Layer matching epitaxy of NiO thin films on atomically stepped sapphire (0001) substrates

Yamauchi, Ryosuke; Hamasaki, Yosuke; Shibuya, Takuto; Saitô, Akira; Tsuchimine, Nobuo; Koyama, Koji; Matsuda, Akifumi; Yoshimoto, Mamoru

doi:10.1038/srep14385

Cited by 26 publications

(21 citation statements)

References 24 publications

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“…7 Preparation of atomically bistepped (step heigth 0.433 nm) c-plane Al 2 O 3 surfaces by annealing prior to growth has been shown to prevent the formation of rotational domains, enabling the growth of single crystalline NiO(111) films thereon as demonstrated by pulsed laser deposition. 51 AFM images of our films showed a surface composed of grains with larger size for higher temperatures or lower activated oxygen flux, indicating an increasing surface diffusion length. Together with the Raman-derived quality metrics a correlation between a high layer quality and a high surface diffusion length is found.…”

Section: Discussionmentioning

confidence: 79%

Structural, optical, and electrical properties of unintentionally doped NiO layers grown on MgO by plasma-assisted molecular beam epitaxy

Budde

Tschammer

Franz

et al. 2018

Journal of Applied Physics

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NiO layers were grown on MgO(100), MgO(110) and MgO(111) substrates by plasma-assisted molecular beam epitaxy under Ni-flux limited growth conditions. Single crystalline growth with a cube-on-cube epitaxial relationship was confirmed by X-ray diffraction measurements for all used growth conditions and substrates except MgO(111). A detailed growth series on MgO(100) was prepared using substrate temperatures ranging from 20°C to 900°C to investigate the influence on the layer characteristics. Energy-dispersive X-ray spectroscopy indicated close-to-stoichiometric layers with an oxygen content of ≈ 47 at.% and ≈ 50 at.% grown under low and high O-flux, respectively. All NiO layers had a root-mean-square surface roughness below 1 nm, measured by atomic force microscopy, except for rougher layers grown at 900°C or using molecular oxygen. Growth at 900°C led to a significant diffusion of Mg from the substrate into the film. The relative intensity of the quasi-forbidden one-phonon Raman peak is introduced as a gauge of the crystal quality, indicating the highest layer quality for growth at low oxygen fluxes and high growth temperature, likely due to the resulting high adatom diffusion length during growth. Optical and electrical properties were investigated by spectroscopic ellipsometry and resistance measurements, respectively. All NiO layers were transparent with an optical band gap around 3.6 eV and semi-insulating at room temperature. However, changes upon exposure to reducing or oxidizing gases of the resistance of a representative layer at elevated temperature was able to confirm p-type conductivity, highlighting their suitability as a model system for research on oxide-based gas sensing.

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Section: Discussionmentioning

confidence: 79%

Structural, optical, and electrical properties of unintentionally doped NiO layers grown on MgO by plasma-assisted molecular beam epitaxy

Budde

Tschammer

Franz

et al. 2018

Journal of Applied Physics

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“…The φ scan of the Mg x Ni 1−x O (111) plane shows sixfold symmetry rather than the conventional threefold symmetry of the bulk. This has occurred because of the coexistence of two types of mirror-symmetrical atomic planes in the sapphire substrate, in accordance with the 2.2Å step height in the sapphire [0001] direction [23].…”

Section: A Lattice Distortionmentioning

confidence: 79%

“…After deposition, the obtained thin films were annealed by rapid thermal annealing in air at a heating rate of 20 K/s up to 1373 K for 60 s and were subsequently quenched to room temperature. The preparation process for layer matching epitaxial growth was similar to that for the NiO thin films that were fabricated in previous work [23]. The Mg x Ni 1−x O epitaxial thin films were then scanned by dynamic force microscopy (Hitachi NanoNaviReals/Nanocute).…”

Section: Experimental Methodsmentioning

confidence: 99%

“…The 111 and 111 reciprocal lattice spots that were obtained were then used to estimate the corresponding d spacings. )] [23], which gave values of 7.3%, 7.7%, and 7.9% for Mg x Ni 1−x O with x = 0, 0.32, and 0.52, respectively. All these values were positive, indicating that in-plane compressed stress is present at the interface, which leads to the higher d film 111 and lower d film 111 .…”

Section: A Lattice Distortionmentioning

confidence: 99%

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Lattice distortion and electronic structure of magnesium-doped nickel oxide epitaxial thin films

et al. 2017

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Magnesium-doped nickel oxide (Mg x Ni 1−x O) thin films are transparent over a wide ultraviolet-visible spectral range and over a wide Mg content range. However, the influence of the Mg dopant on the structure and properties of NiO films is poorly understood. In this work, the lattice distortion and the electronic structure of Mg x Ni 1−x O (0 x 0.52) thin films deposited on ultrasmooth sapphire substrates were investigated using synchrotron x rays. Films with higher Mg content had lower values of Debye temperature and atomic order parameter. The nearest Ni-O distance and the in-plane nearest Ni-Ni distance both expanded with increasing Mg content. The Ni 2p core-level spectra and the valence band spectra of the Mg x Ni 1−x O thin films showed complex multiplet structures that were caused by the strong electron correlation in the Ni 3d states, where the spectral features are strongly dependent on both the distortion of the NiO 6 octahedra and the Mg content. We found that the electronic structures are mainly a result of hybridization of Ni 3d and O 2p in the NiO 6 octahedra and the reduction of the Zhang-Rice bound state following Mg doping. Finally, the flexibility of the band gap tuning in Mg x Ni 1−x O thin films is explained.

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“…However, this method applies high-energy pulses which may cause undesirable defects in the structure, and thereby change the electronic behavior of the films. PLD has been used to deposit various binary compounds [32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47].…”

Section: Introductionmentioning

confidence: 99%

Pulsed Laser Deposition of Rocksalt Magnetic Binary Oxides

et al. 2019

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Magnetic binary oxides with the rocksalt structure constitute an important class of materials for potential applications as electronic or electrochemical devices. Moreover, they often become a theoretical playground, due to the simple electronic and crystal structures, in the quest for novel phenomena. For these possibilities to be realized, a necessary prerequisite would be to grow atomically ordered and controllably-strained binary oxides on proper substrates. Here we systematically explore the use of pulsed laser deposition technique (PLD) to grow three basic oxides that have rocksalt structure but different chemical stability in the ambient atmosphere: NiO (stable), MnO (metastable) and EuO (unstable). By tuning laser fluence FL, an epitaxial single-phase NiO thin-film growth can be achieved in a wide range of growth temperatures 10 ≤ TG ≤ 750 °C. At the lowest TG, the out-of-plane strain raises to 1.5%, which is five times higher than in NiO film grown at 750 °C. MnO thin films that had long-range order were successfully deposited on the MgO substrates after appropriate tuning of deposition parameters. The growth of MnO phase was strongly influenced by FL and the TG. EuO films with satisfactory quality were deposited by PLD after oxygen availability had been minimized. Synthesis of EuO thin films at rather low TG = 350 °C prevented thermally-driven lattice relaxation and allowed growth of strained films. Overall, PLD was a quick and reliable method to grow binary oxides with rocksalt structure in high quality that can satisfy requirements for applications and for basic research.Thin-film deposition is a technique that can be used to control strain in materials [22]. The Curie temperature TC of EuO thin film is strongly dependent on the strain and on film thickness tF [23]. Dislocations in NiO thin films locally change the magnetic ordering from antiferromagnetic to ferromagnetic [24]. Such 'ferromagnetic' dislocations originate from a local non-stoichiometry at in dislocation cores where Ni is deficient. A slight deviation from the stoichiometry also changes the conduction behavior in NiO thin films. Oxygendeficient EuO shows metallic behavior with a substantial increase of the TC to 120 K [25]. The deposition of high-quality magnetic binary oxides, and the ability to control the level of strain and density of defects in their structure, are challenging tasks in materials science and solid-state physics.Pulsed-laser deposition technique (PLD) has many advantages for growing thin films of high-quality oxides [26][27][28][29][30][31]. PLD can preserve the stoichiometry of the film composition,

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Layer matching epitaxy of NiO thin films on atomically stepped sapphire (0001) substrates

Cited by 26 publications

References 24 publications

Structural, optical, and electrical properties of unintentionally doped NiO layers grown on MgO by plasma-assisted molecular beam epitaxy

Structural, optical, and electrical properties of unintentionally doped NiO layers grown on MgO by plasma-assisted molecular beam epitaxy

Lattice distortion and electronic structure of magnesium-doped nickel oxide epitaxial thin films

Pulsed Laser Deposition of Rocksalt Magnetic Binary Oxides

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