采用椭偏法结合分光光度法研究极薄银的光学常数

极薄银在滤光片、高反射镜等中有广泛的应用，其光学常数严重影响着膜系的特性。在室温条件下，采用电阻热蒸发技术分别在硅和玻璃基底上沉积5.3 nm~26 nm不同厚度的极薄银薄膜，用TalySurfCCI非接触式轮廓仪测量了薄膜的厚度，研究了不同厚度银薄膜的光学常数n和k。镀制厚度5.3 nm、7.9 nm、14.1 nm、26.0 nm的银薄膜，结果显示极薄银的光学常数与块状银光学常数不同，当膜厚小于14.1 nm时，折射率n在380 nm~600 nm随波长增加而增加，在600 nm~1 600 nm随波长增加缓慢减小至趋于稳定值2.6；消光系数k在380 nm~500 nm随着波长增加而增加，在500 nm~1 600 nm随波长增加而缓慢减小至趋于0不变；当膜厚大于14.1 nm时，折射率随波长增加而增加，消光系数随波长近似呈线性增加。整体上，膜厚增加时折射率减小且趋于块状银的折射率，k随厚度增加而增加并最终趋于块状膜。用此拟合的光学常数代入TFc膜系设计软件计算其透射率，发现与分光光度计测得的透射率吻合较好。

Optical constants of ultra-thin silver films obtained by ellipsometry and spectrophotometer

The ultra-thin silver films have been widely used in filters, high reflectivity mirror, and etc. The optical constants of ultra-thin silver films have severe impact on the characteristics of films. In order to investigate the optical constants of ultra-thin silver films, a series of different thickness silver films between 5.3 nm~26 nm were deposited on Si and glass substrates by thermal evaporation at room temperature, the thicknesses were measured by TalySurfCCI non-contact surface profiler, the optical constants n and k were measured by ellipsometer. Respectively, the thicknesses of ultra-thin silver films were 5.3 nm, 7.9 nm, 14.1 nm, 26.0 nm. The results show that the optical constants of ultra-thin silver are different from bulk silver. For the thickness of less than 14.1 nm, the refractive index n increases with the wavelength increasing from 380 nm to 600 nm, and decreases slowly then tends to a stable value with the wavelength increasing from 600 nm to 1 600 nm, while the extinction coefficient k increases with the wavelength increasing from 380 nm to 500 nm, then, slows down, tends to 0 and unchanged. When the film thickness is greater than 14.1 nm, the refractive index increases with increasing wavelength, and the extinction coefficient increases linearly with the wavelength.In generally, the refractive index decreases when the film thickness increases and tends to be that of bulk material, while the extinction coefficient k increases following the increase of thickness and tends to the bulk silver in the end. The optical constants fitted by this method were substituted into the TFc film system design software, and the transmittance was calculated. It is found to be in good agreement with the transmittance measured by the spectrophotometer.