Role of aluminum and HMTA in the hydrothermal synthesis of two-dimensional n-doped ZnO nanosheets

This work reports the study of the processes behind the growth of two-dimensional (2D) n-doped ZnO nanostructures on an AlN layer. We have demonstrated that AlN undergoes a slow dissociation process due to the basic controlled environment promoted by the hexamethylenetetramine (HMTA). The Al(OH) ₄ ^- ions created inhibits the growth along the c-axis, effectively promoting the fast formation of a planar geometry selectively grown on top of the AlN layer. With the use of this promoting layer and a standard hydrothermal method, a selective area growth is observed with micrometric resolution. In addition, by using several advanced characterization techniques such as, X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS/EDX), X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL), we observed a resulting doping with aluminum of the ZnO nanostructures, occupying substitutional and interstitial sites, that could lead to new promising applications. These high-quality n-doped ZnO nanosheets (NSs) exhibit strong ultraviolet emission in the 385–405 nm region without broad deep level emission. The piezoelectric nature of these nanostructures has been demonstrated by using piezoresponse atomic force microscope (PFM) and with the support of a piezoelectric test device. Therefore, this low-cost and fast selective-area synthesis of 2D n-doped ZnO NSs can be applicable to other aluminum based materials and paves the way to new promising applications, such as bioelectronic applications, energy generation or self-powered sensing.