Dewetting Process (dewetting + process)

Distribution by Scientific Domains

Selected Abstracts

Contribution to the stability analysis of the dewetted Bridgman growth under microgravity conditions

L. Bizet
Abstract Experimental observations show that the gap between the sample and the crucible, commonly obtained after solidification in microgravity, is remarkably stable. With the aim to understand the reason of this stability, the dewetting phenomenon is studied by Lyapunov's method. After a short review of the existing mechanisms leading to dewetting, the open smooth crucible configuration is chosen as the most representative. The analytical stability analysis, taking into account geometrical and thermal effects, performed under some boundary heat transfer approximations, shows that, in most cases, the dewetting process is intrinsically stable. ( 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Dewetting of an Organic Semiconductor Thin Film Observed in Real-time,

Stefan Kowarik
We study the growth and the post-growth dewetting process of the organic semiconductor diindenoperylene (DIP) using real-time X-ray reflectivity measurements. We show that a DIP monolayer deposited in UHV onto silicon oxide dewets via the formation of bilayer islands. From the time resolved structural data we estimate the rate constant for interlayer diffusion of DIP molecules. Post-growth AFM measurements confirm the conclusions from the X-ray data and show the morphology of the dewetted film. [source]

Self-Assembled, Molecularly Aligned Conjugated Polymer Nanowires via Dewetting

Shion Seng Chang
High aspect-ratio poly(9,9,-dioctylfluorene) (F8) nanowires are fabricated on top of silicon/amorphous Teflon substrates, by dewetting of F8 thin-films. The conjugated nature of the polymers enables the self-assembly of continuous molecularly-aligned nanowires of several micrometers in length and tens of nanometers width, without using a template. The sizescale of the dewetted morphology can be controlled by varying the thickness of the F8 and amorphous Teflon layers. As predicted by van der Waals theory the characteristic sizescale of the dewetted morphology increases with F8 film thickness. However, the dependence of the characteristic sizescale on amorphous Teflon thickness is not accounted for, even qualitatively, by standard spinodal theory with van der Waals forces as the de-stabilizing force across the F8 film. The Rayleigh instability is strongly suppressed in the F8 nanowires in the late stages of dewetting, compared to isotropic, amorphous polymers. Polarized Raman measurements show a systematic increase in molecular alignment along the axis of the nanowires as their width is reduced below the typical liquid-crystalline domain size in polyfluorene films. Thus the dewetting process aligns the polymers, and the aligned polymers suppress the Rayleigh instability and enable the formation of high aspect-ratio continuous nanowires. [source]

Bicolor Pixels from a Single Active Molecular Material by Surface-Tension-Driven Deposition,

I. Viola
The fabrication of a green- and red-emitting pixel structure (see figure, scale bar 10,,m) by the single-step, surface-tension-driven assembly of a single luminescent thiophene-based molecular material is reported. The solid-state organization of the selected thiophene-based oligomer is controlled by exploiting the molecular structural arrangement, induced during a dewetting process and facilitated by the great conformational flexibility of the oligomer, typical of several substituted oligothiophenes. [source]

Aided Self-Assembly of Porphyrin Nanoaggregates into Ring-Shaped Architectures

Marga C. Lensen
Abstract The formation of micrometer-sized, highly ordered porphyrin rings on surfaces has been investigated. The porphyrin-based nanoarchitectures are formed by deposition from evaporating solutions through a surface dewetting process which can be tuned by variations in the substitution pattern of the molecules used, the coating of the surface and the conditions under which the evaporation takes place. Control over the combined self-assembly and surface dewetting results in nanorings possessing a defined internal architecture. The ordering of the molecules within the rings has been studied by a variety of microscopy techniques (TEM, AFM, fluorescence microscopy) and the exact ordering of the porphyrins within the rings has been quantified. [source]