Szwachta Grzegorz, Białek Ewelina, Włodarski Maksymilian, Norek Małgorzata
Institute of Materials Science and Engineering, Faculty of Advanced Technologies and Chemistry, Military University of Technology, Str. Gen Sylwestra Kaliskiego 2, 00-908 Warsaw, Poland.
Institute of Optoelectronics, Military University of Technology, Str. Gen. Sylwestra Kaliskiego 2, 00-908 Warsaw, Poland.
Nanotechnology. 2022 Aug 23;33(45). doi: 10.1088/1361-6528/ac83ca.
Porous anodic alumina (PAA) photonic crystals with a photonic stop-band (PSB) placed in the mid-infrared (MIR) spectral region represent a promising approach for increasing of gas sensors sensitivity. An onion-like layered distribution of anionic impurities is a hallmark of PAA, and its presence is generally considered to demarcate the boundary between transparent and opaque ranges in the infrared spectral region. Here, we study the effect of annealing in the temperature range of 450 °C-1 100 °C on the structural stability and optical properties in photonic crystals based on PAA fabricated by pulse anodization in oxalic acid. Pulse sequences were selected in a way to obtain photonic crystals of different periodic structures with a PSB located in visible and MIR spectral regions. The first photonic crystal was composed of layers with gradually changing porosity, whereas the second photonic crystal consisted of a sequentially repeated double-layer unit with an abrupt change in porosity. We investigated the response of alumina with rationally designed porosities and different arrangements of porous layers for high-temperature treatment. The microstructure (scanning electron microscopy), phase composition (x-ray diffraction), and optical properties (optical spectroscopy) were analysed to track possible changes after annealing. Both photonic crystals demonstrated an excellent structural stability after 24 h annealing up to 950 °C. At the same time, the evaporation of the anionic impurities from PAA walls caused a shift of the PSB towards the shorter wavelengths. Furthermore, the annealing at 1 100 °C induced a high transparency (up to 90%) of alumina in MIR spectral region. It was shown thus that properly selected electrochemical and annealing conditions enable the fabrication of porous photonic crystals with the high transparency spanning the spectral range up to around 10m.
具有位于中红外（MIR）光谱区域的光子禁带（PSB）的多孔阳极氧化铝（PAA）光子晶体是提高气体传感器灵敏度的一种有前途的方法。阴离子杂质的洋葱状分层分布是PAA的一个标志，其存在通常被认为划分了红外光谱区域中透明和不透明范围之间的边界。在此，我们研究了在450℃-1100℃温度范围内退火对基于草酸脉冲阳极氧化制备的PAA光子晶体的结构稳定性和光学性质的影响。选择脉冲序列以获得具有位于可见光和MIR光谱区域的PSB的不同周期性结构的光子晶体。第一个光子晶体由孔隙率逐渐变化的层组成，而第二个光子晶体由孔隙率突然变化的顺序重复双层单元组成。我们研究了具有合理设计的孔隙率和不同多孔层排列的氧化铝对高温处理的响应。分析了微观结构（扫描电子显微镜）、相组成（X射线衍射）和光学性质（光谱学）以追踪退火后可能的变化。两种光子晶体在高达950℃的24小时退火后都表现出优异的结构稳定性。同时，PAA壁上阴离子杂质的蒸发导致PSB向较短波长移动。此外，在1100℃退火导致氧化铝在MIR光谱区域具有高透明度（高达90%）。因此表明，适当选择电化学和退火条件能够制造出在高达约10μm光谱范围内具有高透明度的多孔光子晶体。
