Nagendra C L, Lamb J L
Appl Opt. 1995 Jul 1;34(19):3702-10. doi: 10.1364/AO.34.003702.
Germanium:silver (Ge:Ag) composite thin films having different concentrations of Ag, ranging from 7% to 40%, have been prepared by dc cosputtering of Ge and Ag. The films' surface morphology and optical properties have been characterized using transmission electron microscopy and infrared spectrophotometry. It is seen that, although the films that contain lower concentrations of Ag have islandlike morphology (i.e., Ag particles distributed in a Ge matrix), the higher metallic concentration films tend to have a symmetric distribution of Ag and Ge. The optical constants (i.e., refractive index n and absorption index k) derived from the measured optical properties show a semiconductor behavior even as high as 40% of Ag concentration, beyond which the metallic properties dominate over the entire infrared spectrum. Comparison of the n and k data with the two well-known effective medium theories, namely, the Maxwell-Garnett theory and the Bruggeman theory, shows that both theories have limited scope in predicting the optical properties of semiconductor-metal composite films in the infrared region. However, an empirical polynomial equation can simulate the experimental data at all wave numbers of the IR spectrum.
通过锗（Ge）和银（Ag）的直流共溅射制备了银含量从7%到40%不等的锗银（Ge:Ag）复合薄膜。利用透射电子显微镜和红外分光光度法对薄膜的表面形态和光学性质进行了表征。可以看出，尽管银含量较低的薄膜具有岛状形态（即银颗粒分布在锗基体中），但金属浓度较高的薄膜往往具有银和锗的对称分布。从测量的光学性质得出的光学常数（即折射率n和吸收指数k）即使在银浓度高达40%时仍表现出半导体行为，超过该浓度后，金属性质在整个红外光谱范围内占主导地位。将n和k数据与两种著名的有效介质理论，即麦克斯韦-加内特理论和布鲁格曼理论进行比较，结果表明这两种理论在预测红外区域半导体-金属复合薄膜的光学性质方面都有局限性。然而，一个经验多项式方程可以模拟红外光谱所有波数下的实验数据。
