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Environmental context Nitrate (NO3 − ) and ammonium (NH4 + ) are the most important soil nitrogen forms for plant growth. However, conventional extraction techniques may introduce artefacts affecting the measurement of plant-available N concentrations following sampling and sample preparation processes. This is the first study of the DGT technique being used to measure NO3 -N and NH4 -N in a wide range of soils, compared with conventional KCl extraction, and examined different factors that contribute to the plant-availability of these ions in soils. The knowledge would help to optimise soil nitrogen management practices, increase economic benefits and reduce environmental impacts. Rationale The availability of soil nitrogen for plant uptake can be affected by numerous soil factors such as soil texture, moisture and organic matter content, temperature and microbial activity. Conventional extraction techniques may affect the measurement of plant-available N concentrations following sampling and sample preparation processes, including drying, sieving, homogenising, freezing and thawing. The diffusive gradients in thin-films (DGT) technique can overcome some limitations of the conventional extraction techniques and has been used to successfully estimate the plant-available fractions of nutrients, such as P, K, Zn, Cu and Mn in soils. Therefore, it is important to evaluate the use of DGT for measuring NO3 − and NH4 + in a wide variety of soils and examine the factors that contribute to the plant-availability of these ions in soils. Methodology The experiment evaluated the ability of the DGT technique to measure NO3 -N and NH4 -N in soils using binding layers containing A520E anion exchange resin or Microlite® PrCH cation exchange resin, respectively. The DGT results were compared to those from conventional KCl extraction. Results The A520E- and PrCH-DGTs showed good detection limits for NO3 -N (6.90 µg L−1 ) and NH4 -N (6.23 µg L−1 ) and were able to measure potentially available NO3 -N and NH4 -N in unfertilised soils. The mass of NO3 -N and NH4 -N that accumulated on the DGT device increased linearly across soil concentrations ranging from 5 to 300 mg kg−1 NO3 -N (depending on soil type) and 5–300 mg kg−1 NH4 -N; which is equivalent to fertiliser rates of 75–450 kg ha−1 N. DGTs were used to measure potentially available NO3 -N and NH4 -N in ten soils with various physical and chemical properties. The DGT results were compared with conventional KCl extraction used to determine soil mineral N. DGT and KCl extraction measured values were significantly correlated with each other for NO3 -N (R 2  = 0.53; P -value 4 -N (R 2  = 0.20, P -value = 0.045). Discussion The results suggest that the two methods sample different N pools in the soils, with DGT targeting the NO3 -N and NH4 -N that are available in soil pore water and attached to labile solid phases.

Nonpolar resistive switching (RS), a combination of bipolar and unipolar RS, is demonstrated for the first time in a single nanowire (NW) system. Exploiting Ag@TiO2core–shell (CS) NWs synthesized by postgrowth shell formation, the switching mode is controlled by adjusting the current compliance effectively, tailoring the electrical polarity response. We demonstrate ON/OFF ratios of 105and 107for bipolar and unipolar modes, respectively. In the bipolar regime, retention times could be controlled up to 103s, and in the unipolar mode, >106s was recorded. We show how the unique dual-mode switching behavior is enabled by the defect-rich polycrystalline material structure of the TiO2shell and the interaction between the Ag core and the Ag electrodes. These results provide a foundation for engineering nonpolar RS behaviors for memory storage and neuromorphic applications in CSNW structures.

Two-dimensional (2D) layered semiconductors have recently emerged as attractive building blocks for next-generation low-power nonvolatile memories. However, challenges remain in the controllable fabrication of bipolar resistive switching circuit components from these materials. Here, the experimental realization of lateral memtransistors from monolayer single-crystal molybdenum disulfide (MoS2) utilizing a focused helium ion beam is reported. Site-specific irradiation with the focused probe of a helium ion microscope creates a nanometer-scale defect-rich region, bisecting the MoS2lattice. The reversible drift of these defects in the applied electric field modulates the resistance of the channel, enabling versatile memristive functionality. The device can reliably retain its resistance ratios and set/reset biases for 1180 switching cycles. Long-term potentiation and depression with sharp habituation are demonstrated. This work establishes the feasibility of ion irradiation for controllable fabrication of 2D memristive devices with promising key performance parameters, such as low power consumption. The applicability of these devices for synaptic emulation may address the demands of future neuromorphic architectures.

Urbanization, changes in land use and land cover (LULC), and an increase in population collectively have significant impacts on urban catchments. However, a vast majority of LULC studies have been conducted using readily available satellite imagery, which often presents limitations due to its coarse spatial resolution. Such imagery fails to accurately depict the surface characteristics and diverse spectrum of LULC classifications contained within a single pixel. This study focused on the highly urbanized Dry Creek catchment in Adelaide, South Australia and aimed to determine the impact of urbanization on spatiotemporal changes in LULC and its implications for the land surface condition of the catchment. Very high spatial resolution imagery was utilized to examine changes in LULC over the past four decades. Support Vector Machine-learning-based image classification was utilized to classify and identify the changes in LULC over the study area. The classification accuracy showed strong agreement, with a kappa value greater than 0.8. The findings of this analysis showed that extensive urban development, which expanded the built-up area by 34 km2, were responsible for the decline in grass cover by 43.1 km2over the last 40 years (1979–2019). Moreover, built-up areas, plantation, and water features, in contrast to grass cover, have demonstrated an increasing trend during the study period. The overall urban expansion over the study period was 136.6%. Urbanization intensified impervious area coverage, increasing the runoff coefficient, equivalent impervious area, and curve number by 60.6%, 60.6%, and 7.9%, respectively, while decreasing the retention capacity by 38.6%. These modifications suggest a potential variability in catchment surface runoff, prompting the need for further research to understand the surface runoff changes brought by the changes in LULC resulting from urbanization. The findings of this study can be used for land use planning and flood management.

Nanoscale materials are frequently coated with surface stabilization layers during growth that prevent flocculation in solution and facilitate processing technologies such as ink-jet device printing. Here, we show that few-nanometer-thick stabilization layers typically used swell in the presence of certain solvents and impart significant stresses to the nanomaterial that remains even after the solvent has evaporated. Solvent swelling of the surface layer dramatically enhances nanomaterial–substrate adhesion via the collapse of the stabilization layer during solvent evaporation, preventing stress relaxation. We demonstrate the stress modulation of Ag, Au, and Si nanowires functionalised with surface polymers and surfactant layers and detect strain levels between 0.1 and 0.6% using atomic force microscopy mechanical measurement and Raman spectroscopy. Dry-transferred nanowires exhibit poor adhesion and show no evidence of incorporated stress but become stressed immediately following solvent exposure. Strain engineering is demonstrated by coating nanowires with few-nanometer-thick solvent-responsive polymer layers.

We combine ambient (air) and ultrahigh vacuum (UHV) scanning tunneling microscopy (STM) and spectroscopy (STS) investigations together with density functional theory (DFT) calculations to gain a subnanometer insight into the structure and dynamic of two-dimensional (2D) surface-supported molecular networks. The planar tetraferrocene-porphyrin molecules employed in this study undergo spontaneous self-assembly via the formation of hydrogen bonded networks at the gold substrate–solution interface. To mimic liquid phase ambient deposition conditions, film formation was accomplished in UHV by electro-spraying a solution of the molecule in chloroform onto an Au(111) substrate, thereby providing access to the full spectroscopic capabilities of STM that can be hardly attained under ambient conditions. We show that molecular assembly on Au (111) is identical in films prepared under the two different conditions, and in good agreement with the theoretical predictions. However, we observe the contrast found for a given STM bias condition to be different in ambient and UHV conditions despite the similarity of the structures, and we propose possible origins of the different imaging contrast. This approach could be valuable for the thorough characterization of surface systems that involve large molecules and are prepared mainly in ambient conditions.

Optically transparent photodetectors are crucial in next-generation optoelectronic applications including smart windows and transparent image sensors. Designing photodetectors with high transparency, photoresponsivity, and robust mechanical flexibility remains a significant challenge, as is managing the inevitable trade-off between high transparency and strong photoresponse. Here we report a scalable method to produce flexible crystalline Si nanostructured wire (NW) networks fabricated from silicon-on-insulator (SOI) with seamless junctions and highly responsive porous Si segments that combine to deliver exceptional performance. These networks show high transparency (∼92% at 550 nm), broadband photodetection (350 to 950 nm) with excellent responsivity (25 A/W), optical response time (0.58 ms), and mechanical flexibility (1000 cycles). Temperature-dependent photocurrent measurements indicate the presence of localized electronic states in the porous Si segments, which play a crucial role in light harvesting and photocarrier generation. The scalable low-cost approach based on SOI has the potential to deliver new classes of flexible optoelectronic devices, including next-generation photodetectors and solar cells.

We demonstrate templating of functional materials with unexpected and intricate micro- and nanostructures by controlling the condensation, packing, and evaporation of water droplets on a polymer solution. Spontaneous evaporation of a polymer solution induces cooling of the liquid surface and water microdroplet condensation from the ambient vapor. These droplets pack together and act as a template to imprint an entangled polymer film. This breath figure (BF) phenomenon is an example of self-organization that involves the long-range ordering of droplets. Equilibrium-based analysis provides many insights into contact angles and drop stability of individual drops, but the BF phenomenon remains poorly understood thus far, preventing translation to real applications. Here we investigate the dynamics of this phenomenon to separate out the competing influences and then introduce a modulation scheme to ultimately manipulate the water vapor–liquid equilibrium independently from the solvent evaporation. This approach to BF control provides insights into the mechanism, a rationale for microstructure design, and evidence for the benefits of dynamical control of self-organization systems. We finally present dramatically different porous architectures from this approach reminiscent of microscale Petri dishes, conical flasks, and test tubes.

Networks of silver nanowires appear set to replace expensive indium tin oxide as the transparent conducting electrode material in next generation devices. The success of this approach depends on optimizing the material conductivity, which until now has largely focused on minimizing the junction resistance between wires. However, there have been no detailed reports on what the junction resistance is, nor is there a known benchmark for the minimum attainable sheet resistance of an optimized network. In this paper, we present junction resistance measurements of individual silver nanowire junctions, producing for the first time a distribution of junction resistance values and conclusively demonstrating that the junction contribution to the overall resistance can be reduced beyond that of the wires through standard processing techniques. We find that this distribution shows the presence of a small percentage (6%) of high-resistance junctions, and we show how these may impact the performance of network-based materials. Finally, through combining experiment with a rigorous model, we demonstrate the important role played by the network skeleton and the specific connectivity of the network in determining network performance.

In this article, we present a comprehensive investigation of the photothermal properties of plasmonic nanowire networks. We measure the local steady-state temperature increase, heat source density, and absorption in Ag, Au, and Ni metallic nanowire networks under optical illumination. This allows direct experimental confirmation of increased heat generation at the junction between two metallic nanowires and stacking-dependent absorption of polarized light. Due to thermal collective effects, the local temperature distribution in a network is shown to be completely delocalized on a micrometer scale, despite the nanoscale features in the heat source density. Comparison of the experimental temperature profile with numerical simulation allows an upper limit for the effective thermal conductivity of a Ag nanowire network to be established at 43 Wm–1K–1(0.1 κbulk).

Nanoscale devices that are sensitive to measurement history enable memory applications, and memristors are currently under intense investigation for robustness and functionality. Here we describe the fabrication and performance of a memristor-like device that comprises a single TiO2nanowire in contact with Au electrodes, demonstrating both high sensitivity to electrical stimuli and high levels of control. Through an electroforming process, a population of charged dopants is created at the interface between the wire and electrode that can be manipulated to demonstrate a range of device and memristor characteristics. In contrast to conventional two-terminal memristors, our device is essentially a diode that exhibits memristance in the forward bias direction. The device is easily reset to the off state by a single voltage pulse and can be incremented to provide a range of controllable conductance states in the forward direction. Electrochemical modification of the Schottky barrier at the electrodes is proposed as an underlying mechanism, and six-level memory operations are demonstrated on a single nanowire.

People's views of landscape can have significant impact on their land use choices. This in turn can have climate implications. In the literature, there is significant attention paid to the effect of climate on landscape, but as well, there are more examples than one might expect of the effects of landscape change on climate. I present evidence of this from Western Australia and Africa, and some conjectured negative and positive effects in two locations in South Australia. I argue that the land use change affecting the landscape and thus affecting the climate emanates from one's view of landscape. There are also some personal reflections of perceptions of landscape from someone who started life in a climate and landscape far removed from the South Australian environment within which he has chosen to live.

Networks comprised of randomly oriented overlapping nanowires offer the possibility of simple fabrication on a variety of substrates, in contrast with the precise placement required for devices with single or aligned nanowires. Metal nanowires typically have a coating of surfactant or oxide that prevents aggregation, but also prevents electrical connection. Prohibitively high voltages can be required to electrically activate nanowire networks, and even after activation many nanowire junctions remain nonconducting. Nonelectrical activation methods can enhance conductivity but destroy the memristive behavior of the junctions that comprise the network. We show through both simulation and experiment that electrical stimulation, microstructured electrode geometry, and feature scaling can all be used to manipulate the connectivity and thus electrical conductivity of networks of silver nanowires with a nonconducting polymer coating. More generally, these results describe a strategy to integrate nanomaterials into controllable, adaptive macroscale materials.

Raman spectroscopy is an indispensable tool in the analysis of microplastics smaller than 20 μm. However, due to its limitation, Raman spectroscopy may be incapable of effectively distinguishing microplastics from micro additive particles. To validate this hypothesis, we characterized and compared the Raman spectra of six typical slip additives with polyethylene and found that their hit quality index values (0.93–0.96) are much higher than the accepted threshold value (0.70) used to identify microplastics. To prevent this interference, a new protocol involving an alcohol treatment step was introduced to successfully eliminate additive particles and accurately identify microplastics. Tests using the new protocol showed that three typical plastic products (polyethylene pellets, polyethylene bottle caps, and polypropylene food containers) can simultaneously release microplastic-like additive particles and microplastics regardless of the plastic type, daily-use scenario, or service duration. Micro additive particles can also adsorb onto and modify the surfaces of microplastics in a manner that may potentially increase their health risks. This study not only reveals the hidden problem associated with the substantial interference of additive particles in microplastic detection but also provides a cost-effective method to eliminate this interference and a rigorous basis to quantify the risks associated with microplastic exposure.

In this article, we examine the phenomenon of single-crystal halide salt wire growth at the surface of porous materials. We report the use of a single-step casting technique with a supramolecular self-assembly gel matrix that upon drying leads to the growth of single-crystal halide (e.g., NaCl, KCl, and KI) nanowires with diameters ∼130–200 nm. We demonstrate their formation using electron microscopy and electron-dispersive X-ray spectroscopy, showing that the supramolecular gel stabilizes the growth of these wires by facilitating a diffusion-driven base growth mechanism. Critically, we show that standard non-supramolecular gels are unable to facilitate nanowire growth. We further show that these nanowires can be grown by seeding, forming nanocrystal gardens. This study helps understand the possible prefunctionalization of membranes to stimulate ion-specific filters or salt efflorescence suppressors, while also providing a novel route to nanomaterial growth.

One of the problems with solvent exfoliation of graphene is that the best solvents tend to have high boiling points and so are difficult to remove and can present problems for flake deposition and composite formation. Here, we demonstrate the exfoliation of graphene at relatively high concentration in low boiling point solvents such as chloroform and isopropanol. It is possible to achieve concentrations of up to 0.5 mg/mL, just under half that which can be achieved with high boiling point solvents such as N-methyl-pyrrolidone. These dispersions consist of graphene flakes of ∼1 μm length and with a thickness of less than 10 layers (≤5 layers for isopropanol). For both solvents, >75% of the graphene remains dispersed indefinitely. Raman spectroscopy shows the flakes to be relatively defect-free. A significant advantage of low boiling point solvents is that they allow individual flakes to be spray cast onto substrates. Deposited densities of >10 flakes with length >1 μm per 10 μm × 10 μm square have been controllably achieved. While some on-substrate aggregation is observed, this is much less prevalent than when spraying from high boiling point solvents.

Conductance imaging atomic force microscopy was used to probe the electrical interface between single-walled carbon nanotubes and metal electrodes. The contact resistance was optimized by applying a local voltage pulse (∼2 s) using a conductive probe with controlled loading force to the region of the metal electrode contacting the nanotube. Using this technique, we show that Pd forms superior contacts, resulting in contact resistance values that are among the lowest ever reported.

We have used aqueous dispersions of silver nanowires to prepare thin, flexible, transparent, conducting films. The nanowires are of length and diameter close to 6.5 μm and 85 nm, respectively. At low thickness, the films consist of networks but appear to become bulk-like for mean film thicknesses above ∼160 nm. These films can be very transparent with optical transmittance reaching as high as 92% for low thickness. The transmittance (550 nm) decreases with increasing thickness, consistent with an optical conductivity of 6472 S/m. The films are also very uniform; the transmittance varies spatially by typically <2%. The sheet resistance decreases with increasing thickness, falling below 1 Ω/◻ for thicknesses above 300 nm. The DC conductivity increases from 2 × 105S/m for very thin films before saturating at 5 × 106S/m for thicker films. Similarly, the ratio of DC to optical conductivity increases with increasing thickness from 25 for the thinnest films, saturating at ∼500 for thicknesses above ∼160 nm. We believe this is the highest conductivity ratio ever observed for nanostructured films and is matched only by doped metal oxide films. These nanowire films are electromechanically very robust, with all but the thinnest films showing no change in sheet resistance when flexed over >1000 cycles. Such results make these films ideal as replacements for indium tin oxide as transparent electrodes. We have prepared films with optical transmittance and sheet resistance of 85% and 13 Ω/◻, respectively. This is very close to that displayed by commercially available indium tin oxide.

We have prepared flexible, transparent, and very conducting thin composite films from poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate), filled with both arc discharge and HIPCO single-walled nanotubes, at high loading level. The films are of high optical uniformity. The arc discharge nanotube-filled composites were significantly more conductive, demonstrating DC conductivities of >105S/m for mass fractions >50 wt %. The ratio of DC to optical conductivity was higher for composites with mass fractions of 55−60 wt % than for nanotube-only films. For an 80 nm thick composite, filled with 60 wt % arc discharge nanotubes, this conductivity ratio was maximized at σDC/σOp= 15. This translates into transmittance (550 nm) and sheet resistance of 75 and 80 Ω/◻, respectively. These composites were electromechanically very stable, showing <1% resistance change over 130 bend cycles.

A solvothermal method for growing ZnO nanostructures with different morphologies is presented. Nanowires, nanorods, nanocorns, nanoshuttles, nanoworms, and nanoflowers with excellent crystallinity have been successfully fabricated by combining two different coordination agents and adjusting the ratio of solvents and the reaction time. The nanowires and nanorods are of high aspect ratio (>500 and 50, respectively) and exhibit a perfect single crystalline wurtzite structure. The growth process responsible for the variation in morphology is discussed.

Objective. Considerable controversy persists regarding the use of human antibiotics to promote growth in animals raised for food. The authors examined the economic effect of removing antibiotics used for growth promotion in commercial broiler chickens.Methods. The authors utilized data published by the Perdue company, the fourth largest poultry producer in the United States, in which a non-randomized controlled trial of growth-promoting antibiotic (GPA) use was conducted with seven million broiler chickens to evaluate the impact of removing GPAs on production.Results. Positive production changes were associated with GPA use, but were insufficient to offset the cost of the antibiotics. The net effect of using GPAs was a lost value of $0.0093 per chicken (about 0.45% of total cost). Based upon these data, the authors found no basis for the claim that the use of GPAs lowers the cost of production. Note that this study does not include veterinary cost changes or changes in performance variability associated with the removal of GPAs.Conclusions. This economic analysis is the first study to the authors' knowledge utilizing large-scale empirical data collected by U.S. industry, in which it is demonstrated that the use of GPAs in poultry production is associated with economic losses to the producers. These data are of considerable importance in the ongoing national debate concerning the continued use of antibiotics for growth promotion of food animals. Based on the industry study and the resulting economic impact, the use of GPAs in U.S. poultry production should be reconsidered.

We report the synthesis of high density arrays of coaxial nanocables, consisting of germanium nanowires surrounded by cobalt nanotube sheaths, within anodic aluminium oxide membranes. The nanocable arrays were prepared using a supercritical fluid inclusion process, whereby the cobalt nanotubes were first deposited on the pore walls of the nanoporous membranes and subsequently filled with germanium to form coaxial nanocables. The composition and structure of the metal–semiconductor nanostructures was investigated by electron microscopy, energy dispersive X-ray mapping and X-ray diffraction at high angles. The magnetic properties of the co-axial nanocables were probed using a superconducting quantum interference device SQUID. In essence, this paper describes a technique for merging semiconductor and magnetic technologies into well-defined building blocks which may ultimately lead to new multifunctional devices, such as spin-field effect transistors.

The relationship between seagrass area and the commercial catch of some economically important South Australian fish species is not known in any quantitative sense. However, there is evidence in the literature to suggest that seagrass decline will detrimentally impact on species abundance and composition, and consequently that the presence or absence of seagrass will compromise the commercial and recreational fishery. In this paper we describe the construction of models based on order restricted (isotonic) regression and discuss the role of seagrass area, in terms of its influence on the level of commercial catch through modifying the effect of fishing 'effort'.

The provision of energy for households is a major contributor to greenhouse gas emissions in the domestic sector. There is significant scope for energy savings and thus emission reduction in this sector. This paper constructs a bridge between thermal analysis and environmental assessment in the occupancy stage of the dwelling life cycle, approaching both methods as being on a common system Environment–Dwelling–Inhabitant. The importance of the local level in the thermal analysis and assessment of either a dwelling or an inhabitant's behaviour is demonstrated. It is shown that the researcher can choose between natural experiment, computer experiment and mathematical modelling to analyze the system. Such a choice is discussed for two particular methods of thermal analysis. Thermal Nomograms are the result of mathematical modelling, and the Energy Score Sheet is the result of a computer experiment in energy rating. Despite being developed for the purpose of thermal analysis, these methods can also be utilized for environmental assessment at the local level. The discussion centres on Australian conditions where the majority of the population resides in a relatively benign climate wherein behavioural alterations have significant potential for energy savings and environmental impact. The purpose of the paper is to emphasise benefits apart from energy minimisation to promote the use of energy efficient housing strategies.

Five classes of zero–one programming models for discrete facility location problems are compared to counterpart models for the selection of conservation reserves. The basic problem of siting facilities to cover demand for services is analogous to the problem of selecting reserves to support species diversity. The classes of models include the set covering and maximal covering models, as well as models for backup and redundant coverage. Issues of reliability and uncertainty are addressed by chance constrained covering models and maximal expected covering models. Exact and heuristic solution approaches are discussed. Multi-objective and economic issues are considered.