Electrodeposition of WO3 Nanoparticles for Sensing Applications

The motivation of using metal oxides is mainly due to its charge storage capabilities, and electrocatalytic, electrochromic and photoelectrochemical properties. But comparing with bulk, nanostructured materials present several advantages related with the spatial confinement, large fraction of surface atoms, high surface energy, strong surface adsorption and increased surface to volume ratio, which greatly improves the performances of these materials. The deposition of this materials can be accomplished by a variety of physical and chemical techniques but nowadays, electrodeposited metal oxides are generally used in both laboratories and industries due to the flexibility to control structure and morphology of the oxide electrodes combined with a reduced cost. Tungsten oxide (WO3) is a well-studied semiconductor and is used for several applications as chromogenic material, sensor and catalyst. The major important features is its low cost and availability, improved stability, easy morphologic and structural control of the nanostructures, reversible change of conductivity, high sensitivity, selectivity and biocompatibility. For the electrodeposition of WO3, more than one method can be adopted: electrodeposition from a precursor solution, anodic oxidation, and electrodeposition of already produced nanoparticles; however, in this case the mechanism of the electrodeposition is not fully understood. In this chapter, a review of the latest published work of electrodeposited nanostructured metal oxides is provided to the reader, with a more detailed explanation of WO3 material applied in sensing devices

Validating silicon polytrodes with paired juxtacellular recordings: method and dataset

Cross-validating new methods for recording neural activity is necessary to accurately interpret and compare the signals they measure. Here we describe a procedure for precisely aligning two probes for in vivo “paired-recordings” such that the spiking activity of a single neuron is monitored with both a dense extracellular silicon polytrode and a juxtacellular micropipette. Our new method allows for efficient, reliable, and automated guidance of both probes to the same neural structure with micrometer resolution. We also describe a new dataset of paired-recordings, which is available online. We propose that our novel targeting system, and ever expanding cross-validation dataset, will be vital to the development of new algorithms for automatically detecting/sorting single-units, characterizing new electrode materials/designs, and resolving nagging questions regarding the origin and nature of extracellular neural signals

Gate-bias stress in amorphous oxide semiconductors thin-film transistors

A quantitative study of the dynamics of threshold-voltage shifts with time in gallium-indium zinc oxide amorphous thin-film transistors is presented using standard analysis based on the stretched exponential relaxation. For devices using thermal silicon oxide as gate dielectric, the relaxation time is 3 105 s at room temperature with activation energy of 0.68 eV. These transistors approach the stability of the amorphous silicon transistors. The threshold voltage shift is faster after water vapor exposure suggesting that the origin of this instability is charge trapping at residual-water-related trap sites

Piezoelectricity Enhancement of Nanogenerators Based on PDMS and ZnSnO3Nanowires through Microstructuration

The current trend for smart, self-sustainable, and multifunctional technology demands for the development of energy harvesters based on widely available and environmentally friendly materials. In this context, ZnSnO3 nanostructures show promising potential because of their high polarization, which can be explored in piezoelectric devices. Nevertheless, a pure phase of ZnSnO3 is hard to achieve because of its metastability, and obtaining it in the form of nanowires is even more challenging. Although some groups have already reported the mixing of ZnSnO3 nanostructures with polydimethylsiloxane (PDMS) to produce a nanogenerator, the resultant polymeric film is usually flat and does not take advantage of an enhanced piezoelectric contribution achieved through its microstructuration. Herein, a microstructured composite of nanowires synthesized by a seed-layer free hydrothermal route mixed with PDMS (ZnSnO3@PDMS) is proposed to produce nanogenerators. PFM measurements show a clear enhancement of d33 for single ZnSnO3 versus ZnO nanowires (23 ± 4 pm/V vs 9 ± 2 pm/V). The microstructuration introduced herein results in an enhancement of the piezoelectric effect of the ZnSnO3 nanowires, enabling nanogenerators with an output voltage, current, and instantaneous power density of 120 V, 13 μA, and 230 μW·cm-2, respectively. Even using an active area smaller than 1 cm2, the performance of this nanogenerator enables lighting up multiple LEDs and other small electronic devices, thus proving great potential for wearables and portable electronics

Perspective: Zinc-Tin Oxide Based Memristors for Sustainable and Flexible In-Memory Computing Edge Devices

As the Internet of things (IOT) industry continues to grow with an ever-increasing number of connected devices, the need for processing large amounts of data in a fast and energy-efficient way becomes an even more pressing issue. Alternative computation devices such as resistive random access memories (RRAM), or memristors, started taking centre stage as prime candidates to tackle this issue due to their in-memory computation capabilities. Amorphous oxide semiconductors (AOSs), more specifically eco-friendly zinc-tin oxide (ZTO), show great promise as a memristive active material for flexible and sustainable applications due to its low required fabrication temperature, amorphous structure, low-cost, and critical-raw-material-free composition. In this perspective article, the research progress on ZTO-based memristors is reviewed in terms of device structure and material compositions. The effects on the electrical performance of the devices are studied. Additionally, neuromorphic and optoelectronic capabilities are analyzed with the objective of finding the best approaches toward implementing these devices in novel computing paradigms

Metal oxide nanostructures for sensor applications

Electrorheological fluids have been paying a lot of attention due to their potential use in active control of various devices in mechanics, biomedicine or robotics. An electrorheological fluid consisting of polarizable particles dispersed in a non-conducting liquid is considered to be one of the most interesting and important smart fluids. This work presents the effect of the dopant, camphorsulphonic acid or citric acid, on the electrorheological behaviour of suspensions of doped polyaniline nanostructures dispersed in silicone oil, revealing its key role. The influence of carbon nanoparticle concentration has also been studied for these dispersions. All the samples showed an electrorheological effect, which increased with electric field and nanostructure concentration and decreased with silicone oil viscosity. However, the magnitude of this effect was strongly influenced not only by carbon nanoparticle concentration but also by the dopant material. The electrorheological effect was much lower with a higher carbon nanoparticle concentration and doped with citric acid. The latter is probably due to the different acidities of the dopants that lead to a different conductivity of polyaniline nanostructures. Furthermore, the effect of the carbon nanoparticles could be related to its charge trapping mechanism, while the charge transfer through the polymeric backbone occurs by hopping. Polyaniline/camphorsulphonic acid composite nanostructures dispersed in silicone oil exhibited the highest electrorheological activity, higher than three decades increase in apparent viscosity for low shear rates and high electric fields, showing their potential application as electrorheological smart materials.authorsversionpublishe

Enhanced UV flexible photodetectors and photocatalysts based on TiO2 nanoplatforms

Abstract: In this study, titanium dioxide (TiO2) nanostructured films were synthesized under microwave irradiation through low temperature synthesis (80 °C) and integrated in ultraviolet (UV) photodetectors and as photocatalysts. Bacterial nanocellulose (BNC), tracing paper, and polyester film were tested as substrates, since they are inexpensive, flexible, recyclable, lightweight, and when associated to low temperature synthesis and absence of a seed layer, they become suitable for several low-cost applications. The nanostructured TiO2 films and substrates were structurally characterized by scanning electron microscopy coupled with energy dispersive X-ray spectroscopy, X-ray diffraction, and Raman spectroscopy. The optical properties of all materials were investigated. The TiO2 nanostructured films were implemented as a photoactive layer of UV photodetectors and demonstrated significant increase of conductance upon exposed to UV irradiation. The photodetection behaviour of each material was investigated by in-situ Kelvin probe force microscopy experiments, in which the contact potential difference varied under dark or UV irradiation conditions, demonstrating higher shift for the BNC-based UV photodetector. Photocatalytic activity of the films was assessed from rhodamine B degradation under solar radiation, and BNC based devices revealed to be the best photocatalyst. The structural characteristics of the TiO2 films and substrates were correlated to the differences in the UV photodetection and photocatalytic performances. Graphical Abstract: [Figure not available: see fulltext.] © 2018 Springer Science+Business Media, LLC, part of Springer NatureThe work was supported by the FCT—Portuguese Foundation for Science and Technology, through the scholarship BPD/84215/2012. This work is also funded by FEDER funds through the COMPETE 2020 Program and National Funds through FCT - Portuguese Foundation for Science and Technology under the project number POCI-01-0145-FEDER-007688, Reference UID/CTM/50025/2013. The Center of Biological Engineering acknowledges funding through UID/BIO/04469/2013 unit and COMPETE 2020 (POCI-01-0145-FEDER-006684).info:eu-repo/semantics/publishedVersio

Progress Report on “From Printed Electrolyte‐Gated Metal‐Oxide Devices to Circuits”

Printed electrolyte‐gated oxide electronics is an emerging electronic technology in the low voltage regime (≤1 V). Whereas in the past mainly dielectrics have been used for gating the transistors, many recent approaches employ the advantages of solution processable, solid polymer electrolytes, or ion gels that provide high gate capacitances produced by a Helmholtz double layer, allowing for low‐voltage operation. Herein, with special focus on work performed at KIT recent advances in building electronic circuits based on indium oxide, n‐type electrolyte‐gated field‐effect transistors (EGFETs) are reviewed. When integrated into ring oscillator circuits a digital performance ranging from 250 Hz at 1 V up to 1 kHz is achieved. Sequential circuits such as memory cells are also demonstrated. More complex circuits are feasible but remain challenging also because of the high variability of the printed devices. However, the device inherent variability can be even exploited in security circuits such as physically unclonable functions (PUFs), which output a reliable and unique, device specific, digital response signal. As an overall advantage of the technology all the presented circuits can operate at very low supply voltages (0.6 V), which is crucial for low‐power printed electronics applications