This proposal will use novel in-situ metrology to probe the atomic level mechanisms that govern the growth and device behaviour of nanomaterials in realistic process environments. We focus on the catalytic chemical vapour deposition of carbon nanotubes, graphene, Si/Ge nanowires and related heterostructures. The application potential for these nanostructures is large, but currently limited by insufficient control of growth. We propose to use a range of complementary in-situ probes, including environmental transmission electron microscopy, high-pressure X-ray photoelectron spectroscopy (XPS), in-situ X-ray diffraction (XRD) and in-situ Raman spectroscopy, to significantly advance the understanding of their growth mechanisms. We see these nanomaterials as model systems to advance the fundamental understanding of phase behaviour, nucleation and interface dynamics in nanoscale systems, which is the key to future materials design. Deeper insights into these phenomena are also crucial to understand the behaviour of nanomaterials under device operation conditions. We propose to address critical performance parameters of nano-structured Si-based anodes for Li ion batteries by in-situ nuclear magnetic resonance (NMR) spectroscopy and in-situ XRD methods under repeated Li cycling in an operational battery. We further propose to study the morphological origins of the collective adhesive and mechanical properties of carbon nanotube forests by in-situ scanning electron microscopy as basis for the design of biomimetic, functional dry adhesives and compliant interconnect structures.