Year 2020: A Snapshot of the Last Progress in Flexible Printed Gas Sensors

A review of recent advances in flexible printed gas sensors is presented. During the last years, flexible electronics has started to offer new opportunities in terms of sensors features and their possible application fields. The advent of this technology has made sensors low-cost, thin, with a large sensing area, lightweight, wearable, flexible, and transparent. Such new characteristics have led to the development of new gas sensor devices. The paper makes some statistical remarks about the research and market of the sensors and makes a shot of the printing technologies, the flexible organic substrates, the functional materials, and the target gases related to the specific application areas. The conclusion is a short notice on perspectives in the field

Entropy for the Brain and Applied Computation

An understanding of the interplay between the brain region and the state of consciousness and the evolution of brain complexity, regarded as an entropy-enhancing process, has recently been proposed, leading to an increase in the space of states that can be visited, and to the accessibility of new channels. Nowadays, nonlinear and complex system theories are considered promising candidates for analyzing the principles of operation of neural networks and their entropic content. The concept of computational entropy, for example, has been utilized in cryptographic primitives, namely, in cryptographic algorithms that are used to create cryptographic protocols in computer security systems

Influence of Mechanical Properties on the Piezoelectric Response of UV-Cured Composite Films Containing Different ZnO Morphologies

ZnO flower-like (ZFL) and needle (ZLN) structures were synthesized and embedded into UV-curable acrylic resin (EB), with the aim to study the effect of filler loading on the piezoelectric properties of the resulting composite films. The composites showed uniform dispersion of fillers within the polymer matrix. However, by increasing the filler amount, the number of aggregates increased, and ZnO fillers appeared not to be perfectly embedded in polymer film, indicating poor interaction with acrylic resin. The filler content increase caused an increase in glass transition temperature (Tg) and a decrease in storage modulus in the glassy state. In particular, compared with pure UV-cured EB (Tg = 50 °C), 10 wt.% ZFL and ZLN presented Tg values of 68 and 77 °C, respectively. The piezoelectric response generated by the polymer composites was good when measured at 19 Hz as a function of the acceleration; the RMS output voltages achieved at 5 g were 4.94 and 1.85 mV for the composite films containing ZFL and ZLN, respectively, at their maximum loading levels (i.e., 20 wt.%). Further, the RMS output voltage increase was not proportional to the filler loading; this finding was attributable to the decrease in the storage modulus of the composites at high ZnO loading rather than the dispersion of filler or the number of particles on the surface

Semiconductor Oxide Gas Sensors: Correlation between Conduction Mechanisms and Their Sensing Performances

In this work, a variety of semiconducting oxides were prepared and principally characterized by means of spectroscopic techniques (absorbance FT-IR, diffuse reflectance UV-Vis-NIR) to shed light on the electronic properties and defects involved at the roots of gas sensing capabilities. The thick films were obtained by screen printing technology on which electrical characterization and gas sensing measurements were performed. From the cross analysis of the results, a description of the specific sensing mechanism for each material is proposed

Year 2020: A Snapshot of the Last Progress in Flexible Printed Gas Sensors

A review of recent advances in flexible printed gas sensors is presented. During the last years, flexible electronics has started to offer new opportunities in terms of sensors features and their possible application fields. The advent of this technology has made sensors low-cost, thin, with a large sensing area, lightweight, wearable, flexible, and transparent. Such new characteristics have led to the development of new gas sensor devices. The paper makes some statistical remarks about the research and market of the sensors and makes a shot of the printing technologies, the flexible organic substrates, the functional materials, and the target gases related to the specific application areas. The conclusion is a short notice on perspectives in the field

Spectroscopic–Electrical Combined Analysis to Assess the Conduction Mechanisms and the Performances of Metal Oxide Gas Sensors

Gas sensors that are based on metal oxides are extensively used to detect gaseous compounds in many different applications. One of the main tasks for improving the sensor performances is to understand the mechanism at the base of the sensing properties for each specific material. In this work, pure and mixed oxides were selected and synthesized in the form of nanometric powders. They were characterized by spectroscopic techniques, i.e., absorbance FT–IR and diffuse reflectance UV–Vis–NIR spectroscopies, to obtain information about the electronic properties and the type of defects that are involved at the root of the gas-sensing capabilities. The electrical characterization and the gas-sensing measurements were carried out on the related thick films. Finally, for each material, a description of the specific sensing mechanism is proposed by combining the characterization results

Spectroscopic–Electrical Combined Analysis to Assess the Conduction Mechanisms and the Performances of Metal Oxide Gas Sensors

Gas sensors that are based on metal oxides are extensively used to detect gaseous compounds in many different applications. One of the main tasks for improving the sensor performances is to understand the mechanism at the base of the sensing properties for each specific material. In this work, pure and mixed oxides were selected and synthesized in the form of nanometric powders. They were characterized by spectroscopic techniques, i.e., absorbance FT–IR and diffuse reflectance UV–Vis–NIR spectroscopies, to obtain information about the electronic properties and the type of defects that are involved at the root of the gas-sensing capabilities. The electrical characterization and the gas-sensing measurements were carried out on the related thick films. Finally, for each material, a description of the specific sensing mechanism is proposed by combining the characterization results

Charge Carrier Processes and Optical Properties in TiO2 and TiO2-Based Heterojunction Photocatalysts: A Review

Photocatalysis based technologies have a key role in addressing important challenges of the ecological transition, such as environment remediation and conversion of renewable energies. Photocatalysts can in fact be used in hydrogen (H2) production (e.g., via water splitting or photo-reforming of organic substrates), CO2 reduction, pollution mitigation and water or air remediation via oxidation (photodegradation) of pollutants. Titanium dioxide (TiO2) is a “benchmark” photocatalyst, thanks to many favorable characteristics. We here review the basic knowledge on the charge carrier processes that define the optical and photophysical properties of intrinsic TiO2. We describe the main characteristics and advantages of TiO2 as photocatalyst, followed by a summary of historical facts about its application. Next, the dynamics of photogenerated electrons and holes is reviewed, including energy levels and trapping states, charge separation and charge recombination. A section on optical absorption and optical properties follows, including a discussion on TiO2 photoluminescence and on the effect of molecular oxygen (O2) on radiative recombination. We next summarize the elementary photocatalytic processes in aqueous solution, including the photogeneration of reactive oxygen species (ROS) and the hydrogen evolution reaction. We pinpoint the TiO2 limitations and possible ways to overcome them by discussing some of the “hottest” research trends toward solar hydrogen production, which are classified in two categories: (1) approaches based on the use of engineered TiO2 without any cocatalysts. Discussed topics are highly-reduced “black TiO2”, grey and colored TiO2, surface-engineered anatase nanocrystals; (2) strategies based on heterojunction photocatalysts, where TiO2 is electronically coupled with a different material acting as cocatalyst or as sensitizer. Examples discussed include TiO2 composites or heterostructures with metals (e.g., Pt-TiO2, Au-TiO2), with other metal oxides (e.g., Cu2O, NiO, etc.), direct Z-scheme heterojunctions with g-C3N4 (graphitic carbon nitride) and dye-sensitized TiO2

Photo-assisted nano-crystalline thick film gas sensors for ozone detection

none6Recently, with the aim to improve sensor performances, several investigations on the effect of light (usually UV) have been performed 1,2. The basic idea is arising from the fact that some metal oxides, known for their good sensing capabilities, also show photocatalytic behavior. This work is aimed to investigate the chance offered by this technique of decreasing the working temperature even down to room one as well as to improve the recovery times in dynamical measurements. Moreover, to better approach the problem, two functional materials, ZnO and WS (a solid solution of W and Sn oxides, with Sn:W=10:90) both successfully tested as ozone sensors, have been examined with and without UV light.noneM.C. Carotta; A. Fioravanti; S. Gherardi; A. Giberti; B. Vendemiati; G. MartinelliCarotta, Maria Cristina; Fioravanti, Ambra; Gherardi, Sandro; Giberti, Alessio; Vendemiati, Beatrice; Martinelli, Giulian