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Goswami, S., S. Nandy, A. N. Banerjee, A. Kiazadeh, G. R. Dillip, J. V. Pinto, S. W. Joo, R. Martins, and E. Fortunato, "{“Electro-Typing” on a Carbon-Nanoparticles-Filled Polymeric Film using Conducting Atomic Force Microscopy}", Advanced Materials, vol. 29, no. 47, 2017. Abstract

© 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Next-generation electrical nanoimprinting of a polymeric data sheet based on charge trapping phenomena is reported here. Carbon nanoparticles (CNPs) (waste carbon product) are deployed into a polymeric matrix (polyaniline) (PANI) as a charge trapping layer. The data are recorded on the CNPs-filled polyaniline device layer by “electro-typing” under a voltage pulse (VET, from ±1 to ±7 V), which is applied to the device layer through a localized charge-injection method. The core idea of this device is to make an electrical image through the charge trapping mechanism, which can be “read” further by the subsequent electrical mapping. The density of stored charges at the carbon–polyaniline layer, near the metal/polymer interface, is found to depend on the voltage amplitude, i.e., the number of injected charge carriers. The relaxation of the stored charges is studied by different probe voltages and for different devices, depending on the percolation of the CNPs into the PANI. The polymeric data sheet retains the recorded data for more than 6 h, which can be refreshed or erased at will. Also, a write–read–erase–read cycle is performed for the smallest “bit” of stored information through a single contact between the probe and the device layer.

Centeno, P., M. F. Alexandre, M. Chapa, J. V. Pinto, J. Deuermeier, T. Mateus, E. Fortunato, R. Martins, H. Águas, and M. J. Mendes, {Self-Cleaned Photonic-Enhanced Solar Cells with Nanostructured Parylene-C}, , vol. 2000264, pp. 1–9, 2020. Abstract

Abstract Photonic front-coatings with self-cleaning properties are presented as means to enhance the efficiency and outdoor performance of thin-film solar cells, via optical enhancement while simultaneously minimizing soiling-related losses. This is achieved by structuring parylene-C transparent encapsulants using a low-cost and highly-scalable colloidal-lithography methodology. As a result, superhydrophobic surfaces with broadband light-trapping properties are developed. The optimized parylene coatings show remarkably high water contact angles of up to 165.6° and extremely low adhesion, allowing effective surface self-cleaning. The controlled nano/micro-structuring of the surface features also generates strong anti-reflection and light scattering effects, corroborated by numeric electromagnetic modeling, which lead to pronounced photocurrent enhancement along the UV?vis?IR range. The impact of these photonic-structured encapsulants is demonstrated on nanocrystalline silicon solar cells, that show short-circuit current density gains of up to 23.6%, relative to planar reference cells. Furthermore, the improvement of the devices' angular response enables an enhancement of up to 35.2% in the average daily power generation.

Firmino, R., E. Carlos, J. V. Pinto, J. Deuermeier, R. Martins, E. Fortunato, P. Barquinha, and R. Branquinho, "{Solution Combustion Synthesis of Hafnium-Doped Indium Oxide Thin Films for Transparent Conductors}", Nanomaterials, vol. 12, no. 13, pp. 2167, jun, 2022. AbstractWebsite

{\textless}p{\textgreater}Indium oxide (In2O3)-based transparent conducting oxides (TCOs) have been widely used and studied for a variety of applications, such as optoelectronic devices. However, some of the more promising dopants (zirconium, hafnium, and tantalum) for this oxide have not received much attention, as studies have mainly focused on tin and zinc, and even fewer have been explored by solution processes. This work focuses on developing solution-combustion-processed hafnium (Hf)-doped In2O3 thin films and evaluating different annealing parameters on TCO's properties using a low environmental impact solvent. Optimized TCOs were achieved for 0.5 M{%} Hf-doped In2O3 when produced at 400 °C, showing high transparency in the visible range of the spectrum, a bulk resistivity of 5.73 × 10−2 $Ømega$.cm, a mobility of 6.65 cm2/V.s, and a carrier concentration of 1.72 × 1019 cm−3. Then, these results were improved by using rapid thermal annealing (RTA) for 10 min at 600 °C, reaching a bulk resistivity of 3.95 × 10 −3 $Ømega$.cm, a mobility of 21 cm2/V.s, and a carrier concentration of 7.98 × 1019 cm−3, in air. The present work brings solution-based TCOs a step closer to low-cost optoelectronic applications.{\textless}/p{\textgreater}

Silva, D., C. S. Monteiro, S. O. Silva, O. Frazão, J. V. Pinto, M. Raposo, P. A. Ribeiro, and S. Sério, "{Sputtering Deposition of TiO2 Thin Film Coatings for Fiber Optic Sensors}", Photonics, vol. 9, no. 5: MDPI AG, pp. 342, may, 2022. Abstract

Thin films of titanium dioxide (TiO2) and titanium (Ti) were deposited onto glass and optical fiber supports through DC magnetron sputtering, and their transmission was characterized with regard to their use in optical fiber-based sensors. Deposition parameters such as oxygen partial pressure, working pressure, and sputtering power were optimized to attain films with a high reflectance. The films deposited on glass supports were characterized by UV-Vis spectroscopy, X-ray diffraction (XRD), and scanning electron microscopy (SEM). Regarding the deposition parameters, all three parameters were tested simultaneously, changing the working pressure, the sputtering power, and the oxygen percentage. It was possible to conclude that a lower working pressure and higher applied power lead to films with a higher reflectance. Through the analysis of the as-sputtered thin films using X-ray diffraction, the deposition of both Ti and TiO2 films was confirmed. To study the applicability of TiO2 and Ti in fiber sensing, several thin films were deposited in single mode fibers (SMFs) using the sputtering conditions that revealed the most promising results in the glass supports. The sputtered TiO2 and Ti thin films were used as mirrors to increase the visibility of a low-finesse Fabry–Perot cavity and the possible sensing applications were studied.

Correia, R., J. Deuermeier, M. R. Correia, J. {Vaz Pinto}, J. Coelho, E. Fortunato, and R. Martins, "{Biocompatible Parylene-C Laser-Induced Graphene Electrodes for Microsupercapacitor Applications}", ACS Applied Materials {&} Interfaces, vol. 14, no. 41: American Chemical Society, pp. 46427–46438, oct, 2022. AbstractWebsite
Coelho, J., R. F. Correia, S. Silvestre, T. Pinheiro, A. C. Marques, R. M. P. Correia, J. V. Pinto, E. Fortunato, and R. Martins, "{Paper-based laser-induced graphene for sustainable and flexible microsupercapacitor applications}", Microchimica Acta, vol. 190, no. 1, pp. 1–10, 2023. Abstract

Laser-induced graphene (LIG) is as a promising material for flexible microsupercapacitors (MSCs) due to its simple and cost-effective processing. However, LIG-MSC research and production has been centered on non-sustainable polymeric substrates, such as polyimide. In this work, it is presented a cost-effective, reproducible, and robust approach for the preparation of LIG structures via a one-step laser direct writing on chromatography paper. The developed strategy relies on soaking the paper in a 0.1 M sodium tetraborate solution (borax) prior to the laser processing. Borax acts as a fire-retardant agent, thus allowing the laser processing of sensitive substrates that other way would be easily destroyed under the high-energy beam. LIG on paper exhibiting low sheet resistance (30 $Ømega$ sq−1) and improved electrode/electrolyte interface was obtained by the proposed method. When used as microsupercapacitor electrodes, this laser-induced graphene resulted in specific capacitances of 4.6 mF cm−2 (0.015 mA cm−2). Furthermore, the devices exhibit excellent cycling stability (> 10,000 cycles at 0.5 mA cm−2) and good mechanical properties. By connecting the devices in series and parallel, it was also possible to control the voltage and energy delivered by the system. Thus, paper-based LIG-MSC can be used as energy storage devices for flexible, low-cost, and portable electronics. Additionally, due to their flexible design and architecture, they can be easily adapted to other circuits and applications with different power requirements. Graphical Abstract: [Figure not available: see fulltext.]

Pinheiro, A., A. Ruivo, M. Ferro, J. V. Pinto, J. Deuermeier, T. Mateus, A. Santa, M. J. Mendes, R. Martins, S. Gago, C. A. T. Laia, and Á. Hugo, {Parylene-Sealed Perovskite Nanocrystals Down-Shifting Layer for Luminescent Spectral Matching in Thin Film Photovoltaics}, , 2023. Abstract