Tunable top-down fabrication and functional surface coating of single-crystal titanium dioxide nanostructures and nanoparticles

Abstract

Titanium dioxide (TiO2) is a key component of diverse optical and electronic applications that exploit its exceptional material properties. In particular, the use of TiO2 in its single-crystalline phase can offer substantial advantages over its amorphous and polycrystalline phases for existing and yet-to-be-developed applications. However, the implementation of single-crystal TiO2 has been hampered by challenges in its fabrication and subsequent surface functionalization. Here, we introduce a novel top-down approach that allows for batch fabrication of uniform high-aspect-ratio single-crystal TiO2 nanostructures with targeted sidewall profiles. We complement our fabrication approach with a functionalization strategy that achieves dense, uniform, and area-selective coating with a variety of biomolecules. This allows us to fabricate single-crystal rutile TiO2 nanocylinders tethered with individual DNA molecules for use as force- and torque-transducers in an optical torque wrench. These developments provide the means for increased exploitation of the superior material properties of single-crystal TiO2 at the nanoscale.

Single-Crystal Rutile TiO2 Nanocylinders are Highly Effective Transducers of Optical Force and Torque

“…This configuration allows the precise angular manipulation around z -axis, with a trapping beam linearly polarized in xy -plane (as depicted in Figure 1e). Compared to our previously reported fabrication protocol, 28 we further optimized the chromium mask shape and thickness to obtain more circular cross sections and smaller taper angles (see details in Supporting Information, Figure S10). The steps in the nanofabrication protocol that control nanocylinder diameter and height are electron-beam lithography (EBPG 5000 or EBPG 5200, Vistec) and plasma etching (Fluor Z401S, Leybold Heraeus or Plasmalab System 100, Oxford Instr.…”

“…42 Also, biomolecules with primary amino groups can be directly coupled to epoxysilane layer in the absence of PEG, as previously demonstrated. 28…”

“…Furthermore, rutile TiO 2 in its pure single-crystalline form can be maintained at the nanoscale level via top-down fabrication. 28 This makes it possible to harness its full nominal birefringence and optical index, without any of the reduction observed in porous polycrystalline structures prepared by bottom-up processes. 29,30 Lastly, rutile TiO 2 has demonstrated biocompatibility and biofunctionalizability and is chemically, mechanically, and thermally stable.…”

“…29,30 Lastly, rutile TiO 2 has demonstrated biocompatibility and biofunctionalizability and is chemically, mechanically, and thermally stable. 28 This means that it may be employed under tougher conditions (e.g., high pressure, high temperature, or prolonged exposure to aqueous and biological environments) relative to other birefringent materials such as CaCO 3 (which dissolves in aqueous environments 23 ).…”

Synergistic Coordination of Chromatin Torsional Mechanics and Topoisomerase Activity

“…Quartz cylinders (diameter: 549 ± 56 nm (SD), height: 916 ± 48 nm (SD)) were optically birefringent and nanofabricated based on protocols previously described (Deufel et al, 2007) with some modifications (Ha et al, 2016). In brief, a 4'' quartz wafer (Precision Micro-Optics) was coated with 100 nm of sputtered chromium for an etch mask.…”