Controlling the Structural Properties of Single Step, Dip Coated ZnO Seed Layers for Growing Perfectly Aligned Nanowire Arrays

Abstract

International audienceMastering the structural ordering of ZnO seed layers by sol–gel process in terms of ultrathin thickness (i.e, <10 nm), strong c-axis texture, low mosaicity, low porosity, and low roughness is a critical challenge for the formation of well-ordered ZnO nanowires in solution. The effects of the solution concentration, of the withdrawal speed, and of the annealing process on the formation mechanisms of ZnO seed layers deposited by single dip process are revealed. The size and density of primary clusters in the sol are found to govern the evolution of the film thickness and nanoparticle average diameter through the solution concentration. The Landau–Levich theory modeling the dragging process accounts for the evolution of the film thickness only before annealing and over a reduced range of withdrawal speeds. The texture mechanisms along the c-axis are driven by particle/particle interactions during annealing and explained in the light of thermodynamic considerations. They are further determined locally by electron backscattered diffraction. Importantly, an alternative annealing process under argon flux is specifically developed for sol–gel process and is shown to form remarkably well-textured, compact ZnO seed layers with a very low mosaicity and porosity as well as a thin thickness as small as 10 nm. These ZnO seed layers lead to the growth of well-ordered ZnO nanowires by chemical bath deposition with a remarkable mean tilt angle smaller than 6° as deduced by X-ray pole figures. These findings represent a significant step toward the more efficient integration of ZnO seed layers grown by sol–gel process into ZnO nanowire-based devices

ZnO/CuCrO2 Core–Shell Nanowire Heterostructures for Self‐Powered UV Photodetectors with Fast Response

“…A two‐step heat treatment was subsequently performed at 300 °C for 10 min and at 500 °C for 1 h. The CBD of ZnO NWs was achieved on the ZnO seed layer/ITO/glass substrate by using a 30 × 10 −3 m equimolar solution of zinc nitrate hexahydrate (Zn(NO 3 ) 2 ·6H 2 O, Sigma Aldrich) and hexamethylenetetramine (C 6 H 12 N 4 , Sigma Aldrich), which were dissolved and mixed in deionized water. The substrates were placed face down into a sealed beaker filled with the equimolar solution and heated at 90 °C for 3 h in a regular oven …”

Electrical and Optical Properties of Rectifying ZnO Homojunctions Fabricated by Wet Chemistry Methods

“…After annealing a compact seed layer formed by nanocrystals with the average size of 100 nm was obtained (Figure b). At the same time, the thickness of the seed layer was reduced by ≈30% due to evaporation and crystallization …”

“…The growth direction, the density, and the structural uniformity of the nanorods are strongly affected by the quality of the seed layer . Upright standing arrays of ZnO nanorods can be grown on sol‐gel seed layers with preferential orientation along the c‐axis . While there are plenty of reports on the structural properties of the seed layers prepared by sol‐gel methods, their electrical and optical properties are rarely addressed.…”

Highly Textured Seed Layers for the Growth of Vertically Oriented ZnO Nanorods

“…This allows for the deposition of the seed layer on virtually any substrate including textiles or plastics [22]. For the arrays of vertically oriented nanorods, the seed layer is required to have a strong c-axis texture, low mosaicity, porosity, and surface roughness [23].…”

“…The sol-gel process has become popular for the preparation of ZnO seed layers because it enables the control of the orientation of the crystallites [11,12,[23][24][25][26]. During the sol-gel process a zinc salt is transformed from a solution to a solid deposit by using a sol or a gel as an intermediate step at a low temperature.…”