We investigate the magneto-transport properties of epitaxial graphene single-layer on 4H-SiC(0001), grown by atmospheric pressure graphitization in Ar, followed by H₂ intercalation. We directly demonstrate the importance of saturating the Si dangling bonds at the graphene/SiC(0001) interface to achieve high carrier mobility. Upon successful Si dangling bonds elimination, carrier mobility increases from 3 000 cm²V⁻¹s⁻¹ to >11 000 cm²V⁻¹s⁻¹ at 0.3 K. Additionally, graphene electron concentration tends to decrease from a few 10¹² cm⁻² to less than 10¹² cm⁻². For a typical large (30 × 280 μm²) Hall bar, we report the observation of the integer quantum Hall states at 0.3 K with well developed transversal resistance plateaus at Landau level filling factors of ν = 2, 6, 10, 14… 42 and Shubnikov de Haas oscillation of the longitudinal resistivity observed from about 1 T. In such a device, the Hall state quantization at ν = 2, at 19 T and 0.3 K, can be very robust: the dissipation in electronic transport can stay very low, with the longitudinal resistivity lower than 5 mΩ, for measurement currents as high as 250 μA. This is very promising in the view of an application in metrology.

Two-dimensional (2D) materials have recently been the focus of extensive research. By following a similar trend as graphene, other 2D materials, including transition metal dichalcogenides ($\mathrm{M}{\mathrm{X}}_2$) and metal mono-chalcogenides (MX), show great potential for ultrathin nanoelectronic and optoelectronic devices. Despite the weak nature of interlayer forces in semiconducting MX materials, their electronic properties are highly dependent on the number of layers. Using scanning tunneling microscopy and spectroscopy, we demonstrate the tunability of the quasiparticle energy gap of few-layered gallium selenide (GaSe) directly grown on a bilayer graphene substrate by molecular beam epitaxy. Our results show that the band gap is about 3.50 ± 0.05 eV for single-tetralayer, $3.00\pm 0.05\mathrm{eV}$ for bi-tetralayer, and $2.30\pm 0.05\mathrm{eV}$ for tri-tetralayer GaSe. This band-gap evolution of GaSe, particularly the shift of the valence band with respect to the Fermi level, was confirmed by angle-resolved photoemission spectroscopy (ARPES) measurements and our theoretical calculations. Moreover, we observed a charge transfer in the GaSe/graphene van der Waals (vdW) heterostructure using ARPES. These findings demonstrate the high impact on the GaSe electronic band structure and electronic properties that can be obtained by the control of 2D materials layer thickness and the graphene induced doping.

A promising route towards nanodevice applications relies on the association of graphene and transition metal dichalcogenides with hexagonal boron nitride ($h\text{−}\mathrm{BN}$). Due to its insulating nature, $h\text{−}\mathrm{BN}$ has emerged as a natural substrate and gate dielectric for graphene-based electronic devices. However, some fundamental properties of bulk $h\text{−}\mathrm{BN}$ remain obscure. For example, the band structure and the position of the Fermi level have not been experimentally resolved. Here, we report a direct observation of parabolic dispersions of $h\text{−}\mathrm{BN}$ crystals using high-resolution angle-resolved photoemission spectroscopy (ARPES). We find that $h\text{−}\mathrm{BN}$ exfoliation on epitaxial graphene enables overcoming the technical difficulties of using ARPES with insulating materials. We show trigonal warping of the intensity maps at constant energy. The valence-band maxima are located around the K points, 2.5 eV below the Fermi level, thus confirming the residual $p$-type character of typical $h\text{−}\mathrm{BN}$.