Experimental investigations on the structure and transport properties of amorphous and nano-crystalline carbon nitride

Abstract

In this chapter, we summarize our results and present concluding remarks on our investigations. Key findings on amorphous carbon nitride are followed by results on crystalline carbon nitride. Carbon and its allotropes display remarkable material properties, and attempts to dope them with heteroatoms have broadened our understanding.

Amorphous Carbon Nitride Preparation: Amorphous carbon nitride films were prepared by pyrolysis-assisted CVD of pyrrole.

Microstructure: Films are completely amorphous (no long-range order) with significant C-N bonding.

Nitrogen Content: Films contain 2-6 at.% nitrogen, varying with preparation temperature and annealing time.

Structural Evolution: Higher pyrolysis temperatures and longer annealing times drive graphitic clustering due to nitrogen loss.

Mechanism: Pyrrole’s five-membered ring with nitrogen at the apex promotes ring cleavage, forming a carbon nitride network at high temperatures.

Key Findings:

Pyrolysis-assisted CVD is a simple and effective method for preparing amorphous carbon nitride.

Pyrrole is an ideal precursor for stoichiometric compounds.

Nitrogen escapes at high temperatures, influencing clustering and microstructure.

Magnetotransport Studies Films prepared at lower temperatures exhibit higher disorder.

At ~3 K, conduction shows crossover from Mott to Efros-Shklovskii variable range hopping.

Negative magnetoresistance observed across all samples in the critical regime, explained by weak localization in disordered structures.

Nitrogen acts as a scatterer, dominating conduction processes.

Nitrogen-Induced Metal-Insulator Transition Pure amorphous carbon behaves metallic at high temperatures.

Nitrogen incorporation pushes the system into the critical regime, away from metallic behaviour.

This transition can be exploited to probe criticality in detail.

Electrochemical etching demonstrated as a viable method to pattern a-CNx films; samples on n-Si showed rectification properties.

Nanocrystalline Carbon Nitride Under flash evaporation, nanocrystals of carbon nitride form alongside amorphous phases.

Powder XRD confirmed graphitic-like carbon nitride structures.

Simulated diffraction patterns matched experimental data.

Key Findings:

Evidence of crystalline carbon nitride formation in nanophase.

Flash evaporation responsible for nucleation.

Pyrrole bond enthalpy favours ring opening and network formation.

Future Perspectives Magnetotransport studies down to millikelvin temperatures could provide deeper insights into conduction mechanisms.

Nitrogen-induced metal-insulator transitions are promising for probing critical regimes.

Other heterocyclic precursors should be explored beyond pyrrole.

Isolation of nanocrystalline carbon nitride (e.g., by selective removal of amorphous phases using water) would enable advanced characterization (XPS, TEM, SAED).

Synchrotron-based diffraction with shorter wavelengths could resolve the correct crystal structure.