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Structural, optical and vibrational properties of self-assembled Pbn+1(Ti1-x Fex)nO(3n+1)-δ Ruddlesden-Popper superstructures.

Doig KI, Peters JJ, Nawaz S, Walker D, Walker M, Lees MR, Beanland R, Sanchez AM, McConville CF, Palkar VR, Lloyd-Hughes J - Sci Rep (2015)

Bottom Line: No evidence of macroscopic ferromagnetism was found in SQUID magnetometry.The ultrafast optical response exhibited coherent magnon oscillations compatible with local magnetic order, and additionally was used to study photocarrier cooling on picosecond timescales.An optical gap smaller than that of BiFeO3 and long photocarrier lifetimes may make this system interesting as a ferroelectric photovoltaic.

View Article: PubMed Central - PubMed

Affiliation: University of Oxford, Department of Physics, Clarendon Laboratory, Parks Road, Oxford, OX1 3PU, United Kingdom.

ABSTRACT
Bulk crystals and thin films of PbTi(1-x)FexO3(-δ) (PTFO) are multiferroic, exhibiting ferroelectricity and ferromagnetism at room temperature. Here we report that the Ruddlesden-Popper phase Pbn+1(Ti(1-x)Fex)nO3(n+1)-δ forms spontaneously during pulsed laser deposition of PTFO on LaAlO3 substrates. High-resolution transmission electron microscopy, x-ray diffraction and x-ray photoemission spectroscopy were utilised to perform a structural and compositional analysis, demonstrating that n ≃ 8 and x ≃ 0.5. The complex dielectric function of the films was determined from far-infrared to ultraviolet energies using a combination of terahertz time-domain spectroscopy, Fourier transform spectroscopy, and spectroscopic ellipsometry. The simultaneous Raman and infrared activity of phonon modes and the observation of second harmonic generation establishes a non-centrosymmetric point group for Pbn+1(Ti0.5Fe0.5)nO3(n+1)-δ, a prerequisite for (but not proof of) ferroelectricity. No evidence of macroscopic ferromagnetism was found in SQUID magnetometry. The ultrafast optical response exhibited coherent magnon oscillations compatible with local magnetic order, and additionally was used to study photocarrier cooling on picosecond timescales. An optical gap smaller than that of BiFeO3 and long photocarrier lifetimes may make this system interesting as a ferroelectric photovoltaic.

No MeSH data available.


Related in: MedlinePlus

Linear and non-linear optics of PTFO films: (a) UV-visible absorption coefficient α from transmission at normal incidence (solid lines), and from ellipsometry at various angles of incidence (dashed lines). Vertical lines indicate pump and probe energies used for ultrafast Pump-Probe (PP) spectroscopy and pump energy for Raman. (b) Real (, solid lines) and imaginary (, dashed) parts of complex dielectric function in the UV-visible range, as determined from ellipsometry. Shaded areas show the contribution of each mode to . (c), (d) and (e) show the SHG radiation patterns for PTFO-100, -200 and -300 respectively, as a function of sample azimuthal angle ϕ (ϕ = 0 corresponding to p-polarised input) for θ = 45°. Data are shown for p-polarised (“p-out”) and s-polarised (“s-out”) detection. In (c) and (d) the dashed black lines show the SHG intensities expected for a tetragonal phase from the model described in the text. (f) SHG (blue) can only be detected from the “detection volumes” (blue shaded areas) defined by the film's finite absorption depth at the second harmonic.
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f3: Linear and non-linear optics of PTFO films: (a) UV-visible absorption coefficient α from transmission at normal incidence (solid lines), and from ellipsometry at various angles of incidence (dashed lines). Vertical lines indicate pump and probe energies used for ultrafast Pump-Probe (PP) spectroscopy and pump energy for Raman. (b) Real (, solid lines) and imaginary (, dashed) parts of complex dielectric function in the UV-visible range, as determined from ellipsometry. Shaded areas show the contribution of each mode to . (c), (d) and (e) show the SHG radiation patterns for PTFO-100, -200 and -300 respectively, as a function of sample azimuthal angle ϕ (ϕ = 0 corresponding to p-polarised input) for θ = 45°. Data are shown for p-polarised (“p-out”) and s-polarised (“s-out”) detection. In (c) and (d) the dashed black lines show the SHG intensities expected for a tetragonal phase from the model described in the text. (f) SHG (blue) can only be detected from the “detection volumes” (blue shaded areas) defined by the film's finite absorption depth at the second harmonic.

Mentions: The UV-visible absorption coefficient α at normal incidence and room temperature (see Methods) is reported in Figure 3(a). The absorption coefficient varies with the film thickness, and an increase in the absorption edge (~2.5 eV) is evident with reduced film thickness. The shift is most pronounced for the PTFO-100 film, and coincides with the increased tetragonal distortion for thinner films [Fig. 1(a) and Table 1]. In the region below the band gap, before the film begins to absorb strongly, the reported absorption coefficient exhibits oscillations that are artefacts caused by thin film interference.


Structural, optical and vibrational properties of self-assembled Pbn+1(Ti1-x Fex)nO(3n+1)-δ Ruddlesden-Popper superstructures.

Doig KI, Peters JJ, Nawaz S, Walker D, Walker M, Lees MR, Beanland R, Sanchez AM, McConville CF, Palkar VR, Lloyd-Hughes J - Sci Rep (2015)

Linear and non-linear optics of PTFO films: (a) UV-visible absorption coefficient α from transmission at normal incidence (solid lines), and from ellipsometry at various angles of incidence (dashed lines). Vertical lines indicate pump and probe energies used for ultrafast Pump-Probe (PP) spectroscopy and pump energy for Raman. (b) Real (, solid lines) and imaginary (, dashed) parts of complex dielectric function in the UV-visible range, as determined from ellipsometry. Shaded areas show the contribution of each mode to . (c), (d) and (e) show the SHG radiation patterns for PTFO-100, -200 and -300 respectively, as a function of sample azimuthal angle ϕ (ϕ = 0 corresponding to p-polarised input) for θ = 45°. Data are shown for p-polarised (“p-out”) and s-polarised (“s-out”) detection. In (c) and (d) the dashed black lines show the SHG intensities expected for a tetragonal phase from the model described in the text. (f) SHG (blue) can only be detected from the “detection volumes” (blue shaded areas) defined by the film's finite absorption depth at the second harmonic.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4296293&req=5

f3: Linear and non-linear optics of PTFO films: (a) UV-visible absorption coefficient α from transmission at normal incidence (solid lines), and from ellipsometry at various angles of incidence (dashed lines). Vertical lines indicate pump and probe energies used for ultrafast Pump-Probe (PP) spectroscopy and pump energy for Raman. (b) Real (, solid lines) and imaginary (, dashed) parts of complex dielectric function in the UV-visible range, as determined from ellipsometry. Shaded areas show the contribution of each mode to . (c), (d) and (e) show the SHG radiation patterns for PTFO-100, -200 and -300 respectively, as a function of sample azimuthal angle ϕ (ϕ = 0 corresponding to p-polarised input) for θ = 45°. Data are shown for p-polarised (“p-out”) and s-polarised (“s-out”) detection. In (c) and (d) the dashed black lines show the SHG intensities expected for a tetragonal phase from the model described in the text. (f) SHG (blue) can only be detected from the “detection volumes” (blue shaded areas) defined by the film's finite absorption depth at the second harmonic.
Mentions: The UV-visible absorption coefficient α at normal incidence and room temperature (see Methods) is reported in Figure 3(a). The absorption coefficient varies with the film thickness, and an increase in the absorption edge (~2.5 eV) is evident with reduced film thickness. The shift is most pronounced for the PTFO-100 film, and coincides with the increased tetragonal distortion for thinner films [Fig. 1(a) and Table 1]. In the region below the band gap, before the film begins to absorb strongly, the reported absorption coefficient exhibits oscillations that are artefacts caused by thin film interference.

Bottom Line: No evidence of macroscopic ferromagnetism was found in SQUID magnetometry.The ultrafast optical response exhibited coherent magnon oscillations compatible with local magnetic order, and additionally was used to study photocarrier cooling on picosecond timescales.An optical gap smaller than that of BiFeO3 and long photocarrier lifetimes may make this system interesting as a ferroelectric photovoltaic.

View Article: PubMed Central - PubMed

Affiliation: University of Oxford, Department of Physics, Clarendon Laboratory, Parks Road, Oxford, OX1 3PU, United Kingdom.

ABSTRACT
Bulk crystals and thin films of PbTi(1-x)FexO3(-δ) (PTFO) are multiferroic, exhibiting ferroelectricity and ferromagnetism at room temperature. Here we report that the Ruddlesden-Popper phase Pbn+1(Ti(1-x)Fex)nO3(n+1)-δ forms spontaneously during pulsed laser deposition of PTFO on LaAlO3 substrates. High-resolution transmission electron microscopy, x-ray diffraction and x-ray photoemission spectroscopy were utilised to perform a structural and compositional analysis, demonstrating that n ≃ 8 and x ≃ 0.5. The complex dielectric function of the films was determined from far-infrared to ultraviolet energies using a combination of terahertz time-domain spectroscopy, Fourier transform spectroscopy, and spectroscopic ellipsometry. The simultaneous Raman and infrared activity of phonon modes and the observation of second harmonic generation establishes a non-centrosymmetric point group for Pbn+1(Ti0.5Fe0.5)nO3(n+1)-δ, a prerequisite for (but not proof of) ferroelectricity. No evidence of macroscopic ferromagnetism was found in SQUID magnetometry. The ultrafast optical response exhibited coherent magnon oscillations compatible with local magnetic order, and additionally was used to study photocarrier cooling on picosecond timescales. An optical gap smaller than that of BiFeO3 and long photocarrier lifetimes may make this system interesting as a ferroelectric photovoltaic.

No MeSH data available.


Related in: MedlinePlus