Material physics aims to develop a predictive understanding of the properties and performance of materials. Accordingly, experimental and theoretical studies concern the question how atomic-scale processes control the overall material properties (structural, thermal, electronic, etc.). In this talk I discuss the dynamic of atomic processes in group IV semiconductors and silicate glasses. Radioactive and stable isotopes are utilized to investigate the dynamic of network forming and modifying components in mixed cation silicate glasses. Isotopically modulated semiconductors of silicon, germanium and its alloys are used for studying self-diffusion, the interference between self- and dopant diffusion and radiation enhanced diffusion processes. Apart from fundamental diffusion research, isotopically modulated semiconductors can be considered as a new class of material for thermoelectric applications. First investigations reveal a reduced thermal conductivity due to phonon-scattering at the isotope interfaces.