Hosni Ajlani

Direct transfer and Raman characterization of twisted graphene bilayer

Twisted bilayer graphene (tBLG) is constituted of a two-graphene layer with a mismatch angle θ between the two hexagonal structures. It has recently attracted much attention—thanks to its diverse electronic and optical properties. Here, we study the tBLG fabricated by the direct transfer of graphene monolayer prepared by chemical vapor deposition (CVD) onto another CVD graphene layer remaining attached to the copper foil. We show that high quality and homogeneous tBLG can be obtained by the direct transfer which prevents interface contamination. In this situation, the top graphene layer plays a supporting mechanical role to the bottom graphene layer as confirmed by optical microscopy, scanning electron microscopy, and Raman spectroscopy measurements. The effect of annealing tBLG was also investigated using micro-Raman spectroscopy. The Raman spectra exhibit a splitting of the G peak as well as a change in the 2D band shape indicating a possible decoupling of the two monolayers. We attribute these changes to the different interactions of the top and bottom layers with the substrate.

Graphene-capped InAs/GaAs quantum dots

Graphene was grown by chemical vapor deposition and successfully transferred onto InAs/GaAs quantum dots (QDs) grown by molecular beam epitaxy on a (001) GaAs substrate. To our knowledge, the hybrid structure of graphene replacing the conventional GaAs layer as a cap layer has not been explored until now. In this work, the authors present the photoluminescence (PL) and Raman spectroscopy study of InAs/GaAs graphene-capped QDs. The Raman measurements show an intense 2D peak at 2704 cm−1 which is the main characteristic indicating the presence of graphene. The recorded PL at temperature T = 300 K shows two sharp peaks located at 1.177 and 1.191 eV, which is attributed to radiative emission from the quantum dots. These peaks, which are generally very weak in InAs/GaAs quantum dots at this temperature, are instead very intense. The enhancement of the PL emission evidenced electron transfer from the graphene layer to the QDs.

Improvement of the quality of graphene-capped InAs/GaAs quantum dots

In this paper, we study the transfer of graphene onto InAs/GaAs quantum dots (QDs). The graphene is first grown on Cu foils by chemical vapor deposition and then polymer Polymethyl Methacrylate (PMMA) is deposited on the top of graphene/Cu. High quality graphene sheet has been obtained by lowering the dissolving rate of PMMA using vapor processing. Uncapped as well as capped graphene InAs/GaAs QDs have been studied using optical microscopy, scanning electron microscopy, and Raman spectroscopy. We gather from this that the average shifts Δω of QDs Raman peaks are reduced compared to those previously observed in graphene and GaAs capped QDs. The encapsulation by graphene makes the indium atomic concentration intact in the QDs by the reduction of the strain effect of graphene on QDs and the migration of In atoms towards the surface. This gives us a new hetero-structure graphene–InAs/GaAs QDs wherein the graphene plays a key role as a cap layer.