Optical modeling of nanocrystalline TiO2 films.
Optical modeling of nanocrystalline TiO2 films.
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纳米晶 TiO2 薄膜的光学建模。
DOI：
10.1021/jp040178y
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发表时间：
2005
期刊：
影响因子：
--
通讯作者：
H. Ozaki
中科院分区：
文献类型：
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作者：
A. Usami;H. Ozaki
研究了纳米二氧化钛薄膜的透光率T与光波长、纳米晶半径a和薄膜厚度d的关系。实验采用了两种类型的纳米二氧化钛：商品粉末(P25)和异丙醇钛(SP)合成颗粒。X-射线衍射分析表明，P25和SP均以锐钛矿为主，P25和SP的平均晶体尺寸分别为50.3 nm和23.7 nm。尽管P25和SP的微米级薄膜在视觉上存在差异，但用表面镜面反射比校正的光半球透过率具有明显的依赖关系ln(T)=-0.5beta lambda(-4)a(3)d，从可见光到近红外波长的beta=1.5×10(3)。在瑞利散射理论的基础上，用最简单的模型成功地解释了这种相关性和贝塔值。这表明纳米二氧化钛薄膜是一种典型的介质，最简单的散射模型是一个很好的近似。然而，由于不可忽略的内部多次散射，该模型不适用于1.5-3.0微米的较厚的P25薄膜的光散射。对于中等厚度的薄膜，ln(T)与lambda(Gamma)成正比，其中Gamma与薄膜厚度成比例地从-4增加是另一种近似。利用这些光散射模型，成功地从实验消光速率估算了二氧化钛晶体的光吸收速率。
The light transmittance, T, in nanocrystalline TiO2 films was studied as a function of the light wavelength, lambda, the nanocrystal radius, a, and the film thickness, d. Two types of TiO2 nanoparticles were employed: a commercial powder (P25) and synthesized particles from titanium isopropoxide (SP). The X-ray diffraction measurements revealed that both P25 and SP are mainly anatase and the average crystal sizes, 2a, of P25 and SP are 50.3 and 23.7 nm, respectively. Despite the visual difference between micron-order thin films of P25 and SP, the light hemispherical transmittance corrected with the surface specular reflectance has a clear dependence of ln(T) = -0.5beta lambda(-4)a(3)d, with beta = 1.5 x 10(3) from visible to near-infrared wavelengths. The dependence and beta value were successfully explained by the simplest model on the basis of the Rayleigh scattering theory. This indicates that the nanocrystalline TiO2 thin films are a typical medium where the simplest scattering model is a good approximation. However, the model was inapplicable to light scattering in relatively thick P25 films of 1.5-3.0 microm because of nonnegligible internal multiple scattering. For the moderate thickness films, ln(T) proportional to lambda(gamma), where gamma increases from -4 in proportion to the film thickness is an alternative approximation. With these light scattering models, the light absorption rate of the TiO2 crystal was successfully evaluated from experimental extinction rates.