SiO2薄膜红外波段介电常数谱的高斯振子模型研究

Gaussian oscillator model of the dielectric constant of SiO_2 thin film in infrared range

在无定形SiO_2非晶材料红外波段反常色散区介电常数研究中,复合高斯振乎模型是介电常数重要的色散模型之一,复合振子中振子的数量和物理意义是重要的研究内容.基于化学计量学中的因子分析技术,提出将SiO_2薄膜特征振动峰的数量等效为化学姐分的振子数量的方法.采用离子束漉射沉积方法制备了厚度分别为100,200,...,800 mn的8种SiO_2薄膜样品,以这8个样品的红外光谱透射率作为光谱矩阵元素.通过因子分析技术确定了400—4000 cm^(-1)波数范围内高斯振子数量为9个,使SiO_2薄膜的介电常数反横计算结果具有明确的物理意义.通过对3000—4000 cm^(-1)波数范围内介电常数的分析,确定了薄膜中具有明显的含水(或择基)化学缺陷,并且这种缺陷影响到整个红外波段内的介电常数.

SiO2 thin film is one of the most important low refractive index materials in the area of optical thin films. It is always used in the design and preparation of many kinds of multilayer films. The dielectric constant of the SiO2 thin film is a key characteristic for design of the multilayer thin film. The composite Gaussian oscillator model is one of the most important dispersion models for the dielectric constant of the amorphous SiO2 in the anomalous dispersion regime in the infrared range. More and more researchers have focused on the number and the physical meaning of the oscillators in the composite oscillator. A method to determine the SiO2 thin film oscillator quantity was proposed. In this method, the quantity of oscillator peaks was equivalent to the oscillator number of chemical composition, based on the factor analysis technology of chemometrics. Concretely, the composite oscillators of the dielectric constant were equivalent to the mixture, and the independent oscillators were equivalent to the compositions of the mixture. The absorbance of the mixture changed with the physical thickness of the thin film. Eight SiO2 film samples with different thickness were prepared on the Si substrate by the ion beam sputtering deposition. The infrared transmittances of the eight samples were used as elements in the spectral matrix. There were nine Gaussian oscillators in the range of 400-4000 cm-1, which was determined by the factor analysis technology. The dielectric constant of the SiO2 thin film in this range was obtained by the inverse calculation from the spectral transmittance. It provides the inverse calculation result for the dielectric constant of the SiO2 thin film with a specific physical meaning. By analyzing the dielectric constant in the range of 400-900 cm-1, the symmetric stretching vibrational frequency and the in-plane rocking frequency of the Si-O-Si bond of the SiO2 thin film can be obtained. Compared with fused silica, the symmetric stretching vibrational frequency increased while the rocking frequency was reduced. In fact, the frequency shifts are caused by the strain of the thin film. By analyzing the dielectric constant in the range of 900-1500 cm-1, four anti-symmetric stretching vibrational frequencies of the Si-O-Si bond in the SiO2 thin film were obtained. They have a certain corresponding relation with the anti-symmetric stretching vibrational frequency of the Si-O-Si bond in the fused silica. What＇s more, by analyzing the dielectric constant in the range of 3000-4000 cm-1, the water-cut （or hydroxyl） chemical defects in the films were confirmed. The chemical defects can influence the dielectric constant in the whole infrared range.