Micro-Nano Surface Functionalization of Materials and Thin Films for Optical Applications

A special issue of Coatings (ISSN 2079-6412).

Deadline for manuscript submissions: closed (31 December 2020) | Viewed by 19602

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Special Issue Editors


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Guest Editor
Departamento de Física Aplicada I, Escuela Politécnica Superior, Universidad de Sevilla, Virgen deÁfrica 7, 41011 Sevilla, Spain
Interests: synthesis and characterization of nanostructured materials; design of solar selective coatings for energy applications; tuning optical properties of materials by controlling the microstructure; development of functional materials for additive manufacturing

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Guest Editor
Profactor GmbH, Steyr, Austria
Interests: coatings and nanostructured materials for solar energy applications, additive manufacturing, micro and nanofabrication, nanoimprint lithography, concentrating solar power, photoelectrochemical and spectroscopic characterization of photovoltaic devices

Special Issue Information

Dear Colleagues,

This Special Issue will provide a meaningful overview of recent advances and beyond the state of the art concepts regarding surface functionalization of materials and deposition of thin films to be used in optical applications. Our aim is to cover all relevant aspects of the topic (simulation, design, fabrication, characterization and applications) with a special emphasis on non-conventional methods for surface modification of materials. Design of hierarchical surface structures at different scale lengths, combination of mature fabrication routes with emerging technologies (i.e. additive manufacturing), and large area fabrication concepts, to pave the way to an industrial utilization of the developed materials, will be in the core of this volume.  

 In particular, the topics of interest of this Special Issue include, but are not limited to:

  • Simulation of optical properties of micro and nano structures
  • Modelling and design of micro/nano structures for optical applications
  • Fabrication of optical structures and thin films using vacuum technologies (PVD, CVD, ALD, etc.)
  • Fabrication of optical structures and thin films by non-vacuum and wet chemistry methods
  • Emerging fabrication technologies for nano and micro optical structures (nanoimprint lithography, additive manufacturing, hybrid technologies etc.)
  • Free form fabrication of nano and micro structures and thin films for optical applications
  • Advanced optical characterization or nano and micro structures and thin films, including spatially-resolved, in-situ and in-operando techniques
  • Nano and micro structures and thin films for ultra-broadband optical applications, light guiding and energy conversion
  • New concepts for antireflective nano and micro structures and thin films
  • Nano and micro structured metamaterial surfaces
  • From lab to fab large area fabrication of nano and micro structures and thin films for optical applications

Dr. Ramón Escobar-Galindo
Dr. Elena Guillén Rodríguez
Guest Editors

Manuscript Submission Information

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Coatings is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Nano-micro optical structures
  • Optical thin films
  • Metamaterials
  • Advanced optical characterization
  • Non-conventional, hybrid and large-area fabrication techniques

Published Papers (5 papers)

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Research

18 pages, 5795 KiB  
Article
Spectrally Selective Solar Absorber Coating of W/WAlSiN/SiON/SiO2 with Enhanced Absorption through Gradation of Optical Constants: Validation by Simulation
by K. Niranjan, Paruchuri Kondaiah, Arup Biswas, V. Praveen Kumar, G. Srinivas and Harish C. Barshilia
Coatings 2021, 11(3), 334; https://doi.org/10.3390/coatings11030334 - 15 Mar 2021
Cited by 4 | Viewed by 2364
Abstract
The properties of spectrally selective solar absorber coatings can be fine-tuned by varying the thickness and composition of the individual layers. We have deposited individual layers of WAlSiN, SiON, and SiO2 of thicknesses ~940, 445, and 400 nm, respectively, for measuring the [...] Read more.
The properties of spectrally selective solar absorber coatings can be fine-tuned by varying the thickness and composition of the individual layers. We have deposited individual layers of WAlSiN, SiON, and SiO2 of thicknesses ~940, 445, and 400 nm, respectively, for measuring the refractive indices and extinction coefficients using spectroscopic ellipsometer measurements. Appropriate dispersion models were used for curve fitting of Ψ and Δ for individual and multilayer stacks in obtaining the optical constants. The W/WAlSiN/SiON/SiO2 solar absorber exhibits a high solar absorptance of 0.955 and low thermal emissivity of 0.10. The refractive indices and extinction coefficients of different layers in the multilayer stack decrease from the substrate to the top anti-reflection layer. The graded refractive index of the individual layers in the multilayer stack enhances the solar absorption. In the tandem absorber, WAlSiN is the main absorbing layer, whereas SiON and SiO2 act as anti-reflection layers. A commercial simulation tool was used to generate the theoretical reflectance spectra using the optical constants are in well accordance with the experimental data. We have attempted to understand the gradation in refractive indices of the multilayer stack and the physics behind it by computational simulation method in explaining the achieved optical properties. In brief, the novelty of the present work is in designing the solar absorber coating based on computational simulation and ellipsometry measurements of individual layers and multilayer stack in achieving a high solar selectivity. The superior optical properties of W/WAlSiN/SiON/SiO2 makes it a potential candidate for spectrally selective solar absorber coatings. Full article
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16 pages, 3374 KiB  
Article
Tailoring Crystalline Structure of Titanium Oxide Films for Optical Applications Using Non-Biased Filtered Cathodic Vacuum Arc Deposition at Room Temperature
by Elena Guillén, Matthias Krause, Irene Heras, Gonzalo Rincón-Llorente and Ramón Escobar-Galindo
Coatings 2021, 11(2), 233; https://doi.org/10.3390/coatings11020233 - 15 Feb 2021
Cited by 4 | Viewed by 2143
Abstract
Titanium oxide films were deposited at room temperature and with no applied bias using a filtered cathodic vacuum arc (FCVA) system in a reactive oxygen environment. The dependence of film growth on two process parameters, the working pressure (Pw) and the [...] Read more.
Titanium oxide films were deposited at room temperature and with no applied bias using a filtered cathodic vacuum arc (FCVA) system in a reactive oxygen environment. The dependence of film growth on two process parameters, the working pressure (Pw) and the O2 partial pressure (pO2), is described in detail. The composition, morphological features, crystalline structure, and optical properties of the deposited films were systematically studied by Rutherford Back Scattering (RBS), Scanning Electron Microscopy (SEM), X-Ray diffraction (XRD), Raman Spectroscopy, UV-vis spectroscopy, and spectroscopic ellipsometry. This systematic investigation allowed the identification of three different groups or growth regimes according to the stoichiometry and the phase structure of the titanium oxide films. RBS analysis revealed that a wide range of TiOx stoichiometries (0.6 < × < 2.2) were obtained, including oxygen-deficient, stoichiometric TiO2 and oxygen-rich films. TiO, Ti2O3, rutile-type TiO2, and amorphous TiO2 phase structures could be achieved, as confirmed both by Raman and XRD. Therefore, the results showed a highly versatile approach, in which different titanium oxide stoichiometries and crystalline phases especially suited for diverse optical applications can be obtained by changing only two process parameters, in a process at room temperature and without applied bias. Of particular interest are crystalline rutile films with high density to be used in ultra-high reflectance metal-dielectric multilayered mirrors, and reduced-TiO2 rutile samples with absorption in the visible range as a very promising photocatalyst material. Full article
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14 pages, 4255 KiB  
Article
Indium Tin Oxide Thin Film Deposition by Magnetron Sputtering at Room Temperature for the Manufacturing of Efficient Transparent Heaters
by Jago Txintxurreta, Eva G-Berasategui, Rocío Ortiz, Oihane Hernández, Lucía Mendizábal and Javier Barriga
Coatings 2021, 11(1), 92; https://doi.org/10.3390/coatings11010092 - 15 Jan 2021
Cited by 27 | Viewed by 6573
Abstract
Indium tin oxide (ITO) thin films are widely used as transparent electrodes in electronic devices. Many of those electronic devices are heat sensitive, thus their manufacturing process steps should not exceed 100 °C. Manufacturing competitive high-quality ITO films at low temperature at industrial [...] Read more.
Indium tin oxide (ITO) thin films are widely used as transparent electrodes in electronic devices. Many of those electronic devices are heat sensitive, thus their manufacturing process steps should not exceed 100 °C. Manufacturing competitive high-quality ITO films at low temperature at industrial scale is still a challenge. Magnetron sputtering technology is the most suitable technology fulfilling those requirements. However, ITO layer properties and the reproducibility of the process are extremely sensitive to process parameters. Here, morphological, structural, electrical, and optical characterization of the ITO layers deposited at low temperature has been successfully correlated to magnetron sputtering process parameters. It has been demonstrated that the oxygen flow controls and influences layer properties. For oxygen flow between 3–4 sccm, high quality crystalline layers were obtained with excellent optoelectronic properties (resistivity <8 × 10−4 Ω·cm and visible transmittance >80%). The optimized conditions were applied to successfully manufacture transparent ITO heaters on large area glass and polymeric components. When a low supply voltage (8 V) was applied to transparent heaters (THs), de-icing of the surface was produced in less than 2 min, showing uniform thermal distribution. In addition, both THs (glass and polycarbonate) showed a great stability when exposed to saline solution. Full article
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12 pages, 34969 KiB  
Article
Multilayer Nanoimprinting to Create Hierarchical Stamp Masters for Nanoimprinting of Optical Micro- and Nanostructures
by Amiya R. Moharana, Helene M. Außerhuber, Tina Mitteramskogler, Michael J. Haslinger and Michael M. Mühlberger
Coatings 2020, 10(3), 301; https://doi.org/10.3390/coatings10030301 - 24 Mar 2020
Cited by 9 | Viewed by 4101
Abstract
Nanoimprinting is a well-established replication technology for optical elements, with the capability to replicate highly complex micro- and nanostructures. One of the main challenges, however, is the generation of the master structures necessary for stamp fabrication. We used UV-based Nanoimprint Lithography to prepare [...] Read more.
Nanoimprinting is a well-established replication technology for optical elements, with the capability to replicate highly complex micro- and nanostructures. One of the main challenges, however, is the generation of the master structures necessary for stamp fabrication. We used UV-based Nanoimprint Lithography to prepare hierarchical master structures. To realize structures with two different length scales, conventional nanoimprinting of larger structures and conformal reversal nanoimprinting to print smaller structures on top of the larger structures was performed. Liquid transfer imprint lithography proved to be well suited for this purpose. We used the sample prepared in such a way as a master for further nanoimprinting, where the hierarchical structures can then be imprinted in one single nanoimprinting step. As an example, we presented a diffusor structure with a diffraction-grating structure on top. Full article
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16 pages, 3671 KiB  
Article
Electrical and Optical Properties of Amorphous SnO2:Ta Films, Prepared by DC and RF Magnetron Sputtering: A Systematic Study of the Influence of the Type of the Reactive Gas
by Rainald Mientus, Michael Weise, Stefan Seeger, Rene Heller and Klaus Ellmer
Coatings 2020, 10(3), 204; https://doi.org/10.3390/coatings10030204 - 26 Feb 2020
Cited by 11 | Viewed by 3431
Abstract
By reactive magnetron sputtering from a ceramic SnO2:Ta target onto unheated substrates, X-ray amorphous SnO:Ta films were prepared in gas mixtures of Ar/O2(N2O, H2O). The process windows, where the films exhibit the lowest resistivity values, [...] Read more.
By reactive magnetron sputtering from a ceramic SnO2:Ta target onto unheated substrates, X-ray amorphous SnO:Ta films were prepared in gas mixtures of Ar/O2(N2O, H2O). The process windows, where the films exhibit the lowest resistivity values, were investigated as a function of the partial pressure of the reactive gases O2, N2O and H2O. We found that all three gases lead to the same minimum resistivity, while the width of the process window is broadest for the reactive gas H2O. While the amorphous films were remarkably conductive (ρ ≈ 5 × 10−3 Ωcm), the films crystallized by annealing at 500 °C exhibit higher resistivities due to grain boundary limited conduction. For larger film thicknesses (d ≳ 150 nm), crystallization occurs already during the deposition, caused by the substrate temperature increase due to the energy influx from the condensing film species and from the plasma (ions, electrons), leading to higher resistivities of these films. The best amorphous SnO2:Ta films had a resistivity of lower than 4 × 10−3 Ωcm, with a carrier concentration of 1.1 × 1020 cm−3, and a Hall mobility of 16 cm2/Vs. The sheet resistance was about 400 Ω/□ for 100 nm films and 80 Ω/□ for 500 nm thick films. The average optical transmittance from 500 to 1000 nm is greater than 76% for 100 nm films, where the films, deposited with H2O as reactive gas, exhibit even a slightly higher transmittance of 80%. These X-ray amorpous SnO2:Ta films can be used as low-temperature prepared transparent and conductive protection layers, for instance, to protect semiconducting photoelectrodes for water splitting, and also, where appropriate, in combination with more conductive TCO films (ITO or ZnO). Full article
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