Ion-driven nanograin formation in early-stage degradation of tri-cation perovskite films.

The operational stability of organic-inorganic halide perovskite based solar cells is a challenge for widespread commercial adoption. The mobility of ionic species is a key contributor to perovskite instability since ion migration can lead to unfavourable changes in the crystal lattice and ultimately destabilisation of the perovskite phase. Here we study the nanoscale early-stage degradation of mixed-halide mixed-cation perovskite films under operation-like conditions using electrical scanning probe microscopy to investigate the formation of surface nanograin defects. We identify the nanograins as lead iodide and study their formation in ambient and inert environments with various optical, thermal, and electrical stress conditions in order to elucidate the different underlying degradation mechanisms. We find that the intrinsic instability is related to the polycrystalline morphology, where electrical bias stress leads to the build-up of charge at grain boundaries and lateral space charge gradients that destabilise the local perovskite lattice facilitating escape of the organic cation. This mechanism is accelerated by enhanced ionic mobility under optical excitation. Our findings highlight the importance of inhibiting the formation of local charge imbalance, either through compositions preventing ionic redistribution or local grain boundary passivation, in order to extend operational stability in perovskite photovoltaics.

Ecological drivers of eggshell wettability in birds.

Complex and at times extreme environments have pushed many bird species to develop unique eggshell surface properties to protect the embryo from external threats. Because microbes are usually transmitted into eggs by moisture, some species have evolved hydrophobic shell surfaces that resist water absorption, while also regulating heat loss and the exchange of gases. Here, we investigate the relationship between the wettability of eggshells from 441 bird species and their life-history traits. We measured the initial contact angle between sessile water droplets and the shell surface, and how far the droplet spread. Using phylogenetic comparative methods, we show that body mass, annual temperature and eggshell maculation primarily explained variance in water contact angle across eggshells. Species nesting in warm climates were more likely to exhibit highly hydrophobic eggshells than those nesting in cold climates, potentially to reduce microbial colonization. In non-passerines, immaculate eggs were found to have more hydrophobic surfaces than maculate eggshells. Droplets spread more quickly on eggshells incubated in open nests compared to domed nests, likely to decrease heat transfer from the egg. Here, we identify clear adaptations of eggshell wettability across a diverse range of nesting environments, driven by the need to retain heat and prevent microbial adhesion.

Vm-related extracellular potentials observed in red blood cells.

Even in nonexcitable cells, the membrane potential Vm is fundamental to cell function, with roles from ion channel regulation, development, to cancer metastasis. Vm arises from transmembrane ion concentration gradients; standard models assume homogeneous extracellular and intracellular ion concentrations, and that Vm only exists across the cell membrane and has no significance beyond it. Using red blood cells, we show that this is incorrect, or at least incomplete; Vm is detectable beyond the cell surface, and modulating Vm produces quantifiable and consistent changes in extracellular potential. Evidence strongly suggests this is due to capacitive coupling between Vm and the electrical double layer, rather than molecular transporters. We show that modulating Vm changes the extracellular ion composition, mimicking the behaviour if voltage-gated ion channels in non-excitable channels. We also observed Vm-synchronised circadian rhythms in extracellular potential, with significant implications for cell-cell interactions and cardiovascular disease.

Fabrication and characterization of annular thickness mode piezoelectric micro ultrasonic transducers.

Micromachining techniques, in combination with low temperature ceramic composite sol-gel processing, have been used to fabricate annular array thickness-mode piezoelectric micro ultrasonic transducers (Tm-pMUTs). The processing techniques of low temperature (710 degrees C) composite sol-gel ceramic (sol + ceramic powder) deposition and wet etching were used to deposit and structure 27-microm thick lead zirconate titanate (PZT) films on silicon substrates to produce annular array Tm-pMUTs. Using these techniques, high quality PZT materials with near bulk permittivity have been obtained. The Tm-pMUT devices were shown to resonate at approximately 60 MHz in air and 50 MHz in water. From resonance measurements k(t) values ranging between 0.2 and 0.47 have been calculated and shown to depend on the level of porosity within the film. Lower values of kt were observed for films with higher levels of porosity, which was attributed to the relative decrease in the effective piezoelectric coefficient epsilon(33) with respect to stiffness and permittivity as a function of increasing porosity. This paper presents the successful micro-fabrication of a Tm-pMUT device and discusses the optimization of the poling conditions and effect of PZT microstructure on the coupling coefficient k(t). Pulse echo measurements in water, showing a -6 dB center frequency of 53 MHz and 47% -6 dB bandwidth, using a target 15 mm away from the transducer, have been included to demonstrate successful operation of the device. Full analysis of these results will be conducted in later publications.

Fabrication and modeling of high-frequency PZT composite thick film membrane resonators.

High-frequency, thickness mode resonators were fabricated using a 7 microm piezoelectric transducer (PZT) thick film that was produced using a modified composite ceramic sol-gel process. Initial studies dealt with the integration of the PZT thick film onto the substrate. Zirconium oxide (ZrO2) was selected as a diffusion barrier layer and gave good results when used in conjunction with silicon oxide (SiO2) as an etch stop layer. Using these conditions, devices were produced and the acoustic properties measured and modeled. The resonators showed a resonant frequency of about 200 MHz, an effective electromechanical coupling coefficient of 0.34, and a Q factor of 22. Modeling was based on a Mason-type model that gave good agreement between the experimental data and the simulations. The latter showed, for the PZT thick film, an electromechanical coupling coefficient of 0.35, a stiffness of 8.65 x 10(10) N x m(-2) and an e33,f piezoelectric coefficient of 9 C x m(-2).

Development of a thick film PZT foil sensor for use in structural health monitoring applications.

Acoustic emission (AE) monitoring is a technique of growing interest in the field of nondestructive testing (NDT). The use of AE devices to monitor the health of structural components is currently limited by the cost of AE equipment, which prohibits the permanent placement of AE devices on structures for the purposes of continuous monitoring and the monitoring of areas with limited access. Micro electromechanical systems (MEMS) can provide solutions to these problems. We present the manufacture of a 4.4-µm-thick lead zirconate titanate (PZT) film on a 110-µm-thick titanium foil substrate for use as an AE sensor. The thick-film sensor is benchmarked against commercially available AE sensors in static and dynamic monitoring applications. The thick-film AE device is found to perform well in the detection of AE in static applications. A low signal-to-noise ratio is found to prohibit the detection of AE in a dynamic application.

The impact of zero-valent iron nanoparticles upon soil microbial communities is context dependent.

Nanosized zero-valent iron (nZVI) is an effective land remediation tool, but there remains little information regarding its impact upon and interactions with the soil microbial community. nZVI stabilised with sodium carboxymethyl cellulose was applied to soils of three contrasting textures and organic matter contents to determine impacts on soil microbial biomass, phenotypic (phospholipid fatty acid (PLFA)), and functional (multiple substrate-induced respiration (MSIR)) profiles. The nZVI significantly reduced microbial biomass by 29 % but only where soil was amended with 5 % straw. Effects of nZVI on MSIR profiles were only evident in the clay soils and were independent of organic matter content. PLFA profiling indicated that the soil microbial community structure in sandy soils were apparently the most, and clay soils the least, vulnerable to nZVI suggesting a protective effect imparted by clays. Evidence of nZVI bactericidal effects on Gram-negative bacteria and a potential reduction of arbuscular mycorrhizal fungi are presented. Data imply that the impact of nZVI on soil microbial communities is dependent on organic matter content and soil mineral type. Thereby, evaluations of nZVI toxicity on soil microbial communities should consider context. The reduction of AM fungi following nZVI application may have implications for land remediation.

Thick-film acoustic emission sensors for use in structurally integrated condition-monitoring applications.

Monitoring the condition of complex engineering structures is an important aspect of modern engineering, eliminating unnecessary work and enabling planned maintenance, preventing failure. Acoustic emissions (AE) testing is one method of implementing continuous nondestructive structural health monitoring. A novel thick-film (17.6 µm) AE sensor is presented. Lead zirconate titanate thick films were fabricated using a powder/sol composite ink deposition technique and mechanically patterned to form a discrete thick-film piezoelectric AE sensor. The thick-film sensor was benchmarked against a commercial AE device and was found to exhibit comparable responses to simulated acoustic emissions.