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ABSTRACT: In this work we present a method for the deposition of periodically ordered, c-axis aligned ZnO nanorod arrays. By using chemical bath deposited films in conjunction with silica templating through nanosphere monolayers, masks suitable for high temperature deposition are created. A vapour phase transport technique is then used to deposit ordered arrays, quickly and inexpensively in a manner ideal for low cost, scalable and reproducible growth on a diverse range of substrates.
Nanoscale 02/2011; 3(4):1675-82. · 5.91 Impact Factor
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ABSTRACT: We report low temperature cathodoluminescence spectroscopy measurements of the band edge emission from ZnO nanostructures grown by vapour phase transport on Si. A range of donor bound exciton emission lines are found and the Al-related emission at 3.3605 eV in particular shows a marked inhomogeneity in its distribution throughout the sample. Increased 3.3605 eV emission is seen at a range of locations in nanorods and nanosheets where different nanostructures cross or coalesce, suggesting aggregation of Al donors in ZnO in regions of crystal structure disruption. However, localized crystal structure disruption appears to be a necessary rather than a sufficient condition for Al aggregation, since increased 3.3605 eV emission is seen only in such regions, but not all such regions show increased emission, implying that the microscopic nature of such regions is important in determining Al aggregation. Supporting data are presented from well-aligned, non-crossing, nanorods on a-sapphire.
Nanotechnology 07/2009; 20(25):255703. · 3.98 Impact Factor
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ABSTRACT: We found that a ZnO film of 2 μm thickness which was laser-deposited at room temperature onto a plain soda lime glass substrate, exhibits notable antibacterial activity against a biofilm of Staphylococcus epidermidis when back-illuminated by a UVA light source with a peak emission wavelength of about 365 nm. X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), UV-visible absorption spectroscopy, Raman spectroscopy and x-ray photoemission spectroscopy (XPS) were used to characterize the ZnO films before and after the interactions with the biofilm and the ultraviolet light, respectively. The as-deposited film was highly textured with the wurtzite (0002) in-plane orientation (c-axis perpendicular to ZnO surface) and had a surface rms roughness of 49.7 nm. In the as-deposited film, the Zn to O ratio was 1 to 0.95. After the UV and biofilm treatments, the ZnO film surface had become rougher (rms roughness 68.1 nm) and presented uniform micron-sized pitting randomly distributed, while the zinc to oxygen ratio had become 1 to 2.2. In this case, both the UV-visible and Raman spectra pointed to degradation of the structural quality of the material. On the strength of these data, we propose a model for the mediation of the bactericidal activity in which the photogeneration of highly oxidizing species and the presence of active surface defect sites both play an important role. This study is of particular interest for the acute problem of disinfection of pathogenic biofilms which form on medical device/implant surfaces.
Science and Technology of Advanced Materials. 01/2009;
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ABSTRACT: We point out the connection between the 'pole in a barn paradox' and the phenomenon of alterations in charge in a segment of a current-carrying conductor as perceived by observers in different inertial reference frames. This connection appears to offer a useful pedagogical strategy helping students to appreciate that the issues which underlie the explanation of the paradox can be important and significant in everyday phenomena such as magnetic forces on moving charges and at the very modest speeds associated with electron drift in conductors.
European Journal of Physics 09/2008; 29(6):N63. · 0.82 Impact Factor
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ABSTRACT: We present optically pumped emission data for ZnO, showing that high excitation effects and stimulated emission/lasing are observed in nanocrystalline ZnO thin films at room temperature, although such effects are not seen in bulk material of better optical quality. A simple model of exciton density profiles is developed which explains our results and those of other authors. Inhibition of exciton diffusion in nanocrystalline samples compared to bulk significantly increases exciton densities in the former, leading—via the nonlinear dependence of emission in the exciton bands on the pump intensity—to large increases in emission and to stimulated emission.
Applied Physics Letters 03/2006; · 3.84 Impact Factor
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ABSTRACT: Polar ZnO surfaces with O- and Zn-termination were studied with atomic and lateral force microscopy and force curves. Adsorbed fluid layers on both surfaces are found to dominate their adhesion properties in air. The hydrophilic O-surface has a substantially thicker adsorbed layer and larger residual particle densities. Our data suggest that different preparation is required for the two surfaces before use in epitaxy, and may resolve some contradictions in the literature. The data also indicate that adsorbed fluid layers may be important in the growth of certain ZnO nanostructures.
Nanotechnology 11/2004; 15(12):1797. · 3.98 Impact Factor
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ABSTRACT: The first European Union Science Olympiad (EUSO2003) took place at Dublin City University in April 2003. In this paper we discuss the philosophy behind and implementation of this new competition, and the role third-level institutions can play in making science more attractive to second-level students via competitions of this nature. Emphasis is placed on the interdisciplinary nature of the experiments, the team-working skills required and the potential for stimulating the uptake of science at second and third levels. We use an experimental problem on photosynthesis, which has a strong physics component, to illustrate our ideas and methodology and assess the overall success of the first EUSO competition.
European Journal of Physics 10/2003; 25(1):23. · 0.82 Impact Factor
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ABSTRACT: Multiphoton-absorption MPA induced ultraviolet UV luminescence of ZnO nanorods grown by vapor phase transport was demonstrated using ultrafast excitation at pulse energies in the few nanojoules range, directly generated by a Ti:sapphire laser oscillator at wavelengths around 800 nm. The dependence of the UV luminescence on the excitation density reveals a two-photon absorption process as the responsible excitation mechanism. The broad spectral bandwidth of the excitation pulses obviously promotes the feasibility of the observed two-photon channel. Theoretical estimates concerning the contribution of nonlinear absorbance strongly support the experimental findings. The essential conditions for proper utilization of this process are discussed. © 2010 American Institute of Physics.
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ABSTRACT: In April 2003 the first European Science Olympiad took place in Dublin City University in Ireland. In this competition second level students were asked to carry out a number of tasks involving biology, physics and chemistry. Students had qualified initially in competitions in one of these subjects and were organised into integrated teams which worked together to complete the tasks. This paper examines the background to the competition, describes aspects of the biological input in developing the tasks and discusses the value of the approach and its potential benefits in improving both interest levels in science and the quality of science education.
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ABSTRACT: We report detailed reflectance studies of the exciton-polariton structure of thin film polycrystalline ZnO and comparison with bulk crystal behaviour. Near-normal incidence reflectance spectra of these samples are fitted using a two-band dielectric response function. Our data show that the reflectance data in polycrystalline ZnO differ substantially from the bulk material, with Fabry-Perot oscillations at energies below the transverse A exciton and above the longitudinal B exciton in the films. In the strong interaction regime between these energies no evidence is seen of the normally rapid oscillations associated with the anomalous waves. We demonstrate that the strong interaction of the damped exciton with the photon leads to polaritons in this region with substantial damping such that the Fabry-Perot modes are eliminated. Good qualitative agreement is achieved between the model and data. The importance of the polariton model in understanding the reflectance data of polycrystalline material is clearly seen.
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ABSTRACT: We report detailed reflectance studies of the exciton–polariton structure of thin film polycrystalline ZnO
and comparison with bulk crystal behaviour. Near-normal incidence reflectance spectra of these samples are
fitted using a two-band dielectric response function. Our data show that the reflectance data in polycrystalline
ZnO differ substantially from the bulk material, with Fabry–Perot oscillations at energies below the transverse A
exciton and above the longitudinal B exciton in the films. In the strong interaction regime between these energies no
evidence is seen of the normally rapid oscillations associated with the anomalous waves. We demonstrate that the
strong interaction of the damped exciton with the photon leads to polaritons in this region with substantial damping
such that the Fabry–Perot modes are eliminated. Good qualitative agreement is achieved between the model and
data. The importance of the polariton model in understanding the reflectance data of polycrystalline material is clearly
seen
McGlynn, Enda and Fryar, James and Henry, Martin O. and Mosnier, Jean-Paul and Lunney, James G. and O'Mahony, Donagh and de Posada, Eduardo (2003) Exciton-polariton behaviour in bulk and polycrystalline ZnO. Physica B: Condensed Matter, 340-342 . pp. 230-234. ISSN 0921-4526.
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ABSTRACT: We report ZnO nanowire/nanowall growth using a two-step vapour phase transport method on a-plane sapphire. X-ray diffraction and scanning electron microscopy data establish that the nanostructures are vertically well-aligned with c-axis normal to the substrate, and have a very low rocking curve width. Photoluminescence data at low temperatures demonstrate the exceptionally high optical quality of these structures, with intense emission and narrow bound exciton linewidths. We observe a high energy excitonic emission at low temperatures close to the band-edge which we assign to the surface exciton in ZnO at ~ 3.366 eV, the first time this feature has been reported in ZnO nanorod systems. This assignment is consistent with the large surface to volume ratio of the nanowire systems and indicates that this large ratio has a significant effect on the luminescence even at low temperatures. The band-edge intensity decays rapidly with increasing temperature compared to bulk single crystal material, indicating a strong temperature-activated non-radiative mechanism peculiar to the nanostructures. No evidence is seen of the free exciton emission due to exciton delocalisation in the nanostructures with increased temperature, unlike the behaviour in bulk material. The use of such nanostructures in room temperature optoelectronic devices appears to be dependent on the control or elimination of such surface effects.
Grabowska, J. and Meaney, Alan and Nanda, Karuna. K. and Mosnier, Jean-Paul and Henry, Martin O. and Duclère, J-R. and McGlynn, Enda (2006) Surface excitonic emission and quenching effects in ZnO nanowire/nanowall systems: limiting effects on device potential. Physical Review B, 71 (11). ISSN 1098-0121.
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ABSTRACT: We report the results of photoluminescence and reflectance measurements on highly c-axis oriented polycrystalline ZnO grown by pulsed laser deposition. The samples measured were grown under identical conditions and were annealed in-situ at various temperatures for 10-15 min. The band-edge photoluminescence spectra of the material altered considerably with an increase in grain size, with increased free exciton emission and observable excitonic structure in the reflectance spectra. The green band emission also increased with increasing grain size. A deformation potential analysis of the effect of strain on the exciton energy positions of the A- and B-excitons demonstrated that the experimental exciton energies could not be explained solely in terms of sample strain. We propose that electric fields in the samples due to charge trapping at grain boundaries are responsible for the additional perturbation of the excitons. This interpretation is supported by theoretical estimates of the exciton energy perturbation due to electric fields. The behaviour of the green band in the samples provides additional evidence in favour of our model.
McGlynn, Enda and Fryar, James and Tobin, Ger and Roy, C. and Henry, Martin O. and Mosnier, Jean-Paul and de Posada, Eduardo and Lunney, James G. (2004) Effect of polycrystallinity on the optical properties of highly oriented ZnO grown by pulsed laser deposition. Thin Solid Films, 458 (1-2). pp. 330-335. ISSN 0040-6090.
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ABSTRACT: Raman spectroscopy, X-ray diffractometry and atomic force microscopy have been used to characterise ZnO thin films grown by pulsed laser deposition as a function of the post-growth annealing temperature. The results show substantial enhancement and broadening of certain Raman features which correlate excellently with the change in width of the X-ray diffraction peaks. The 570 cm[-1] Raman feature showed pronounced asymmetry and enhanced intensity in the unannealed sample. An increase in grain size observed after subsequent annealing produced a substantial reduction in both the asymmetry and intensity of this peak. Our experimental data suggest that electric fields, due to charge trapping at grain boundaries, in conjunction with localised and surface phonon modes are the cause of the intensity enhancement and asymmetry of this feature.
Roy, C. and Byrne, Sarah and McGlynn, Enda and Mosnier, Jean-Paul and de Posada, Eduardo and O'Mahony, Donagh and Lunney, James G. and Henry, Martin O. and Ryan, Brendan and Cafolla, Attilio A. (2003) Correlation of Raman and X-Ray Diffraction Measurements of Annealed Pulsed Laser Deposited ZnO Thin Films. Thin Solid Films, 436 (2). pp. 273-276. ISSN 0040-6090.
