Methods for patterning solid surfaces are the focus of significant scientific efforts because micropatterned surfaces are important materials for modern technologies, such as microelectronics, optoelectronics, optics, and biological microanalysis.[1] Among the many surface-patterning options, nanosphere lithography [2] is unique in that it uses a self-assembled mask with hexagonal symmetry, consisting of densely packed monodispersed colloidal particles deposited on a substrate by either a Langmuir-type technique [3] or by direct evaporation of the aqueous particle suspension.[4] Non-densely packed 2Dcolloidal crystals also form at air/water or oil/water interfaces. [5] In these cases, charged particles with a hydrophobic surface self-organize into large 2D hexagonal lattices directed by electrostatic repulsion and capillary attraction between neighboring particles. [6] The interparticle spacing in the lattice is adjustable by varying the surface pressure of the film. Such interfacial films would be very attractive for surface patterning if they could be transferred intact from the aqueous interface onto solid substrates. Although densely packed particle films are routinely transferred, the transfer of non-densely packed films, where the particles are not physically touching each other and can easily be moved out of their lattice positions, is yet to be accomplished. We report on a methodology for the transfer of non-densely packed particle films at an air/water interface onto silicon substrates (Scheme 1) and also demonstrate that the transferred particle arrays can be used as an etching mask to generate hexagonal arrays of divot-like holes in the surface of the silicon-wafer substrate. In this work, monodispersed polystyrene latex particles were used with an average diameter of 2.7 lm and a sulfatefunctionalized surface having a charge density of 8.9 lC cm -2 . The particles were suspended in isopropyl alcohol (IPA) and allowed to age for 10 days before use. During this time, the water/particle surface contact angle progressively increased until approaching an asymptote at ca. 84°(see Supporting Information). The high contact angle was critical for irreversible particle attachment to the interface [5] and also strengthens the interparticle repulsion at the aqueous/air interface. [6a,b] After aging in IPA, the particles had readily spread over the air/ water interface with minimal particle flocculation and virtually no loss to the bulk aqueous phase. A continuous nondensely packed hexagonal particle array formed when the particle coverage on the surface approached 1.1 × 10 4 particles mm -2 .Under the pragmatic assumption that strong attractive forces between the substrate surface and the particle surface were necessary for the successful transfer of the interfacial film onto the solid substrate, we modified the surface of the silicon wafer to have a compatible degree of hydrophobicity and an opposite charge to that of the particle surface. This was achieved by treating the silicon wafer with tetradecyldimethy...

A dynamic self-assembling process is reported which involves drying a droplet of positively charged colloidal suspension on a flat negatively charged hydrophilic surface. This extremely simple method affords lines of colloidal particles with regular 1.5-4.5 microm line spacing and smaller than 2 microm line width over a broad surface area. The ordered region diffracts light to display an iridescent appearance and generates first-order diffraction spots when illuminated by a He-Ne laser. A periodic stick-slip motion of the drying liquid front is observed during the drying process using optical microscopy. The periodic motion must be related to the periodic particle deposition. We propose that the simultaneous deposition of the particles at a fixed distance (i.e., the line spacing) behind the previous line of particles where the contact line is pinned is in turn responsible for the periodic stick-slip motion. The key distinguishing feature of the present system is the attractive interaction between the particles and the surface, which instigates the periodicity of the particle deposition.

Hexagonal noncontiguously packed (HNCP) arrays of submicrometer-sized particles trapped at an air-water interface are successfully transferred to solid substrates. The long-range order of the hexagonal arrays at the interface can be improved by compression-relaxation cycles. The interparticle distance (i.e., the periodicity of the hexagonal array) can be controlled by varying the degree of compression of the particle film. The critical characteristics of the substrate surface are hydrophobicity (advancing water contact angle of >70 degrees) and a charge complementary to the surface of the particles. Suitable silicon and glass substrates are easily prepared by treatment with commercially available organosilicon compounds. Two transfer processes have been developed. When the parallel transfer process is used, the HNCP arrays are deposited on the solid substrates with minimal pattern distortion. The vertical dipping transfer distorts the pattern and renders a sense of directionality perpendicular to the dipping direction. This surface patterning technique is applied to fabrication of subwavelength grating for antireflection in the visible region. Antireflective HNCP arrays comprising varied particle diameters and pattern periodicities are fabricated on glass substrates to demonstrate the effects of these parameters on the antireflection performance.