Hexagonally closed packed monolayers of colloids have found more and more applications, e.g. as lithographic masks. The monolayers are usually produced with the help of a self-organizing process where a suspension of colloids is applied to the desired substrate and left to dry. This method requires a good wettability and smoothness of the substrate, which severely limits the number of possible substrates. We present a new method for the application of colloid monolayers to almost any surface where these difficulties are circumvented. At first the monolayers are fabricated on glass substrates and afterwards floated off on a water surface. From there, they are transferred to the desired substrate. Examples where transferred monolayers were used as lithographic masks are shown on glass, indium tin oxide, and tungsten diselenide. The transfer of a colloid monolayer to a copper grid for transmission electron microscopy demonstrates the applicability of the technique to curved surfaces as well.
Monolayers of colloidal particles formed in a self-organizingpmcess upon dryingof a colloidal suspension arc used as lithographic masks. After deposition of a thin metal layer, the mask is detached from the surface. The resulting surface is examined with optical, scanning electron, and atomic force microscopes. In addition to the well-known triangular structures, which reflect the gaps in the hexagonal arrangement of the particles, we observed the following additional features: hillocks (nano-dots) found just below and nano-rings found around the original location of the particles. These features m a y develop during detachment (hillocks) and formation (rings) of the mask, respectively. Hillocks develop as a consequence of the adhesion of the particles on the surface, whereas rings are formed h m organic residuals in the suspension. We show that these features can be used to fabricate fluorescent dye rings of submicron size.
Structures with a lateral size of ≈ 100 nm have been created using a new replication method based on the demixing of a ternary polymer mixture during spin‐coating. The technique, which relies on the interfacial wetting of one of the polymer components at the interface of the other two, produces structures (see Figure) that are significantly smaller than the lateral dimensions of the substrate prepattern.
We study the evaporation behavior of regular arrays of volatile droplets on a solid substrate. We observe that under certain conditions the droplets do not evaporate independently of each other but in a cooperative manner. This results in the development of a superlattice which is explained in terms of matter exchange between adjacent droplets. PACS numbers: 64.70.Fx, 05.70.Ln, 64.70.Rh When bulk mixtures are rapidly quenched below their critical point (e.g., by lowering the temperature) phase separation occurs which leads to an isotropic, disordered morphology of the coexisting phases. This process is initiated by the formation of small nuclei in a supersaturated solution. When approaching local equilibrium, larger supercritical droplets grow at the expense of smaller ones thus causing the first peak in the structure factor to be shifted to smaller values. The latter is also known as Ostwald ripening or coarsening [1] and is experimentally observed in many systems like fluid mixtures, binary metal alloys [2], polymers [3], and colloidal systems [4].Lifshitz, Slyosov, and, independently, Wagner (LSW) [5,6] pointed out that for small degrees of supersaturation, when the density of nucleated droplets is small, a singledroplet picture can be used to describe the late stage growth of the condensate in an infinite system. Even at small supersaturations, however, many experiments of initially disordered droplets show that the late-stage droplet distribution is broader and more symmetric than predicted by LSW [7]. In order to understand this behavior, it has been suggested that additional interactions between the droplets have to be taken into account [7][8][9].Lacasta et al.[10] investigated theoretically the kinetics and pattern formation emerging during the evaporation of periodically arranged droplets. Based on numerical solutions of the Cahn-Hilliard equation they found that initial equal-sized droplets of a volatile liquid which are arranged in a quasi-one-dimensional (1D) system with open (absorbing) boundaries do not evaporate independently of each other, but in a cooperative process by matter exchange through the gas phase. This leads to the remarkable effect that rows of droplets which are farther away from the absorbing boundary may evaporate earlier than those at the boundary's vicinity. The effect is explained in terms of a complex interplay of matter loss through the boundary and its redistribution between droplets.Here we report the first experimental observation of such a cooperative droplet evaporation. Our results show that under appropriate geometrical constraints a periodic array of initially equal-sized droplets decays into a twodimensional (2D) regular superlattice where every second droplet disappears by evaporation. This phenomenon is also observed in 2D numerical solutions of the CahnHilliard equation, which were carried out in addition.Surfaces with well-defined adsorption sites for droplets were obtained by microcontactprinting (mCP) of alkanethiols. Since there is a vast amount of literat...
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