In situ scanning electron microscopy observations of filler material transport in branched carbon microtubes by Joule heating

Abstract

Y-branched or side-by-side-branched carbon microtubes with metal filler material were fabricated, and material transport in the branched microtubes with Joule heating was investigated using in situ scanning electron microscopy with micro-electrode probes. When a voltage and electric current were applied, the material enclosed in the microtubes moved from its original position. The movement was not related to the direction of the electric current; therefore, it is concluded that the movement was not due to electromigration, but rather a temperature gradient, volume expansion and increased vapor pressure by Joule heating. In Y-branched microtubes, a part of the metal filler material moved from one branch to another branch, which would be useful for microfluidic flow switching. A cylindrical filler material was also observed to be expelled from a branch while its shape was maintained, and this phenomenon is presumably caused by vaporization-induced high pressure and could find application in micro-mechanical manipulators such as punching needles. In side-by-side-branched carbon microtubes, Joule heating caused thermal volume expansion to fill the spaces in the branches that were initially empty. The microtubes then reverted to a state almost identical to the initial state with empty spaces when the electric current was turned off. These results suggest that thermal volume expansion could be employed for flow switching.

Kinematics of electromigration-driven sliding of Co nanorod fillers inside multi-walled carbon nanotubes

“…This phenomenon has been studied intensively because electromigration is a cause of integrated circuit failure. [7][8][9][10][11] The development of methods for mass transport at the nanoscale is important; 12 in addition to the utilization of thermal gradients, 13,14 electromigration is also useful for this purpose because the direction of transport can be easily controlled, i.e., the direction of mass transport is along the ow of electrons, the electron wind force. It should be noted that an entire nano-object can be moved through the use of electromigration, while only atoms/ions move with macroscopic electromigration.…”

“…The development of methods for mass transport at the nanoscale is important; 12 in addition to the utilization of thermal gradients, 13,14 electromigration is also useful for this purpose because the direction of transport can be easily controlled, i.e. , the direction of mass transport is along the flow of electrons, the electron wind force.…”