Filling Fraction Dependent Properties of Inverse Opal Metallic Photonic Crystals

Abstract

Metallic photonic crystals, metal-based structures with periodicities on the scale of the wavelength of light, have attracted considerable attention due to the potential for new properties, including the possibility of a complete photonic bandgap with reduced structural constraints compared to purely dielectric photonic crystals, [1] unique optical absorption, thermally stimulated emission behavior, [2,3] and interesting plasmonic physics.[4]Photonic applications may include high-efficiency light sources, [5] chemical detection, [6] and photovoltaic energy conversion. [3] Other applications for 3D porous metals, so-called "metal foams", include acoustic damping, high strength to weight structures, catalytic materials, and battery electrodes.[7]The photonic properties of metallic inverse opal structures have been of significant interest because of the simplicity of fabrication and potential for large-area structures. However, in practice, experiments on metal inverse opals have been inconclusive, [8][9][10] presumably because of structural inhomogeneities due to synthetic limitations. In this work, we demonstrate an electrochemical approach for fabricating high-quality metal inverse opals with complete control over sample thickness, surface topography, and, for the first time, the structural openness (metal filling fraction (FF)). Optical measurements conclusively demonstrate that metal inverse opals modulate the absorption and thermal emission of the metal and that these effects only become 3D in nature at high degrees of structural openness. Various metals, for example, Au, Ag, W, Pt, Pd, Co, Ni, and Zn, [10][11][12][13][14] have been formed into inverse opals. Here, Ni is selected because of its high reflectivity in the IR, temperature stability, and ease of electrochemical processing. Ni inverse opals are fabricated by using electrodeposition through a polystyrene (PS) opal template that was first deposited on a surface-treated Au film evaporated on a Si wafer. PS opals formed from microspheres ranging in diameter from 460 nm to 2.2 lm were used as templates; this paper focuses on metal inverse opals formed using 2.2 lm microspheres. Templated electrodeposition is observed in all systems; this range of microsphere diameters is not an upper or lower limit. The final thickness of the sample is regulated by controlling the total charge. After electrodeposition, the PS microspheres are removed with tetrahydrofuran, resulting in a Ni inverse opal. Although the electrodeposition is quite homogeneous, gradual thickness variations do occur over the sample surface. These variations turn out to be useful, as they generate regions of different number of layers and surface terminations over the same sample (Fig. 1)

Three-dimensional self-assembled photonic crystals with high temperature stability for thermal emission modification

“…Periodic structuring of materials on the order of the wavelength of light is one approach to spectrally alter emissivity [13][14][15][16][17] . Both two- 10,16,17 and three-dimensional (3D) architectures [13][14][15] can enhance or suppress thermal emission in desired frequency regimes yielding a spectral emissivity that can be more efficiently converted to electricity using a single-junction PV cell.…”

“…Both two- 10,16,17 and three-dimensional (3D) architectures [13][14][15] can enhance or suppress thermal emission in desired frequency regimes yielding a spectral emissivity that can be more efficiently converted to electricity using a single-junction PV cell. 3D photonic crystals [18][19][20] are attractive because they may provide control of emissivity in all directions relative to the emitter, as well as more degrees of freedom for the design of structures with desired emission properties [12][13][14]21 .…”

Optimized nanoporous materials.

“…Upon sintering, the contact area is enlarged due to necking; the contacted areas form the windows between spherical pores in the inverted structure. By controlling the degree of sintering or by electropolishing the inverted Ni structure, [135] the size of the interconnecting windows can be adjusted to enhance mass transport during electrodeposition, etching, atomic layer deposition, and other subsequent procedures. A scanning electron microscope (SEM) image of a Ni inverse opal is shown in Figure 6-4.…”

Periodic order and defects in Ni-based inverse opal-like crystals on the mesoscopic and atomic scale

“…Filling the voids in these opal-like structures with ferromagnetic metals, such as Ni, Co, and Fe, and removing the colloidal particles allows the fabrication of inverse opals possessing tunable magneto-optical properties [1][2][3][4][5][6][7]. An artificial magnetic anisotropy on a mesoscale can also make such inverse opal-like crystals (IOLCs) a unique test bench for the study of unusual magnetic phenomena.…”