Publications

2018

1. ChemNanoMat

   Effect of Material Structure on Photoluminescence of ZnO/MgO Core-Shell Nanowires

   Claire E. Marvinney, Xiao Shen, James R. McBride, Dominic Critchlow, and 5 more authors

   ChemNanoMat, 2018

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   Abstract Zinc oxide (ZnO) nanowires are widely studied for use in ultraviolet optoelectronic devices, such as nanolasers and sensors. Nanowires (NWs) with an MgO shell exhibit enhanced band-edge photoluminescence (PL), a result previously attributed to passivation of ZnO defects. However, we find that processing the ZnO NWs under low oxygen partial pressure leads to an MgO-thickness-dependent PL enhancement owing to the formation of optical cavity modes. Conversely, processing under higher oxygen partial pressure leads to NWs that support neither mode formation nor band-edge PL enhancement. High-resolution electron microscopy and density-functional calculations implicate the ZnO m-plane surface morphology as the key determinant of core-shell structure and cavity-mode optics. A ZnO surface with atomic steps along the m-plane in the c-axis direction stimulates the growth of a smooth MgO shell that supports guided-wave optical modes and enhanced UV PL. On the other hand, a smoother ZnO surface leads to nucleation of a rough cladding layer which supports neither enhanced UV PL nor optical cavity modes. Finite-element analysis shows a clear correlation between allowed Fabry-Perot and whispering gallery modes and enhanced UV-PL. These results point the way to fabricating ZnO/MgO core-shell nanowires for more efficient UV nanolasers, scintillators, and sensors.

   @article{https://doi.org/10.1002/cnma.201700313,
     author = {Marvinney, Claire E. and Shen, Xiao and McBride, James R. and Critchlow, Dominic and Li, Zhineng and Mayo, Daniel C. and Mu, Richard R. and Pantelides, Sokrates T. and Haglund, Richard F.},
     title = {Effect of Material Structure on Photoluminescence of ZnO/MgO Core-Shell Nanowires},
     journal = {ChemNanoMat},
     volume = {4},
     number = {3},
     pages = {291-300},
     keywords = {density functional calculations, zinc oxide, nanostructures, nanowires, photoluminescence},
     doi = {https://doi.org/10.1002/cnma.201700313},
     url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/cnma.201700313},
     year = {2018},
   }

2017

1. arXiv

   Alignment of dynamic networks

   Vipin Vijayan, Dominic Critchlow, and Tijana Milenkovic

   2017

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   Networks can model real-world systems in a variety of domains. Network alignment (NA) aims to find a node mapping that conserves similar regions between compared networks. NA is applicable to many fields, including computational biology, where NA can guide the transfer of biological knowledge from well- to poorly-studied species across aligned network regions. Existing NA methods can only align static networks. However, most complex real-world systems evolve over time and should thus be modeled as dynamic networks. We hypothesize that aligning dynamic network representations of evolving systems will produce superior alignments compared to aligning the systems’ static network representations, as is currently done. For this purpose, we introduce the first ever dynamic NA method, DynaMAGNA++. This proof-of-concept dynamic NA method is an extension of a state-of-the-art static NA method, MAGNA++. Even though both MAGNA++ and DynaMAGNA++ optimize edge as well as node conservation across the aligned networks, MAGNA++ conserves static edges and similarity between static node neighborhoods, while DynaMAGNA++ conserves dynamic edges (events) and similarity between evolving node neighborhoods. For this purpose, we introduce the first ever measure of dynamic edge conservation and rely on our recent measure of dynamic node conservation. Importantly, the two dynamic conservation measures can be optimized using any state-of-the-art NA method and not just MAGNA++. We confirm our hypothesis that dynamic NA is superior to static NA, under fair comparison conditions, on synthetic and real-world networks, in computational biology and social network domains. DynaMAGNA++ is parallelized and it includes a user-friendly graphical interface.

   @article{vijayan2017alignment,
     title = {Alignment of dynamic networks},
     author = {Vijayan, Vipin and Critchlow, Dominic and Milenkovic, Tijana},
     year = {2017},
     eprint = {1701.08842},
     archiveprefix = {arXiv},
     primaryclass = {cs.SI},
   }