Direct Visualization of Molecularly Thin Lubricant Films Using Low-Coherence Phase-Shifting Interferometry

We have developed a method utilizing low-coherence phase-shifting interferometry (LCPSI) to directly visualize molecularly thin lubricant films coated on diamond-like carbon (DLC) surfaces. The measurement accuracy is guaranteed by the use of a low-coherence light source, a feedback-controlled phase-shifting system, and an image subtraction method. By measuring nanometer-thick perfluoropolyether films coated on DLC surfaces, we demonstrated that the LCPSI is capable of providing real-time three-dimensional measurements at a sub-nanometer thickness resolution and a spatial resolution of several micrometers.