Development of a low-cost Arduino-based potentiostat

A simple Arduino-based potentiostat has been developed. This potentiostat design is cost effective for low budget applications and educational purposes. The resolution and linear response of the developed potentiosat was evaluated. A cyclic voltammetry of potassium ferricyanide K3[Fe(CN)6] was performed to compare the potentiostat electrochemical performance with a commercial one. To show the portable potentiostat capabilities, cyclic voltammograms were also performed at different scan rates. Finally, the diffusion coefficient of potassium ferricyanide was calculated in a solution containing a known concentration of the salt using the Randles-Sevcik equationMechanical Engineerin

Light management with quantum nanostructured dots-in-host semiconductors

Funding Information: The authors would like to thank Dr. Iñigo Ramiro for fruitful discussions. This work was funded by FCT (Fundação para a Ciência e Tecnologia, I.P.) under the projects UIDB/50025/2020 and SuperSolar (PTDC/NAN-OPT/28430/2017) and TACIT (PTCD/NAN-OPT/28837/2017). M. Alexandre also acknowledges funding by FCT, I.P. through the grant SFRH/BD/148078/2019. We also acknowledge the support of SYNERGY, H2020-WIDESPREAD-2020-5, CSA, proposal n° 952169.Insightful knowledge on quantum nanostructured materials is paramount to engineer and exploit their vast gamut of applications. Here, a formalism based on the single-band effective mass equation was developed to determine the light absorption of colloidal quantum dots (CQDs) embedded in a wider bandgap semiconductor host, employing only three parameters (dots/host potential barrier, effective mass, and QD size). It was ascertained how to tune such parameters to design the energy level structure and consequent optical response. Our findings show that the CQD size has the biggest effect on the number and energy of the confined levels, while the potential barrier causes a linear shift of their values. While smaller QDs allow wider energetic separation between levels (as desired for most quantum-based technologies), the larger dots with higher number of levels are those that exhibit the strongest absorption. Nevertheless, it was unprecedently shown that such quantum-enabled absorption coefficients can reach the levels (104–105cm−1) of bulk semiconductors. [Figure not available: see fulltext.]publishersversionpublishe

Transduction mechanisms, micro-structuring techniques, and applications of electronic skin pressure sensors: A review of recent advances

PD/BD/105876/2014Electronic skin (e-skin), which is an electronic surrogate of human skin, aims to recreate the multifunctionality of skin by using sensing units to detect multiple stimuli, while keeping key features of skin such as low thickness, stretchability, flexibility, and conformability. One of the most important stimuli to be detected is pressure due to its relevance in a plethora of applications, from health monitoring to functional prosthesis, robotics, and human-machine-interfaces (HMI). The performance of these e-skin pressure sensors is tailored, typically through micro-structuring techniques (such as photolithography, unconventional molds, incorporation of naturally micro-structured materials, laser engraving, amongst others) to achieve high sensitivities (commonly above 1 kPa−1), which is mostly relevant for health monitoring applications, or to extend the linearity of the behavior over a larger pressure range (from few Pa to 100 kPa), an important feature for functional prosthesis. Hence, this review intends to give a generalized view over the most relevant highlights in the development and micro-structuring of e-skin pressure sensors, while contributing to update the field with the most recent research. A special emphasis is devoted to the most employed pressure transduction mechanisms, namely capacitance, piezoelectricity, piezoresistivity, and triboelectricity, as well as to materials and novel techniques more recently explored to innovate the field and bring it a step closer to general adoption by society.publishersversionpublishe

Characterisation of Archaeological High-tin Bronze Corrosion Structures

Part of this work was carried out in the framework of the projects: 'Singing Bronze', funded by Banco Santander through the prize Santander/NOVA 2016; 'IberianTin' (PTDC/HAR-ARQ/32290/2017), funded by European Regional Development Fund funds through the regional program of Lisbon and through national funds through the Fundacao para a Ciencia e a Tecnologia (FCT) (Foundation for Science and Technology); UID/CTM/50025/2019 granted to CENIMAT/i3N, financed through FEDER funds by COMPETE 2020 and national funds through FCT.Since ancient times, the use of high-tin bronze alloys (>17 wt.%) has been mainly limited to the production of specific objects such as mirrors and bells. High-tin bronzes can show distinctive colour reflection, as well as mechanical properties and corrosion resistance that clearly distinguish them from the classical bronze composition (with 8–12 wt.% tin). In the present study samples of archaeological high-tin bronze bells were studied by optical microscopy, SEM-EDX, and Raman imaging with the aim of characterising their microstructural long-term corrosion patterns. Results show the presence of high quantities of δ phase, when compared to the classical bronze composition, which makes some corrosion structures more visible in these alloys. The corrosion morphologies show selective corrosion of different metal phases along depth of corrosion, which were attributed to different oxygen potentials. This study proposes a classification of four types of corrosion structures occurring in two-phase bronzes as a consequence of aeration conditions during burial time and aeration within the corrosion structure.authorsversionepub_ahead_of_prin

Microsite Drivers of Natural Seed Regeneration of Eucalyptus globulus Labill. in Burnt Plantations

Fire regimes are changing in several regions of the world. In those regions, some exotic species may be better adapted to new regimes than the native species. This study focused on identifying the microsite characteristics associated with the occurrence of post-fire Eucalyptus globulus regeneration from seeds, outside the species native-range. This information is important in helping to assess the naturalization status of the species, to understand its invasion risk, and to manage wildlings in plantations. To characterize the establishment niche, pairs of microsites (sapling presence/ absence) were sampled in four salvage-logged plantations of E. globulus two years after fire (20 pairs/plantation). Microsites of wildlings from three size classes and control microsites were established in one of these plantations (20 quartets) in order to characterize the recruitment niche and to assess ontogenic niche shifts. Two post-fire wildling cohorts were identified. The first emerged just after fire and was abundant. The second emerged after logging and was scarce, probably due to seed limitation. First-cohort wildlings were observed in microsites characterized by a high incidence of fire-related variables (charcoal, ash, increased soil pH and K). The aggregated distribution of these wildlings and their association with other species may indicate the existence of facilitative relationships and/or the exploitation of resource-rich patches. All these factors were relevant for first-cohort persistence and likely also for its establishment and recruitment. Second-cohort wildlings occurred in microsites where salvage-logging disturbance was evident, showing the importance of this disturbance for its emergence. Wildling size diversity was explained by the two recruitment events and by the asymmetrical competition between wildlings and adults. No niche shifts were detected. The high densities of E. globulus wildlings found established in burnt plantations indicated naturalization was in progress. The timing of major recruitment events and the phenology of the species should be considered for monitoring this regeneration and scheduling control interventions, if requiredinfo:eu-repo/semantics/publishedVersio

Design of wave-optical structured substrates for ultra-thin perovskite solar cells

grant agreement No 763989 UID/CTM/50025/2019 PTDC/NAN-OPT/28430/2017 PD/BD/143031/2018 SFRH/BD/148078/2019Photonic micro/nano-structures in the wave-optics regime have shown to be a promising strategy for effective broadband light capture in ultra-thin devices, opening a window of opportunity for cheap, efficient, lightweight and flexible photovoltaics (PV). Here we design, from an optical standpoint, a novel industrially-attractive concept where light trapping is obtained by conformably depositing the solar cell materials onto previously-patterned photonic substrates. This solution is applied and optimized for perovskite solar cells (PSCs) with distinct thicknesses of the perovskite absorber - the conventional (500 nm) and ultra-thin (300 nm) in view of enhanced flexibility - yielding photocurrent improvements up to 22.8% in superstrate cell configuration and 24.4% in substrate-type configuration; thereby coming relatively close to the fundamental Lambertian limits. Furthermore, these structures also show an omni-direction optical response for incidence angles up to 70° for all cases, therefore demonstrating the viability of this light trapping method for implementation in flexible PV devices operating under bending. The photonic-enhanced ultra-thin solar cells designed here ultimately support the reduction of material usage in PSC technology, which is especially beneficial to mitigate lead usage, without impacting the device's performance.preprintpublishe

All-Thin-Film Perovskite/C-Si Four-Terminal Tandems: Interlayer and Intermediate Contacts Optimization

ALTALUZ (Reference PTDC/CTM-ENE/5125/2014). SuperSolar (PTDC/NAN-OPT/28430/2017). TACIT (PTDC/NAN-OPT/28837/2017). FCT-MEC, Grant SERH/BPD/115566/2016.Combined perovskite/crystalline-silicon four-terminal tandem solar cells promise >30% efficiencies. Here we propose all-thin-film double-junction architectures where high-bandgap perovskite top cells are coupled to ultrathin c-Si bottom cells enhanced with light trapping. A complete optoelectronic model of the devices was developed and applied to determine the optimal intermediate layers, which are paramount to maximize the cells' photocurrent. It was ascertained that by replacing the transparent conductive oxides by grid-based metallic contacts in the intermediate positions, the parasitic absorption is lowered by 30%. Overall, a 29.2% efficiency is determined for ∼2 um thick tandems composed of the optimized interlayers and improved with Lambertian light trapping.authorsversionpublishe

Optimum Luminescent Down-Shifting Properties for High Efficiency and Stable Perovskite Solar Cells

PTDC/CTM-ENE/5125/2014. PTDC/NAN-OPT/28430/2017. TACIT (PTDC/NAN-OPT/28837/2017). SFRH/BPD/115566/2016. PD/BD/143031/2018 (via AdvaMTech PhD program).In recent years, the discovery of the excellent optical and electrical properties of perovskite solar cells (PSCs) made them a main focus of research in photovoltaics, with efficiency records increasing astonishingly fast since their inception. However, problems associated with the stability of these devices are hindering their market application. UV degradation is one of the most severe issues, chiefly caused by TiO 2 's photogenerated electrons that decompose the perovskite absorber material, coupled with the additional intrinsic degradation of this material under UV exposure. The solution presented here can minimize this effect while boosting the cells' generated photocurrent, by making use of combined light-trapping and luminescent down-shifting effects capable of changing the harmful UV radiation to higher wavelengths that do not affect the stability and can be effectively "trapped" in the cell. This work focuses in the optimization of the photocurrent gains that can be attained by emulating the changed spectrum resulting from applying down-shifting media as encapsulant in photonic-enhanced PSCs, as well as the reduction in the harmful effects of UV radiation on the devices. Such optimized photonic solution allows current enhancement while reducing the harmful UV photocarrier generation both in the TiO 2 (by 1 order of magnitude) and in the perovskite (by 80%) relative to a standard PSC without light management.authorsversionpublishe

Copper-Arsenic-Sulfide Thin-Films from Local Raw Materials Deposited via RF Co-Sputtering for Photovoltaics

LA/P/0037/2020 DFA/BD/7882/2020The inexorable increase of energy demand and the efficiency bottleneck of monocrystalline silicon solar cell technology is promoting the research and development of alternative photovoltaic materials. Copper-arsenic-sulfide (CAS) compounds are still rather unexplored in the literature, yet they have been regarded as promising candidates for use as p-type absorber in solar cells, owing to their broad raw material availability, suitable bandgap and high absorption coefficient. Here, a comprehensive study is presented on the structural and optoelectronic properties of CAS thin-films deposited via radio-frequency magnetron co-sputtering, using a commercial Cu target together with a Cu-As-S target with material obtained from local resources, specifically from mines in the Portuguese region of the Iberian Pyrite Belt. Raman and X-ray diffraction analysis confirm that the use of two targets results in films with pronounced stoichiometry gradients, suggesting a transition from amorphous CAS compounds to crystalline djurleite (Cu31S16), with the increasing proximity to the Cu target. Resistivity values from 4.7 mΩ·cm to 17.4 Ω·cm are obtained, being the lowest resistive films, those with pronounced sub-bandgap free-carrier absorption. The bandgap values range from 2.20 to 2.65 eV, indicating promising application as wide-bandgap semiconductors in third-generation (e.g., multi-junction) photovoltaic devices.publishersversionpublishe

Fast prototyping microfluidics: Integrating droplet digital lamp for absolute quantification of cancer biomarkers

UID/CTM/50025/2019 UID/Multi/04378/2019 Inn-INDIGO/0002/2015 PTDC/BTM-SAL/31201/2017 SFRH/BPD/124311/2016Microfluidic (MF) advancements have been leveraged toward the development of state-of-the-art platforms for molecular diagnostics, where isothermal amplification schemes allow for further simplification of DNA detection and quantification protocols. The MF integration with loop-mediated isothermal amplification (LAMP) is today the focus of a new generation of chip-based devices for molecular detection, aiming at fast and automated nucleic acid analysis. Here, we combined MF with droplet digital LAMP (ddLAMP) on an all-in-one device that allows for droplet generation, target amplification, and absolute quantification. This multilayer 3D chip was developed in less than 30 minutes by using a low-cost and extremely adaptable production process that exploits direct laser writing technology in “Shrinky-dinks” polystyrene sheets. ddLAMP and target quantification were performed directly on-chip, showing a high correlation between target concentration and positive droplet score. We validated this integrated chip via the amplification of targets ranging from five to 500,000 copies/reaction. Furthermore, on-chip amplification was performed in a 10 µL volume, attaining a limit of detection of five copies/µL under 60 min. This technology was applied to quantify a cancer biomarker, c-MYC, but it can be further extended to any other disease biomarker.publishersversionpublishe