Peer-reviewed Publications |
Basalgete, R., Torres-Diaz, D., Lafosse, A., Amiaud, L., Feraud, G., Jeseck, P., Philippe, L., Michaut, X., Fillion, J. - H., & Bertin, M. (2022). Indirect x-ray photodesorption of N215 and CO13 from mixed and layered ices. JOURNAL OF CHEMICAL PHYSICS, 157(8), 084308.
Résumé: X-ray photodesorption yields of N215 and CO13 are derived as a function of the incident photon energy near the N ( approximately 400 eV) and O K-edge ( approximately 500 eV) for pure N215 ice and mixed CO13:N215 ices. The photodesorption spectra from the mixed ices reveal an indirect desorption mechanism for which the desorption of N215 and CO13 is triggered by the photoabsorption of CO13 and N215, respectively. This mechanism is confirmed by the x-ray photodesorption of CO13 from a layered CO13/N215 ice irradiated at 401 eV on the N 1s --> pi* transition of N215. This latter experiment enables us to quantify the relevant depth involved in the indirect desorption process, which is found to be 30-40 monolayers in that case. This value is further related to the energy transport of Auger electrons emitted from the photoabsorbing N215 molecules that scatter toward the ice surface, inducing the desorption of CO13. The photodesorption yields corrected from the energy that can participate in the desorption process (expressed in molecules desorbed by eV deposited) do not depend on the photon energy; hence, they depend neither on the photoabsorbing molecule nor on its state after Auger decay. This demonstrates that x-ray induced electron stimulated desorption, mediated by Auger scattering, is the dominant process explaining the desorption of N215 and CO13 from the ices studied in this work.
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Hamoudi, H., Berdiyorov, G. R., Zekri, A., Tong, Y., Mansour, S., Esaulov, V. A., & Youcef-Toumi, K. (2022). Building block 3D printing based on molecular self-assembly monolayer with self-healing properties. SCIENTIFIC REPORTS, 12(1), 6806.
Résumé: The spontaneous formation of biological substances, such as human organs, are governed by different stimuli driven by complex 3D self-organization protocols at the molecular level. The fundamentals of such molecular self-assembly processes are critical for fabrication of advanced technological components in nature. We propose and experimentally demonstrate a promising 3D printing method with self-healing property based on molecular self-assembly-monolayer principles, which is conceptually different than the existing 3D printing protocols. The proposed molecular building-block approach uses metal ion-mediated continuous self-assembly of organic molecular at liquid-liquid interfaces to create 2D and 3D structures. Using this technique, we directly printed nanosheets and 3D rods using dithiol molecules as building block units.
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Lucero Manzano, A. M., Fuhr, J. D., Cantero, E. D., Famá, M., Sánchez, E. A., Esaulov, V. E., & Grizzi, O. (2022). Hydroxylation of the Zn terminated ZnO(0 0 0 1) surface under vacuum conditions. APPLIED SURFACE SCIENCE, 572, 151271.
Résumé: Under vacuum conditions, the polar surface ZnO(0 0 0 1) evolves in time forming a layer with H and additional O which changes the top layer stoichiometry and other properties such as its work function. In this work we present a study of the evolution of the ZnO(0 0 0 1) surface in ultra-high vacuum performed with time of flight direct recoil spectroscopy to detect the adsorbed H and O, plus other standard techniques including photoelectron spectroscopy and low energy electron diffraction. The experimental results are complemented with density functional theory (DFT) calculations for surfaces perfectly terminated and with triangular defects plus O adatoms. We show that the ZnO surface reaches a stable condition at an OH coverage of around 0.25 ML. We also studied the effect of increasing the partial pressure of H2 and of H2O on the layer growth. We observe that during the formation of the OH layer the work function decreases. Analysis of this variation of the work function with DFT reveals the role of the O adatoms in the adsorption process. Finally we show that the OH coverage decreases continuously with the increase of the sample temperature, without showing a well-defined desorption peak, which is in agreement with earlier predictions of the thermodynamics evolution. We believe that the present results contribute to clarify the behavior of the ZnO(0 0 0 1) surface under vacuum and will be useful in future works, particularly where H cannot be detected by standard techniques.
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Mery, M., González-Fuentes, C., Romanque-Albornoz, C., García, C., León, A. M., Arista, N. R., Esaulov, V. A., & Valdés, J. E. (2022). The free electron model and the electronic energy losses of protons at low velocities interacting with polycrystalline tantalum. RADIATION EFFECTS AND DEFECTS IN SOLIDS, 177(1-2), 161–172.
Résumé: In this letter, we report experimental data and theoretical work on the electronic energy loss and energy loss straggling of protons transmitted through self-supported thin films of tantalum in a polycrystalline tetragonal phase (beta-Ta). Low-energy protons with energies below 10 keV and Ta films with nominal thickness of 6, 9 and 12 nm are used. The aim of this work is to understand the unexpected values of the Ta stopping power for low-energy proton backscattering reported recently, which are far from the prediction of the standard free electron gas model and semi-empirical approaches. This had led the authors to conclude the failure of the free electron model. Our transmission measurements confirm these experimental results. In this work, a qualitative discussion and quantitative explanation of our experimental results is given, using an approach based on the density functional theory within the framework of the free electron gas (FEG) model. We performed semiclassical deterministic trajectory simulations and employ the local density approximation model, using an inhomogeneous electron density distribution and the polycrystalline character of Ta samples.
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Pan, P., Debiossac, M., & Roncin, P. (2022). Temperature dependence in fast-atom diffraction at surfaces. PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 24(20), 12319–12328.
Résumé: Grazing incidence fast atom diffraction at crystal surfaces (GIFAD or FAD) has demonstrated coherent diffraction both at effective energies close to one eV (lambda( perpendicular) approximately 14 pm for He) and at elevated surface temperatures offering high topological resolution and real time monitoring of growth processes. This is explained by a favorable Debye-Waller factor specific to the multiple collision regime of grazing incidence. This paper presents the first extensive evaluation of the temperature behavior between 177 and 1017 K on a LiF surface. Similarly to diffraction at thermal energies (TEAS), an exponential attenuation of the elastic intensity is observed but, contrarily to TEAS, the maximum coherence is not directly reduced by the attraction forces that increase the effective impact energy. It is more influenced by the surface stiffness and appears very sensitive to surface defects.
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Pan, P., Rad, J. N., & Roncin, P. (2022). A setup for grazing incidence fast atom diffraction. REVIEW OF SCIENTIFIC INSTRUMENTS, 93(9), 093305.
Résumé: We describe a UHV setup for grazing incidence fast atom diffraction (GIFAD) experiments. The overall geometry is simply a source of keV atoms facing an imaging detector. Therefore, it is very similar to the geometry of reflection high energy electron diffraction experiments used to monitor growth at surfaces. Several custom instrumental developments are described making GIFAD operation efficient and straightforward. The difficulties associated with accurately measuring the small scattering angle and the related calibration are carefully analyzed.
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Shao, F., Woo, S. Y., Wu, N., Schneider, R., Mayne, A. J., de Vasconcellos, S. M., Arora, A., Carey, B. J., Preuß, J. A., Bonnet, N., Och, M., Mattevi, C., Watanabe, K., Taniguchi, T., Niu, Z., Bratschitsch, R., & Tizei, L. H. G. (2022). Substrate influence on transition metal dichalcogenide monolayer exciton absorption linewidth broadening. Physical Review Materials, 6, 074005.
Résumé: The excitonic states of transition metal dichalcogenide (TMD) monolayers are heavily influenced by their external dielectric environment and depend on the substrate used. In this work, various wide band gap dielectric materials, namely hexagonal boron nitride (h−BN) and amorphous silicon nitride (Si3N4), under different configurations as support or encapsulation material for WS2 monolayers, are investigated to disentangle the factors contributing to inhomogeneous broadening of exciton absorption lines in TMDs using electron energy loss spectroscopy in a scanning transmission electron microscope. In addition, monolayer roughness in each configuration was determined from tilt series of electron diffraction patterns by assessing the broadening of diffraction spots by comparison with simulations. From our experiments, the main factors that play a role in linewidth broadening can be classified, in increasing order of importance, by monolayer roughness, surface cleanliness, and substrate-induced charge trapping. Furthermore, because high-energy electrons are used as a probe, electron-beam-induced damage on bare TMD monolayers is also revealed to be responsible for irreversible linewidth increases. h−BN not only provides clean surfaces of TMD monolayers and minimal charge disorder, but can also protect the TMD from irradiation damage. This work provides a better understanding of the mechanisms by which h−BN remains, to date, the most compatible material for 2D material encapsulation, facilitating the realization of intrinsic material properties to their full potential.
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Shi, Y., Yin, L., Ding, B., Song, X., Zhang, L., Guo, Y., Chen, L., Chen, X., Melkozerova, J. A., Klavsyuk, A. L., Gainullin, I. K., & Esaulov, V. A. (2022). Thickness-dependent neutralization of low-energy alkali-metal ions scattering on graphene. PHYSICAL REVIEW A, 105(4), 042807.
Résumé: A challenging effort is under way to understand the essence of the quantum size effect of two-dimensional materials in order to achieve the ultimate goal of arbitrarily tailoring their properties in the near future. Here we present experimental and theoretical study of resonant neutralization of low-energy alkali-metal ions on clean and graphene-covered polycrystalline copper surfaces. The ion neutralization strongly depends on the number of graphene layers, and it gradually saturates for three to five layers of graphene. This result is consistent with that for the graphite surface. The neutral fraction for the clean polycrystalline copper surface is found to be significantly higher than that for the graphene-covered surface, which is not consistent with known regularities. We quantitatively explain those observations through the small energy level width of resonant electron transfer that is determined by the special electronic structure of graphene layers. This finding indicates that resonant neutralization spectroscopy has promising applications in the detection of the quantum size effects of two-dimensional materials at an atomic layer level.
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Actes de Conférences |
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Shao, F., Woo, S. Y., Wu, N., Schneider, R., Mayne, A. J., Michaelis, S., Arora, A., Carey, B. J., Preuß, J. A., Bonnet, N., Mattevi, C., Watanabe, K., Taniguchi, T., Bratschitsch, R., & Tizei, L. H. G. (2022). Disentangling Exciton Linewidth Broadening Factors in Transition Metal Dichalcogenide Monolayer with Electron Energy Loss Spectroscopy. In MICROSCOPY & MICROANALYSIS (Vol. 28, pp. 1778–1779).
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Woo, S. Y., Shao, F., Wu, N., Schneider, R., Arora, A., Preuß, J. A., Carey, B. J., de Vasconcellos, S. M., Mayne, A. J., Bratschitsch, R., & Tizei, L. H. G. (2022). Strain Relaxation and Excitonic Absorption of Atomically-Reconstructed WSe2 Moiré Superlattices. In MICROSCOPY & MICROANALYSIS (Vol. 28, pp. 2462–2463).
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