Preparation of functionally graded optical filter

介质多层膜用于光通信中的带通滤光片和太阳能电池中的减反射膜。在这些情况下，应该通过平滑界面和减少薄膜中的缺陷来降低光学损耗。在螺旋溅射方法中，可以在低气压下保持高密度等离子体。溅射离子由于长的平均自由通道而保持其动能，这使得人们能够拉长目标-衬底的距离。本工作采用螺旋溅射法制备了二氧化硅/二氧化钛多层膜或鲁格特滤光片。对薄膜的结构和光学性能进行了测试。用等离子体发射光谱仪研究了螺旋波功率的影响.等离子体发射强度随着射频功率的增加而增加，但等离子体密度在100W以上几乎饱和，从而使射频功率固定在100W；二氧化钛薄膜的折射率随着总气压的降低从2.42下降到2.35，而二氧化硅薄膜的折射率保持不变(1.48).二氧化硅和二氧化钛薄膜均为非晶态。设计了反射峰为800 nm的二氧化硅-二氧化钛多层膜。结果表明，多层膜的透过率谱与计算值基本一致。透射电子显微镜观察表明，多层膜界面光滑。

Dielectric multilayres are used for bandpass filters in optical communication and for antireflection coatings in solar cells. In these cases.optical losses should be lowered by smoothing interfaces and reducing defects in films. In a helicon sputtering method, high density plasma can be maintained under a low gas pressure. Sputtering ions keep their kinetic energy due to a long mean-free-pass, which enables one to elongate a target-substrate distance. Therefore less plasma-damaged films having a smooth surface can be obtained.In the present work, silica/titania multilayres or Rugert filter were prepared by helicon sputtering. The structure and optical properties of films were measured. Effect of helicon wave power was studied with a plasma-emission spectrometer.The plasma emission intensity increased with increasing radio frequency (RF) power, but plasma density was almost saturated at more than 100W.Thus the RF power was fixed at 100W.Refractive index of titania film decreased from 2.42 to 2.35 with decreasing total gas pressure, but that of silica film was constant (1.48). Both silica and titania films were amorphous. A silica-titania multilayr whose reflection peak is 800nm was designed. It was confirmed that the multilayr had almost the same transmittance spectrum as that of calculation. A transmission electron micrograph showed that the multilayred films had smooth interface.