Papers by Author: Leif I. Johansson

Abstract: Graphene samples were grown on the C-face of SiC, at high temperature in a furnace and an Ar ambient, and were investigated using LEEM, XPEEM, LEED, XPS and ARPES. Formation of fairly large grains (crystallographic domains) of graphene exhibiting sharp 1x1 patterns in m-LEED was revealed and that different grains showed different azimuthal orientations. Selective area constant initial energy photoelectron angular distribution patterns recorded showed the same results, ordered grains and no rotational disorder between adjacent layers. A grain size of up to a few mm was obtained on some samples.

Abstract: Detailed studies of Li deposition on monolayer graphene grown on the Si-face SiC surface were performed using LEEM, µ- LEED, PES and ARPES. Li found to intercalate directly after the deposition at room temperature. However, excess Li was also observed on the surface and found to form a compound with carbon atoms. This compound is suggested to give rise to a new (√3x√3) R30° surface reconstruction. After annealing the (√3x√3) R30° reconstruction was vanished and only a (1x1) graphene diffraction pattern was visible. At the same time a sever change was observed on the graphene morphology, especially from the ex-situ grown graphene, i.e. extended area of cracks/wrinkles were observed. These wrinkles/cracks did not disappear even after heating at temperature of 500-1000°C when no Li signal was detected.

Abstract: We report graphene thickness, uniformity and surface morphology dependence on the growth temperature and local variations in the off-cut of Si-face 4H-SiC on-axis substrates. The transformation of the buffer layer through hydrogen intercalation and the subsequent influence on the charge carrier mobility are also studied. A hot-wall CVD reactor was used for in-situ etching, graphene growth in vacuum and the hydrogen intercalation process. The number of graphene layers is found to be dependent on the growth temperature while the surface morphology also depends on the local off-cut in the substrate and results in a non-homogeneous surface. Additionally, the influence of dislocations on surface morphology and graphene thickness uniformity is also presented.

Abstract: We are aiming at understanding the graphene formation mechanism on different SiC polytypes (6H, 4H and 3C) and orientations with the ultimate goal to fabricate large area graphene (up to 2 inch) with controlled number of monolayers and spatial uniformity. To reach the objectives we are using high-temperature atmospheric pressure sublimation process in an inductively heated furnace. The epitaxial graphene is characterized by ARPES, LEEM and Raman spectroscopy. Theoretical studies are employed to get better insight of graphene patterns and stability. Reproducible results of single layer graphene on the Si-face of 6H and 4H-SiC polytypes have been attained. It is demonstrated that thickness uniformity of graphene is very sensitive to the substrate miscut.