Structural Changes in N, P, and Si-Doped Few-Layer Graphite Fragments at Spark Plasma Sintering and Plasma Treatment

Abstract—Nitrogen, phosphorous, and silicon-doped few-layer graphite fragments (FGFs) are synthesized by pyrolyzing acetonitrile, triphenylphosphine, and tetramethylsilane, using a MgO template. The N, P, and Si-FGFs are consolidated using spark plasma sintering (SPS) at 1100°С and 30 MPa and also treated with the high-frequency induction discharge plasma. The materials are studied using transmission electron microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy. After the SPS treatment, the samples of N, P, and Si-FGFs are transformed into nonuniform materials with complex morphology, containing substantially lower amounts of heteroatoms compared to nonsintered samples. It is shown that the pressure applied during the SPS plays a less significant role as compared to the resistive heating. The latter induces a plasma breakdown, thus facilitating phase transitions. The treatment of N, P, and Si-FGFs with high-frequency induction discharge plasma facilitates their transformation into N-doped bulbous carbon structures (BCSs) ~10 nm in diameter, and amorphous P and Si-doped carbon.