Structural, Raman and photoluminescence studies on nanocrystalline diamond films: Effects of ammonia in feedstock

TL;DR

This study investigates how varying ammonia in the feedstock affects the structural, Raman, and photoluminescent properties of nanocrystalline diamond films, revealing optimal doping conditions for enhanced emission.

Contribution

It provides new insights into the effects of nitrogen doping levels on nanocrystalline diamond film properties and identifies optimal conditions for improved photoluminescence.

Findings

Crystallite size varies with N/C ratio, initially increasing then decreasing.

Raman peak shifts indicate increasing lattice strain up to N/C 0.50.

Enhanced PL emission at specific N/C ratios due to N-related defect centers.

Abstract

Herein, we report on the improvement of structural quality and enhancement of photoluminescence (PL) emission for an optimally N doped nanocrystalline diamond (NCD) film. Pure and N doped nanocrystalline diamond films are synthesized on Si by hot filament chemical vapour deposition using NH3:CH4:H2 at different nominal N/C ratios viz. 0, 0.13, 0.35, 0.50 and 0.75 in feedstock. X ray diffraction analysis reveal a systematic initial increase and then a decrease in crystallite size with N/C ratio in feedstock. Further, a monotonic increase in Raman line width and peak position of diamond band indicates that the compressive strain in diamond lattice increases as a function of N/C ratio upto 0.50. However, at higher N/C ratio of 0.75, the compressive strain gets relaxed a little and produces a lower strain. Furthermore, a unique Raman mode at 1195 cm-1 is observed corresponding to the C=N-H vibrations indicating a significant N concentration in the NCD films. In addition, visible and UV PL studies reveal the presence of several N related color centres with multiple emission lines in the range of 380 to 700 nm. An optimally N doped diamond film grown at N/C ratio of 0.35 in feedstock shows a significant enhancement in room temperature PL emission at about 505 and 700 nm. This PL enhancement is attributed to H3 and other aggregates of N related defect centres, under 355 and 532 nm laser excitations respectively.