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Accueil > Équipes scientifiques > Surfaces, Interfaces, Molecules & 2D Materials (SIM2D) > Publications > 2023
2023
Peer-reviewed Publications |
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Basalgète, R., Torres-Díaz, D., Lafosse, A., Amiaud, L., Féraud, G., Jeseck, P., Philippe, L., Michaut, X., Fillion, J. - H., & Bertin, M. (2023). X-ray photodesorption of complex organic molecules in protoplanetary disks: I. Acetonitrile CH3CN. ASTRONOMY & ASTROPHYSICS, 676, A13.
Résumé: Context. X-rays emitted from pre-main-sequence stars at the center of protoplanetary disks can induce nonthermal desorption from interstellar ices populating the cold regions of the disk. This process, known as X-ray photodesorption, needs to be quantified for complex organic molecules (COMs), including acetonitrile CH3CN, which has been detected in several disks.
Aims. The purpose of this work is to experimentally estimate the X-ray photodesorption yields of neutral species from pure CH3CN ices and from interstellar ice analogs for which CH3CN is mixed either in a CO-dominated ice or in a H2O-dominated ice. Methods. The ices, grown in an ultrahigh vacuum chamber, were irradiated at 15 K by soft X-rays from synchrotron light (SOLEIL synchrotron) in the N K edge region (395–420 eV) and in the O K edge region (530–555 eV). X-ray photodesorption was probed in the gas phase via quadrupole mass spectrometry by monitoring the changes in the mass signals due to the X-ray irradiation of the ices. X-ray photodesorption yields were derived from the mass signals and were extrapolated to higher X-ray energies in order to provide astrophysical yields adapted to astrochemical models. |
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Bretel, R., Le Moal, S., Oughaddou, H., & Le Moal, E. (2023). Hydrogen-bonded one-dimensional molecular chains on ultrathin insulating films: Quinacridone on KCl/Cu(111). Phys. Rev. B, 108, 125423.
Résumé: We report on the growth of one-dimensional (1D) chains of the prochiral quinacridone (QA) molecule on ultrathin KCl films on Cu(111) in ultrahigh vacuum. Using low-temperature scanning tunneling microscopy (STM), we observe straight homochiral 1D chains of QA molecules on one (1L), two (2L), and three (3L) atomic layer thick (100)-terminated KCl islands. The KCl films mostly consist of 2L-thick KCl islands delineated by long polar and short nonpolar edges. These 2L-thick KCl islands are topped by smaller one-atom-thick KCl islands or pits, which are delineated by nonpolar step edges. We find that QA chains can nucleate at these nonpolar step edges or on top of KCl terraces without assistance of step edges. In both cases, the longest straight QA chains observed grow along the KCl ⟨100⟩ directions or slightly rotated (typically less than 10∘) from them. Intermolecular distances ranging from 6.4 Å to 6.8 Å are measured for QA chains on KCl/Cu(111), which is compatible with hydrogen bonds between neighboring flat-lying QA molecules. These intermolecular distances being larger than the measured KCl lattice parameter (i.e., 6.21 Å at 78 K), QA chain growth on KCl/Cu(111) is incommensurate. Molecular arrangement models for the QA chains on KCl are proposed, based on the analysis of the STM images.
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Pan, P., Kanitz, C., Debiossac, M., Le-Guen, A., Rad, J. N., & Roncin, P. (2023). Lateral line profiles in fast-atom diffraction at surfaces. PHYSICAL REVIEW B, 108(3), 035413.
Résumé: Grazing incidence fast-atom diffraction (GIFAD) uses keV atoms to probe the topmost layer of crystalline surfaces. The atoms are scattered by the potential energy landscape of the surface onto elastic diffraction spots located at the Bragg angles and on the Laue circle. However, atoms transfer a significant momentum to the surface, giving rise to possible phonon excitation. This causes the inelastic intensity to spread above and below the circle along the direction of the surface normal. The relative intensity of the elastic contribution is well fitted by the Debye-Waller model adapted to GIFAD, but the composite azimuthal line profile governing the ability to resolve diffraction spots has not been investigated in detail. The paper reports a series of diffraction measurements of helium on a LiF(001) surface revealing marked differences in the polar (θ) and lateral (ϕ) inelastic profiles but also similarities in the evolution of their line widths σθ and σϕ. We observe two regimes: When elastic diffraction is significant, the Laue circle appears as a reference for inelastic diffraction; the azimuthal inelastic line shape is an exponential decay and its width increases almost linearly as the scattering angle deviates from the specular condition. When elastic diffraction weakens, the inelastic line shape evolves towards a Gaussian and its width is no longer minimum on the Laue circle. As a possible difference with x ray, neutrons, and electrons, the in-plane motion of surface atoms may not be the dominant cause of the broadening of the lateral profile in GIFAD.
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