Mar 27, 2013
Towards the engineering of molecular nanostructures
The fabrication methods of the microelectronic industry have been improved to produce ever smaller devices, but will soon reach their fundamental limits. A promising strategy to produce even smaller functional systems with nanometre dimensions is the bottom-up fabrication of molecular nanostructures. The ultimate goal is to fabricate functional molecular devices with precise control of both the position and the lateral size of the deposited structure. In this regard, it has been demonstrated that the scanning tunneling microscope (STM) is a powerful tool for investigating molecular nanostructures.
Local anchoring and functionalization
The Marbach group based at the University of Erlangen-Nürnberg, Germany, has explored a concept to locally anchor and/or to functionalize porphyrins as prototype functional molecules on certain surface regions. The basic idea is to create a laterally structured surface, which allows for selective adsorption or local functionalization of the porphyrins. A metal surface, which is partly pre-covered with a chemically different layer (oxide or other metal), is used as a model template.
To prove the general validity of this concept the researchers have chosen two different model template structures, as shown in the figure: copper oxide islands on Cu(111) and nickel islands on Cu(111). Both are preferentially grow in a two dimensional fashion at room temperature (RT).
Tetraphenylporphyrins (TPP) were used as functional molecules because the adsorption and dynamic behavior of TPP on Cu(111) at room temperate shows very specific properties, which can be investigated by STM.
In the study, the researchers observed that the copper oxide/Cu(111) model template is able to steer the adsorption of different TPP molecules: free-base porphyrins (2HTPP) selectively occupy the bare copper substrate areas, whereas metalated porphyrins (CoTPP) are anchored at the rim of the copper oxide islands.
On the other hand, nickel islands on Cu(111) strongly influence the dynamic behaviour of TPP molecules: they are pinned on the nickel areas while they are mobile on the bare copper surface.
Next, the team plans to fabricate templates with predefined shapes for the adsorption of functional molecules on the nanometre scale by the use of focused electron beam induced processing (FEBIP), which enables lithographic control. Here a focused electron beam is applied to locally modify adsorbed precursor molecules or the substrate itself.
The researchers presented their work in the journal Nanotechnology.
About the author
The study was carried out by Stefanie Ditze as a part of her PhD thesis in the group of Hubertus Marbach, who is leader of the independent research group “Microscopy and Nanolithography” at the University of Erlangen-Nürnberg, Germany. One of the main projects of the group is to fabricate tailor-made nanoscaled structures on well defined surfaces.