Detection of subsurface defects and measurement of thickness of screen layers made of graphene and carbon nanotubes with application of full-field optical coherence tomography in Linnik configuration

Optical coherence tomography (OCT) is noncontact and nondestructive interferometric method which allows visualization of internal structure of an investigated sample. Till now it has found many applications in measurements of biological tissues, technical materials and conservation of art. Optical coherence tomography in full-field configuration is a great technique for visualization of subsurface structures of measured sample with high resolution. In this technique, en-face data acquisition is applied, which allows application of microscope objectives with high numerical aperture while the depth of field is not a problem. These objectives allow obtaining ultra high transverse resolution like in traditional microscopy. Additionally, light sources with broad spectrum, like low cost incandescent lamps (i.e. halogen lamp), allow measurements with micrometer scaleaxial resolution. In this paper the authors present application of full-field optical coherence tomography with a Linnik microscope for the thickness measurement of layers in flexible display with electrodes made of graphene and carbone nanotubes. Thicknesses of layer have a huge impact on the display parameters. There is a correlation between the thickness of the graphene layer and its electrical resistance. Graphene is a new and very promising material which is durable, flexible and has a good adhesion to diverse substrates. It gives a theoretical possibility to create flexible electronics, such as graphene bendable screens. Using OCT we can evaluate the quality of printed layers and detect subsurface defects.