Browsing by Author "Engheta, Nader"

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Air-stable, nanostructured electronic and plasmonic materials from solution-processable, silver nanocrystal building blocks
(American Chemical Society, 2014) Fafarman, Aaron T.; Hong, Sung-Hoon; Oh, Soong Ju; Caglayan, Humeyra; Ye, Xingchen; Diroll, Benjamin T.; Engheta, Nader; Murray, Christopher B.; Kagan, Cherie R.; 0000-0002-0656-614X; AGÜ, Mühendislik Fakültesi, Elektrik - Elektronik Mühendisliği Bölümü; Caglayan, Humeyra
Herein we describe a room-temperature, chemical process to transform silver nanocrystal solids, deposited from colloidal solutions, into highly conductive, corrosion-resistant, optical and electronic materials with nanometer-scale architectures. After assembling the nanocrystal solids, we treated them with a set of simple, compact, organic and inorganic reagents: ammonium thiocyanate, ammonium chloride, potassium hydrogen sulfide, and ethanedithiol. We find that each reagent induces unique changes in the structure and composition of the resulting solid, giving rise to films that vary from insulating to, in the case of thiocyanate, conducting with a remarkably low resistivity of 8.8 × 10-6 ·cm, only 6 times that of bulk silver. We show that thiocyanate mediates the spontaneous sintering of nanocrystals into structures with a roughness of less than 1/10th of the wavelength of visible light. We demonstrate that these solution-processed, low-resistivity, optically smooth films can be patterned, using imprint lithography, into conductive electrodes and plasmonic mesostructures with programmable resonances. We observe that thiocyanate-treated solids exhibit significantly retarded atmospheric corrosion, a feature that dramatically increases the feasibility of employing silver for electrical and plasmonic applications.
Role of epsilon-near-zero substrates in the optical response of plasmonic antennas
(OPTICAL SOC AMER, 2010 MASSACHUSETTS AVE NW, WASHINGTON, DC 20036 USA, 2016) Kim, Jongbum; Dutta, Aveek; Naik, Gururaj V.; Giles, Alexander J.; Bezares, Francisco J.; Ellis, Chase T.; Tischler, Joseph G.; Mahmoud, Ahmed M.; Caglayan, Humeyra; Glembocki, Orest J.; Kildishev, Alexander V.; Caldwell, Joshua D.; Boltasseva, Alexandra; Engheta, Nader; AGÜ, Mühendislik Fakültesi, Elektrik & Elektronik Mühendisliği Bölümü;
Radiation patterns and the resonance wavelength of a plasmonic antenna are significantly influenced by its local environment, particularly its substrate. Here, we experimentally explore the role of dispersive substrates, such as aluminum-or gallium-doped zinc oxide in the near infrared and 4H-silicon carbide in the mid-infrared, upon Au plasmonic antennas, extending from dielectric to metal-like regimes, crossing through epsilon-near-zero (ENZ) conditions. We demonstrate that the vanishing index of refraction within this transition induces a "slowing down" of the rate of spectral shift for the antenna resonance frequency, resulting in an eventual "pinning" of the resonance near the ENZ frequency. This condition corresponds to a strong backward emission with near-constant phase. By comparing heavily doped semiconductors and undoped, polar dielectric substrates with ENZ conditions in the near- and mid-infrared, respectively, we also demonstrate the generality of the phenomenon using both surface plasmon and phonon polaritons, respectively. Furthermore, we also show that the redirected antenna radiation induces a Fano-like interference and an apparent stimulation of optic phonons within SiC. (C) 2016 Optical Society of America