Ellipsometric microscope: novel method for direct visualization of molecularly thin liquid films

In a magnetic disk drive, a molecularly thin film is currently used as a lubricant and controlling its kinetic behaviors is a key technology to design the head disk interface. Direct visualization of molecularly thin lubricant films is useful in investigating the kinetic properties. We demonstrated that the real time visualization is possible by using the ellipsometric microscope with a laser light source and white light source. Laser light source provides the narrow band and high intensity light. However, the SNR of the image was limited by noises due to the optical interference and the improvement of the SNR was needed for a thickness resolution of sub-nm. In this paper, we explained that the noises due to the optical interference can be reduced by using a white light source with lower coherence. In addition, combination of image processing techniques can provides a higher SNR. Subtracting an original image from the contrast-reversal image obtained by rotating the polarizer setting, weak contrasts can be enhanced and noise intensity reduced. The achieved SNR for a 3.2-nm PFPE film image is 61.4. This result indicates that the white light source-based and digitally enhanced ellipsometric microscope can provide the real time visualization of molecularly thin liquid films with a sub-nm thickness resolution