Correlation between electrical direct current resistivity and plasmonic properties of CMOS compatible titanium nitride thin films.

Damping distances of surface plasmon polariton modes sustained by different thin titanium nitride (TiN) films are measured at the telecom wavelength of 1.55 µm. The damping distances are correlated to the electrical direct current resistivity of the films sustaining the surface plasmon modes. It is found that TiN/Air surface plasmon mode damping distances drop non-linearly from 40 to 16µm as the resistivity of the layers increases from 28 to 130µΩ.cm, respectively. The relevance of the direct current (dc) electrical resistivity for the characterization of TiN plasmonic properties is investigated in the framework of the Drude model, on the basis of parameters extracted from spectroscopic ellipsometry experiments. By probing a parametric space of realistic values for parameters of the Drude model, we obtain a nearly univocal dependence of the surface plasmon damping distance on the dc resistivity demonstrating the relevance of dc resistivity for the evaluation of the plasmonic performances of TiN at telecom frequencies. Finally, we show that better plasmonic performances are obtained for TiN films featuring a low content of oxygen. For low oxygen content and corresponding low resistivity, we attribute the increase of the surface plasmon damping distances to a lower confinement of the plasmon field into the metal and not to a decrease of the absorption of TiN.

Characterization of CMOS metal based dielectric loaded surface plasmon waveguides at telecom wavelengths.

Dielectric loaded surface plasmon waveguides (DLSPPWs) comprised of polymer ridges deposited on top of CMOS compatible metal thin films are investigated at telecom wavelengths. We perform a direct comparison of the properties of copper (Cu), aluminum (Al), titanium nitride (TiN) and gold (Au) based waveguides by implementing the same plasmonic waveguiding configuration for each metal. The DLSPPWs are characterized by leakage radiation microscopy and a fiber-to-fiber configuration mimicking the cut-back method. We introduce the ohmic loss rate (OLR) to analyze quantitatively the properties of the CMOS metal based DLSPPWs relative to the corresponding Au based waveguides. We show that the Cu, Al and TiN based waveguides feature extra ohmic loss compared to Au of 0.027 dB/µm, 0.18 dB/µm and 0.52 dB/µm at 1550nm respectively. The dielectric function of each metal extracted from ellipsometric spectroscopic measurements is used to model the properties of the DLSP-PWs. We find a fairly good agreement between experimental and modeled DLSPPWs properties except for Al featuring a large surface roughness. Finally, we conclude that TiN based waveguides sustaining intermediate effective index (in the range 1.05-1.25) plasmon modes propagate over very short distances restricting the the use of those modes in practical situations.

From patterned optical near-fields to high symmetry acoustic vibrations in gold crystalline platelets.

Noble metal particles allow enhanced interaction with light and efficient light to heat conversion. In the present paper, we report on non-linear optical spectroscopy of individual gold crystalline platelets and address two of the energy relaxation steps following optical excitation of the metallic nano-objects. In particular, at short timescales we show that optical excitation yields intense two-photon photoluminescence at particular locations of the gold platelets. Our experimental results are interpreted with numerical simulations based on the Green Dyadic Method. Subsequent conversion from optical to thermal energy triggers acoustic vibrations that modulate the optical response of the nano-object on a 10 ps-100 ps timescale. We address the different contributions to the damping of the associated mechanical oscillations focusing on the high frequency thickness vibrations (100 GHz) of these nanometer-thin metallic structures.