Identification of exfoliated monolayer hexagonal boron nitride films with a digital color camera under white light illumination

Optical microscopy with white light illumination has been employed when obtaining exfoliated monolayer hexagonal boron nitride (1L hBN) films from a large number of randomly placed films on a substrate. However, real-time observation of 1L hBN using a color camera under white light illumination remains challenging since hBN is transparent in the visible wavelength range. The poor optical constant of 1L hBN films in microphotographs is significantly improved using a Si substrate coated with a SiN<i>_x</i>thin-film (SiN<i>_x</i>/Si). When observing hBN thin films on SiN<i>_x</i>/Si using a color digital camera in an optical microscope under white light illumination, the clarity of the captured color images depends on the thickness of the SiN<i>_x</i>film (<i>d</i>). For real-time direct observation, the<i>d</i>was optimized based on quantitative chromatic studies tailored to Bayer filters of a color image sensor. Through image simulation, it was determined that the color difference between 1L hBN and the bare substrate is maximized at<i>d</i>= 59 or 70 nm, which was experimentally verified. The SiN<i>_x</i>/Si with optimized<i>d</i>values visualized 1L hBN films without requiring significant contrast enhancement via image processing under white light illumination in real-time. Furthermore, the captured color photographs facilitate the reliable determination of the number of layers in few-layer hBN films using the contrast of the green channel of the images.