Structural characterisation of crystalline carbon nitride thin films synthesised by electrolysis of urea–methanol solution

Abstract

Polycrystalline carbon nitride thin films were deposited on Si(400) and ITO coated glass substrates by electrolysis of methanol–urea solution under high voltage, at atmospheric pressure and at temperatures below 350 K. Fourier transform infrared spectroscopy (FTIR) measurements of the films deposited on Si suggested the existence of single, double and triple carbon–nitrogen bonds in the films. A maximum N/C atomic ratio of 0·81 was achieved in the films as measured by C/H/N analysis. X-ray diffraction spectra of the films grown with different urea concentrations showed various peaks for different d values, which could be assigned to different crystalline carbon nitride phases. Selected area electron diffraction patterns measured by transmission electron microscopy (TEM) showed a number of concentric sharp rings, corresponding to various planes of theoretically predicted β-C3N4 phase. Scanning electron microscopy (SEM) images of the films indicated the existence of grains, the number density and size of which were dependent on the solute concentration. Optical transmission measurements of the films on ITO coated glass substrates revealed a band gap value of around 2·87 eV for direct transition. The hardness of the films on Si substrates was as high as 28 GPa.