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Accueil > Équipes scientifiques > Nanosciences moléculaires > STM basse température - Excitations électroniques/optiques - Manipulation - Dispositifs Moléculaires

STM basse température - Excitations électroniques/optiques - Manipulation - Dispositifs Moléculaires

MND AXIS

The Molecular Nanodevices Research Axis (MND) ACTIVITIES

Our research is devoted to the study of individual molecule or molecular architectures that are adsorbed on semiconductor surfaces for the development of molecular devices.
Aiming to understand the electronic, chemical, magnetic, or optical properties of these 1D or 2D molecular structures, we wish to exploit these molecular assemblies to create functions or specific physical processes related to the nanoscale laws.
With scanning tunneling microscope (STM) working in ultra high vacuum at low temperature (9K) we can control the conformation, the electronic structure, the magnetic or charge state parameters for this purpose.

Here are the main topics developed in our team :

- Atomic and molecular manipulation
- STS spectroscopy for electronic and/or vibrational analysis
- Ultra thin insulating layers on semiconductors
- Nanoscale metallic pads
- Atomic and molecular contact
- Point defect interactions
- Charge transfer at the nanoscale
- Molecular dynamics
- Laser combined STM
- DFT simulations

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contact : Damien RIEDEL (damien.riedel at u-psud.fr)

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HIGHLIGHTS_______________________________________________________________________________________________

NEW « NAMUS III workshop at JSU : a new success for this third version !!  »


The third version of the Namus Workshop has been largely appreciated by our group of students that could see the graphite surface that they prepared by themselves in the class room and do the ensuing DFT simulations on the STEMPEDE super calculator"
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NEW « Charge Transfer at the Nanoscale »


Acquiring quantitative information on molecular dynamics at the nanoscale remains one of the most challenging scientific quest for the next decades. In particular, charge transfer (CT) processes, being at the heart of these quantum effects, needs to be understood in single molecules to be properly controlled in various devices. Using the switching properties of a Nickel-tetraphenylporphyrin molecule adsorbed on the Si(100) surface allows to study the CT processes that runs the reversible activation of two chiral molecular conformations. Via the electrons of a scanning tunneling microscope (STM), a statistical study of the molecular switching reveals two specific locations of the molecule for which the efficiency is optimized. Numerical simulations provide a precise description of the molecular conformations and unveil the molecular energy levels that are involved in the CT process. This mechanism is shown to propagate from two physisorbed lateral aryl groups towards the porphyrin macrocycle inducing an intramolecular movement of two switching pyrroles groups. The measured switching efficiencies are thus fitted by a Markus-Jordner model to estimate relevant parameters that describe the dynamics of the CT process. This quantitative method opens a completely original approach to study CT at the nanoscale. Physical Chemistry Chemical Physics, 2017, DOI : 10.1039/C7CP05906J link at : http://pubs.rsc.org/en/content/articlelanding/2017/cp/c7cp05906j#!divAbstract”
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NEW « Annoucement of the third NAMUS workshop at JSU »

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_We are pleased to announce the third version of the NAMUS workshop from a collaboration between the MND axis at ISMO and the icnanotox group at JSU. The "Nano Manipulation of Atom & molecule using STM" workshop is devoted to specific lectures that will introduce basic STM techniques and DFT simulations methods. It will provide to graduated and PhD students general tools to understand and handle the first steps that may conduct them to prepare future experiments that combine scanning probe techniques and simulations using the density functional theory. Students may attend to 6 various lessons and 3 hands-on sessions with real DFT simulations and testing their skills on a small portable STM. link at http://icnanotox.org
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NEW « Charge Transfer at the Nanoscale »

It was very pleasant to visit Prof. Pavanello’s research group last week and spend some nice time at the University of Rutgers in the theoretical chemistry departement. Interesting progresses have been made in the modelization of the local excitation with STM and the ensuing possible charge transfer processes.”

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NEW BOOK CHAPTER in « Advances in Atom and Single Molecule Machines », SPRINGER"

In this chapter, we give a short review about the methods that are commonly used to passivate the Si(100) surface with hydrogen atoms. The wet technique is discussed in terms of surface pollution and surface roughness. A basic recipe is given. A second part is devoted to the methods commonly used with vacuum techniques. A discussion is done on the hydrogenation parameters to improve the surface quality at the atomic scale in particular the one that concerns the formation of various phases such as the 3x1 and dihydride. A third method is also detailed and enable the surface hydrogenation at the atomic scale. ”

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NEW "The ATERSIIQ research proposal has been supported by the PALM Labex "

This project will be peformed in collaboration with another team of the Laboratoire Aimé Cotton (LAC). We aim to explore electronic properties of specific adatoms on Si surface during their optical excitation”

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NEW "The MND team is now involved in a PICS program supported by the CNRS Institute of Physics"

The PICS program is a CNRS International Scientific Cooperation agreement. In this framework, the THEBES exchange program will involve the MND axis at ISMO, PARIS with the Interdisciplinary Center for Nanotoxicity (ICN) at Jackson university, USA”.

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NEW "Picture taken during the 23rd CCTCC conference at JSU"

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It was a great time at JSU while participating to the 23rd CCTCC conference to organize the NAMUS II Workshop about “Nanomanipulation of Atoms and Molecules using STM : Experiment and Modelization”.
The participants could have lessons about scanning probe microscopy, modelisation of a STM junction as well as experimental exemples that were succesfully combined with DFT simulations. They could also run simple simulations of a surface using the STEMPEDE supercomputer with 120 cores allocated to each of them.

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NEW "Elctronic transport through CoSi2 silicide pads at low temperature

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Evidence of Low Schottky Barrier Effects and the Role of Gap States in the Electronic Transport through Individual CoSi2 Silicide Nanoislands at Low Temperature (9 K)

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Mayssa Yengui, Damien Riedel*

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In this article, we study the electronic properties of CoSi2 metallic islands grown on the 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 low temperature STM stability. A statistical study of the I-V and dI/dV signals acquired along the islands show 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 towards the macroscopic contact of the sample can be explained. Published in J. Phys. Chem. C DOI : 10.1021/acs.jpcc.5b06816

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NEW "Discovery of anticorrugating states on the Si(100) surface

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Atomic scale study of corrugating and anticorrugating states on the bare Si(100) surface

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Mayssa Yengui, Henry P. Pinto, Jerzy Leszczynski, Damien Riedel*

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In this article, we study the origin of the corrugating and anticorrugating states through the electronic properties of the Si(100) surface via a low temperature (9K) 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 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 reveal that the Si(100) surface exhibit two anticorrugating states at + 0.8 V and + 2.8 V 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 which origin is discussed and associated with the presence of Van Hove singularities.

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NEW "BOOK CHAPTER : Practical Aspects of Computational Chemistry III" :

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The Scanning Tunneling Microscopy of Adsorbed Molecules on Semiconductors : Some Theoretical Answers to the Experimental Observations

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P. Sonnet and D. RIEDEL

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Theoretical and Computational Chemistry research has made unparalleled advancements in understanding every expanding area of science and technology. This volume presents the state-of-the-art research and progress made by eminent researchers in the area of theoretical computational chemistry and physics. The title mirrors the name of the annual international conference “Conference on Current Trends on Computational Chemistry” (CCTCC) which has become a popular discussion ground for eminent Theoretical and Computational Chemists and has been honored by the presence of several Nobel Laureates. Practical Aspects of Computational Chemistry III is aimed at theoretical and computational chemists, physical chemists, material scientists, and those who are eager to apply computational chemistry methods to problems of chemical and physical importance. The book is a valuable resource for undergraduate, graduate, and PhD students as well as established researchers.

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http://www.springer.com/chemistry/theoretical+and+computational+chemistry/book/978-1-4899-7444-0

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NEW "SILICON DOES NOT LOSE MEMORY" : The storage of an atomic ’bit’ can be reversibly controlled on a single silicon atom

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The ultimate miniaturization of electronic memory is to use a single atom to store one bit of information. This performance was achieved for example by controlling the magnetic state of a single atom. However, if the information is actually stored on a single atom, the volume required for this memory is much larger, both because of the insulating structures that decouple the ensuing atom and those allowed to access this memory. For the first time, physicists from the Institute for Molecular Sciences of Orsay - ISMO ( CNRS / University Paris -Sud) , Laboratory of Materials and Quantum Phenomena - MPQ (CNRS / University Paris Diderot), Institute Materials Science of Mulhouse and the Institut Jean Lamour were able to control the state of charge of a single silicon atom without having to electronically isolate it from the substrate. By combining experiments with a scanning tunneling microscope at low temperature with theoretical simulations, researchers have shown that the highly boron-doped silicon has very specific surface properties that can be exploited to make memory. This work is published in Physical Review B and was selected as Editor suggestion by the newspaper. While the silicon atoms located at the heart of the silicon crystal have four neighbors (i.e. four bonds), the surface atoms have only three bonds. Hence, the silicon atoms located at the surface of the sample have one dangling bond. This unused connection is exploited by the researchers as a "quantum box" that contains (or not) one additional electron. To stabilize this box, the researchers have used a passivated silicon surface with hydrogen atoms for which each of the surface silicon atoms is, in principle, bond to a hydrogen atom. In practice, few silicon atoms remain unpassivated and still have therefore their dangling bond. The researchers found that when the silicon sample is doped with boron atoms, the surface silicon atoms can locally accept an additional electron or eject it under the effect of an electric field. The obtained memory effect is shown to be stable over several days. The charging and discharging processes are obtained by using the tip of a scanning tunneling microscope that is made of tungsten atoms. A negative voltage between the surface and the tip will thus allow the negative charging of the silicon atom. Thus, when applying a positive voltage, the charge will be able to escape from the memory atom. Theoretical analysis of the electronic structure show that the boron doping provides a memory effect that remains stable in these two charge states : neutral or negative. Conversely, in the absence of doping or with arsenic doping, the extra charge is stable and can’t be controlled and therefore can’t provide a memory effect.
Phys. Rev. B 88, 241406 (2013)] Published Tue Dec 10, 2013 .
http://prb.aps.org/abstract/PRB/v88/i24/e241406
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.This research has been pointed out on the CNRS’s website of the National Institut of Physics (INP) at http://www.cnrs.fr/inp/spip.php?article2347

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NEW : The adsorption of Co atoms on the Si(100) surface at 9K reveals manipulable interstitial sites and the formation of dimer-vacancy lines

Cobalt adsorption on the bare Si(100)-2x1 surface at low temperature (12 K)

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 (< 0.1 monolayer). The ensuing surface is studied by means of a low temperature (9 K) 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.
M. Yengui and D. Riedel, Surface Science 2013 – in press
http://www.sciencedirect.com/science/article/pii/S003960281300294X#

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NEW : A new manipulation process for physisorbed molecule on Si(100)

Electronic Control of the Tip-Induced Hopping of an Hexaphenyl-Benzene Molecule Physisorbed on a Bare Si(100) Surface at 9 K


<font color = bluecolor :#00458f ;>This work has been cited by :
CNRS : http://www.cnrs.fr/endirectdeslabos/lettre.php and http://www.cnrs.fr/inp/IMG/pdf/13_07_deplacer-molecule.pdf,
German ambassy : http://www.wissenschaft-frankreich.de/de/physik/ein-neues-verfahren-zur-bewegung-von-atomen/
Vulgarization : http://www.pro-physik.de/details/news/5093031/Beruehrungslos_bewegt.html


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) 2x1 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 reveal that the hopping process is related to a strong decrease of the tunnel junction conductance. This process is associated to 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.
J. Phys. Chem C – in press

NEW> : A new surface hydrogenation process discovered

Atomic-scale control of hydrogen bonding on a bare Si(100) 2x1 surface

http://prb.aps.org/abstract/PRB/v86/i16/e165441
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 exposed to 10-6 torr of H2 and by probing the bare Si(100) 2x1 surface at positive bias. This effect is very localized and induced by the tunnel electrons. The statistical study of this process reveals an activation energy threshold matching the creation of at the surface of the STM tip. Our results are supported by ab-inito density functional calculations of a hydrogenated silicon dimer. (Phys. Rev. B 86, 165441 – Published 25 October 2012
MOVIES____________________________________________________________________________________________________

(clic on the picture below to start the movie)

The CNRS logo revisited

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The Manipulation of Molecules with electrons

for more informations, please contact damien.riedel@u-psud.fr


MEMBERS____________________________________________________________________________________________________

Actual or former PhD student working in this team :

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Zhang Luqiong is working on molecular interactions with surface defects on semiconductors.

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Mayssa Yengui devoted his research on the fabrication of silicide nanoscrystals on Si(100) for nanoscale molecular contacts.

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Hatem Labidi devoted his research to the study of the electronic exctiation on functionalized molecules and in particular on bi-molecular structures.

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Franco Chiaravalloti devoted his research to study the growth of CaF2 insulating layers on Si(100) to electronically decouple and manipulate molecules

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Amandine Bellec devoted his research to non local excitation processes of atomic bistable on the Si(100):H surface .

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RESEARCH ACTIVITIES ________________________________________________________________________________________


biphenyle
Single electron electronically induced manipulation of individual molecules . We have shown that electronically induced excitation (EIE) with tunnel electrons can open up a new way of manipulating single molecules. When using a LT-STM, we showed that one-electron ionization through charge transfer processes can be induced at various locations inside individual molecules. Furthermore, while the manipulation of a single molecule via EIE is performed through an electron (oxidation) or hole (reduction) attachment, the resulting process can be used to induce different molecular reactions (or motions). Both reactions can be triggered and used on various molecular systems. (see Refs).

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Effect of the substrate dopant type (n or p) and local modification of the Individual Nano Object (INO) environment . We have recently studied that the chosen semiconductor dopant type (n or p) and its concentration play a crucial role in INOs molecular electronics. These effects are often wrongly neglected, in particular, in the dynamics of the excitation of single molecule via EIE processes. We were also able to show that the activation efficiency of INOs is strongly influenced by its environment (see Refs).

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Molecular electronic decoupling through the formation of CaF2 ultra-thin insulating layers and surface passivation . Since the beginning of the 90’s, techniques to build ultra-thin atomic or molecular insulating layers have been developed for metallic substrate but rarely for semiconductors. We could show that the formation of CaF2 on silicon leads to the functionalization of the Si(100) surface through the fabrication of insulating long parallel stripes areas. These stripes have been used as molecular insulating rails to manipulate long hexaphenyl molecules (to be published). In parallel, we have shown, for the first time, that hydrogenated semiconductor surfaces can be used to efficiently decouple aromatic molecules from the Si surface and thus to map the molecular orbital as in the gas phase. (see Refs).

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Non-local manipulation of an individual atom through sub-surface density of state . This research is of major importance for my future projects. We could explain in details the origin of the non-local activation of a single bistable atom, on Si(100):H. By combining theoretical calculation of the surface local density of states distribution, we could show that the ‘contact’ area of the bistable atom onto the surface is of crucial importance in affecting the efficiency of the charge transfer processes. (see Refs).

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Control and mapping of the Optical-field enhancement into an STM junction . There is a major international interests linked to this problem. To address it, we have investigated a new approach by combining a VUV laser radiation with a low temperature STM. Using this particular setup we could show that the optical-field enhancement can be controlled and precisely tuned while varying the tip-surface distance with a very good accuracy. In addition, using an atomic scale photosensitive surface we could map the optical field strength at the silicon surface through a local photodesorption process. (see Refs).

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