Changes of thickness and refractive index of silica sol-gel film by dip coating process

The porous sol-gel silica film was prepared on silicon substrate by the dip coating process. Coating thickness and refractive index were measured by ellipsometry method. Influence of withdrawal speed and concentration of silica was investigated for the thickness and refractive index of silica. The relation of the thickness and withdrawal speed was fitted by the linear and power functions, and the results were analyzed and compared. It was found that the film thickness increased with the withdrawal speed for the same colloid concentration. Linear relation between film thickness and withdrawal speed was better than power function relation for describing the experiment data. The refractive index of the film decreased with the withdrawal speed. For the same thickness, the refractive index of the film increased with the concentration of silica. The experimental results indicated that the thickness and refractive index of the film can be controlled by changing the withdrawal speed and concentration of silica.