Ultrathin Titanium Nitride Epitaxial Structures for Tunable Infrared Plasmonics

Abstract

Titanium nitride (TiN) is an ideal material for infrared plasmonics due to its excellent optical properties, high melting temperature, mechanical and chemical stabilities, and bioand CMOS compatibilities. In this work, we demonstrate that ultrathin and scalable TiN epitaxial structures can be applied for tunable infrared plasmonics, extending into near-to mid-infrared spectral regions. The ultrathin (111)-oriented TiN epitaxial films studied here were grown on c-plane sapphire wafers without any wetting layer by ultrahigh-vacuum nitrogen-plasma-assisted molecular-beam epitaxy. This method allows for stoichiometric TiN growth without the issue of contamination (especially oxygen) in conventional TiN growth techniques. Structural analyses for these films validate their single-crystalline properties with continuous film morphologies down to a few nanometers in thickness. Furthermore, the frequency-tunable (wavelength range: 1−4 μm) plasmonic metasurfaces have been demonstrated by controlling surface plasmon resonances via lithographically patterning of ultrathin TiN epitaxial films with varying thicknesses (4−30 nm) and grating structure parameters (pitch: 300−1200 nm, width: 200−800 nm). The tunable plasmonic metasurfaces based on ultrathin TiN epitaxial films hold great promise for emerging infrared plasmonic applications, such as thermal photovoltaics requiring narrow-band emitters, photodetectors, and biosensors in the near-and midinfrared spectral regions.

Stoichiometry-Led Electronic Structure Reconstruction Finetunes the Color Characteristics of Titanium Nitride Thin Films

“…Thin films of titanium nitrides (TiN x ) have been employed in application ranging from wear resistant coatings for tools, − diffusion barrier layers, − to decorative layers , in order to use their outstanding material properties, such as high hardness, thermal and chemical stability and good electrical conductivity. The versatility of this early transition metal nitride is due to its ability to crystallize in a rock-salt structure in a wide range of compositions exhibiting considerable microstructural variation .…”