Peer-reviewed Publications |
Alsalama, M., Tong, Y., Berdiyorov, G. R., Esaulov, V., & Hamoudi, H. (2023). Refilling strategy of crosslinked aromatic SAMs for enhancing the molecular packing density. APPLIED SURFACE SCIENCE, 612, 155867.
Résumé: The stability and uniform coverage of molecular self-assembled monolayers (SAMs) on metal substrates is of crucial importance for device integration. One strategy to enhance the stability of the SAMs is based on electron irradiation-induced intermolecular crosslinking. During this process, the coverage area of the SAMs decreases due to the formation of carbon-carbon covalent bonds between the neighboring molecules, which leaves empty spaces at the interfaces. Therefore, to increase molecular coverage, the empty spaces can be refilled either by the same or different types of molecules. In this article, we demonstrate a multistep method of creating densely packed SAMs of biphenyl-4-4-thiol molecules after electron radiation. 4 '-Mercapto-[1,1 '-biphenyl]-4-carbonitrile molecules are used for refilling because of the distinct signature of nitrogen atoms as a marker in the X-ray photoelectron spectroscopy (XPS) spectra. We used these molecules to estimate the reduction of the area of SAM coverage after electron radiation. As a result, 28.9% +/- 5.9% of the total surface area was released. The exper-imental results are supplemented by density functional theory calculations to estimate the area of the empty regions caused by intermolecular crosslinking. The theoretical predictions align closely with the experimental results. These findings can be of practical importance in creating stable molecular SAM devices using the pro-posed alternating irradiation and refilling procedure.
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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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Buhler, J., Roncin, P., & Brand, C. (2023). Describing the scattering of keV protons through graphene. FRONTIERS IN CHEMISTRY, 11, 1291065.
Résumé: Implementing two-dimensional materials in technological solutions requires fast, economic, and non-destructive tools to ensure efficient characterization. In this context, scattering of keV protons through free-standing graphene was proposed as an analytical tool. Here, we critically evaluate the predicted effects using classical simulations including a description of the lattice's thermal motion and the membrane corrugation via statistical averaging. Our study shows that the zero-point motion of the lattice atoms alone leads to considerable broadening of the signal that is not properly described by thermal averaging of the interaction potential. In combination with the non-negligible probability for introducing defects, it limits the prospect of proton scattering at 5 keV as an analytic tool.
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Debiossac, M., Pan, P., & Roncin, P. (2023). Elastic and inelastic diffraction of fast neon atoms on a LiF surface. PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 25(45), 30966–30974.
Résumé: Grazing incidence fast atom diffraction has mainly been investigated with helium atoms, considered as the best possible choice for surface analysis. This article presents experimental diffraction profiles recorded with neon projectile, between 300 eV and 4 keV kinetic energy with incidence angles theta(i) between 0.3 and 1.5 degrees along three different directions of a LiF(001) crystal surface. These correspond to perpendicular energy ranging from a few meV up to almost 1 eV. A careful analysis of the scattering profile allows us to extract the diffracted intensities even when inelastic effects become so large that most quantum signatures have disappeared. The relevance of this approach is discussed in terms of surface topology.
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Neziri, E., Zhang, W., Smogunov, A., Mayne, A. J., Kara, A., Dappe, Y. J., & Oughaddou, H. (2023). Structural properties of Bi/Au(110). NANOTECHNOLOGY, 34(23), 235601.
Résumé: Atomically thin bismuth films (2D Bi) are becoming a promising research area due to their unique properties and their wide variety of applications in spintronics, electronic and optoelectronic devices. We report on the structural properties of Bi on Au(110), explored by low-energy electron diffraction (LEED), scanning tunneling microscopy (STM) and density functional theory (DFT) calculations. At a Bi coverage lower than one monolayer (1 ML) various reconstructions are observed, we focus on Bi/Au(110)-c(2 x 2) reconstruction (at 0.5 ML) and Bi/Au(110)-(3 x 3) structure (at 0.66 ML). We propose models for both structures based on STM measurements and further confirm by DFT calculations.
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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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Quertite, K., Enriquez, H., Trcera, N., Lagarde, P., Bendounan, A., Mayne, A. J., Dujardin, G., El kenz, A., Benyoussef, A., Kara, A., & Oughaddou, H. (2023). First steps of silicene growth on an insulating thin-film: effect of the substrate temperature. THE EUROPEAN PHYSICS JOURNAL APPLIED PHYSICS, 98, 41.
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Valdés, J. E., León, A. M., Arista, N., & Esaulov, V. A. (2023). Anomalous electronic energy losses in protons passing through Gd thin films. RADIATION EFFECTS AND DEFECTS IN SOLIDS, 178(1-2), 20–27.
Résumé: We report a theoretical analysis of recent data on the unexpectedly high electronic energy loss protons in a polycrystalline gadolinium target. These results led the authors of this data to conclude that the free electron model used to analyse these results fails. In this work we provide a quantitative explanation of the experimental results, using an approach based on density functional theory within the framework of the free electron gas model. We performed semi-classical trajectory simulations (SCTS) and employ the local-density-approximation model (LDA), using an inhomogeneous electron density distribution and the polycrystalline character of Gd samples. The good agreement obtained, delineates the need of considering a realistic description of a particle trajectory and the effective electron density 'seen' along it, whose description remains within a FEG model.
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