Academic literature on the topic 'Air stability, flexible biosourced substrate'

In this paper, mechanical aspects of magnetic recording technology and nonimpact printing are discussed. In the recording area, theoretical and experimental aspects of air bearing theory, head/disk dynamics, and head/disk tribology are studied. Flutter of rotating disks is investigated, the flow field between rotating disks is described, and nonrepeatable run-out of disk file spindles is studied. Furthermore, the head/disk interface for flexible media is discussed and dimensional stability of flexible substrate is examined. In the printing area, experimental and theoretical investigations using continuous and drop-on-demand fluid jets are presented, and numerical calculations of the drop formation process in drop-on-demand fluid jets are described.

Flexible photovoltaics with extreme mechanical compliance present appealing possibilities to power Internet of Things (IoT) sensors and wearable electronic devices. Although improvement in thermal stability is essential, simultaneous achievement of high power conversion efficiency (PCE) and thermal stability in flexible organic photovoltaics (OPVs) remains challenging due to the difficulties in maintaining an optimal microstructure of the active layer under thermal stress. The insufficient thermal capability of a plastic substrate and the environmental influences cannot be fully expelled by ultrathin barrier coatings. Here, we have successfully fabricated ultraflexible OPVs with initial efficiencies of up to 10% that can endure temperatures of over 100 °C, maintaining 80% of the initial efficiency under accelerated testing conditions for over 500 hours in air. Particularly, we introduce a low-bandgap poly(benzodithiophene-cothieno[3,4-b]thiophene) (PBDTTT) donor polymer that forms a sturdy microstructure when blended with a fullerene acceptor. We demonstrate a feasible way to adhere ultraflexible OPVs onto textiles through a hot-melt process without causing severe performance degradation.

The long-term stability of n-type single-walled carbon nanotubes (SWCNTs) in air makes all-carbon thermoelectric generators (TEGs) viable. To increase the performance of TEGs, we developed a dual-type flexible-film thermoelectric generator (DFTEG). The vacuum filtering was used to form p- and n-type SWCNT films from ethanol-based dispersion and water-based solutions with cationic surfactant, respectively. DFTEGs were fabricated as follows: strip-shaped p- and n-type SWCNT films were attached on the top and back sides of a polyimide substrate, respectively, and were connected alternately in series by bending copper tapes on the edge of the polyimide substrate. The thermoelectric performance was measured after attaching the DFTEG outside a beaker full of water, where the water surface reached the center of the DFTEG. For a 10 mm long film and 15 p-n pairs, the DFTEG had an output voltage of 40 mV and a maximum power of 891 nW at a temperature difference of 25 K. The measured thermoelectric performance was significantly higher than that of the single-type TEG for almost the same SWCNT films. This result demonstrates that thermoelectric performance can be improved by using DFTEGs that are fabricated with optimum structural designs.

Triboelectric nanogenerators (TENG) can convert mechanical energy into electricity and exhibit unique advantages in the field of low-frequency and discrete energy harvesting. However, the interfacial state and stability between the triboelectric layer and electrode layer influence the output and applications of TENG. Herein, an in situ sputtering Ag process for fabricating induction electrodes is proposed to match with TENG. The sputtering Ag process is optimized by a variety of parameters, such as sputtering power, single-cycle time, number of cycles, cycle interval, and vacuum degree. In addition, the chemical state of Ag as a function of air placement is investigated, showing the sputtered Ag has excellent conductivity and stability. Moreover, four kinds of polymers are selected for fabricating TENGs based on the sputtered Ag induction electrodes, i.e., nylon 66, polyimide (PI), fluorinated ethylene propylene (FEP), and polydimethylsiloxane (PDMS), which shows great applicability. Considering the demand of flexible power suppliers, the sputtered Ag is integrated with a PDMS substrate, and shows good adhesion, flexibility, and ductility after severe deformation of the PDMS. Finally, the developed induction electrode processing technology is used in flexible TENG and shows great prospects in self-powered electronics for practical applications.

Abstract Electrochemical amperometric gas sensors represent a well-established and versatile type of devices with unique features: good sensitivity and stability, short response/recovery times, and low power consumption. These sensors operate at room temperature, and therefore have been applied in monitoring air pollutants and detection of toxic and hazardous gases in a number of areas. Some drawbacks of classical electrochemical sensors are overcome by the solid polymer electrolyte (SPE) based on ionic liquids. This work presents evaluation of an SPE-based amperometric sensor from the point of view of current fluctuations. The sensor is based on a novel three-electrode sensor platform with solid polymer electrolytes containing ionic liquid for detection of nitrogen dioxide − a highly toxic gas that is harmful to the environment and presenting a possible threat to human health even at low concentrations. The paper focuses on using noise measurement (electric current fluctuation measurement) for evaluation of electrochemical sensors which were constructed by different fabrication processes: (i) lift-off and drop-casting technology, (ii) screen printing technology on a ceramic substrate and (iii) screen printing on a flexible substrate.

Background: Magnetic nanoparticles (NPs) must not only be well-defined in composition, shape and size to exhibit the desired properties (e.g., exchange-bias for thermal stability of the magnetization) but also judiciously functionalized to ensure their stability in air and their compatibility with a polymer matrix, in order to avoid aggregation which may seriously affect their physical properties. Dipolar interactions between NPs too close to each other favour a collective magnetic glass state with lower magnetization and coercivity because of inhomogeneous and frustrated macrospin cluster freezing. Consequently, tailoring chemically (through surface functionalization) and magnetically stable NPs for technological applications is of primary importance. Results: In this work, well-characterized exchange-biased perfectly epitaxial Co x Fe3− x O4@CoO core@shell NPs, which were isotropic in shape and of about 10 nm in diameter, were decorated by two different polymers, poly(methyl methacrylate) (PMMA) or polystyrene (PS), using radical-controlled polymerization under various processing conditions. We compared the influence of the synthesis parameters on the structural and microstructural properties of the resulting hybrid systems, with special emphasis on significantly reducing their mutual magnetic attraction. For this, we followed two routes: the first one consists of the direct grafting of bromopropionyl ester groups at the surface of the NPs, which were previously recovered and redispersed in a suitable solvent. The second route deals with an “all in solution” process, based on the decoration of NPs by oleic acid followed by ligand exchange with the desired bromopropionyl ester groups. We then built various assemblies of NPs directly on a substrate or suspended in PMMA. Conclusion: The alternative two-step strategy leads to better dispersed polymer-decorated magnetic particles, and the resulting nanohybrids can be considered as valuable building blocks for flexible, magnetic polymer-based devices.

Conductive polymers, such as polyaniline (PANI), Polythiophene (PTh), polypyrrole (PPy), etc., are widely used for gas sensors due to their excellent electrical conductivity and low cost to manufacture [1]. In particular, PANI has attracted more attention due to its ease of synthesis, high environmental stability, and high reactivity with ammonia gas. In addition, the selection of acid-base dopant during the preparation process of polyaniline can adjust carrier concentrations for the change in electrical conduction or resistance to improve sensing properties. There have been many reports on the fabrication of flexible gas sensors using PANI [2-4]. Bandgar et al. [5] synthesized a low-temperature flexible polyaniline gas sensor by in-situ chemical oxidation polymerization of aniline on a polyethylene terephthalate (PET) substrate, showing 99% reproducibility, rapid response and recovery. Still, the response value was only 26% in 100 ppm ammonia atmosphere. Qi et al. [6] prepared a gas sensor by in-situ polymerization of aniline on non-woven fabric. The high air permeability of the fabric effectively improved the performance of the polyaniline-based gas sensor. Due to the outbreak of the COVID-19 pandemic, the use of face masks in public has become essential to reduce the spread of the virus. Some reports claim that the increased carbon dioxide in the mask over time may cause medical issues related to the respiratory system. Therefore, monitoring breathing air quality can help detect the wearer's vital conditions. In this study, we used a disposable mask as a flexible substrate to prepare polypropylene/carbon nanotube/polyaniline composite film through a layer-by-layer method. The polypropylene/carbon nanotube composite films were prepared by applying the carbon nanotube aqueous solution with surfactants evenly on the surface of a mask filter layer by a drop-coating method. Then, the in-situ polyaniline polymerization was performed on the surface of the polypropylene/carbon nanotube composite film through ammonium sulfate. The polypropylene/carbon nanotube /polyaniline composite film exhibits high sensitivity, fast sensing response/recovery time, room temperature operation, reliable flexibility, and cycle stability. The synthesized and wearable masks have demonstrated real-time detection respiratory rate and other breathing conditions such as CO2 and humidity. The ammonia gas sensing can also be used as a potential biomarker for health screening. The design and integration of multiple gas sensing materials in masks will help wearers better understand their own body conditions. References [1] Y. Jiang, N. Tang, C. Zhou, Z.Y. Han, H. Qu, X.X. Duan, et al., A chemiresistive sensor array from conductive polymer nanowires fabricated by nanoscale soft lithography, Nanoscale, 10(2018) 20578-86. [2] T.F. Wu, E. Gray, B.Q. Chen, A self-healing, adaptive and conductive polymer composite ink for 3D printing of gas sensors, J Mater Chem C, 6(2018) 6200-7. [3] D.Z. Zhang, Z.L. Wu, X.Q. Zong, et al., Flexible and highly sensitive H2S gas sensor based on in-situ polymerized SnO2/rGO/PANI ternary nanocomposite with application in halitosis diagnosis, Sensor Actuators B: Chem, 289(2019) 32-41. [4] C.H. Liu, H.L. Tai, P. Zhang, Z. Yuan, X.S. Du, G.Z. Xie, et al., A high-performance flexible gas sensor based on self-assembled PANI-CeO2 nanocomposite thin film for trace-level NH3 detection at room temperature, Sensor Actuators B: Chem, 261(2018) 587-97. [5] D.K. Bandgar, S.T. Navale, S.R. Nalage, R.S. Mane, F.J. Stadler, D.K. Aswal, et al., Simple and low-temperature polyaniline-based flexible ammonia sensor: a step towards laboratory synthesis to economical device design, J Mater Chem C, 3(2015) 9461-8. [6] J. Qi, X. Xu, X. Liu, K.T. Lau, Fabrication of textile based conductometric polyaniline gas sensor, Sensors and Actuators B: Chemical, 202(2014) 732-40.

Flexible electronics such as wearable electronics, electronic skins, implantable devices, and flexible displays are started influencing our lives in various aspects due to their lightweight, portability, and human-friendly interface. In these applications, nonvolatile memory (NVM) and synaptic devices are essential elements to implement high speed integrated circuits and neuromorphic computing at low power consumption. Perovskite-based ferroelectric (FE) materials such as Pb(Zr,Ti)O3 (PZT), BaTiO3 (BTO), and SrBi2Ta2O9 (SBT) have been studied widely because of their fast switching speed, large polarization, and high dielectric constant. However, it is very difficult to integrate these materials with conventional semiconductor technology owing to their poor compatibility with complementary metal-oxide-semiconductor (CMOS) technology. Therefore, hafnium (Hf) based FE-materials could be a suitable candidate for next-generation flexible electronics. Which exhibits immense prospects due to their excellent performance, CMOS compatibility, high scalability, and chemical simplicity with various dopants (Al, Zr, Gd, La, Sr, and Y). Among these, Zr-doped HfO2 (Hf0.5Zr0.5O2 (HZO)) has been attracted intensive attention because of its low annealing temperature and large remnant polarization. We study the inverted staggered structured flexible HZO FE-TFTs on polyimide (PI) substrate with zinc oxide (ZnO) as the active layer. A 50 nm molybdenum (Mo) layer was deposited by sputtering and patterned to form the gate electrode. Then, the HZO precursor solution was spin-coated at 2000 rpm for 30 s and cured at 250 °C on a hot plate for 5 min, followed by UV/O3 curing at 100 °C for 5 min in ambient air as a gate insulator (GI). Thereafter, the Al2O3 precursor solution was deposited as a capping layer on top of the HZO film using the same process steps but the rpm was 3500. The crystallization was performed by furnace annealing at 450 °C for 2 h in N2 environment. The thicknesses of HZO and Al2O3 films are 20 and 15 nm, respectively. Afterwards, the ZnO (25 nm) channel layer was deposited using spray pyrolysis at 350 °C substrate temperature. The ZnO and GI films were patterned sequentially to form the active island and via-hole, respectively. Finally, a 50 nm thick Mo film was sputtered and patterned to form the source/drain (S/D) electrodes. The origin of ferroelectricity in HZO GI was analyzed by grazing incidence X-ray diffraction (GI-XRD) measurement from film and drain current vs gate voltage (ID vs VGS), gate leakage current (IG), and drain current vs drain voltage (ID vs VDS) characteristics measurements from TFT structures using Agilent 4156C semiconductor parameter analyzer. Channel width and length were 50 and 10 μm, respectively. Fig. 1 (a) shows the schematic structure of an inverted staggered HZO FE-TFT on PI substrate. Fig. 1 (b) and (c) show the ID vs VGS characteristics with anticlockwise hysteresis of HZO and Al2O3 capped HZO TFTs on PI substrate. The Al2O3 capped HZO TFT exhibits clear ferroelectric property with a large memory window (MW) of ≈1.9 V. A thin Al2O3 capping layer on top of HZO enhances the microstructure and morphology of HZO even at a low annealing temperature of 450 °C and helps to induce the ferroelectricity in HZO GI. Fig. 1 (d) shows the photograph of the measurement setup of HZO FE-TFTs during electrical measurements under tensile stress at 2 mm. Fig. (e) and (f) exhibit the ID vs VGS and IG vs VGS characteristics with anticlockwise hysteresis of Al2O3 capped HZO FE-TFTs under different tensile stress, respectively. The ID vs VGS curves exhibit almost identical performance during forward and reverse bias at different bending radii without showing significant changes in the electrical characteristics. The MWs were evaluated under different bending radii and they show the almost same value of ≈1.9 V from flat state and down to 2 mm bent state. The corresponding IG vs VGS curves at different bending radii exhibit a clear butterfly shape with current peaks at about ±2 V. These findings indicate that the solution-processed flexible HZO FE-TFTs have high stability under mechanical stress and contain ferroelectricity even at 2 mm bending radius without deteriorating MW. Therefore, the low-cost solution-processed FE-HZO GI has significant potential to be employed in nonvolatile memory and synaptic devices for future flexible electronics. Figure 1

In this article, the design of an efficient wireless power transfer (WPT) system using antenna-based topology for the applications in wearable devices is presented. To implement the wearable WPT system, a simple circular patch antenna is initially designed on a flexible felt substrate by placing over a three-layer human tissue model to utilize as a receiving element. Meanwhile, a high gain circular patch antenna is also designed in the air environment to use as a transmitter for designing the wearable WPT link. The proposed WPT system is built to operate at the industrial, scientific and medical (ISM) band of 2.40–2.48 GHz. In addition, to improve the power transfer efficiency (PTE) of the system, a metamaterial (MTM) slab built with an array combination of 3 × 3 unit cells has been employed. Further, the performance analysis of the MTM integrated system is performed on the different portions of the human body like hand, head and torso model to present the versatile applicability of the system. Moreover, analysis of the specific absorption rate (SAR) has been performed in different wearable scenarios to show the effect on the human body under the standard recommended limits. Regarding the practical application issues, the performance stability analysis of the proposed system due to the misalignment and flexibility of the Rx antenna is executed. Finally, the prototypes are fabricated and experimental validation is performed on several realistic wearable platforms like three-layer pork tissue slab, human hand, head and body. The simulated and measured result confirms that by using the MTM slab, a significant amount of the PTE improvement is obtained from the proposed system.

At present, there are many reports on the preparation of large area CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub> perovskite solar cells based on ink-jet printing. These researches focus mainly on the ink-jet printing and electrode printing of perovskite active layer films. The hole transport layer, electron transport layer and other modified layers in the cell structure are still completed by spin coating or coating. In this work, we successfully realize large area CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub> perovskite solar cells based on full ink-jet printing, including pen/Ag NWs bottom electrode, agnws top electrode, PEDOT: PSS hole transport layer, etc. It is found that the full inkjet printing can greatly reduce the material cost and simplify the production process, and obtain PC<sub>61</sub>BM layer, PEDOT: PSS layer, PEI layer and CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub> perovskite thin film with high density and good uniformity. On this basis, we prepare the CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub> perovskite solar cells with areas of 60, 80 and 100 cm<sup>2</sup>, respectively. The results show that when the concentration of perovskite ink is 1 mol/L, the printing speed is 30 mm/s and the substrate temperature is 50 ℃, the surface of perovskite film is smooth and the grain size is in a range of 500–600 nm. The surface roughness of the film is only 10 nm, so high-quality perovskite film can be obtained. The power conversion efficiency of the perovskite solar cell with an effective area of 60 cm<sup>2</sup> is as high as 14.25% (<i>V</i><sub>OC</sub> = 1.03 V, <i>J</i><sub>SC</sub> = 19.21 mA/cm<sup>2</sup>, FF = 72%), which is the highest efficiency of perovskite solar cell prepared by full ink-jet printing method reported so far. In addition, when the device is placed in the air for 12 months without packaging, the photoelectric conversion efficiency is reduced to 80% of the initial value. However, the photoelectric conversion efficiency of FTPU package is reduced only by 5%, demonstrating good device stability.

L’utilisation de matériaux organiques permet la conception de différents dispositifs électroniques à basse température et sur différents types de substrats. Les transistors à effet de champ organiques (OFETs) en font partie, leurs performances électriques encourageantes permettent la réalisation de circuits intégrés. Cependant, ces performances et la stabilité électrique et à l’air des OFETs nécessitent encore des améliorations. Cette thèse s’inscrit dans ce contexte et se compose de deux volets principaux : 1) la réalisation d’OFETs sur substrat rigide à très basse température et 2) le transfert technologique vers des OFETs sur substrat flexible biosourcé afin d’envisager de nouvelles applications bas coûts, portables et voire même viser une électronique verte et écoresponsable. Pour le premier volet, les objectifs étaient les suivants : 1) l’optimisation, la caractérisation électrique d’OFETs de type N et l’analyse de leurs performances électriques, 2) l’étude de leur stabilité électrique sous l’effet d’une polarisation continue de longue durée et 3) l’amélioration de la stabilité à l’environnement ambiant de ces OFETs. Pour le second volet, différents objectifs ont été visés : 1) l’optimisation d’un film à base d’agar pour la fabrication d’un substrat biosourcé, 2) assurer la résistance du film aux différentes étapes de fabrication de l’OFET et 3) étudier la faisabilité de l’OFET à base d’agar, évaluer sa stabilité électrique et comparer ses performances à celles d’un OFET sur verre. Les résultats obtenus sont très encourageants et ont démontré la faisabilité d’OFET fabriqué sur ces substrats biosourcés flexibles avec une mobilité d'effet de champ µFElin = 7.10-2 cm2/V.s, une tension de seuil VTH = 7 V, et un rapport de courant IDON/ IDOFF = 7.103<br>The use of organic materials allows the fabrication of electronic devices at low temperature and on different types of substrates. Organic field effect transistors (OFETs) are one of them, their encouraging electrical performances allow the realization of complex integrated circuits. However, these performances and the electrical and air stability of OFETs still need to be improved. This thesis was part of this context, and consist of two main parts: 1) the achievement of OFETs on rigid substrate at very low temperature 2) the technology transfer to OFETs on flexible biosourced substrate in order to consider new low-cost, portable and even aiming at green and ecoresponsible electronics. For the first part, the objectives were the following : 1) the optimization, the characterization of N-type OFETs and the analysis of their electrical performances, 2) the study of their electrical stability under the effect of a continuous bias, and 3) the improvement of the stability to the ambient environment of these OFETs. For the second part, different objectives were targeted: 1) the optimization of an agar-based film for the fabrication of a biosourced substrate, 2) to ensure the resistance of the film to the different steps of the OFET fabrication, and 3) to study the feasibility of the agar-based OFET to evaluate its electrical stability and to compare its performances to those of the OFET on glass. The obtained results are very encouraging and demonstrated the feasibility of OFET fabricated on these soft biosourced substrates with a field effect mobility µFElin = 7.10-2 cm2/V.s, a threshold voltage VTH = 7 V and a current ratio IDON/ IDOFF = 7.103