Structural investigations of pulsed laser-deposited NiO epitaxial layers under different fluence values

The epitaxial NiO layers deposited with higher fluence values are found to be strained, and the strain increases with the fluence values. The X-ray diffraction (XRD) profile taken from the synchrotron beam shows the presence of relaxed grains of NiO in addition to the strained grains, where the fraction of relaxed grains gradually increases with the fluence values. The presence of Pendellosung fringes in the XRD profile for the layers deposited at lower fluence values confirms good interfacial and crystalline qualities. As the fluence value is increased, the Pendellosung fringes start merging indicating relatively poor interfacial and crystalline qualities. The NiO layers are of epitaxial nature and grown along [111] direction with two domain structures that are in-plane rotated by 60° with respect to each other. The analysis of local structures from extended X-ray absorption fine structure measurements also indicates that the NiO lattice is strained at higher fluence values. The Ni–O bond distance does not change with the fluence values; however, Ni–Ni bond distance increases with the fluence values in corroboration with XRD results. The surface topography shows island growth of NiO at lower fluence values giving larger roughness, and these islands start merging with an increase in the fluence values leading to relatively smoother layers.