Amina Kimouche | Aalto University, School of Science (original) (raw)

Papers by Amina Kimouche

Resumen del trabajo presentado a la 20th Edition of Trends in Nanotechnology International Confer... more Resumen del trabajo presentado a la 20th Edition of Trends in Nanotechnology International Conference (TNT), celebrada en San Sebastian (Espana) del 30 de septiembre al 4 de octubre de 2019.

Nature Communications, 2017

The use of graphene in electronic devices requires a band gap, which can be achieved by creating ... more The use of graphene in electronic devices requires a band gap, which can be achieved by creating nanostructures such as graphene nanoribbons. A wide variety of atomically precise graphene nanoribbons can be prepared through on-surface synthesis, bringing the concept of graphene nanoribbon electronics closer to reality. For future applications it is beneficial to integrate contacts and more functionality directly into single ribbons by using heterostructures. Here, we use the on-surface synthesis approach to fabricate a metal-semiconductor junction and a tunnel barrier in a single graphene nanoribbon consisting of 5- and 7-atom wide segments. We characterize the atomic scale geometry and electronic structure by combined atomic force microscopy, scanning tunneling microscopy, and conductance measurements complemented by density functional theory and transport calculations. These junctions are relevant for developing contacts in all-graphene nanoribbon devices and creating diodes and t...

Physical Chemistry Chemical Physics

We have investigated the self-assembly of the graphene nanoribbon molecular precursor 10,10'-... more We have investigated the self-assembly of the graphene nanoribbon molecular precursor 10,10'-dibromo-9,9'-bianthryl (DBBA) on Au(111) with frequency modulation scanning force microscopy (FM-SFM) at room temperature combined with ab initio calculations....

Epitaxial graphene grown on metal substrates is a promising platform for developing new hybrid sy... more Epitaxial graphene grown on metal substrates is a promising platform for developing new hybrid systems, in which interface effects can be exploited to engineer novel properties. The insertion of foreign species between graphene and its substrate, referred to as “intercalation”, was shown very powerful in this respect. With the help of surface science tools, we have studied three graphene/metal systems, two of which are intercalated hybrid systems, and the other is a candidate for such a system: (i) graphene/Ir(111) intercalated with an ultrathin oxide, (ii) graphene/Ir(111) intercalated with cobalt (sub) atomic layers, and (iii) graphene on Re(0001). We found that some defects, especially wrinkles (linear delaminations of graphene from its substrate) and other curve graphene regions, play a crucial, yet unanticipated role in the intercalation process. We also found that the intercalation proceeds in a markedly different fashion under ultra-high vacuum and under atmospheric pressure....

Le graphene epitaxie sur des substrats metalliques est un modele prometteur pour le developpement... more Le graphene epitaxie sur des substrats metalliques est un modele prometteur pour le developpement de nouveaux systemes hybrides, dans lesquelles les effets d'interface peuvent etre exploites pour concevoir de nouvelles proprietes. L'insertion d'especes entre le graphene et son substrat, une operation connues sous le nom d'-«intercalation», est une approche tres puissante a cet egard. Avec l'aide des outils de la physique des surfaces, nous avons etudie trois systemes graphene/metal, dont deux sont des systemes hybrides intercales, et l'autre est un candidat pour un tel systeme : (i) le graphene/Ir(111) intercale avec un oxyde ultra-mince, (ii) graphene/Ir(111) intercale avec des couches sub-atomiques du cobalt et (iii) de graphene sur Re(0001). Nous avons montre que certains defauts, en particulier les ridules (delamination du graphene de son substrat) et d'autres regions courbees du graphene, jouent un role crucial, non anticipe, dans le processus d'...

Journal of Physics: Condensed Matter

C60 is a model system to study molecule–surface interactions and phase transitions due to its hig... more C60 is a model system to study molecule–surface interactions and phase transitions due to its high symmetry and strong covalent π bonding within the molecule versus weak van-der-Waals coupling between neighboring molecules. In the solid, at room temperature, the molecule rotates and behaves as a sphere. However, the pentagonal and hexagonal atomic arrangement imposes deviations from the spherical symmetry that become important at low temperatures. The orientation of the C60 can be viewed to represent classic spins. For geometrical reasons the preferred orientation of neighboring C60 cannot be satisfied for all of the neighboring molecules, making C60 a model for disordered spin systems with frustration. We study several molecular layers of C60 islands on highly oriented pyrolytic graphite using scanning tunneling microscopy at liquid nitrogen temperatures. By imaging several layers we obtain a limited access to the three-dimensional rotational structure of the molecules in an island...

Graphene grown by chemical vapor deposition (CVD) on Cu is very promising for future graphene app... more Graphene grown by chemical vapor deposition (CVD) on Cu is very promising for future graphene applications, as it meets the two requirements for batch production, namely: 1) large size and self limitation to a single-layer of graphene and 2) easy transfer onto arbitrary substrates [1-4]. New insights for controlling CVD processes, e.g. leading to dendritic growth of graphene flakes [5], or allowing for controlling the size of hexagonal islands [6], were recently demonstrated.

Vers de nouveaux matériaux hybrides à base de graphene épitaxié: contrôle de la formation de défa... more Vers de nouveaux matériaux hybrides à base de graphene épitaxié: contrôle de la formation de défauts et leur rôle dans l’intercalation Thèse soutenue publiquement le 20/11/2013 devant le jury composé de:

Physical Review Materials

Using low-energy electron microscopy, we image in real time the intercalation of a cobalt monolay... more Using low-energy electron microscopy, we image in real time the intercalation of a cobalt monolayer between graphene and the (111) surface of iridium. Our measurements reveal that the edges of a graphene flake represent an energy barrier to intercalation. Based on a simple description of the growth kinetics, we estimate this energy barrier and find small, but substantial, local variations. These local variations suggest a possible influence of the graphene orientation with respect to its substrate and of the graphene edge termination on the energy value of the barrier height. Besides, our measurements show that intercalated cobalt is energetically more favorable than cobalt on bare iridium, indicating a surfactant role of graphene.

The journal of physical chemistry letters, Jan 17, 2018

In crystal growth, surfactants are additive molecules used in dilute amount or as dense, permeabl... more In crystal growth, surfactants are additive molecules used in dilute amount or as dense, permeable layers to control surface morphologies. We investigate the properties of a strikingly different surfactant: a 2D and covalent layer with close atomic packing, graphene. Using in situ, real-time electron microscopy, scanning tunneling microscopy, kinetic Monte Carlo simulations, and continuum mechanics calculations, we reveal why metallic atomic layers can grow in a 2D manner below an impermeable graphene membrane. Upon metal growth, graphene dynamically opens nanochannels called wrinkles, facilitating mass transport while at the same time storing and releasing elastic energy via lattice distortions. Graphene thus behaves as a mechanically active, deformable surfactant. The wrinkle-driven mass transport of the metallic layer intercalated between graphene and the substrate is observed for two graphene-based systems, characterized by different physicochemical interactions, between graphen...

Nature communications, Jan 14, 2015

Graphene nanoribbons (GNRs)-narrow stripes of graphene-have emerged as promising building blocks ... more Graphene nanoribbons (GNRs)-narrow stripes of graphene-have emerged as promising building blocks for nanoelectronic devices. Recent advances in bottom-up synthesis have allowed production of atomically well-defined armchair GNRs with different widths and doping. While all experimentally studied GNRs have exhibited wide bandgaps, theory predicts that every third armchair GNR (widths of N=3m+2, where m is an integer) should be nearly metallic with a very small bandgap. Here, we synthesize the narrowest possible GNR belonging to this family (five carbon atoms wide, N=5). We study the evolution of the electronic bandgap and orbital structure of GNR segments as a function of their length using low-temperature scanning tunnelling microscopy and density-functional theory calculations. Already GNRs with lengths of 5 nm reach almost metallic behaviour with ∼100 meV bandgap. Finally, we show that defects (kinks) in the GNRs do not strongly modify their electronic structure.

Physical Review Letters, 2013

We report a new way to strongly couple graphene to a superconductor. The graphene monolayer has b... more We report a new way to strongly couple graphene to a superconductor. The graphene monolayer has been grown directly on top of a superconducting Re(0001) thin film and characterized by scanning tunneling microscopy and spectroscopy. We observed a moiré pattern due to the mismatch between Re and graphene lattice parameters, that we have simulated with ab initio calculations. The density of states around the Fermi energy appears to be position dependent on this moiré pattern. Tunneling spectroscopy performed at 50 mK shows that the superconducting behavior of graphene on Re is well described by the Bardeen-Cooper-Schrieffer theory and stands for a very good interface between the graphene and its metallic substrate.

Carbon, 2014

Changes of paradigms, in terms of new functionalities, architectures, and performances, are fores... more Changes of paradigms, in terms of new functionalities, architectures, and performances, are foreseen with graphene, an atomically thin sheet of carbon atoms in a honeycomb lattice. These prospects are urging the development of efficient production methods. 1 Preparation by chemical vapor deposition (CVD), in this respect, has reached such maturity that graphene now appears as an alternative to indium tin oxide as a transparent conductive electrode 2 or to Si and II-IV semiconductors in high-frequency electronics. 3 Intercalation of species between the metallic substrate needed for CVD and graphene, a method known since the 1980's, 4 is an efficient and versatile way to achieve quasi free-standing graphene 5 and to engineer the properties of graphene, for instance to induce electronic band-gaps, 6 magnetic moments, 7 and strains. 8 Dual intercalation, of Si and O, even showed great promise for the transfer-free preparation of graphene-on-oxide field effect transistors. 9 Despite the numerous reports devoted to graphene/substrate intercalated systems, two key questions remain open. First, the surmised role of defects as pathways for intercalation has only been established, yet partially in some cases, for a few defects, namely graphene free edges 5 and point defects. 10,11 Unveiling other intercalation pathways will help better envisioning the full potentialities of intercalation for building up advanced graphene-based hybrids. Second, all studies of intercalation reported thus far were performed under ultra-high vacuum (UHV). While this approach offers optimum control over the processes, it is a prohibitively costly one in the view of the production of graphene decoupled from its substrate. While atmospheric pressure intercalation

ABSTRACT Almost free-standing graphene can be obtained on metals by decoupling graphene from its ... more ABSTRACT Almost free-standing graphene can be obtained on metals by decoupling graphene from its substrate, for instance by intercalation of atoms beneath graphene, as it was shown with oxygen atoms [1]. We show that the interaction of oxygen with epitaxial graphene on iridium leads to the formation of an ultrathin crystalline oxide extending between graphene and the metallic substrate via the graphene wrinkles. Graphene studied in this work was prepared under ultra-high vacuum by CVD [2,3]. The samples were studied by combining scanning probe microscopy (STM, AFM) and spatially resolved spectroscopy (Raman, STS). The ultrathin oxide forms a decoupling barrier layer between graphene and Ir, yielding truly free-standing graphene whose hybridization and charge transfers with the substrate have been quenched [4]. Our work presents novel types of graphene-based nanostructures, and opens the route to the transfer-free preparation of graphene directly onto an insulating support contacted to the metallic substrate which could serve as a gate electrode. References [1] Sutter, P. et al. J. Am. Chem. Soc. 132, 8135 (2010). [2] Coraux, J. et al. Nano Lett. 8, 565 (2008). [3] Vo-Van, C ; Kimouche, A et al. Appl. Phys. Lett. 98, 181903 (2011). [4] Kimouche, A et al. Fully decoupling graphene from its substrate via wrinkles. Submitted

ABSTRACT The extended carbon–metal contact in graphene–metal hybrids opens new avenues for manipu... more ABSTRACT The extended carbon–metal contact in graphene–metal hybrids opens new avenues for manipulating the properties of both constituents of the hybrid and for combining the functionalities of each of them. We developed a two-step ultrahigh vacuum route to fabricate high-quality nanometer-thick metal films having abrupt interfaces, sandwiched between a protective graphene layer and its substrate, using chemical vapor deposition and metal intercalation made effective at mild temperatures. We demonstrate functional hybrid systems with ferromagnetic metal films whose topmost graphene interface allows us to manipulate the direction of the magnetization of the film to a large extent. We obtain prominently perpendicular magnetization for a large range of Co thickness. The preparation and properties of the graphene/ferromagnet hybrid are analyzed using a set of surface-sensitive in situ and ex situ techniques together with first-principles calculations, altogether providing extensive topographic, chemical, magnetic, and vibrational characterization.

Advanced Functional Materials, 2014

Nano Letters, 2015

We measure uniaxial strain fields in the vicinity of edges and wrinkles in graphene prepared by c... more We measure uniaxial strain fields in the vicinity of edges and wrinkles in graphene prepared by chemical vapor deposition (CVD), by combining microscopy techniques and local vibrational characterization. These strain fields have magnitudes of several tenths of a percent and extend across micrometer distances. The nonlinear shear-lag model remarkably captures these strain fields in terms of the graphene-substrate interaction and provides a complete understanding of strain-relieving wrinkles in graphene for any level of graphene-substrate coherency.

Physical Review B, 2015

ABSTRACT We report the coexistence of charge puddles and topographic ripples in graphene decouple... more ABSTRACT We report the coexistence of charge puddles and topographic ripples in graphene decoupled from the Ir(111) substrate it was grown on. We show the topographic and the charge disorder to be locally correlated as a result of the intercalation of molecular species. From the analysis of quasiparticle scattering interferences, we find a linear dispersion relation, demonstrating that graphene on a metal can recover its intrinsic electronic properties. The measured Fermi velocity vF=0.9ifmmodepmelsetextpmfi0.04ifmmodetimeselsetexttimesfi106{v}_{F}=0.9\ifmmode\pm\else\textpm\fi{}0.04\ifmmode\times\else\texttimes\fi{}{10}^{6}vF=0.9ifmmodepmelsetextpmfi0.04ifmmodetimeselsetexttimesfi106 m/s is lower than in graphene on dielectric substrates, pointing to a strong screening of electron-electron interactions in graphene by the nearby metallic substrate.