Freestanding Silver-Doped Zinc Oxide 2D Crystals Synthesized by a Surface Energy-Controlled Hydrothermal Strategy

Two-dimensional transition metal oxides (2DTMOs) are in great demand for electronic gadgets and sensing devices due to their flexibility, structural immunity, and economic cost. Silver-doped 2DTMOs have suitable candidature for wavelength-selective photoresistive switching; therefore, band-gap engineering in 2DTMOs via silver doping is crucial. We report our discovery via hydrothermal synthesis of Ag-doped 2D ZnO (AZO) using an equimolar concentration of zinc nitrate (Zn(NO3)(2)center dot 6H(2)O) and silver nitrate (AgNO3) as precursors and hexamethylenetetramine (HMTA) as a reducing agent, which helps to optimize surface energy for 2D crystal growth. Monolayers and a few-layered atomically thin AZO sheets up to 3 mu m lateral dimensions are formed, as evidenced from atomic force microscopy line profiling. High-resolution electron imaging suggests the emergence of hexagonal (six-fold), square lattice (four-fold), and numerous other strain-mediated crystallographic phases of AZO. X-ray photoelectron spectroscopy demonstrates tunable (up to similar to 20%) Ag doping resulting in midgaps opening at 1.8 and 2.8 eV. Apart from the successful demonstration of the synthesis of 2D AZO atomic sheets and their thorough characterizations, unique electronic, optical, optoelectronic, photoluminescence, and ferromagnetic behavior paves the way for future generations of emergent devices and sensors.