Lithographic positioning, areal density increase and fluid transport in rolled-up nanotubes

We study the formation process of rolled-up InAs/GaAs nanotubes (RUNTs) as a function of etching time and sacrificial layer thickness for tube diameters between 20 and 560 nm. Within this diameter range the roll-up velocity strongly depends on the sacrificial layer thickness but is independent of the tube diameter. We also find that the roll-up distance saturates with etching time for distances around 8-16 mum. Since we define the starting edge of the roll-up process by optical lithography, we are able to position individual RUNTs on a substrate surface with reasonable accuracy. We also show that the areal density of the tubes on a surface can be doubled if a two-fold stack of strained bilayers is selectively underetched. Finally, we record organic fluid transport within a RUNT in real time and we report intense red light emission from such filled-up nanotubes. (C) 2004 Elsevier B.V. All rights reserved.