Nov 8, 2011
Expanded EBID technique writes capping layer protected iron nanostructures
The focused electron beam of a scanning electron microscope is an excellent tool for nanolithography. For example, in electron-beam-induced deposition (EBID), precursor molecules adsorbed on the surface are locally decomposed by the impact of the electron beam, leaving a deposit of the non-volatile dissociation products. To picture the technique, you can imagine the electron beam as a pen and the precursor molecules as ink. In a collaborative effort, researchers from laboratories in Germany and the US have considerably expanded this EBID writing method by successively using two different precursors: in the first EBID step, a clean iron line was generated and in a second EBID step this line was capped with an ultra-thin titanium oxide layer, as shown in the image below.
Even though the capping layer had a thickness of only ~3 nm, it effectively protects the iron structure underneath from oxidation under ambient conditions, as confirmed by photoelectron microscopy. In this way, the lithographic fabrication of layered nanostructures has been realized, with significant potential for future applications.
More specifically, the EBID team from Erlangen can perform the EBID under well defined and clean conditions; that is, in an ultra high vacuum (UHV) environment. With this unique approach, the group was recently able to overcome existing limitations concerning the purity of EBID nanostructures and fabricated pure iron deposits from the precursor iron pentacarbonyl, Fe(CO)5.
Safeguarding the structure
In order to further characterize the electronic and magnetic properties of these iron nanostructures, they have to be removed from the UHV chamber, leading to oxidation of the iron and to changes in its physical properties. The newly established process enables the metallic iron nanostructure to be protected with a titanium oxide capping layer, grown with the precursor titanium isopropoxide (TTIP). The effectiveness of this 3 nm thick cap was verified using X-ray photoelectron microscopy at BESSY II in Berlin.
From a more general point of view, the stepwise application of two or more precursors in EBID opens up a novel pathway for tailoring the fabrication of nanostructures. For example, the assembly of functional multilayer components for use in nanoelectronic applications, which might consist of magnetic, conducting, semiconducting and/or insulating materials.
The researchers presented their work in the journal Nanotechnology.
About the author
Hubertus Marbach, PhD, is leader of the independent research group "Microscopy and Nanolithography" at the University of Erlangen, Germany. One of his main projects is to explore and further develop focused electron-beam-induced processing techniques for the fabrication of nanostructures.