Publications

2016
Gui, Lili, Shahin Bagheri, Nikolai Strohfeldt, Mario Hentschel, Christine M. Zgrabik, Bernd Metzger, Heiko Linnenbank, Evelyn L. Hu, and Harald Giessen. 2016. “Nonlinear Refractory Plasmonics with Titanium Nitride Nanoantennas.” Nano Letters 16 (9): 5708-5713. Publisher's Version
Zhang, X., and E. L. Hu. 2016. “Templated growth of diamond optical resonators via plasma-enhanced chemical vapor deposition.” Applied Physics Letters 109 (8). Publisher's Version
2015
Zgrabik, Christine M., and Evelyn L. Hu. 2015. “Optimization of sputtered titanium nitride as a tunable metal for plasmonic applications.” Opt. Mater. Express 5 (12). OSA: 2786–2797. Publisher's VersionAbstract
Alternative materials for plasmonic devices have garnered much recent interest. A promising candidate material is titanium nitride. Although there is a substantial body of work on the formation of this material, its use for plasmonic applications requires a more systematic and detailed optical analysis than has previously been carried out. This paper describes an initial optimization of sputtered TiN thin films for plasmonic performance from visible into near-IR wavelengths. The metallic behavior of TiN films exhibits a sensitive dependence on the substrate and deposition details. We explored reactive and non-reactive sputter deposition of TiN onto various substrates at both room temperature and 600&\#x00B0;C. Metallic character was compared for films grown under different conditions via spectroscopic ellipsometry and correlated with compositional and structural measurements via x-ray photoelectron spectroscopy (XPS), x-ray diffraction (XRD), and scanning transmission electron microscopy (STEM).
Bracher, David O., and Evelyn L. Hu. 2015. “Fabrication of High-Q Nanobeam Photonic Crystals in Epitaxially Grown 4H-SiC.” Nano Letters 15 (9): 6202-6207. Publisher's Version
Cui, Shanying, Andrew S Greenspon, Kenichi Ohno, Bryan A Myers, Ania Bleszynski C Jayich, David D Awschalom, and Evelyn L Hu. 2015. “Reduced Plasma-Induced Damage to Near-Surface Nitrogen-Vacancy Centers in Diamond.” Nano Letters 15: 2887-2891. Publisher's Version
Cui, Shanying, Xingyu Zhang, Tsung-Li Liu, Jonathan Lee, David Bracher, Kenichi Ohno, David Awschalom, and Evelyn L Hu. 2015. “Hybrid Plasmonic Photonic Crystal Cavity for Enhancing Emission from near-Surface Nitrogen Vacancy Centers in Diamond.” ACS Photonics 2: 465-469. Publisher's Version
2014
Lee, Jonathan C, David O Bracher, Shanying Cui, Kenichi Ohno, Claire A McLellan, Xingyu Zhang, Paolo Andrich, et al. 2014. “Deterministic coupling of delta-doped nitrogen vacancy centers to a nanobeam photonic crystal cavity.” Applied Physics Letters 105 (26). Publisher's VersionAbstract

The negatively charged nitrogen vacancy center (NV) in diamond has generated significant interest as a platform for quantum information processing and sensing in the solid state. For most applications, high quality optical cavities are required to enhance the NV zero-phonon line (ZPL) emission. An outstanding challenge in maximizing the degree of NV-cavity coupling is the deterministic placement of NVs within the cavity. Here, we report photonic crystal nanobeamcavities coupled to NVs incorporated by a delta-doping technique that allows nanometer-scale vertical positioning of the emitters. We demonstrate cavities with Q up to ∼24 000 and mode volume V ∼ 0.47(λ/n)3 as well as resonant enhancement of the ZPL of an NV ensemble with Purcell factor of ∼20. Our fabrication technique provides a first step towards deterministic NV-cavity coupling using spatial control of the emitters.

Woolf, Alexander, Tim Puchtler, Igor Aharonovich, Tongtong Zhu, Nan Niu, Danqing Wang, Rachel Oliver, and Evelyn L Hu. 2014. “Distinctive signature of indium gallium nitride quantum dot lasing in microdisk cavities.” Proceedings of the National Academy of Sciences. Publisher's Version
Zhang, Huiliang, Igor Aharonovich, David R Glenn, Richard Schalek, Andrew P Magyar, Jeff W Lichtman, Evelyn L Hu, and Ronald L Walsworth. 2014. “Silicon-Vacancy Color Centers in Nanodiamonds: Cathodoluminescence Imaging Markers in the Near Infrared.” Small DOI: 10.1002/smll.201303582.Abstract
Nanodiamonds doped with silicon-vacancy (Si-V) color centers are shown to be a promising candidate for cathodoluminescence (CL) imaging at the nanoscale, providing bright, non-bleaching, narrow-linewidth emission at wavelengths within the near-IR window of biological tissue. CL emission intensity from negative charge-state Si-V centers is greatly enhanced by increasing the nitrogen concentration during nanodiamond growth.
Deravi, Leila F, Andrew P Magyar, Sean P Sheehy, George RR Bell, Lydia M Mathger, Stephen L Senft, Trevor J Wardill, et al. 2014. “The structure–function relationships of a natural nanoscale photonic device in cuttlefish chromatophores.” Journal of The Royal Society Interface 11 (93).Abstract
Cuttlefish, Sepia officinalis, possess neurally controlled, pigmented chromatophore organs that allow rapid changes in skin patterning and coloration in response to visual cues. This process of adaptive coloration is enabled by the 500% change in chromatophore surface area during actuation. We report two adaptations that help to explain how colour intensity is maintained in a fully expanded chromatophore when the pigment granules are distributed maximally: (i) pigment layers as thin as three granules that maintain optical effectiveness and (ii) the presence of high-refractive-index proteins—reflectin and crystallin—in granules. The latter discovery, combined with our finding that isolated chromatophore pigment granules fluoresce between 650 and 720 nm, refutes the prevailing hypothesis that cephalopod chromatophores are exclusively pigmentary organs composed solely of ommochromes. Perturbations to granular architecture alter optical properties, illustrating a role for nanostructure in the agile, optical responses of chromatophores. Our results suggest that cephalopod chromatophore pigment granules are more complex than homogeneous clusters of chromogenic pigments. They are luminescent protein nanostructures that facilitate the rapid and sophisticated changes exhibited in dermal pigmentation.
Pooley, Kathryn J, John H Joo, and Evelyn L Hu. 2014. “Constrained, aqueous growth of three-dimensional single crystalline zinc oxide structures.” Applied Physics Letters Materials 2: 012111. Publisher's VersionAbstract
We study low temperature (90 °C) aqueous growth of single crystal zinc oxide structures through patterned PMMA molds of different sizes, shapes, and orientations. We demonstrate the ability to create 3D shapes with smooth vertical sidewalls. Although the unconstrained growth is influenced by the hexagonal geometry of the underlying crystal structure, the ZnO is shown to conform exactly to any shape patterned. Using electron backscatter diffraction and scanning electron microscopy we show that the mold orientation, in conjunction with control of the growth rates of the c and m planes of the ZnO, is crucial in determining the final structure shape.
apl_materials_paper.pdf
Magyar, Andrew, Wenhao Hu, Toby Shanley, Michael E Flatte, Evelyn Hu, and Igor Aharonovich. 2014. “Synthesis of luminescent europium defects in diamond.” Nature Communications 5: 3523.Abstract
Lanthanides are vital components in lighting, imaging technologies and future quantum memory applications owing to their narrow optical transitions and long spin coherence times. Recently, diamond has become a pre-eminent platform for the realisation of many experiments in quantum information science. Here we demonstrate a promising approach to incorporate Eu ions into diamond, providing a means to harness the exceptional characteristics of both lanthanides and diamond in a single material. Polyelectrolytes are used to electrostatically assemble Eu(III) chelate molecules on diamond and subsequently chemical vapour deposition is employed for the diamond growth. Fluorescence measurements show that the Eu atoms retain the characteristic optical signature of Eu(III) upon incorporation into the diamond lattice. Computational modelling supports the experimental findings, corroborating that Eu(III) in diamond is a stable configuration. The formed defects demonstrate the outstanding chemical control over the incorporation of impurities into diamond enabled by the electrostatic assembly together with chemical vapour deposition growth.
Magyar, Andrew P, David Bracher, Jonathan C Lee, Igor Aharonovich, and Evelyn L Hu. 2014. “High quality SiC microdisk resonators fabricated from monolithic epilayer wafers.” Applied Physics Letters 104: 051109.Abstract
The exquisite mechanical properties of SiC have made it an important industrial material with applications in microelectromechanical devices and high power electronics. Recently, the optical properties of SiC have garnered attention for applications in photonics, quantum information, and spintronics. This work demonstrates the fabrication of microdisks formed from a p-N SiC epilayer material. The microdisk cavities fabricated from the SiC epilayer material exhibit quality factors of as high as 9200 and the approach is easily adaptable to the fabrication of SiC-based photonic crystals and other photonic and optomechanical devices.
Liu, Tsung-Li, Kasey J Russell, Shanying Cui, and Evelyn L Hu. 2014. “Two-dimensional hybrid photonic/plasmonic crystal cavities.” Optics Express 22 (7): 8219-8225.Abstract
We present a 2-D plasmonic crystal design with visible band-gap by combining a 2-D photonic crystal with TM band-gap and a silver surface. Simulations show that the presence of the silver surface gives rise to an expanded band-gap. A plasmonic crystal defect cavity with Q ~300 and mode volume ~1.9x10−2 (λ/n) 3 can be formed using our design. The total Q of such a cavity is determined by both the radiative loss of the dielectric component, as well as absorption loss to the metal. We provide design criteria for the optimization of the total Q to allow high radiative or extraction efficiency.
2013
Liu, Tsung-Li, Kasey J Russell, Shanying Cui, and Evelyn L Hu. 2013. “Controlled mode tuning in 1-D 'RIM' plasmonic crystal trench cavities probed with coupled optical emitters.” Optics Express 21 (24): 30074-80081.
Cui, Shanying, and Evelyn Hu. 2013. “Increased negatively charged nitrogen-vacancy centers in fluorinated diamond.” Applied Physics Letters 103 (5): 051603-051607.Abstract
We present a design of plasmonic cavities that consists of two sets of 1-D plasmonic crystal reflectors on a plasmonic trench waveguide. A 'reverse image mold' (RIM) technique was developed to pattern high-resolution silver trenches and to embed emitters at the cavity field maximum, and FDTD simulations were performed to analyze the frequency response of the fabricated devices. Distinct cavity modes were observed from the photoluminescence spectra of the organic dye embedded within these cavities. The cavity geometry facilitates tuning of the modes through a change in cavity dimensions. Both the design and the fabrication technique presented could be extended to making trench waveguide-based plasmonic devices and circuits.
Aharonovich, Igor, Alexander Woolf, Kasey J Russell, Tongtong Zhu, Nan Niu, Menno J Kappers, Rachel A Oliver, and Evelyn L Hu. 2013. “Low threshold, room-temperature microdisk lasers in the blue spectral range.” APPLIED PHYSICS LETTERS 103 (2). apl_1um_microdisk_lasers.pdf
Magyar, Andrew P, Igor Aharonovich, Mor Baram, and Evelyn L Hu. 2013. “Photoluminescent {SiC} Tetrapods.” Nano Letters 13: 1210–1215. Publisher's VersionAbstract
Recently, significant research efforts have been made to develop complex nanostructures to provide more sophisticated control over the optical and electronic properties of nanomaterials. However, there are only a handful of semiconductors that allow control over their geometry via simple chemical processes. Herein, we present a molecularly seeded synthesis of a complex nanostructure, {SiC} tetrapods, and report on their structural and optical properties. The {SiC} tetrapods exhibit narrow line width photoluminescence at wavelengths spanning the visible to near-infrared spectral range. Synthesized from low-toxicity, earth abundant elements, these tetrapods are a compelling replacement for technologically important quantum optical materials that frequently require toxic metals such as Cd and Se. This previously unknown geometry of {SiC} nanostructures is a compelling platform for biolabeling, sensing, spintronics, and optoelectronics.
Lee, Jonathan C, Andrew P Magyar, David O Bracher, Igor Aharonovich, and Evelyn L Hu. 2013. “Fabrication of thin diamond membranes for photonic applications.” Diamond and Related Materials 33: 45-48.
Joo, John H, Kathryn J Greenberg, Mor Baram, David R Clarke, and Evelyn L Hu. 2013. “Aqueous Epitaxial Growth of {ZnO} on Single Crystalline Au Microplates.” Crystal Growth & Design 13: 986–991. Publisher's VersionAbstract
Epitaxial {ZnO} thin films were grown on single crystalline Au microplates from an aqueous solution at 90 {°C.} The composite structures were approximately 100 ?m wide. The epitaxial {ZnO} films were smooth, continuous, and several micrometers thick. We examined the epitaxial relationship between the {ZnO} and Au through scanning electron microscopy, electron backscatter diffraction, high-resolution transmission electron microscopy, and electron diffraction and demonstrated control over the resulting film morphology through the kinetics of growth. An epitaxial relationship of {ZnO[11?00](0002)?Au[21?1?](111)} was dominant in the structures.

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