Longitudinal Spin Seebeck Effect Thermopiles Based on Flexible Co-Rich Amorphous Ribbons/Pt Thin-Film Heterostructures.

Thermoelectric phenomena, such as the Anomalous Nernst and Longitudinal Spin Seebeck Effects, are promising for sensor applications in the area of renewable energy. In the case of flexible electronic materials, the request is even larger because they can be integrated into devices having complex shape surfaces. Here, we reveal that Pt promotes an enhancement of the thermoelectric response in Co-rich ribbon/Pt heterostructures due to the spin-to-charge conversion. Moreover, we demonstrated that the employment of the thermopiles configuration in this system increases the induced thermoelectric current, a fact related to the considerable decrease in the electric resistance of the system. By comparing present findings with the literature, we were able to design a flexible thermopile based on LSSE without the lithography process. Additionally, the thermoelectric voltage found in the studied flexible heterostructures is comparable to the ones verified for rigid systems.

Anomalous Nernst Effect in Flexible Co-Based Amorphous Ribbons.

Fe3Co67Cr3Si15B12 ribbons with a high degree of flexibility and excellent corrosion stability were produced by rapid quenching technique. Their structural, magnetic, and thermomagnetic (Anomalous Nernst Effect) properties were studied both in an as-quenched (NR) state and after stress annealing during 1 h at the temperature of 350 °C and a specific load of 230 MPa (AR). X-ray diffraction was used to verify the structural characteristics of our ribbons. Static magnetic properties were explored by inductive technique and vibrating sample magnetometry. The thermomagnetic curves investigated through the Anomalous Nernst Effect are consistent with the obtained magnetization results, presenting a linear response in the thermomagnetic signal, an interesting feature for sensor applications. Additionally, Anomalous Nernst Effect coefficient SANE values of 2.66µV/K and 1.93µV/K were estimated for the as-quenched and annealed ribbons, respectively. The interplay of the low magnetostrictive properties, soft magnetic behavior, linearity of the thermomagnetic response, and flexibility of these ribbons place them as promising systems to probe curved surfaces and propose multifunctional devices, including magnetic field-specialized sensors.

High Performance of Metallic Thin Films for Resistance Temperature Devices with Antimicrobial Properties.

Titanium-copper alloy films with stoichiometry given by Ti1-xCux were produced by magnetron co-sputtering technique and analyzed in order to explore the suitability of the films to be applied as resistive temperature sensors with antimicrobial properties. For that, the copper (Cu) amount in the films was varied by applying different DC currents to the source during the deposition in order to change the Cu concentration. As a result, the samples showed excellent thermoresistivity linearity and stability for temperatures in the range between room temperature to 110 °C. The sample concentration of Ti0.70Cu0.30 has better characteristics to act as RTD, especially the αTCR of 1990 ×10-6°C-1. The antimicrobial properties of the Ti1-xCux films were analyzed by exposing the films to the bacterias S. aureus and E. coli, and comparing them with bare Ti and Cu films that underwent the same protocol. The Ti1-xCux thin films showed bactericidal effects, by log10 reduction for both bacteria, irrespective of the Cu concentrations. As a test of concept, the selected sample was subjected to 160 h reacting to variations in ambient temperature, presenting results similar to a commercial temperature sensor. Therefore, these Ti1-xCux thin films become excellent antimicrobial candidates to act as temperature sensors in advanced coating systems.

Flexible TiCux Thin Films with Dual Antimicrobial and Piezoresistive Characteristics.

The eradication of microorganisms from high traffic surfaces to prevent either viral or bacterial infections represents an urgent need, mainly in the scope of the present pandemic scenario. In this context, this work explores the dual functionality of titanium-copper thin films as pressure elements with antimicrobial properties, aiming for the implementation of touch and sensing capabilities in high traffic surfaces. Copper was employed as the antibacterial agent within a titanium matrix. The film's geometry and deposition parameters were varied in order to optimize antimicrobial and piezoresistive response. A considerable antimicrobial response has been obtained, increasing the copper amount (from 23 to 63 at. %) in the titanium matrix, leading to an outstanding 8 log10 CFU bacterial reduction in the case of Escherichia coli. Moreover, for the same amount of copper, the piezoresistive sensibility of the thin films increases up to a maximum gauge factor of 5.18 ± 0.09, which indicates an adequate electromechanical behavior for sensing applications. Our findings demonstrate the best combined antimicrobial and piezoresistive characteristics for the films with a Cu content of 63 at. %, indicating a potential use of these films for electromechanical sensor applications.

Structural, Mechanical, and Decorative Properties of Sputtered TiN and Ti (N, C) Films for Orthodontic Applications; an In Vitro Study.

In this paper, we explore and modify the structural, mechanical, and decorative properties of films composed by TiN and Ti (N, C) with a wide range of N2 gas flow during the deposition in order to be used on orthodontic systems. The films were grown using reactive DC magnetron sputtering from a pure Ti target and customized with C pellets onto Si and stainless steel 316L substrates. The structural properties were studied using X-ray diffraction and scanning electron microscopy, while the mechanical ones were obtained through hardness, elastic modulus, and friction coefficient. Moreover, the wear rate has been measured under an artificial saliva medium to simulate the oral cavity. The color of the films deposited onto stainless steel 316 L substrate was characterized through CIELab color code. Our findings show that the addition of N2 and C in the Ti matrix improves the mechanical properties of the films. With the increase in the amount of N2 and C, the hardness reaches a value of 739 HV, higher than the one reported in the literature (600 HV), a low value of the coefficient of elasticity (8.0 GPa), and also a low friction coefficient (0.30). Moreover, with the addition of N2 and C in the Ti films, the color of the films changes from metallic aspect until "with" gold, which means that our coatings exhibit versatile mechanical and color characteristics to be used in orthodontic wires applications.

Improving the Room-Temperature Ferromagnetism in ZnO and Low-Doped ZnO:Ag Films Using GLAD Sputtering.

ZnO and doped ZnO films with non-ferromagnetic metal have been widely used as biosensor elements. In these studies, the electrochemical measurements are explored, though the electrical impedance of the system. In this sense, the ferromagnetic properties of the material can be used for multifunctionalization of the sensor element using external magnetic fields during the measurements. Within this context, we investigate the room-temperature ferromagnetism in pure ZnO and Ag-doped ZnO films presenting zigzag-like columnar geometry. Specifically, we focus on the films' structural and quasi-static magnetic properties and disclose that they evolve with the doping of low-Ag concentrations and the columnar geometry employed during the deposition. The magnetic characterization reveals ferromagnetic behavior at room temperature for all studied samples, including the pure ZnO one. By considering computational simulations, we address the origin of ferromagnetism in ZnO and Ag-doped ZnO and interpret our results in terms of the Zn vacancy dynamics, its substitution by an Ag atom in the site, and the influence of the columnar geometry on the magnetic properties of the films. Our findings bring to light an exciting way to induce/explore the room-temperature ferromagnetism of a non-ferromagnetic metal-doped semiconductor as a promising candidate for biosensor applications.

Directional Field-Dependence of Magnetoimpedance Effect on Integrated YIG/Pt-Stripline System.

We investigated the magnetization dynamics through the magnetoimpedance effect in an integrated YIG/Pt-stripline system in the frequency range of 0.5 up to 2.0 GHz. Specifically, we explore the dependence of the dynamic magnetic behavior on the field orientation by analyzing beyond the traditional longitudinal magnetoimpedance effect of the transverse and perpendicular setups. We disclose here the strong dependence of the effective damping parameter on the field orientation, as well as verification of the very-low damping parameter values for the longitudinal and transverse configurations. We find considerable sensitivity results, bringing to light the facilities to integrate ferrimagnetic insulators in current and future technological applications.

Magnetic Response Dependence of ZnO Based Thin Films on Ag Doping and Processing Architecture.

Multifunctional and multiresponsive thin films are playing an increasing role in modern technology. This work reports a study on the magnetic properties of ZnO and Ag-doped ZnO semiconducting films prepared with a zigzag-like columnar architecture and their correlation with the processing conditions. The films were grown through Glancing Angle Deposition (GLAD) co-sputtering technique to improve the induced ferromagnetism at room temperature. Structural and morphological characterizations have been performed and correlated with the paramagnetic resonance measurements, which demonstrate the existence of vacancies in both as-cast and annealed films. The magnetic measurements reveal changes in the magnetic order of both ZnO and Ag-doped ZnO films with increasing temperature, showing an evolution from a paramagnetic (at low temperature) to a diamagnetic behavior (at room temperature). Further, the room temperature magnetic properties indicate a ferromagnetic order even for the un-doped ZnO film. The results open new perspectives for the development of multifunctional ZnO semiconductors, the GLAD co-sputtering technique enables the control of the magnetic response, even in the un-doped semiconductor materials.

A new heterofunctional support for enzyme immobilization: PEI functionalized Fe3O4 MNPs activated with divinyl sulfone. Application in the immobilization of lipase from Thermomyces lanuginosus.

Lipase from Thermomyces lanuginosus (TLL) was immobilized onto a novel heterofunctional support, divinyl sulfone (DVS) superparamagnetic nanoparticles (SPMNs) functionalized with polyethyleneimine (PEI). Particle size and zeta potential measurements, elemental analysis, X-ray powder diffraction, magnetic measurements, and infrared spectroscopy analysis were used to characterize the TLL preparations. At pH 10, it was possible to achieve 100 % of immobilization yield in 1 h. The immobilization pH gives TLL preparations with different stabilities; indeed the TLL preparation immobilized at pH 5.0 was the most stable during the thermal inactivation at all pH values. For the hydrolysis of racemic methyl mandelate, the nanobiocatalysts immobilized at pH 5.0 and blocked with ethylenediamine (EDA) and ethanolamine (ETA) obtained good enantioselectivities (68 % and 72 %, respectively) with high catalytic activities in the reaction medium at pH 7.0. The operational stability of the systems was evaluated in the esterification reaction of benzyl alcohol, obtaining up to 61 % conversion after the seventh reaction cycle. These results show that SPMN@PEI-DVS support is a robust strategy for the easy and rapid recovery of the nanobiocatalyst by applying a magnetic field, showing great potential for industrial applications.

Further stabilization of lipase from Pseudomonas fluorescens immobilized on octyl coated nanoparticles via chemical modification with bifunctional agents.

The lipase from Pseudomonas fluorescens (PFL) was adsorbed on superparamagnetic NiZnFe2O4 octyl-nanoparticles via interfacial activation, producing the biocatalyst OCTYL-NANO-PFL. In order to further improve the stability of the immobilized lipase, the immobilized enzyme biocatalyst was chemically modified with different concentrations of diverse bifunctional molecules (glutaraldehyde (GA), divinylsulfone (DVS) or p-benzoquinone (BQ)). The concentrations of bifunctional agents were varied (0.5, 1, 2.5 and 5% (v/v for GA and DVS and w/v for BQ)). The results showed a greatly improved stability after chemical modification with all bifunctional molecules, mainly with 5% (v/v) GA or 1% (v/v) DVS. The biocatalysts OCTYL-NANO-PFL-GA 5% and -DVS 1% were about 60 folds more stable at pH 7 than the unmodified preparation and, at pH 5, >200 folds for 5% GA modified enzyme. The most stable BQ treated biocatalysts, OCTYL-NANO-PFL-BQ 0.5%, was about 8.3 more stable than OCTYL-NANO-PFL at pH 7, while was 20 fold more stable at pH 9.