2021 |
Wang, Y., Boyer, A. - G., Sauriat-Dorizon, H., Duverger, E., & Riedel, D. (2021). Electronic Structure and Bistable Conformational Study of the Tetraphenylporphyrin Erbium(III) Acetylacetonate Complex on the CaF2/Si(100) Surface at Low Temperatures. J. Phys. Chem. C, 125(26), 14453–14460.
Résumé: The synthesis of tetraphenylporphyrin erbium(III) acetylacetonate (acac) complexes is realized and their properties studied at the nanoscale when adsorbed on a semi-insulating CaF2/Si(100) surface. Our findings reveal that the ErTPP-(acac) molecules can adsorb in two main on-site conformations. Following precisely located dI/dV measurements at various specific positions [phenyls, pyrroles, and Er-(acac)], the relative locations of the Er cation and the apical ligand (acac) can be deciphered for each observed conformation. Hence, one of the adsorbate conformations presents the acac ligand parallel to the porphyrin plane with the Er atom outside the macrocycle plane. The second conformation is related to what is known in the gas phase, where the acac ligand is oriented vertically on top of the Er atom. This work is combined with a theoretical investigation that uses density functional theory methods to bring into light details of the two observed conformations. Additional proofs of our discoveries are related to the vibrational excitations of ErTPP-(acac). A comparison with a theoretical estimation of the vibrational modes reveals how the electronic resonance near the valence-band edge of the insulting layer is suitable to distinguish between the two adsorbed conformations.
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2020 |
Duverger, E., Boyer, A. - G., Sauriat-Dorizon, H., Sonnet, P., Stephan, R., Hanf, M. - C., & Riedel, D. (2020). Two-Dimensional Functionalized Ultrathin Semi-Insulating CaF2 Layer on the Si(100) Surface at a Low Temperature for Molecular Electronic Decoupling. ACS Appl. Mater. Interfaces, 12(26), 29661–29670.
Résumé: The ability to precisely control the electronic coupling/decoupling of adsorbates from surfaces is an essential goal. It is important for fundamental studies not only in surface science but also in several applied domains including, for example, miniaturized molecular electronic or for the development of various devices such as nanoscale biosensors or photovoltaic cells. Here, we provide atomic-scale experimental and theoretical investigations of a semi-insulating layer grown on a silicon surface via its epitaxy with CaF2. We show that, following the formation of a wetting layer, the ensuing organized unit cells are coupled to additional physisorbed CaF2 molecules, periodically located in their surroundings. This configuration shapes the formation of ribbons of stripes that functionalize the semiconductor surface. The obtained assembly, having a monolayer thickness, reveals a surface gap energy of ∼3.2 eV. The adsorption of iron tetraphenylporphyrin molecules on the ribbons of stripes is used to estimate the electronic insulating properties of this structure via differential conductance measurements. Density functional theory (DFT) including several levels of complexity (annealing, DFT + U, and nonlocal van der Waals functionals) is employed to reproduce our experimental observations. Our findings offer a unique and robust template that brings an alternative solution to electronic semi-insulating layers on metal surfaces such as NaCl. Hence, CaF2/Si(100) ribbon of stripe structures, whose lengths can reach more than 100 nm, can be used as a versatile surface platform for various atomic-scale studies of molecular devices.
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2019 |
Yengui, M., Duverger, E., Sonnet, P., & Riedel, D. (2019). Translational Manipulation of Magnetic Cobalt Adatoms on the Si(100)-2 × 1 Surface at 9 K. J. Phys. Chem. C, 123(43), 26415–26423.
Résumé: The controlled motion of magnetic impurities on semiconductor (SC) surfaces is of crucial importance for atomic scale magnetic devices. Still challenging because of their strong reactivity with SCs, magnetic impurities are usually studied in bulk SCs, thus preventing their manipulation. Here, we show that a single Co adatom can be steadied on the bare Si(100)-2 × 1 surface in a pedestal configuration at low temperature, 9 K, and moved along the reconstructed silicon dimer rows via the use of a scanning tunneling microscope. The electronic characteristics of the Co adatom and its surroundings are investigated via topography and dI/dV measurements. Our findings reveal that the Si–Co bonding involves hybridization between the Si-p and the Co-pxpy orbitals. This configuration indicates that the Co-d orbitals remain weakly hybridized with the silicon atoms. These results are supported by density functional theory calculations where the role of the As dopant is discussed as well as the surface reconstruction. Therefore, we show that the motion direction of the Co adatom can be influenced by the surrounding c(4 × 2) or p(2 × 2) surface reconstruction phases, thus opening future interesting magnetic applications.
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2018 |
Ramos, P., Mankarious, M., Pavanello, M., & Riedel, D. (2018). Probing Charge Transfer Dynamics in a Single Iron Tetraphenylporphyrin Dyad Adsorbed on an Insulating Surface. Nanoscale, 10(37), 17603–17616.
Résumé: Although the dynamics of charge transfer (CT) processes can be probed with ultimate lifetime resolution, the helplessness to control CT at the nanoscale constitutes one of the most important road-blocks to revealing some of its deep fundamental aspects. In this work, we present an investigation of CT dynamics in a single iron tetraphenylporphyrin (Fe-TPP) donor/acceptor dyad adsorbed on a CaF2/Si(100) insulating surface. The tip of a scanning tunneling microscope (STM) is used to create local ionic states in one fragment of the dyad. The CT process is monitored by imaging subsequent changes in the neighbor acceptor molecule and its efficiency is mapped revealing the influence of the initial excited state in the donor molecule. In validation of the experiments, simulations based on density functional theory show that holes have a higher donor acceptor CT rate compared to electrons and highlight a noticeable initial state dependence on the CT process. We leverage the unprecedented spatial resolution achieved in our experiments to show that the CT process in the dyad is governed via molecule-molecule coherent tunneling with negligible surface-mediated character.
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2017 |
Labidi, H., Pinto, H. P., Leszczynski, J., & Riedel, D. (2017). Exploiting a single intramolecular conformational switching Ni-TPP molecule to probe charge transfer dynamics at the nanoscale on bare Si(100)-2x1. PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 19, 28982–28992.
Résumé: Acquiring quantitative information on charge transfer (CT) dynamics at the nanoscale remains an important scientific challenge. In particular, CT processes in single molecules at surfaces need to be investigated to be properly controlled in various devices. To address this issue, the dynamics of switching molecules can be exploited. Here, nickel-tetraphenylporphyrin adsorbed on the Si(100) surface is used to study the CT process ruling the reversible activation of two chiral molecular conformations. Via the electrons of a scanning tunneling microscope (STM), a statistical study of molecular switching reveals two specific locations of the molecule for which their efficiency is optimized. The CT mechanism is shown to propagate from two lateral aryl groups towards the porphyrin macrocycle inducing an intramolecular movement of two symmetric pyrroles. The measured switching efficiencies can thus be related to a Markus-Jordner model to estimate relevant parameters that describe the dynamics of the CT process. Numerical simulations provide a precise description of the molecular conformations and unveil the molecular energy levels that are involved in the CT process. This quantitative method opens a completely original approach to study CT at the nanoscale.
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Riedel, D. (2017). Surface Hydrogenation of the Si(100)-2x1 and Electronic Properties of Silicon Dangling Bonds on the Si(100):H Surfaces. In On-Surface Atomic Wires And Logic Gates (pp. 1–24). Advances in Atom and Single Molecule Machines. M. Kolmer & C. Joachim.
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Yengui, M., Duverger, E., Sonnet, P. & Riedel, D. (2017). A two-dimensional ON/OFF switching device based on anisotropic interactions of atomic quantum dots on Si(100):H. Nat. Commun., 8, 2211.
Résumé: Controlling the properties of quantum dots at the atomic scale, such as dangling bonds, is a general motivation as they allow studying various nanoscale processes including atomic switches, charge storage, or low binding energy state interactions. Adjusting the coupling of individual silicon dangling bonds to form a 2D device having a defined function remains a challenge. Here, we exploit the anisotropic interactions between silicon dangling bonds on n-type doped Si(100):H surface to tune their hybridization. This process arises from interactions between the subsurface silicon network and dangling bonds inducing a combination of
Jahn–Teller distortions and local charge ordering. A three-pointed star-shaped device prototype is designed. By changing the charge state of this device, its electronic properties are shown to switch reversibly from an ON to an OFF state via local change of its central gap. Our results provide a playground for the study of quantum information at the nanoscale.
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2015 |
Chiaravalloti, F., Dujardin, G. & Riedel, R. (2015). Atomic scale control of hexaphenyl molecules manipulation along functionalized ultra-thin insulating layer on the Si(100) surface at low temperature (9 K). JOURNAL OF PHYSICS-CONDENSED MATTER, 27(5), 054006.
Résumé: Ultra-thin CaF2 layers are grown on the Si(100) surface by using a Knudsen cell evaporator. These epitaxial structures are studied with a low temperature (9 K) scanning tunneling microscope and used to electronically decouple hexaphenyl molecules from the Si surface. We show that the ultra-thin CaF2 layers exhibit stripe structures oriented perpendicularly to the silicon dimer rows and have a surface gap of 3.8 eV. The ultra-thin semi-insulating layers are also shown to be functionalized, since 80 % of the hexaphenyl molecules adsorbed on these structures self-orients along the stripes. Numerical simulations using time-dependent density functional theory allow comparison of computed orbitals of the hexaphenyl molecule with experimental data. Finally, we show that the hexaphenyl molecules can be manipulated along or across the stripes, enabling the molecules to be arranged precisely on the insulating surface.
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Yengui, M., & Riedel, D. (2015). Evidence of Low Schottky Barrier Effects and the Role of Gap State in the Electronic Transport Through Individual CoSi2 Silicide Nano-Islands at Low Temperature (9K). JOURNAL OF PHYSICAL CHEMISTRY C, 119, 22700.
Résumé: In this paper, we study the electronic properties of CoSi2 metallic islands grown on a Si(100) surface with a low-temperature (9 K) scanning tunneling microscope (STM). The atomic scale structures of the flat and ridge silicide islands surfaces are described with an ultimate resolution, thanks to the stability of low-temperature STM. A statistical study of the I−V and dI/dV signals acquired along the islands shows their metallic-like properties and a very small residual conduction band gap of ∼30 mV. This reveals that the electronic transport through the individual metallic islands at the silicide−silicon interface is mainly ruled by electronic tunnel processes for positive sample biases and driven by the presence of gap states for negative sample voltage. The role of the gap states is demonstrated by performing conductance measurements along the dimer vacancy lines in which interstitial Co atoms are accessible at the silicon surface. Hence, the electronic transport that occurs from the silicide−silicon interface toward the macroscopic contact of the sample can be explained.
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Yengui, M., Pinto, H., Leszczynski, J. & Riedel, D. (2015). Atomic scale study of corrugating and anticorrugating states on the bare Si(1 0 0) surface. JOURNAL OF PHYSICS-CONDENSED MATTER, 27(4), 045001.
Résumé: In this article, we study the origin of the corrugating and anticorrugating states through the electronic properties of the Si(1 0 0) surface via a low-temperature (9 K) scanning tunneling microscope (STM). Our study is based on the analysis of the STM topographies corrugation variations when related to the shift of the local density of states (LDOS) maximum in the [1-10] direction. Our experimental results are correlated with numerical simulations using the density-functional theory with hybrid Heyd–Scuseria–Ernzerhof (HSE06) functional to simulate the STM topographies, the projected density of states variations at different depths in the silicon surface as well as the three dimensional partial charge density distributions in real-space. This work reveals that the Si(1 0 0) surface exhibits two anticorrugating states at +0.8 and +2.8V that are associated with a phase shift of the LDOS maximum in the unoccupied states STM topographies. By comparing the calculated data with our experimental results, we have been able to identify the link between the variations of the STM topographies corrugation and the shift of the LDOS maximum observed experimentally. Each surface voltage at which the STM topographies corrugation drops is defined as anticorrugating states. In addition, we have evidenced a sharp jump in the tunnel current when the second LDOS maximum shift is probed, whose origin is discussed and associated with the presence of Van Hove singularities.
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2014 |
Sonnet, P., & Riedel, D. (2014). The Scanning Tunneling Microscopy of Adsorbed Molecules on Semiconductors : Some Theoretical Answers to the Experimental Observations. In Practical Aspects of Computational Chemistry III (Vol. 3, pp. 1–40). Jerzy Leszczynski; Manoj K. Shukla.
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Yengui, M., & Riedel, D. (2014). Cobalt adsorption on the bare Si(100)-2x1 surface at low temperature (12 K). SURFACE SCIENCE, 619(1), 10–18.
Résumé: The adsorption of Co atoms on the bare Si(100)-2×1 surface at low temperature (12 K) is performed in the low coverage regime (b 0.1monolayer). The ensuing surface is studied by means of a lowtemperature (9K) scanning tunneling microscope (STM). Several adsorption sites are described via STM topographies and differential conductance spectroscopy. Our study reveals that at low temperature (12 K), a significant fraction of the Co atoms diffuse into the surface and form the first stage reaction sites that are relevant for the silicidation mechanism of the Si(100). Furthermore, the low temperature conditions allow to describe surface Co adatoms conformations that are stabilized on the Si(100)-c(4×2) surface. Interestingly,we have observed the irreversible transformation of the symmetric pedestal site (Ps) to the under dimer site (UD) via specific STM scanning conditions. Finally, the presence of dimer vacancy lines is discussed and reveals that the activated etching process of the silicon dimer with metals can be induced at very low temperature.
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2013 |
Bellec, A., Chaput, L., Dujardin, G., Riedel, D., Stauffer, L., & Sonnet, P. (2013). Reversible charge storage in a single silicon atom. Phys. Rev. B, 88(24), 241406.
Résumé: The ultimate miniaturization of electronic devices at the atomic scale with single electrons requires controlling the reversible charge storage in a single atom. However, reversible charge storage is difficult to control as usually only one charge state can be stabilized. Here, combining scanning tunneling microscopy (STM) and density functional theory (DFT), we demonstrate that a single silicon dangling bond of a hydrogenated p-type doped Si(100) surface has two stable charge states (neutral and negatively charged) at low temperature (5 K). Reversible charge storage is achieved using a gate electric field between the STM tip and the surface.
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Labidi, H., Sonnet, P., & Riedel, D. (2013). Electronic Control of the Tip-Induced Hopping of an Hexaphenyl-Benzene Molecule Physisorbed on a Bare Si(100) Surface at 9 K. JOURNAL OF PHYSICAL CHEMISTRY C, 117(26), 13663–13675.
Résumé: In this work, we show that the hopping directivity of individual hexaphenyl-benzene (HPB) molecules physisorbed along the SA step edge of a bare Si(100)-2×1 surface can be reversibly controlled with a periodic hopping length. This is achieved by using the tunnel electrons of a low temperature (9 K) scanning tunneling microscope (STM). A statistical analysis of the electronic excitations applied at various positions on the HPB molecule reveals that the hopping process is related to a strong decrease of the tunnel junction conductance. This process is associated with a charge transfer from the silicon surface to the HPB molecule leading to a hopping mechanism that occurs in two sequential steps. The first step of the hopping process involves the formation of an HPB− anion that triggers the molecular motion into a metastable state. The second step is related to the neutralization of the HPB− anion which provokes the manipulation of the molecule to its final steady position. Our experimental data are supported by the calculations of the relaxed molecule using the density functional theory on the Si(100) surface that takes the van der Waals forces interactions into account. Additional calculations of the HPB− anion orbitals depict the spatial localization of the extra charge inside the HPB molecule and the relative energies of the HPB− molecular orbitals. Finally, our study shows that the hopping direction can be optimized by positioning the STM tip at specific locations along the hopping pathway.
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2012 |
Labidi, H., Kantorovich, L., & Riedel, D. (2012). Atomic-scale control of hydrogen bonding on a bare Si(100)-2x1 surface. PHYSICAL REVIEW B, 86(16), 165441.
Résumé: The control of the dissociative adsorption of individual hydrogen molecules is performed on the silicon surface at the atomic scale. It is achieved using the tip of a low-temperature (9 K) scanning tunneling microscope (STM) exposed to 10(-6) torr of H-2 and by probing the bare Si(100)-2 x 1 surface at a positive bias. This effect is very localized and is induced by the tunnel electrons. The statistical study of this process reveals an activation energy threshold matching the creation of H-2(-) at the surface of the STM tip. Our results are supported by ab inito density functional calculations of a hydrogenated silicon dimer.
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2011 |
Chiaravalloti, F., Dujardin, G., Riedel, D., Pinto, H. P., & Foster, A. S. (2011). Atomic-scale study of the adsorption of calcium fluoride on Si(100) at low-coverage regime. PHYSICAL REVIEW B, 84(15), 155433.
Résumé: We investigate, experimentally and theoretically, the initial stage of the formation of Ca/Si and Si/F structures that occurs during the adsorption of CaF(2) molecules onto a bare Si(100) surface heated to 1000 Kin a low-coverage regime (0.3 monolayer). A low-temperature (5 K) scanning tunneling microscope (STM) is used to observe the topographies and the electronic properties of the exposed silicon surfaces. Our atomic-scale study reveals that several chemical reactions arise during CaF(2) deposition, such as dissociation of the CaF(2) molecules and etching of the surface silicon dimers. The experimental and calculated STM topographies are compared using the density functional theory, and this comparison enables us to identify two types of reacted structures on the Si(100) surface. The first type of observed complex surface structure consists of large islands formed with a semiperiodic sequence of 3 x 2 unit cells. The second one is made of isolated Ca adatoms adsorbed at specific sites on the Si(100)-2 x 1 surface.
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2010 |
Bellec, A., Riedel, D., Dujardin, G., Boudrioua, O., Chaput, L., Stauffer, L., & Sonnet, P. (2010). Nonlocal Activation of a Bistable Atom through a Surface State Charge-Transfer Process on Si(100)-(2 x 1):H. Phys. Rev. Lett., 105(4), 048302.
Résumé: The reversible hopping of a bistable atom on the Si(100)-(2 x 1):H surface is activated nonlocally by hole injection into Si-Si bond surface states with a low temperature (5 K) scanning tunneling microscope. In the contact region, at short distances (<1.5 nm) between the hole injection site and the bistable atom, the hopping yield of the bistable atom exhibits remarkable variations as a function of the hole injection site. It is explained by the density of state distribution along the silicon bond network that shows charge-transfer pathways between the injection sites and the bistable atom.
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Riedel, D. (2010). Single molecule manipulation at low temperature and laser scanning tunnelling photo-induced processes analysis through time-resolved studies. JOURNAL OF PHYSICS-CONDENSED MATTER, 22(26), 264009.
Résumé: This paper describes, firstly, the statistical analysis used to determine the processes that occur during the manipulation of a single molecule through electronically induced excitations with a low temperature (5 K) scanning tunnelling microscope (STM). Various molecular operation examples are described and the ability to probe the ensuing molecular manipulation dynamics is discussed within the excitation context. It is, in particular, shown that such studies can reveal reversible manipulation for tuning dynamics through variation of the excitation energy. Secondly, the photo-induced process arising from the irradiation of the STM junction is also studied through feedback loop dynamics analysis, allowing us to distinguish between photo-thermally and photo-electronically induced signals.
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Riedel, D., Delattre, R., Borisov, A. G., & Teperik, T. V. (2010). A Scanning Tunneling Microscope as a Tunable Nanoantenna for Atomic Scale Control of Optical-Field Enhancement. Nano Lett., 10(10), 3857–3862.
Résumé: The high stability of a low temperature (9 K) scanning tunneling microscope junction is used to precisely adjust the enhancement of an external pulsed vacuum ultraviolet (VUV) laser The ensuing VUV optical-field strength is mapped on an hydrogenated Si(100) surface by imprinting locally one-photon atomic scale hydrogen desorption Subsequent to irradiation, topography of the Si(100) H surface at the reacted area revealed a desorption spot with unprecedented atomic precision Our results show that the shapes. positions. and sizes of the desorption spots are correlated to the calculated optical-field structure, offering real control of the optical-held distribution at molecular scale
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2009 |
Bellec, A., Ample, F., Riedel, D., Dujardin, G., & Joachim, C. (2009). Imaging Molecular Orbitals by Scanning Tunneling Microscopy on a Passivated Semiconductor. Nano Lett., 9(1), 144–147.
Résumé: Decoupling the electronic properties of a molecule from a substrate is of crucial importance for the development of single-molecule electronics. This is achieved here by adsorbing pentacene molecules at low temperature on a hydrogenated Si(100) surface (12 K). The low temperature (5 K) scanning tunneling microscope (STM) topography of the single pentacene molecule at the energy of the highest occupied molecular orbital (HOMO) tunnel resonance clearly resembles the native HOMO of the free molecule. The negligible electronic coupling between the molecule and the substrate is confirmed by theoretical STM topography and diffusion barrier energy calculations.
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Bellec, A., Riedel, D., Dujardin, G., Boudrioua, O., Chaput, L., Stauffer, L., & Sonnet, P. (2009). Electronic properties of the n-doped hydrogenated silicon (100) surface and dehydrogenated structures at 5 K. PHYSICAL REVIEW B, 80(24), 245434.
Résumé: We present a comparative study of the electronic properties of the clean Si(100) and the hydrogenated Si(100):H surfaces performed with a low-temperature (5 K) scanning tunneling microscope. Various surface structures such as single silicon dangling bonds and bare silicon dimers created by local desorption of hydrogen atoms from the Si(100):H surface are also investigated. The experimental scanning tunneling spectroscopy (STS) curves acquired locally on each of these structures are compared with STS measurements performed on the Si(100) and Si(100):H surfaces. First principle density-functional theory calculations of the projected local density of states, taking into account the influence of the dopant atoms (As), enable to assign the observed STS spectra.
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Chiaravalloti, F., Riedel, D., Dujardin, G., Pinto, H. P., & Foster, A. S. (2009). STM topography and manipulation of single Au atoms on Si(100). Phys. Rev. B, 79(24), 245431.
Résumé: The low-temperature (12 K) adsorption of single Au atoms on Si(100) is studied by scanning tunneling microscopy (STM). Comparison between experimental and calculated STM topographies as well as density-functional-theory calculations of the adsorption energies enable us to identify two adsorption configurations of Au atoms between Si-dimer rows (BDRs) and on top of Si-dimer rows (TDRs). In both adsorption configurations, the Au atoms are covalently bound to two Si atoms through a partial electron transfer from Si to Au. STM manipulation confirms that the TDR adsorption configuration is metastable, whereas the BDR one is the most stable configuration.
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Riedel, D., Bocquet, M. L., Lesnard, H., Lastapis, M., Lorente, N., Sonnet, P., & Dujardin, G. (2009). Selective Scanning Tunnelling Microscope Electron-induced Reactions of Single Biphenyl Molecules on a Si(100) Surface. J. Am. Chem. Soc., 131(21), 7344–7352.
Résumé: Selective electron-induced reactions of individual biphenyl molecules adsorbed in their weakly chemisorbed configuration on a Si(100) surface are investigated by using the tip of a low-temperature (5 K) scanning tunnelling microscope (STM) as an atomic size source of electrons. Selected types of molecular reactions are produced, depending on the polarity of the surface voltage during STM excitation. At negative surface voltages, the biphenyl molecule diffuses across the surface in its weakly chemisorbed configuration. At positive surface voltages, different types of molecular reactions are activated, which involve the change of adsorption configuration from the weakly chemisorbed to the strongly chemisorbed bistable and quadristable configurations. Calculated reaction pathways of the molecular reactions on the silicon surface, using the nudge elastic band method, provide evidence that the observed selectivity as a function of the surface voltage polarity cannot be ascribed to different activation energies. These results, together with the measured threshold surface voltages and the calculated molecular electronic structures via density functional theory, suggest that the electron-induced molecular reactions are driven by selective electron detachment (oxidation) or attachment (reduction) processes.
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Riedel, D., Cranney, M., Martin, M., Guillory, R., Dujardin, G., Dubois, M., & Sonnet, P. (2009). Surface-Isomerization Dynamics of trans-Stilbene Molecules Adsorbed on Si(100)-2x1. J. Am. Chem. Soc., 131(15), 5414–5423.
Résumé: Photoinduced trans-cis isomerization studies of stilbene molecules in the gas phase have led to a precise understanding of the corresponding molecular dynamics. Yet, when such molecules are adsorbed on surfaces, these reactions are expected to be strongly modified as compared to what is know in the gas phase. In this work, a low temperature (5 K) scanning tunneling microscope (STM) is used to image the trans-stilbene molecules deposited on a Si(100)-2x1 surface at 12 K. trans-Stilbene undergoes conformational changes during the adsorption process such that four different stilbene conformers are observed: trans-stilbene (TS), cis-stilbene (CS), and two new conformers I(1) and I(2). Furthermore, electronic excitation of individual stilbene molecules, by means of tunnel electrons, is shown to activate specific reversible molecular surface isomerization (TS <-> I(1) and CS <-> I(2)) combined with diffusion across the surface. Calculated STM topographies, using the tight binding method, indicate that the CS and TS molecules are physisorbed. The molecular conformations of the surface isomers I(1) and I(2) are suggested to be analogous to transient states conformations of the stilbene molecule when stabilized by the silicon surface. The measurements of the molecular surface isomerization and diffusion reaction yields are used to build a qualitative potential energy surface of the various stilbene reactions. The molecular surface-isomerization dynamics is shown to be influenced by the type of dopant (n or p). This is related to surface charging, which reveals modifications in the stilbene ionization potential.
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2008 |
Bellec, A., Riedel, D., Dujardin, G., Rompotis, N., & Kantorovich, L. N. (2008). Dihydride dimer structures on the Si(100):H surface studied by low-temperature scanning tunneling microscopy. Phys. Rev. B, 78(16), 165302.
Résumé: Surface reconstructions on the hydrogenated Si(100):H surface are observed and investigated by using a low-temperature (5 K) scanning tunneling microscope (STM). In addition to the well established 2x1 and 3x1 phases, linear structures extending over one to six silicon dimers along the same dimer row are observed. After a careful analysis of the corresponding STM topographies for both n-type and p-type doped silicon substrates, we conclude that these structures are dihydride dimers. This assignment is supported by ab initio density-functional calculations of the local density of states of dihydride structures of one or two dimers long. Furthermore, the calculation of the free-energy formation of our observed structure shows that their creation is closely linked with the hydrogenation process. These results demonstrate that the previous assignments of “split dimer” and “bow-tie” structures to dihydride dimers and dopant pairs, respectively, need to be reconsidered.
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Lastapis, M., Martin, M., Riedel, D., & Dujardin, G. (2008). Role of the dopant in silicon on the dynamics of a single adsorbed molecule. Phys. Rev. B, 77(12), 125316.
Résumé: We investigate the role of the dopant in silicon on the dynamics of a single adsorbed molecule. We demonstrate that the dynamics of a single bistable molecule, a biphenyl molecule, adsorbed on a Si (100)-(2x1) surface is markedly dependent on the silicon type of doping (p or n) even though the electronic excitation and relaxation processes are unchanged. Both strongly and weakly chemisorbed individual biphenyl molecules are shown to interact differently with p- or n-doped Si (100) surfaces, thus inducing different stabilities of the adsorption configurations and different molecular dynamics. These effects rely on electrostatic interactions between distributed charges inside the molecule and charged surface states. The described phenomenon, which is a priori general, should be applicable to most of the molecules adsorbed on doped semiconductors having surface states in their band gap. This result is anticipated to have important applications in molecular electronic for positioning individual molecules with precision.
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