Espalhamento ressonante de raios X aplicado ao estudo de nano-estruturas

Abstract

In this thesis, resonant X-ray scattering techniques were used to study two different systems. First, grazing incidence difraction associated with dispersion corrections in the atomic scattering factor were employed to probe the chemical concentration profile in self-assembled islands of InP epitaxially grown on GaAs(001). The strain relaxation and substrate atoms diffusion were determined for three samples grown at different temperatures. Concentration maps in real space were obtained for two samples and showed high gallium interdiffusion in the islands grown at high temperature, indicating a high indium desorption rate.Next, magnetic resonant scattering in the non-specular reflectivity geometry was used to study the magnetic behavior of a thin MnAs film grown epitaxially on GaAs(001). Coexistence of the ferromagnetic and the paramagnetic phases was studied as function of temperature. The influence of temperature on the magnetic configuration on the MnAs was also addressed, and it was found that magnetic domain reconfiguration occurs at higher temperatures, within the MnAs ferromagnetic phase. This behavior is explained by the minimization of the energy term associated with the MnAs demagnetizing field. Finally, we took advantage of the chemical selectivity of resonant magnetic scattering to study separately a magnetic double layer composed of a MnAs film covered with a thin iron cap. Within a certain temperature range, the magnetic moments on the Fe layer align anti-parallel to the MnAs moments as well as to the applied external magnetic field. This anti-parallel ordering is also associated to the demagnetizing field of the MnAs layer, which varies within the phase coexistence range, due to the variable ferromagnetic phase width.