Abstract
Single-crystal nickel oxide (NiO) was grown, using epitaxial titanium nitride (TiN) as a preorienting interlayer, on both the lattice-matching substrate of magnesium oxide in the (100) surface orientation, MgO-(100), and a lattice-mismatched silicon (100) substrate, Si-(100), by high-temperature pulsed-laser deposition. To the best of the authors' knowledge, this is the first report of its kind in the literature. The high-temperature sputter-deposited TiN interlayer is crucial for forming a bottom contact for the implementation of a device, and as a lattice-matching layer for NiO and MgO. The structural, surface-related, and elemental properties of the as-grown NiO/TiN/MgO(100) and NiO/TiN/Si(100) samples were determined by high-resolution transmission electron microscopy (HRTEM), x-ray diffraction (XRD), thin-film x-ray diffraction, atomic force microscopy, and scanning transmission electron microscopy in conjunction with energy-dispersed x-ray spectroscopy. XRD rocking curve data confirmed that the NiO layers were single crystalline on both template substrates, and the structural quality of NiO/TiN on the lattice-matching MgO substrate surpassed that on the Si substrate. XRD phi -scan data confirmed the cube-on-cube stacking of NiO and TiN. An analysis of HRTEM fast Fourier transform (FFT) images further confirmed the single crystallinity of the NiO and TiN layers, while lattice mismatches at the NiO/TiN, TiN/MgO, and TiN/Si interfaces were examined using the FFT line profile measurements of HRTEM. The resulting thin film of single-crystalline NiO can be used as a transparent conducting electrode in group-III oxide and group-III nitride semiconductor devices, and in such electrochemical processes as solar hydrogen generation and nitrogen reduction reactions.