Damien ESCHIMESE
Thesis defence
03/05/2019
IEMN Amphitheatre
Summary:
Since the 2000s, the development of high-excitation Raman spectroscopy (TERS) has provided highly localised access to structural and molecular properties at the surface of matter and combined physico-chemical analyses. TERS technology combines local probe microscopy techniques - in this case the atomic force microscope (AFM) - with the optical near-field. In particular, it benefits from the generation, on the surface of noble metals, of surface plasmons that cause the exaltation of electromagnetic waves that can be confined in a sub-wavelength volume at the end of the AFM-TERS probes.
Today, the main technological challenge in TERS is the design of AFM probes in terms of reproducibility on a nanometric scale and mass production. The aim of this work, carried out as part of a CIFRE thesis (HORIBA Scientific), was to design a new type of AFM-TERS probe that meets current performance and manufacturing requirements.
To achieve this objective, a numerical simulation study led to a proposal for metallic nanostructuring of the end of an AFM lever, in order to achieve optimised electromagnetic excitation. A nano- and micro-fabrication process has been developed at the IEMN's micro and nano-fabrication platform, combining electronic and optical lithography, metal evaporation and etching on silicon wafers. It enables the mass production of AFM probes, each end of which consists of a metallic nano-antenna of sub-wavelength size, made up of a nanodisk supporting a nanocone. The proposed fabrication method enables plasmonic responses to be controlled in terms of field amplification and resonance tunability, which are key to performance in peak-excitation Raman spectroscopy.
A study of inclined evaporation during the nano-fabrication process developed by electron lithography was also carried out with the aim of controlling the shape of nanoparticles - from conical to cylindrical with porous walls - isolated or in dense arrays. Numerical simulations suggest that such objects may be potential candidates for TERS or SERS (surface exaltation Raman spectroscopy).
Abstract:
Since the start of the 2000s the evolution of tip-enhanced Raman spectroscopy (TERS) has enabled the simultaneous measurement of localized structural, molecular, and physicochemical properties. TERS technology combines scanning probe microscopy - atomic force microscopy (AFM) - with near field optical microscopy. The combined technique is referred to as AFM-TERS. The technique harnesses and exploits the generation of surface plasmons on metal surfaces. These plasmons lead to the generation of confined electromagnetic waves in a sub-wavelength volume at the very tip of the AFM-TERS probe.
The main technological challenge today is the design and optimization of an AFM-TERS probe having nanometer-sized dimensions - and the controlled, reproducible batch fabrication of such structures. The objective of the work presented in this PhD thesis was to design, fabricate, and characterize a new type of AFM probe capable of bettering the current state-of-the-art performances. The PhD was carried out in collaboration with HORIBA and funded partly by a French 'CIFRE' grant.
In order to meet these objects, comprehensive numerical modelling led to the design of an optimized metal nanostructuring having maximum electromagnetic exaltation - placed at the extremity of a silicon-based AFM cantilever. A new combined micro and nano fabrication process was developed to achieve this - to be performed using the existing equipment found in the IEMN cleanroom. The process encompasses techniques such as masking using electron beam (ebeam) lithography and UV photolithography, thermal evaporation of metals and 'lift-off' techniques, and highly-controlled dry etching of small silicon mesas structures and deep etching for MEMS cantilever releasing. The process enables the batch-fabrication manufacture of AFM-TERS probes containing matter on the millimeter scale (the silicon probe support), the micrometer scale (the silicon cantilever), and the nanometer scale (the combined metallic disk and cone having sub-wavelength dimensions). This method allows nanostructuring on the optical/plasmonic behavior of TERS probes, the key factor which will lead to higher performance in TERS.
Finally, a further study concerning the inclined evaporation of metallic nanostructures via an ebeam-derived lithographic shadow mask was performed in order to control the size and shape of the nanostructuring. The study proved this approach to be feasible. Furthermore, numerical modelling of such structures suggests that they are potential original candidates for both TERS and SERS (surface-enhanced Raman spectroscopy).
JURY :
- Thierry MELIN, IEMN, Thesis supervisor
- Stephen ARSCOTT, IEMN, Thesis Co-Director
- Frédérique DE FORNEL, University of Burgundy, Rapporteur
- Cédric AYELA, Materials and Systems Integration Laboratory, Bordeaux, Rapporteur
- Gaëtan LÉVÊQUE, University of Lille - IEMN, Examiner
- Anne-Laure BAUDRION, Université de Technologie de Troyes, L2n, Examiner
- Bernard HUMBERT, Jean Rouxel Materials Institute, Nantes, Examiner
