Electron doping of graphene has been extensively studied on graphene-supported surfaces, where the metallicity is influenced by the substrate. Herewith we propose potassium adsorption on free-standing nanoporous graphene, thus eluding any effect due to the substrate. We monitor the electron migration in the π* downward-shifted conduction band. In this rigid band shift, we correlate the spectral density of the π* state in the upper Dirac cone with the associated plasmon, blue-shifted with increasing K dose, as deduced by electron energy loss spectroscopy. These results are confirmed by the Dirac plasmon activated by the C 1s emitted electrons, thanks to spatially resolved photoemission. This crosscheck constitutes a reference on the correlation between the electronic π* states in the conduction band and the Dirac plasmon evolution upon in situ electron doping of fully free-standing graphene.

Atomic deuterium (D) adsorption on free-standing nanoporous graphene obtained by ultra-high vacuum D2 molecular cracking reveals a homogeneous distribution all over the nanoporous graphene sample, as deduced by ultra-high vacuum Raman spectroscopy combined with core-level photoemission spectroscopy. Raman microscopy unveils the presence of bonding distortion, from the signal associated to the planar sp2 configuration of graphene toward the sp3 tetrahedral structure of graphane. The establishment of D–C sp3 hybrid bonds is also clearly determined by high-resolution X-ray photoelectron spectroscopy and spatially correlated to the Auger spectroscopy signal. This work shows that the low-energy molecular cracking of D2 in an ultra-high vacuum is an efficient strategy for obtaining high-quality semiconducting graphane with homogeneous uptake of deuterium atoms, as confirmed by this combined optical and electronic spectro-microscopy study wholly carried out in ultra-high vacuum conditions.

Tuning the electrocatalytic properties of MoS 2 layers can be achieved through different paths, such as reducing their thickness, creating edges in the MoS 2 flakes, and introducing S-vacancies. We combine these three approaches by growing MoS 2 electrodes by using a special salt-assisted chemical vapor deposition (CVD) method. This procedure allows the growth of ultrathin MoS 2 nanocrystals (1−3 layers thick and a few nanometers wide), as evidenced by atomic force microscopy and scanning tunneling microscopy. This morphology of the MoS 2 layers at the nanoscale induces some specific features in the Raman and photoluminescence spectra compared to exfoliated or microcrystalline MoS 2 layers. Moreover, the S-vacancy content in the layers can be tuned during CVD growth by using Ar/H 2 mixtures as a carrier gas. Detailed optical microtransmittance and microreflectance spectroscopies, micro-Raman, and X-ray photoelectron spectroscopy measurements with sub-millimeter spatial resolution show that the obtained samples present an excellent homogeneity over areas in the cm 2 range. The electrochemical and photoelectrochemical properties of these MoS 2 layers were investigated using electrodes with relatively large areas (0.8 cm 2 ). The prepared MoS 2 cathodes show outstanding Faradaic efficiencies as well as long-term stability in acidic solutions. In addition, we demonstrate that there is an optimal number of Svacancies to improve the electrochemical and photoelectrochemical performances of MoS 2 .

Free-standing nanoporous graphene was hydrogenated at about 60 at.% H uptake, as determined by the emerging of the sp3 bonding component in the C 1s core level investigated by high-resolution X-ray photoelectron spectroscopy (XPS). Fully unsupported graphane was investigated by XPS under optical excitation at 2.4 eV. At a laser fluence of 1.6 mJ/cm2, a partial irreversible dehydrogenation of the graphane was observed, which could be attributed either to the local temperature increase or to a photo-induced softening of the H-to-C stretching mode. The sub-ns dynamics of the energy shift and peak broadening of the C 1s core level revealed two different decay constants: 210 ps and 130 ps, respectively, the former associated with photovoltage dynamics and the latter with thermal heating on a time scale comparable with the synchrotron temporal resolution.

No abstract