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Scanning tunneling microscopy identification of van Hove singularities and negative thermal expansion in highly oriented pyrolytic graphite with hexagonal moiré superlattices

Boi, Filippo S., Taallah, Ayoub, Gao, Shuai, Guo, Jian, Wang, Shanling, Corrias, Anna (2021) Scanning tunneling microscopy identification of van Hove singularities and negative thermal expansion in highly oriented pyrolytic graphite with hexagonal moiré superlattices. Carbon Trends, 3 . Article Number 100034. ISSN 2667-0569. (doi:10.1016/j.cartre.2021.100034) (KAR id:85921)

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https://doi.org/10.1016/j.cartre.2021.100034

Abstract

We report a novel investigation on the structural, electronic and magnetic properties of highly-oriented-pyrolytic-graphite (HOPG) by employing STM/S, TEM and SQUID. Van Hove singularities (vHs) were identified by STS-acquisition of local-density-of-states spectra (LDOS) acquired from moiré-superlattice-periodicities D ∼0.5 nm (θ rot ∼28.6°), ∼2 nm (θ rot of ∼7.08°) and ∼ 4 nm (θ rot ∼3.6°). A possible interlayer-coupling- or moiré-thickness-induced variation of the vHs-separation-parameter was identified. Investigation of the spatial-distribution of the moiré-superlattices by exfoliation revealed also D ∼13.87 nm (θ rot ∼1.02°), ∼13.0 nm (θ rot ∼1.09°), ∼12.65 nm (θ rot ∼1.12°) and ∼2.03 nm (θ rot ∼7.0°). These observations were further supported by additional LDOS spectra acquired on HOPG from moiré-superlattice-periodicities D ∼8 nm (θ rot ∼1.8°). In the latter, the unusual presence of four vHs peaks evidenced the existence of multiple rotational effects between internal sublattices. Extended analyses were further performed by T-XRD from 12K to 298K. Unknown peak-features exhibiting unusual T-dependent shifts were analysed at 2θ ∼ 21° (Fig. 6A-C) and ∼ 43 ° (Fig. 6D). ZFC and FC-signals from the exfoliated lamellae further evidenced an anisotropic ferromagnetic behaviour, possibly involving the coexistence of 1) disorder induced percolative ferromagnetism and 2) additional magnetic components arising from the locally twisted sublattices, which were found to exhibit the moiré superlattices.

Item Type: Article
DOI/Identification number: 10.1016/j.cartre.2021.100034
Uncontrolled keywords: HOPG, Graphite, van Hove singularity, Hexagonal Superlattice, Negative thermal, Expansion, Spin-glass-like behaviour
Subjects: Q Science > QD Chemistry
Divisions: Divisions > Division of Natural Sciences > School of Physical Sciences
Depositing User: Anna Corrias
Date Deposited: 08 Feb 2021 12:23 UTC
Last Modified: 16 Feb 2021 14:18 UTC
Resource URI: https://kar.kent.ac.uk/id/eprint/85921 (The current URI for this page, for reference purposes)
Corrias, Anna: https://orcid.org/0000-0002-5190-8196
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