Optical and structural properties of NiMgO thin films formed by sol–gel spin coating

Boutwell, R. Casey; Wei, Ming; Scheurer, A.; Mares, Jeremy W.; Schoenfeld, Winston V.

doi:10.1016/j.tsf.2012.02.065

Cited by 27 publications

(14 citation statements)

References 17 publications

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“…5. The optical band gaps which have been determined in previous studies of Ni x Mg 1−x O thin films prepared by electron beam evaporation12, molecular beam epitaxy17, magnetron sputtering1418, pulsed laser deposition23 and sol-gel spin coating19 are included for comparison. In this work, the measured optical band gap of pure NiO is 3.7 eV and by alloying with MgO it increases linearly to 4.8 eV for Ni 0.12 Mg 0.88 O.…”

Section: Resultsmentioning

confidence: 99%

“…The Ni x Mg 1−x O band gap dependence has been determined by optical absorption spectra of epitaxial thin films on MgO substrates prepared by molecular beam epitaxy17, textured thin films on quartz substrates prepared by magnetron sputtering1418 and sol-gel spin coated thin films on quartz substrates19. Despite the large 7.8 eV MgO band gap, it has been observed that the Ni x Mg 1−x O band gap increases only marginally to 4.8 eV, even at a small NiO fraction of only 8 at.%.…”

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confidence: 99%

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Band gap bowing in NixMg1−xO

Niedermeier

Råsander

Rhode

et al. 2016

Sci Rep

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Epitaxial transparent oxide NixMg1−xO (0 ≤ x ≤ 1) thin films were grown on MgO(100) substrates by pulsed laser deposition. High-resolution synchrotron X-ray diffraction and high-resolution transmission electron microscopy analysis indicate that the thin films are compositionally and structurally homogeneous, forming a completely miscible solid solution. Nevertheless, the composition dependence of the NixMg1−xO optical band gap shows a strong non-parabolic bowing with a discontinuity at dilute NiO concentrations of x < 0.037. Density functional calculations of the NixMg1−xO band structure and the density of states demonstrate that deep Ni 3d levels are introduced into the MgO band gap, which significantly reduce the fundamental gap as confirmed by optical absorption spectra. These states broaden into a Ni 3d-derived conduction band for x > 0.074 and account for the anomalously large band gap narrowing in the NixMg1−xO solid solution system.

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Section: Resultsmentioning

confidence: 99%

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confidence: 99%

Band gap bowing in NixMg1−xO

Niedermeier

Råsander

Rhode

et al. 2016

Sci Rep

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“…32 Using the lattice constant vs. Mgcontent data of Ref. [32] a Mg concentration of x=46 % can be estimated using the lattice constant of 0.419 nm deduced from the 2θ peak position of S1-900. Thus, the measured (200) peak position shift indicates significant diffusion of Mg from the substrate into the layer acti- vated by the high growth temperature, which would also explain the missing XRR oscillations as diffusion leads to a smeared-out density profile at the substrate-film interface.…”

Section: A Growth Temperaturementioning

confidence: 99%

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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“…For example, lithium-doped nickel oxide Li x Ni 1−x O undergoes a phase transformation from cubic to a rhombohedral structure at x = 0.31; as a result, only lightly doped materials can be used in the devices described above [11,12]. However, previous studies indicated that the lattice tended to expand in polycrystalline Mg x Ni 1−x O thin films over a wide Mg dopant content range from x = 0 to x = 1 [13,14]. The effects of the Mg dopant in these polycrystalline thin films on the lattice parameters were on the preparation process used.…”

Section: Introductionmentioning

confidence: 99%

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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Optical and structural properties of NiMgO thin films formed by sol–gel spin coating

Cited by 27 publications

References 17 publications

Band gap bowing in NixMg1−xO

Band gap bowing in NixMg1−xO

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

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