期刊
DIAMOND AND RELATED MATERIALS
卷 121, 期 -, 页码 -出版社
ELSEVIER SCIENCE SA
DOI: 10.1016/j.diamond.2021.108729
关键词
HOPG; Sulfur-doping; Insulator; Metallicity
类别
资金
- NSFC [11950410752]
- National Key R&D Program of China [2017YFA0303600]
- Science Speciality Program of Sichuan University [2020SCUNL210]
- Sichuan University [SCU201208]
- Fundamental Research Funds for the Central Universities [2021SCU12116]
In this study, the electronic and magnetic properties of sulfur-doped highly-oriented-pyrolytic-graphite (HOPG) lamellae were investigated. The sulfur-doping process caused amorphization within hexagonal moire superlattices. Raman spectroscopy analysis revealed a dominant carbon-sulfur band. Temperature dependent electron paramagnetic resonance (T-EPR) showed shifts in the position of the differential absorption feature and anomalous signal broadening. Magnetometry results indicated the absence of superconductive transitions but a critical ferromagnetic temperature. Density functional theory (DFT) calculations showed that sulfur doping affected the system's metallicity.
We report a novel investigation of the electronic and magnetic properties of exfoliated lamellae of highly-oriented-pyrolytic-graphite (HOPG) doped with great excess of sulfur. The sulfur-doping process was achieved through annealing at T similar to 250 degrees C, similar to 500 degrees C and similar to 990 degrees C. The obtained lamellae were investigated by employing transmission electron microscopy (TEM), Raman point/map spectroscopy and temperature dependent electron paramagnetic resonance (T-EPR). HRTEM analyses of samples doped at T similar to 990 degrees C revealed an unusual amorphization-effect arising within hexagonal moire ' superlattices as a consequence of the sulfur-doping. Com-plete amorphization was found at T-500 degrees C. Raman-spectroscopy point/mapping analyses highlighted a dominant carbon-sulfur-band, appearing at Raman-Shifts of 1450 cm(-1). T-EPR of heavily doped samples revealed presence of shifts in the position of the pi-electron differential absorption feature together with an anomalous signal broadening at T-doping similar to 500 degrees C (from g similar to 1.99 to g similar to 2.10), while zero field cooled (ZFC) and field cooled FC superconducting quantum interference device (SQUID) magnetometry from 2 K to 300 K revealed a critical percolative ferromagnetic temperature at T similar to 25 K and the absence of superconductive transitions. Density functional theory (DFT) calculations applied to a Bernal (AB stacked) bilayer-graphene-system in presence of sulfur-bonding revealed a significant variation of the system-metallicity. We highlight the appear-ance of insulating states (E-gap of 0.325 eV) at sulfur concentrations of similar to 1%, which then vanish at similar to 5.5% of sulfur-doping, due to an enhanced degree of system-metallicity and a modification of the pi-bonding-and anti-bonding-signals.
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