Special Issue "Thin Films for Sensing Applications"

A special issue of Materials (ISSN 1996-1944). This special issue belongs to the section "Thin Films".

Deadline for manuscript submissions: 30 June 2020.

Special Issue Editor

Dr. Joel Borges
E-Mail Website1 Website2
Guest Editor
Centro de Física das Universidades do Minho e Porto (CF-UM-UP), Campus de Gualtar, 4710 - 057 Braga, Portugal
Interests: thin films; sputtering; gold nanoparticles; oxides; plasmonic sensing

Special Issue Information

Dear Colleagues,

Thin films are becoming widely used in a growing range of different applications. The change from bulk materials to thin films has arisen in many different fields, thanks to advancements in bottom-up fabrication methods and the use of nanomaterials. Depending on the type of application, there are several technologies that may be used to prepare a thin-film system, ranging from physical vapor deposition (PVD) techniques, to chemical vapor deposition (CVD) methods or atomic layer deposition (ALD), among others. Thin films are typically more sensitive to changes in a local environment than many bulk materials, which is widening their use and the research for different approaches and systems. Every single property of a thin film can be controlled/modified at the nano- or micro-scale by the deposition process, offering multiple advantages (e.g., high surface-to-volume ratios or excellent deformation behavior) over bulk counterparts. Thus, thin films have a wide range of uses in sensing applications as they are more prone to be used, e.g., for adsorbing molecules on their surfaces (important in gas- and biosensing), in flexible sensors to measure pressure fields or even to record a biosignal from a human body, or to accurately measure the temperature of a system.

This Special Issue is devoted to the dissemination of new and original knowledge on all aspects related to thin films, that selectively sense physical signals and chemical or biological species or processes. Articles should be focused on the synthesis, characterization, functionalization, and development of thin-film sensors that may be used to provide new and improved sensing applications. Papers may also address new thin-film preparation strategies or systems to enhance the response and detection limits of a given thin-film sensor. The scope of this Special Issue encompasses, but is not restricted to, the following list of materials and types of thin-film sensors:

  • Refractive index sensors based on nanoparticles, or nanopatterned films, manifesting localized surface plasmon resonances (LSPR);
  • Molecular sensors based on surface-enhanced Raman spectroscopy (SERS);
  • Surface plasmon resonance (spr) sensors;
  • Biomolecular sensors employing enhanced photocatalysis;
  • Gas sensors, using 2D materials (Graphene, Transition Metal Dichalcogenides, etc.) and metal oxides;
  • Strain sensors based on the piezoresistive effect;
  • Piezoelectric sensors;
  • Temperate sensors, based on thermoelectric effect and RTDs;
  • Flexible and paper-based thin-film transistors (TFTs) applied to sensing;
  • Biopotential electrodes (transducers) for biosignal acquisition (e.g., EMG, EEG, ECG, or EOG).

Dr. Joel Borges
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All papers will be peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

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. Materials is an international peer-reviewed open access semimonthly 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 2000 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

  • Thin-film synthesis
  • Thin-film characterization
  • Thin-film properties
  • Thin-film sensors
  • Physical sensors
  • Chemical and biological sensors

Published Papers (3 papers)

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Research

Open AccessArticle
Enhancing the Sensitivity of Nanoplasmonic Thin Films for Ethanol Vapor Detection
Materials 2020, 13(4), 870; https://doi.org/10.3390/ma13040870 - 14 Feb 2020
Abstract
Nanoplasmonic thin films, composed of noble metal nanoparticles (gold) embedded in an oxide matrix, have been a subject of considerable interest for Localized Surface Plasmon Resonance (LSPR) sensing. Ethanol is one of the promising materials for fuel cells, and there is an urgent [...] Read more.
Nanoplasmonic thin films, composed of noble metal nanoparticles (gold) embedded in an oxide matrix, have been a subject of considerable interest for Localized Surface Plasmon Resonance (LSPR) sensing. Ethanol is one of the promising materials for fuel cells, and there is an urgent need of a new generation of safe optical sensors for its detection. In this work, we propose the development of sensitive plasmonic platforms to detect molecular analytes (ethanol) through changes of the LSPR band. The thin films were deposited by sputtering followed by a heat treatment to promote the growth of the gold nanoparticles. To enhance the sensitivity of the thin films and the signal-to-noise ratio (SNR) of the transmittance–LSPR sensing system, physical plasma etching was used, resulting in a six-fold increase of the exposed gold nanoparticle area. The transmittance signal at the LSPR peak position increased nine-fold after plasma treatment, and the quality of the signal increased six times (SNR up to 16.5). The optimized thin films seem to be promising candidates to be used for ethanol vapor detection. This conclusion is based not only on the current sensitivity response but also on its enhancement resulting from the optimization routines of thin films’ architectures, which are still under investigation. Full article
(This article belongs to the Special Issue Thin Films for Sensing Applications)
Open AccessFeature PaperArticle
Under-Etched Plasmonic Disks on Indium Tin Oxide for Enhanced Refractive Index Sensing on a Combined Electrochemical and Optical Platform
Materials 2020, 13(4), 853; https://doi.org/10.3390/ma13040853 - 13 Feb 2020
Abstract
A simple approach to enhance the refractive index sensitivity of gold nanodisks immobilized on electrically conducting indium tin oxide (ITO) substrates has been demonstrated. A two-fold increase in sensitivity to bulk refractive index change was achieved by substrate under-etching of gold nanodisks on [...] Read more.
A simple approach to enhance the refractive index sensitivity of gold nanodisks immobilized on electrically conducting indium tin oxide (ITO) substrates has been demonstrated. A two-fold increase in sensitivity to bulk refractive index change was achieved by substrate under-etching of gold nanodisks on ITO in 50 mM sulfuric acid. The influence of an intermediate titanium adhesion layer was investigated and was found to markedly influence the etching pattern and time. Etching with an adhesion layer resulted in enhanced refractive index sensitivity on disk-on-pin like structures after long etching times, whereas etching of disks deposited directly on ITO resulted in a disk-on-pincushion like configuration and similarly enhanced sensitivity already at shorter times. The gold disks remained electrically connected to the ITO substrate throughout etching and allowed site-specific electrodeposition of poly(3-aminophenol) at the nanodisks, showing enhanced thin-film refractive index sensitivity. This work demonstrates a simple method for enhancing refractive index sensitivity of nanostructures on ITO substrates for combined electrochemical and optical platforms, and subsequently a method to modify the surface of the electrically connected nanostructures, which has potential application in biosensing. Full article
(This article belongs to the Special Issue Thin Films for Sensing Applications)
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Open AccessArticle
Au-WO3 Nanocomposite Coatings for Localized Surface Plasmon Resonance Sensing
Materials 2020, 13(1), 246; https://doi.org/10.3390/ma13010246 - 06 Jan 2020
Abstract
Localized surface plasmon resonance (LSPR) gas sensors are gaining increasing importance due to their unique tuneable functional properties. Au-WO3−x nanocomposite coatings, in particular, can be outstandingly sensitive to many different gases. However, a proper understanding of their optical properties and the way [...] Read more.
Localized surface plasmon resonance (LSPR) gas sensors are gaining increasing importance due to their unique tuneable functional properties. Au-WO3−x nanocomposite coatings, in particular, can be outstandingly sensitive to many different gases. However, a proper understanding of their optical properties and the way in which those properties are correlated to their structure/microstructure, is still needed. In this work, Au-WO3 nanocomposite coatings, with Au contents between 0–11 atomic percent, were grown using reactive magnetron co-sputtering technique and were characterized concerning their optical response. The precipitation of Au nanoparticles in the oxide matrix was promoted through thermal annealing treatments until 500 °C. Along with the Au nanoparticles’ morphological changes, the annealing treatments stimulated the crystallization of WO3, together with the appearance of oxygen-deficient WO3−x phases. Through theoretical simulations, we have related the LSPR effect with the different structural and morphological variations (namely, size and distribution of the nanoparticles and their local environment), which were a function of the Au content and annealing temperature. Our results suggest that local voids were present in the vicinity of the Au nanoparticles, for all temperature range, and that they should be present in a wide variety of Au-WO3 nanocomposites. A theoretical study concerning the refractive index sensitivity was carried out in order to predict the optimal coating design parameters for gas sensing experiments. Full article
(This article belongs to the Special Issue Thin Films for Sensing Applications)
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Planned Papers

The below list represents only planned manuscripts. Some of these manuscripts have not been received by the Editorial Office yet. Papers submitted to MDPI journals are subject to peer-review.

(1)Optimization of plasmonic sensors based on thin films composed by gold nanoparticles embedded in a dielectric matrix

Marco S. Rodrigues, Joel Borges, Filipe Vaz

Centro de Física, Universidade do Minho, Campus de Gualtar, Braga, Portugal

Nanoplasmonic thin films, composed by noble metal nanoparticles (gold) embedded in an oxide matrix, have been a subject of considerable interest for optical sensing, due to their localized surface plasmon resonance (LSPR) properties. The aim of this work is to develop plasmonic platforms capable of sensing molecular analytes through changes on the LSPR band. The thin films were deposited using reactive DC magnetron sputtering, followed by an annealing treatment to promote the growth and coalescence of gold nanoparticles. Results showed that the sensitivity to different environments can be optimized by changing the nanostructure of the films and surface properties.

 

(2)Development of dry-electrodes for Electromyography signal acquisition based on architectured titanium thin films

Marco S. Rodriguesa, Patrique Fiedlerb,c, Nora Küchlerb, Rui P. Dominguesa, Cláudia Lopesa, Joel Borgesa, Jens Haueisenb,d, Filipe Vaza

aCentro de Física, Universidade do Minho, Campus de Gualtar, 4710-057 Braga, Portugal

bInstitute of Biomedical Engineering and Informatics, Technische Universität Ilmenau, Ilmenau, 98693, Germany

cEemagine Medical Imaging Solutions GmbH, Berlin, 10243, Germany

dBiomagnetic Center, Department of Neurology, University Hospital Jena, Jena, 07747, Germany

ABSTRACT (Short)

Biosignal acquisition in Electromyography (EMG) is challenging because the signal is recorded during motion, which causes additional noise and artefacts. Wet silver/silver chloride (Ag/AgCl) electrodes are dominant in clinical settings for biosignal acquisitions. However, an electrolyte gel is required, which dries out during long time measurements and causes skin irritation. To overcome these drawbacks, dry electrodes based on thin films have been proposed. Magnetron sputtering combined with glancing angle deposition were used to deposit architectured thin films of titanium on top of a base material (e.g. polymer). The electrodes were tested on volunteers, recording electromyograms and skin-electrode impedances. It was concluded that the thin film electrodes behave similarly as conventional EMG electrodes.

(3)Photocatalytic Bi2O3 / TiO2 heterostructured nanocone coatings
Luís Brioso Dias, Joana Margarida Ribeiro, Filipe Costa Correia, Carlos José Tavares

Centre of Physics of the University of Minho and Porto, University of Minho, Campus Azurém, 4804-533 Guimarães, Portugal

Abstract

Bi2O3 nanocone films were deposited by d.c. reactive sputtering. The 3-dimensional dendritic structures developed from a starting catalytic Bi seed film through a vapour-liquid-solid (VLS) mechanism. The resulting nanocones have an enhanced projected surface area, measured by atomic force microscopy, when compared to non-VLS deposition of the same metal oxide. A very thin TiO2 layer (~6 nm thick) was deposited also by d.c. reactive sputtering on top of these nanocones, in order to functionalize the dendritic structures with a self-cleaning cap material. The photocatalytic efficiency was tested upon mineralisation of a chosen pollutant. X-ray diffraction texture analysis enabled the determination of the correct crystallographic phase of Bi2O3.

Keywords: Photocatalysis, vapour-liquid-solid, sputtering, TiO2, Bi2O3

(4)Title: "Clean-room lithographical processes for the fabrication of graphene biosensors"

Pedro Alpuim et al

 

 

 

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