Kinetically driven self assembly of highly ordered nanoparticle monolayers

Abstract

When a drop of a colloidal solution of nanoparticles dries on a surface, it leaves behind coffee-stain-like rings of material with lace-like patterns or clumps of particles in the interior. These non-uniform mass distributions are manifestations of far-from-equilibrium effects, such as fluid flows and solvent fluctuations during late-stage drying. However, recently a strikingly different drying regime promising highly uniform, long-range-ordered nanocrystal monolayers has been found. Here we make direct, real-time and real-space observations of nanocrystal self-assembly to reveal the mechanism. We show how the morphology of drop-deposited nanoparticle films is controlled by evaporation kinetics and particle interactions with the liquid-air interface. In the presence of an attractive particle-interface interaction, rapid early-stage evaporation dynamically produces a two-dimensional solution of nanoparticles at the liquid-air interface, from which nanoparticle islands nucleate and grow. This self-assembly mechanism produces monolayers with exceptional long-range ordering that are compact over macroscopic areas, despite the far-from-equilibrium evaporation process. This new drop-drying regime is simple, robust and scalable, is insensitive to the substrate material and topography, and has a strong preference for forming monolayer films. As such, it stands out as an excellent candidate for the fabrication of technologically important ultra thin film materials for sensors, optical devices and magnetic storage media.

Light-Controlled Conductance Switching of Ordered Metal−Molecule−Metal Devices

“…The role of the nanoparticles is to define a highly ordered, two-dimensional template. 33 The molecules in turn, form conductive bridges between the particles. Hence, they offer their specific functional properties, or, more exactly, their switchability, to these nanostructured metamaterials.…”

Pt/CdTe/Pt asymmetric nano-Schottky diodes from colloidal quantum dots

“…After evaporation, suspended particles are left highly concentrated along the original drop edge and leave a ring-shaped structure at rim. [12][13][14][15] The morphology of the dropcasted film is shown in Fig. 2(c) [confocal microscopy image, WI Tec], which indicates the formation of a ring pattern near the contact line due to coffee ring effect.…”

Sequential Tasks Performed by Catalytic Pumps for Colloidal Crystallization

“…These active swimmers and pumps are driven by catalytic reactions on their surface which triggers electrohydrodynamic forces [5,8,. The growth of colloidal crystals with swimmers and pumps is an interesting alternative to the more traditional colloidal self-assembly triggered by external fields [53][54][55][56][57][58][59][60][61][62][63][64][65]. However, artificial active systems have accomplished tasks that are rather simple thus far.…”