Automation of an atomic force microscope via Arduino

The Dimension 3000 AFM used in this work was kindly donated by Prof. Nicholas D. Spencer, and facilitated by Prof. Lucio Isa, and Dr. Shivaprakash N. Ramakrishna, from ETH-Zurich. We thank Prof. David Cuartielles for encouraging us to publish this work in this special issue on Arduino Science Hardware. We also thank Llorenc Mercadal Fernandez for frutiful discussions and ideas, and the BiblioMaker unit in the Faculty of Sciences of the University of Granada for their help in 3D printing the gears used here. MAFR acknowledges support by the project PID2020-116615RA-I00 funded by MCIN/AEI/10.13039/501100011033, and the EMERGIA grant with reference EMC21_00008 funded by Consejeria de Universidad, Investigacion e Innovacion de la Junta de Andalucia, and by FEDER "ERDF A way of making Europe". JGGF and CLMM acknowledge support from grant A1S35536 by Conacyt Mexico.The Atomic Force Microscopy is a very versatile technique that allows to characterize surfaces by acquiring topographies with sub-nanometer resolution. This technique often overcomes the problems and capabilities of electron microscopy when characterizing few nanometers thin coatings over solid substrates. They are expensive, in the half million dollar range for standard units, and therefore it is often difficult to upgrade to new units with improved characteristics. One of these improvements, motorization and automation of the measurements is very interesting to sample different parts of a substrate in an unattended way. Here we report a low cost upgrade under 60 $ to a Dimension 3000 AFM based on a control unit using an Arduino Leonardo. It enables to acquire dozens or hundreds of images automatically by mimicking keyboard shortcuts and interfacing the AFM PCI card.MCIN/AEI PID2020-116615RA-I00Consejeria de Universidad, Investigacion e Innovacion de la Junta de Andalucia EMC21_00008Marie Curie ActionsConsejo Nacional de Ciencia y Tecnologia (CONACyT) A1S3553

Laser-synthesis of conductive carbon-based materials from two flexible commercial substrates: A comparison

One of the key challenges in the field of flexible electronics relies on finding conductive materials that can withstand bending and stretching stresses while maintaining their performance. In this context, this work presents a comparative study of laser-induced conductive materials from the direct laser-scribing of two commercial flexible films: the benchmark Kapton® HN polyimide (PI) precursor and the UltemTM 1000 polyetherimide (PEI) alternative contender. The synthesis process on both materials is optimized in terms of electrical conductivity using a high-performance galvanometric laser with a wavelength of 532 nm for the fabrication of multiple samples at different laser powers and speeds. The samples are structurally characterized using Scanning Electron Microscopy (SEM), Raman spectroscopy, X-ray Photoelectron Spectroscopy (XPS), and Fourier-Transform Infrared Spectroscopy (FTIR) aiming at understanding the chemical and physical changes of the ablated material. The results demonstrate that the proposed setup is feasible for the synthesis of uniform and reliable conductive patterns on the surface of both substrates with high reproducibility. In particular, it is proved that PEI is more suitable precursor for flexible electronics applications which demand high electrical conductivity, leading to a sheet resistance of 3.62 ± 0.35 Ω/sq at 0.8 W and 5 mm/s once the laser-synthesis process is optimized (against the 6.04 ± 0.63 Ω/sq at 0.6 W and 5 mm/s offered by the LIG on PI). The performance of both laser-induced patterns as electrodes for the fabrication of electrochemical capacitors is also studied and compared in terms of areal specific capacitance.FEDER/Junta de Andalucía-Consejería de Transformaci´on Econ´omica, IndustriaConocimiento y Universidades Project P20_00265 and Project BRNM-680-UGR20; Project TED2021-129949A-I00MCIN/AEI/10.13039/ 501100011033European Union NextGenerationEU/PRTRGrant PID2020-117344RB-I00MCIN/AEI 10.13039/ 501100011033Junta de Andalucía – Consejería de Universidad, Investigaci´on e Innovaci´on through the project ProyExcel_00268Spanish Ministry of Sciences and Innovation through the Ram´on y Cajal fellow RYC2019- 027457-I,María Zambrano fellow C21.I4.P1grant PRE2021-096886

Demonstration of bare Laser reduced Graphene Oxide sensors for Ammonia and Ethanol

This work was mainly supported by TED2021-129949A-I00 funded by MCIN/AEI/10.13039/501100011033. It was also partially funded by the Andalusian regional projects supported through the Junta de Andalucía - Consejería de Universidad, Investigación e Innovación and FEDER funds: ProyExcel_00268, B-RNM-680-UGR20, P20_00265, P20_00633, as well as by the Spanish Ministry of Sciences and Innovation through the National Project PID2020-117344RB-I00, the Ramón y Cajal fellow RYC2019-027457-I and the María Zambrano fellow C21.I4.P1.In this work, gas sensors using laser-reduced graphene oxide (LrGO) as sensitive layer have been fabricated and studied. The laser-synthetized material were structurally and electrically characterized by means of Scanning Electron Microscopy (SEM), Raman spectroscopy, X-ray Photoelectron Spectroscopy (XPS) and the four-point contact method. The gas-sensing properties of the samples were studied by their exposition to 10 ppm to 100 ppm of ethanol and 25 ppm to 130 ppm of ammonia. The results show that the devices present an electrical response corresponding to a purely resistive behavior up to 100 kHz. It is also demonstrated that the resistivity of the sensing layer increases as the gas concentration increases; being of 0.0402 ± 0.001 [%/ppm] for the case of ammonia and 0.0140 ± 0.001 [%/ppm] for the case of ethanol. These results outperform existing sensors and establish a better balance in terms of simplicity, sensitivity, linearity and technology sustainability. In summary, this work especially shows the potential of LrGO for low-cost and low-energy gas sensors fabrication.MCIN/AEI/10.13039/501100011033: TED2021-129949A-I00Junta de AndalucíaFEDER funds: ProyExcel_00268, B-RNM-680-UGR20, P20_00265, P20_00633Spanish Ministry of Sciences and Innovation PID2020-117344RB-I00Ramón y Cajal fellow RYC2019-027457-IMaría Zambrano fellow C21.I4.P

Optimization of Dry Laser-Induced Graphene (LIG) Electrodes for Electrocardiography (ECG) Signals Monitoring

This work presents the optimization of the fabrication procedure for laser-induced graphene (LIG) electrodes intended for biopotentials acquisition. The results presented in this study demonstrate a significant improvement with respect to the performance obtained for other LIG-based electrodes previously reported in the literature. In particular, we propose the use of a galvanometric laser instead of a CNC laser to improve the engraving resolution and the LIG synthesis process, thus enhancing the surface area of the interface skin-electrode. For that, we have studied the resistance of the resulting LIG patterns as a function of the laser parameters (engraving power and scan speed) seeking their optimization. After tunning the laser fabrication process, we have fabricated and characterized electrocardiogram (ECG) electrodes with different surface areas using a commercial silver-based electrode as a reference. Thus, circular electrodes with a diameter of 15 mm, 10 mm and 6.5 mm were used to acquire the ECG on different volunteers using a commercial equipment. The signals acquired were processed afterwards with cutting edge processing techniques to perform a statistical analysis in terms of sensitivity, specificity, positive prediction and accuracy for the detection of QRS complexes. The results demonstrate that the proposed electrodes improve the signal acquisition with respect to the previously reported LIG-based electrodes in terms of noise and do present comparable or even better results than commercial electrodes (even with a smaller surface area) with the additional advantage of not requiring the use of an electrolyte gelThis work was supported by the Grant PID2020-117344RB-I00 funded by MCIN/AEI/10.13039/501100011033, also by FEDER/Junta de Andalucía-Consejería de Transformación Económica, Industria, Conocimiento y Universidades Projects P20_00265 and BRNM-680-UGR20; Project TED2021-129949A-I00 funded by MCIN/AEI/10.13039/501100011033 and by European Union NextGenerationEU/PRTR; In addition, this work was also supported by the Junta de Andalucía – Consejería de Transformación Económica, Industria, Conocimiento y Universidades through the project ProyExcel-00268 as well as by the Spanish Ministry of Sciences and Innovation through the the María Zambrano fellow C21.I4.P1 and the predoctoral grant PRE2021-096886. This work has also been partially funded by the National Council of Science and Technology CONACYT (grant number: 777736) and the Iberoamerican University Association of Postgraduate (AUIP) by means of the program “Mobility Program among all the institutions associated to the AUIP”

Nanoparticle deposits formed at driven contact lines

Drying of colloidal suspensions appears in many applications such as coatings (paints, ink printing, paving), colloidal assembly/templating , discrimination of particles with different size even medical diagnostics. Complex liquids, namely suspensions of solid particles, polymeric dispersions, emulsions.., and simple liquids behave in different way at interfacial regions. The formation of stains at the periphery of drying drops of any colloidal dispersion is known as the "coffee stain" effect or "coffee ring" effect. Desiccation of colloidal suspensions is governed by the coupling between hydrodynamics, heat and mass transfer and wetting. It is not always clear what the mechanisms of formation for the different deposits are. Besides, although the time scale of the process is extremely long, it is not clear how to treat such a nonequilibrium situation. A better understanding of the driving mechanisms of the drying of colloidal suspension drops would improve the productivity and competitiveness of the concerning industries. In this work, we propose standardize the contact line dynamics of sessile drops upon evaporation-like conditions but without any significant convective flows within the drop. This way, special attention was addressed to receding contact lines. As reported in literature, driven contact lines also enable the formation of particle deposits. Our methodology allows examining separately the impact of contact line dynamics and the properties of the nanoparticle suspensions (bulk concentration, surface electric charge, wettability). We probed the arrangement of nanoparticles at driven contact lines, with low capillary numbers and at time scales shorter than during evaporation. Unlike typical commercial curtain coating, we operated in the quasi-static regime of contact line motion where the viscous effects are excluded (Ca << 10-4). In this scenario, the observed contact angle was speed-independent. The present dissertation is essentially arranged in two parts in order to explore separately the behaviour of receding contact lines with pure liquids (part I) and complex liquids (part II), namely nanoparticle aqueous suspensions. With a variable rate of withdrawal of liquid, we controlled the dynamics of receding contact lines of millimeter-sized drops (~ 100 ul). Following this approach, we were able to emulate the first stages of drop evaporation, but at shorter times. We monitored the contact line dynamics of shrinking drops containing nanoparticles to identify stick-slip events. We analyzed the effect of several parameters such as wettability contrast between particle and substrate, particle concentration, particle size and electrostatic interactions (particle-particle and substrate-particle) on the formation and morphology of the nanoparticle ring-like deposits. Special attention was addressed to the effect of pinning time on the formation of particle deposits. As far as we know, this is the first work devoted to study the role of the particle-particle and substrate-particle interactions on the deposits formation without macroscopic evaporation.Tesis Univ. Granada. Departamento de Física AplicadaThis work was supported by the "Ministerio Español de Ciencia e Innovación" (project MAT2011-23339) and the "Junta de Andalucía" (projects P07-FQM-02517, P08-FQM-4325 and P09-FQM-4698)

Nanoparticle deposits formed at driven contact lines

Drying of colloidal suspensions appears in many applications such as coatings (paints, ink printing, paving), colloidal assembly/templating , discrimination of particles with different size even medical diagnostics. Complex liquids, namely suspensions of solid particles, polymeric dispersions, emulsions.., and simple liquids behave in different way at interfacial regions. The formation of stains at the periphery of drying drops of any colloidal dispersion is known as the "coffee stain" effect or "coffee ring" effect. Desiccation of colloidal suspensions is governed by the coupling between hydrodynamics, heat and mass transfer and wetting. It is not always clear what the mechanisms of formation for the different deposits are. Besides, although the time scale of the process is extremely long, it is not clear how to treat such a nonequilibrium situation. A better understanding of the driving mechanisms of the drying of colloidal suspension drops would improve the productivity and competitiveness of the concerning industries. In this work, we propose standardize the contact line dynamics of sessile drops upon evaporation-like conditions but without any significant convective flows within the drop. This way, special attention was addressed to receding contact lines. As reported in literature, driven contact lines also enable the formation of particle deposits. Our methodology allows examining separately the impact of contact line dynamics and the properties of the nanoparticle suspensions (bulk concentration, surface electric charge, wettability). We probed the arrangement of nanoparticles at driven contact lines, with low capillary numbers and at time scales shorter than during evaporation. Unlike typical commercial curtain coating, we operated in the quasi-static regime of contact line motion where the viscous effects are excluded (Ca << 10-4). In this scenario, the observed contact angle was speed-independent. The present dissertation is essentially arranged in two parts in order to explore separately the behaviour of receding contact lines with pure liquids (part I) and complex liquids (part II), namely nanoparticle aqueous suspensions. With a variable rate of withdrawal of liquid, we controlled the dynamics of receding contact lines of millimeter-sized drops (~ 100 ul). Following this approach, we were able to emulate the first stages of drop evaporation, but at shorter times. We monitored the contact line dynamics of shrinking drops containing nanoparticles to identify stick-slip events. We analyzed the effect of several parameters such as wettability contrast between particle and substrate, particle concentration, particle size and electrostatic interactions (particle-particle and substrate-particle) on the formation and morphology of the nanoparticle ring-like deposits. Special attention was addressed to the effect of pinning time on the formation of particle deposits. As far as we know, this is the first work devoted to study the role of the particle-particle and substrate-particle interactions on the deposits formation without macroscopic evaporation.Tesis Univ. Granada. Departamento de Física AplicadaThis work was supported by the "Ministerio Español de Ciencia e Innovación" (project MAT2011-23339) and the "Junta de Andalucía" (projects P07-FQM-02517, P08-FQM-4325 and P09-FQM-4698)

Impact of the collective diffusion of charged nanoparticles in the convective/capillary deposition directed by receding contact lines

The motion of electrically charged particles under crowding conditions and subjected to evaporation-driven capillary flow might be ruled by collective diffusion. The concentration gradient developed inside an evaporating drop of colloidal suspension may reduce by diffusion the number of particles transported toward the contact line by convection. Unlike self-diffusion coefficient, the cooperative diffusion coefficient of interacting particles becomes more pronounced in crowded environments. In this work, we examined experimentally the role of the collective diffusion of charge-stabilized nanoparticles in colloidal patterning. To decouple the sustained evaporation from the contact line motion, we conducted evaporating menisci experiments with driven receding contact lines at low capillary number. This allowed us to explore convective assembly at fixed and low bulk concentration, which enabled to develop high concentration gradients. At fixed velocity of receding contact line, we explored a variety of substrate-particle systems where the particle-particle electrostatic interaction was changed (via p H) as well as the substrate receding contact angle and the relative humidity. We found that the particle deposition directed by receding contact lines may be controlled by the interplay between evaporative convection and collective diffusion, particularly at low particle concentration