Group-IV 2D materials such as germanene, silicene and stanene have attracted considerable research attention since graphene was first fabricated. Amongst these materials, stanene stands out owing to the unique characteristics it exhibits. Recently done studies have shown that tin forms a buckled honeycomb lattice. Intercalation of various elements into the graphene/silicon carbide interface has been a popular research topic in recent years. Related studies have reported that intercalated silicon forms reconstructions differently from adsorbed silicon on the surface at low silicon coverages. Therefore, by analogy, a similar behavior for tin is expected, since the interface comprises of a confined space and promotes the growth of the two-dimensional structures.
A team of researchers led by professor Satoru Tanaka from the Department of Applied Quantum Physics and Nuclear Engineering at Kyushu University in Japan proposed a study whose main aim was to further cross-examine tin atomic layers that have over the years become popular materials of research interest owing to their spin-related physical properties caused by their strong spin–orbit interactions. Additionally, their main objective was to perform tin intercalation into the graphene/silicon carbide(0001) interface to survey the tin interlayer structure and identify correlations with electronic structures. Their work is now published in the research journal, Applied Physics Express.
The empirical procedure employed commenced by etching the silicon carbide (SiC) substrate using hydrogen gas. Next, the research team introduced the sample into an ultrahigh vacuum chamber and annealed so as to decompose the silicate layer, in order to obtain an adatom silicon (R3) structure. They then prepared a graphene buffer layer, (6R3) in an analogous way. Tin was then supplied on the surface at room temperature until the reflection high-energy electron diffraction pattern became cloudy.
The authors observed that upon annealing of the tin-deposited sample, the low-energy electron diffraction pattern appeared differently from the original one of well-ordered 6R3 of bright and clean superreflexes. The researchers also noted that the graphene spots significantly increased in intensity, suggesting the decoupling of the 6R3 buffer layer induced by the tin intercalation at the 6R3/SiC interface. Moreover, both low-energy- and reflection high-energy electron diffraction revealed clear (1 × 1) reflexes, which were a clear indication of the formation of the (1 × 1)-tin interface structure (Fig. 1(a)). This was also confirmed by other experimental techniques as well as first principles calculations.
The study has presented the intercalation of tin atoms into graphene/SiC interface. It has been seen that the intercalation procedure resulted in decoupling of the 6R3 buffer layer and its transformation into a non-doped freestanding graphene as has been confirmed by angle-resolved photoemission spectroscopy (ARPES) (Fig. 1(b)). Tin atoms have also been observed to occupy on-top sites of silicon-terminated SiC(0001) with in-plane tin–tin bonding, thereby resulting in a triangular lattice (Fig. 1(a)). ARPES indicated evident electronic structures of a tin layer, which were in good agreement with the density functional theory calculations using the VASP code based on the proposed model (Fig. 1(c)). Altogether, the tin triangular lattice atomic layer at the interface has shown no oxidation upon exposure to air, which is useful for characterization and device fabrication ex situ.
Fig. 1. (a) The (1×1) triangular lattice atomic Sn layer formation at graphene/SiC(0001) interface by Sn atoms intercalation. (b) ARPES data of band dispersion near graphene’s K point of Brillouin zone, liner dispersion with Dirac point lying at Fermi level indicate conversion of buffer layer into non-doped graphene layer by Sn intercalation. (c) Characteristic band dispersion of Sn triangular layer exhibits Dirac-cone-like feature near (1×1) cell Brillouin zone K point, indicative that Sn layer could be a Dirac material (line overlay shows calculated data).
Shingo Hayashi, Anton Visikovskiy, Takashi Kajiwara, Takushi Iimori, Tetsuroh Shirasawa, Kan Nakastuji, Toshio Miyamachi, Shuhei Nakashima, Koichiro Yaji, Kazuhiko Mase, Fumio Komori, Satoru Tanaka. Triangular lattice atomic layer of Sn(1 × 1) at graphene/SiC(0001) interface. Applied Physics Express 11, 015202 (2018)
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