en

Surface structure and dynamics

Leader: Frédéric Leroy

Introduction

Our team mainly studies mechanisms at the surface of crystalline materials, with a particular interest in real-time and in situ characterization. We are also interested in the modeling of phenomena influencing nanomaterials structural and electronic properties.

Our research is based mainly on a UHV experimental set-up combining slow electron microscopy (Low-Energy Electron Microscopy / Photo-Emission Electron Microscopy LEEM/PEEM) and local probe microscopy (Scanning Tunneling Microscopy / Atomic Force Microscopy-STM/AFM) and chambers dedicated to MBE elaboration.

Structure Surface et Dynamique 3

News

  03.2024

 We are looking for candidates for two funded PhD projects:

    • Epitaxial growth and electronic properties control in inversion symmetry-breaking materials for spin-orbitronics (details).
    • Electron-phonon dynamics in epitaxial thin films of ferroelectric chalcogenides (details).

 Please do not hesitate to contact us!
Surface Dynamics


Using LEEM microscopy, we study various surface phenomena in real time and in operando, such as surface reconstructions, epitaxial growth, the dynamics of atomic walks, the decomposition of silicon oxide thin films, the spontaneous movement of nanoparticles, the preparation of surfaces of interest for microelectronics…

For some years now, we have been studying in detail the spontaneous movement of solid islands or liquid droplets induced by interfacial reactivity and/or electromigration. Our systems of choice for these studies are Si/SiO2, Au/Si and Au/Ge.

 

Structure Surface et Dynamique 4
AuSi eutectic droplet climbing steps on a Si(111) surface. Surf. Sci. 632 (2015) 1
Triple-line Control

 

The description of the triple line at the substrate-film-vacuum interface is one of the open questions of wetting statics and dynamics. An abundant literature exists in the case of liquid films. Although crystalline films are the building blocks of many technological applications, the description of the triple line remains partial in the case of solids, particularly in out-of-equilibrium situations (de-wetting, etc.).

Our approach to the statics and dynamics of the triple line at the solid-solid-vacuum interface is based on three fundamental questions: (i) How do non-equilibrium conditions modify Young’s equation? (ii) What is the influence of chemical reactivity on the triple line? (iii) What is the role of substrate heterogeneity on the behavior of the triple line?
To this end, we are combining LEEM/PEEM and STM/AFM microscopy to monitor in real time several phenomena linked to the triple line: solid-state dewetting (ultra-thin SOI and GeOI films), film decomposition (SiO2), spontaneous movement of droplets or 3D islands (Au/Si, Au/Ge,Si/SiO2…), island growth.
Theoretical models and numerical simulations (Monte Carlo Kinetics, Continuum Models) are being developed in collaboration with O. Pierre-Louis of the Institut Lumière-Matière (Lyon).

The ultimate goal is to propose new strategies for controlling the morphology and stability of nanostructures.

Funding: LOTUS – ANR Project
Collaborations:
  • O. Pierre-Louis (ILM, Lyon)
  • C. Barbé & Ł. Borowik (CEA/LETI, Grenoble)
  • Y. Saito (Keio Univ., Japon)
  • C. V. Thompson (MIT, Cambridge, USA)

 

Structure Surface et Dynamique 5
Ligne triple solide-solide-vide (ligne rouge) en recul dans le cas du démouillage à l’état solide. Surf. Sci. Rep. 71 (2016) 391
LEEM Microscopy and Instrument developments


The growing demand for advanced characterization techniques in the field of nanomaterials calls for the development of new microscopy techniques. In this context, we are seeking to develop an instrument combining electron holography using low-energy electrons (qqs. eV) in reflection. LEEM slow electron microscopy is based on wave optics. However, as with any conventional electron optics technique, information on the phase of the electron wave is lost during acquisition. Since the original work of Aharonov and Bohm and the major advances in holography in transmission electron microscopy, so-called pure-phase objects such as magnetic leakage fields or electric fields, as well as stress fields, are now accessible.

We aim to take advantage of the reflection geometry and low electron energy of LEEM microscopy to measure the phase of reflected and diffracted waves by implementing an electrostatic biprism in the optical path, thus enabling a new imaging mode in LEEM microscopy using electron holography. To demonstrate the potential of this technique, we will focus on the surface properties of nanomaterials: charge transfer at the interface between semiconductors and insulating materials, ferromagnetism, and surface stresses induced by structural defects such as dislocations.

Funding: projet ANR HoloLEEM
Collaborations:

F. Houdelier (CEMES, Toulouse)

 

Structure Surface et Dynamique 6
Biprisme électrostatique et holographie.
Tiré de Adv. in Phys. 41 (1992) 59
2D MATERIALS


Graphene, a material composed of a single atomic layer of carbon, and 2D materials with an analogous honeycomb atomic structure, are being intensively studied for their strong applicative potential in information technology.

Despite major efforts to study the optical and electronic properties of these materials, many questions remain as to the mechanisms of growth on the atomic scale and the couplings between atomic structure and measured properties.

Various materials (graphene, MoS2, etc.) are currently being developed (MBE, CVD) and studied within the group and in collaboration.

 

Collaborations:
  • A. Michon & M. Portail (CHREA, Valbonne)
  • J. Coraux (Institut Néel, Grenoble)
  • Y. Fagot-Revurat, B. Kierren (Institut Jean Lamour, Nancy)
  • D. Voiry (IEM, Montpellier)
Structure Surface et Dynamique 7
A. Geim et K. Novoselov : Winners of the 2010 Nobel Prize in Physics “for groundbreaking experiments regarding the two-dimensional material graphene”
Elasticity


The aim is to describe the elastic properties of surfaces from a theoretical (concepts of surface stress/strain, surface elastic constants, etc.) and experimental (measurements of elastic deformations induced by surface atomic walks using grazing incidence X-ray diffraction) point of view. Effects on other surface phenomena are also studied (epitaxial growth, nanoelasticity, surface instabilities, etc.).

Collaborations:
  • G. Prévot (INSP, Paris)
  • B. Ranguelov, M. Michailov (IPC, BAS, Bulgary)
Structure Surface et Dynamique 8
Cross-section representation of the atomic displacement field induced by a double atomic step on a vicinal Si(001) surface. Phys. Rev. B 93 (2016) 045416

 

Publications

Financement

Logo ANR

  • 2023-2027 : HEBUTERNE Project (ANR-23-CE08 - PRC)
    Helium Bubble formation in Tungsten: from Nanoscience understanding to macroscale impact
    (Coordinateur : E. Bernard, CEA/IRFM)

  • 2022-2026 : Projet FETh ( ANR-22-CE08 - PRC)
    Ferroelectric control of nanoscale Electric and Thermal conduction in GeTe
    (Coordinateur: F. Leroy)

  • 2022-2026 : Projet Thermotweez (ANR-22-CE09 - PRME)
    Déplacement de nanostructures de surface contrôlé par thermomigration
    (Coordinateur: S. Curiotto)

  • ANR Project 2DTransformers (ANR-14-OHRI-0004)

  • ANR Project HoloLEEM (ANR-15-CE09-0012)

  • ANR Project LOTUS (ANR-13-BS04-0004-02)

Logo A*MIDEX

  • 2024-2028 : Projet HIBERNIA
    Helium bubbles in plasma-facing material of fusion reactors: a nanoscience
    approach
    (Coordinateur: F. Leroy)

  • 2023-2027 : Projet FRICTION
    Ferroelectric Rashba semiconductors for spin orbitronics
    (Coordinateur: F. Cheynis)

  • 2023-2027 : Projet INDIGENA
    Interfacial Design of Optical High-Harmonic Generation
    (Coordinateur: C. Attaccalite, CINaM)

Collaborations

Aix-Marseille Univ. collaborations

  • O. M. Texier & O. Thomas (IM2NP, Marseille)
  • C. Martin (PIIM, Marseille)

 

French Collaborations

    • O. Pierre-Louis (ILM, Lyon)
    • E. Bernard (CEA/IRFM, Saint Paul-lez-Durance)
    • S. Cherifi-Hertel (IPCMS, Strasbourg)
    • Y. Fagot-Revurat, B. Kierren & D. Malterre (Institut Jean Lamour, Nancy)
    • A. Michon, M. Al Khalfioui  & M. Portail (CRHEA, Valbonne)
    • J.-P. Attané & L. Vila (CEA/SPINTEC, Grenoble)
    • J. Coraux (Institut Néel, Grenoble)
    • L. Martinelli & G. Renaud (ESRF, beamline BM32, Grenoble)

 

International collaborations

  • B. Ranguelov & M. Michailov (IPC, BAS, Bulgary)
  • Y. Saito (Keio Univ., Japan)
  • C. V. Thompson (MIT, Cambridge, USA)

Patents

Ł. Borowik, J.-C. Barbé, E. Bussmann, F. Cheynis, F. Leroy, D. Mariolle and P. Müller. Publication Number: US2012282758.

Ł. Borowik, J.-C. Barbé, E. Bussmann, F. Cheynis, F. Leroy, D. Mariolle and P. Müller. Publication Number: US2012282759.

Experimental techniques

UHV set-up @ CINaM

On a daily basis, we use a UHV experimental set dedicated to surface physics, including a LEEM/PEEM microscope [1,2], a STM/AFM microscope [3,4] and a surface preparation chamber. An overview of the equipment can be seen below. The LEEM microscopy technique enables us to visualize and film crystalline surfaces (typical acquisition time 0.1-1s) in a UHV environment (a few 10-10 Torr or typ. 10-13 bar) or under a partial pressure (a few 10-7 Torr : H2, N2, O2, ...) at high temperatures (≈1300K)or below room temperature (≈150K).

this technique is therefore particularly well suited to in-situ, real-time characterization of crystalline surfaces and thin films on a mesoscopic scale (field of view: a few 1µm to 50µm with a typical lateral resolution of 5nm and a vertical atomic resolution).
In diffraction mode, this equipment can acquire LEED (Low-Energy Electron Diffraction) images, enabling to determine the atomic structure of the imaged surface. As with transmission electron microscopy (TEM), LEEM microscopy enables both bright-field and dark-field imaging of the surface to be characterized. This makes it possible to distinguish regions with different atomic arrangements on the surface.

A full description of the instrumental set-up can be found in the following reference: Rev. Sci. Instr. 85 (2014) 043705

Structure Surface et Dynamique 9

Examples of LEEM images obtained with our microscope are available below.
Left: Si(001) surface at 1000°C in dark field. The white-black contrast results from the difference in crystallographic structure between adjacent atomic terraces in the case of Si(001) (field of view: 15µm). A film illustrating the sublimation of the silicon surface at high temperatures is also available here.
Right: Mo(110) surface at 1070°C in bright-field mode. The contrast used to visualize atomic steps (black lines) is due to the phase difference between electron waves scattered by two terraces separating a step. The black circle indicates a screw dislocation emerging from the crystal surface, and the black arrow indicates a circular atomic step at the top of a circular pyramid (field of view: 7.5µm).

Structure Surface et Dynamique 18

Nanofabrication @PLANETE (CINaM)

Nanoscience research frequently relies on the use of artificially structured samples on the nanometric scale. For this reason, we are regular users of the nanofabrication platform PLANETE at CINaM. More specifically, our scientific projects require the use of clean-room technology processes such as :

  • Chemical cleaning
  • Optical and/or electronic lithography
  • Plasma etching

Characterization techniques and Synchrotron facilities

For a detailed understanding of the relationships between atomic structure, surface dynamics and electronic properties, characterizations complementary to those available in our experimental set are generally required. Surface characterization techniques based on synchrotron radiation offer the possibility of combining real-space and reciprocal-space approaches. Here is a short (and non-exhaustive!) list of the techniques we regularly use:

  • Grazing Incidence X-ray diffraction (GIXD) & Grazing Incidence Small-Angles X-ray scattering (GISAXS) @BM32 (ESRF)
  • Angle-resolved photoemission spectroscopy (ARPES) @CASSIOPEE (SOLEIL)
  • Spectromicroscopy XPEEM @HERMES (SOLEIL), @Nanospectroscopy (ELETTRA)

LEEM movies

Electromigration of Au on Ge(111)

2D Au islands (dark grey) detach from step edges and migrate in the direction opposite to the current. Temperature: 500°C. Field of view: 6.5x4.5µm2. Time: 4min. (unpublished results).

 

Electromigration on Si(111)

Electromigration of two single-atom deep holes (dark grey) on a Si(111)-7x7 terrace (light grey). They migrate in the direction opposite to the electric current (that is reversed twice). The holes are in a metastable Si(111)-(1x1) surface reconstruction. Field of view: 28x12µm2. Temperature ≤830°C. Time: 35min (unpublished results).

 

Electromigration on Si(100)

Single-atom deep holes (black ellipses) move under the effect of an electric current. The current direction is from left to right. The sample temperature is at 1170K, the window width is 18µm and the real-time experiment duration is 9 minutes. Appl. Surf. Sci., 469, 463 (2019).

 

2D elec. gas induced by a Ag deposition

At ε=24 eV, the image shows the Ag adatom concentration variations. At ε=1.8 eV, the LEEM image illustrates qualitatively the surface work function time evolution (i.e. the 2DEG doping). Sci. Rep. 7 (2017) 10642.

 

Dewetting of a Si(100) film on a SiO2 substrate

The black-white regions at the top of the imaged area are Si(100) terraces with 2x1 or 1x2 surface reconstruction. The dewetting front advances and when O2 is introduced in the chamber it stops. The Si terraces alternatively blink between white and black during O2 exposure because Si is consumed according to the reaction Si+1/2O2=SiO(gas). The sample temperature is 1100K.

 

Au-Si droplets moving on Si(111)

The droplets climb up and locally dissolve the Si steps (field-of-view: 10µm).

 

Surface phase transformation on Si(111)

White and dark regions are 7x7 and 1x1 surface phases respectively. Below 830ºC the 7x7 phase is stable with a small amount of residual, metastable 1x1. Upon heating the sample above 830ºC, the 7x7 phase reduces and disappears while the 1x1 domains widen. Decreasing the temperature below 830ºC, the 7x7 domains nucleate and grow. The process is reversible. The window width is 7µm.

© 2026 CINaM