Material science is at the core of a large majority of research topics at the Centre for Nanoscience and Nanotechnology (C2N)....

The flow of a single ML step

Material science is at the core of a large majority of research topics at the Centre for Nanoscience and Nanotechnology (C2N). Innovating in this field is of crucial...

Material science is at the core of a large majority of research topics at the Centre for Nanoscience and Nanotechnology (C2N). Innovating in this field is of crucial importance. The Materials Department has two general objectives:

  • To conduct its own research activities in material science, from the physics of growth to the control of various material properties
  • To interact with the 3 other departments (Photonics, Nanoelectronics, Microsystems and Nanobiofluidics), collaborate with external groups and provide samples and devices

Understanding growth mechanisms and correlating the material properties with their growth conditions is one of the main challenges of the Department. To this aim, we use advanced equipment for growth and analysis. We also develop adapted theoretical and numerical tools. Our activities in material science focus mainly on nanostructures made of III-V semiconductors, Si/Ge, novel 2D materials (2D Materials team) and functional oxides (OXIDE team). Hybridization of these various materials is another challenge, opening the way to novel functionalities. These activities are pursued in strong interaction with photonics, nanoelectronics, devices, and systems.

Lab Highlight

In-situ growth in a transmission electron microscope of semiconductor nanostructures: Atomic Step Flow on a Nanofacet

The project Nanomax associates specialists (from the Ecole Polytechnique and C2N) in the epitaxial growth of nano-objects from the experimental and theoretical points of view. 

The goal is to investigate fundamental issues of solid phase nucleation and growth (from a supersaturated vapor phase) that cannot be solved by ex situ observation (due to the evolution of nanostructures during post-growth cooling). The pilot project in NANOMAX is MBE of III-V semiconductor nanowires. Other investigations include chemical vapor deposition of various nano-objects ranging from semiconductor quantum dots to carbon nanotubes. NANOMAX is the first ever attempt to implement MBE in a TEM column. Moreover, its goal is real atomic resolution during growth, which has never been achieved so far. NANOMAX thus implies significant technical developments, regarding both hardware and software, such as the implementation of effusion cells in the vicinity of a modified objective lens and stage (

A remarkable specificity of nanocrystals is the strong influence of their surfaces and edges on their properties. The important role of crystal boundaries also manifests itself at the growth stage. Indeed, surfaces influence the morphology and crystalline arrangement of nanostructures, not only as regards thermodynamics but also via their growth dynamics. This is notably illustrated in the vapor-liquid-solid (VLS) growth of semiconductor nanowires (NWs). In this method, vapor containing the NW constituents is supplied to a liquid catalyst nanoparticle. Upon supersaturation of the catalyst droplet, crystallization occurs: A nanocrystal forms, one of its facets in contact with the droplet. This nanofacet is where crystal growth further proceeds. A detailed and real-time observation of the liquid-solid interface is thus expected to clarify the role of the boundaries in the crystallization process. We observe the VLS growth of GaAs NWs in real time. We use a modified FEI environmental TEM equipped with an image aberration corrector. Two ports were designed to implement Ga and As4 molecular beam sources in the TEM. NW formation is catalyzed by Au particles dispersed on a heating carrier membrane, and in situ growth is performed by molecular beam epitaxy at 400 °C. At this temperature, the Au particles alloy with Ga to form liquid droplets. Upon As supersaturation of the droplets, GaAs NWs of hexagonal shape crystallize under the droplets. The boundaries of this system consist of the NW-catalyst interface, the NW sidewalls, and the surface of the liquid catalyst particle. We examine the formation of the WZ phase. The sidewalls of the NWs are {11-20} facets, and the hexagon sides are ⟨10-10⟩ directions. We first present an atomically resolved growth observation in a ⟨11-20⟩ zone axis. The electron beam is then parallel to the LS interface, and the atomic columns parallel to the beam produce a strong contrast.

Nevertheless, the observation conditions adopted in these studies, with the electron beam parallel to the LS interface, provide an incomplete picture of ML formation and progression. Here, we present in addition bird’s eye views of growing NWs which reveal essential complementary information. A two-dimensional projection of the growing ML is visualized, from the early stage of formation to ML completion. We confirm that WZ layers start from the periphery of the NW top facet, and we image, analyze, and model the progression of the step within this hexagonal perimeter. Relevant edge energies are extracted. This leads to a better understanding of the formation of the nanocrystal and ultimately to a better control of its structure.

Reference :

Atomic step flow on a nanofacet
J.-C. Harmand, G. Patriarche, F. Glas, F. Panciera, I. Florea, J.-L. Maurice, L. Travers et Y. Ollivier; Physical Review Letters, 121, 166101 (2018)
DOI : 10.1103/PhysRevLett.121.166101

Electron Beam Induced Artifacts During In-Situ TEM

At the Lab at ASU, their research is primarily focused on the synthesis and characterization of nanostructured materials for structural and functional applications. They...

At the Lab at ASU, their research is primarily focused on the synthesis and characterization of nanostructured materials for structural and functional applications. They develop new synthesis techniques for thin films and investigate their synthesis-structure-property relationships. The overarching goal is to engineer the microstructure of thin films to enhance their mechanical properties and functionality. The lab also has an active interest in creating soft, polymer-based micro platforms that can be used as scaffolds for biohybrid devices or for studying cellular mechanics.

Publication Highlights

Izadi, E.; Darbal, A.; Sarkar, R.; Rajagopalan, J. Grain rotations in ultrafine-grained aluminum films studied using in situ TEM straining with automated crystal orientation mapping. Mater. Des.113 (Jan. 2017), pp. 186-194; doi: 10.1016/j.matdes (2016)

" In-situ TEM straining allows probing deformation mechanisms of ultrafine-grained and nanocrystalline metals. While obtaining statistically meaningful information about microstructural changes using conventional bright-field/dark-field imaging or diffraction is time-consuming, automated crystal orientation mapping in TEM (ACOM-TEM) enables tracking orientation changes of hundreds of grains simultaneously. We use this technique to uncover extensive grain rotations during in-situ tensile deformation of a freestanding, ultrafine-grained aluminum film (thickness 200 nm, mean grain size 180 nm). During loading, both the fraction of grains that undergo rotations and the magnitude of their rotations increase with strain. The rotations are partially or fully reversible in a significant fraction of grains during unloading, leading to notable inelastic strain recovery. More surprisingly, the direction of rotation remains unchanged for a small fraction of grains during unloading, despite a sharp reduction in the applied stress. The ACOM-TEM measurements also provide evidence of reversible and irreversible grain/twin boundary migrations in the film. These microstructural observations point to a highly inhomogeneous and constantly evolving stress distribution in the film during both loading and unloading."

Lab Focus

Sarkar, R. et al. Electron beam induced artifacts during in situ TEM deformation of nanostructured metals. Sci. Rep. 5, 16345; doi: 10.1038/srep16345 (2015).

"A critical assumption underlying in-situ transmission electron microscopy studies is that the electron beam (e-beam) exposure does not fundamentally alter the intrinsic deformation behavior of the materials being probed. Here, we show that e-beam exposure causes increased dislocation activation and marked stress relaxation in aluminum and gold films spanning a range of thicknesses (80 – 400 nm) and grain sizes (50 – 220 nm). Furthermore, the e-beam induces anomalous sample necking, which unusually depends more on the e-beam diameter than intensity. Notably, the stress relaxation in both aluminum and gold occurs at beam energies well below their damage thresholds. More remarkably, the stress relaxation and/or sample necking is significantly more pronounced at lower accelerating voltages (120 kV versus 200 kV) in both the metals. These observations in aluminum and gold, two metals with highly dissimilar atomic weights and properties, indicate that e-beam exposure can cause anomalous behavior in a broad spectrum of nanostructured materials, and simultaneously suggest a strategy to minimize such artifacts."

Additional Publications

21. E. Izadi, A. Darbal, R. Sarkar, J. Rajagopalan, “Grain rotations in ultrafine-grained aluminum films studied using in situ TEM straining with automated crystal orientation mapping,” Materials and Design 113, 186–194, 2017 (pdf).

20. R. Sarkar, C. Ebner, I. Izadi, C. Rentenberger, and J. Rajagopalan, “Revealing anelasticity and structural rearrangements in nanoscale metallic glass films using in situ TEM diffraction,” Materials Research Letters, 2016 DOI:10.1080/21663831.2016.1228709 (pdf).

19. T. W. Sowers, R. Sarkar, S. E. Prameela, E. Izadi and J. Rajagopalan, “Capillary driven flow of polydimethylsiloxane in open rectangular micro channels,” Soft Matter 12, 5818-5823, 2016 (pdf).

18. C. Ebner, R. Sarkar, J. Rajagopalan, and C. Rentenberger, “Local, atomic-­level elastic strain measurements of metallic glass thin films by electron diffraction,” Ultramicroscopy 165, 51–58, 2016 (pdf).

17. E. Izadi and J. Rajagopalan, “Texture dependent strain rate sensitivity of ultrafine-grained aluminum films,” Scripta Materialia 114, 65-69, 2016 (pdf).

16. R. Sarkar, C. Rentenberger and J. Rajagopalan, “Electron beam induced artifacts during in situ TEM deformation of nanostructured metals,” Scientific Reports 5, 16345, 2015 (pdf).

15. S. Singh, R. Sarkar, H.-X. Xie, C. Mayer, J. Rajagopalan, and N. Chawla, “Tensile behavior of single-crystal tin whiskers,” Journal of Electronic Materials 43, 978-982, 2014 (pdf)

14. B. J. Williams, S. A. Anand, J. Rajagopalan and M. T. A. Saif, “A self-propelled biohybrid swimmer at low Reynolds number,” Nature Communications 5, 3081, 2014 (pdf)

13. J. Rajagopalan and M. T. A. Saif, “Fabrication of freestanding 1-D PDMS microstructures using capillary micromolding,” Journal of Microelectromechanical Systems 22, 992-994, 2013 (pdf)

12. J. Rajagopalan and M. T. A. Saif, “Effect of microstructural heterogeneity on the mechanical behavior of nanocrystalline metal films,” Journal of Materials Research 26, 2826-2832, 2011 (pdf)

11. J. Rajagopalan and M. T. A. Saif, “MEMS sensors and microsystems for cell mechano-biology,” Journal of Micromechanics and Microengineering 21, 054002, 2011 (pdf)

10. J. Rajagopalan, A. Tofangchi and M. T. A. Saif, “Linear, high-resolution bioMEMS force sensors with large measurement range,” Journal of Microelectromechanical Systems 19, 1380-1389, 2010 (pdf)

9. W. Kang, J. Rajagopalan and M. T. A. Saif, “In situ uniaxial mechanical testing of small scale materials – a review,” Nanoscience and Nanotechnology Letters 2, 282-287, 2010 (pdf)

8. J. Rajagopalan, A. Tofangchi and M. T. A. Saif, “Drosophila neurons actively regulate axonal tension in vivo,” Biophysical Journal 99, 3208-3215, 2010 (pdf)

7. J. Rajagopalan, C. Rentenberger, P. H. Karnthaler, G. Dehm and M. T. A. Saif, “In situ TEM study of microplasticity and Bauschinger effect in nanocrystalline metals,” Acta Materialia 58, 4772-4782, 2010 (pdf)

6. J. Rajagopalan, J. H. Han and M. T. A. Saif, “On plastic strain recovery in freestanding nanocrystalline metal thin films,” Scripta Materialia 59, 921-926, 2008 (pdf)

5. J. Rajagopalan, J. H. Han and M. T. A. Saif, “Bauschinger effect in unpassivated freestanding nanoscale metal films,” Scripta Materialia 59, 734-737, 2008 (pdf)

4. J. Rajagopalan, J. H. Han, and M. T. A. Saif, “Plastic deformation recovery in freestanding nanocrystalline aluminum and gold thin films,” Science 315, 1831-1834, 2007 (pdf)

3. J. Rajagopalan and M. T. A. Saif, “A single degree of freedom model for thermoelastic damping,” Journal of Applied Mechanics 74, 461-468, 2007 (pdf)

2. J. Rajagopalan, K. Balasubramaniam and C. V. Krishnamurthy, “A phase reconstruction algorithm for Lamb wave based structural health monitoring of anisotropic multilayered composite plates,” Journal of the Acoustical Society of America 119, 872-878, 2006 (pdf)

1. J. Rajagopalan, K. Balasubramaniam and C. V. Krishnamurthy, “A single transmitter multi receiver (STMR) PZT array for guided ultrasonic wave based structural health monitoring of large isotropic plate structures,” Smart Materials and Structures 15, 1190-1196, 2006 (pdf)

Lab focus

The Ringe Group was established in 2014 in the department of Materials Science and NanoEngineering (MSNE) at Rice University, Houston, TX, USA. Emilie Ringe and her...

Lab focus

The Ringe Group was established in 2014 in the department of Materials Science and NanoEngineering (MSNE) at Rice University, Houston, TX, USA. Emilie Ringe and her group focus on understanding and controlling light-matter interactions in small metallic nanoparticles for applications in biological sensing, enhanced spectroscopy, and light-driven heterogeneous catalysis.

By using correlated optical spectroscopy and electron microscopy tools, the group studies a phenomenon called localized surface plasmon resonance (LSPR), a type of light-matter interaction. LSPRs are a collective oscillation of the conduction electrons in a metal particle that leads to bright colors as well as strong electric fields at the surface of the particle. The resonance frequency changes with the surrounding environment, such that LSPR have exciting applications as nanosensors. Moreover, the strong fields can boost the catalytic activity of the metal surfaces.

Both electrons and photons can interact with plasmon resonances, yielding either photons or electrons. Using electron energy loss spectroscopy (EELS) and cathodoluminescence (CL), techniques using an electron-based excitation and yielding an electron and a photon signal, respectively, the Ringe group studies the symmetry and localization of plasmon modes. Recently, work on Au/Pd nanoparticles has demonstrated that these alloy nanoparticles containing a poor plasmonic metal (Pd in this case) can nevertheless sustain a strong plasmonic response, enabling applications such as plasmon-enhanced photocatalysis and in-situ reaction monitoring and switching. Multiple size-dependent LSPRs and strong spatially localized fields at the Pd-rich tip of stellated particles were observed, where the composition is in fact least favorable for plasmon resonances. A strong substrate coupling was demonstrated via EELS tilt series and shows that Pd is fully participating in the resonances observed. Results are shown below.









Please visit the lab's website for more information.


E. Ringe, C.J. DeSantis, S.M. Collins, M. Duchamp, R.E. Dunin-Borkowski, S.E. Skrabalak, P.A. Midgley. "Resonances of nanoparticles with poor plasmonic metal tips" Scientific Reports 5. 2015, 17431, doi:10.1038/srep17431.

Lab focus

The team at Electron Microscopy Group in Nano-Materials Research Institute of AIST aims to realize the characterization of nano-materials at a single atomic level by using the high performance electron microscopy. They have developed the low-accelerating voltage transmission electron microscopy (TEM) and scanning TEM (STEM) equipped with high-order aberration correctors to visualize the atomic structures of low-dimensional materials such as carbon nanotubes, graphene and transition-metal dichalcogenides as well as soft matters such as organic molecules and bio-materials. They have also focused on the chemical assignment of single atoms or molecules correlated to the atomic structures including defects and dopants by means of electron energy-loss spectroscopy (EELS).

Publication highlights

The lab has reported the ionic atomic chain in which two chemical elements line up alternately (Fig.1), showing distinct physical properties from the bulk structures1,2. Connected to this work, they have also demonstrated the single atom identification of light elements including Lithium (Fig. 2) which is the lightest element ever identified as a single atom by using EELS combined a STEM2.

Figure 1. STEM EELS characterization for a CsCl atomic chain inside a double-walled carbon nanotube (DWNT). The Cs and Cl atoms are lined up alternatively as shown in the left model. Since Cl is much lighter than Cs, the ADF image only shows the Cs atomic positions as brighter spots and the Cl atoms are hardly visible. However this, the EELS map for the Cl L-edge (purple spots in the left panel) clearly shows the existence of Cl atoms in between Cs atoms2. EELS data are recorded by a GIF Quantum® spectrometer designed for the low-voltage TEM.

Figure 2. STEM-EELS characterization for a LiI atomic chain inside double-walled carbon nanotube (DWNT). The LiI atomic chain exists as a double lined chain inside the DWNT as shown in the left model. While the ADF image only shows the I atomic positions, the EELS chemical map for the Li K-edge shows the Li atomic position as a zigzag pattern between I atoms2. EELS data are recorded by a GIF Quantum spectrometer designed for the low-voltage TEM.

Electron Microscopy group is in Nano-Materials Research Institute of AIST, Japan. Please visit the lab's website for more information.


  1. R. Senga, H.-P. Komsa, Z. Liu, K. Hirose-Takai, A. V. Krasheninnikov and K. Suenaga Nature Mat. 2014, 13 (11), 1050–1054.
  2. R. Senga and K. Suenaga, Nature Commun. 2015, 6, 7943.

Additional Publications

Y.-C. Lin, P. -Y. Teng, P. -W. C, K. Suenaga. "Exploring the Single Atom Spin State by Electron Spectroscopy" Phys. Rev. Lett. 2015, 115, 206803.