Peer-reviewed Publications |
Basalgète, R., Dupuy, R., Féraud, G., Romanzin, C., Philippe, L., Michaut, X., Michoud, J., Amiaud, L., Lafosse, A., Fillion, J. - H., & Bertin, M. (2021). Complex organic molecules in protoplanetary disks: X-ray photodesorption from methanol-containing ices: I. Pure methanol ices. ASTRONOMY & ASTROPHYSICS, 647, A35.
Résumé: Context. Astrophysical observations show complex organic molecules (COMs) in the gas phase of protoplanetary disks. X-rays emitted from the central young stellar object that irradiate interstellar ices in the disk, followed by the ejection of molecules in the gas phase, are a possible route to explain the abundances observed in the cold regions. This process, known as X-ray photodesorption, needs to be quantified for methanol-containing ices. This Paper I focuses on the case of X-ray photodesorption from pure methanol ices.
Aims. We aim at experimentally measuring X-ray photodesorption yields (in molecule desorbed per incident photon, displayed as molecule/photon for more simplicity) of methanol and its photo-products from pure CH3OH ices, and to shed light on the mechanisms responsible for the desorption process.
Methods. We irradiated methanol ices at 15 K with X-rays in the 525–570 eV range from the SEXTANTS beam line of the SOLEIL synchrotron facility. The release of species in the gas phase was monitored by quadrupole mass spectrometry, and photodesorption yields were derived.
Results. Under our experimental conditions, the CH3OH X-ray photodesorption yield from pure methanol ice is ~10−2 molecule/photon at 564 eV. Photo-products such as CH4, H2CO, H2O, CO2, and CO also desorb at increasing efficiency. X-ray photodesorption of larger COMs, which can be attributed to either ethanol, dimethyl ether, and/or formic acid, is also detected. The physical mechanisms at play are discussed and must likely involve the thermalization of Auger electrons in the ice, thus indicating that its composition plays an important role. Finally, we provide desorption yields applicable to protoplanetary disk environments for astrochemical models.
Conclusions. The X-rays are shown to be a potential candidate to explain gas-phase abundances of methanol in disks. However, more relevant desorption yields derived from experiments on mixed ices are mandatory to properly support the role played by X-rays in nonthermal desorption of methanol (see Paper II).
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Basalgète, R., Dupuy, R., Féraud, G., Romanzin, C., Philippe, L., Michaut, X., Michoud, J., Amiaud, L., Lafosse, A., Fillion, J. - H., & Bertin, M. (2021). Complex organic molecules in protoplanetary disks: X-ray photodesorption from methanol-containing ices: II. Mixed methanol-CO and methanol-H<sub>2</sub>O ices. ASTRONOMY & ASTROPHYSICS, 647, A36.
Résumé: Context. Astrophysical observations show complex organic molecules (COMs) in the gas phase of protoplanetary disks. X-rays emitted from the central young stellar object (YSO) that irradiate interstellar ices in the disk, followed by the ejection of molecules in the gas phase, are a possible route to explain the abundances observed in the cold regions. This process, known as X-ray photodesorption, needs to be quantified for methanol-containing ices.
Aims. We aim at experimentally measuring X-ray photodesorption yields (in molecule desorbed per incident photon, displayed as molecule/photon for more simplicity) of methanol and its photo-products from binary mixed ices: 13CO:CH3OH ice and H2O:CH3OH ice.
Methods. We irradiated these ices at 15 K with X-rays in the 525–570 eV range from the SEXTANTS beam line of the SOLEIL synchrotron facility. The release of species in the gas phase was monitored by quadrupole mass spectrometry, and photodesorption yields were derived.
Results. For 13CO:CH3OH ice, CH3OH X-ray photodesorption yield is estimated to be ∼10−2 molecule/photon at 564 eV. X-ray photodesorption of larger COMs, which can be attributed to either ethanol, dimethyl ether, and/or formic acid, is detected with a yield of ∼10−3 molecule/photon. When methanol is mixed with water, X-ray photodesorption of methanol and of the previous COMs is not detected. X-ray induced chemistry, dominated by low-energy secondary electrons, is found to be the main mechanism that explains these results. We also provide desorption yields that are applicable to protoplanetary disk environments for astrochemical models.
Conclusions. The X-ray emission from YSOs should participate in the enrichment of the protoplanetary disk gas phase with COMs such as methanol in the cold and X-ray dominated regions because of X-ray photodesorption from methanol-containing ices.
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Bouaziz, M., Zhang, W., Tong, Y., Oughaddou, H., Enriquez, H., Mlika, R., Korri-Youssoufi, H., Chen, Z., Xiong, H., Cheng, Y., & Bendounan, A. (2021). Phase transition from Au–Te surface alloy towards tellurene-like monolayer. 2D MATERIALS, 8, 015029.
Résumé: Two-dimensional (2D) chalcogen-based layers will be among the next generation of materials for potential high-tech applications. We present the structural and electronic properties of Tellurium (Te) deposited on the Au(111) surface by high temperature vapor deposition in UHV. We discuss the possible scenarios for the formation of 2D layers ; either AuTe2 metal dichalcogenide, or Au–Te alloy or a single Tellurene layer. Low energy electron diffraction (LEED) and scanning tunneling microscopy (STM) show the existence of several surface reconstructions depending on the Te film thickness in the sub-monolayer regime. We observe the survival of the well-known spin-split Shockley state of the Au(111) surface after Te deposition. The state is shifted to higher binding energy, suggesting a charge transfer at the interface. For 0.33 ML Te, new dispersive bands in the angle-resolved photoemission (ARPES), are due to the strong hybridization between the electronic states of Te and Au. The low intensity and back-folding at the boundaries of the reduced surface Brillouin zone (R-SBZ), prove that these electronic bands represent a naturel 2D electron gas, strongly disturbed by the surface reconstruction. This indicates the fromation of a surface Au–Te alloy. At 0.5 ML Te, a rich, thickness-dependent transition develops from the surface alloy to Tellurene-like structure which excludes the growth of AuTe2 monolayer. Both the surface alloy and the Tellurene monolayer are semiconducting with an occupied-state gap of 0.65 eV.
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Dai, J., Frantzeskakis, E., Aryal, N., Chen, K. - W., Fortuna, F., Rault, J. E., Le Fevre, P., Balicas, L., Miyamoto, K., Okuda, T., Manousakis, E., Baumbach, R. E., & Santander-Syro, A. F. (2021). Experimental Observation and Spin Texture of Dirac Node Arcs in Tetradymite Topological Metals. PHYSICAL REVIEW LETTERS, 126, 196407.
Résumé: We report the observation of a nontrivial spin texture in Dirac node arcs, i.e., novel topological objects formed when Dirac cones of massless particles extend along an open one-dimensional line in momentum space. We find that such states are present in all the compounds of the tetradymite M{2}Te{2}X family (M=Ti, Zr, or Hf and X=P or As) regardless of the weak or strong character of the topological invariant. The Dirac node arcs in tetradymites are thus the simplest possible textbook example of a type-I Dirac system with a single spin-polarized node arc.
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Debiossac, M., Pan, P., & Roncin, P. (2021). Grazing incidence fast atom diffraction, similarities and differences with thermal energy atom scattering (TEAS). PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 23, 7615–7636.
Résumé: Grazing incidence fast atom diffraction (GIFAD) at surfaces has made rapid progress and has established itself as a surface analysis tool where effective energy E perpendicular of the motion towards the surface is in the same range as that in thermal energy atom scattering (TEAS). To better compare the properties of both techniques, we use the diffraction patterns of helium and neon atoms impinging on a LiF (001) surface as a model system. E-Scan, theta-scan, and phi-scan are presented where the primary beam energy E is varied between a few hundred eV up to five keV, the angle of incidence theta between 0.2 and 2 degrees and the azimuthal angle phi around 360 degrees . The resulting diffraction charts are analyzed in terms of high and low values of effective energy E perpendicular. The former provides high resolution at the positions of the surface atoms and the attached repulsive interaction potentials while the second is sensitive to the attractive forces towards the surface. The recent progress of inelastic diffraction is briefly presented.
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Frantzeskakis E, Dai J, Bareille C, Rodel TC, Guttler M, Ran S, Kanchanavatee N, Huang K, Pouse N, Wolowiec CT, Rienks EDL, Lejay P, Fortuna F, Maple MB, & Santander-Syro AF. (2021). From hidden order to antiferromagnetism: Electronic structure changes in Fe-doped URu2Si2. PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA, 118(27), 2020750118.
Résumé: In matter, any spontaneous symmetry breaking induces a phase transition characterized by an order parameter, such as the magnetization vector in ferromagnets, or a macroscopic many-electron wave function in superconductors. Phase transitions with unknown order parameter are rare but extremely appealing, as they may lead to novel physics. An emblematic and still unsolved example is the transition of the heavy fermion compound [Formula: see text] (URS) into the so-called hidden-order (HO) phase when the temperature drops below [Formula: see text] K. Here, we show that the interaction between the heavy fermion and the conduction band states near the Fermi level has a key role in the emergence of the HO phase. Using angle-resolved photoemission spectroscopy, we find that while the Fermi surfaces of the HO and of a neighboring antiferromagnetic (AFM) phase of well-defined order parameter have the same topography, they differ in the size of some, but not all, of their electron pockets. Such a nonrigid change of the electronic structure indicates that a change in the interaction strength between states near the Fermi level is a crucial ingredient for the HO to AFM phase transition.
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Mery, M., Uribe, J. D., Flores, M., Arista, N. R., Esaulov, V. A., & Valdés, J. E. (2021). Electronic energy loss and straggling in low energy H+and H2+interaction with silicon films. RADIATION EFFECTS AND DEFECTS IN SOLIDS, 176(1-2), 73–91.
Résumé: The appearance of atomic structures of nanoscopic dimensions, with new and interesting physical properties, requires revisiting various aspects of particle interaction with solid matter. For this purpose in this work we present a study of electronic energy loss of H+ and protons (fragments) from the dissociation of H-2 (+) ions interacting with ultra-thin amorphous silicon films for incident beam energies from 1 to 10 keV/u. We report measurements of energy distributions of transmitted protons and molecular fragments through these films, from which we derive the average energy losses and the energy loss straggling. Our experimental findings turn out to be in good agreement with nonlinear electronic stopping power models and some previous experimental data.
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Pan, P., Debiossac, M., & Roncin, P. (2021). Polar inelastic profiles in fast-atom diffraction at surfaces. PHYSICAL REVIEW B, 104, 165415.
Résumé: Elastic diffraction of fast atoms at crystal surfaces under grazing incidence θ ≈ 1° has strong similarities with atomic diffraction at thermal energies discovered almost hundred years ago. Here, we focus on the polar scattering profile, which does not exhibit diffraction features but shows well-defined elastic and inelastic components that are found to be essentially independent of the crystallographic axis. The width σθ of the inelastic component is very sensitive to the weak attractive forces responsible for the physisorption. This effect is visible on an energy range almost ten times larger than the depth D of the physisorption well. Experimental data are analyzed using a binary collision model with a Morse potential where the width σθ of the scattering profile is connected to the classical energy loss and is governed by the surface stiffness, defined as the logarithmic derivative of the interaction potential along the surface normal. The main outcome is that the weak attractive forces make the mean surface potential almost twice harder at low energy.
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Quertite, K., Enriquez, H., Trcera, N., Tong, Y., Bendounan, A., Mayne, A. J., Dujardin, G., Lagarde, P., El Kenz, A., Benyoussef, A., Dappe, Y. J., Kara, A., & Oughaddou, H. (2021). Silicene Nanoribbons on an Insulating Thin Film. ADVANCED FUNCTIONAL MATERIALS, 31, 2007013.
Résumé: Silicene, a new 2D material has attracted intense research because of the
ubiquitous use of silicon in modern technology. However, producing freestanding
silicene has proved to be a huge challenge. Until now, silicene could be synthesized only on metal surfaces where it naturally forms strong interactions with the metal substrate that modify its electronic properties. Here, the authors report the first experimental evidence of silicene sheet on an insulating NaCl thin film. This work represents a major breakthrough, for the study of the intrinsic properties of silicene, and by extension to other 2D materials that have so far only been grown on metal surfaces.
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Rathore, A., Cipriani, M., Huang, C. - C., Amiaud, L., Dablemont, C., Lafosse, A., Ingolfsson, O., De Simone, D., & De Gendt, S. (2021). Electron-induced fragmentation mechanisms in organic monomers and their implications for photoresist optimization for EUV lithography. PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 23, 9228–9234.
Résumé: Secondary electrons generated during the Extreme Ultraviolet Lithography (EUVL) process are predominantly responsible for inducing important patterning chemistry in photoresist films. Therefore, it is crucial to understand the electron-induced fragmentation mechanisms involved in EUV-resist systems to improve their patterning performance. To facilitate this understanding, mechanistic studies were carried out on simple organic EUV-resist monomers, methyl isobutyrate (MIB) and methacrylic acid (MAA), both in the condensed and gas phases. Electron-stimulated desorption (ESD) studies on MIB in the condensed phase showed desorption peaks at around 2 and 9 eV electron energies. The gas-phase study on MIB showed that the monomer followed the dissociative ionization (DI) fragmentation pathway, under single collision conditions, which opened up at electron energies above about 11 eV. No signs of dissociative electron attachment (DEA) were detected for MIB in the gas phase under single collision conditions. However, DEA was an active process in MAA in the gas phase under single collision conditions at around 2 eV, showing that slight modifications of the molecular structures of photoresists may serve to sensitize them to certain electron-induced processes.
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Tong, Y., Berdiyorov, G. R., Sinopoli, A., Madjet, M. E., Esaulov, V. A., & Hamoudi, H. (2021). An estimation on the mechanical stabilities of SAMs by low energy Ar(+) cluster ion collision. SCIENTIFIC REPORTS, 11(1), 12772.
Résumé: The stability of the molecular self-assembled monolayers (SAMs) is of vital importance to the performance of the molecular electronics and their integration to the future electronics devices. Here we study the effect of electron irradiation-induced cross-linking on the stability of self-assembled monolayer of aromatic 5,5'-bis(mercaptomethyl)-2,2'-bipyridine [BPD; HS-CH(2)-(C(5)H(3)N)(2)-CH(2)-SH] on Au (111) single crystal surface. As a refence, we also study the properties of SAMs of electron saturated 1-dodecanethiol [C12; CH(3)-(CH(2))(11)-SH] molecules. The stability of the considered SAMs before and after electron-irradiation is studied using low energy Ar(+) cluster depth profiling monitored by recording the X-ray photoelectron spectroscopy (XPS) core level spectra and the UV-photoelectron spectroscopy (UPS) in the valance band range. The results indicate a stronger mechanical stability of BPD SAMs than the C12 SAMs. The stability of BPD SAMs enhances further after electron irradiation due to intermolecular cross-linking, whereas the electron irradiation results in deterioration of C12 molecules due to the saturated nature of the molecules. The depth profiling time of the cross-linked BPD SAM is more than 4 and 8 times longer than the profiling time obtained for pristine and BPD and C12 SAMs, respectively. The UPS results are supported by density functional theory calculations, which show qualitative agreement with the experiment and enable us to interpret the features in the XPS spectra during the etching process for structural characterization. The obtained results offer helpful options to estimate the structural stability of SAMs which is a key factor for the fabrication of molecular devices.
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Vallejo Bustamante, J., Wu, N. J., Fermon, C., Pannetier-Lecoeur, M., Wakamura, T., Watanabe, K., Taniguchi, T., Pellegrin, T., Bernard, A., Daddinounou, S., Bouchiat, V., Gueron, S., Ferrier, M., Montambaux, G., & Bouchiat, H. (2021). Detection of graphene's divergent orbital diamagnetism at the Dirac point. SCIENCE, 374(6573), 1399–1402.
Résumé: The electronic properties of graphene have been intensively investigated over the past decade. However, the singular orbital magnetism of undoped graphene, a fundamental signature of the characteristic Berry phase of graphene’s electronic wave functions, has been challenging to measure in a single flake. Using a highly sensitive giant magnetoresistance (GMR) sensor, we have measured the gate voltage–dependent magnetization of a single graphene monolayer encapsulated between boron nitride crystals. The signal exhibits a diamagnetic peak at the Dirac point whose magnetic field and temperature dependences agree with long-standing theoretical predictions. Our measurements offer a means to monitor Berry phase singularities and explore correlated states generated by the combined effects of Coulomb interactions, strain, or moiré potentials.
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Zhang, W., Enriquez, H., Tong, Y., Mayne, A. J., Bendounan, A., Smogunov, A., Dappe, Y. J., Kara, A., Dujardin, G., & Oughaddou, H. (2021). Flat epitaxial quasi-1D phosphorene chains. NATURE COMMUNICATIONS, 12, 5160.
Résumé: The emergence of peculiar phenomena in 1D phosphorene chains (P chains) has been proposed in theoretical studies, notably the Stark and Seebeck effects, room temperature magnetism, and topological phase transitions. Attempts so far to fabricate P chains, using the top-down approach starting from a few layers of bulk black phosphorus, have failed to produce reliably precise control of P chains. We show that molecular beam epitaxy gives a controllable bottom-up approach to grow atomically thin, crystalline 1D flat P chains on a Ag(111) substrate. Scanning tunneling microscopy, angle-resolved photoemission spectroscopy, and density functional theory calculations reveal that the armchair-shaped chains are semiconducting with an intrinsic 1.80 ± 0.20 eV band gap. This could make these P chains an ideal material for opto-electronic devices.
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Actes de Conférences |
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Shao, F., Woo, S. Y., Wu, N., Mayne, A. J., Schneider, R., Michaelis, S., Arora, A., Carey, B., Preuß, J., Bratschitsch, R., & Tizei, L. H. G. (2021). Understanding transition metal dichalcogenide absorption line widths in electron energy loss spectroscopy. In MICROSCOPY & MICROANALYSIS (Vol. 27, pp. 1170–1172).
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Tong, Y., Oughaddou, H., Enriquez, H., Kubsky, S., Esaulov, V., & Bendounan, A. (2021). Adsorption of Se on Cu(1 0 0) and formation of two-dimensional copper selenide layer. In MATERIALS TODAY PROCEEDINGS (Vol. 39, pp. 1170–1174).
Résumé: In order to understand the adsorption process of selenium (Se) and Se-based molecules on noble metal surfaces, we report here on the properties of a thin film of Se on Cu(1 0 0) substrate. The deposition was carried out by incubating of a clean Cu(1 0 0) surface into Na2Se solution under controlled conditions. The film properties were analysed as a function of the annealing temperature of the sample, using Low Energy Electron Diffraction (LEED) and photoemission techniques. A progressive structural transition from disordered thick layer to a two-dimensional Copper Selenide CuSe thin layer is obtained upon the thermal treatment. Our study proves that a large scale, well-ordered, and highly-stabilized metal chalcogenide layer can be produced for promising use in potential applications.
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Zhang, W., Enriquez, H., Mayne, A. J., Bendounan, A., Seitsonen, A. P., Kara, A., Dujardin, G., & Oughaddou, H. (2021). First steps of blue phosphorene growth on Au(1 1 1). In MATERIALS TODAY PROCEEDINGS (Vol. 39, pp. 1153–1156).
Résumé: Blue phosphorene (blue-P) has attracted considerable attention due to its potential applications in optical and electronic devices. However, its synthesis has remained a challenge. Here, we report an experimental investigation of the first steps of blue-P growth on Au(1 1 1) surface by molecular-beam epitaxy. The structure was characterized by in situ low temperature scanning tunneling microscopy, low-energy electron diffraction, combined with density functional theory calculations. We reveal two-dimensional (2D) phosphorus clusters (P-clusters) formed on surface at 150 °C, where the most prevalent structure of P-clusters is composed of triangles with six protrusions. We also demonstrate the transformation of these P-clusters into a single layer of blue-P after post-annealing at 260 °C. Our observation of the growth process is a necessary step for exploring the growth mechanisms further.
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