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Etude des corrélations entre les propriétés morphologiques, structurales et plasmoniques au cours de la croissance de nanoparticules d'or sur TiO2(110)

Abstract : This thesis concerns the study of supported gold nanoparticles (NP) onTiO2(110) as a model system. The aim is improving the comprehension ofthe correlation between morphological and structural properties andlocal surface plasmon resonances (LSPR) of the NP.In situ measurements during NP growth were performed by grazingincidence X-ray diffraction (GIXD), grazing incidence small angle X-raydiffusion (GISAXS) and surface differential reflectance spectroscopy(SDRS). NP were deposited by molecular beam epitaxy in ultra-high vacuum.Simultaneous study of LSPR phenomena by SDRS and GISAXS allowed thedescription of resonance frequency evolution with the NP mean diameterincrease from 2 to 6 nm.Typically, position of the plasmon peak in both p and s measuredpolarizations is found to blue-shift when NP size decreases, butdetailed behavior is influenced by TiO2(110) surface state.At the same NP dimension, in one case plasmon pics position is the samefor both s and p polarization, whereas in the second studied sample theyare different, but only in the small size range (diameter<5nm). Thisphenomenon was analyzed thanks to the decomposition of plasmonexcitation into parallel (A//, contributing to both s and p signal) andperpendicular (Az, contributing only to p polarization) modes withrespect to the surface.When A// dominates (same peak positions for s and p polarizations at thesame NP mean diameter) the observed blue-shift with size decrease isvery close to that reported in literature for embedded Au NP. Thissuggests that the underlying quantum size effect, due to s-electronsspill-out and diminishing of d-electrons screening for surface atoms, isan intrinsic property of the NP. Interaction with the substrate inducesa global red-shift compared to NP in vacuum.In the other case (s /= p for sizes smaller than 5 nm), Az contributionin noticeable. Substrate influence on this mode is different, its effectincreases as size decreases, countering the intrinsic size effect.Blue-shift with size decrease is slowed down in p polarization comparedto the s one. These results were linked to GIXD measurements performedafter NP growth. They show epitaxial differences between the two studiedcases. In the former (p=s), a fair amount of NP is oriented such thatgold [110] direction is aligned with the TiO2(110) surface bridgingoxygen arrays. In the second case (p/=s), NP show a strong orientationaldisorder, possibly due to the presence of a large amount of steps on theTiO2(110) surface.
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Submitted on : Monday, October 15, 2018 - 8:56:10 AM
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Antoine Abisset. Etude des corrélations entre les propriétés morphologiques, structurales et plasmoniques au cours de la croissance de nanoparticules d'or sur TiO2(110). Science des matériaux [cond-mat.mtrl-sci]. Université Grenoble Alpes, 2018. Français. ⟨NNT : 2018GREAY018⟩. ⟨tel-01895289⟩

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