Metal oxides such as titanium oxide (TiO2) and zirconium oxide (ZrO2) have attracted a great interest in recent years due to their many remarkable physical and chemical properties. The high performance of these materials allows their use in a wide range of applications such as photocatalysis, mechanics and chemistry. They are also used in optical applications; as sensors, anti-counterfeiting devices, or in medical applications for dental implants. In this paper, we present a process for structuring thin films of metal oxides using a sol-gel deposition method. Unlike more conventional methods such as reactive sputtering, chemical vapor deposition and atomic layer deposition, this technique facilitates the micro-nano structuring of films by optical lithography techniques, in particular colloidal lithography.
Zirconium nitride (ZrN) combines plasmonic properties in the visible and near infrared spectral region with good mechanical properties, high thermal and chemical stability making it a very promising alternative to noble metals for optical applications at high temperature or in extreme environments. The authors present a new process for the elaboration of micro-nanostructured ZrN from a photo-patternable ZrO2 sol-gel and a nitridation process, by rapid thermal annealing. This sol-gel is patternable by optical lithography, it allows to easily and quickly produce patterned ZrN layer.
A subwavelength structure made of a resonant waveguide grating embedded in a luminescent sol-gel layer enables a dual color effect. The resonant waveguide grating consists of a diffraction grating and a high refractive index guiding layer using a TiO2 based sol-gel with a higher refractive index (ng = 2.2) than its silica sol-gel surroundings (ns=1.5). The resonant waveguide grating is designed to achieve visible resonant reflection of TE polarized incident waves in the green color spectrum. The resonant structure is then coated with a thick layer of silicone doped with a luminescent material of formulation Y2O2S:Eu3+. This latter leads to emission in the red domain under UV excitation. This quasi-symmetric structure is transparent in the visible range for observing the various phenomena. Nano-imprint technology is used for the fabrication of the grating on the sol gel layer to demonstrate its fabrication potential. Therefore, it is a low-cost fabrication technique used to replicate the microstructure, which can be up scaled for industrial applications. Preliminary results will be presented at the conference, covering modelling through the design of the optimized microstructures. Experimental results will be showcased with first demonstrators comprising Nanoimprinted sol-gel layers with a resonant waveguide grating and a luminescent layer. Experimental measurements will be carried out to characterise both the optical performance of the luminescent coating and the resonant waveguide grating.
Nanoimprint lithography (NIL) is nowadays the most popular and effective method to develop new environmentally-friendly and low-cost photonic nanodevices. Combined with titanium dioxide (TiO2) in the form of sol-gel, photonic nanostructures with low absorption and high refractive index can be produced, which can be of interest for many applications for which sustainability becomes increasingly important. In this paper, we present a patterning process based on soft NIL of TiO2 sol-gel, and show that the pattern transfer is almost perfect independently from the feature size, shape and height of the patterns. We also propose a low-temperature (400°C) calcination process to crystallize the TiO2 nanostructures, which leads to very similar crystalline structures to higher-temperature processes, and a vertical shrinkage of about 61% compared to the imprinted pattern. Using this environmentally-friendly combined soft-NIL + calcination process, we show that submicron patterns with heights above 300 nm can be obtained. Such a large pattern height, combined with the wide range of pattern shapes and dimensions that can be fabricated, opens the possibility of a wide diversity of designs for the eco-friendly fabrication of TiO2 nanostructures with highly-interesting photonic properties.
Zirconium oxide (ZrO2) is an intensively studied and used material due to its many remarkable physical and chemical properties. The high performances of ZrO2 allows its use in many applications such as coatings against corrosion, wear and oxidation, optical applications, anti-counterfeiting, or in medical applications such as dental or prosthesis. There are many methods to synthesize ZrO2 among which we can mention reactive sputtering, chemical vapor deposition, atomic layer deposition. These techniques are well known in thin film deposition processes. However, they do not allow to easily structure the coatings to produce complex patterns (shapes, micro-nanostructures) on variable substrates in shape and size. Another process of elaboration of ZrO2 thin films is the sol-gel method. This technique makes possible the micro-nanostructuring of the films by optical and nanoimprint-based lithography. In this paper, the authors will describe how the ZrO2 sol-gel can be used to obtain both complex patterns (shapes, micro-nanostructures) by optical lithography (mask lithography, colloidal lithography) and by nanoimprint lithography. The authors will also show the possibility to use this versatile sol-gel and the associated structuring methods to structure complex patterns on variable substrates in their nature and geometry, as well as the possibility of using this process in optical applications. Preliminary results will be presented through several microstructured ZrO2 demonstrators obtained from the microstructuring process on sol-gel layers. The produced layers have been characterized by Raman spectroscopy, scanning electron microscopy, atomic force microscopy. The optical properties (transmittance, reflectance) have also been investigated and a study of the influence of a thermal treatment on the refractive index and thickness of the layer has been carried out.
In this paper, a direct and cost-effective sol-gel method enables to produce stable titanium dioxide and titanium oxynitride photoresists is described. This approach is compatible with many photolithographic techniques. We show that laser interference lithography and nanosphere lithography can be used, respectively, to obtain homogeneous TiO2 diffraction gratings and periodic nanopillars over large areas. Further developments permit to transform TiO2 microstructured based sol-gel to TiN metallic microstructured layer, with good optical properties, by using an innovative rapid thermal nitridation process, which opens the way towards plasmonics and NIR filters based on periodic metallic microstructured layers.
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