Influence of the vertical alignment of nanowires on the quality of printed electronic layers

Contact printed intrinsically flexible inorganic nanomaterials such Si and ZnO nanowires (NWs) have shown great promise for the development of high-performance flexible electronics. In this paper, we study the effect of the vertical alignment in ZnO NWs on the quality (printed NW’s density, and directional alignment) of contact printed nanoscale thick electronic layers over large area. By changing the epitaxial relation of ZnO NWs with the growth substrates, we tune the growth alignment of NWs. The ZnO NWs were grown using bottom-up Vapor Phase Transport (VPT) method on two different substrates: (i) cubic (100) oriented silicon and (ii) hexagonal (0001) c-axis oriented sapphire. The scanning electron microscopy (SEM) images (from an area ~100 mm2) show that the majority of grown ZnO NWs on sapphire substrate are vertically aligned as compared with the NWs on silicon. Further, by detailed SEM image analysis, we show that aligned, or partially aligned NWs required additional shear force (from sliding) for the directional alignment of NWs forming the electronic layer (printed samples from both donors showed 93% of aligned NWs with sliding). We further show that the printed NWs from sapphire substrate exhibit superior density as compared with the NWs grown on silicon. These results show the significance of suitable vertically aligned NWs for the high-density NWs based printed electronic layers and hence the high-performance flexible and printed electronics.