In this work, a hybrid n-diamond-carbon nanowalls structure was synthesized on a 100 mm diameter silicon wafer using RF-PECVD (CCP type). This structure was analyzed by transmission microscopy, electron microscopy and X-ray diffraction. It was found that the addition of carbon monoxide (CO) to a gas mixture of methane (CH4), argon (Ar), and hydrogen (H2) leads to the formation of n-diamond nanocrystals in the basal layer. Using plasma surface treatment techniques, the carbon nanowalls were fully removed and the lower layer consisting of n-diamond was studied separately, for which X-ray diffraction results of a separate n-diamond phase were obtained for the first time.