Fractal characteristics of TiO2-Ag nanocomposite films deposited by a grid-assisted co-sputtering method

Zamani-Meymian, Mohammad-Reza; Abdolvahab, Rouhollah Haji; Mehr, Ali Kosari

doi:10.1016/j.apsusc.2019.03.026

Cited by 17 publications

(7 citation statements)

References 29 publications

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“…Peak F at ∼4.0 eV has been identified as the direct optical band gap ( E g ′ ) at the L-valley. , Figure c,d shows Tauc plots to determine direct and indirect ( E g ) for x = 0.0, 0.01, 0.05, and 0.10. In the Tauc method, , absorption is associated with the band edge such that [ F ( R ∞ )ℏω] n ∝ (ℏω – E g ′ ), where ℏ is the reduced Planck constant, ω is the optical frequency, and the exponent is set as n = 2 or 1/2 for direct or indirect transitions, respectively. , From the measurements, the fundamental gap corresponding to the indirect F –Γ transition is ∼3.8 eV, and the direct optical gap ( E g ′ ) corresponding to the L-valley transition is ∼3.2 eV. Both values are consistent with the calculated range of fundamental and optical band gaps, E g and E g ′ , respectively.…”

Section: Resultsmentioning

confidence: 99%

Identification of a Fe-Dependent Optical Mode in CuAl_1–xFe_xO₂

et al. 2021

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Delafossites are promising candidates for photocatalysis applications because of their chemical stability and absorption in the solar region of the electromagnetic spectrum. For example, CuAlO2 has good chemical stability but has a large indirect band gap, so that efforts to improve its absorption in the solar region through alloying are investigated. The effect of dilute alloying on the optical absorption of powdered CuAl1–x Fe x O2 (x = 0.0–1.0) is measured and compared to electronic band structures calculations using a generalized gradient approximation with Hubbard parameter and spin. A new absorption feature is observed at 1.8 eV for x = 0.01, which red-shifts to 1.4 eV for x = 0.10. This feature is associated with transitions from the L-point valence band maximum to the Fe-3d state that appears below the conduction band of the spin-down band structure. The feature increases the optical absorption below the band gap of pure CuAlO2, making dilute CuAl1–x Fe x O2 alloys better suited for solar photocatalysis.

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Section: Resultsmentioning

confidence: 99%

Identification of a Fe-Dependent Optical Mode in CuAl_1–xFe_xO₂

et al. 2021

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“…Delafossites (AMO 2 with A: Cu or Ag; M: Al, Ga, La, Fe, or Cr) are one of a number of families of less-studied complex oxides with many attractive properties. − In particular, CuAlO 2 is a p -type wide-band-gap compound, an attractive candidate for transparent conductive oxide applications. − For CuAlO 2 thin films, the reported indirect and direct allowed optical band gaps are 1.8 and 3.5 eV, respectively. , It has been suggested that doping CuAlO 2 with transition metal ions, such as Fe, Mn, Ni, etc., may modify the indirect band gap, which is otherwise forbidden due to symmetry considerations . CuAlO 2 has an indirect fundamental band gap, which is due to phonon-assisted optical transitions.…”

Section: Introductionmentioning

confidence: 99%

Phonon Dynamics in Anisotropic Dilute CuAl_1–xFe_xO₂ Delafossite Alloys by a Weighted Dynamical Matrix Approach

et al. 2019

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Here we report a new versatile approach for the calculation of phonon modes which is applicable to anisotropic, dilute alloys with allowance for a large variety of alloying elements. This approach has significant advantages over previously reported methods, especially for the lattice dynamics of such complex alloys. We use this approach to model the effects of Fe-doping on the vibrational modes in dilute alloys of CuAl 1−x Fe x O 2 (x = 0, 0.01, 0.05, and 0.10) delafossite powders. These samples were structurally characterized with X-ray diffraction (XRD) combined with Rietveld refinement to measure their lattice parameters and Raman and FTIR spectroscopies to measure optical phonon frequencies. To compare experimental results from XRD with calculations for lattice parameters, we use a disordered supercell for x in the range 0−0.1. Both results agree well with Vegard's law. For the phonon calculations, an approach using a disordered supercell is not feasible because it is too computationally expensive. Instead, we developed our weighted dynamical matrix (WDM) approach that uses a straightforward ordered supercell for forceconstant calculations of the CuAlO 2 and CuFeO 2 parent end points, and combines them using a WDM approach leading to an effective medium for vibrational mode calculation in random alloys. Computationally, when Fe is substituted for Al (increasing x), an increase in the bond length is observed leading to a red-shift in the peak positions in all of the phonon modes vs x, in agreement with the experimentally observed trend.

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“…From a theoretical point of view, research into the roughness of empirically prepared layers with the help of data obtained from AFM is an interesting topic. In this case, Abdolvahab et al recently showed that silver thin films are characterised by using roughness and multifractal analysis even in small thicknesses of the order of tens of nanometres [10,11].…”

Section: Introductionmentioning

confidence: 99%

“…In this case, Abdolvahab et al. recently showed that silver thin films are characterised by using roughness and multifractal analysis even in small thicknesses of the order of tens of nanometres [10, 11].…”

Section: Introductionmentioning

confidence: 99%

Fractality and roughness of the ZnO:Cu composite thin films annealed in different temperatures

Abdolvahab

Zamani-Meymian

Saravi

et al. 2019

Surface Engineering

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In this study, we co-sputtered zinc dioxide and copper in order to manufacture a composite thin film. We then used atomic force microscopy (AFM), scanning electron microscopy and energydispersive X-ray spectroscopy to investigate the surface morphology of samples. We annealed four samples to temperatures 100 • C,200 • C,400 • C and 800 • C for 90 minutes. Afterwards, we employed height distribution, roughness, permutation entropy(PE) and fractality of the height data from AFM to analyse samples theoretically. Our results reveal that although the roughness will increase by temperature and the multifractal spectrum widens by it; the PE does not change both from 100 • C to 200 • C and from 400 • C to 800 • C. Both PE and height distribution are changing meaningfully only in increasing the temperature from 200 • C to 400 • C.

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Fractal characteristics of TiO2-Ag nanocomposite films deposited by a grid-assisted co-sputtering method

Cited by 17 publications

References 29 publications

Identification of a Fe-Dependent Optical Mode in CuAl_1–xFe_xO₂

Identification of a Fe-Dependent Optical Mode in CuAl_1–xFe_xO₂

Phonon Dynamics in Anisotropic Dilute CuAl_1–xFe_xO₂ Delafossite Alloys by a Weighted Dynamical Matrix Approach

Fractality and roughness of the ZnO:Cu composite thin films annealed in different temperatures

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Fractal characteristics of TiO2-Ag nanocomposite films deposited by a grid-assisted co-sputtering method

Cited by 17 publications

References 29 publications

Identification of a Fe-Dependent Optical Mode in CuAl1–xFexO2

Identification of a Fe-Dependent Optical Mode in CuAl1–xFexO2

Phonon Dynamics in Anisotropic Dilute CuAl1–xFexO2 Delafossite Alloys by a Weighted Dynamical Matrix Approach

Fractality and roughness of the ZnO:Cu composite thin films annealed in different temperatures

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Identification of a Fe-Dependent Optical Mode in CuAl_1–xFe_xO₂

Identification of a Fe-Dependent Optical Mode in CuAl_1–xFe_xO₂

Phonon Dynamics in Anisotropic Dilute CuAl_1–xFe_xO₂ Delafossite Alloys by a Weighted Dynamical Matrix Approach