Dr. Daria Szewczyk 1

Talk: "Graphitization and Size Effects on Low-Temperature Heat Capacity of Carbon Allotropes: Insights from Nanodiamonds and Microdiamonds"

Co-workers: O. Romantsova1,2, A. Jeżowski1, A.I. Krivchikov1,2, P. Klimczyk3
1 W. Trzebiatowski Institute of Low Temperature and Structure Research, PAS, Wrocław, Poland
2 B. Verkin Institute for Low Temperature Physics and Engineering, NASU, Kharkov, Ukraine
3 Sieć Badawcza Łukasiewicz – Krakowski Instytut Technologiczny, Kraków, Poland

We conduct a detailed study of the low-temperature heat capacity (1.9–50 K) across a variety of diamond samples. The investigation encompasses detonated nanodiamonds annealed at 1000°C, 1600°C, and 2000°C; nanodiamonds synthesized under pressures ranging from 1 GPa to 5 GPa; and larger microdiamonds produced via spark plasma sintering, subjected to annealing temperatures between 1400°C and 1900°C, with an unaltered room-temperature sample included as a reference. Our results demonstrate that graphitization significantly impacts the specific heat of the diamonds. Notable size-dependent effects are observed, alongside a novel phenomenon manifesting as an additional term in the low-temperature heat capacity, which correlates with the extent of graphitization. This phenomenon is explored in depth concerning sample size (micro versus nano), annealing temperatures, and sintering pressures. Finally, we compare our findings with data from a pure graphene sample, serving as a benchmarkd.

Acknowledgements: The research was supported by the Polish National Science Center (Grant No. 2022/45/B/ST3/02326).