Nanoporous antireflection coating for high-temperature applications in the infrared.

Antireflection (AR) coatings are essential to the performance of optical systems; without them, surface reflections increase significantly at steep angles and become detrimental to the functionality. AR coatings apply to a wide range of applications from solar cells and laser optics to optical windows. Many times, operational conditions include high temperatures and steep angles of incidence (AOIs). The implementation of AR coatings is extremely challenging in these conditions. Nanoporous coatings made from high-temperature-tolerant materials offer a solution to this problem. The careful selection of materials is needed to prevent delamination when exposed to high temperatures, and an optimal optical design is needed to lower surface reflections at both the normal incidence and steep AOIs. This paper presents nanoporous silicon dioxide and hafnium dioxide coatings deposited on a sapphire substrate using oblique angle deposition by electron beam evaporation, a highly accurate deposition technique for thin films. Developed coatings were tested in a controlled temperature environment and demonstrated thermal stability at temperatures up to 800°C. Additional testing at room temperature demonstrated the reduction of power reflections near optimal for AOIs up to 70° for a design wavelength of 1550 nm. These findings are promising to help extend the operation of technology at extreme temperatures and steep angles.

Imaging of surface plasmon polaritons in low-loss highly metallic titanium nitride thin films in visible and infrared regimes.

Titanium nitride (TiN) has been identified as a promising refractory material for high temperature plasmonic applications such as surface plasmon polaritons (SPPs) waveguides, lasers and light sources, and near field optics. Such SPPs are sensitive not only to the highly metallic nature of the TiN, but also to its low loss. We have formed highly metallic, low-loss TiN thin films on MgO substrates to create SPPs with resonances between 775-825 nm. Scanning near-field optical microscopy (SNOM) allowed imaging of the SPP fringes, the accurate determination of the effective wavelength of the SPP modes, and propagation lengths greater than 10 microns. Further, we show the engineering of the band structure of the plasmonic modes in TiN in the mid-IR regime and experimentally demonstrate, for the first time, the ability of TiN to support Spoof Surface Plasmon Polaritons in the mid-IR (6 microns wavelength).

A comparison of inverted and upright laser-activated titanium nitride micropyramids for intracellular delivery.

The delivery of biomolecules into cells relies on porating the plasma membrane to allow exterior molecules to enter the cell via diffusion. Various established delivery methods, including electroporation and viral techniques, come with drawbacks such as low viability or immunotoxicity, respectively. An optics-based delivery method that uses laser pulses to excite plasmonic titanium nitride (TiN) micropyramids presents an opportunity to overcome these shortcomings. This laser excitation generates localized nano-scale heating effects and bubbles, which produce transient pores in the cell membrane for payload entry. TiN is a promising plasmonic material due to its high hardness and thermal stability. In this study, two designs of TiN micropyramid arrays are constructed and tested. These designs include inverted and upright pyramid structures, each coated with a 50-nm layer of TiN. Simulation software shows that the inverted and upright designs reach temperatures of 875 °C and 307 °C, respectively, upon laser irradiation. Collectively, experimental results show that these reusable designs achieve maximum cell poration efficiency greater than 80% and viability greater than 90% when delivering calcein dye to target cells. Overall, we demonstrate that TiN microstructures are strong candidates for future use in biomedical devices for intracellular delivery and regenerative medicine.

Nonlinear Refractory Plasmonics with Titanium Nitride Nanoantennas.

Titanium nitride (TiN) is a novel refractory plasmonic material which can sustain high temperatures and exhibits large optical nonlinearities, potentially opening the door for high-power nonlinear plasmonic applications. We fabricate TiN nanoantenna arrays with plasmonic resonances tunable in the range of about 950-1050 nm by changing the antenna length. We present second-harmonic (SH) spectroscopy of TiN nanoantenna arrays, which is analyzed using a nonlinear oscillator model with a wavelength-dependent second-order response from the material itself. Furthermore, characterization of the robustness upon strong laser illumination confirms that the TiN antennas are able to endure laser irradiation with high peak intensity up to 15 GW/cm(2) without changing their optical properties and their physical appearance. They outperform gold antennas by one order of magnitude regarding laser power sustainability. Thus, TiN nanoantennas could serve as promising candidates for high-power/high-temperature applications such as coherent nonlinear converters and local heat sources on the nanoscale.