Morphological, structural, electrical, and piezoelectric analysis of hydrothermally grown ZnO nanowires on various substrates

In this present work, we have successfully fabricated a piezoelectric structure based on ZnO nanowires (ZnO NWs) using a simple, low cost and environmentally friendly hydrothermal method. This structure forms the basis to fabricate vertically integrated nanogenerator device. This paper attempts to study the effect of several parameters such as the seed layer morphology, seed layer roughness, seed layer annealing temperature, growth temperature, and growth time on three different substrates, which are silicon substrate with a gold & platinum film as lower metal contact, and stainless steel. The structure and morphology of the seed layer and the as obtained nanowires were characterized using scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), and X-ray diffraction (XRD). SEM analysis shows that the non-aqueous seed solution must be stirred to avoid the formation of the two phases (milky and translucid) and thus the formation of ZnO particles with different sizes and morphologies. In addition, the annealing temperature influences the diameter of the ZnO seed layer and thus ZnO nanowires diameter. This work also shows that the length of the nanowires increases with the growth duration without affecting ZnO diameter (70 & PLUSMN; 30 nm). HRTEM and XRD studies show the high crystalline quality of the one-dimensional nanomaterials deposited on stainless steel and confirm their high density along the c-axis direction. In this paper, we have also investigated the electrical and piezoelectric performances of the structure obtained. Indeed, the I-V curves exhibit nonlinear and asymmetric electrical characteristics, which confirms the formation of Schottky contacts between the metal and ZnO NWs. According to the piezo-response force microscope, an effective piezoelectric coefficient d33 between 5 and 7 pm/V as a function of the substrate was measured.