The state of the art in the oxide thin film technology allows layer-by-layer growth of ultrathin films and heterostructures with controls to the atomic level. Such never-before-available capability of nanoengineering leads to possibilities in new physics, new devices, as well as new designer materials which do not exist in the bulk form. In this talk, I will present two examples from the research at Temple University to illustrate this point. The first example is the effect of strain relaxation on the 2D electron gas at the LaAlO3/SrTiO3 interface. Direct measurement of the in-plane lattice constants of LaAlO3 films on SrTiO3 with thickness as thin as 4 unit cells using grazing incident x-ray diffraction (GIXRD) showed two layers in the LaAlO3 films: one thin layer remains almost coherently strained to the SrTiO3 substrate and the other starts to relax above a critical thickness, when a two orders of magnitude drop of sheet resistance was observed. It shows a clear correlation between the strain state and the conductivity of the 2DEG at the LaAlO3/SrTiO3 interface. The second example is the atomic layer-by-layer growth of homoepitaxial SrTiO3 films by Laser MBE. By performing Laser MBE from separate SrO and TiO2 targets, we have grown Sr1+xTiO3 films with -0.2 ≤ x ≤ 0.2 by controlling the numbers of pulses on each target. X-ray diffraction spectra show the same lattice constant in the stoichiometric SrTiO3 film as in the SrTiO3 substrate, while both strontium-rich and strontium-poor Sr1+xTiO3 films show lattice expansion. We can conclude that Laser MBE in the atomic layer-by-layer deposition mode has the same capability of precise controls of growth at the atomic layer level and film stoichiometry as the Reactive MBE.