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Laser and Micro-/Nano-Electronics

  • Surface nanostructuring

The trend towards nanotechnology makes it necessary to address the key issues of photonics on the nanometer scale. Since the diffraction limit does not allow focusing propagative waves to dimensions smaller than roughly half a wavelength, we develop near-field scattering techniques to convert propagative waves to highly localized light energy.

In the framework of this project, we work on a simple method using laser light interaction with small particles to produce so-called photonic nanojets. Taking benefit of the self-assembly properties of transparent dielectric microspheres (R=250nm-5µm), we directly produce a well-ordered array of small light spots at the surface of any substrate used to support the spheres. When modest energy laser pulses are used, only locations of the substrate at the touch of the photonic nanojets are modified. This leaves behind periodic features with size on the order of 100 nm, depending on the material response.

Focusing properties of a 500nm diameter silica spheres for 193nm wavelength laser light

We concentrate on this approach for thin-film nanostructuring. This allows mapping out the near-field enhancements in 3D-space. When the film is transparent, the localized light energy is absorbed at the layer/substrate interface leading to the local ejection of the film (see Fig.x). Then, the lateral extend of the enhancement translates in hole width ( 100nm). Varying the thickness of the film, we monitor over which distance photonic nanojets propagate (>l/2). By comparing near-field simulations (FDTD) with experiments, we establish the relationship between the laser parameters (polarization, wavelength, pulse duration), the materials (microspheres/substrate) and the near-field properties.

Fabrication of nanodot arrays by a 4 photonic steps

The microspheres we consider here are today routinely available. Then the approach opens a new route to fabricating nanomaterials. We show that our beautifully ordered nanodrilled films can be used as user-defined evaporation masks for the preparation of nanodot arrays with controlled dot size and dot-to-dot spacing (see references). Such surface nanomaterials have potential applications in microscopy and sensors.

- D. Grojo, A. Cros, Ph. Delaporte, M. Sentis, “Experimental investigation of ablation mechanisms involved in dry laser cleaning”, Applied Surface Science, 253 (2007) 8309–8315
- A. Pereira, D. Grojo, M. Chaker, Ph. Delaporte, D. Guay, M. Sentis, “Laser-fabricated porous alumina membrane (LF-PAM) for the preparation of metal nanodot arrays”, Small, 4 (2008) 572-575
- A.V. Kabashin, Ph. Delaporte, A. Pereira, D. Grojo, R. Torres, Th. Sarnet, M. Sentis, “Nanofabrication with pulsed lasers”, Nanoscale Research Letters, 5 (2010) 454-463