Publications

2021

• Exciton band structure of Molybdenum Disulfide: from monolayer to bulk
  
  • Fugallo Giorgia
  • Cudazzo Pierluigi
  • Gatti Matteo
  • Sottile Francesco
  Electronic Structure, IOPScience, 2021, 3 (1), pp.014005. Exciton band structures analysis provides a powerful tool to identify the exciton character of materials, from bulk to isolated systems, and goes beyond the mere analysis of the optical spectra. In this work, we focus on the exciton properties of Molibdenum Disulfide (MoS2) by solving the ab initio many-body Bethe-Salpeter equation, as a function of momentum, to obtain the excitation spectra of both monolayer and bulk MoS2. We analyse the spectrum and the exciton dispersion on the basis of a model excitonic Hamiltonian capable of providing an efficient description of the excitations in the bulk crystal, starting from the knowledge of the excitons of a single layer. In this way, we obtain a general characterization of both bright and darks excitons in terms of the interplay between the electronic band dispersion (i.e. interlayer hopping) and the electron-hole exchange interaction. We identify for both the 2D and the 3D limiting cases the character of the lowestenergy excitons in MoS2, we explain the effects and relative weights of both band dispersion and electron-hole exchange interaction and finally we interpret the differences observed when changing the dimensionality of the system. (10.1088/2516-1075/abdb3c)
  DOI : 10.1088/2516-1075/abdb3c
• Ultrafast electron energy-dependent delocalization dynamics in germanium selenide
  
  • Chen Zhesheng
  • Xiong Heqi
  • Zhang Hao
  • Gao Chaofeng
  • Cheng Yingchun
  • Papalazarou Evangelos
  • Perfetti Luca
  • Marsi Marino
  • Rueff Jean-Pascal
  Communications Physics, Nature Research, 2021, 4, pp.138. Ultrafast scattering process of high-energy carriers plays a key role in the performance of electronics and optoelectronics, and have been studied in several semiconductors. Core-hole clock spectroscopy is a unique technique for providing ultrafast charge transfer information with sub-femtosecond timescale. Here we demonstrate that germanium selenide (GeSe) semiconductor exhibits electronic states-dependent charge delocalization time by resonant photo exciting the core electrons to different final states using hard-x-ray photoemission spectroscopy. Thanks to the experiment geometry and the different orbital polarizations in the conduction band, the delocalization time of electron in high energy electronic state probed from Se 1s is~470 as, which is three times longer than the delocalization time of electrons located in lower energy electronic state probed from Ge 1s. Our demonstration in GeSe offers an opportunity to precisely distinguish the energy-dependent dynamics in layered semiconductor, and will pave the way to design the ultrafast devices in the future. (10.1038/s42005-021-00635-y)
  DOI : 10.1038/s42005-021-00635-y
• Crucial Role of Conjugation in Monolayer-Protected Metal Clusters with Aromatic Ligands: Insights from the Archetypal Au$_{144}$L$_{60}$ Cluster Compounds
  
  • Sinha-Roy Rajarshi
  • López-Lozano Xóchitl
  • Whetten Robert
  • Weissker H.C.
  Journal of Physical Chemistry Letters, American Chemical Society, 2021, 12 (38), pp.9262-9268. Ligand-protected metal clusters are employed in a great many applications that include notably energy conversion and biomedical uses. The interaction between the ligands and the metallic cores, mediated by an often complex interface, profoundly influences the properties of small clusters, in particular. Nonetheless, the mechanisms of interaction remain far from fully understood. The Au144L60 class of cluster compounds has long played a central role in the study of monolayer-protected clusters, but total structure determination has been achieved only recently for a thiolated and an all-alkynyl cluster. Both ligands contain aromatic rings but differ in their ligation to the metal core: conjugation along a triple bond in the latter, saturation in the former. We demonstrate the paramount importance of the conjugation in the connection between aromatic ligand rings and metal cores for the electronic and optical properties and, by extension, the critical transport properties, providing a crucial element for the development of design-principle-based synthesis. (10.1021/acs.jpclett.1c02597)
  DOI : 10.1021/acs.jpclett.1c02597
• Synthesis of boron carbide from its elements up to 13 GPa
  
  • Chakraborti Amrita
  • Guignot Nicolas
  • Vast Nathalie
  • Le Godec Yann
  Journal of Physics and Chemistry of Solids, Elsevier, 2021, 159, pp.110253. The synthesis of boron carbide from its elements (boron and carbon) has been studied under pressures up to 13 GPa and optimum parameters have been determined by varying the (P, T, reactants) conditions. Stoichiometric mixtures of amorphous boron and amorphous carbon have been subjected to a range of temperatures from 1673 K to 2273 K at the pressure values of 2 GPa and 5 GPa. The formation temperatures have been compared to those obtained from mixtures of β rhombohedral boron and graphite, and β rhombohedral boron and amorphous carbon at 2 GPa and 5 GPa. The formation temperature is thus shown to be affected by the pressure and the choice of the reactants. The carbon concentration of boron carbide is also shown to be affected by the pressure at which it is synthesised from elements, and we propose pressure as a means to control the carbon content. Temperature cycling has also been shown to reduce the formation temperature of boron carbide at 13 GPa. The formation of α rhombohedral boron as an intermediate phase is seen at 5 GPa before the formation of boron carbide. (10.1016/j.jpcs.2021.110253)
  DOI : 10.1016/j.jpcs.2021.110253
• H2 production under gamma irradiation of a calcium aluminate cement: an experimental study on both cement pastes and its stable hydrates
  
  • Acher Loren
  • de Noirfontaine Marie-Noëlle
  • Chartier David
  • Gorse -Pomonti Dominique
  • Courtial Mireille
  • Tusseau-Nenez Sandrine
  • Cavani Olivier
  • Haas Jérémy
  • Dannoux- Papin Adeline
  • Dunstetter Frédéric
  Radiation Physics and Chemistry, Elsevier, 2021, 189, pp.109689. The objective of this paper is to investigate the use of calcium aluminate cements as alternative cements within the context of nuclear waste stabilization by solidification. Using an external 60 Co source, the effect of γ-radiation on H2 gas production of one of the calcium aluminate cement-based materials (cement "Ciment Fondu") and its stable hydrates, was studied. The amount of H2 produced by these cement pastes is found to be much lower (up to five times less) than that of the Portland cement pastes containing the same amount of water, especially in the low range of water to cement ratios (W/C ≤ 0.4) where water is essentially engaged in the hydrates. The H2 production of the two major hydrates of Ciment Fondu, gibbsite AH3 and katoite hydrogarnet C3AH6, is very low compared with that of the main hydrates of other cements (Portland cement, Calcium Sulfo-Aluminate and Magnesium Phosphate cements). The type of water engaged in the hydrates, as hydroxyl groups and/or molecular water, influences significantly the H2 production. Thus, the nature of the hydrate is a key parameter to the aim of optimizing cement matrices with respect to the gas production under irradiation. XRD analysis shows that the crystal structures of gibbsite and katoite are preserved up to very high doses under electron irradiation (3 GGy). This makes calcium aluminate cements (CAC) potential good candidates for nuclear waste conditioning from the point of view of their stability under irradiation. (10.1016/j.radphyschem.2021.109689)
  DOI : 10.1016/j.radphyschem.2021.109689
• High-temperature quantum anomalous Hall regime in a MnBi2Te4/Bi2Te3 superlattice
  
  • Deng Haiming
  • Chen Zhiyi
  • Wołoś Agnieszka
  • Konczykowski Marcin
  • Sobczak Kamil
  • Sitnicka Joanna
  • Fedorchenko Irina V
  • Borysiuk Jolanta
  • Heider Tristan
  • Pluciński Łukasz
  • Park Kyungwha
  • Georgescu Alexandru B
  • Cano Jennifer
  • Krusin-Elbaum Lia
  Nature Physics, Nature Publishing Group [2005-....], 2021, 17 (1), pp.36-42. (10.1038/s41567-020-0998-2)
  DOI : 10.1038/s41567-020-0998-2
• Key parameters for surface plasma wave excitation in the ultra-high intensity regime
  
  • Marini S
  • Kleij P S
  • Amiranoff F
  • Grech M
  • Riconda C
  • Raynaud Michèle
  Physics of Plasmas, American Institute of Physics, 2021, 28 (7), pp.073104. Ultra-short high-power lasers can deliver extreme light intensities (!10 20 W/cm 2 and 30 f s) and drive large amplitude Surface Plasma Wave (SPW) at over-dense plasma surface. The resulting current of energetic electron has great interest for applications, potentially scaling with the laser amplitude, provided that the laser-plasma transfer to the accelerated particles mediated by SPW is still efficient at ultra-high intensity. By means of particle-in-cell simulations, we identify the best condition for SPW excitation and show a strong correlation between the optimum surface plasma wave excitation angle and the laser's angle of incidence that optimize the electron acceleration along the plasma surface. We also discuss how plasma density and plasma surface shape can be adjusted in order to push to higher laser intensity the limit of surface plasma wave excitation. Our results open the way to new experiments on forthcoming multi-petawatt laser systems. (10.1063/5.0052599)
  DOI : 10.1063/5.0052599