Oil costs the U.S. over a quarter-trillion dollars a year, of which about three-quarters of that expenditure is related to the transportation sector. Only about 12-13% of the available fuel energy moves the average personal vehicle, and since the average person is only ~5% of the total mass being moved, less than 1% of the fuel energy moves the driver. Replacing steel with ultralight and ultrastrong materials such as fiber-reinforced composites can enable production of lightweight vehicles to significantly improve fuel efficiencies and reduce emissions. However, the mechanical performance of fiber-reinforced composites is often limited by the material properties of the interphase that forms at the fiber-matrix interface. Current manufacturing processes for many fiber composites can generate disordered interphases at the micro/nano scale, hindering their performance. To address these limitations, atomically-precise manufacturing processes are needed to allow for specifically defined interfacial mechanical and chemical properties, which would enable tunable synthetic control of the interphase properties of composites. Furthermore, improved control of the surface architectures can also be achieved through hierarchical nanostructuring. Through a combination of ALD/MLD processes and hierarchical nanostructuring, our group is able to rationally design “artificial interphases” with controllable interfacial properties, paving the way for next-generation lightweight nanocomposite materials.