Excitation of Strong Localized Surface Plasmon Resonances in Highly Metallic Titanium Nitride Nano-Antennas for Stable Performance at Elevated Temperatures

Abstract

New opportunities for plasmonic applications at high temperatures have stimulated interest in refractory plasmonic materials that show greater stability at elevated temperatures than the more commonly used silver and gold (Au). Titanium nitride (TiN) has been identified as a promising refractory material, with deposition of TiN thin films through techniques ranging from plasma-enhanced atomic laser deposition to sputter deposition to pulsed laser deposition, on a variety of substrates, including MgO, polymer, SiO2, and sapphire. A variety of plasmonic devices have been evaluated, including gratings, nanorods, and nanodisks. An implicit metric for TiN behavior has been the comparison of its plasmonic performance to that of Au, in particular at various elevated temperatures. This paper carries out a one-to-one comparison of bowtie nanoantennas formed of TiN and Au (on both Si and MgO substrates), examining the far-field characteristics, related to the measured near-field resonances. In both cases, the optical constants of the TiN films were used to simulate the expected plasmonic responses and enjoyed excellent agreement with the experimental measurements. Furthermore, we examined the consistency of the plasmonic response and the morphological changes in the TiN and Au nanoantennas at different temperatures up to 800 °C in the atmosphere. This comparison of the measured plasmonic response from nanoscale resonances to the far-field response allows for anomalies or imperfections that may be introduced by the nanofabrication processes and provides a more accurate comparison of TiN plasmonic behavior relative to the Au standard.

A Platform for Complementary Metal‐Oxide‐Semiconductor Compatible Plasmonics: High Plasmonic Quality Titanium Nitride Thin Films on Si (001) with a MgO Interlayer

“…[15][16][17][18] In the area of plasmonics, TiN-based waveguides, [19] gyroidal metamaterials, [20] nanohole metasurfaces, [21] nanoantennas, [22][23][24] and use of TiN nanoparticles for solar energy conversion [25,26] and biomedicine [27] have been reported.However, the majority of the demonstrations of TiN's device potential in plasmonics have been on sapphire and bulk MgO substrates featured by their small lattice mismatch with TiN, enabling the best-performing plasmonic films. [24,[28][29][30][31][32][33] Even then, high deposition temperatures (not congruent with CMOS processes) were usually used to ensure the high structural quality of the TiN films. For example, using reactive sputtering and at a substrate temperature of 650 C, a peak plasmonic figure of merit (FOM ¼ Àε 0 /ε 00 ) of %4.5 has been demonstrated for TiN films on a bulk MgO substrate.…”

“…[14] TiN has been widely used as a gate electrode in various CMOS devices. [15][16][17][18] In the area of plasmonics, TiN-based waveguides, [19] gyroidal metamaterials, [20] nanohole metasurfaces, [21] nanoantennas, [22][23][24] and use of TiN nanoparticles for solar energy conversion [25,26] and biomedicine [27] have been reported.…”

“…This requires the growth of high plasmonic quality TiN on Si substrates at CMOS-compatible temperatures. However, so far, only moderate plasmonic properties could be attained for TiN films grown on Si substrates using various deposition methods such as sputtering, [24,33,34] pulsed laser deposition (PLD), [35] and atomic layer deposition (ALD) [23] primarily due to the associated large lattice mismatch (21.9%). A relatively low resistivity of 1.5 Â 10 À5 Ω cm could be achieved by PLD only at temperatures as high as 700 C, [35] and TiN films grown on Si at lower temperatures of 250 C by ALD, although used to demonstrate fully CMOS-compatible plasmonic nanoantennas, exhibited weak metallic character (i.e., insufficiently large negative ε 0 of À24) and much higher loss (larger ε 00 of 41) compared with TiN films on MgO (ε 0 þiε 00 ¼ À30 þ 26i) at telecommunication wavelength 1550 nm.…”

Etchless Fabrication of High‐Quality Refractory Titanium Nitride Nanostructures

“…Indeed, the array of nanoislands is periodic with a few stacking faults of the PS spheres. Well‐defined and isolated trigonal TiN islands were produced with size (150 nm) comparable with trigonal plasmonic nanoantennas produced by electron beam lithography, [ 19 ] and contrastingly different than the continuous mesh of TiN deposited without O‐plasma treatment of the mask and for ion energy of 20 eV (Figure 1a). It is noteworthy that in the centers of all hexagonal sets of trigonal nanoislands there are well‐defined rings of 60 nm radius and height smaller than 2 nm.…”

“…In this quest, special emphasis has been given to titanium nitride (TiN) [ 1–14 ] as a refractory plasmonic conductor that resembles gold, [ 11,12 ] with the additional asset of enduring the extreme electric fields of high‐power lasers. [ 13 ] The refractory character of TiN and its growth predominantly by reactive sputtering, which provides the CMOS compatibility, are simultaneously blessings and curses, as they limit the fabrication of nitride plasmonic nanostructures to top‐down processes, such as focused ion beam, [ 15 ] the combination of electron beam lithography [ 16–19 ] and nanoimprint lithography with reactive ion etching, [ 20,21 ] or laser patterning with wet chemical etching [ 13,22 ] so far. Despite the spatial accuracy of top‐down processing, such fabrication is time‐consuming, costly, and of limited scalability.…”