2024 |
Zhang, W., Zhang, X., Ono, L. K., Qi, Y., & Oughaddou, H. (2024). Recent Advances in Phosphorene: Structure, Synthesis, and Properties. SMALL, 20, 2303115.
Résumé: Phosphorene is a 2D phosphorus atomic layer arranged in a honeycomb lattice like graphene but with a buckled structure. Since its exfoliation from black phosphorus in 2014, phosphorene has attracted tremendous research interest both in terms of synthesis and fundamental research, as well as in potential applications. Recently, significant attention in phosphorene is motivated not only by research on its fundamental physical properties as a novel 2D semiconductor material, such as tunable bandgap, strong in-plane anisotropy, and high carrier mobility, but also by the study of its wide range of potential applications, such as electronic, optoelectronic, and spintronic devices, energy conversion and storage devices. However, a lot of avenues remain to be explored including the fundamental properties of phosphorene and its device applications. This review recalls the current state of the art of phosphorene and its derivatives, touching upon topics on structure, synthesis, characterization, properties, stability, and applications. The current needs and future opportunities for phosphorene are also discussed.
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2023 |
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Kaddar, Y., Zhang, W., Enriquez, H., Dappe, Y. J., Bendounan, A., Dujardin, G., Mounkachi, O., El kenz, A., Benyoussef, A., Kara, A., & Oughaddou, H. (2023). Dirac Fermions in Blue Phosphorene Monolayer. ADVANCED FUNCTIONAL MATERIALS, 33(21), 2213664.
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Neziri, E., Zhang, W., Smogunov, A., Mayne, A. J., Kara, A., Dappe, Y. J., & Oughaddou, H. (2023). Structural properties of Bi/Au(110). NANOTECHNOLOGY, 34(23), 235601.
Résumé: Atomically thin bismuth films (2D Bi) are becoming a promising research area due to their unique properties and their wide variety of applications in spintronics, electronic and optoelectronic devices. We report on the structural properties of Bi on Au(110), explored by low-energy electron diffraction (LEED), scanning tunneling microscopy (STM) and density functional theory (DFT) calculations. At a Bi coverage lower than one monolayer (1 ML) various reconstructions are observed, we focus on Bi/Au(110)-c(2 x 2) reconstruction (at 0.5 ML) and Bi/Au(110)-(3 x 3) structure (at 0.66 ML). We propose models for both structures based on STM measurements and further confirm by DFT calculations.
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Oughaddou, H., Kara, A., Rochdi, N., Dappe, Y. J., & Tetard, L. (2023). Special issue on advances in renewable energies, materials and technology. THE EUROPEAN PHYSICS JOURNAL APPLIED PHYSICS, 98, E2.
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Quertite, K., Enriquez, H., Trcera, N., Lagarde, P., Bendounan, A., Mayne, A. J., Dujardin, G., El kenz, A., Benyoussef, A., Kara, A., & Oughaddou, H. (2023). First steps of silicene growth on an insulating thin-film: effect of the substrate temperature. THE EUROPEAN PHYSICS JOURNAL APPLIED PHYSICS, 98, 41.
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2021 |
Bouaziz, M., Zhang, W., Tong, Y., Oughaddou, H., Enriquez, H., Mlika, R., Korri-Youssoufi, H., Chen, Z., Xiong, H., Cheng, Y., & Bendounan, A. (2021). Phase transition from Au–Te surface alloy towards tellurene-like monolayer. 2D MATERIALS, 8, 015029.
Résumé: Two-dimensional (2D) chalcogen-based layers will be among the next generation of materials for potential high-tech applications. We present the structural and electronic properties of Tellurium (Te) deposited on the Au(111) surface by high temperature vapor deposition in UHV. We discuss the possible scenarios for the formation of 2D layers ; either AuTe2 metal dichalcogenide, or Au–Te alloy or a single Tellurene layer. Low energy electron diffraction (LEED) and scanning tunneling microscopy (STM) show the existence of several surface reconstructions depending on the Te film thickness in the sub-monolayer regime. We observe the survival of the well-known spin-split Shockley state of the Au(111) surface after Te deposition. The state is shifted to higher binding energy, suggesting a charge transfer at the interface. For 0.33 ML Te, new dispersive bands in the angle-resolved photoemission (ARPES), are due to the strong hybridization between the electronic states of Te and Au. The low intensity and back-folding at the boundaries of the reduced surface Brillouin zone (R-SBZ), prove that these electronic bands represent a naturel 2D electron gas, strongly disturbed by the surface reconstruction. This indicates the fromation of a surface Au–Te alloy. At 0.5 ML Te, a rich, thickness-dependent transition develops from the surface alloy to Tellurene-like structure which excludes the growth of AuTe2 monolayer. Both the surface alloy and the Tellurene monolayer are semiconducting with an occupied-state gap of 0.65 eV.
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Quertite, K., Enriquez, H., Trcera, N., Tong, Y., Bendounan, A., Mayne, A. J., Dujardin, G., Lagarde, P., El Kenz, A., Benyoussef, A., Dappe, Y. J., Kara, A., & Oughaddou, H. (2021). Silicene Nanoribbons on an Insulating Thin Film. ADVANCED FUNCTIONAL MATERIALS, 31, 2007013.
Résumé: Silicene, a new 2D material has attracted intense research because of the
ubiquitous use of silicon in modern technology. However, producing freestanding
silicene has proved to be a huge challenge. Until now, silicene could be synthesized only on metal surfaces where it naturally forms strong interactions with the metal substrate that modify its electronic properties. Here, the authors report the first experimental evidence of silicene sheet on an insulating NaCl thin film. This work represents a major breakthrough, for the study of the intrinsic properties of silicene, and by extension to other 2D materials that have so far only been grown on metal surfaces.
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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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Zhang, W., Enriquez, H., Mayne, A. J., Bendounan, A., Seitsonen, A. P., Kara, A., Dujardin, G., & Oughaddou, H. (2021). First steps of blue phosphorene growth on Au(1 1 1). In MATERIALS TODAY PROCEEDINGS (Vol. 39, pp. 1153–1156).
Résumé: Blue phosphorene (blue-P) has attracted considerable attention due to its potential applications in optical and electronic devices. However, its synthesis has remained a challenge. Here, we report an experimental investigation of the first steps of blue-P growth on Au(1 1 1) surface by molecular-beam epitaxy. The structure was characterized by in situ low temperature scanning tunneling microscopy, low-energy electron diffraction, combined with density functional theory calculations. We reveal two-dimensional (2D) phosphorus clusters (P-clusters) formed on surface at 150 °C, where the most prevalent structure of P-clusters is composed of triangles with six protrusions. We also demonstrate the transformation of these P-clusters into a single layer of blue-P after post-annealing at 260 °C. Our observation of the growth process is a necessary step for exploring the growth mechanisms further.
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Zhang, W., Enriquez, H., Tong, Y., Mayne, A. J., Bendounan, A., Smogunov, A., Dappe, Y. J., Kara, A., Dujardin, G., & Oughaddou, H. (2021). Flat epitaxial quasi-1D phosphorene chains. NATURE COMMUNICATIONS, 12, 5160.
Résumé: The emergence of peculiar phenomena in 1D phosphorene chains (P chains) has been proposed in theoretical studies, notably the Stark and Seebeck effects, room temperature magnetism, and topological phase transitions. Attempts so far to fabricate P chains, using the top-down approach starting from a few layers of bulk black phosphorus, have failed to produce reliably precise control of P chains. We show that molecular beam epitaxy gives a controllable bottom-up approach to grow atomically thin, crystalline 1D flat P chains on a Ag(111) substrate. Scanning tunneling microscopy, angle-resolved photoemission spectroscopy, and density functional theory calculations reveal that the armchair-shaped chains are semiconducting with an intrinsic 1.80 ± 0.20 eV band gap. This could make these P chains an ideal material for opto-electronic devices.
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2020 |
Tchalala, M. R., Enriquez, H., Bendounan, A., Mayne, A. J., Dujardin, G., Kara, A., Ali, M. A., & Oughaddou, H. (2020). Tip-induced oxidation of silicene nano-ribbons. NANOSCALE ADVANCES, 2, 2309–2314.
Résumé: We report on the oxidation of self-assembled silicene nanoribbons grown on the Ag (110) surface using scanning tunneling microscopy and high-resolution photoemission spectroscopy. The results show that silicene nanoribbons present a strong resistance towards oxidation using molecular oxygen. This can be overcome by increasing the electric field in the STM tunnel junction above a threshold of +2.6 V to induce oxygen dissociation and reaction. The higher reactivity of the silicene nanoribbons towards atomic oxygen is observed as expected. The HR-PES confirm these observations: even at high exposures of molecular oxygen, the Si 2p core-level peaks corresponding to pristine silicene remain dominant, reflecting a very low reactivity to molecular oxygen. Complete oxidation is obtained following exposure to high doses of atomic oxygen; the Si 2p core level peak corresponding to pristine silicene disappears.
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Tiouitchi, G., Ali, M. A., Benyoussef, A., Hamedoun, M., Lachgar, A., Kara, A., Ennaoui, A., Mahmoud, A., Boschini, F., Oughaddou, H., El Moutaouakil, A., El Kenz, A., & Mounkachi, O. (2020). Efficient production of few-layer black phosphorus by liquid-phase exfoliation. Royal Society Open Source, 7(10), 201210.
Résumé: Phosphorene is a new two-dimensional material that has recently attracted much attention owing to its fascinating electrical, optical, thermal and chemical properties. Here, we report on high-quality exfoliation of black phosphorus nanosheets, with controllable size produced in large quantities by liquid-phase exfoliation using N-methyl-2-pyrrolidone (NMP) as a solvent under ambient conditions. The as-synthesized few layers show a great potential for solar energy conversion based on the optical results shown in this work.
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Tiouitchi, G., ElManjli, E., Mounkachi, O., Mahmoud, A., Boschini, F., Kara, A., Oughaddou, H., Hamedoun, M., Benyoussef, A., & Ait Ali, M. (2020). From Amorphous Red Phosphorus to a Few Layers of Black Phosphorus: A Low-cost and Efficient Preparation Process. JORDAN JOURNAL OF PHYSICS, 13(2), 149–155.
Résumé: In this work, we present an efficiency synthesis method of phosphorene from red phosphorus by means of black phosphorus. The latter was synthesized by using copper, tin, tin iodide and red phosphorus as precursor at low pressure-temperature. Characterizations with powder X-ray diffraction, scanning electron microscopy (SEM), energy dispersive spectrometry (EDX), high-resolution TEM (HR-TEM) and Raman spectroscopy were performed to confirm the high quality and purity of black phosphorus crystal. Liquid phase method was used to exfoliate black phosphorus to phosphorene in N-methyl-2-pyrrolidone (NMP) as solvent. Atomic force microscopy and STEM were used to confirm the exfoliation of black phophorus in a few layers of phophorene.
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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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Zhang, W., Enriquez, H., Zhang, X., Mayne, A. J., Bendounan, A., Dappe, Y. J., Kara, A., Dujardin, G., & Oughaddou, H. (2020). Blue phosphorene reactivity on the Au(111) surface. NANOTECHNOLOGY, 31(49), 495602.
Résumé: The synthesis of blue phosphorene by molecular beam epitaxy (MBE) has recently come under the spotlight due to its potential applications in electronic and optoelectronic devices. However, this synthesis remains a significant challenge. The surface reactivity between the P atoms and the Au atoms should be considered for the P/Au(111) system. In the MBE process, the temperature of the substrate is a key parameter for the growth of blue phosphorene. During the initial growth stage, irregularly shaped Phosphorus clusters grow on top of Au(111) surface at room temperature. When the substrate temperature is increased, these clusters transform into a phosphorene-like structure with a honeycomb lattice. An atom exchange reaction is observed between the P and first layer Au atoms under thermal activation at higher temperature, where the P atoms replace Au atoms to form a blue phosphorene structure within the top Au layer and at the step edges.
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Zhang, W., Enriquez, H., Tong, Y., Mayne, A. J., Bendounan, A., Dappe, Y. J., Kara, A., Dujardin, G., & Oughaddou, H. (2020). Phosphorus Pentamers: Floating Nanoflowers form a 2D network. ADVANCED FUNCTIONAL MATERIALS, 30, 2004531.
Résumé: An experimental investigation of a new polymorphic 2D single layer of phosphorus on Ag(111) is presented. The atomically-resolved scanning tunneling microscopy images show a new 2D material composed of freely-floating phosphorus pentamers organized into a 2D layer, where the pentamers are aligned in close-packed rows. The scanning tunneling spectroscopy measurements reveal a semiconducting character with a band gap of 1.20 eV. This work presents the formation at low temperature of a new polymorphic 2D phosphorus layer composed of a floating 2D pentamer structure. The smooth curved terrace edges and a lack of any clear crystallographic orientation with respect to the Ag(111) substrate at room temperature indicates a smooth potential energy surface that is reminiscent of a liquid-like growth phase. This is confirmed by density functional theory calculations that find a small energy barrier of only 0.17 eV to surface diffusion of the pentamers (see Supporting Information). The formation of extended, homogeneous domains is a key ingredient to opening a new avenue to integrate this new 2D material into electronic devices.
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2019 |
Kleimeier, N. F., Wenzel, G., Urban, A. J., Tchalala, M. R., Oughaddou, H., Dedkov, Y., Voloshina, E., & Zacharias, H. (2019). Unoccupied electronic band structure of pentagonal Si nanoribbons on Ag(110). PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 21(32), 17811–17820.
Résumé: Silicon nanoribbons – one dimensional silicon structures with a pentagonal atomic structure and mixed sp(2)- and sp(3)-hybridisation – grow on Ag(110) upon deposition of silicon. These nanostructures are viewed as promising candidates for modern day electronics as they are comprised of the same element as today's semiconductor devices. Even though they have been studied extensively over the last decade, only little is known about their unoccupied band structure which is important for possible future optoelectronics, semiconductor, and spintronics applications. In order to elucidate the unoccupied band structure of the nanoribbons, k-resolved inverse photoemission spectroscopy (KRIPES) studies were performed on both nanoribbon structures reported in the literature as well as on the bare Ag(110) substrate within the energy range of E-EF = 0-6.5 eV. The obtained experimental results are compared to density functional theory (DFT) calculated band structures to assign individual spectral features to specific bands. Since even small changes in the structural model of the nanoribbons lead to a change in the calculated band structure, this comparison allows us to assess the validity of the proposed structural models.
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Tiouitchi, G., Ali, M. A., Benyoussef, A., Hamedoun, M., Lachgar, A., Benaissa, M., Kara, A., Ennaoui, A., Mahmoud, A., Boschini, F., Oughaddou, H., El Kenz, A., & Mounkachi, O. (2019). An easy route to synthesize high-quality black phosphorus from amorphous red phosphorus. MATERIALS LETTERS, 236, 56–59.
Résumé: The development of an easy and efficient process for producing black phosphorus (BP) remains a bottleneck for the use of BP in large-scale applications. In this work, we present a simple, potentially scalable, and economically viable method for the preparation of high-quality BP from amorphous red phosphorus. BP was synthesized under low pressure and temperature conditions from red phosphorus via the addition of small quantities of copper, tin, and tin(IV) iodide. Characterization by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectrometry (EDX), high-resolution transmission electron microscopy (HR-TEM), and Raman spectroscopy were performed to confirm the high quality and purity of the formed BP.
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Tong, Y., Fuhr, J. D., Martiarena, M. L., Oughaddou, H., Enriquez, H., Nicolas, F., Chaouchi, K., Kubsky, S., & Bendounan, A. (2019). Properties of NTCDA Thin Films on Ag(110): Scanning Tunneling Microscopy, Photoemission, Near-Edge X-ray Fine Structure, and Density Functional Theory Investigations. JOURNAL OF PHYSICAL CHEMISTRY C, 123(1), 379–386.
Résumé: It is well proven that the properties of organic/metal interfaces play an utmost role in the performance of organic devices. Here we present a study on structural and electronic properties of high-quality 1,4,5,8-naphthalene tetracarboxylic dianhydride (NTCDA) films grown on an Ag(110) surface. High-resolution scanning tunneling microscopy and low-energy electron diffraction show the presence of two molecular domains. Density functional theory calculations indicate that the most stable location of NTCDA corresponds to anhydride oxygen attached to the Ag atoms along the [110] direction. Photoemission results of the C 1s and O 1s core levels demonstrate a strong interfacial bonding, inducing a charge transfer from the Ag metal to the molecular monolayer. An angular-dependent study of the C K-edge near-edge X-ray fine structure spectra provides detailed information concerning the evolution of the NTCDA orientation with the film thickness.
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2018 |
Tchalala, M. R., Kara, A., Lachgar, A., Yagoubi, S., Foy, E., Vega, E., Nitsche, S., Chaudanson, D., Aufray, B., EL Firdoussi, L., Ali, M. A., & Oughaddou, H. (2018). Silicon nanoparticles synthesis from calcium disilicide by Redox assisted chemical exfoliation. Materials Today Communications, 16, 281–284.
Résumé: We report the preparation of single-crystal silicon nanoparticles with 15 to 22 nm diameter from calcium disilicide (CaSi2) by redox assisted chemical exfoliation using solution phase synthesis route. Silicon nanoparticles are found to be highly oriented with a predominant size of 18 nm. X-Ray diffraction, as well as transmission electron microscopy studies, confirm that the silicon nanoparticles are a diamond type and highly crystalline.
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Tchalala, R. M., Enriquez, H., Mayne, A. J., Kara, A., Dujardin, G., & Oughaddou, H. (2018). First steps of silicene growth on Ag(111). Journal of Physics: Conference Series, 1081, 012005.
Résumé: In this paper we report on the first steps of silicene growth on Ag(111) using scanning tunneling microscopy. We show that the topmost atomic layer is composed of both silicon and silver. The STM observations are consistent with an exchange process between the silicon and silver atoms preferentially taking place at the step edges of the Ag substrate. In addition, silicon stripes are observed as precursors of the formation of the silicene sheet.
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Zhang, W., Enriquez, H., Tong, Y., Bendounan, A., Kara, A., Seitsonen, A. P., Mayne, A. J., Dujardin, G., & Oughaddou, H. (2018). Epitaxial Synthesis of Blue Phosphorene. SMALL, 14, 1804066.
Résumé: Phosphorene is a new 2D material composed of a single or few atomic layers of black phosphorus. Phosphorene has both an intrinsic tunable direct bandgap and high carrier mobility values, which make it suitable for a large variety of optical and electronic devices. However, the synthesis of single-layer phosphorene is a major challenge. The standard procedure to obtain phosphorene is by exfoliation. More recently, the epitaxial growth of single-layer phosphorene on Au(111) was investigated by molecular beam epitaxy and the obtained structure described as a blue phosphorene sheet. In the present study, large areas of high-quality monolayer phosphorene, with a bandgap value equal to at least 0.8 eV, are synthesized on Au(111). The experimental investigations, coupled with density functional theory calculations, give evidence of two distinct phases of blue phosphorene on Au(111), instead of one as previously reported, and their atomic structures are determined.
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2017 |
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Quertite, K., Lasri, K., Enriquez, H., Mayne, A. J., Bendounan, A., Dujardin, G., Trcera, N., Malone, W., EL Kenz, A., Benyoussef, A., Kara, A., & Oughaddou, H. (2017). Atomic structure of sub-monolayer NaCl grown on Ag(110) surface. JOURNAL OF PHYSICAL CHEMISTRY C, 121, 20272–20278.
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Quertite, K., Zaari, H., Ez-Zahraouy, H., El Kenz, A., Oughaddou, H., & Benyoussef, A. (2017). Theoretical investigation of electronic, magnetic, transport and optical properties of the pure and doped cuprate superconductor HgBa 2 CuO 4+δ. CURRENT APPLIED PHYSICS, 17(10), 1271–1278.
Résumé: We report detailed DFT calculations and Monte Carlo simulations on the pure and doped cuprate superconductor HgBa2CuO4+δ. For the pure compound (δ = 0), we have obtained an insulating behavior with strong antiferromagnetic copper spin correlations in the CuO2 plane. The high value of the calculated Néel temperature TN = 333 K reflects the large in-plane exchange interaction J = -145 meV. The obtained optical properties and critical exponents demonstrate the anisotropic quasi-2D character of this type of materials. As for the doped compound the electronic structure and the transport properties have been investigated for various values of doping. Based on these data, we suggest a prediction of the value of optimum doping for HgBa2CuO4+δ (δoptimal = 0.125).
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Sadeddine, S., Enriquez, H., Bendounan, A., Das, P. K., Vobornik, I., Mayne, A. J., Dujardin, G., Sirotti, F., & Kara A. & Oughaddou H. (2017). Compelling experimental evidence of a Dirac cone in the electronic structure of a 2D Silicon layer. SCIENTIFIC REPORTS, 7, 44400.
Résumé: The remarkable properties of graphene stem from its two-dimensional (2D) structure, with a linear dispersion of the electronic states at the corners of the Brillouin zone (BZ) forming a Dirac cone. Since then, other 2D materials have been suggested based on boron, silicon, germanium, phosphorus, tin, and metal di-chalcogenides. Here, we present an experimental investigation of a single silicon layer on Au(111) using low energy electron diffraction (LEED), high resolution angle-resolved photoemission spectroscopy (HR-ARPES), and scanning tunneling microscopy (STM). The HR-ARPES data show compelling evidence that the silicon based 2D overlayer is responsible for the observed linear dispersed feature in the valence band, with a Fermi velocity of vF = 10+6 m.s−1 comparable to that of graphene. The STM images show extended and homogeneous domains, offering a viable route to the fabrication of silicene-based opto-electronic devices.
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Tong, Y., Nicolas, F., Kubsky, S., Oughaddou, H., Sirotti, F., Esaulov, V., & Bendounan, A. (2017). Interplay between Structural and Electronic Properties in 1,4,5,8-Naphthalenetetracarboxylic Dianhydride Films on Cu(100). JOURNAL OF PHYSICAL CHEMISTRY C, 121(9), 5050–5057.
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2016 |
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Oughaddou, H., Enriquez, H., Tchalala, M. R., Bendounan, A., Mayne, A. J., Sirotti, F., & & Dujardin, G. (2016). Silicene on Ag(111) and Au(110) surfaces. In Silicene; Structure, Properties and Applications (pp. 167–181). Springer Series in Materials Science, 235. Berlin: Spencer, M.J.S. & T. Morishita, T.
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2015 |
Oughaddou, H., Enriquez, H., Tchalala, M.R., Yildirim, H., Mayne, A.J., Bendounan, A., Dujardin, G., Ait Ali, M. & Kara, A. (2015). Silicene: A promising new 2D material. PROGRESS IN SURFACE SCIENCE, 90, 46–83.
Résumé: Silicene is emerging as a two-dimensional material with very attractive electronic properties for a wide range of applications; it is a particularly promising material for nano-electronics in silicon-based technology. Over the last decade, the existence and stability of silicene has been the subject of much debate. Theoretical studies were the first to predict a puckered honeycomb structure
with electronic properties resembling those of graphene. Though these studies were for free-standing silicene, experimental fabrication of silicene has been achieved so far only through epitaxial growth on crystalline surfaces. Indeed, it was only in 2010 that researchers presented the first experimental evidence of the formation
of silicene on Ag(110) and Ag(111), which has launched silicene in a similar way to graphene. This very active field has naturally led to the recent growth of silicene on Ir(111), ZrB2(0001)and Au(110) substrates. However, the electronic properties of epitaxially grown silicene on metal surfaces are influenced by the
strong silicene–metal interactions. This has prompted experimental studies of the growth of multi-layer silicene, though the nature of its ‘‘silicene’’ structure remains questionable. Of course, like graphene, synthesizing free-standing silicene represents the ultimate challenge. A first step towards this has been reported recently through chemical exfoliation from calcium disilicide (CaSi2). In this review, we discuss the experimental and theoretical studies of silicene performed to date. Special attention is given to different experimental studies of the electronic properties of silicene on metal substrates. New avenues for the growth of silicene on other substrates with different chemical characteristics are presented along with foreseeable applications such as nano-devices and novel batteries.
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2014 |
Bocchetti, V., Diep, H. T., Enriquez, H., Oughaddou, H., & Kara, A. (2014). Thermal stability of standalone silicene sheet. In JOURNAL OF PHYSICS-CONFERENCE SERIES (Vol. 491, 012008). 3RD INTERNATIONAL MEETING ON SILICENE (IMS-3).
Résumé: Extensive Monte Carlo simulations are carried out to study thermal stability of an infinite standalone silicon sheet. We used the Tersoff potential that has been used with success for silicon at low temperatures. However, the melting temperature T-m calculated with the original parameters provided by Tersoff is too high with respect to the experimental one. Agrawal, Raff and Komanduri have proposed a modified set of parameters to reduce T-m. For comparison, we have used these two sets of parameters to study the stability and the melting of a standalone 2D sheet of silicon called “silicene”, by analogy with graphene for the carbon sheet. We find that 2D crystalline silicene is stable up to a high temperature unlike in 2D systems with isotropic potentials such as Lennard-Jones. The differences in the obtained results using two sets of parameters are striking.
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Enriquez, H., Kara, A., Mayne, A. J., Dujardin, G., Jamgotchian, H., Aufray, B., & Oughaddou, H. (2014). Atomic structure of the (2 root 3 x 2 root 3)R30 degrees of silicene on Ag(111) surface. In JOURNAL OF PHYSICS-CONFERENCE SERIES (Vol. 491, 012004). 3RD INTERNATIONAL MEETING ON SILICENE (IMS-3).
Résumé: The deposition of one monolayer of silicon on a Ag(111) substrate induces the formation of silicene structures exhibiting different ordered phases, including a (2 root 3x2 root 3)R30 degrees, a (4 x 4) and a (root 13x root 13)R13.9 degrees superstructures. In this paper we focus on the (2 root 3x root 3)R30 degrees phase. Using a combination of scanning tunneling microscopy and LEED observations, we show that this phase corresponds to a 11 degrees rotation of the silicene sheet relative to the substrate orientation.
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Tchalala, M. R., & Ait Ali, M. (2014). Chemical Synthesis of Silicon sheets from Calcium Silicide. In JOURNAL OF PHYSICS-CONFERENCE SERIES (Vol. 491, 12009).
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Tchalala, M. R., Enriquez, H., Mayne, A. J., Kara, A., Dujardin, G., Ali, M. A., & Oughaddou, H. (2014). Atomic structure of silicene nanoribbons on Ag(110). In JOURNAL OF PHYSICS-CONFERENCE SERIES (Vol. 491, 012002). 3RD INTERNATIONAL MEETING ON SILICENE (IMS-3).
Résumé: The growth of silicene nano-ribbons (NRs) on Ag(110) substrate is re-investigated using scanning tunneling microscopy (STM) and low energy electron diffraction (LEED). Deposition of one silicon monolayer at 230 degrees C induces the formation of one-dimensional 1.6 nm wide silicene nanoribbons into a well-ordered compact array with a nanometer-scale pitch of just 2 nm. Based on the STM analysis we derived an atomic model of the silicene nanoribbons (NRs) where they are substantially buckled, and quantum confinement of the electrons in the NRs contribute to electronic density of states.
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Tchalala, M. R., Enriquez, H., Yildirim, H., Kara, A., Mayne, A. J., Dujardin, G., Ali, M. A., & Oughaddou, H. (2014). Atomic and electronic structures of the (root 13 x root 13)R13.9 degrees of silicene sheet on Ag(111). APPLIED SURFACE SCIENCE, 303, 61–66.
Résumé: Using scanning tunneling microscopy, low energy electron diffraction measurements, and ab initio calculations based on density functional theory, we present atomic models of the (root 13 x root 13)R13.9 degrees silicene superstructure grown on Ag(1 1 1). The STM images reveal two co-existing atomic arrangements with two different orientations of the silicene sheet relative to the Ag(1 1 1) surface. DFT calculations with and without the inclusion of van der Waals interactions show corrugated Si atomic positions for both orientations implying a significant interaction with Ag(1 1 1) surface. The electronic structure of both silicene and Ag(1 1 1) surface are sufficiently affected that new interface states emerge close to the Fermi level. (C) 2014 Elsevier B.V. All rights reserved.
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2013 |
Majzik, Z., Tchalala, M. R., Svec, M., Hapala, P., Enriquez, H., Kara, A., Mayne, A. J., Dujardin, G., Jelinek, P., & Oughaddou, H. (2013). Combined AFM and STM measurements of a silicene sheet grown on the Ag(111) surface. JOURNAL OF PHYSICS-CONDENSED MATTER, 25(22), 225301.
Résumé: In this paper, we present the first non-contact atomic force microscopy (nc-AFM) of a silicene on a silver (Ag) surface, obtained by combining non-contact atomic force microscopy and scanning tunneling microscopy (STM). STM images over large areas of silicene grown on the Ag(111) surface show both (root 13 x root 13)R13.9 and (4 x 4) superstructures. For the widelyobserved (4 x 4) structure, the observed nc-AFM image is very similar to the one recorded by STM. The structure resolved by nc-AFM is compatible with only one out of two silicon atoms being visible. This indicates unambiguously a strong buckling of the silicene honeycomb layer.
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Tchalala, M. R., Ali, M. A., Enriquez, H., Kara, A., Lachgar, A., Yagoubi, S., Foy, E., Vega, E., Bendounan, A., Silly, M. G., Sirotti, F., Nitshe, S., Chaudanson, D., Jamgotchian, H., Aufray, B., Mayne, A. J., Dujardin, G., & Oughaddou, H. (2013). Silicon sheets by redox assisted chemical exfoliation. JOURNAL OF PHYSICS-CONDENSED MATTER, 25(44), 442001.
Résumé: In this paper, we report the direct chemical synthesis of silicon sheets in gram-scale quantities by chemical exfoliation of pre-processed calcium disilicide (CaSi2). We have used a combination of x-ray photoelectron spectroscopy, transmission electron microscopy and energy-dispersive x-ray spectroscopy to characterize the obtained silicon sheets. We found that the clean and crystalline silicon sheets show a two-dimensional hexagonal graphitic structure.
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Tchalala, M. R., Enriquez, H., Mayne, A. J., Kara, A., Roth, S., Silly, M. G., Bendounan, A., Sirotti, F., Greber, T., Aufray, B., Dujardin, G., Ali, M. A., & Oughaddou, H. (2013). Formation of one-dimensional self-assembled silicon nanoribbons on Au(110)-(2 x 1). APPLIED PHYSICS LETTERS, 102(8), 083107.
Résumé: We report results on the self-assembly of silicon nanoribbons (NRs) on the (2 x 1) reconstructed Au(110) surface under ultra-high vacuum conditions. Upon adsorption of 0.2 monolayer (ML) of silicon, the (2 x 1) reconstruction of Au(110) is replaced by an ordered surface alloy. Above this coverage, a new superstructure is revealed by low energy electron diffraction (LEED), which becomes sharper at 0.3 Si ML. This superstructure corresponds to Si nanoribbons all oriented along the [(1) over bar 10] direction as revealed by LEED and scanning tunneling microscopy (STM). STM and high-resolution photoemission spectroscopy indicate that the nanoribbons are flat and predominantly 1.6 nm wide. In addition, the silicon atoms show signatures of two chemical environments corresponding to the edge and center of the ribbons. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4793536]
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Vizzini, S., Oughaddou, H., Hoarau, J. Y., Biberian, J. P., Bertoglio, M., & Aufray, B. (2013). Unexpected behaviour of one Pb monolayer deposited on aluminum oxide thin film grown on Ag(111). APPLIED PHYSICS LETTERS, 103(26), 261601.
Résumé: Using scanning tunneling microscopy (STM), Auger electron spectroscopy, and low energy electron diffraction, we have observed a surprising complete dissolution at room temperature of one lead monolayer deposited by evaporation on an aluminum oxide thin film (similar to 0.8 nm thick) previously grown on Ag (111). We have observed the quasi-instantaneous diffusion of the lead deposit through the oxide layer to the silver/oxide interface. After the diffusion process, lead atoms form a Moire superstructure, which is characterized by STM through the oxide layer. This unexpected behavior puts in light the very weak interaction between the aluminum oxide and the silver substrate. (C) 2013 AIP Publishing LLC.
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2012 |
Enriquez, H., Mayne, A. J., Kara, A., Vizzini, S., Roth, S., Lalmi, B., Seitsonen, A. P., Aufray, B., Greber, T., Belkhou, R., Dujardin, G., & Oughaddou, H. (2012). Adsorption of silicon on Au(110): An ordered two dimensional surface alloy. APPLIED PHYSICS LETTERS, 101(2), 021605.
Résumé: We report on experimental evidence for the formation of a two dimensional Si/Au(110) surface alloy. In this study, we have used a combination of scanning tunneling microscopy, low energy electron diffraction, Auger electron spectroscopy, and ab initio calculations based on density functional theory. A highly ordered and stable Si-Au surface alloy is observed subsequent to growth of a sub-monolayer of silicon on an Au(110) substrate kept above the eutectic temperature. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4735310]
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Enriquez, H., Vizzini, S., Kara, A., Lalmi, B., & Oughaddou, H. (2012). Silicene structures on silver surfaces. JOURNAL OF PHYSICS-CONDENSED MATTER, 24(31), 314211.
Résumé: In this paper we report on several structures of silicene, the analog of graphene for silicon, on the silver surfaces Ag(100), Ag(110) and Ag(111). Deposition of Si produces honeycomb structures on these surfaces. In particular, we present an extensive theoretical study of silicene on Ag(111) for which several recent experimental studies have been published. Different silicene structures were obtained only by varying the silicon coverage and/or its atomic arrangement. All the structures studied show that silicene is buckled, with a Si-Si nearest neighbor distance varying between 2.28 and 2.5 angstrom. Due to the buckling in the silicene sheet, the apparent (lateral) Si-Si distance can be as low as 1.89 angstrom. We also found that for a given coverage and symmetry, one may observe different scanning tunneling microscopy images corresponding to structures that differ by only a translation.
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Kara, A., Enriquez, H., Seitsonen, A. P., Voon, L. C. L. Y., Vizzini, S., Aufray, B., & Oughaddou, H. (2012). A review on silicene-New candidate for electronics (vol 67, pg 1, 2012). SURFACE SCIENCE REPORTS, 67(5), 1–18.
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Oughaddou H., & Kara, A. (2012). First European Mediterranean Conference on Materials & Renewable Energies (Vol. 1). Simplex Academic Publishers.
Résumé: Proceedings of the First European Mediterranean Conference on Materials & Renewable Energies (EMCMRE-1), Marrakech, Morocco, 21-25 Novembre 2011
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2011 |
Enriquez, H., Oughaddou H., & Kara, A. (2011). International Conference on Nano-Materials and Renewable Energies (Vol. 2). Simplex Academic Publishers.
Résumé: International Conference on Nano-Materials and Renewable Energies, ICNMRE, July 5-9, 2010, Safi-Morocco
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2010 |
Aufray, B., Kara, A., Vizzini, S., Oughaddou, H., Leandri, C., Ealet, B., & Le Lay, G. (2010). Graphene-like silicon nanoribbons on Ag(110): A possible formation of silicene. APPLIED PHYSICS LETTERS, 96(18), 183102.
Résumé: Scanning tunneling microscopy (STM) and ab initio calculations based on density functional theory (DFT) were used to study the self-aligned silicon nanoribbons on Ag(110) with honeycomb, graphene-like structure. The silicon honeycombs structure on top of the silver substrate is clearly observed by STM, while the DFT calculations confirm that the Si atoms adopt spontaneously this new silicon structure. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3419932]
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De Padova, P., Quaresima, C., Ottaviani, C., Sheverdyaeva, P. M., Moras, P., Carbone, C., Topwal, D., Olivieri, B., Kara, A., Oughaddou, H., Aufray, B., & Le Lay, G. (2010). Evidence of graphene-like electronic signature in silicene nanoribbons. APPLIED PHYSICS LETTERS, 96(26), 261905.
Résumé: We report on the electronic properties of straight, 1.6 nm wide, silicene nanoribbons on Ag(110), arranged in a one-dimensional grating with a pitch of 2 nm, whose high-resolution scanning tunneling microscopy images reveal a honeycomb geometry. Angle-resolved photoemission shows quantum confined electronic states of one-dimensional character. The silicon band dispersion along the direction of the nanoribbons suggests a behavior analogous to the Dirac cones of graphene on different substrates. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3459143]
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Kara, A., Vizzini, S., Leandri, C., Ealet, B., Oughaddou, H., Aufray, B., & Lelay, G. (2010). Silicon nano-ribbons on Ag(110): a computational investigation. JOURNAL OF PHYSICS-CONDENSED MATTER, 22(4), 045004.
Résumé: We report results of a computational investigation, based on density functional theory, of silicon self-assembled nano-ribbons (Si NRs) on Ag(110). These NRs present a honeycomb-like structure arched on the substrate and forming a closed-packed structure. The calculated STM images match the experimental ones, hinting to a possible new Si structure, mediated by the Ag substrate. The observed new electronic states near the Fermi level were reproduced by the calculations and attributed to a confinement/hybridization tandem.
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Lalmi, B., Oughaddou, H., Enriquez, H., Kara, A., Vizzini, S., Ealet, B., & Aufray, B. (2010). Epitaxial growth of a silicene sheet. APPLIED PHYSICS LETTERS, 97(22), 223109.
Résumé: Using atomic resolved scanning tunneling microscopy, we present here the experimental evidence of a silicene sheet (graphenelike structure) epitaxially grown on a close-packed silver surface [Ag(111)]. This has been achieved via direct condensation of a silicon atomic flux onto the single-crystal substrate in ultrahigh vacuum conditions. A highly ordered silicon structure, arranged within a honeycomb lattice, is synthesized and present two silicon sublattices occupying positions at different heights (0.02 nm) indicating possible sp(2)-sp(3) hybridizations. (C) 2010 American Institute of Physics. [doi:10.1063/1.3524215]
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Raissi, M., Vizzini, S., Langer, G., Rochdi, N., Oughaddou, H., Coudreau, C., Nitsche, S., D'Avitaya, F. A., Aufray, B., & Lazzari, J. L. (2010). Interfacial solid phase reactions in cobalt/aluminum oxide/silicon(001) system. THIN SOLID FILMS, 518(21), 5992–5994.
Résumé: Auger electron spectroscopy, secondary neutral mass spectrometry and high-resolution transmission electron microscopy were used to assess the chemical, morphological and structural modifications after annealing of cobalt/aluminum oxide/silicon(001) hetero-structure The results show that the aluminum oxide forms a diffusion barrier for temperatures lower than 200 degrees C. Beyond this temperature, cobalt atoms diffuse in the silicon region without apparent modification of the barrier At 340 degrees C, the asymmetric diffusion could be explained by the formation of an AlCoO complex oxide playing the role of a diffusion barrier for Si atoms. (C) 2010 Elsevier B V All rights reserved
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2009 |
Kara, A., Leandri, C., Davila, M., Padova, P., Ealet, B., Oughaddou, H., Aufray, B., & Lay, G. (2009). Physics of Silicene Stripes. JOURNAL OF SUPERCONDUCTIVITY AND NOVEL MAGNETISM, 22(3), 259–263.
Résumé: Silicene, a monolayer of silicon atoms tightly packed into a two-dimensional honeycomb lattice, is the challenging hypothetical reflection in the silicon realm of graphene, a one-atom thick graphite sheet, presently the hottest material in condensed matter physics. If existing, it would also reveal a cornucopia of new physics and potential applications. Here, we reveal the epitaxial growth of silicene stripes self-aligned in a massively parallel array on the anisotropic silver (110) surface. This crucial step in the silicene “gold rush” could give a new kick to silicon on the electronics road-map and open the most promising route towards wide-ranging applications. A hint of superconductivity in these silicene stripes poses intriguing questions related to the delicate interplay between paired correlated fermions, massless Dirac fermions and bosonic quasiparticles in low dimensions.
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Le Lay, G., Aufray, B., Leandri, C., Oughaddou, H., Biberian, J. P., De Padova, P., Davila, M. E., Ealet, B., & Kara, A. (2009). Physics and chemistry of silicene nano-ribbons. APPLIED SURFACE SCIENCE, 256(2), 524–529.
Résumé: We review our recent discovery of silicene in the form of silicon nano-ribbons epitaxially grown on silver (1 1 0) or (1 0 0) surfaces, which paves the way for the growth of graphene-like sheets. We further draw some perspectives for this unique novel material upon mild hydrogenation. (C) 2009 Elsevier B.V. All rights reserved.
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2008 |
De Padova, P., Leandri, C., Vizzini, S., Quaresima, C., Perfetti, P., Olivieri, B., Oughaddou, H., Aufray, B., & Le Lay, G. (2008). Burning match oxidation process of silicon nanowires screened at the atomic scale. NANO LETTERS, 8(8), 2299–2304.
Résumé: Silicon oxide nanowires hold great promise for functional nanoscale electronics. Here, we investigate the oxidation of straight, massively parallel, metallic Si nanowires. We show that the oxidation process starts at the Si NW terminations and develops like a burning match. While the spectroscopic signatures on the virgin, metallic part, are unaltered we identify four new oxidation states on the oxidized part, which show a gap opening, thus revealing the formation of a transverse internal nanojunction.
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Oughaddou, H., Aufray, B., Biberian, J. P., Ealet, B., Le Lay, G., Treglia, G., Kara, A., & Rahman, T. S. (2008). Self-organization of Ge tetramers on Ag(001) surface: A 2D realization of unusual substrate mediated interactions. SURFACE SCIENCE, 602(2), 506–510.
Résumé: Scanning tunneling microscopy (STM) images recorded during dissolution of a half-monolayer Ge on a Ag(0 0 1) show that it proceeds by the disappearance of tetramer entities. Moreover, they reveal that the successive slowing down in the kinetics, observed during this dissolution, correspond to the formation of ordered 2D arrangements of tetramer vacancies. A lattice gas analysis of the latter predicts a very unusual sequence of pair interactions between these vacancies, probably mediated by the substrate. (C) 2007 Elsevier B.V. All rights reserved.
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