As chips further shrink toward smaller scales, fabrication processes based on the self-assembly of individual particles into patterns or structures are often sought. One of the most popular techniques for two-dimensional assembly (self-assembled monolayers) is based on capillary forces acting on particles placed at a liquid interface. Capillarity-induced clustering, however, has several limitations: it applies to relatively large (radius > Ϸ10 m) particles only, the clustering is usually non-defect-free and lacks long-range order, and the lattice spacing cannot be adjusted. The goal of the present article is to show that these shortcomings can be addressed by using an external electric field normal to the interface. The resulting self-assembly is capable of controlling the lattice spacing statically or dynamically, forming virtually defect-free monolayers, and manipulating a broad range of particle sizes and types including nanoparticles and electrically neutral particles.nterparticle force-driven self-assembly processes are often used to form materials with desired micro-and nanostructures (1, 2). In these processes, the forces, such as intermolecular or capillary forces, bring the particles together and cause them to arrange locally according to a pattern that depends on the orientational nature of these forces (1-5). Many envisioned applications of nanotechnology and fabrication of mesoscopic objects strongly rely on the manufacturing of such micro-and nanostructured materials (6-8). Future progress in this area will critically depend on our ability to accurately control the particle arrangement (e.g., lattice spacing, defect-free capability, and long-range order) in three dimensions (3D) and in two dimensions (2D) for a broad range of particle sizes, shapes, and types. Such a control in 2D will lead to the manufacture of controlled monolayers or ultrafine porous membranes with adjustable, but regular, pore sizes, and therefore with adaptable mechanical, thermal, electrical, and/or optical properties (e.g., controlled nanofluidic drug delivery patches with adjustable mass transfer properties across the patch, nanofilters for protein separation based on their sizes, electronic nanocircuits with improved performance in absence of defects, photonic devices, etc.).A popular mean used to assemble particles is based on the phenomenon of capillarity (3-5, 9-15). A common example of capillarity-driven self-assembly is the clustering of cereal flakes floating on the surface of milk. The floating cereal particles experience attractive capillary forces, because when two such particles are close to each other, the deformed interface around them is not symmetric because the interface height between the particles is lowered owing to the interfacial tension (9-15). This lowering of the interface between the particles gives rise to lateral forces that cause them to come together. Capillarityinduced clustering has several deficiencies: (i) the resulting particle structure is usually not defect-free: defects take place because...
