Larger Polystyrene Spheres Research Articles

Monitoring Photonic Nanojets from Microsphere Arrays by Femtosecond Laser Ablation of Thin Films

By comparing finite-difference time-domain near field simulations and femtosecond laser ablation of thin films, we characterize in three dimensional-space photonic nanojets from microsphere arrays. We demonstrate periodic drilling of transparent films with thickness up to 100 nm (onto absorbing substrates) is feasible with 1-microm diameter silica spheres. Working with larger polystyrene spheres, the apparent increase of the propagation length of the photonic nanojets makes possible to drill films as thick as 500 nm. Interestingly, the lateral width of the produced craters can be maintained below 400 nm evidencing the low divergence of the nanojets. For backside illumination of the arrays, the ablation features are located at the top of the microspheres. We reveal field enhancements in and out the spheres as well as laser energy confinement at the particle substrate interface. The wide variety of features observed in the experiments open routes to fabricating nanomaterials.

Fabrication of TiO2 and Ag wires and arrays using opal polystyrene crystal templates

Monodispersed polystyrene (PS) colloids suspended in an aqueous phase with diameters of 46±2.0 and 903±9nm were employed to deposit opal templates on electrically conductive diamond substrates using a drop-dry method. Ordered close-packed polystyrene opals were produced in the case of the larger PS spheres. In contrast the smaller spheres exhibited a more disordered packing and produced a periodic arrangement of linear voids as a result of the capillary forces operating during the drying process. The PS arrays produced in this way were infiltrated with titania colloidal solution (particle size of 230nm), followed by drying, dissolution of the PS and calcination. This produced inverse opal titania in the anatase phase for the 903nm PS spheres, whereas it is shown that the structure using the smaller PS spheres is dominated by microwire arrays as a result of the linear voids present in the original template. It is shown that electrochemically deposited Ag also adopts a similar microstructure when using this template.

Microscopic observation of ordered colloids in sedimentation equilibrium and the importance of the Debye-screening length. 9. Compressed crystals of giant colloidal spheres (diam. 2?66 ?m)

Compressed crystal-like structures of very large polystyrene spheres (specific gravity=1.05, diameter=2–66 μm) are observed directly by a metallurgical microscope in sedimentation equilibrium and in deionized aquueous and 20 vol % methanol aqueous suspensions. Spheres of 2–42 μm in diameter float above the cover glass apart from each other. The center-to-center intersphere distance decreases as the initial concentration of spheres increases, from which Young's elastic moduli (G) for the crystal-like structures are estimated to be between 1 to 10 dyn/cm2, irrespective of the spheres size.G's in aqueous suspension are smaller than those in methanol aqueous mixtures. The crystal-like structures are compressed substantially by the gravitational field. These results are consistent with the significant role of the electrical double layers under the influence of purely electrostatic repulsive forces in the effective hard-sphere model.

The Assessment of a New Range of Large Monosized Polystyrene Spheres and their Potential as Calibration Material for Particle Size Analysis Equipment

Large polystyrene spheres (nominally 5-, 7-, 10-, and 15-μm diameter) form a new range. The spheres have been sized using a Magiscan Image Analyzer, a scanning electron microscope, and a Coulter counter. Spheres of each nominal size have been found to have a tight size distribution.