Titre :	High spatial resolution investigation of spin crossover phenomena using scanning probe microscopies
Type de document :	texte imprimé
Auteurs :	Edna Magdalena Hernandez Gonzalez, Auteur ; Azzedine Bousseksou, Directeur de thèse ; Gabor Molnar, Directeur de thèse
Année de publication :	2015
Langues :	Anglais (eng)
Tags :	SCANNING PROBE MICROSCOPY  ATOMIC FORCE MICROSCOPY  NEAR-FIELD SCANNING OPTICAL MICROSCOPY  SPIN TRANSITION.
Résumé :	"Recently a variety of nanoscale objects, including nanoparticles, thin films and nanometric assemblies, exhibiting molecular spin-state switching phenomena have been developed for applications in sensors, nanophotonic, nanoelectronic and nanomechanical systems. These spin crossover nanomaterials have been also reported to exhibit interesting size-dependent properties. Indeed, even if the origin of the spin crossover phenomenon is purely molecular, the macroscopic behavior of these systems in the solid state is strongly influenced by elastic interactions between the molecules. These cooperative properties and, in general, the phase diagram are expected to depend strongly on the size of the material. Beyond the phase stability, the transformation kinetics is likely to display also size dependence. Indeed, the strong elastic interactions in these materials lead, in many cases, to first-order phase transitions and phase separation phenomena. Details of the associated spatio-temporal dynamics of spin crossover systems remain largely unexplored. All these size dependent and spatially heterogeneous phenomena in spin crossover materials call for appropriate characterization methods with high spatial resolution imaging capability, but to date only far-field optical microscopy has been used to this aim. Hence, the overall objective of this PHD thesis was to develop new approaches allowing to trigger and detect the spin crossover phenomenon with nanometric spatial resolution. For the detection of the thermally induced spin crossover in thin films, we used for the first time Near-Field Scanning Optical Microscopy (NSOM) and Atomic Force Microscopy (AFM) in conjunction with an original nano-heater device, based on Joule-heated metallic nanowires. Using these techniques the spin-state change in the films was inferred with sub-wavelength resolution through the associated optical and mechanical property changes of the material. Apertured NSOM used either in luminescence or reflectivity mode provided useful signal for detecting the spin-state switching phenomena, but rather limited quantification was possible due to sample stability issues. On the other hand, AFM mechanical modes, including fast force spectroscopy and multifrequency analysis, allowed for quantitative and well-reproducible measurements with nanometric resolution. In particular, we have measured for the first time the increase of the Young’s modulus (ca. 25-30 %) when going from the high spin to the low spin state and used this property for quantitative imaging of the spin transition. AFM measurements were also performed on spin crossover single crystals. We have shown that probe-sample thermal interactions can be used to manipulate the nucleation and propagation of the high spin and low spin phases in the crystals. On the other hand, these interactions make for difficulties for the AFM imaging of these phenomena. Nevertheless changes of the surface topography during the spin transition could be observed and discussed in conjunction with far-field optical microscopy and Raman spectroscopy data. The ensemble of these results open up new possibilities for the investigation and manipulation of these bistable objects at the nanoscale."
Document :	Thèse de doctorat
Etablissement_delivrance :	Université de Toulouse 3
Date_soutenance :	21/07/2015
Ecole_doctorale :	Science de la matière (université Toulouse III P. Sabatier)
Domaine :	Physique de la matière
Localisation :	LCC
En ligne :	http://thesesups.ups-tlse.fr/2767/

High spatial resolution investigation of spin crossover phenomena using scanning probe microscopies [texte imprimé] / Edna Magdalena Hernandez Gonzalez, Auteur ; Azzedine Bousseksou, Directeur de thèse ; Gabor Molnar, Directeur de thèse . - 2015.
Langues : Anglais (eng)

Tags :	SCANNING PROBE MICROSCOPY  ATOMIC FORCE MICROSCOPY  NEAR-FIELD SCANNING OPTICAL MICROSCOPY  SPIN TRANSITION.
Résumé :	"Recently a variety of nanoscale objects, including nanoparticles, thin films and nanometric assemblies, exhibiting molecular spin-state switching phenomena have been developed for applications in sensors, nanophotonic, nanoelectronic and nanomechanical systems. These spin crossover nanomaterials have been also reported to exhibit interesting size-dependent properties. Indeed, even if the origin of the spin crossover phenomenon is purely molecular, the macroscopic behavior of these systems in the solid state is strongly influenced by elastic interactions between the molecules. These cooperative properties and, in general, the phase diagram are expected to depend strongly on the size of the material. Beyond the phase stability, the transformation kinetics is likely to display also size dependence. Indeed, the strong elastic interactions in these materials lead, in many cases, to first-order phase transitions and phase separation phenomena. Details of the associated spatio-temporal dynamics of spin crossover systems remain largely unexplored. All these size dependent and spatially heterogeneous phenomena in spin crossover materials call for appropriate characterization methods with high spatial resolution imaging capability, but to date only far-field optical microscopy has been used to this aim. Hence, the overall objective of this PHD thesis was to develop new approaches allowing to trigger and detect the spin crossover phenomenon with nanometric spatial resolution. For the detection of the thermally induced spin crossover in thin films, we used for the first time Near-Field Scanning Optical Microscopy (NSOM) and Atomic Force Microscopy (AFM) in conjunction with an original nano-heater device, based on Joule-heated metallic nanowires. Using these techniques the spin-state change in the films was inferred with sub-wavelength resolution through the associated optical and mechanical property changes of the material. Apertured NSOM used either in luminescence or reflectivity mode provided useful signal for detecting the spin-state switching phenomena, but rather limited quantification was possible due to sample stability issues. On the other hand, AFM mechanical modes, including fast force spectroscopy and multifrequency analysis, allowed for quantitative and well-reproducible measurements with nanometric resolution. In particular, we have measured for the first time the increase of the Young’s modulus (ca. 25-30 %) when going from the high spin to the low spin state and used this property for quantitative imaging of the spin transition. AFM measurements were also performed on spin crossover single crystals. We have shown that probe-sample thermal interactions can be used to manipulate the nucleation and propagation of the high spin and low spin phases in the crystals. On the other hand, these interactions make for difficulties for the AFM imaging of these phenomena. Nevertheless changes of the surface topography during the spin transition could be observed and discussed in conjunction with far-field optical microscopy and Raman spectroscopy data. The ensemble of these results open up new possibilities for the investigation and manipulation of these bistable objects at the nanoscale."
Document :	Thèse de doctorat
Etablissement_delivrance :	Université de Toulouse 3
Date_soutenance :	21/07/2015
Ecole_doctorale :	Science de la matière (université Toulouse III P. Sabatier)
Domaine :	Physique de la matière
Localisation :	LCC
En ligne :	http://thesesups.ups-tlse.fr/2767/