In Situ Observation of Graphene Growth by Chemical Vapor Deposition Using Ultraviolet Reflection: Implications for Efficient Growth Control in the Industrial Process

We demonstrate an in situ optical observation of graphene growth on a Cu substrate during chemical vapor deposition (CVD). An optical reflection microscope with an ultraviolet (UV) light source was mounted on a conventional CVD setup with a hot-wall chamber. The optical reflection of graphene largely changed at wavelengths of around 270 nm, which is attributed to an interband optical transition at the M point in the Brillouin zone of graphene. As a result, the in situ observation in the UV region gives stronger image contrast than that in visible regions. Moreover, the imaging with the UV light source is not influenced by strong thermal radiation in the visible and infrared regions from the hot-wall chamber heated to a growth temperature of around 1050 °C. We also show that the number of graphene layers can be distinguished from the image contrast. This in situ observation captures a series of growth processes from the early stage of graphene domain formation to grain growth and film formation in a single experiment and provides more detailed growth features compared to conventional ex situ evaluations. Our in situ observation method will deepen our understanding of the growth mechanism as well as improve controllability and reproducibility in real time to obtain high-quality graphene, thus making it useful for industrial process.