Direct Laser Writing and CVD Combined for Fabrication of 3D Photonic Metamaterials
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The researchers have observed that doping an LC cell with a small amount of polyhedral oligomeric silsequioxane (POSS) nanoparticles induced spontaneous vertical alignment without the need for conven-
tional alignment layers. In the July issue of Optics Letters (DOI: 10.1364/OL.33.001663; p. 1663), the researchers described the application of the NIVA technique to fabricate a GH-LCD with normally white char-
acteristics and also made a plastic timepiece. The experimental display medium incorporated 5 wt% aminoethyl-aminopropylisobutyl-POSS nanoparticles along with 5 wt% dichroic dye into negative
Direct Laser Writing and CVD Combined for Fabrication of 3D Photonic Metamaterials Photonic metamaterials are artificial structures with unusual properties that might lead to quantum levitation, optical cloaking, and lenses for subwavelength imaging. While natural materials at optical frequencies have a magnetic permeability (μ) of unity, metamaterials present researchers with the ability to tune μ to arbitrary values, for example, μ < 0. Usual building blocks of this materials class (typically periodic structures) are split ring resonators (SRRs), which effectively act as “magnetic atoms” with local magnetic dipole moments. Although most photonic metamaterials have been fabricated with two-dimensional techniques—electron-beam lithography and physical evaporation of metal films— and stacking the functional layers, a genuinely three-dimensional (3D) fabrication process is preferable. Toward this end, M.S. Rill and colleagues at the Institut für Angewandte Physik, Universität Karlsruhe (TH), Germany, and S. Linden and colleagues at the Institut für Nano tech nologie, Forschungszentrum Karlsruhe in der Helmholtz-Gemeinschaft, Ger many, have combined direct laser writing (DLW) and silver chemical vapor deposition (CVD) to fabricate a planar test
Figure 1. Oblique view of an arrangement of bars fabricated by direct laser writing and silver chemical vapor deposition after it was cut by a focused-ion beam to disclose the interior. The scanning electron micrograph (SEM) shows the potential of the presented technique to fabricate three-dimensional metallic nanostructures. Note that the silver layer covers the bars all around.
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structure composed of elongated SRRs. The researchers found that optical characterization of their structure is in good agreement with theory. Additionally, they fabricated a structure composed of bars, which was metallized uniformly around the structure even in 3D (see Figure 1). As reported in the July issue of Nature Materials (DOI 10.1038/nmat2197; p. 543), the researchers made a template from a glass substrate covered with a 2-μm thick polymerized resist film (SU-8). Onto this film, a second SU-8 film was spun, exposing it using DLW, baking, and developing. A thin SiO2 coating (several dozen nanometers thick), which provides the SU-8 backbone with mechanical stability and chemical protection, was then applied by using atomic layer deposition. CVD of Ag was then performed using the metal–organic
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