was used to generate an alternative current (AC) electric field while simultaneously measuring the impedance variation. IMPEDANCE MODEL When assembling by DEP, CNTs are first dispersed in a dielectric liquid medium. In an AC electric field which is spatially non-uniform, polarized CNTs align themselves to the electric field and, when the complex dielectric function of the CNTs is greater than that of the liquid, the CNTs move toward the electrode gap, finally depositing and bridging the gap (Figure 1). During DEP, one CNT first deposits and bridges the electrode gap, then a second, third, and so forth.
(a) (b) Figure 1. (a) Schematic of DEP assembly of CNTs onto an electrode gap; (b) Top view of (a) after assembly The DEP assembly process
Data Loading...
