Abstract
Amorphous carbon nitride (a-Cx Ny ) thin films were synthesized by plasma-enhanced chemical vapor deposition (PECVD) in a nitrogen–methane radiofrequency (RF) discharge plasma (13.56 MHz) using pulsed plasma modulation. The evolution of the DC self-bias voltage (Vdc) was monitored as an in situ diagnostic parameter to track nanoparticle nucleation, growth, and agglomeration during synthesis. It was found that the absolute value of Vdc decreases monotonically following plasma ignition, and that the onset of nanoparticle agglomeration can be reliably identified from a characteristic change in the Vdc(t) curve, consistent with the three-stage model of dustparticle formation in low-temperature plasma. The agglomeration onset time (tagl) was shown to depend strongly on methane flow rate, working pressure, and RF power: at baseline conditions (0.86 mbar, 20 W), increasing the CH4 flow rate from 2 to 7 sccm reduced tagl from 4.4 s to 200 ms, while pressure and power exhibited dominant and nonmonotonic effects, respectively. These findings guided the selection of plasma-on pulse durations for controlled film growth. Samples deposited under pulsed modulation were characterized by SEM, EDS, FTIR, and XRD, confirming the formation of continuous, nonstoichiometric carbon nitride films dominated by C–N and C=N bonding. The results demonstrate that self-bias voltage monitoring is an effective, accessible method for in situ control of a-Cx Ny nanoparticle growth kinetics and for tailoring film thickness, morphology, and chemical structure via pulsed RF plasma parameters.