Nanostructuration by ion-beam sputtering
Un article de Surface du verre et interfaces.
Elin Sondergard - Etienne Barthel - Sébastien Le Roy
Sommaire |
Description
Rapid and cheap elaboration of high aspect ratio nanostructures is currently subject of intense research. The easy generation of controlled distributions of these structures would provide large-area low-cost materials with advanced functionalities in very diverse areas, such as photonics, adhesion properties or life sciences.
Upon low-energy ion sputtering, a surface may exhibit spontaneous formation of nano-patterns, such as ripples or dots. This opens up a road toward fast and cost-effective production of large nanostructured surfaces. Bradley and Harper provided a good explanation for the structure formation under ion erosion, but their theory fails to explain the unique behaviour of III/V semi-conductors. Indeed, for materials like GaSb or InSb, ion sputtering can produce within a few minutes high aspect ratio pillars (Figure 1). Moreover the orientation of the pillars can be tuned by changeing the incident angle of the ion beam, leading to tilted nanopillars (Figure 2).
We study the physics of the structuration in order to understand the mechanism of the cone formation. Thanks to a combination of STEM, EELS and XPS of ion-sputtered GaSb pillars (Figure 3), we revealed that considerable segregation occurs during the abrasion process on the material GaSb. Based on these observations, we proposed a simultaneous segregation and shielding mechanism : the surface is enriched in Ga due to the difference in sputtering yield between Ga and Sb, and above a critical concentration, Ga segregates to form the Ga cap which acts as a sputtering shield. Thanks to a phase-field simulation, we were able to reproduce the morphology of the structure under ion sputtering (Figure 4).
We further demonstrated that in situ spectroscopic ellipsometry can be used to measure the height evolution of growing nanostructures during sputtering. The in situ observations gave new physical insight into the formation process of under ionsputtering. The influence of different parameters (flux, energy, temperature) can be investigated.
In parallel, we study the mechanical properties of the nano-dots.
Collaborations
Theory
- M. Plapp - Laboratoire PMC, Ecole Polytechnique - Palaiseau, France
Optical Characterisation
- I. S. Nerbø, M. Kildemo, I. Simonsen - Applied Optics Group, Departement of Physics, Norwegian University of Science et Technology - NO-7491 Trondheim, Norway
Mechanical proprieties
- Frédéric Restagno - CNRS, Laboratoire de physique des solides (UMR 8502) - Orsay, France
Publications
- S. Le Roy, E. Søndergård, I. S. Nerbø, M. Kildemo and M. Plapp, Diffuse-interface model for nanopatterning induced by self-sustained ion etch masking, submitted to PRL.
- S. Le Roy, E. Barthel, N. Brun, A. Lelarge, and E. Søndergård, Self-sustained etch masking: A general concept to initiate the formation of nanopatterns during ion erosion J. Appl. Phys. 106, 094308 (2009).
- I. S. Nerbø, S. Le Roy, M. Kildemo, and E. Søndergård, Real-time in-situ spectroscopic ellipsometry of GaSb nanostructures during sputtering: Identification of growth regimes Appl. Phys. Lett. 94, 213105 (2009).
- I. S. Nerbø, M. Kildemo, S. Le Roy, I. Simonsen, E. Søndergård, L. Holt and J. C. Walmsley Characterisation of nanostructured GaSb : Comparison between large-area optical and local direct microscopic techniques, Appl. Opt. 47, 5130 (2008).
- M. Kildemo, I.S. Nerbø, S. Hagen, S. Le Roy and E. Søndergård Spectroscopic ellipsometry of nanostructured GaSb surfaces consisting of densely packed 80–230 nm long cones Mater. Sci. Eng. B 165, 3 (2009).
- M. Kildemo, Y. Inntjore Levinsen, S. Le Roy and E. Søndergård Staircase and saw-tooth field emission steps from nanopatterned n-type GaSb surfaces J. Vac. Sci. Technol. A 27 5 (2009)