We probe the local and global structure of spin-coated colloidal crystals via laser diffraction measurements and scanning electron and atomic force microscopies, and find that they are unique three-dimensional orientationally correlated polycrystals, exhibiting short-range positional order but long-range radial orientational correlations, reminiscent of-but distinct from-two-dimensional colloidal hexatic phases. Thickness and symmetries are controllable by solvent choice and spin speed. While the polycrystallinity of these colloidal films limits their applicability to photonics, we demonstrate their feasibility as templates to make crack-free magnetic patterns. DOI: 10.1103/PhysRevE.77.050402 PACS number͑s͒: 82.70.Dd, 64.70.pv, 64.75.Yz The self-assembly of colloidal microspheres has been used to address the fundamental questions of how materials crystallize ͓1-6͔ or fail to crystallize ͓7-9͔. Micrometer-scale colloidal crystals can be used as a template that, using further processing methods, can be used to create photonic materials ͓10-12͔, optical sensors ͓13͔, and antireflection coatings ͓14͔. However, the high density of missing-sphere defects and cracks in photonic crystals produced via self-assembly ͓15͔ remains a serious limitation, and thus the study of colloidal defects ͓16͔ is an active area of research. Spin-coating of colloidal suspensions is the quickest and most reproducible method to make large-area colloidal crystals. While spin-coating has been proposed to fabricate single crystals for photonic applications ͓17,18͔, the symmetric radial optical interference patterns observed are unexpected for single crystals. We find here that spin-coated colloidal films are indeed neither single crystals nor powder polycrystals, but are in fact a unique polycrystal phase. While true singledomain sizes are ϳ10 m, there is orientational correlation on the centimeter scale. Our results demonstrate a novel crystal packing strategy by which long-range orientational order develops in the absence of long-range positional order, reminiscent of two-dimensional colloidal hexatic phases ͓19,20͔, and leading to crack-free crystals. Distinct from colloidal hexatic phases, our polycrystals exhibit centimeterscale orientational order, which arises due to the spinning axis and can be produced with fourfold, sixfold, or mixed symmetries for a range of thicknesses as a function of spin speed. The electrodeposition of magnetic material through colloidal polycrystals demonstrates their feasibility for material templating applications.The standard technique to make large-area close-packed crystals is controlled ͑vertical͒ drying, utilizing capillary forces ͓21-23͔ to direct self-assembly. Other external shear ͓24͔, electric ͓25͔, electrohydrodynamic ͓26,27͔, and gravitational forces ͓28͔ have also been used. Making dried colloidal crystals with these methods is slow, taking from hours to days. Spin-coating has been shown to be a robust technique ͓17,18,29,30͔ to make large-area colloidal crystals in minutes. In this work, we ...

Colloidal crystals of polystyrene particles of 1.0, 1.4 and 2.8 μm diameter have been prepared by vertical deposition. The influence of parameters such as temperature, particle size and concentration as well as dispersion medium has been studied. The size of domain and the crystalline structure of the particle arrays have been analyzed by optical microscopy. The quality of the crystals has been improved (minimizing cracks) by controlling sedimentation (density matching), evaporation (volatility of the medium) and drying (co-solvents).