My first thanks and praise go to God, the almighty, who has provided me with strength and encouragement in all the challenging moments of this work. Then I would like to take this opportunity to express my gratitude to the people who have always been there for me and who have influenced my life in so many ways.First and foremost, I am deeply indebted to my doctoral advisor Prof. Dr. Alain André Quivy. To him, I extend my sincere gratitude for all his support, encouragement, guidance, help, and especially his patience and advices over the past seven years since I have been under his supervision as a master's student.I am also deeply indebted to Prof. Paul Simmonds and his group at Boise State University, especially Kevin Vallejo and Katie Sautter, for their efforts in growing some samples included in this thesis. I thank you for the financial support you provided for growing and shipping the samples at your own expense.My special thanks to Prof. Paul Koenraad and Dr. Raja Gajjela of the Eindhoven University for performing X-STM measurements on the samples of this thesis.In addition, I would like to thank Prof. Christoph Deneke and Ailton Garcia for their assistance in training me for using the MBE system at the Brazilian Nanotechnology National Laboratory (LNNano). A special thanks should be given to Dr. Jefferson Bettini, from LNNano, who measured one sample shown in this thesis by transmission electron microscopy (TEM). I am extremely grateful to all the members of the MBE group at LNMS,