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The Semiconductor Spectroscopy and Devices research group is part of the Nanoscience division of the Department of Physics at the University of Strathclyde. The Department is a member of the Scottish Universities Physics Alliance (SUPA).

Research interests


Group news
  • August 2017: Elena Pascal was jointly awarded the Corbett Prize at the 29th ICDS conference, Matsue, Japan.
  • July 2017: The Group was well represented at the ICNS-12 conference in Strasbourg, presenting invited and contributed talks and several posters.
  • July 2017: Our new JEOL JXA-8530F field-emission electron probe microanalyser (EPMA) is now up and running.
Latest publications
A complete list of our papers can be found here.

  • D. McArthur, B. Hourahine, and F. Papoff, “Coherent control of plasmons in nanoparticles with nonlocal response,” Optics Communications, vol. 382, pp. 258-265, 2017.
    [BibTeX] [Abstract] [Download PDF]

    We discuss a scheme for the coherent control of light and plasmons in nanoparticles that have nonlocal dielectric permittivity and contain nonlinear impurities or color centers. We consider particles which have a response to light that is strongly influenced by plasmons over a broad range of frequencies. Our coherent control method enables the reduction of absorption and/or suppression of scattering.

    @article{strathprints57291,
    volume = {382},
    month = {January},
    title = {Coherent control of plasmons in nanoparticles with nonlocal response},
    author = {D. McArthur and B. Hourahine and F. Papoff},
    year = {2017},
    pages = {258--265},
    journal = {Optics Communications},
    keywords = {plasmonics, nanoparticles, nonlocality, optical routing, Optics. Light, Atomic and Molecular Physics, and Optics},
    url = {http://strathprints.strath.ac.uk/57291/},
    abstract = {We discuss a scheme for the coherent control of light and plasmons in nanoparticles that have nonlocal dielectric permittivity and contain nonlinear impurities or color centers. We consider particles which have a response to light that is strongly influenced by plasmons over a broad range of frequencies. Our coherent control method enables the reduction of absorption and/or suppression of scattering.}
    }

  • A. K. Singh, K. P. O’Donnell, P. R. Edwards, K. Lorenz, M. J. Kappers, and M. Boćkowski, “Hysteretic photochromic switching of Eu-Mg defects in GaN links the shallow transient and deep ground states of the Mg acceptor,” Scientific Reports, vol. 7, 2017.
    [BibTeX] [Abstract] [Download PDF]

    Although p-type activation of GaN by Mg underpins a mature commercial technology, the nature of the Mg acceptor in GaN is still controversial. Here, we use implanted Eu as a `spectator ion’ to probe the lattice location of Mg in doubly doped GaN(Mg):Eu. Photoluminescence spectroscopy of this material exemplifies hysteretic photochromic switching (HPS) between two configurations, Eu0 and Eu1(Mg), of the same Eu-Mg defect, with a hyperbolic time dependence on `switchdown’ from Eu0 to Eu1(Mg). The sample temperature and the incident light intensity at 355 nm tune the characteristic switching time over several orders of magnitude, from less than a second at 12.5 K, ~100 mW/cm2 to (an estimated) several hours at 50 K, 1 mW/cm². Linking the distinct Eu-Mg defect configurations with the shallow transient and deep ground states of the Mg acceptor in the Lany-Zunger model, we determine the energy barrier between the states to be 27.7(4) meV, in good agreement with the predictions of theory. The experimental results further suggest that at low temperatures holes in deep ground states are localized on N atoms axially bonded to Mg acceptors.

    @Article{strathprints59279,
    author = {A. K. Singh and K. P. O'Donnell and P. R. Edwards and K. Lorenz and M. J. Kappers and M. Bo{\'c}kowski},
    title = {Hysteretic photochromic switching of {Eu-Mg} defects in {GaN} links the shallow transient and deep ground states of the {Mg} acceptor},
    journal = {Scientific Reports},
    year = {2017},
    volume = {7},
    month = {February},
    abstract = {Although p-type activation of GaN by Mg underpins a mature commercial technology, the nature of the Mg acceptor in GaN is still controversial. Here, we use implanted Eu as a `spectator ion' to probe the lattice location of Mg in doubly doped GaN(Mg):Eu. Photoluminescence spectroscopy of this material exemplifies hysteretic photochromic switching (HPS) between two configurations, Eu0 and Eu1(Mg), of the same Eu-Mg defect, with a hyperbolic time dependence on `switchdown' from Eu0 to Eu1(Mg). The sample temperature and the incident light intensity at 355 nm tune the characteristic switching time over several orders of magnitude, from less than a second at 12.5 K, ~100 mW/cm2 to (an estimated) several hours at 50 K, 1 mW/cm². Linking the distinct Eu-Mg defect configurations with the shallow transient and deep ground states of the Mg acceptor in the Lany-Zunger model, we determine the energy barrier between the states to be 27.7(4) meV, in good agreement with the predictions of theory. The experimental results further suggest that at low temperatures holes in deep ground states are localized on N atoms axially bonded to Mg acceptors.},
    keywords = {photoluminescence spectroscopy, hysteretic photochromic switching, Lany-Zunger model, energy barrier, shallow transient state, deep ground state, acceptor state, Physics, Physics and Astronomy(all)},
    url = {http://strathprints.strath.ac.uk/59279/}
    }

  • S. Vespucci, A. Winkelmann, K. Mingard, D. Maneuski, V. O’Shea, and C. Trager-Cowan, “Exploring transmission Kikuchi diffraction using a Timepix detector,” Journal of Instrumentation, vol. 12, 2017.
    [BibTeX] [Abstract] [Download PDF]

    Electron backscatter diffraction (EBSD) is a well-established scanning electron microscope (SEM)-based technique [1]. It allows the non-destructive mapping of the crystal structure, texture, crystal phase and strain with a spatial resolution of tens of nanometers. Conventionally this is performed by placing an electron sensitive screen, typically consisting of a phosphor screen combined with a charge coupled device (CCD) camera, in front of a specimen, usually tilted 70? to the normal of the exciting electron beam. Recently, a number of authors have shown that a significant increase in spatial resolution is achievable when Kikuchi diffraction patterns are acquired in transmission geometry; that is when diffraction patterns are generated by electrons transmitted through an electron-transparent, usually thinned, specimen. The resolution of this technique, called transmission Kikuchi diffraction (TKD), has been demonstrated to be better than 10 nm [2, 3]. We have recently demonstrated the advantages of a direct electron detector, Timepix [4, 5], for the acquisition of standard EBSD patterns [5]. In this article we will discuss the advantages of Timepix to perform TKD and for acquiring spot diffraction patterns and more generally for acquiring scanning transmission electron microscopy micrographs in the SEM. Particularly relevant for TKD, is its very compact size, which allows much more flexibility in the positioning of the detector in the SEM chamber. We will furthermore show recent results using Timepix as a virtual forward scatter detector, and will illustrate the information derivable on producing images through processing of data acquired from different areas of the detector. We will show results from samples ranging from gold nanoparticles to nitride semiconductor nanorods.

    @Article{strathprints59555,
    author = {S. Vespucci and A. Winkelmann and K. Mingard and D. Maneuski and V. O'Shea and C. Trager-Cowan},
    title = {Exploring transmission {K}ikuchi diffraction using a {T}imepix detector},
    journal = {Journal of Instrumentation},
    year = {2017},
    volume = {12},
    month = {February},
    abstract = {Electron backscatter diffraction (EBSD) is a well-established scanning electron microscope (SEM)-based technique [1]. It allows the non-destructive mapping of the crystal structure, texture, crystal phase and strain with a spatial resolution of tens of nanometers. Conventionally this is performed by placing an electron sensitive screen, typically consisting of a phosphor screen combined with a charge coupled device (CCD) camera, in front of a specimen, usually tilted 70? to the normal of the exciting electron beam. Recently, a number of authors have shown that a significant increase in spatial resolution is achievable when Kikuchi diffraction patterns are acquired in transmission geometry; that is when diffraction patterns are generated by electrons transmitted through an electron-transparent, usually thinned, specimen. The resolution of this technique, called transmission Kikuchi diffraction (TKD), has been demonstrated to be better than 10 nm [2, 3]. We have recently demonstrated the advantages of a direct electron detector, Timepix [4, 5], for the acquisition of standard EBSD patterns [5]. In this article we will discuss the advantages of Timepix to perform TKD and for acquiring spot diffraction patterns and more generally for acquiring scanning transmission electron microscopy micrographs in the SEM. Particularly relevant for TKD, is its very compact size, which allows much more flexibility in the positioning of the detector in the SEM chamber. We will furthermore show recent results using Timepix as a virtual forward scatter detector, and will illustrate the information derivable on producing images through processing of data acquired from different areas of the detector. We will show results from samples ranging from gold nanoparticles to nitride semiconductor nanorods.},
    keywords = {radiation, imaging detectors, electron backscatter diffraction, Kikuchi diffraction patterns, transmission Kikuchi diffraction, direct electron detector, Timepix, scanning transmission electron microscopy micrographs, Physics, Instrumentation, Mathematical Physics},
    url = {http://strathprints.strath.ac.uk/59555/}
    }

  • M. V. Yakushev, M. A. Sulimov, J. Márquez-Prieto, I. Forbes, J. Krustok, P. R. Edwards, V. D. Zhivulko, O. M. Borodavchenko, A. V. Mudryi, and R. W. Martin, “Influence of the copper content on the optical properties of CZTSe thin films,” Solar Energy Materials and Solar Cells, vol. 168, pp. 69-77, 2017.
    [BibTeX] [Abstract] [Download PDF]

    We present an optical spectroscopy study of Cu₂ZnSnSe₄ (CZTSe) thin films deposited on Mo/glass substrates. The [Cu]/[Zn+Sn] ratio in these films varies from nearly stoichiometric to strongly Cu deficient and Zn rich. Increasing Cu deficiency and Zn excess widens the bandgap Eg, determined using photoluminescence excitation (PLE) at 4.2 K, from 0.99 eV to 1.03 eV and blue shifts the dominant band in the photoluminescence (PL) spectra from 0.83 eV to 0.95 eV. The PL spectra of the near stoichiometric film reveal two bands: a dominant band centred at 0.83 eV and a lower intensity one at 0.93 eV. The temperature and excitation intensity dependence of the PL spectra help to identify the recombination mechanisms of the observed emission bands as free-to-bound: recombination of free electrons with holes localised at acceptors affected by randomly distributed potential fluctuations. Both the mean depth of such fluctuations, determined by analysing the shape of the dominant bands, and the broadening energy, estimated from the PLE spectra, become smaller with increasing Cu deficiency and Zn excess which also widens Eg due to an improved ordering of the Cu/Zn atoms. These changes in the elemental composition induce a significant blue shift of the PL bands exceeding the Eg widening. This is attributed to a change of the dominant acceptor for a shallow one, and is beneficial for the solar cell performance. Film regions with a higher degree of Cu/Zn ordering are present in the near stoichiometric film generating the second PL band at 0.93 eV.

    @Article{strathprints60524,
    author = {M. V. Yakushev and M. A. Sulimov and J. M{\'a}rquez-Prieto and I. Forbes and J. Krustok and P. R. Edwards and V. D. Zhivulko and O. M. Borodavchenko and A. V. Mudryi and R. W. Martin},
    title = {Influence of the copper content on the optical properties of {CZTSe} thin films},
    journal = {Solar Energy Materials and Solar Cells},
    year = {2017},
    volume = {168},
    pages = {69-77},
    month = {April},
    abstract = {We present an optical spectroscopy study of Cu₂ZnSnSe₄ (CZTSe) thin films deposited on Mo/glass substrates. The [Cu]/[Zn+Sn] ratio in these films varies from nearly stoichiometric to strongly Cu deficient and Zn rich. Increasing Cu deficiency and Zn excess widens the bandgap Eg, determined using photoluminescence excitation (PLE) at 4.2 K, from 0.99 eV to 1.03 eV and blue shifts the dominant band in the photoluminescence (PL) spectra from 0.83 eV to 0.95 eV. The PL spectra of the near stoichiometric film reveal two bands: a dominant band centred at 0.83 eV and a lower intensity one at 0.93 eV. The temperature and excitation intensity dependence of the PL spectra help to identify the recombination mechanisms of the observed emission bands as free-to-bound: recombination of free electrons with holes localised at acceptors affected by randomly distributed potential fluctuations. Both the mean depth of such fluctuations, determined by analysing the shape of the dominant bands, and the broadening energy, estimated from the PLE spectra, become smaller with increasing Cu deficiency and Zn excess which also widens Eg due to an improved ordering of the Cu/Zn atoms. These changes in the elemental composition induce a significant blue shift of the PL bands exceeding the Eg widening. This is attributed to a change of the dominant acceptor for a shallow one, and is beneficial for the solar cell performance. Film regions with a higher degree of Cu/Zn ordering are present in the near stoichiometric film generating the second PL band at 0.93 eV.},
    keywords = {copper, thin films, optical spectroscopy, photoluminescence excitation, stoichiometric film, Cu2ZnSnSe4, defects, zinc, Physics, Surfaces, Coatings and Films, Electronic, Optical and Magnetic Materials, Renewable Energy, Sustainability and the Environment},
    url = {http://strathprints.strath.ac.uk/60524/},
    }

  • C. Ni, G. J. Hedley, J. Payne, V. Svrcek, C. McDonald, L. K. Jagadamma, P. Edwards, R. Martin, D. Mariotti, P. Maguire, I. Samuel, and J. Irvine, “Charge carrier localised in zero-dimensional (CH₃NH₃)₃Bi₂I₉ clusters,” Nature Communications, vol. 8, p. 170, 2017.
    [BibTeX] [Abstract] [Download PDF]

    A metal-organic hybrid perovskite with 3-D framework of metal halide octahedra has been reported as a low-cost, solution processable absorber for a thin film solar cell with a power conversion efficiency over 20%. Low-dimensional layered perovskites with metal halide slabs separated by the insulating organic layers are reported to show higher stability, but the efficiencies of the solar cells are limited by the anisotropy of the crystals because of the confinement of excitons. In order to explore the confinement and transport of excitons in zero-dimensional metal-organic hybrid materials, a highly-orientated film of methylammonium bismuth halide, (CH₃NH₃)₃Bi₂I₉, with a nanometer sized core cluster of Bi₂I₉³⁻ surrounded by insulating CH₃NH₃⁺, was deposited on a quartz substrate via solution processing. The (CH₃NH₃)₃Bi₂I₉ film shows highly anisotropic photoluminescence emission and excitation due to the large proportion of localized excitons coupled with a small number of delocalised excitons from inter-cluster energy transfer. The abrupt increase in photoluminescence quantum yield at excitation energy above twice band gap could indicate a quantum cutting due to the low dimensionality.

    @Article{strathprints60928,
    author = {Chengsheng Ni and Gordon J. Hedley and Julia Payne and Vladimir Svrcek and Calum McDonald and Lethy Krishnan Jagadamma and Paul Edwards and Robert Martin and Davide Mariotti and Paul Maguire and Ifor Samuel and John Irvine},
    title = {Charge carrier localised in zero-dimensional {(CH₃NH₃)₃Bi₂I₉} clusters},
    journal = {Nature Communications},
    year = {2017},
    volume = {8},
    pages = {170},
    abstract = {A metal-organic hybrid perovskite with 3-D framework of metal halide octahedra has been reported as a low-cost, solution processable absorber for a thin film solar cell with a power conversion efficiency over 20%. Low-dimensional layered perovskites with metal halide slabs separated by the insulating organic layers are reported to show higher stability, but the efficiencies of the solar cells are limited by the anisotropy of the crystals because of the confinement of excitons. In order to explore the confinement and transport of excitons in zero-dimensional metal-organic hybrid materials, a highly-orientated film of methylammonium bismuth halide, (CH₃NH₃)₃Bi₂I₉, with a nanometer sized core cluster of Bi₂I₉³⁻ surrounded by insulating CH₃NH₃⁺, was deposited on a quartz substrate via solution processing. The (CH₃NH₃)₃Bi₂I₉ film shows highly anisotropic photoluminescence emission and excitation due to the large proportion of localized excitons coupled with a small number of delocalised excitons from inter-cluster energy transfer. The abrupt increase in photoluminescence quantum yield at excitation energy above twice band gap could indicate a quantum cutting due to the low dimensionality.},
    keywords = {perovskite, metal-organic, metal-halide, octahedra, absorber , thin-film solar cell, photoluminescence quantum yield, Physics, Chemistry, Biochemistry, Genetics and Molecular Biology(all), Chemistry(all), Physics and Astronomy(all)},
    url = {http://strathprints.strath.ac.uk/60928/}
    }