Jul 9, 2009
What causes nanopillars to bend?
Electron-beam induced deposition (EBID) is a nanofabrication technique capable of directly writing arbitrary 3D structures with a variety of materials. EBID was discovered in the 1930s soon after fabrication of the first electron microscopes, and for a long time was treated as a nuisance as it caused contamination of samples during imaging. It is known to be a result of the decomposition of surface-adsorbed organic molecules that are usually present in the microscope's vacuum chamber.
Lately, it has been recognized that EBID can be used to fabricate nanoscale free-standing structures for applications in scanning probe microscopy, field emission and for nanoscale electronics. However, a set of problems is often encountered in the deposition of closely spaced structures. In particular, when free-standing pillars are grown it is observed that a new growth process often causes bending of previously grown pillars. There is currently no clear understanding of the mechanism of this proximity effect.
In a recent study, which was published in Nanotechnology, researchers at Bath University, UK, have performed a number of experiments demonstrating that the bending arises not during growth but during electron microscopy imaging of the grown pillars. They also found that this effect cannot be attributed to electrostatic interactions between the pillars during growth, as was previously thought. Instead they suggest a mechanism based on structural changes in the grown pillars caused by secondary electrons that are produced during the after-growth imaging. The authors analyse experimental conditions that would prevent bending of deposited structures.
About the author
Dan Burbridge is currently writing up a PhD at the University of Bath, in applications of electron-beam-induced deposition. Dr Sergey Gordeev is a senior lecturer in the Department of Physics with research interests in areas of nanofabrication and scanning probe microscopy.