Nanostructured surfaces: challenges and frontiers in nanotechnology

Nanostructured surfaces can be broadly defined as substrates in which the typical features have dimensions in the range 1-100 nm (although the upper limit of 100 nm may be relaxed to greater sizes in some cases, depending on the material and the specific property being investigated). The recent surge of interest in these systems stems from the remarkable effects that may arise from the critical size reduction. Interesting novel properties (catalytic, magnetic, ferroelectric, mechanical, optical and electronic) occur as we reduce the dimensions from a practically infinite (and periodic) solid crystal to a system composed of a relatively small number of atoms. So far, nanostructured materials or nanomaterials are perhaps the only sub-field of nanoscience that has made the transition from fundamental science to real world applications, thus becoming a technology (a good example of this are nanostructured surface coatings). This paper describes some selected examples of recent progress in the study of nanostructured surfaces. Surface reconstructions, which occur either naturally or as a consequence of the interaction with adsorbates, are discussed because of their importance in model chemical reactions and for their potential use as templates for the ordered growth of nanostructures. Supramolecular assemblies and molecular nanostructures, resulting from the balance between molecule-molecule and molecule-surface interactions, are described because of their fundamental interest and their potential use in nanoelectronic devices. Recent progress in the growth of semiconductor nanostructures, in particular Ge-Si and InAs-GaAs, is briefly reviewed. A few selected examples of nanostructured functional materials, such as ferroelectric and magnetic nanostructures, are discussed in view of their potential for applications in future data storage devices. Nanostructured materials used in catalysis and gas sensor applications are briefly described. Finally, perspectives and future challenges in this emerging field of research are also discussed.