"Nanowires are a powerful and versatile platform for a broad range of applications. Among all semiconductors, the heavy-elements materials exhibit the highest electron mobilities, strongest spin-orbit coupling and best thermoelectric properties. Nonetheless, heavy-element nanowires have been unexplored. With this proposal we unite the unique advantages of design freedom of nanowires with the special properties of heavy-element semiconductors. We specifically reveal the potential of heavy-element nanowires in the areas of thermoelectrics, and topological insulators. Using our strong track record in this area, we will pioneer the synthesis of this new class of materials and study their intrinsic materials properties. Starting point are nanowires of InSb and PbTe grown using the vapor-liquid-solid mechanism. Our aims are 1) to obtain highest-possible electron mobilities for these bottom-up fabricated materials by investigating new materials combinations of different semiconductor classes to effectively passivate the nanowire surface and we will eliminate impurities; 2) to investigate and optimize thermoelectric properties by developing advanced superlattice and core/shell nanowire structures where electronic and phononic transport is decoupled; and 3) to fabricate high-quality planar nanowire networks, which enable four-point electronic transport measurements and allow precisely determining carrier concentration and mobility. Besides the fundamentally interesting materials science, the heavy-element nanowires will have major impact on the fields of renewable energy, new (quasi) particles and quantum information processing. Recently, the first signatures of Majorana fermions have been observed in our InSb nanowires. With the proposed nanowire networks the special properties of this recently discovered particle can be tested for the first time."