This thesis describes research performed on two types of complex oxide heterostructures. The first consists of ultrathin LaAlO3 films grown on SrTiO3 substrates. At the interface between these two insulating oxides, a quasi two dimensional electron gas may form under proper conditions. This interface has remarkable properties such as interfacial superconductivity, interfacial magnetism and a hysteretic voltage-controlled metal-insulator transition. We developed an Atomic Force Microscope (AFM) lithography technique which is capable of switching reversibly at room temperature this metal-insulator transition with nanometer scale spatial resolution. Based on this technique, conducting nanowires as thin as 2 nm and nanodots array with density up to 1014 inch-2 were written, probed and erased. Sketch-defined field effect transistors (SketchFET) with channel lengths as short as 2 nm were fabricated. These structures were characterized over a temperature range 15 K-300 K, revealing a complex energy landscape. Magnetotransport measurements performed at temperatures at and below 1 K reveal a variety of intriguing quantum phenomena, including integer and fractional quantum Hall states. The second material system consists of thin films of SrTiO3 grown directly on silicon. Although SrTiO3 is not ferroelectric at any temperature in bulk form, when strained to the silicon lattice it can become ferroelectric at and above room temperature. Temperature-dependent piezo force microscopy was performed to verify that those strain engineered films with certain thickness are indeed ferroelectric. Ultrafast optical experiments were carried out to measure lattice dynamics in these strained films. A coherent acoustic phonon mode was observed and studied as a function of film thickness and laser polarization. Using SrTiO3 grown on silicon-on-insulator structures, ferroelectric field effect transistors (FeFET) were fabricated and characterized at room temperature
