TiO_2 Inverse Opals Fabricated Using Low-Temperature Atomic Layer Deposition

摘要

We report the low-temperature fabrication of TiO_2 inverse shell opals using ALD. Self-assembled 200 to 440 nm sized silica opals were infiltrated using conventional precursors at 100 ℃, annealed for 2 h at 400 ℃, and inverted using HE The shifts in the Γ-L PBG position and width were confirmed by specular reflectance and transmission spectros-copy, revealing behavior consistent with photonic-band calculations. The peak positions indicate that filling terminated at ～88% of the pore volume, as estimated from the modified Bragg equation, supporting the theoretical prediction that maximum filling for a shell opal is 86%. SEM and AFM analysis revealed ultra-smooth (RMS roughness of < 0.5 nm), highly conformal anatase films as a result of the combination of low-temperature deposition with a short heat treatment. In addition, precise infiltration control (< 1 nm) was achieved with this technique, making the fine-tuning of photonic crystal properties a reality. The success of this work shows that precisely controlling the placement of dielectric materials is possible using ALD, enabling the fabrication of many of the "optimized" structures that have been predicted to have the best optical properties. The digital nature of ALD growth has been demonstrated to allow angstrom-scale fine-tuning of complex structures, and since it can be used to deposit metals, insulators, and semiconductors, many different structures can be fabricated.