Chemical vapor deposition growth of bilayer graphene in between molybdenum disulfide sheets

Efficient preparation of high-quality graphene via anodic and cathodic simultaneous electrochemical exfoliation under the assistance of microwave

Currently, the electrochemical exfoliation of graphene stands out as an efficient, scalable approach to access high-quality products, due to its simplicity, low cost, and environmental friendliness. Here we have proposed an electrochemical method for preparing graphene at both the anode and cathode simultaneously. Graphite was first subjected to ion intercalation sufficiently on the anode and cathode and then expanded ultrafast under the assistance of microwave irradiation. With plenty of ion intercalation and proper microwave irradiation, graphene would be successfully exfoliated. The as-prepared graphene flakes from anode and cathode behave few-layer feature (more than 80% ≤ 4 layers) and large sizes (about 94% are larger than 1 μm), possess low oxygen content and little defects (6.1% and 1.9% oxygen for anodic and cathodic graphene, respectively). In addition, the high yields in our method (the maximum yields for anode and cathode were 81% and 76%, respectively) and the recycling of electrolytes suggest that our method owns great potential for large-scale production and provide an important reference for the commercial preparation of green and low-cost graphene.

The Effect of Ion Irradiation Density on the Defect of Graphene: A Molecular Dynamics Study

This paper analyzes graphene irradiation effects using a molecular dynamic simulation software, large-scale atomic / molecular massively parallel simulator (LAMMPS). We propose a hypothesis for the effective range of incident ions based on simulation results of irradiation effects that were found using a suspended single-layer graphene. This explains the influence mechanism of irradiation density on the degree of material defects. This paper does key research on how copper substrate influences a single- and bi-layer graphene. The results show that for a single-layer graphene (SLG) the substrate increases the effective range of the incident ions. Within a certain range of the irradiation density, the substrate enhances the defect production on graphene in low-energy irradiation (<5 keV). However, due to the shielding effect of the substrate, the overall trend of graphene damage will be reduced. For the bi-layer graphene (BLG), the effect of the indirect action range is more obvious than that of the direct-action range. In the case of low irradiation density, the knock-on atoms of BLG are much less than suspended SLG.

Chemical Vapor Transport Deposition of Molybdenum Disulfide Layers Using H2O Vapor as the Transport Agent

Molybdenum disulfide (MoS2) layers show excellent optical and electrical properties and have many potential applications. However, the growth of high-quality MoS2 layers is a major bottleneck in the development of MoS2-based devices. In this paper, we report a chemical vapor transport deposition method to investigate the growth behavior of monolayer/multi-layer MoS2 using water (H2O) as the transport agent. It was shown that the introduction of H2O vapor promoted the growth of MoS2 by increasing the nucleation density and continuous monolayer growth. Moreover, the growth mechanism is discussed.

Intercalation of Si between MoS2 layers

We report a combined experimental and theoretical study of the growth of sub-monolayer amounts of silicon (Si) on molybdenum disulfide (MoS₂). At room temperature and low deposition rates we have found compelling evidence that the deposited Si atoms intercalate between the MoS₂ layers. Our evidence relies on several experimental observations: (1) Upon the deposition of Si on pristine MoS₂ the morphology of the surface transforms from a smooth surface to a hill-and-valley surface. The lattice constant of the hill-and-valley structure amounts to 3.16 Å, which is exactly the lattice constant of pristine MoS₂. (2) The transitions from hills to valleys are not abrupt, as one would expect for epitaxial islands growing on-top of a substrate, but very gradual. (3) I(V) scanning tunneling spectroscopy spectra recorded at the hills and valleys reveal no noteworthy differences. (4) Spatial maps of dI/dz reveal that the surface exhibits a uniform work function and a lattice constant of 3.16 Å. (5) X-ray photo-electron spectroscopy measurements reveal that sputtering of the MoS₂/Si substrate does not lead to a decrease, but an increase of the relative Si signal. Based on these experimental observations we have to conclude that deposited Si atoms do not reside on the MoS₂ surface, but rather intercalate between the MoS₂ layers. Our conclusion that Si intercalates upon the deposition on MoS₂ is at variance with the interpretation by Chiappe et al. (Adv. Mater.2014, 26, 2096-2101) that silicon forms a highly strained epitaxial layer on MoS₂. Finally, density functional theory calculations indicate that silicene clusters encapsulated by MoS₂ are stable.