The 0D–2D nucleation and growth mode is presented in molybdenum disulfide (MoS2) chemical vapor deposition synthesis. Partially sulfured molybdenum suboxide nucleation centers are demonstrated experimentally, followed by these centers being converted to MoS2 nanoparticles and MoS2 layer growth initiation from the nanoparticle edges. The work reveals the mechanism for MoS2 nucleation and growth.

Graphene's practical applications require its reproducible production with controlled means. In particular, graphene synthesis by chemical vapor deposition on metals has been shown to be a promising way to produce large-size and high-quality graphene film at low cost. Understanding the reaction mechanisms during the synthesis process is vital for process and product controllability. There have been a great deal of studies regarding the mutual interplays between the metal, graphene, and hydrogen in graphene production, leading to significant advances in controllable graphene synthesis. Recently, oxygen has been found to play a key role in each step of graphene synthesis, especially on Cu. Taking oxygen into consideration, one can explain the divergent experimental results under similar conditions reported before and can grasp it as another powerful tool that can help to regulate the synthesis processes. The primary discoveries of the function of oxygen in graphene synthesis are summarized and discussed herein, divided into four aspects, corresponding to the elementary steps in graphene synthesis. Oxygen may also further promote graphene synthesis toward the final goal of developing wafer-scale single crystals with definite layer numbers and defects.

Graphene is an ideal membrane for selective separation because of its unique properties and single-layer structure. Considerable efforts have been made to alter the permeability of graphene. In this study, we investigate the pathways for an oxygen atom to pass through graphene sheets. We also identify the effect of the ripple's curvature in graphene sheets on the energy barrier of permeation through density functional theory calculations. Results show that oxygen atoms can easily pass through the concave side of graphene ripples with a large curvature. The analysis of transition states reveals that the space where an oxygen atom passes through keeps an almost identical structure with similar bond lengths regardless of the curvature. We find that the Cu(111) substrate may draw out the C–C bond lengths of graphene at the Cu(111) surface because of the strong interaction between the graphene edge and copper atoms. Consequently, the energy barrier of the permeation of oxygen atoms through graphene is reduced. These results suggest that the rippling of graphene significantly affects its permeation.

Atomically thin, two-dimensional materials ranging from superconductors, metals, semiconductors to insulators are emerging as potential candidates for the next-generation digital electronics and optoelectronic applications. Their synthesis on a commonly used substrate and fast transfer to a plenty of desired substrates need to be addressed to meet the industrialization criteria for practical applications. In this study, fused silica, which is amorphous, transparent, and inexpensive, was examined as a substrate for MoS2 synthesis. The MoS2 growth behavior on fused silica and its crystal quality were evaluated. In addition, a novel way was developed to quickly peel off MoS2 from the fused silica surface within 15 s (i.e., etching in an acidic solution to detach the edge and completing the delamination via a capillary force at the interface between air and water). The fused silica could be reused at least three times. Moreover, the produced MoS2 domains showed no obvious degradation of quality. These results support the feasibility of MoS2 synthesis on amorphous and recyclable substrates and also the time-saving transfer for the cost-effective and high-quality production of other two-dimensional materials.

Hierarchical architecture of ultrathin interlayer-expanded WS2 nanosheets supported on three-dimensional graphene (3DG) frameworks is fabricated by a facile hydrothermal method for the first time. The 3DG frameworks could provide large surface area for assembling WS2 nanosheets and continuous pathways for rapid electron transfer and ion transport; and the WS2 nanosheets with an expanded interlayer spacing of 9.58 Å, due to oxygen incorporation, could afford more space for lithium ion intercalation and more active sites for hydrogen evolution. The as-prepared WS2/3DG composite exhibits a high capacity of 766 mA h g−1 and excellent cycling stability for lithium storage, much better than its annealed counterpart and bulk WS2. The hydrated sheet of WS2/3DG also demonstrates boosted electrocatalytic activity for the hydrogen evolution reaction, possessing a low onset overpotential of 75 mV and an extremely large current density of 137 mA cm−2 at 300 mV with remarkable durability. This work may open up a new pathway for improving the electrochemical properties by synergistically optimizing the electrode architectures and the intrinsic electroactivity of the active materials.

Nanoscale morphology is of significance to the electronic properties of semiconducting polymers. Solution-processed poly-3-hexylthiophene (P3HT) has been demonstrated as a promising active-layer material in organic thin film transistors (OTFTs) and solar cells. Controlling the crystallinity of P3HT chains is critical for gaining high-performance devices. Here we demonstrated the immediate crystallization of P3HT induced by two-dimensional MoS2 nanosheets under ultrasonication. The resulting aggregation was attributed to the presence of interaction between the MoS2 nanosheets and P3HT, which could enhance the inter-chain ordering and association of P3HT. The crystallization of P3HT contributed to the 38-fold enhancement in the hole mobility of the thin film as compared to the non-crystallized thin films because of the absence of MoS2. Our approach of using 2D MoS2 nanosheets to induce immediate aggregation of P3HT provides a facile process to control the crystallization of conjugated polymers for the development of high-performance organic electronics.

A novel hole transport layer (HTL) composed of ultrathin two-dimensional, molybdenum disulfide (MoS2) sheets decorated with 20 nm gold nanoparticles (NPs) (MoS2@Au) was developed to make use of plasmonics for organic solar cells (OSCs). Both experimental and theoretical simulations revealed that the device with the MoS2@Au composite as the HTL exhibited enhanced short-circuit photocurrent density (Jsc) and efficiency compared to that with MoS2 alone as the HTL.

Graphene-like two-dimensional materials (2DMats) show application potential in optoelectronics and biomedicine due to their unique properties. However, environmental and biological influences of these 2DMats remain to be unveiled. Here we reported the antibacterial activity of two-dimensional (2D) chemically exfoliated MoS2 (ce-MoS2) sheets. We found that the antibacterial activity of ce-MoS2 sheets was much more potent than that of the raw MoS2 powders used for the synthesis of ce-MoS2 sheets possibly due to the 2D planar structure (high specific surface area) and higher conductivity of the ce-MoS2. We investigated the antibacterial mechanisms of the ce-MoS2 sheets and proposed their antibacterial pathways. We found that the ce-MoS2 sheets could produce reactive oxygen species (ROS), different from a previous report on graphene-based materials. Particularly, the oxidation capacity of the ce-MoS2 sheets toward glutathione oxidation showed a time and concentration dependent trend, which is fully consistent with the antibacterial behaviour of the ce-MoS2 sheets. The results suggest that antimicrobial behaviors were attributable to both membrane and oxidation stress. The antibacterial pathways include MoS2–bacteria contact induced membrane stress, superoxide anion (O2˙−) induced ROS production by the ce-MoS2, and the ensuing superoxide anion-independent oxidation. Our study thus indicates that the tailoring of the dimension of nanomaterials and their electronic properties would manipulate antibacterial activity.

The effects of different local crystalline structures on two-dimensional (2D) MoS2 sheets are studied to provide new insights into how the local characteristics affect the performance of organic solar cells (OSCs) and how to tailor the local characteristics towards high-performance devices. UV–ozone post-treatment of 2D MoS2 sheets led to incorporation of oxygen atoms into the lattice of the sheets. The incorporated oxygen in 2D MoS2 sheets significantly improved the performance of OSCs, where 2D MoS2 sheets were used as hole transport layers.

A simple and effective procedure was developed to modify chemically exfoliated MoS2 surfaces with a hydrophilic surfactant through electrostatic interaction. The modified ce-MoS2 colloidal solution shows ultra long-term stability, making it a storable solution ready for highly efficient organic solar cells.

The identification of physicochemical factors that govern toxic effects of nanomaterials (NMs) is important for the safe design and synthesis of NMs. The release of metal cations from NMs in cell culture medium and the role of the metal cations in cytotoxicity are still under dispute. Here, we report that removal of NMs such as ZnO nanoparticles (NPs) by centrifugation, the procedure commonly used for the estimation of released ion concentration in nanotoxicology, was incomplete even at a relative centrifugal force of 150000 × g. In this sense, the Zn concentration in supernatant measured by inductively coupled plasma-mass spectrometry cannot be regarded as the concentration of free Zn2+ ions which were released from ZnO NPs in cell culture medium. This suggests the urgent need to develop relevant analytical techniques for nanotoxicology. The toxic contribution of released Zn2+ ions to the A549 cell lines was estimated to be only about 10%. We conclude that the cytotoxicity associated with ZnO NPs is not a function of the Zn concentration, suggesting that other factors play an important role in the toxic effect of ZnO NPs.

We report a simple solution-based approach to form ordered patterns of an indium tin oxide (ITO) electrode and underlying reasons for the improvement in power conversion efficiency (PCE) of organic solar cells (OSCs) built on the nanostructured ITO electrode. The patterning of ITO was achieved by using nanospheres as the template to erode ITO by wet chemical etching. Using a textured ITO anode for poly(3-hexylthiophene) (P3HT):[6,6]-phenyl C61-butyric acid methylester (PCBM) (P3HT:PCBM) OSCs enhanced PCE by 15% with respect to the non-patterned ITO anode. The improvement is mostly attributed to the morphological and interfacial changes stemming from the textured ITO electrode as well as enhanced light absorption due to the optimal morphology and refractive index change of patterned ITO. With its simplicity and time-saving, this method of fabricating a unique pattern of ITO electrodes can be widely applicable to a variety of large-area thin film solar cells.

We report that few-layer hexagonal boron nitride (h-BN) nanosheets can be produced by using a surface segregation method. The formation of h-BN sheets is via an intermediate boron–nitrogen buffer layer. Our results suggest that surface segregation of boron and nitrogen from a solid source is an alternative approach to tailoring synthesis of h-BN sheets for potential applications such as in graphene electronics.

We report the synthesis of CdS crystals with novel dendritic structures by a simple amino acid mediated hydrothermal process, in which various amino acids were used as capping agents. We elaborated that a slight change of the side group of amino acids can significantly influence the type and the structure of CdS crystals. We found that the reaction temperature and the time also have effects on the formation of CdS crystals. The resulting different-shaped CdS crystals exhibited different UV–vis absorption characteristics. Our results suggest that the biomolecule-assisted hydrothermal route using amino acids as capping agents provides an effective and green approach to produce hierarchical CdS crystals with rich morphologies.Highlights► We use an amino acid mediated hydrothermal process to synthesize CdS crystals. ► Various CdS crystals with novel dendritic structures are synthesized. ► Amino acid, reaction temperature and time have great effects on morphologies. ► These CdS crystals show morphology-related UV–vis absorptions.

Nanoscale morphology is of significance to the electronic properties of semiconducting polymers. Solution-processed poly-3-hexylthiophene (P3HT) has been demonstrated as a promising active-layer material in organic thin film transistors (OTFTs) and solar cells. Controlling the crystallinity of P3HT chains is critical for gaining high-performance devices. Here we demonstrated the immediate crystallization of P3HT induced by two-dimensional MoS2 nanosheets under ultrasonication. The resulting aggregation was attributed to the presence of interaction between the MoS2 nanosheets and P3HT, which could enhance the inter-chain ordering and association of P3HT. The crystallization of P3HT contributed to the 38-fold enhancement in the hole mobility of the thin film as compared to the non-crystallized thin films because of the absence of MoS2. Our approach of using 2D MoS2 nanosheets to induce immediate aggregation of P3HT provides a facile process to control the crystallization of conjugated polymers for the development of high-performance organic electronics.

Hierarchical architecture of ultrathin interlayer-expanded WS2 nanosheets supported on three-dimensional graphene (3DG) frameworks is fabricated by a facile hydrothermal method for the first time. The 3DG frameworks could provide large surface area for assembling WS2 nanosheets and continuous pathways for rapid electron transfer and ion transport; and the WS2 nanosheets with an expanded interlayer spacing of 9.58 Å, due to oxygen incorporation, could afford more space for lithium ion intercalation and more active sites for hydrogen evolution. The as-prepared WS2/3DG composite exhibits a high capacity of 766 mA h g−1 and excellent cycling stability for lithium storage, much better than its annealed counterpart and bulk WS2. The hydrated sheet of WS2/3DG also demonstrates boosted electrocatalytic activity for the hydrogen evolution reaction, possessing a low onset overpotential of 75 mV and an extremely large current density of 137 mA cm−2 at 300 mV with remarkable durability. This work may open up a new pathway for improving the electrochemical properties by synergistically optimizing the electrode architectures and the intrinsic electroactivity of the active materials.

We report a simple solution-based approach to form ordered patterns of an indium tin oxide (ITO) electrode and underlying reasons for the improvement in power conversion efficiency (PCE) of organic solar cells (OSCs) built on the nanostructured ITO electrode. The patterning of ITO was achieved by using nanospheres as the template to erode ITO by wet chemical etching. Using a textured ITO anode for poly(3-hexylthiophene) (P3HT):[6,6]-phenyl C61-butyric acid methylester (PCBM) (P3HT:PCBM) OSCs enhanced PCE by 15% with respect to the non-patterned ITO anode. The improvement is mostly attributed to the morphological and interfacial changes stemming from the textured ITO electrode as well as enhanced light absorption due to the optimal morphology and refractive index change of patterned ITO. With its simplicity and time-saving, this method of fabricating a unique pattern of ITO electrodes can be widely applicable to a variety of large-area thin film solar cells.

A novel hole transport layer (HTL) composed of ultrathin two-dimensional, molybdenum disulfide (MoS2) sheets decorated with 20 nm gold nanoparticles (NPs) (MoS2@Au) was developed to make use of plasmonics for organic solar cells (OSCs). Both experimental and theoretical simulations revealed that the device with the MoS2@Au composite as the HTL exhibited enhanced short-circuit photocurrent density (Jsc) and efficiency compared to that with MoS2 alone as the HTL.

The effects of different local crystalline structures on two-dimensional (2D) MoS2 sheets are studied to provide new insights into how the local characteristics affect the performance of organic solar cells (OSCs) and how to tailor the local characteristics towards high-performance devices. UV–ozone post-treatment of 2D MoS2 sheets led to incorporation of oxygen atoms into the lattice of the sheets. The incorporated oxygen in 2D MoS2 sheets significantly improved the performance of OSCs, where 2D MoS2 sheets were used as hole transport layers.