Study of NiO-NiMn₂O₄-Patterned Surfaces Fabricated by a Vapor-Solid Process

Nickel manganite (NiMn2O4) samples synthesized by a vapor-solid method at temperatures in the range of 1000-1400 degree celsius are studied in this work. The stability and properties of this ternary compound together with the presence of NiO in the form of p-n heterostructures have been analyzed by means of diverse electron microscopy and spectroscopy techniques. The formation of the ternary compound with improved crystallinity is promoted as the temperature of the synthesis is increased. Moreover, the samples synthesized at higher temperatures exhibit the growth of microcrystals with micro- and nanoislands on top of their lateral surfaces, leading to patterned surfaces with variable Ni and Mn composition. The combination of Raman spectroscopy, including wavenumber-filtered images, and electron backscattered diffraction confirms that most of these micro- and nanoislands consist of NiMn2O4 grown on top of NiO surfaces. X-Ray photoelectron spectroscopy and microscopy at synchrotron facilities confirm the presence of nickel manganite nanoislands covering the surface of NiO surfaces. Aspects such as the growth mechanisms, nickel manganite vibrational modes, and inversion factor of NiMn2O4 have been discussed in this work.