A variety of nanowires can be grown in a tube furnace via the transport of evaporated species by a carrier gas toward substrates. The insufficient understanding and the resulting limited control typical for this research area motivated us to systematically study the distribution of the growth species in such processes and evaluate its effect on the nanowire growth. Calculations based on simple considerations as well as more sophisticated numerical (COMSOL) simulations were utilized to follow the time evolution of the species distribution at different carrier gas pressures and flow rates. We demonstrate that the balance between diffusion and convection must be appropriately tuned to ensure steady growth conditions (not achieved in many of the previously reported experiments). Experimental data of Si and ZnO nanowires growth is presented and supports the simulations. Insight into the appropriate design of nanowires growth experiments and a universal basis to compare between the results of different laboratories are provided.

ZnO nanowires (NWs) growth is commonly performed by heating a ZnO:C powder applying the carbothermal reactions ZnO s + C s → Zn v + CO g ; ZnO s + CO g → Zn v + CO 2g . A carrier gas transfers the evaporated Zn species to the growth region where they are oxidized and NWs form. This work explores the role of different gases (O 2 , CO 2 , H 2 ), introduced to Ar in different concentrations in the carbothermal growth of ZnO NWs. Scanning electron microscopy (SEM) is used to study the grown NWs. Residual gas analysis (RGA) is employed to monitor the gaseous species during growth. Insight into the physical chemical processes involved both in the source and in the growth regions is obtained. This deep understanding of the processes enables optimization of reactive gas concentration, flow, and type achieving homogeneous NW growth over large areas as requested for industrial applications.

A unique approach of ZnO nanowire growth mediated via reduction of ZnO by H2 is presented. It is less complex and more controllable than the conventional carbothermal method (reduction of ZnO by C). The chemical vapor deposition system employed allows precise control of all deposition parameters: (1) source and substrate temperatures, (2) carrier gas compositions, flow and pressure of several gases, (3) growth along a large range of distances from the source. In situ residual gas analysis allows real-time feedback of the process reactions. Controlled, stabilized, homogenous growth (characterized by scanning electron microscopy and x-ray diffraction) over relatively large areas is demonstrated.