Stop-band structure in complementary three-dimensional opal-based photonic crystals

Abstract

The stop-band width and angular dispersion have been traced by angle-resolved reflectance spectroscopy for two opposite configurations of opal-based photonic crystals where either the silica balls possess a higher refractive index than the voids or vice versa. It has been demonstrated that filling the empty voids of opal with a material of higher refractive index than silica results in widening of the stop-band and squeezing of its dispersion, thus improving the stop-band of the opal grating towards the omnidirectional photonic band-gap situation.

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“…Preparation of the silica microsphere suspension 25 mg of the silica beads were suspended in 1.5 ml of a 1.67610 23 M sodium dodecylsulfate (Aldrich, 98%) solution in chloroform/ethanol (80/20 v/v). Prior to spreading, the suspension was ultrasonicated for at least half an hour.…”

“…15,17 A promising basic structure for the preparation of PBG materials is synthetic opal. [21][22][23][24][25] Ideally, it consists of an array of monodisperse SiO 2 spheres ordered into a face centred cubic (fcc) packing. The fcc structure can be envisaged as an ABC stacking of layers with a 2D hexagonal close-packing (hcp) of spheres.…”

“…26 Usually, synthetic opal is prepared by sedimentation of SiO 2 spheres in a dilute colloidal suspension. [21][22][23][24][25] Here we explore Langmuir-Blodgett deposition as a method for the preparation of large area 2D synthetic opal as a basis for the preparation of advanced optical materials. This approach can be envisaged as a first step in a controlled, layer-by-layer procedure for the preparation of large area synthetic opal.…”

Infiltration of silica colloidal crystals with molten salts and semiconductors under capillary forces

“…A few authors reported the use of melts of metals [17,18], semiconductors [19][20][21], salts [22], and organic materials [23] for opal pore filling. The infiltration with non-wetting melts (contact angle  > 90 • ) is carried out under an external hydrostatic pressure (Pb [17], Ga [18], Te [19], and InSb [20]) to overcome the negative capillary pressure ( P < 0) that tends to reject a fluid from pores [24].…”

“…This means that colloidal crystal pores can be infiltrated with melts by using the techniques similar to those using solutions. Wetting low-melting substances (sulphur [21], sodium nitrite [22], and sodium nitrate [22]) were infiltrated into pores of bulk opals. Low-melting sugar (ribose) was introduced into an opal film pores under the action of capillary forces [23].…”