ABSTRACT Granular nanocrystalline Bi2(Se1-xTex)3 films were prepared from highly crystalline bulk alloys used as source materials by means of thermal evaporation under vacuum (2 × 10−6 mbar). The nanofilms were deposited onto highly cleaned glass substrates of BK7 type. The structural characteristics, including surface morphology, roughness, and crystallite size, were studied by X-ray diffraction (XRD), atomic force microscopy (AFM), and transmission electron microscopy (TEM) analysis. Perfect crystallinity and nanoscalability of the prepared samples were asserted. Transmittance and reflectance spectra of the prepared nanofilms were investigated over the wavelength range of 400–2,700 nm. In the visible light region, all of the films showed an opaque behavior; however, as the wavelength increased into the infrared region, a growing transparency was observed. Based on the measured transmission and reflection spectra, the coefficients of absorbance and extinction as well as the optical band gap were determined. The refractive index was deduced from the reflectance measurements using the determined extinction coefficient. Direct allowed band transitions were confirmed in all films with a band gap energy of 0.85–1.05 eV, depending on the Te content. The possibility of an indirect band gap in the lower photon energy region was discussed. The Seebeck coefficient and electrical conductivity were measured in the temperature range of 300–500 K. Very large values of the power factor of 80 and 131 were obtained for Be2Se3 films at room temperature and 473 K, respectively; the latter is three times larger than best previously reported values for similar film systems.

中文翻译：

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纳米晶Bi2(Se1-xTex)3薄膜的光学和热电性能

摘要 颗粒状纳米晶 Bi2(Se1-xTex)3 薄膜是通过在真空（2 × 10−6 mbar）下热蒸发的方法由用作源材料的高结晶体合金制备的。纳米膜沉积在高度清洁的 BK7 型玻璃基板上。通过 X 射线衍射 (XRD)、原子力显微镜 (AFM) 和透射电子显微镜 (TEM) 分析研究了结构特征，包括表面形貌、粗糙度和微晶尺寸。所制备的样品具有完美的结晶度和纳米级可扩展性。在 400-2,700 nm 的波长范围内研究了制备的纳米膜的透射率和反射率光谱。在可见光区，所有的薄膜都表现出不透明的行为；然而，随着波长增加到红外区域，观察到越来越透明。根据测量的透射和反射光谱，确定吸光度和消光系数以及光学带隙。使用确定的消光系数从反射测量中推导出折射率。直接允许的能带跃迁在所有带隙能量为 0.85-1.05 eV 的薄膜中得到证实，具体取决于 Te 含量。讨论了较低光子能量区域中间接带隙的可能性。在 300-500 K 的温度范围内测量了塞贝克系数和电导率。 Be2Se3 薄膜在室温和 473 K 下分别获得了 80 和 131 的非常大的功率因数值；后者是类似薄膜系统先前报告的最佳值的三倍。根据测量的透射和反射光谱，确定吸光度和消光系数以及光学带隙。使用确定的消光系数从反射测量中推导出折射率。直接允许的能带跃迁在所有带隙能量为 0.85-1.05 eV 的薄膜中得到证实，具体取决于 Te 含量。讨论了较低光子能量区域中间接带隙的可能性。在 300-500 K 的温度范围内测量了塞贝克系数和电导率。 Be2Se3 薄膜在室温和 473 K 下分别获得了 80 和 131 的非常大的功率因数值；后者是类似薄膜系统先前报告的最佳值的三倍。根据测量的透射和反射光谱，确定吸光度和消光系数以及光学带隙。使用确定的消光系数从反射测量中推导出折射率。直接允许的能带跃迁在所有带隙能量为 0.85-1.05 eV 的薄膜中得到证实，具体取决于 Te 含量。讨论了较低光子能量区域中间接带隙的可能性。在 300-500 K 的温度范围内测量了塞贝克系数和电导率。 Be2Se3 薄膜在室温和 473 K 下分别获得了 80 和 131 的非常大的功率因数值；后者是类似薄膜系统先前报告的最佳值的三倍。