•Carbon nanoflake films (CNFFs) were synthesized by PEHFCVD.•The structure of CNFFs is related to the aggregation of carbon hydrocarbon radicals.•The PL intensity of CNFFs is lowered with the thickness increase of CNFFs.•The change of PL intensity of CNFFs is due to the dangling bonds in CNFFs.•The widening of PL bands of CNFFs results from the diversity of carbon nanofalkes.Carbon nanoflake films (CNFFs) were directly synthesized by plasma-enhanced hot filament chemical vapor deposition. The results of field emission scanning electron microscope, transmission electron microscope, micro-Raman spectroscope, X-ray photoelectron spectroscope and Fourier transform infrared spectroscope indicate that the CNFFs are composed of bending carbon nanoflakes with the hydrocarbon and hydroxyl functional groups, and the carbon nanoflakes become thin in a long deposition time. The structural change of carbon nanoflakes is related to the formation of structural units and the aggregation of hydrocarbon radicals near the carbon nanoflakes. Moreover, the photoluminescence (PL) properties of CNFFs were studied in a Ramalog system and a PL spectroscope. The PL results indicate that the PL intensity of CNFFs is lowered with the increase of thickness of CNFFs. The lowering of PL intensity for the thick CNFFs originates from the effect of more dangling bonds in the CNFFs. In addition, we studied the structural difference of carbon nanoflakes grown by different CVD systems and the PL difference of carbon nanoflakes in different measurement systems. The results achieved here are important to control the growth and structure of graphene-based materials and fabricate the optoelectronic devices related to carbon-based materials.

•The carbon nanosheets (CNSs) were synthesized on different Si surfaces by HFCVD.•A new formation mechanism of CNSs was suggested.•The photoluminescence (PL) of CNSs was studied.•The PL of CNSs is different with graphene sheets.•The PL properties of CNSs were interpreted by the interband transition.Carbon nanowalls (CNWs) were grown on different Si substrates by hot filament chemical vapor deposition, where CH4 was used as the reactive gas. The structure and composition of synthesized CNWs were studied using a field emission scanning electron microscope, a transmission electron microscope, a micro-Raman spectroscope, and an X-ray photoelectron spectroscope. The results indicate that the thick CNWs can be well grown on the Si substrate deposited with carbon nanodots while the thin CNWs are formed on the mirror-polished Si substrate. Beginning with the nucleation of carbon, the formation of CNWs with different structures was studied. The photoluminescence (PL) of CNWs on the two Si substrates was studied using a photoluminescence spectroscope, in which the 325 nm line of He–Cd laser was used as the irradiation source. The PL spectra show the two strong blue and green PL peaks centered at about 442 and 549 nm and a weak red PL peak centered at about 657 nm and the intensity of every PL peak of thin CNWs is stronger than that of thick CNWs. According to the interband transition mechanism of carbon materials, the PL properties of CNWs were analyzed. The outcomes of this study are significant to control the structure of CNWs and contribute to the development of next optoelectronic devices.