2023 |
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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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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2022 |
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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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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2021 |
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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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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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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2020 |
Hamoudi, H., Berdiyorov, G. R., Ariga, K., & Esaulov, V. (2020). Bottom-up fabrication of the multi-layer carbon metal nanosheets. RSC ADVANCES, 10(13), 7987–7993.
Résumé: Ordered carbon composite materials have great potential for practical applications in many areas such as energy conversion, quantum computing, biotechnologies, and electronics. In this work, we demonstrate a state-of-the-art self-assembly driven building block approach to create new layered carbon-metal composite materials with advanced properties. We fabricate molecular nanocomposites using self-assembled metal intercalated multi-layers of dithiol derivatives. The obtained structures are analysed using different characterization tools (such as X-ray photoelectron and Raman spectroscopy and atomic force microscopy) and their electronic transport properties are studied by four-point probe measurements supplemented by density functional theory calculations. This work demonstrates a new strategy for low-cost, high-yield and eco-friendly nanofabrication of hybrid organometallic membranes.
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Liu, P., Yin, L., Zhang, Z., Ding, B., Shi, Y., Li, Y., Zhang, X., Song, X., Guo, Y., Chen, L., Chen, X., Gainullin, I. K., & Esaulov, V. A. (2020). Anomalous neutralization characteristics in Na+ neutralization on Al(111) surfaces. PHYSICAL REVIEW A, 101(3), 032706.
Résumé: The jellium model of free electron gas and its extended version have been widely used to understand the neutralization of alkali-metal ions on metal surfaces. We report an unexpected deviation from its prediction that we observed in the neutralization of Na+ ions scattering from an Al(111) surface. We find that the neutralization probability decreases monotonically with increasing ion velocity for the specular scattering condition, which is consistent with the well-known parallel velocity effect. However, the neutralization probability exhibits an unexpected bell shape with the variation of outgoing angle for a given incident energy. Calculations based on the jellium model using the rate equation and including the dynamic parallel velocity effect are presented. Their results agree with the velocity dependence of the neutral fraction, but completely fail in reproducing the angle dependence. This anomalous angle dependence could be due to the appearance of inelastic processes, corresponding to inner 2p electron promotion in hard encounters with Al atoms for large incidence angles, when the interatomic distances become small. This can lead to the formation of autoionizing Na states that result in the formation of extra Na+ ions, not accounted for in the jellium model.
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Mery, M., Chen, L., Valdés, J. E., & Esaulov, V. A. (2020). On the determination of stopping cross-sections in ion scattering in solids and deviations from standard models. RADIATION EFFECTS AND DEFECTS IN SOLIDS, 175(1-2), 160–176.
Résumé: When atomic particles traverse solids they suffer energy losses due to elastic scattering from nuclei and excitation of electron-hole pairs. These are referred to as nuclear and electronic stoppings respectively. In this paper we discuss methods of determining energy losses and 'stopping' cross-sections in ion transmission through thin films, as well as in large angle and grazing backscattering from surfaces. This is done on the basis of deterministic simulations of ion scattering by following ion trajectories as they pass through the solid and sample regions of different electron densities depending on the distance from atomic nuclei. The ab initio calculated electron densities in the crystal are used to determine the stopping power, as predicted by the free electron gas model, and including a threshold value for d electron excitation. We discuss some aspects that are not included in standard descriptions based on the use of free electron models and averaged effective electron densities. In this context, we point out the possibility of inelastic processes involving inner-shell excitations, and briefly summarise main findings.
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Tong, Y., Bouaziz, M., Oughaddou, H., Enriquez, H., Chaouchi, K., Nicolas, F., Kubsky, S., Esaulov, V., & Bendounan, A. (2020). Phase transition and thermal stability of epitaxial PtSe2 nanolayer on Pt(111). RSC ADVANCES, 10(51), 30934–30943.
Résumé: This work relates to direct synthesis of the two-dimensional (2D) transition metal dichalchogenide (TMD) PtSe2 using an original method based on chemical deposition during immersion of a Pt(111) surface into aqueous Na2Se solution. Annealing of the sample induces significant modifications in the structural and electronic properties of the resulting PtSe2 film. We report systematic investigations of temperature dependent phase transitions by combining synchrotron based high-resolution X-ray photoemission (XPS), low temperature scanning tunnelling microscopy (LT-STM) and low energy electron diffraction (LEED). From the STM images, a phase transition from TMD 2H-PtSe2 to Pt2Se alloy monolayer structure is observed, in agreement with the LEED patterns showing a transition from (4 × 4) to (√3 × √3)R30° and then to a (2 × 2) superstructure. This progressive evolution of the surface reconstruction has been monitored by XPS through systematic de-convolution of the Pt4f and Se3d core level peaks at different temperatures. The present work provides an alternative method for the large scale fabrication of 2D transition metal dichalchogenide films.
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Tong, Y., Bouaziz, M., Zhang, W., Obeid, B., Loncle, A., Oughaddou, H., Enriquez, H., Chaouchi, K., Esaulov, V., Chen, Z., Xiong, H., Cheng, Y., & Bendounan, A. (2020). Evidence of new 2D material: Cu2Te. 2D MATERIALS, 7(3), 035010.
Résumé: The number of two-dimensional (2D) materials has grown steadily since the discovery of graphene. Each new 2D material demonstrated unusual physical properties offering a large flexibility in their tailoring for high-tech applications. Here, we report on the formation and characterization of an uncharted 2D material: 'Cu2Te alloy monolayer on Cu(111) surface'. We have successfully grown a 2D binary Te-Cu alloy using a straightforward approach based on chemical deposition method. Low electron energy diffraction (LEED) and scanning tunneling microscopy (STM) results reveal the existence of a well-ordered alloy monolayer characterized by (√3 × √3)R30° superstructure, while the x-ray photoemission spectroscopy (XPS) measurements indicate the presence of single chemical environment of the Te atoms associated with the Te-Cu bonding. Analysis of the valence band properties by angle resolved photoemission spectroscopy (ARPES); in particular the electronic states close to the Fermi level suggests a strong hybridization between Te and Cu electronic states leading to an appearance of new dispersive bands localized at the surface alloy, which is confirmed by first-principles calculations. These bands are strongly influenced by the surface reconstruction and undergo a back-folding at the boundaries of the reduced surface Brillouin zone (SBZ). More interesting, a band gap of about 0.91 eV and a Rashba splitting in the conduction band are obtained. These findings taken together clearly prove the presence of 2D-type electron system within the Cu2Te alloy layer, which is promising for spintronic application.
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Wang, J., Ding, B., Song, X., Shi, Y., Guo, X., Liu, X., Wang, L., Wei, M., Liu, P., Liu, Y., Hu, B., Valdés, J. E., Esaulov, V. A., Chen, L., Guo, Y., & Chen, X. (2020). Nuclear versus electronic energy loss in slow Ar ion scattering on a Cu (100) surface: Experiment and simulations. PHYSICAL REVIEW A, 102(1), 012805.
Résumé: In the scattering and stopping of heavy ions on a few surface layers in solids, contributions of the electronic and nuclear energy losses can become comparable. In this work we present a study of 0.6-5-keV Ar ion scattering on a Cu (100) surface. Energy-loss spectra were measured and displayed some changes as the incident ion energy changes. Thus, a structured spectrum is observed at the higher energies. We analyze the characteristics of the spectra and contributions from the nuclear and electronic energy-loss components using both a Monte Carlo kinetics simulation assuming an averaged electron density and a semiclassical deterministic simulation with an inhomogeneous electron density in the solid. The general features of the experimental spectra were well reproduced, and semiclassical simulations allow us to identify contributions from trajectories coming from below and on top of the surface atomic layer. The relative contribution of nuclear energy loss and electronic energy loss (EEL) were delineated and a more refined analysis of the EEL for different trajectories is presented.
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2019 |
Mery, M., Gonzalez, C., García, C., Romero, C. P., Esaulov, V. A., & Valdés, J. E. (2019). Sputtering yields of tantalum by hydrogen ions in the energy range of 3–11 keV. RADIATION EFFECTS AND DEFECTS IN SOLIDS, 174(1-2), 2–8.
Résumé: The total sputtering yield of 6nm thick polycrystalline tantalum films resulting from H-2(+) ion bombardment, at normal incidence, has been determined. For this purpose, we study the evolution of the energy loss of protons transmitted through very thin films of tantalum following bombardment with controlled doses of H-2(+). The energy of the incident ions ranges from 3 to 11 keV. Our method allows us to determine how to find the limit of the thin film surface contamination which is important for stopping power measurements of pure samples. It also allows to prepare films of predetermined variable thickness.
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Xiao, Y., Shi, Y., Liu, P., Zhu, Y., Gao, L., Guo, Y., Chen, L., Chen, X., & Esaulov, V. A. (2019). Neutralization of keV-energy alkali-metal ions colliding at gold surfaces. NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS, 450, 73–76.
Résumé: Li+ and Na+ ions are scattered from Au(1 1 0) and Au(1 1 1) surfaces in the keV-energy range, respectively. The pronounced Li degrees and Na degrees fractions non-monotonically vary with incident energy and exit angle for high work function gold surfaces. In particular, the azimuthal angle dependence of Li degrees fraction has been observed at low incident energies for a grazing exit angle. The simple calculations are presented to compare with the experimental data. Our findings clearly indicate that both the perpendicular and parallel exit velocity affect the final neutral fraction.
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2018 |
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Tong, Y., Jiang, T., Qiu, S., Koshmak, K., Giglia, A., Kubsky, S., Bendounan, A., Chen, L., Pasquali, L., Esaulov, V. A., & Hamoudi, H. (2018). ZnO Functionalization: Metal–Dithiol Superstructures on ZnO(0001) by Self-Assembly. JOURNAL OF PHYSICAL CHEMISTRY C, 122(5), 2880–2889.
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Uribe J. D., M. M., Fierro B., Cardoso-Gil R., Abril I., Garcia-Molina R., Valdés J. E., Esaulov V. A. (2018). Proton energy loss in multilayer graphene and carbon nanotubes. RADIATION EFFECTS AND DEFECTS IN SOLIDS, 173(1-2), 93–101.
Résumé: Results of a study of electronic energy loss of low keV protons interacting with multilayer graphene targets are presented. Proton energy loss shows an unexpectedly high value as compared with measurements in amorphous carbon and carbon nanotubes. Furthermore, we observe a classical linear behavior of the energy loss with the ion velocity but with an apparent velocity threshold around 0.1 a.u., which is not observed in other carbon allotropes. This suggests low dimensionality effects which can be due to the extraordinary graphene properties.
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2017 |
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Alarcón, L. S., Cristina, L. J., Jia, J., Chen, L., Giglia, A., Pasquali, L., Sánchez, E. A., Esaulov, V. A., & Grizzi, O. (2017). Adsorption and thermal stability of 1,4 benzenedimethanethiol on InP(110). Surface Science, 664, 101–109.
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Correa-Puerta, J., Del Campo, V., Henriquez, R., Esaulov, V. A., Hamoudi, H., Flores, M., & Haberle, P. (2017). Unoccupied Interface and Molecular States in Thiol and Dithiol Monolayers. Langmuir, 33(43), 12056–12064.
Résumé: The electronic structure of self-assembled monolayers (SAMs) formed by thiols of different lengths and dithiol molecules bound to Au(111) has been characterized. Inverse photoemission spectroscopy (IPES) and density functional theory have been used to describe the molecule/Au substrate system. All molecular layers display a clear signal in the IPES data at the edge of the lowest unoccupied system orbital (LUSO), roughly 3 eV above the Fermi level. There is also evidence, in both the experimental data and the calculation, of a finite density of states just below the LUSO edge, which has been recognized as localized at the Au-substrate interface. Regardless of the molecular lengths and in addition to this induced density of interface states, an apparent antibonding Au-S state has been identified in the IPES data for both molecular systems. The main difference between the electronic structures of thiol and dithiol SAMs is a shift in the energy of the antibonding state.
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Jia, J., Esaulov, V. A., & Bendounan, A. (2017). Adsorption and desorption kinetics of NTCDA molecules on Ag(111) and Au(111) surfaces studied by ion scattering. Radiation Effects and Defects in Solids, 172(1-2), 39–47.
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Jiang, T., Malone, W., Tong, Y., Dragoe, D., Bendounan, A., Kara, A., & Esaulov, V. A. (2017). Thiophene Derivatives on Gold and Molecular Dissociation Processes. J. Phys. Chem. C, 121(50), 27923–27935.
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2016 |
Hamoudi, H., & Esaulov, V. A. (2016). Selfassembly of α,ω-dithiols on surfaces and metal dithiol heterostructures. Ann.Phys, , 1–22.
Résumé: α,ω-Dithiols present an interesting case of molecules with
two reactive terminal -SH groups (HS-R-SH) that allow their
use as binders between different metallic entities. They have
thus been used in molecular electronics conduction measurements,
in “nanogap” electrodes of interest in plasmonics,
as building blocks of more complex structures such as
metal intercalated superlattices and in the formation of
metalized organic thin films, including doped graphene
type films. There exist however many problems, because
the molecules may end up in undesirable configurations
with both thiol terminals bound to the same metal particle/
substrate or link with other molecules to produce
“multi-molecule” or “multilayer” structures. This report discusses
various key questions on dithiol linking with metal
surfaces and the quest of protocols of making problem free
dithiol metal structures. It then describes the use of dithiols
and their SAMs to produce various metal organic heterostructures
useful for molecular electronics and formation
of doped metalized organic thin films. We discuss the
build up of these structures by self assembly and lithography,
their chemical composition and functional properties.
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Jiang, T., Tong, Y., Bendounan, A., Nicolas, F., Kubsky, S., & Esaulov, V. A. (2016). Selenium and benzeneselenol interaction with Cu(111). RSC Adv., 6(88), 84627–84633.
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Tong, Y., Jiang, T., Bendounan, A., Harish, M. N. K., Giglia, A., Kubsky, S., Sirotti, F., Pasquali, L., Sampath, S., & Esaulov, V. A. (2016). Case studies on the formation of chalcogenide self-assembled monolayers on surfaces and dissociative processes. Beilstein J Nanotechnol, 7, 263–277.
Résumé: This report examines the assembly of chalcogenide organic molecules on various surfaces, focusing on cases when chemisorption is accompanied by carbon-chalcogen atom-bond scission. In the case of alkane and benzyl chalcogenides, this induces formation of a chalcogenized interface layer. This process can occur during the initial stages of adsorption and then, after passivation of the surface, molecular adsorption can proceed. The characteristics of the chalcogenized interface layer can be significantly different from the metal layer and can affect various properties such as electron conduction. For chalcogenophenes, the carbon-chalcogen atom-bond breaking can lead to opening of the ring and adsorption of an alkene chalcogenide. Such a disruption of the pi-electron system affects charge transport along the chains. Awareness about these effects is of importance from the point of view of molecular electronics. We discuss some recent studies based on X-ray photoelectron spectroscopy that shed light on these aspects for a series of such organic molecules.
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Tong, Y., Jiang, T., Bendounan, A., Nicolas, F., Kubsky, S., & Esaulov, V. A. (2016). Selenium, Benzeneselenol, and Selenophene Interaction with Cu(100). J. Phys. Chem. C, 120(38), 21486–21495.
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Valdés, J. E., Vargas, P., & Esaulov, V. A. (2016). Energy losses of slow ions traveling through crystalline solids and scattered on crystalline surfaces. Radiation Effects and Defects in Solids, 171(1-2), 60–76.
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2015 |
Jia, J., Kara, A., Pasquali, L., Bendounan, A., Sirotti, F., & Esaulov, V. A. (2015). On sulfur core level binding energies in thiol self-assembly and alternative adsorption sites: An experimental and theoretical study. J.Phys.Chem C, 143(10), 104702.
Résumé: Characteristic core level binding energies (CLBEs) are regularly used to infer the modes of molecular adsorption: orientation, organization, and dissociation processes. Here, we focus on a largely debated situation regarding CLBEs in the case of chalcogen atom bearing molecules. For a thiol, this concerns the case when the CLBE of a thiolate sulfur at an adsorption site can be interpreted alternatively as due to atomic adsorption of a S atom, resulting from dissociation. Results of an investigation of the characteristics of thiol self-assembled monolayers (SAMs) obtained by vacuum evaporative adsorption are presented along with core level binding energy calculations. Thiol ended SAMs of 1,4-benzenedimethanethiol (BDMT) obtained by evaporation on Au display an unconventional CLBE structure at about 161.25 eV, which is close to a known CLBE of a S atom on Au.Adsorption and CLBE calculations for sulfur atoms and BDMT molecules are reported and allow delineating trends as a function of chemisorption on hollow, bridge, and atop sites and including the presence of adatoms. These calculations suggest that the 161.25 eV peak is due to an alternative adsorption site, which could be associated to an atop configuration. Therefore, this may be an alternative interpretation, different from the one involving the adsorption of atomic sulfur resulting from the dissociation process of the S–C bond. Calculated differences in S(2p) CLBEs for free BDMT molecules, SH group sulfur on top of the SAM, and disulfide are also reported to clarify possible errors in assignments.
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Shen, J., Jia, J., Bobrov, K., Guillemot, L., & Esaulov, V. A. (2015). Electron Transfer Processes on Supported Au Nanoclusters and Nanowires and Substrate Effects. J.Phys.Chem.C, 119(27), 15168–15176.
Résumé: The catalytic activity of metal nanoclusters is considered to depend on their size, morphology, and substrate type. Here we address this problem by studying changes in electron transfer processes, that are important in surface chemistry, on the example of the interaction of Li ions with gold nanostructures as a function of their sizes and substrate type. The Au nanoclusters were grown on highly ordered pyrolytic graphite (HOPG) and Al2O3 surfaces. In the case of Al2O3 and sputtered HOPG surface, a wide surface coverage distribution of nanoclusters is formed, whereas on pristine HOPG scanning tunneling microscopy (STM) images show that Au clusters nucleate at step edges and can coalesce into “nanowires”. We found that electron transfer is much more probable on small clusters than on bulk Au surfaces. For distributed clusters, electron transfer is most probable for lateral size is of the order of 2–3 nm and height is in the 1 nm range, that is, of the order of a few atomic layers. Interestingly, larger electron transfer rates were found on cluster chains or nanowires nucleated on HOPG step edges in the case of pristine HOPG than on isolated clusters on HOPG planes. Our results suggest that the main effects that are observed are largely related to cluster size and morphology.
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2014 |
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Alarcón, L. S., Jia, J., Carrera, A., Esaulov, V. A., Ascolani, H., Gayone, J. E., Sánchez, E. A., & Grizzi, O. (2014). Direct recoil spectroscopy of adsorbed atoms and self-assembled monolayers on Cu(001). Vacuum, 105, 80–87.
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Chen, L., & Esaulov, V. A. (2014). Energy loss of keV ions in grazing scattering on gold surfaces. In JOURNAL OF PHYSICS-CONFERENCE SERIES (Vol. 488, 132016).
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Hamoudi, H., Uosaki, K., Ariga, K., & Esaulov, V. A. (2014). Going beyond the self-assembled monolayer: metal intercalated dithiol multilayers and their conductance. RSC Adv., 4(75), 39657.
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Jia, J., Bendounan, A., Chaouchi, K., & Esaulov, V. A. (2014). Sulfur Interaction with Cu(100) and Cu(111) Surfaces: A Photoemission Study. J. Phys. Chem. C, , 24583–24590.
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Jia, J., Bendounan, A., Chaouchi, K., Kubsky, S., Sirotti, F., Pasquali, L., & Esaulov, V. A. (2014). Chalcogen Atom Interaction with Palladium and the Complex Molecule–Metal Interface in Thiol Self Assembly. J. Phys. Chem. C, 118(43), 24983–24994.
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Jia, J., Giglia, A., Flores, M., Grizzi, O., Pasquali, L., & Esaulov, V. A. (2014). 1,4-Benzenedimethanethiol Interaction with Au(110), Ag(111), Cu(100), and Cu(111) Surfaces: Self-Assembly and Dissociation Processes. J. Phys. Chem. C, 118(46), 26866–26876.
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Pasquali, L., Mukherjee, S., Terzi, F., Giglia, A., Mahne, N., Koshmak, K., Esaulov, V., Toccafondi, C., Canepa, M., & Nannarone, S. (2014). Structural and electronic properties of anisotropic ultrathin organic films from dichroic resonant soft x-ray reflectivity. Phys. Rev. B, 89(4), 045401.
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2013 |
Canario, A. R., L. Guillemot, J. Diaz-Valdés, J.E. Valdés, P. Vargas, & V.A. Esaulov. (2013). Electron transfer and energy loss processes in fluorine scattering on oxygen covered Ag (110) – crystal azimuthal dependence. NIM B, 315, 36–41.
Résumé: Measurements of energy-losses and electron transfer processes in 1 to 4 keV fluorine ions and atoms scattering on clean and oxygen covered Ag(110) were studied. We report data for surface channeling conditions for different surface azimuths for the clean and oxygen covered O(2×1)–Ag(110) (2x1) reconstructed surface. Adsorption of oxygen results in strong changes in energy losses and a decrease in the negative ion fraction. Energy loss results are discussed in the light of calculations using non-linear models for stopping power, ab initio crystal structure calculations of the electronic density and semi-classical deterministic simulations.
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Canepa M., M. G., Chiara T., Cavalleri O., Prato M., Chaudhari V.R. and Esaulov V.A. (2013). Spectroscopic ellipsometry of Self assembled Monolayers: interface effects. The case of phenyl selenide SAMs on gold. PCCP, 15, 11559–11565.
Résumé: This work focuses on the quantitative application of spectroscopic ellipsometry to the study of optical properties and thickness of self assembled monolayers (SAMs) of phenyl selenide SAMs deposited from the liquid phase on gold. STM, XPS and cyclic voltammetry measurements provide additional chemical and morphological characterization of the SAMs. While routine ellipsometry analysis of SAMs often relies on the film-induced δΔ change of the Δ ellipsometric angle and discard SAM-substrate interface effects, the present data show a distinctive behaviour of the δΨ data that we assign to interface effects, stronger than those previously found for densely packed alkanethiols SAMs. An inaccurate modelling of the variations of Ψ related to the nano-structured SAM-substrate interface leads to a large overestimation of the film thickness. A simple model, accounting effectively for the interface layer between the film and the substrate and for the molecular optical absorptions, provides a good agreement with the data and a reliable thickness estimate of the SAM.
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Datta, D., Shen, J., & Esaulov, V. A. (2013). Hydrogen negative ion formation on a graphite HOPG surface. Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and , 315, 42–44.
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Jia, J., Bendounan, A., Harish M.N.K., Chaouchi, K., Sirotti, F., Sampath, S., & and Esaulov V.A. (2013). Selenium Adsorption on Au(111) and Ag(111) Surfaces: Adsorbed Selenium and Selenide Films. JPhys Chem C, 117(19), 9835–9842.
Résumé: Results of a high resolution photoemission and electrochemistry study of Se adsorption on Au(111) and Ag(111) surfaces performed by immersion of pristine samples into an aqeuous solution of Na2Se are presented. Cyclic voltammetry on Au shows formation of selenium adsorbed species and the structures observed in reductive desorption are related to the atomic and polymeric species observed in XPS. In the case of Au(111) XPS spectra in the Se(3d) region indeed show two main features attributed to Se chemisorbed atomically and polymeric Se8 features. Smaller structures due to other types of Se conformations were also observed. The Au(4f) peak line shape does not show core level shifts indicative of Au selenide formation. In the case of silver, XPS spectra for the Ag(3d) show a broadening of the peak and a deconvolution into AgB bulk like and AgSe components shows that the AgSe is located at a lower binding energy, an effect similar to oxidation and sulfidation of Ag. The Se(3d) XPS spectrum is found to be substantially different from the Au case and dominated by atomic type Se due to the selenide, though a smaller intensity Se structure at an energy similar to the Se8 structure for Au is also observed. Changes in the valence band region related to Se adsorption are reported.
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Jia, J., Mukherjee, S., Hamoudi, H., Nannarone, S., Pasquali, L., & Esaulov, V. A. (2013). Lying-Down to Standing-Up Transitions in Self Assembly of Butanedithiol Monolayers on Gold and Substitutional Assembly by Octanethiols. J. Phys. Chem. C, 117(9), 4625–4631.
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O’Rourke, B. E., Flores, M., Esaulov, V. A., & Yamazaki, Y. (2013). Modification of self assembled monolayers by highly charged ions. Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and , 299, 68–70.
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Salazar Alarcón, L., Cristina, L. J., Shen, J., Jia, J., Esaulov, V. A., Sánchez, E. A., & Grizzi, O. (2013). Growth of 1,4-Benzenedimethanethiol Films on Au, Ag, and Cu: Effect of Surface Temperature on the Adsorption Kinetics and on the Single versus Multilayer Formation. J. Phys. Chem. C, 117(34), 17521–17530.
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Shen, J., Jia, J., Bobrov, K., Guillemot, L., & Esaulov, V. A. (2013). Electron transfer processes on Au nanoclusters supported on graphite. Gold Bull, 46(4), 343–347.
Résumé: Electron transfer processes play an important role in surface chemistry. This paper presents results of a study of changes in resonant electron transfer processes, as a function of gold cluster sizes, on the example of electron transfer between Li+ ions scattered on Au clusters on highly oriented pyrolytic graphite (HOPG). The gold nanoclusters were grown on lightly sputtered HOPG surface in order to obtain a wide coverage distribution of clusters. The growth of clusters was monitored by scanning tunneling microscopy. We found that electron transfer is much more probable on small clusters, whose lateral size is of the order of 2 to 3 nm and height in the 1-nm range, than on bulk Au or thin Au films. A comparison with Au clusters grown on the semiconducting titania did not reveal significant differences with HOPG.
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2012 |
Prato, M., Toccafondi, C., Maidecchi, G., Chaudhari, V., Harish, M. N. K., Sampath, S., Parodi, R., Esaulov, V. A., & Canepa, M. (2012). Mercury Segregation and Diselenide Self-Assembly on Gold. JOURNAL OF PHYSICAL CHEMISTRY C, 116(3), 2431–2437.
Résumé: We have investigated the self-assembly of didecyldiselenide on gold containing mercury using X-ray photoelectron spectroscopy, cyclic voltammetry and infrared spectroscopy. The analysis of intensity and chemical shift of selected Se, Hg, and Au photoelectron lines on samples with increasing Hg content, show that didecyldiselenide adsorption strongly contributed to segregation of bulk Hg to the surface. The voltammetry results support this conclusion and suggest the formation of Hg-Au surface amalgam. The Hg surface segregation effect must be related to the restructuring of the surface following initial adsorption, and to the strong selenophilicity of Hg. The reflectance absorbance infrared spectroscopy studies show that the molecular layer on Hg-Au substrates lacks good order.
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Vladimir A.Esaulov. (2012). Low Energy Ion Scattering and Recoiling Spectroscopy in Surface Science. (Vol. 51, pp. 423–460). Springer Series in Surface Science. Springer-Verlag.
Résumé: This chapter presents an overview of low energy ion scattering spectroscopy and time of flight scattering and recoiling spectroscopy for the study of the structure and composition of surfaces as well as of fundamental ion surface interaction processes. The emphasis is on basic concepts regarding scattering, energy losses and charge transfer phenomena and experimental aspects involved in measurements of ion energies and time of flight measurements of scattered atoms. Some examples are provided to illustrate the type of information that can be obtained.
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2011 |
Chaudhari, V., Harish M.N.K., Srinivasan, S., & Esaulov, V. A. (2011). Substitutional Self-Assembly of Alkanethiol and Selenol SAMs from a Lying-Down Doubly Tethered Butanedithiol SAM on Gold. JOURNAL OF PHYSICAL CHEMISTRY C, 115(33), 16518–16523.
Résumé: Substitutional self-assembly of thiol and selenol SAMs from a lying-down phase of butanedithiol (C4DT) (SAM) were investigated using thiols, disulfide, and diselenide molecules. The intent was to address the question if formation of a lying-down dithiol phase is an impediment to formation of standing-up dithiol phases as it has been assumed. It is demonstrated that this is not the case, and the C4DT SAM, where both the sulfur atoms are chemisorbed on gold, is removed and replaced in all cases. Differences in substitution kinetics are observed.
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Chen, L., Shen, J., Jia, J. J., Kandasamy, T., Bobrov, K., Guillemot, L., Fuhr, J. D., Martiarena, M. L., & Esaulov, V. A. (2011). Li+-ion neutralization on metal surfaces and thin films. PHYSICAL REVIEW A, 84(5), 052901.
Résumé: Li+ ions with energies ranging from 0.3 to 2 keV are scattered from Au(110) and Pd(100) surfaces and from ultrathin Ag film grown on Au(111) in order to study electron transfer phenomena. We find that neutralization occurs quite efficiently and find an anomalous ion energy dependence of the neutral fraction for Au(110) and Pd(100) surfaces previously noted for Au(111). The dependence of the neutral fraction on the azimuthal angle of the Au(110) and Pd(100) surfaces is reported. In the case of Ag monolayer on Au(111), results are similar to the case of the Ag(111) surface. To understand the anomalous ion energy dependence, we present a theoretical study using density functional theory (DFT) and a linearized rate equation approach, which allows us to follow the Li charge state evolution for the (111) surfaces of Ag, Au, and Cu, and for the Ag-covered Au(111) surface.
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Chen, L., Shen, J., Valdes, J. E., Vargas, P., & Esaulov, V. A. (2011). Energy loss of keV fluorine ions scattered off a missing-row reconstructed Au(110) surface under grazing incidence. PHYSICAL REVIEW A, 83(3), 032901.
Résumé: A joint experimental and theoretical study of energy loss is presented for 1-to-4-keV fluorine negative ions in grazing scattering on a missing-row reconstructed Au(110) surface. Measurements of energy losses for various azimuthal orientations of the crystal have been performed by means of a time-of-flight method with a pulsed beam. The dependence of the fraction of surviving negative ions on azimuthal angles, was determined. Our energy-loss data are discussed in light of trajectory and stopping-power calculations, where the explicit inclusion of the nonuniform electron density at the surface provides good agreement with the experimental data. The simulation allows us to delineate various trajectory classes that correspond to different contributions in the energy-loss spectra for various azimuthal orientations of the surface.
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Chen, L., Valdes, J. E., Vargas, P., Shen, J., & Esaulov, V. A. (2011). Energy losses of H and F ions in grazing scattering on a missing row reconstructed Au(110) surface. PHYSICA SCRIPTA, T144, 014042.
Résumé: A joint experimental and theoretical study of low-keV H and F ions in grazing scattering on a missing row reconstructed Au(110) surface is presented. We show the influence of surface electronic corrugation and trajectory effects on energy-loss spectra. Measurements of energy losses for grazing angles scattering in surface channeling conditions for various azimuthal orientations of the crystal have been performed and discussed in semi-classical simulations, which allow us to delineate various trajectory classes that correspond to different contributions in the energy-loss spectra for various azimuthal orientations of the surface.
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Flores, M., Esaulov, V., & Yamazaki, Y. (2011). Molecular ion emission from alkanethiol-SAMs by HCI bombardment. PHYSICA SCRIPTA, T144, 014045.
Résumé: In this work, we employ highly charged ions to study the sputtering of positive molecular fragments from two different alkanethiol self-assembled monolayers (SAMs) on gold surfaces: undecanethiol and dodecanethiol. The SAMs are bombarded with a pulsed Arq+ beam (3 < q < 12) with kinetic energies ranging from 1 to 15 keV. The desorbed positive molecular ions were detected and analyzed from time-of-flight spectra, and thereby the masses and yields of secondary ions were obtained. The proton yields are dependent on the charge state of the incident ion. On the other hand, the positive molecular ion yields, such as CnHm+, are charge state independent. The positive molecular ion yields decay with the molecular size n.
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Hamoudi, H., Dablemont, C., & Esaulov, V. A. (2011). Disorder, solvent effects and substitutional self-assembly of alkane dithiols from alkane thiol SAMs. SURFACE SCIENCE, 605(1-2), 116–120.
Résumé: Substitutional self-assembly of nonanedithiol from a hexanethiol self-assembled monolayer and the effects of use of ethanol and n-hexane as solvents were investigated. It was found that presence of original solvents in the HT SAM allowed easy replacement, while dried SAMs were more resilient to substitution and much longer times are necessary for substitution to occur. In general substitution in ethanol leads to production of a disordered dithiol SAM, with existence of extra molecules bonded to the SAM. Well ordered substituted SAMs were obtained with degassed n-hexane solutions and in absence of ambient light. (C) 2010 Elsevier B.V. All rights reserved.
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Kojima, T. M., Ikeda, T., Kanai, Y., Yamazaki, Y., & Esaulov, V. A. (2011). Ion beam guiding with straight and curved Teflon tubes. JOURNAL OF PHYSICS D-APPLIED PHYSICS, 44(35), 355201.
Résumé: In an effort to develop a flexible ion beam guiding scheme, the guiding capabilities of straight and curved Teflon tubes were tested with 8 keV Ar(8+) ions. The tubes used were about 50 mm long and of 1 mm/2mm inner and outer diameters. One was straight, and the others were bent with different radii of curvature corresponding to bending angles from 9.6 degrees to 26.7 degrees. Transmission of several tens of per cent of the injected beam was observed for the curved tubes, while transmission through the tilted straight tube vanished when the tilt was more than 7 degrees. This demonstrates the possibility of efficient ion beam guiding with flexible insulator tubes.
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Pasquali, L., Terzi, F., Seeber, R., Nannarone, S., Datta, D., Dablemont, C., Hamoudi, H., Canepa, M., & Esaulov, V. A. (2011). UPS, XPS, and NEXAFS Study of Self-Assembly of Standing 1,4-Benzenedimethanethiol SAMs on Gold. LANGMUIR, 27(8), 4713–4720.
Résumé: We report a study of the self-assembly of 1,4-benzenedimethanethiol monolayers on gold formed in n-hexane solution held at 60 degrees C for 30 mm and in dark conditions. The valence band characteristics, the thickness of the layer, and the orientation of the molecules were analyzed at a synchrotron using high resolution photoelectron spectroscopy and near edge X-ray adsorption spectroscopy. These measurements unambiguously attest the formation of a single layer with molecules arranged in the upright position and presenting a free -SH group at the outer interface. Near edge X-ray absorption fine structure (NEXAFS) measurements suggest that the molecular axis is oriented at 24 degrees with respect to the surface normal. In addition, valence band features could be successfully associated to specific molecular orbital contributions thanks to the comparison with theoretically calculated density of states projected on the different molecular units.
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2010 |
Chen, L., Valdes, J. E., Vargas, P., & Esaulov, V. A. (2010). Surface channelling and energy losses of 4 keV hydrogen and fluorine ions in grazing scattering on Au(111) and missing row reconstructed Au(110) surfaces. Journal of physics, 22(34), 345005.
Résumé: We present the results of an experimental and theoretical study of surface channelling and energy loss of 4 keV hydrogen and fluorine ions in grazing scattering on a missing row reconstructed Au(110) surface and a Au(111) surface. We performed measurements of energy losses for grazing angle scattering in surface channelling conditions for various azimuthal orientations of the crystal. Experimental results are discussed in the light of trajectory calculations of hydrogen and fluorine ions scattered under grazing incidence conditions on the surface. A nonlinear model is used in order to calculate the ion energy loss in these crystalline systems. Ab initio electronic crystal structure calculations and semi-classical simulations are performed and allow us to delineate various trajectory classes that correspond to different contributions in the energy loss spectra for various azimuthal orientations of the surface.
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Hamoudi, H., Prato, M., Dablemont, C., Cavalleri, O., Canepa, M., & Esaulov, V. A. (2010). Self-Assembly of 1,4-Benzenedimethanethiol Self-Assembled Monolayers on Gold. LANGMUIR, 26(10), 7242–7247.
Résumé: A study of the self-assembly of 1,4-benzenedimethanethiol (BDMT; HS-CH(2)-(C(6)H(4))-CH(2)-SH) monolayers on gold is presented. Self-assembled monolayers (SAM) are characterized by reflection absorption infrared spectroscopy (RAIRS), X-ray photoelectron spectroscopy (XPS), and spectroscopic ellipsometry (SF) measurements. The ensemble of measurements consistently shows that well-organized BDMT SAMs, with “standing-up” molecules, can be obtained on high quality gold films with incubation in n-hexane provided that N(2)-degassed solutions are used and all preparation steps are performed at 60 degrees C in the absence of ambient light. SE data indicate that the optical interface properties of the BDMT-Au system are different from those of simple alkanethiol SAMs. A possible mechanism for the formation of the “standing-up” phase from the lying-down phase via a hydrogen exchange reaction involving chemisorbed lying-clown and free dithiol molecules is discussed.
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Salazar Alarcon, L., Chen, L., Esaulov, V. A., Gayone, J. E., Sanchez, E. A., & Grizzi, O. (2010). Thiol Terminated 1,4-Benzenedimethanethiol Self-Assembled Monolayers on Au(111) and InP(110) from Vapor Phase. JOURNAL OF PHYSICAL CHEMISTRY C, 114(47), 19993–19999.
Résumé: We present results of a clean vacuum evaporative adsorption method of assembly of the conjugated dithiol molecule 1,4-benzenedimethanethiol on the surfaces of gold and indium phosphide. Measurements of direct recoil spectroscopy with time-of-flight analysis show in both cases formation of a self-assembled monolayer (SAM) with S atoms available at the SAM-vacuum interface. Investigation of the adsorption kinetics shows that a lying-down phase is formed at low exposures, which precedes the standing up SAM phase. The standing up SAM formation requires exposures of the order of a mega Langmuir. A study of the SAM stability with temperature shows that the S terminated layer survives up to similar to 370 K, above this temperature a reordering of the layer takes piece where S atoms are no longer available at the vacuum interface. Final desorption occurs around 450 K for Au and around 500K for InP.
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2009 |
Canario, A. R., Guillemot, L., Grizzi, O., Bandurin, Y., & Esaulov, V. A. (2009). Scattering of F atoms and anions on a TiO2(110) surface. SURFACE SCIENCE, 603(8), 1099–1105.
Résumé: Results of a study of energy losses and electron transfer processes for grazing scattering of fluorine atoms and anions scattering along different azimuthal orientations of the TiO2 crystal are presented. We observe strong variations in the overall intensity of scattered particles which are due to channelling effects. The energy losses do not show strong variations as a function of crystal azimuth except for the case of scattering along the (001) direction between the bridging oxygen atom rows, where we also observe differences in the energy losses of scattered ions and neutrals. We attribute this to the fact that larger F- survival occurs for trajectories staying farther from the surface, when also the energy losses remain small. The overall characteristics of energy losses are attributed mainly to trajectory effects due to scattering in regions of different electron density. Measurements of the ratio of scattered ions to the total scattered flux, i.e. the ion fractions which reflect electron capture and loss processes, show that these are not the same for incident anions and atoms. A strong difference for scattering along the (001) direction is observed, where at low incident energies a strong survival of incident ions occurs. These results are tentatively discussed in terms of non resonant electron capture at lattice O- sites and electron loss into the conduction band or by collisional detachment with bridging O atoms. (C) 2009 Elsevier B.V. All rights reserved.
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Flores, M., O'Rourke, B. E., Yamazaki, Y., & Esaulov, V. A. (2009). Potential and kinetic sputtering of alkanethiol self-assembled monolayers by impact of highly charged ions. PHYSICAL REVIEW A, 79(2).
Résumé: Highly charged ions have been used to study the sputtering of positive molecular fragments from mercaptoundecanoic acid and dodecanethiol self-assembled monolayers on gold surfaces. The samples were bombarded with Arq+ (4 <= q <= 10) ions with kinetic energies from 2 to 18 keV. The main fragments detected were H+, CnH2n+, and Cn+1O2H2n+1+ from mercaptoundecanoic and H+, CnH2n+, and Cn+1H2n+3+ from dodecanethiol. The proton yields were increased with larger charge state q of the highly charged ion (HCI) in both samples, scaling as q(gamma), with gamma similar to 5. The charge state dependence is discussed in terms of electron transfer to the HCI. The final yield of protons depends on molecular functional group characteristics, orientation on the surface, and reneutralization phenomena.
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Millone, M. A. D., Hamoudi, H., Rodriguez, L., Rubert, A., Benitez, G. A., Vela, M. E., Salvarezza, R. C., Gayone, J. E., Sanchez, E. A., Grizzi, O., Dablemont, C., & Esaulov, V. A. (2009). Self-Assembly of Alkanedithiols on Au(111) from Solution: Effect of Chain Length and Self-Assembly Conditions. LANGMUIR, 25(22), 12945–12953.
Résumé: A comparative study on the adsorption of buthanedithiol (BDT). hexanedithiol (HDT), and nonanedithiol (NDT) oil Au(111) from ethanolic and n-hexane solutions and two different preparation procedures is presented. SAM characterization is based oil reflection-absorption infrared spectroscopy, electrochemistry, X-ray photoelectron spectroscopy, and time of flight direct recoil spectroscopy. Results indicate that one can obtain a standing-Up phase of dithiols and that the amount of the precursor lying-down phase decreases from BDT to NDT, irrespective of the solvent and self-assembly conditions. A good ordering of the hydrocarbon chains in the standing-up configuration is observed for HDT and NDT when the system is prepared in degassed n-hexane with all operations carried out in the dark. Disulfide bridges at the free SH terminal groups are formed for HDT and to a lesser extent for NDT prepared in ethanol in the presence of oxygen, but We found no evidence of ordered multilayer formation in our experiments. No disulfides were observed for BDT that only forms the lying-clown phase. Our results demonstrate the key role of the chain length and the procedure (solvent nature and oxygen presence) in controlling the surface structure and chemistry of SAMs dithiols on Au(111).
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Serkovic Loli, L. N., Hamoudi, H., Esteban Gayone, J., Luz Martiarena, M., Sanchez, E. A., Grizzi, O., Pasquali, L., Nannarone, S., Doyle, B. P., Dablemont, C., & Esaulov, V. A. (2009). Growth of N,N '-Bis(1-ethylpropyl)perylene-3,4,9,10-tetracarboxdiimide Films on Ag (111). JOURNAL OF PHYSICAL CHEMISTRY C, 113(41), 17866–17875.
Résumé: We have studied the self-assembly characteristics, the electronic structure, and the thermal stability of thin N,N'-bis(1-ethylpropyl)perylene-3,4,9,10-tetracarboxdiimide (EP-PTCDI) films grown on Ag (111) by a broad set of surface science analysis techniques. The deposition of single molecules to the formation of very thin films performed at room temperature under ultrahigh-vacuum (UHV) conditions was followed by atomic force microscopy (AFM), scanning tunneling microscopy (STM), ultraviolet photoemission spectroscopy (UPS), X-ray photoemission spectroscopy (XPS), and near edge X-ray absorption fine structure (NEXAFS), and was modeled by density functional theory (DFT) calculations. STM pictures show that substrate step edges are the starting point for molecule adsorption, which is followed by formation of islands and eventually a monolayer. The monolayer is composed of large domains with ordered molecules with their perylene-3,4,9,10-tetracarboxdiimide (PTCDI) core lying almost parallel to the surface. For further exposure, multilayer stacked domains are formed. For thicker films molecular order could not be established. Upon heating it is found that the multilayer is stable up to 150 degrees C where a rapid desorption takes place, followed by the dissociation of the molecules, leaving an ordered monolayer of presumably perylene core type molecules.
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Serkovic Loli, L. N., Sanchez, E. A., Gayone, E., Grizzi, O., & Esaulov, V. A. (2009). Assembly and thermal stability of thin EP-PTCDI films on Ag(111). PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 11(20), 3849–3853.
Résumé: We report a multi-technique study of the adsorption kinetics and self-assembly characteristics of EP-PTCDI grown on Ag(111) at UHV conditions and room temperature. Changes in the valence band characteristics for the mono and the multilayer film and the stability as a function of the annealing temperature are discussed. The results show that the molecules start to adsorb on the step edges forming ordered islands that grow to fully cover a monolayer. Further exposure results in the stacking of similarly ordered islands of several layers. The desorption experiment shows that the film is stable up to 150 degrees C where a rapid desorption of the multilayer takes place, followed by a decomposition of the molecules for temperatures higher than 170 degrees C.
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2008 |
Guillemot, L., Bandurin, Y., Bobrov, K., & Esaulov, V. A. (2008). Electron transfer processes between sputtered O atoms and Ag(110): O(n x 1) reconstructed surfaces. JOURNAL OF PHYSICS-CONDENSED MATTER, 20(35).
Résumé: We present results of a study of sputtered oxygen atom outgoing trajectory dependence of the electron transfers with oxidized Ag(110) surfaces reconstructed in different (n x 1) added row structures. With a charge state resolved time-of-flight-direct recoil spectroscopy investigation using 4 keV Ar(+) incident ions, we determine relative yields of sputtered O and Ag atoms as well as the fraction of sputtered O-ions, for different incident polar and azimuthal angles. The relative yields of sputtered O atoms are satisfactorily reproduced by a classical dynamics simulation. No sputtered Ag-ions were detected. A qualitative discussion of the features of the oxygen negative ion fractions suggests that its description needs, in general, to take into account both capture and loss of electrons as the oxygen atom leaves the surface. The experimental data also suggest that one needs to correctly describe the corrugation of the surface and that the electron loss rates should be site-specific.
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Guo, Z., Zheng, W., Hamoudi, H., Dablemont, C., Esaulov, V. A., & Bourguignon, B. (2008). On the chain length dependence of CH3 vibrational mode relative intensities in sum frequency generation spectra of self assembled alkanethiols. SURFACE SCIENCE, 602(23), 3551–3559.
Résumé: A global modelling of Sum Frequency Generation (SFG) spectra of the self assembly of alkanethiols is presented. All CH modes are modelled together. CH2 modes are assumed local to allow easy calculation of the spectrum as a function of molecular conformation. Ab initio molecular hyperpolarizabilities are used. A phenomenological approach is used to include the Fermi resonance in the model: the calculated intensity of the CH3 symmetric stretch is redistributed according to intensity borrowing by the Fermi resonance. The model is applied to octadecanethiol (ODT) and pentadecanethiol (PDT). The even/odd intensity alternation of SFG CH3 vibrational bands as a function of chainlength is used to test the model. It is found that the relative magnitudes of the hyperpolarizability tensors of the CH3 asymmetric and symmetric modes need to be adjusted. The model provides tilt and twist angles of the alkyl chain in agreement with the literature. It shows that the all trans conformation does not imply the absence of CH2 bands in SFG spectra. In addition, new information is obtained. In particular, if two types of molecular conformations are assumed, the C planes of the two molecules must be perpendicular to each other. (C) 2008 Elsevier B.V. All rights reserved.
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Hamoudi, H., Dablemont, C., & Esaulov, V. A. (2008). Interaction of Li+ with a Au(100) surface. SURFACE SCIENCE, 602(14), 2486–2490.
Résumé: Results of a study of Li+ neutralisation on Au(1 0 0) are presented and compared with an earlier study of neutralisation on Au(1 1 1), where anomalously high neutralisation had been tentatively related to the existence of the L-bandgap and occupied surface state. Neutralisation probability on Au(1 0 0) has a similar magnitude to that on Au(1 1 1) and a similar incident energy dependence, though the electronic structure is different. These results for surfaces with high workfunctions are very unexpected, since significantly smaller values may be expected in a “traditional” picture of a Li+ ion departing from the surface. We can account for the relatively large value of the neutral fraction by considering that the Li(2s) level lies below the Fermi level at short atom-surface separations as this has been shown to be the case for the Cu surface by Goldberg et al. This allows electron capture at small distances and the surviving neutrals account well for the behaviour of the neutral fraction at energies above 500 eV but not at lower energies. This could be due to various reasons including intermediate Li- formation and non-adiabatic effects. (C) 2008 Published by Elsevier B.V.
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Hamoudi, H., Guo, Z., Prato, M., Dablemont, C., Zheng, W. Q., Bourguignon, B., Canepa, M., & Esaulov, V. A. (2008). On the self assembly of short chain alkanedithiols. PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 10(45), 6836–6841.
Résumé: A study of the self-assembly of nonane-alkanedithiol monolayers on gold in n-hexane and ethanol solvents is presented. Self-assembled monolayers (SAMs) are characterised by reflection-absorption infrared spectroscopy (RAIRS), sum frequency generation (SFG) and spectroscopic ellipsometry (SE) measurements. Data obtained for alkanethiols SAMs are also shown for comparison. The measurements show that nicely organized HSC(9)SH SAMs can be obtained in n-hexane provided that N(2)-degassed solutions are used and all preparation steps are performed in the absence of ambient light. SFG measurements show that these SAMs have free standing SH groups. Use of an un-degassed and/or light-exposed n-hexane solutions leads to a worse layer organization. Preparation in ethanol, even in degassed solutions with processing in the dark, leads to poorly organized layers and no sign of free-SH groups was observed.
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Valdes, J. E., Vargas, P., Celedon, C., Sanchez, E., Guillemot, L., & Esaulov, V. A. (2008). Electronic density corrugation and crystal azimuthal orientation effects on energy losses of hydrogen ions in grazing scattering on a Ag(110) surface. PHYSICAL REVIEW A, 78(3).
Résumé: We present a detailed study of the energy losses of hydrogen ions that are scattered off an Ag (110) single-crystal surface for primary energies between 1 and 4 keV. We performed measurements for grazing angles as a function of crystal azimuthal orientation, which show large differences in energy losses. Experimental results are discussed by means of trajectory calculations of protons scattered under grazing-incidence conditions on the surface. Using nonlinear models for the stopping power, ab initio crystal structure calculations of the electronic density, and semiclassical simulations, we obtain data that are in very good agreement with experimental results. These simulations allow us to properly take into account the variations of the surface electronic density and hence obtain an accurate description of the energy loss processes for ion scattering along various azimuthal orientations of the target.
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2007 |
Valdes, J. E., Vargas, P., Guillemot, L., & Esaulov, V. A. (2007). Effect of oxygen adsorption on the energy losses in grazing scattering of hydrogen ions on Ag(110). NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS, 256(1), 81–85.
Résumé: In this work we present a study of the effect of oxygen adsorption on the energy loss of 4 keV hydrogen ions, which are scattered off an Ag (110) single-crystal surface with varying coverages of oxygen. In this case oxygen adsorption leads to an added row reconstruction of the surface. We performed measurements for grazing angles as a function of crystal azimuthal orientation, which show large differences in energy losses. Experimental results are discussed in the light of trajectory calculations of protons scattered under grazing incidence conditions on the surface. Using non-linear models for stopping power, ab initio crystal structure calculations of the electronic density and semi-classical simulations, we obtain data that is in very good agreement with experimental results. These simulations in particular allow us to properly take into account the variations of the surface electronic density and hence obtain an accurate description of the energy loss processes for ion scattering along various azimuthal orientations of the target. (c) 2006 Elsevier B.V. All rights reserved.
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