Query: Epitaxial superlattices with titanium nitride as a plasmonic component for optical hyperbolic metamaterials.

Candidate papers:

abstract: Significance Plasmonic and metamaterial devices require high performance material building blocks, both plasmonic and dielectric, to be useful in any real world application. Here, we develop both plasmonic and dielectric materials that can be grown epitaxially into ultrathin and ultrasmooth layers with sharp interfaces. We show that a superlattice consisting of titanium nitride as a plasmonic component behaves as an optical hyperbolic metamaterial and exhibits extremely high photonic density of states. Titanium nitride (TiN) is a plasmonic material having optical properties resembling gold. Unlike gold, however, TiN is complementary metal oxide semiconductor compatible, mechanically strong, and thermally stable at higher temperatures. Additionally, TiN exhibits low index surfaces with surface energies that are lower than those of the noble metals which facilitates the growth of smooth, ultrathin crystalline films. Such films are crucial in constructing low loss, high performance plasmonic and metamaterial devices including hyperbolic metamaterials (HMMs) HMMs have been shown to exhibit exotic optical properties, including extremely high broadband photonic densities of states (PDOS) which are useful in quantum plasmonic applications. However, the extent to which the exotic properties of HMMs can be realized has been seriously limited by fabrication constraints and material properties. Here, we address these issues by realizing an epitaxial superlattice as an HMM. The superlattice consists of ultrasmooth layers as thin as 5 nm and exhibits sharp interfaces which are essential for high quality HMM devices. Our study reveals that such a TiN based superlattice HMM provides a higher PDOS enhancement than gold or silver based HMMs.
author_names: Gururaj V Naik

Bivas Saha

Jing Liu

Sammy M Saber

Eric A Stach

Joseph M K Irudayaraj

Timothy D Sands

Vladimir M Shalaev

Alexandra Boltasseva
title: Epitaxial superlattices with titanium nitride as a plasmonic component for optical hyperbolic metamaterials
venue: Proceedings of the National Academy of Sciences
year: 2014

abstract: Noble metals such as gold and silver are conventionally used as the primary plasmonic building blocks of optical metamaterials. Making subwavelength scale structural elements from these metals not only seriously limits the optical performance of a device due to high absorption, it also substantially complicates the manufacturing process of nearly all metamaterial devices in the optical wavelength range. As an alternative to noble metals, we propose to use heavily doped oxide semiconductors that offer both functional and fabrication advantages in the near infrared wavelength range. In this letter, we replace a metal with aluminum doped zinc oxide as a new plasmonic material and experimentally demonstrate negative refraction in an Al:ZnO/ZnO metamaterial in the near infrared range.
author_names: Gururaj V Naik

Jingjing Liu

Alexander V Kildishev

Vladimir M Shalaev

Alexandra Boltasseva
title: Demonstration of Al:ZnO as a plasmonic component for near infrared metamaterials
venue: Proceedings of the National Academy of Sciences
year: 2012

abstract: As alternatives to conventional metals, new plasmonic materials offer many advantages in the rapidly growing fields of plasmonics and metamaterials. These advantages include low intrinsic loss, semiconductor based design, compatibility with standard nanofabrication processes, tunability, and others. Transparent conducting oxides such as Al:ZnO, Ga:ZnO and indium tin oxide (ITO) enable many high performance metamaterial devices operating in the near IR. Transition metal nitrides such as TiN or ZrN can be substitutes for conventional metals in the visible frequencies. In this paper we provide the details of fabrication and characterization of these new materials and discuss their suitability for a number of metamaterial and plasmonic applications.
author_names: Gururaj V Naik

Jongbum Kim

Alexandra Boltasseva
title: Oxides and nitrides as alternative plasmonic materials in the optical range [Invited]
year: 2011

abstract: We investigate the absorption properties of planar hyperbolic metamaterials (HMMs) consisting of metal dielectric multilayers, which support propagating plane waves with anomalously large wavevectors and high photonic density of states over a broad bandwidth. An interface formed by depositing indium tin oxide nanoparticles on an HMM surface scatters light into the high k propagating modes of the metamaterial and reduces reflection. We compare the reflection and absorption from an HMM with the nanoparticle cover layer versus those of a metal film with the same thickness also covered with the nanoparticles. It is predicted that the super absorption properties of HMM show up when exceedingly large amounts of high k modes are excited by strong plasmonic resonances. In the case that the coupling interface is formed by non resonance scatterers, there is almost the same enhancement in the absorption of stochastically perturbed HMM compared to that of metal.
author_names: Jingjing Liu

Gururaj V Naik

Satoshi Ishii

Clayton Devault

Alexandra Boltasseva

Vladimir M Shalaev

Evgenii Narimanov
title: Optical absorption of hyperbolic metamaterial with stochastic surfaces.
venue: Optics express
year: 2014

abstract: We have fabricated two dimensional periodic arrays of titanium nitride (TiN) nanoparticles from epitaxial thin films. The thin films of TiN, deposited on sapphire and single crystalline magnesium oxide substrates by a pulsed laser deposition, are metallic and show reasonably small optical loss in the visible and near infrared regions. The thin films prepared were structured to the arrays of nanoparticles with the pitch of 400 nm by the combination of nanoimprint lithography and reactive ion etching. Optical transmission indicates that the arrays support the collective plasmonic modes, where the localized surface plasmon polaritons in TiN nanoparticles are radiatively coupled through diffraction. Numerical simulation visualizes the intense fields accumulated both in the nanoparticles and in between the particles, confirming that the collective mode originates from the simultaneous excitation of localized surface plasmon polaritons and diffraction. This study experimentally verified that the processing of TiN thin films with the nanoimprint lithography and reactive ion etching is a powerful and versatile way of preparing plasmonic nanostructures.
author_names: Shunsuke Murai

Koji Fujita

Yohei Daido

Ryuichiro Yasuhara

Ryosuke Kamakura

Katsuhisa Tanaka
title: Plasmonic arrays of titanium nitride nanoparticles fabricated from epitaxial thin films.
venue: Optics express
year: 2016

abstract: High aspect ratio titanium nitride (TiN) grating structures are fabricated by the combination of deep reactive ion etching (DRIE) and atomic layer deposition (ALD) techniques. TiN is deposited at 500 degC on a silicon trench template. Silicon between vertical TiN layers is selectively etched to fabricate the high aspect ratio TiN trenches with the pitch of 400 nm and height of around 2.7 mm. Dielectric functions of TiN films with different thicknesses of 18 105 nm and post annealing temperatures of 700 900 degC are characterized by an ellipsometer. We found that the highest annealing temperature of 900 degC gives the most pronounced plasmonic behavior with the highest plasma frequency, op 2.53 eV (lp 490 nm) Such high aspect ratio trench structures function as a plasmonic grating sensor that supports the Rayleigh Woods anomalies (RWAs) enabling the measurement of changes in the refractive index of the ambient medium in the wavelength range of 600 900 nm. We achieved the bulk refractive index sensitivity (BRIS) of approximately 430 nm/RIU relevant to biosensing liquids.
author_names: Evgeniy Shkondin

Taavi Repan

Osamu Takayama

Andrei V Lavrinenko
title: High aspect ratio titanium nitride trench structures as plasmonic biosensor
year: 2017

abstract: 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 600degC. 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)
author_names: Christine M Zgrabik

Evelyn L Hu
title: Optimization of sputtered titanium nitride as a tunable metal for plasmonic applications
year: 2015

abstract: An ideal hyperbolic metamaterial (HMM) which has a perfect hyperbolic dispersion curve, theoretically can support modes with indefinite wavenumbers, leading to large photon local density of states (LDOS) and many applications such as enhancing light matter interactions, spontaneous emission and thermal radiation. Here in this presentation, HMMs based on ultrathin metal dielectric multilayers have been studied by considering the nonlocal response of electrons in metal. Based on the hydrodynamic model of the nonlocal response, we investigate the effect of nonlocality on the performance (dispersion relation, ray refraction, LDOS and spontaneous emission) of HMMs when gradually approaching the ultrathin limit of the unit cell. We show that nonlocality will induce topological transitions of the iso frequency surfaces and limit the wavenumber as well as LDOS for both type I and type II HMMs. Under nonlocal treatment, the iso frequency surface of type II HMM transforms from a hyperbola to a bullet shape, while for type I HMM, the surface splits into two branches: a cylindrical like branch at high k region and an elliptical branch at the low k region. In the high k region, the nonlocality set a cut off k for the allowed wavenumbers in both type I and type II HMMs. This cut off k which is defined by the electron Fermi velocity of the metal intrinsically limits the LDOS and light matter interactions. These results indicate that in the aim of achieving high performance HMMs, merely thinning the constituent films according to the local theories is no longer valid.
author_names: L R Chen

Cheng Zhang

Jing Zhou

L Jay Guo
title: Probing the ultrathin limit of hyperbolic metamaterial: nonlocality induced topological transitions (Presentation Recording)
venue: SPIE NanoScience Engineering
year: 2015

abstract: Highly efficient second harmonic generation (SHG) bridging the mid infrared (IR) and near IR wavelengths in a coupled hyperbolic metamaterial waveguide with a nonlinear polymer filled nanoscale slot is theoretically investigated. By engineering the geometrical parameters, the collinear phase matching condition is satisfied between the even hybrid modes at the fundamental frequency (3,100 nm) and the second harmonic (1,550 nm) Two modes manifest the great field overlap and the significant field enhancement in the nonlinear integration area (i.e. the slot) which leads to extreme large nonlinear coupling coefficient. For a low pumping power of 100 mW, the device length is as short as 2.19 um and the normalized conversion efficiency comes up to more than 6.37 x 10(5) W( 1)cm( 2) which outperforms that of the plasmonic based structures. Moreover, the efficient SHG can be achieved with great phase matching tolerance, i.e. a small theoretical fabrication error sensitivity to filling ratio and a broad pump bandwidth in a compact device length of 2.19 um using 100 mW pump. The proposed scheme links the mature near IR devices to the mid IR regime and have a great potential for integrated chip scale all optical signal processes.
author_names: Yu Sun

Zheng Zheng

Jiangtao Cheng

Guodong Sun

Guofu Qiao
title: Highly efficient second harmonic generation in hyperbolic metamaterial slot waveguides with large phase matching tolerance.
venue: Optics express
year: 2015

abstract: The refractory metal titanium nitride is promising for high temperature nanophotonic and plasmonic applications, but its optical properties have not been studied at temperatures exceeding 400 degC. Here, we perform in situ high temperature ellipsometry to quantify the permittivity of TiN films from room temperature to 1258 degC. We find that the material becomes more absorptive at higher temperatures but maintains its metallic character throughout visible and near infrared frequencies. X ray diffraction, atomic force microscopy, and mass spectrometry confirm that TiN retains its bulk crystal quality and that thermal cycling increases the surface roughness, reduces the lattice constant, and reduces the carbon and oxygen contaminant concentrations. The changes in the optical properties of the material are highly reproducible upon repeated heating and cooling, and the room temperature properties are fully recoverable after cooling. Using the measured high temperature permittivity, we compute the emissivity, surf.
author_names: Justin A Briggs

Gururaj V Naik

Yang Zhao

Trevor A Petach

Kunal Sahasrabuddhe

David Goldhaber-Gordon

Nicholas A Melosh

Jennifer A Dionne
title: Temperature dependent optical properties of titanium nitride
year: 2017