Influence of interfaces on the transport properties of graphite revealed by nanometer thickness reduction

Abstract

We investigated the influence of thickness reduction on the transport properties of graphite microflakes. Using oxygen plasma etching we decreased the thickness of highly oriented pyrolytic graphite (HOPG) microflakes from ∼ 100 nm to ∼ 20 nm systematically. Keeping current and voltage electrodes intact, the electrical resistance R(T ), the magnetoresistance (MR) and Raman spectra were measured in every individual sample and after each etching step of a few nm. The results show that R(T ) and MR can increase or decrease with the sample thickness in a non-systematic way. The results indicate that HOPG samples are inhomogeneous materials, in agreement with scanning transmission electron microscopy images and X-ray diffraction data. Our results further indicate that the quantum oscillations in the MR are not an intrinsic property of the ideal graphite structure but their origin is related to internal conducting interfaces.

Diamagnetism of Bulk Graphite Revised

“…The galvanomagnetic results obtained for samples of different thickness indicate that a highly conducting path in graphite samples is localized at the 2D interfaces [12][13][14]18], which upon twist angle [10] or stacking order [19,20], can even show 2D superconducting properties [15,[21][22][23]. The origin of the SdH oscillations in the electrical resistance is related to the 2D interfaces, as recent detailed electrical measurements clearly revealed [14].…”

“…Experimental evidence obtained in graphite bulk samples and thin flakes over the last 10 years reveals that the observed thickness dependence of the magneto-electric properties of graphite has its origin in the internal microstructure of the samples [10,[12][13][14]. In particular, scanning transmission electron microscopy (STEM) studies (as an example, see Figure 1) reveal the existence of two-dimensional (2D) interfaces between regions with different stacking order and/or between regions with similar stacking order, but twisted around a common c-axis [10].…”

Anomalous low-temperature saturation effects and negative thermal expansion in the c-axis of highly oriented pyrolytic graphite at the magic angle

“…The recent discoveries of superconductivity in pure highly oriented pyrolytic graphite (HOPG) materials [1][2][3][4][5][6][7][8][9][10], water doped graphite [3] and twisted bilayer graphene [11] have attracted a significant attention in the fields of condensed matter physics and materials science. Formation of such granular superconductive features has been attributed to the existence of rotational misfits between the graphene layers in Bernal graphite systems and to possible formation of rhombohedral phases in interfacial contact with the hexagonal one.…”

Magnetic vortex and unsaturated magnetization components in highly oriented pyrolytic graphite

“…Understanding the origin of magnetic ordering in pure carbon-based graphitic materials has recently become a crucial focus of research towards translation of these systems into technological applications. Graphite is a layered material with hexagonal symmetry (space group P6 3 /mmc) characterized by delocalized π-electrons along the graphene layers and Van der Waals forces in between (layers) [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]. The stacking between graphene layers and the layer orientation have been shown to play a crucial role towards modifications of band gap and energy dispersion relation characteristics of these materials.…”

“…The stacking between graphene layers and the layer orientation have been shown to play a crucial role towards modifications of band gap and energy dispersion relation characteristics of these materials. In particular, formation of unusual superconductive features in bilayer graphene and highly oriented pyrolytic graphite (HOPG) has been recently reported for specific rotational angle, known as magic angle of rotation [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17]. Presence of sequential stacking consisting of Bernal and rhombohedral phases has been also acknowledged as one of the possible factors governing such high temperature superconductive effects [4].…”