Propane/hydrogen CVD growth of graphene on SiC, studied since 2010 [1], consists simply to grow graphene from propane in a hydrogen/argon atmosphere. The presence of hydrogen in the gas phase promotes Si excess on the surface, hence making impossible graphene growth without propane flow [2]. This makes propane/hydrogen CVD very different from silicon sublimation where graphene grows from a carbon excess on SiC. Graphene films are mainly grown in a propane/hydrogen/argon gas mixture at high temperature (1550°C) near atmospheric pressure, conditions allowing to grow uniform n-doped monolayers on 2” SiC wafers. Graphene films prepared in such conditions have been widely used for applications in electrical metrology [3] or as a substrate for van der Waals epitaxy [4]. Though, a complete growth study for these specific growth conditions was still missing. Our contribution will present first elements of this study and discuss the growth and hydrogenation mechanisms occurring both during growth step and cooling down.In order to study the different steps of graphene formation, we have grown samples with different growth time in conditions leading to the formation of a buffer layer interface. Surprisingly, incomplete graphene layers presented hydrogenated interfaces, suggesting hydrogenation of the interface during cooling down. This led us to optimize the cooling down to minimize changes in graphene interface during this last step. The new set of graphene samples with different growth time allows to observe the different steps of graphene formation (figure) : first, the rapid (less than 1 minute) formation of a buffer layer fully covering the SiC and the nucleation of graphene ribbons and islands, followed by their lateral growth leading to a coalescence in about 10 minutes. Surprisingly, the growth of the graphene monolayer is self-limited, so that no increase in graphene coverage is observed after 30 minutes of growth. This self-limitation is attributed to a thermodynamical equilibrium [5]. Finally, these self-limited conditions are used to grow graphene films on 2’’ wafers. Their uniformity and reproducibility appear to be mainly limited by the local offcut of the SiC substrates.

A number of factors have been identified that influence the intensity of photoluminescence in a 4H-SiC:V sample. A photoluminescence temperature study shows trapping behaviour. An unexpected dependence of epitaxial growth rate on VCl 4 presence has been demonstrated.

Raman spectroscopy is a widely used technique to characterize nanomaterials because of its convenience, non-destructiveness, and sensitivity to materials change. The primary purpose of this work is to determine via Raman spectroscopy the average thickness of MoS 2 thin films synthesized by direct liquid injection pulsed-pressure chemical vapor deposition (DLI-PP-CVD). Such samples are constituted of nanoflakes (with a lateral size of typically 50 nm, i.e., well below the laser spot size), with possibly a distribution of thicknesses and twist angles between stacked layers. As an essential preliminary, we first reassess the applicability of different Raman criteria to determine the thicknesses (or layer number, N ) of MoS 2 flakes from measurements performed on reference samples, namely well-characterized mechanically exfoliated or standard chemical vapor deposition MoS 2 large flakes deposited on 90 ± 6 nm SiO 2 on Si substrates. Then, we discuss the applicability of the same criteria for significantly different DLI-PP-CVD MoS 2 samples with average thicknesses ranging from sub-monolayer up to three layers. Finally, an original procedure based on the measurement of the intensity of the layer breathing modes is proposed to evaluate the surface coverage for each N (i.e., the ratio between the surface covered by exactly N layers and the total surface) in DLI-PP-CVD MoS 2 samples.

Since the introduction of hybrid van der Waals heterostructures (h-vdWHs) for device architecture development, many vertically staked organic two-dimensional materials have been investigated in order to control transport properties. This article introduces a novel h-vdWH that achieves periodicinteraction by the development of a superlattice. We describe a complete investigation of the diphenyl-functionalized p-benzoquinonemonoimine zwitterion on highly oriented pyrolytic graphiteand monolayer graphene using high-resolution scanning tunneling microscopy images and numerical simulations. The molecular phase on both substrates exhibits a structurally identical antiparallel dipole alignment in a head-to-tail dimer configuration. Density functional theory calculations reveal that this molecularadsorption induces a local dipole at the graphene interface due to the rearrangement of the electron density distribution.