Fluorescent organic dyes photobleach under intense light. Graphene has been shown to improve the photo-stability of organic dyes. In this paper, we investigated the Raman spectroscopy and photo-bleaching kinetics of dyes in the absence/presence of chemical vapor deposition (CVD)-grown graphene. We show that graphene enhances the Raman signal of a wide range of dyes. The photo-bleaching of the dyes was reduced when the dyes were in contact with graphene. In contrast, monolayer hexagonal boron nitride (h-BN) was much less effective in reducing the photo-bleaching rate of the dyes. We attribute the suppression of photo-bleaching to the energy or electron transfer from dye to graphene. The results highlight the potential of CVD graphene as a substrate for protecting and enhancing Raman response of organic dyes.

Molybdenum disulfide (MoS 2 ) layers show excellent optical and electrical properties and have many potential applications. However, the growth of high-quality MoS 2 layers is a major bottleneck in the development of MoS 2 -based devices. In this paper, we report a chemical vapor transport deposition method to investigate the growth behavior of monolayer/multi-layer MoS 2 using water (H 2 O) as the transport agent. It was shown that the introduction of H 2 O vapor promoted the growth of MoS 2 by increasing the nucleation density and continuous monolayer growth. Moreover, the growth mechanism is discussed.

Tungsten disulfide (WS 2 ) monolayer is a direct band gap semiconductor. The growth of WS 2 monolayer hinders the progress of its investigation. In this paper, we prepared the WS 2 monolayer through chemical vapor transport deposition. This method makes it easier for the growth of WS 2 monolayer through the heterogeneous nucleation-and-growth process. The crystal defects introduced by the heterogeneous nucleation could promote the photoluminescence (PL) emission. We observed the strong photoluminescence emission in the WS 2 monolayer, as well as thermal quenching, and the PL energy redshift as the temperature increases. We attribute the thermal quenching to the energy or charge transfer of the excitons. The redshift is related to the dipole moment of WS 2 .

Molybdenum disulphide (MoS 2) monolayer is a two-dimensional semiconductor material with potential applications in nano electronic devices. However, it is still a challenge to reproducibly synthesize single layer MoS 2 in high quality. Herein, we report the growth of monolayer of MoS 2 on the SiO 2 /Si substrate with manganese heterogeneous nucleation. It was shown that the Mn promotes the growth of monolayer MoS 2 via heterogeneous nucleation. The growth temperature range expanded twofold , the nucleation density increased as well. The monolayer prepared in the presence of Mn exhibits a unique red emission peak at 732 nm at room temperature compared to the sample in the absence of Mn.