α-Fe₂O₃ and ε-Fe₂O₃ thin-film hematite polymorphs, as well as Fe₂O₃ polymorphs’ thin films coated with TiO₂ nanolayer, all deposited on Si substrate plates, were investigated by an open photoacoustic cell set-up within the 20 Hz–20 kHz modulation frequency range. Theoretical analysis of experimental results was based on a two-layer model which includes both substrate and thin-film parameters. For different combinations of the substrate and polymorphic layer, noticeable differences in the total photoacoustic signals are observed at high-frequency range (> 1 kHz), mainly due to elastic bending effect. It was also observed that an ultra-thin TiO₂ surface layer deposited on polymorphs influences the signal of the whole structure, which is attributed to the changed quality of sample surfaces. Presented experimental results and theoretical analysis demonstrate the suitability of open PA cell technique to determine thermal parameters of thin two-layer materials and detect minute differences in their structures originating either from the native structure of the material or from the deposition of ultra-thin coatings. High reproducibility of the photoacoustic measurements and good agreement with values reported in literature and with previous experiments were found.

中文翻译：

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开放光声电池对纳米结构Fe 2 O 3多晶型物和TiO 2包覆的Fe 2 O 3的热和弹性表征

α -Fe ₂ O ₃和ε -Fe ₂ O ₃薄膜赤铁矿多晶型物，以及涂覆有TiO _2的Fe ₂ O ₃多晶型物薄膜通过在20 Hz–20 kHz调制频率范围内的开放式光声电池装置研究了全部沉积在Si基板上的纳米层。对实验结果的理论分析是基于两层模型，其中包括衬底和薄膜参数。对于衬底和多晶型层的不同组合，主要是由于弹性弯曲效应，在高频范围（> 1 kHz）上观察到了总光声信号的明显差异。还观察到超薄TiO ₂沉积在多晶型物上的表面层会影响整个结构的信号，这归因于样品表面质量的变化。提出的实验结果和理论分析表明，开放式PA电池技术适用于确定薄两层材料的热参数，并检测其结构的微小差异，这些差异源自材料的固有结构或超薄涂层的沉积。发现光声测量的高再现性，并且与文献中报道的值和先前的实验有很好的一致性。