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.
We have fabricated highly crystallized thin films of niobium-doped anatase type titania (Ti 1−x Nb x O 2) to examine the relationship between the electronic transport properties and the plasmonic response. Ti 1−x Nb x O 2 thin films were epitaxially grown on LaTiO 3 substrates by using pulsed laser deposition. Attenuated total reflectance spectra in the infrared (IR) region measured using the Otto configuration show a dip for p-polarized light, corresponding to an excitation of surface plasmon polaritons. The IR reflectivity data can be well reproduced by the theoretical calculation based on the Fresnel model, in which the dielectric function of Ti 1−x Nb x O 2 can be modeled by the combination of a Lorentz term and a Drude term. The real part of dielectric function for Ti 1−x Nb x O 2 (x = 0.03) is negative at the wavelengths longer than 2.78 μm in the IR region.
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