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.
Titanium nitride (TiN) 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 easy and fast process for the elaboration of micro-nanostructured TiN layers. This process combines photo-patternable TiO2 sol-gel by optical lithography and a nitridation process, by rapid thermal annealing (RTA). During this presentation, the elaboration of sol-gel, its structuring by different optical lithography methods, as well as its nitridation by RTA are presented.
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 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. Further technological processes were conducted to produce micro and nanostructured TiO2 and TiN layers from a NanoImprint approach.
This work demonstrates the versatility of this complete process of soft chemistry new process of patterning TiO2 and TiN thin films avoiding expensive processes (etching, lift-off…) while preserving their diffractive properties and a high thermal stability, up to 1000°C. It is thus compatible to various types of substrates (of different shape and size). These results open up the opportunity to develop a cost-effective and low time-consuming approach to address different fields of cutting-edge applications (metasurfaces, sensors, luxury and decorative industry…).
This work improves period uniformity over larger-area gratings in a two-spherical beam interference lithography (IL) setup. Using a concave vacuum chuck, we have experimentally demonstrated the modified optical setup to reduce period variation (chirp) on a 4-inch silicon substrate. The change in the grating period is significantly reduced compared with the interference exposure on a flat silicon substrate. Wavefront aberration measurement on a curved exposed substrate showed improved grating linearity.
Significant enhancement of the longitudinal magneto-optical effect accompanied with high transmission was demonstrated by experimental measurements and confirmed by numerical simulations for small angles of incidence. The work was led with a subwavelength resonant structure consisting of a 1D dielectric grating structured on top of a magneto-optical waveguide. The simplicity of the fabricated structure associated to the significant achieved magneto-optical effect, make the structure a promising tool for applications like magnetic field sensors or in non-destructive testing.
Periodic structuration of magnetic material is a way to enhance the magneto-optical behavior of optical devices like isolators. It is useful to reduce the footprint of such integrated devices or to improve their features. However, the structuration and/or integration of efficient magnetic materials on photonic platforms is still a difficult problem, because classical magneto-optical materials require an annealing temperature as high as 700°C. A novel wafer-scale approach is to incorporate that material into an already structured template through a single step deposition at low temperature. Using the dip-coating method, a magneto-optical thin film (~300nm) of CoFe2O4 nanoparticles in silica matrix prepared by sol-gel technique was coated on a 1D and 2D TiO2 subwavelength gratings. Such gratings were realized by the patterning of TiO2 films obtained by a sol-gel process. It was confirmed by Scanning Electron Microscope images that the magneto-optical composite completely occupies the voids of the 2D structuration showing a good compatibility between both materials. This composite shows a specific Faraday rotation of about 200°cm-1 at 1,5μm for 1% of volume fraction of nanoparticles. Spectral studies of the transmission and the reflection of a 1D TiO2 grating filled with the MO composite have evidenced the presence of a guided-mode optical resonance at 1,55μm. The position of this resonance was confirmed by numerical simulations, as well as its quite low efficiency. Based on simulations results, one can conclude that an increase of the grating depth is required to improve the efficiency of the resonance.
Due to their surface plasmon resonance silver nanoparticles are known to absorb visible light and give glasses
various colors. Grown in mesoporous titania films, they give the material a photochromic behaviour that can be used to
produce rewritable data carriers. On the one hand, UV light forms silver nanoparticles thanks to the photo-induced
generation of electrons by titania matrix. On the other hand, visible light oxidizes the silver nanoparticles via the
photoexcitation of electrons on Ag and their stabilization by oxygen molecules. The well controlled porosity of the
mesoporous films allows to tune the nanoparticles size and to obtain, under UV illumination, homogenous distributions
of small nanoparticles embedded within the titania matrix, which color the films. As all nanoparticles absorb light
similarly, the film can then be completely bleached under exposure to a visible laser beam whose wavelength falls in the
SPR band of the particles. Therefore, CW UV and visible focused-laser radiations, respectively, can repeatedly print and
completely erase colored micropatterns within TiO2/Ag films. The paper shows patterns printed under different
conditions, deals with the reproducibility of the process and the inscription stability, and explains the nanoscale
mechanisms, including silver migration during exposures, leading to the reversible color changes on the basis of TEM,
SEM, absorption spectroscopy and Raman micro-spectroscopy characterizations. This paper also evidences that CW
laser illuminations at higher intensity locally crystallize the titania matrix and investigates the influence of the
absorption-induced heating around nanoparticles.
Whereas microelectronic lithography is heading to the 32 nm node and discussing immersion and double-patterning
strategies, there is much which can be done with the 45 nm node in microoptics for white light processing. For instance,
one of the most demanding applications in terms of achievable period is the LCD lossless polarizer, which can transmit
the TM polarization and reflect the TE polarization evenly all through the visible spectrum - provided that a 1D metal
grid of 100 nm period can be fabricated. The manufacture of such polarizing panels cannot resort to the step & repeat
cameras of microelectronics since the substrates are too large, too thin, too wavy and full of contaminants. There is
therefore a need for specific fabrication techniques. It is one of these techniques that a subgroup of partners belonging to
two of the Networks of Excellence of the European Community, NEMO and ePIXnet, have decided to explore together.
The method presented here is an optical technique allowing the high productivity printing of long submicron period gratings by means of a phase mask illuminated by an intensity modulated laser beam. The continuous writing of the grating permits to avoid stitching errors and the fabrication of very long gratings. The main applications concern the fabrication of long optical scales for high resolution optical encoders. The experimental results presented here show 100
mm long resist gratings with 500 nm period.
A sinusoidally weakly undulated continuous thin gold film embedded between a polymer substrate and a thin cover of the same polymer, the metal film thickness, the period and the wavelength being such that a normally incident wave excites the long range plasmon mode of the metal film, is shown to exhibit strong resonant transmission for the local TM polarization and strong reflection of the TE polarization. Such structure represents a very simple, average performance polarization beam splitter for white light processing.
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