Graphene produced by chemical vapor deposition (CVD) is a promising candidate for implementing graphene in a range of technologies. In most device configurations, one side of the graphene is supported by a solid substrate, wheras the other side is in contact with a medium of interest, such as a liquid or other two-dimensional material within a van der Waals stack. In such devices, graphene interacts on both faces via noncovalent interactions and therefore surface energies are key parameters for device fabrication and operation. In this work, we directly measured adhesive forces and surface energies of CVD-grown graphene in dry nitrogen, water, and sodium cholate using a modified surface force balance. For this, we fabricated large (∼1 cm) and clean graphene-coated surfaces with smooth topography at both macro- and nanoscales. By bringing two such surfaces into contact and measuring the force required to separate them, we measured the surface energy of single-layer graphene in dry nitrogen to be 115 ± 4 mJ/m, which was similar to that of few-layer graphene (119 ± 3 mJ/m). In water and sodium cholate, we measured interfacial energies of 83 ± 7 and 29 ± 6 mJ/m, respectively. Our work provides the first direct measurement of graphene surface energy and is expected to have an impact both on the development of graphene-based devices and contribute to the fundamental understanding of surface interactions.

Precise control of graphene properties is an essential step toward the realization of future graphene devices. Defects, such as individual nitrogen atoms, can strongly influence the electronic structure of graphene. Therefore, state-of-the-art characterization techniques, in conjunction with modern modeling tools, are necessary to identify these defects and fully understand the synthesized material. We have directly visualized individual substitutional nitrogen dopant atoms in graphene using scanning transmission electron microscopy and conducted complementary electron energy loss spectroscopy experiments and modeling which demonstrates the influence of the nitrogen atom on the carbon K-edge.

Ammonia borane (AB) is among the most promising precursors for the large-scale synthesis of hexagonal boron nitride (h-BN) by chemical vapour deposition (CVD). Its non-toxic and non-flammable properties make AB particularly attractive for industry. AB decomposition under CVD conditions, however, is complex and hence has hindered tailored h-BN production and its exploitation. To overcome this challenge, we report in-depth decomposition studies of AB under industrially safe growth conditions. In situ mass spectrometry revealed a time and temperature-dependent release of a plethora of NxBy-containing species and, as a result, significant changes of the N:B ratio during h-BN synthesis. Such fluctuations strongly influence the formation and morphology of 2D h-BN. By means of in situ gas monitoring and regulating the precursor temperature over time we achieve uniform release of volatile chemical species over many hours for the first time, paving the way towards the controlled, industrially viable production of h-BN.

Large-area synthesis of high-quality graphene by chemical vapour deposition on metallic substrates requires polishing or substrate grain enlargement followed by a lengthy growth period. Here we demonstrate a novel substrate processing method for facile synthesis of mm-sized, single-crystal graphene by coating polycrystalline platinum foils with a silicon-containing film. The film reacts with platinum on heating, resulting in the formation of a liquid platinum silicide layer that screens the platinum lattice and fills topographic defects. This reduces the dependence on the surface properties of the catalytic substrate, improving the crystallinity, uniformity and size of graphene domains. At elevated temperatures growth rates of more than an order of magnitude higher (120 μm min−1) than typically reported are achieved, allowing savings in costs for consumable materials, energy and time. This generic technique paves the way for using a whole new range of eutectic substrates for the large-area synthesis of 2D materials.

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We report a method for transferring graphene, grown by chemical vapor deposition, which produces ultraflat graphene surfaces (root-mean-square roughness of 0.19 nm) free from polymer residues over macroscopic areas (>1 cm2). The critical step in preparing such surfaces involves the use of an intermediate mica template, which itself is atomically smooth. We demonstrate the compatibility of these model surfaces with the surface force balance, opening up the possibility of measuring normal and lateral forces, including friction and adhesion, between two graphene sheets either in contact or across a liquid medium. The conductivity of the graphene surfaces allows forces to be measured while controlling the surface potential. This new apparatus, the graphene surface force balance, is expected to be of importance to the future understanding of graphene in applications from lubrication to electrochemical energy storage systems.

In this work it has been established that 3D nanoflowers of WS2 synthesized by chemical vapour deposition are composed of few layer WS2 along the edges of the petals. An experimental study to understand the evolution of these nanostructures shows the nucleation and growth along with 10 the compositional changes they undergo.The structural analogy of transition metal dichalcogenides 1 to graphite's layered structure, held together by van In this work, a fast, catalyst free and easily scalable chemical vapour deposition (CVD) technique for the controlled synthesis of well-defined tungsten disulphide (WS2) nanomaterials on (100) silicon-based substrates using tungsten(VI)chloride (WCl6-40 2 mmol at 99.9% purity) and sulphur (20 mmol at 80% purity) as precursors is presented in Fig S1. The predominant morphology (>90%) obtained by this process is WS2 nanoflower confirmed using electron microscopy as shown in Fig.1a and the chemistry verified using XRD and Raman in Fig S2. The morphology of the 45 WS2 nanostructures synthesised by the CVD technique can be tailored through the variation of just two key parameters: time 22 , as yet, a detailed analysis of their structure has not been undertaken. This 60 study looks to comprehend the structure of the nanoflower by disassembling it with the help of sonication. The nanoflowers disassembled into triangular petals (flakes) on sonication with one corner always broken, which suggests that these triangles are connected at only one of the edges to form the assembly of 3D 65 nanoflowers. We observed 10-100's of these triangular petals combining together to form spherical nanoflower structures as suggested by Li et al. 22 and evident from the SEM micrograph in Fig 1a. The nanoflowers are made up of molecular sheets stacked 70 together with a lattice spacing of 3.1 Å and lattice fringes of 0.62 nm, inferred for WS2. In Fig 2a, a cluster of the petals which constitute the nanoflowers is visualised from the edge view (beam perpendicular to c-axis), to reveal 6-8 molecular layers of WS2. These WS2 were stacked on top of each other to form the 75 petals. The distribution of the number of molecular layers to form the petal is not very uniform and varies from few layer (2-4) to increased number of layers up to 12/14. With the beam parallel to the c axis, the hexagonal packing can be clearly observed at the edges where the number of layers have reduced considerably to 80 1 µm

NanoBuds exist in a variety of stable structures. Our studies show that engineering NanoBud geometries is indeed possible and we visualise the transformation of one Nanobud geometry to another using in situ aberration corrected imaging techniques. Such NanoBuds are precursors for generating nanotube junctions which could be used in composite and electronic applications.