Playing Tetris at the nanoscale

Abstract

The ability to fabricate arrays of functional nanostructures with controlled size, shape and stability, precisely positioned on a substrate of choice, is an ongoing challenge in nanotechnology [1,2]. In this context, the bottom-up approach is emerging as a promising method for the growth and processing of nanostructured materials. This approach is based on the concepts of (organic) self-assembly [3] or (inorganic) selforganization [4] of nanostructures on a suitable substrate [5]. Surface nanotemplates [6], i.e. substrates that are artificially or naturally patterned at the nanoscale, are frequently used to control self-assembly or selforganization processes. Such templates are often able to provide surface cues that may guide the formation of ordered structures, including e.g. tissue regeneration [7]. The 6H-SiC(0001) nanomesh is a particularly interesting template in that it expresses a periodic array of nanopores whose size and spacing can be tailored in the 2–3 nm range [8]. Chen et al. had previously identified this SiC nanomesh as a chemically inert nanoscale template which directs the nucleation and controls the growth of Co clusters during metal vapor deposition, so that a 2D array of Co nanoparticles with relatively uniform spacing and a very narrow size distribution results [8,9]. On page 176 of a recent issue, Chen et al. [10] report the first thorough structural characterization of this 6H-SiC(0001) nanomesh template using complementary surface sensitive techniques. Other recent examples of templates include long-range (e.g. mesoscale) reconstructions [11,12] and step bunching [13], host–guest inclusions formed by metal–organic coordinated networks [14,15] and other types of ‘nanomeshes’ [16]. Despite the widespread use of patterned substrates, the structure and properties of such templates are often poorly understood. Silicon carbide (SiC) is a wide band-gap ( 2.35 eV) semiconductor which has been extensively investigated both for its fundamental interest and for possible applications. This extraordinary IV–IV compound