Estudo das terminações de superfície, coexistência de fases e absorção de água em materiais bidimensionais pela análise de crystal truncation rods

Abstract

This dissertation is focused on the study of surfaces of two-dimensional materials using the Crystal Truncation Rod (CTR) method and synchrotron radiation. We developed a kinematic scattering model capable of combining the coexistence of different surface terminations in materials in which surface cleavage leads to inhomogeneous positional behavior observed by techniques such as tunneling microscopy and spectroscopy, near-field infrared microscopy, and atomic force microscopy combined with Kelvin Probe Force Microscopy (KPFM). CTR measurements differ from microscopy techniques in their inherent statistical nature, provided by a large illuminated sample area (in this case, about 20 × 30 µm2). This allows the identification of coexistence of surface structures, yielding the fraction of the surface terminated in each phase or constituent subunit for a lamellar sample. The technique also make possible to illuminate single-crystalline domain such as exfoliated flakes with lateral sizes of tens of micrometers (usual sample size for two-dimensional materials). Our model was initially tested on binary materials such as In2Se3 and Sb4Te3, and was later extended to mineral-derived phyllosilicates. Finally, the main focus of the study was on three phyllosilicates with different compositions: talc, phlogopite, and clinochlore. In these three materials, different water absorption mechanisms are responsible for distinct behaviors observed in infrared spectroscopy. The CTR measurements and analyses carried out in these minerals allow for the generation of structural models that describe and complement the results for surface potentials observed by KPFM and infrared, constructing a comprehensive scenario for understanding their potential use on forthcoming applications.