When an electronic system is confined in one or more dimensions to a length scale comparable to the de Broglie wavelength, quantum confinement occurs. In metallic quantum thin films grown on semiconductor substrates, such confinement occurs between the vacuum-solid and the solid-solid interfaces, which results in the formation of distinctive quantum well states (QWS). Due to this confinement, many physical phenomena occurring in the thin metal system are totally different from the bulk system, which makes the study of quantum thin films interesting and important. In this thesis, quantum thin film studies, mainly based on the Pb/Si(111) system, were performed utilizing low-temperature scanning tunneling microscopy/spectroscopy (STM/STS) with a focus on three main aspects: phase relationship, surface reactivity, and coherent coupling. The Pb/Si(111) system is chosen due to its unique phase matching between the Fermi wavelength and the lattice spacing along [111], leading to a bi-layer quantum oscillation in many physical properties, including the surface energy and the work function. Surprisingly, STM/STS measurement revealed that quantum oscillations of work function and surface energy have identical phase, in contrast to a theoretically predicted 1/4 wavelength phase shift in the phase relationship. Here, a new solution to this puzzle is provided. Furthermore, it is found out that the oxidation rate of Pb/Si(111) system is greatly enhanced in the presence of atomic scale catalyst -- Cs substitutional atoms, while the reactivity to CO is saturated after the initial enhanced nucleation. Finally, by inserting thin Ag layers in between Pb/Si(111) system, the coherent coupling of double quantum wells (a Pb quantum well and a Ag quantum well) are probed, where combined QWS features are observed by STS measurement. The growth mechanism of these heterostructures -- Pb/Ag/Si(111) -- is also investigated. / text

Ce travail de thèse a pour but de clarifier le mécanisme de la transition métal-isolant (MIT) pilotée par le dopage électronique x du système quasi-2D BaCo1-xNixS2.Une optimisation de la croissance de monocristaux pour des taux de substitution allant de x = 0 à 1 a été nécessaire. Cela a permis de synthétiser de manière reproductible des monocristaux non lacunaires en soufre, de taille millimétrique et de haute qualité. L'analyse structurale de ces cristaux a permis d'établir une relation précise entre les distances métal-soufres et le taux de substitution x.Le travail de thèse a ensuite été focalisé sur l'étude des propriétés électroniques et de transport de BaNiS2 la phase métallique précurseur de la MIT. Les études de la structure électronique par photoémission résolue en angle (ARPES) et par des mesures d'oscillations quantiques ont révélées une surface de Fermi composée d'une poche d'électrons 2D centrée en Γ(Z) et d'une poche de trous positionnée à mi-distance suivant ΓM(ZA) quasi-2D avec une dispersion conique à kz =0. Une levée de dégénérescence des bandes à Γ et à X révèle la présence inattendue et importante d'un couplage spin-orbite et d'un couplage Rashba. Les mesures de magnétotransport ont pu être expliquées par un modèle qui implique que BaNiS2 est un semi-métal compensé avec trois voies de conduction. Des trous p1 et électrons e1 largement majoritaires et présentant des mobilités modérées ainsi que des trous p2 minoritaires de très haute mobilité.La cohérence de l'ensemble des mesures donne une image précise de la surface de Fermi de BaNiS2 et de ses propriétés électroniques plus bidimensionnelle que celle prévu par le calculs de bandes conventionnelle. / This work aims to clarify the mechanism of the metal-insulator transition (MIT) driven by doping x in the quasi-2D BaCo1-xNixS2 system. First of all, synthesize of high quality single crystals with substitution level x varying in the full 0 - 1 range was fundamental. It appears that the mechanism of the metal-insulator transition is associated to a continuous modification of metal-sulfurs distances. Then, we focus on an investigated the electronic properties of BaNiS2, precursor metallic phase of the MIT. Studies of the electronic structure of BaNiS2 by angle-resolved photoemission spectroscopy (ARPES) and by quantum oscillation measurements reveal the existence of two pockets at the Fermi surface: an electron-like 2D pocket centered in Γ(Z) and a hole-like pocket quasi-2D at mi-distance along ΓM(ZA) with a conic-like dispersion in kz = 0 . Furthermore, data also show a very large spin-orbit splitting at Γ and Z which is unexpected in a 3d metal compound. From previous studies, we developed a model to explain magnetotransport properties of BaNiS2. This model involves that BaNiS2 is a three carriers compensated metal: a majority holes p1 and electrons e1 carriers with moderate mobilities and a minor holes p2 carriers with a high mobility. The two different holes carries observed in magneto-transport could be explain by an important variation of the hole-like pocket dispersion along kz. Measures realized during this thesis are consistent and allowed to know precisely the form of the Fermi surface of BaNiS2 and its electronic properties which are more bi-dimensional than predict by conventional calculation.