This is a copy of the slides presented at the meeting but not formally written up for the volume.

The physical properties of thin films exhibit remarkable quantum size effects due to the discrete quantum well (QW) states that are caused by electron confinement. Measurements of the elastically reflected electrons from thin films often reveal intensity peaks at very low energy that are associated with QW resonances above the vacuum level. In direct correspondence with the binding energies of QW states below vacuum, the energies of QW resonances are very sensitive to film thickness. This talk will focus on the three-dimensional view of thin film growth and nanostructure that is obtained from highly laterally resolved measurements of QW resonances in low energy electron microscopy. Details of the buried interface and strained layer spacings in coherently strained Ag films on the W(110) surface are determined accurately by dynamical theory analysis of the intensity peaks associated with QW resonances. Information on unoccupied band structure is also obtained from a phase accumulation model analysis of QW resonances in Ag films on the Fe(100) surface. The surface morphology of these films during growth at high temperature is found to be governed by minima in the global energy landscape that are defined by QW states at the gamma-bar point. Novel growth morphologies are also observed at lower temperature that highlight the competition between kinetic limitations and QW state energetics.