Self-organization of nano-lines and dots triggered by a local mechanical stimulus

Abstract

When a local mechanical perturbation is applied to the surface of a thin film of a mechanically interlocked molecule (a rotaxane), the molecules self-organize into periodic arrays of discrete dots or lines. The dimensionality of the nanostructures depends on whether the mechanical stimulus acts along a 1D line or over a 2D area. The size (50 -500 nm) and periodicity (100 -600 nm) of the patterns are controlled solely by the film thickness. This selforganization at the mesoscopic scale occurs via a nucleationripening mechanism eased by the relatively low energy barriers of the intramolecular rearrangement introduced by the mechanical bond. The phenomenon can be exploited as a bottom-up nanofabrication method.bottom-up fabrication ͉ dynamics ͉ rotaxanes ͉ surfaces B ottom-up fabrication requires a hierarchical organization of materials that starts at the molecular level and reaches extended, mesoscopic-length scales. A substantial measure of supramolecular self-organization has already been achieved through specific design and fine-tuning of noncovalent interactions. A variety of supramolecular objects of nanometer size and low dimensionality, such as spheres (1), wires (2), stripes (3), rods (4), toroids (5), and dendrimers (6) have so far been produced. However, self-organization of size-defined objects greater than tens or, more rarely, hundreds of molecules represents a formidable challenge in technologically relevant environments such as surfaces or thin films. On the other hand, a host of organization phenomena at interfaces exhibit spatial correlations across several orders of spatial length scales. Examples are self-affine growth (7), wetting͞dewetting transitions (8), Ostwald ripening (9), spinodal decomposition (10), and breath figures (11). The spatial correlations of these interfacial phenomena, which would be extremely convenient to exploit in fabrication, have diverse origins that range from far-fromequilibrium growth conditions, to the presence of metastability, to the competition between intermolecular and surface interactions. Indeed, if possible, one would want to combine the supramolecular and the interfacial organization to obtain a deterministic assembly, where spatial correlations exist from a few molecular objects to mesoscopic constructs.Our aim was to find suitable molecular systems that would not stay steadily ''anchored'' to a surface but, instead, upon an external stimulus, would change the pattern of interactions, thereby providing the input for long-scale reorganization. This is the case of rotaxane thin films that self-organize into patterns of dots upon a thermal treatment (12).Rotaxanes consist of a macrocycle (molecular ring) mechanically interlocked with a dumbbell (13). Their dynamical properties (14, 15) have heralded them as attractive systems for a number of applications that include molecular switches (16, 17), nanorecording (18), and protection of electroluminescent emitters (19). Earlier, we have shown that films of three rotaxanes, stimulated locally with the tip of an a...

Applications of dewetting in micro and nanotechnology

“…Size and positions emerge in time as characteristic length scales of the transformation. 57 This mechanism has been observed and then controlled on thin films made of rotaxanes. Interlocked molecular systems like rotaxanes and catenanes 58 were of potential interest for switchable surfaces, because the interconversion (a rotation or translation of a molecular ring around or across an axle) in the solid state changes both the intermolecular interactions and the interactions with the surface.…”

“…This event triggers an instability resembling spinodal dewetting along a line, that propagates across larger length scales. 57 The reorganization phenomenon in rotaxane thin films occurs when the AFM tip scans the thin film at a load force just above a threshold force. A string of regularly spaced dots appears along the line.…”

Catenanes and threaded systems: from solution to surfaces

“…This is the case of the thin films of an amide [2]rotaxane prepared by drop casting of a diluted acetone solution onto highly oriented pyrolytic graphite (HOPG). 37 The rotaxane consists of a rod incorporating a N,N-dimethyl fumaramide hydrogen bonding unit encircled by a benzylic amide macrocycle (Fig. 19).…”

Fabrication of Biomimetic Micropatterned Surfaces by Sol–Gel Dewetting

“…When the polymer film is brought below its T g , the pattern is frozen in and preserved . Spatially controlled alignment of the droplets or confinement of the dewetted areas can be induced by external stimuli such as stamp or probe, or by using pre‐patterned substrates …”