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Layered molybdenum disulphide (MoS2) crystals in combination with graphene create the opportunity for the development of heterostructures with tailored surface and structural properties for energy storage applications. Herein, 2D heterostructures are developed by growing MoS2 on epitaxial and self-standing nanoporous graphene (NPG) using chemical vapor deposition (CVD). The effect of substrate as well as different CVD growth parameters such as temperature, amount of sulfur and MoO3 precursors, and argon flow on the growth of MoS2 is systematically investigated. Interestingly, various structures of MoS2 such as monolayer triangular islands, spirals, standing sheets, and irregular stacked multilayered MoS2 are successfully developed. The growth mechanism is proposed using different advanced characterization techniques. The formation of a continuous wetting layer with grain boundaries over the surface prior to formation of any other structures is detected. As a proof of principle, MoS2/NPG is employed for the first time as anode material in potassium ion battery. The electrode delivers a specific capacity of 389 mAh g−1 with over 98% stability after 200 cycles. The porous structures clearly facilitate the ion transport which is beneficial for the ion battery. These encouraging results open new opportunities to develop hierarchical heterostructures of 2D-materials for next-generation energy storage technologies.

We report on a spatial mapping of the electronic and vibrational structure of three-dimensional (3D) nanoporous graphene architectures, which have a hierarchical pore structure. We demonstrate that the topology, curvature, and pores lead to local changes in the electronic and vibrational structure and in the hybridization states of the carbon atoms (sp2 vs. sp3-like). Nitrogen substitutions in pyrrolic bonding configurations also contribute to local distortions of the planar geometry of graphene. The distortions influence the electronic density of states at the Fermi level by shifting the Dirac cone apex, opening potential avenues for applications of two-dimensional graphene in 3D devices.

Scaling graphene from a two-dimensional (2D) ideal structure to a three-dimensional (3D) millimeter-sized architecture without compromising its remarkable electrical, optical, and thermal properties is currently a great challenge to overcome the limitations of integrating single graphene flakes into 3D devices. Herewith, highly connected and continuous nanoporous graphene (NPG) samples, with electronic and vibrational properties very similar to those of suspended graphene layers, are presented. We pinpoint the hallmarks of 2D ideal graphene scaled in these 3D porous architectures by combining the state-of-the-art spectromicroscopy and imaging techniques. The connected and bicontinuous topology, without frayed borders and edges and with low density of crystalline defects, has been unveiled via helium ion, Raman, and transmission electron microscopies down to the atomic scale. Most importantly, nanoscanning photoemission unravels a 3D NPG structure with preserved 2D electronic density of states (Dirac cone like) throughout the porous sample. Furthermore, the high spatial resolution brings to light the interrelationship between the topology and the morphology in the wrinkled and highly bent regions, where distorted sp2 C bonds, associated with sp3-like hybridization state, induce small energy gaps. This highly connected graphene structure with a 3D skeleton overcomes the limitations of small-sized individual graphene sheets and opens a new route for a plethora of applications of the 2D graphene properties in 3D devices.

Etching with atomic hydrogen as a preparation step before the high-temperature growth process of graphene onto a thin 3C-SiC film grown on Si(111) greatly improves the structural quality of topmost graphene layers. Pit formation and island coalescence, which are typical of graphene growth by SiC graphitization, are quenched and accompanied by widening of the graphene domain sizes to hundreds of nm, and by a significant reduction in surface roughness down to a single substrate bilayer. The surface reconstructions expected for graphene and the underlying layer are shown with atomic resolution by scanning tunnelling microscopy (STM). Spectroscopic features typical of graphene are measured by core-level photoemission and Raman spectroscopy.

Scanning tunneling microscopy and X-ray spectroscopy measurements are combined to first-principles simulations to investigate the formation of graphene nanoribbons (GNRs) on Au(110), as based on the surface-mediated reaction of 10,10′-dibromo-9,9′-bianthracene (DBBA) molecules. At variance with Au(111), two different pathways are identified for the GNR self-assembly on Au(110), as controlled by both the adsorption temperature and the surface coverage of the DBBA molecular precursors. Room-temperature DBBA deposition on Au(110) leads to the same reaction steps obtained on Au(111), even though with lower activation temperatures. For DBBA deposition at 470 K, the cyclodehydrogenation of the precursors preceds their polymerization, and the GNR formation is fostered by increasing the surface coverage. While the initial stages of the reaction are found to crucially determine the final configuration and orientation of the GNRs, the molecular diffusion is found to limit in both cases the formation of high-density long-range ordered GNRs. Overall, the direct comparison between the Au(110) and Au(111) surfaces unveils the delicate interplay among the different factors driving the growth of GNRs. © 2014 American Chemical Society.

A single layer (SL) of pentacene molecules deposited on the Cu(119) surface and on an organic selfassembled monolayer (SAM) has been investigated by near-edge x-ray absorption fine structure (NEXAFS) at the C K edge, and by photoemission at the C 1s core level. The lowest unoccupied molecular orbitals (LUMOs) of the pentacene SL on the SAM are basically unaffected with respect to that of pentacene in the gas phase, indicating a weak interaction of pentacene with the SAM, while a strong redistribution of the LUMO-related final states is observed when the molecules are deposited on the Cu(119) substrate, sign of an electronic mixing between molecular and metal electronic states, in agreement with recent theoretical predictions. The strong dichroic response of the NEXAFS signal indicates upstanding pentacene molecules oriented 16° off normal for the organic-organic heterostructure. The rehybridization of pentacene orbitals with Cu states at the pentacene/Cu interface hinders an accurate determination of the molecule orientation, which is, however, compatible with molecules lying flat on the Cu(119) terraces.

We investigate the morphology of a pentacene (C22H14) film adsorbed on the Cu(119) vicinal surface by scanning tunnelling microscopy (STM). Thermal treatment of a thick film of molecules generates a long-range ordered structure. Series of molecular rows are alternated with areas where the molecules assume two equivalent orientations. STM data analysis suggests that the ordered structure can be described by a rippled morphology. The behaviour of the film at different annealing temperatures suggests a possible explanation of the film structure as due to an adsorbate-induced modification of the substrate

The authors present a combined photoemission and scanning-tunneling spectroscopy study of the filled electronic states, the molecular energy gap, and the energy level diagram of highly ordered arrays of pentacene deposited on the Cu(119) vicinal surface. The states localized at the interface are clearly singled out, comparing the results at different pentacene thicknesses and with gas-phase photoemission data. The molecular gap of 2.35 eV, the hole injection barrier of 1.05 eV, and the electron injection barrier of 1.30 eV determine the energy level diagram of the states localized at the pentacene molecules.

The C K-edge photoabsorption and 1s core-level photoemission of pentacene (C22H14) free molecules are experimentally measured, and calculated by self-consistent-field and static-exchange approximation ab initio methods. Six nonequivalent C atoms present in the molecule contribute to the C 1s photoemission spectrum. The complex near-edge structures of the carbon K-edge absorption spectrum present two main groups of discrete transitions between 283 and 288 eV photon energy, due to absorption to * virtual orbitals, and broader structures at higher energy, involving * virtual orbitals. The sharp absorption structures to the * empty orbitals lay well below the thresholds for the C 1s ionizations, caused by strong excitonic and localization effects. We can definitely explain the C K-edge absorption spectrum as due to both final (virtual) and initial (core) orbital effects, mainly involving excitations to the two lowest-unoccupied molecular orbitals of * symmetry, from the six chemically shifted C 1s core orbitals. ©2005 American Institute of Physics