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2015
2015
Peer-reviewed Publications |
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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