Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: High-quality photonic crystals with a nearly complete band gap obtained
  by direct inversion of woodpile templates with titanium dioxide   Photonic crystal materials are based on a periodic modulation of the
dielectric constant on length scales comparable to the wavelength of light.
These materials can exhibit photonic band gaps; frequency regions for which the
propagation of electromagnetic radiation is forbidden due to the depletion of
the density of states. In order to exhibit a full band gap, 3D PCs must present
a threshold refractive index contrast that depends on the crystal structure. In
the case of the so-called woodpile photonic crystals this threshold is
comparably low, approximately 1.9 for the direct structure. Therefore direct or
inverted woodpiles made of high refractive index materials like silicon,
germanium or titanium dioxide are sought after. Here we show that, by combining
multiphoton lithography and atomic layer deposition, we can achieve a direct
inversion of polymer templates into TiO$_{2}$ based photonic crystals. The
obtained structures show remarkable optical properties in the near-infrared
region with almost perfect specular reflectance, a transmission dip close to
the detection limit and a Bragg length comparable to the lattice constant.

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The categories of this paper are: hep-ph
31
The categories of this paper are: ao-sci
19
The categories of this paper are: eess
13
The categories of this paper are: quant-ph
33
The categories of this paper are: plasm-ph
14
The categories of this paper are: math-ph
35
The categories of this paper are: mtrl-th
32
The categories of this paper are: atom-ph
6
The categories of this paper are: astro-ph
7
The categories of this paper are: hep-th
2
The categories of this paper are: math
34
The categories of this paper are: chem-ph
8
The categories of this paper are: hep-ex
11
The categories of this paper are: hep-lat
22
The categories of this paper are: chao-dyn
18
The categories of this paper are: econ