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Conventional metal oxide semiconductor (MOS) gas sensors have been investigated for decades to protect our life and property. However, the traditional devices can hardly fulfill the requirements of our fast developing mobile society, because the high operating temperatures greatly limit their applications in battery-loaded portable systems that can only drive devices with low power consumption. As ammonia is gaining importance in the production and storage of hydrogen, there is an increasing demand for energy-efficient ammonia detectors. Hence, in this work, a Schottky diode resulting from the contact between zinc oxide nanorods and gold is designed to detect gaseous ammonia at room temperature with a power consumption of 625 μW. The Schottky diode gas sensors benefit from the change of barrier height in different gases as well as the catalytic effect of gold nanoparticles. This diode structure, fabricated without expensive interdigitated electrodes and displaying excellent performance at room temperature, provides a novel method to equip mobile devices with MOS gas sensors.

We report the chemical solution deposition (CSD) of a phase-pure Bi2Fe4O9 thin film for use as a photoanode in photoelectrochemical (PEC) water splitting. The energy levels of Bi2Fe4O9 films have been measured and n-type characteristics have been confirmed. With band gaps determined as 2.05 eV (indirect) and 2.80 eV (direct) and valence and conduction bands straddling the water oxidation and reduction potentials, this material is highly promising as a photocatalyst for solar water splitting. The photocurrent of a planar photoanode reached 0.1 mA cm−2 at 1.23 VNHE under AM1.5G illumination. The addition of H2O2 as a hole scavenger increased the photocurrent to 0.25 mA cm−2, indicating hole injection is one limiting factor to the performance. The performance was enhanced by nearly 5-fold when the Bi2Fe4O9 photoanode is coupled to a Co–Pi surface co-catalyst. The photoanode also shows excellent stability with no change in photocurrent over three hours of continuous illumination. These results indicate that this material represents a promising addition to the growing selection of low-cost, stable photocatalysts for use in solar water splitting.

© 2019 Elsevier Ltd Water splitting by thermal cycling of a pyroelectric element that acts as an external charge source offers an alternative method to produce hydrogen from transient low-grade waste heat or natural temperature changes. In contrast to conventional energy harvesting, where the optimised load resistance is used to maximise the combination of current and voltage, for water splitting applications there is a need to optimise the system to achieve a sufficiently high potential difference for water electrolysis, whilst also maintaining a high current output. For the thermal harvesting system examined here, a high impedance 0.5 M KOH electrolyte with working electrodes connected to a rectified pyroelectric harvester produced the highest voltage of 2.34 V, which was sufficient for H2 generation. In addition to electrolyte concentration, the frequency of the temperature oscillations was examined and reducing the heating-cooling frequency led to a larger change in temperature to generate increased pyroelectric charge and a higher potential difference for pyro-water splitting. Finally, in the absence of sacrificial reagents, cyclic production of H2 (0.654 μmol/h) was demonstrated for the optimised processing parameters of electrolyte and thermal cycling frequency using the external pyroelectric element as a charge source for water splitting.

New hybrid materials consisting of ZnO nanorods sensitized with three different biomass-derived carbon quantum dots (CQDs) were synthesized, characterized, and used for the first time to build solid-state nanostructured solar cells. The performance of the devices was dependent on the functional groups found on the CQDs. The highest efficiency was obtained using a layer-by-layer coating of two different types of CQDs.

ZnO is an interesting material for photoactive and optoelectronic devices because of the wide range of available nanostructures and advantageous semiconducting properties. However, a significant drawback of ZnO is the low stability in high or low pH solutions. This has limited the development of ZnO core-shell materials for use in Z-scheme systems or photovoltaics, where any secondary phase is produced using chemical solution processing at low or high pH. Here, we show a simple process to produce an organic capping layer of 3-aminopropyltriethoxysilane that can successfully stabilize nanostructured ZnO for processing below pH 1. We demonstrate that this process can be used to produce a ZnO-BiFeO3 (BFO) core-shell structure by a sol-gel process. Using a range of physical and analytical techniques, we show that BFO is highly crystalline and produces a conformal coating with a thickness of 2.5 nm. X-ray photoelectron spectroscopy and X-ray diffraction confirm the phase and expected chemical composition of BFO. Finally we are able to demonstrate that diodes produced using the ZnO-BFO core-shell structure have improved performance with a rectification ratio at ±3 V of 2800 because of the reduction in reverse current typically associated with surface recombination on ZnO. Our process opens a route to producing a range of hitherto prohibited ZnO core-shell structures that may have applications ranging from photovoltaic devices to core-shell photocatalysts.

We report the sol–gel synthesis of a CuWO4 (Eg ∼ 2.0–2.15 eV) thin film loaded with Ag nanowires. The incorporation of Ag nanowires into the semiconductor matrix significantly improves the performance of CuWO4 as a photoanode for use in photochemical water splitting (PEC). Here, we have developed a planar electrode to test the photoactivity of the catalyst using standard electrochemical procedures under simulated solar light. The sol–gel synthesis of CuWO4 is modified such that we add Ag nanowires during sol aging. We demonstrate that there is negligible change to the CuWO4 matrix microstructure, morphology or crystal structure. When we compare the pristine CuWO4 to the material with Ag nanowires embedded in the CuWO4 matrix there is a fourfold improvement of photocurrent at 1.23 V vs. NHE to ca. 1.5 mA cm−2 (pH 9) under simulated AM1.5G illumination. This photocurrent is very competitive against more well developed photoanode structures when consideration for surface area is allowed. The Ag nanowires increase carrier mobility film enabling a sufficiently thick sample of catalyst, measured at 750 nm, to effectively harvest incident light. The addition of the Ag nanowires removes the plateau region found for CuWO4 further indicating that there is a good flow of carriers to the surface of the catalyst, a significant improvement as carrier mobility has been shown to be low in CuWO4. The Faradaic efficiency of the catalyst was measured at 31%. Our flat band potential is found to be 0 vs. NHE. The ability to make a highly photoactive catalyst using a simple chemical process opens up opportunities in a wide range of areas that focus on PEC and other light harvesting processes.

Hydrogen fuel cells are a promising energy conversion technology due to its high energy density and zero greenhouse gas emission. As a result, the production of hydrogen from renewable and alternative resources has gained significant interest in recent decades. This paper demonstrates a new approach which uses a pyroelectric energy harvester for water splitting and represents a novel alternative hydrogen source. Pyroelectrics are attractive for harvesting waste heat due to their ability to convert temperature fluctuations into electrical energy. A range of pyroelectric materials and geometries for water electrolysis are analysed to determine, (i) the minimum material thickness to generate a critical potential to initialise water decomposition and, (ii) to maximize the charge and hydrogen mass production. We then successfully demonstrate that an appropriate pyroelectric material, when combined with rectification of the alternating current, can harvest heat fluctuations and generate a sufficient electric potential difference and current for water splitting. By harvesting the pyroelectric electrical energy, a continuous hydrogen bubble production was observed during thermal cycling. Practical routes to maximize the level of hydrogen production for this new concept are also explored.

ZnO nanostructure based energy harvesting devices (ZnO nanogenerator) were fabricated using ZnO nanorods with the surface modified using a polyelectrolyte assembly comprising bi-layers of Polydiallyldimethylammonium chloride and Polystyrene sulfonate. The peak open-circuit voltage device characteristics and power delivered across a load increased in relation to the number of bi-layers in the polyelectrolyte deposition. At the highest loading of polyelectrolyte the energy harvesters generated a peak power density of 426 µW cm−2 and 1 V peak open-circuit voltage at a peak tip acceleration of 50 g. This compares to 35 µW cm−2 without polyelectrolyte. We relate this significant enhancement in device performance to the screening of mobile carriers due to an interaction of the polar polyelectrolyte materials with the surface of the ZnO nanostructures. It is proposed that the adsorption of the polyelectrolyte on the ZnO interacts with the surface defects and reduces the rate of screening and trapping of carriers leading to increased performance.

This review provides a detailed overview of the energy harvesting technologies associated with piezoelectric materials along with the closely related sub-classes of pyroelectrics and ferroelectrics. These properties are, in many cases, present in the same material, providing the intriguing prospect of a material that can harvest energy from multiple sources including vibration, thermal fluctuations and light. Piezoelectric materials are initially discussed in the context of harvesting mechanical energy from vibrations using inertial energy harvesting, which relies on the resistance of a mass to acceleration, and kinematic energy harvesting which directly couples the energy harvester to the relative movement of different parts of a source. Issues related to mode of operation, loss mechanisms and using non-linearity to enhance the operating frequency range are described along with the potential materials that could be employed for harvesting vibrations at elevated temperatures. In addition to inorganic piezoelectric materials, compliant piezoelectric materials are also discussed. Piezoelectric energy harvesting devices are complex multi-physics systems requiring advanced methodologies to maximise their performance. The research effort to develop optimisation methods for complex piezoelectric energy harvesters is then reviewed. The use of ferroelectric or multi-ferroic materials to convert light into chemical or electrical energy is then described in applications where the internal electric field can prevent electron–hole recombination or enhance chemical reactions at the ferroelectric surface. Finally, pyroelectric harvesting generates power from temperature fluctuations and this review covers the modes of pyroelectric harvesting such as simple resistive loading and Olsen cycles. Nano-scale pyroelectric systems and novel micro-electro-mechanical-systems designed to increase the operating frequency are discussed.

Since 1595 when Gerardus Mercator first published his collection of maps, teachers have used the paper atlas as the first means of teaching spatial literacy. The second wave took another four hundred years to evolve as the moving image developed from film, to TV, video tape and DVD bringing the real world to life into classrooms across the globe. Now we are embarking on the third wave and a new era in teaching spatial literacy in schools has now dawned. Teaching with geotechnologies [Geographic Information Systems (GIS), Global Positioning Systems, virtual globes and remote sensing)] not only engages the learner in inquiry-driven, problem-based, investigations of real-world issues, but involves essential skills for the twenty-first century workplace. This skill set and the critical thinking they stimulate enables us as educators to lay the foundations for the next generation of decision makers, a generation who will become the next custodians of the planet and who therefore need every opportunity to develop a deeper understanding and knowledge of sustainability. If we do not foster spatial thinking about issues such as water quality and availability, energy, sustainable agriculture, land use, urban sprawl, biodiversity loss, human health, natural hazards, and soil erosion, population and migration, at scales from local to global, who will?

P-type copper(I) thiocyanate (β-CuSCN) was deposited using a pneumatic micro-spray gun from a saturated solution in propyl sulphide. An as-produced 6 μm CuSCN film exhibited a hole mobility of 70 cm 2 /V·s and conductivity of 0.02 S·m −1 . A zinc oxide (ZnO) nanorod array was filled with CuSCN, demonstrating the capability of the process for filling nanostructured materials. This produced a diode with a n-type ZnO and p-type CuSCN junction. The best performing diodes exhibited rectifications of 3550 at ± 3 V. The electronic characteristics exhibited by the diode were attributed to a compact grain structure of the β-CuSCN giving increased carrier mobility and an absence of cracks preventing electrical shorts between electrode contacts that are typically associated with β-CuSCN films.

It has recently been shown that waste biomass can be converted into a wide range of functional materials, including those with desirable optical and electronic properties, offering the opportunity to find new uses for these renewable resources. Photovoltaics is one area in which finding the combination of abundant, low-cost and non-toxic materials with the necessary functionality can be challenging. In this paper the performance of carbon nanodots derived from a wide range of biomaterials obtained from different biomass sources as sensitisers for TiO

Perovskite materials are now an important class of materials in the application areas of photovoltaics and photocatalysis. Inorganic perovskites such as BiFeO3 (BFO) are promising photocatalyst materials with visible light activity and inherent stability. Here we report the large area sol-gel synthesis of BFO films for solar stimulated water photo oxidation. By modifying the sol-gel synthesis process we have produced a perovskite material that has p-type behaviour and a flat band potential of ∼1.15 V (versus NHE). The photocathode produces a density of -0.004 mA cm(-2) at 0 V versus NHE under AM1.5 G illumination. We further show that 0.6 μmol h(-1) of O2 was produced at an external bias of -0.5 V versus Ag/AgCl. The addition of a non-percolating conducting network of Ag increases the photocurrent to -0.07 mA cm(-2) at 0 V versus NHE (at 2% Ag loading) with an increase to 2.7 μmol h(-1) for O2 production. We attribute the enhancement in photoelectrochemical performance to increased light absorption due light scattering by the incorporated Ag particles, improved charge transfer kinetics at the Ag/BFO interface and reduced over potential losses. We support these claims by an observed shift in flat band and onset potentials after Ag modification through UV-vis spectroscopy, Mott-Schottky plots and j-v curve analysis.

These photodetectors typically require an external bias as the driving force to prevent the recombination of photogenerated electron-hole pairs. Over recent years, it has been realized that for functional nanosystems (where multiple nanoscale-devices are integrated) to be a possibility, these devices must be selfsuffi cient; that is, to function independently of external power sources that typically create the bulk of a system. It has been common in the literature to call devices of this type “selfpowered” although it should be noted that almost all previously published devices demonstrate a measurable dark current at the nominal zero-volt, or short-circuit, position. [ 2–5 ] We ascribe this to the measurement systems used, where a small bias exists, even when set to apply zero volts. ZnO is an increasingly well-studied material for optoelectronic devices due to its wide bandgap ( ≈ 3.3eV), its high exciton binding energy ( ≈ 60 meV), and the chemical and radiation hardness of the material. [ 6 ] ZnO has been considered in a range of optoelectronic and electronic devices that include photovoltaics, [ 7 , 8 ] fi eld-effect transistors, [ 9 ] and energy-harvesting devices. [ 10 , 11 ] In recent years, there has been growing interest in using nanostructured ZnO as a UV photodetector. [ 12–15 ]

ZnO is widely used as an n-type semiconductor in various solar cell structures; including dye-sensitized, organic, hybrid and solid-state solar cells. Here, we review advances in ZnO-based solar cell applications, looking at the influence of morphology, as well as the effect of different materials and sensitizers. ZnO morphologies play an important role in changing the surface area and charge transport properties, affecting the performance of the solar cells. External quantum efficiencies using purely ZnO as the active material has generally been below 3% with some dye-sensitized solar cells using liquid electrolytes above 5%. Sensitizers such as organic and inorganic dyes, quantum dots and hole conductors have been shown to influence cell efficiency by improving the absorption or providing improved charge transport. The combination of ZnO with other nanomaterials such as, TiO2, SiO2 and ZrO2 in core-shell structures or buffer layers creates improved electron transport by controlling recombination at interfaces and increasing stability of the device. The highest reported efficiencies to date were from combinational structures at 7.07% for ZnO nanosheets with TiO2 nanoparticulate coating and 7% for ZnO core-TiO2 shell structures.

We produce four distinct ZnO nanorod diode structures that are based on ZnO nanorods produced at pH 6 and pH 11 and have the p-type material PEDOT:PSS (hybrid device) or CuSCN (all inorganic device). After testing the performance of the diodes we show a rectification of 1050 at ±1V in the dark for the inorganic device. The device also exhibits good UV photodetection showing a rapid ca0.1ms turn on and off to a source of illumination. The hybrid devices performed as previously reported with a rectification of 25 at ±1V in both dark and under illumination. We ascribe the performance of the devices to the differences in morphology in the ZnO brought about by the processing conditions and the way in which the p-type layer coats the nanostructure.

ZnO nanorods grown on plastic substrates by chemical methods are combined with both inorganic and organic p-type materials to make flexible p-n junction devices. When bent the devices generate both voltage and current peaks, which is attributed to the piezoelectric effect in the ZnO nanorods. The best device produces a maximum possible power density of 100 nWcm‑2. When vibrated at a constant frequency the voltage output by the devices scales linearly with vibration amplitude. Also, when illuminated the output of the devices drops. These effects are consistent with a piezoelectric source of the voltage.

Conformal coating of ZnO nanorods with CdTe nanoparticles using layer-by-layer (LbL) processing produces a quantum dot-sensitised solar cell. Filling of the semiconductor composite structure with CuSCN provides the solar cell with a p-type semiconductor to collect the photogenerated holes. Annealing the CdTe-polymer coated nanorods lowers the series resistance of the cell by removing the polymer component of the film. A cell annealed at 350°C has a Jsc of 0.12 mAcm−2, and a Voc of 49 mV under 0.25 mW/cm2 illumination.

The continued development of ferroelectric materials into more and more consumer led applications has been at the forefront of recent ferroelectric material research. It is, however, possible to view a ferroelectric as a wide band gap semi-conductor that can sustain a surface charge density. This charge density arises from the movement of ions in the crystal lattice and the need to compensate for this charge. When viewing ferroelectrics as polarisable semi-conductors a large number of new interactions are possible. One such is the use of super band gap illumination to generate electron–hole pairs. These photogenerated carriers can then perform local electrochemistry. What is most interesting for ferroelectric materials is that the REDOX chemistry can be chosen by selectively modifying the domain structure of the ferroelectric—we can perform oxidation and reduction on the surface of the same material at spatially separate locations, or use the material to drive photoexcited carriers apart. This means we can separate the REDOX products or produce patterns of photogenerated material in places we have predetermined. This review aims to introduce the background research that has led to the current understanding as well a highlight some of the current areas that require further development.

In this work, we have investigated the photochemical reaction with a variety of metal salts on a polarizable semiconductor, lead zirconate titanate (PZT 30/70 [111]). The exact position of the band edges can influence properties such as the width of the space-charge region and barriers for charge injection, which play an important role in devices built with such materials such as FeRAM and MLC. Observations show that there can be metal deposition on positive domains or photodecomposition on negative domains. The exact reaction was found to be dependent on the reduction potential of the cation and whether a nitrate or chloride salt was used. We show that for certain cations such as Fe2+, with a reduction potential near the edge of the conduction band of the PZT, either reduction or photodecomposition can happen. This effect can be explained because of the presence of an uncertainty in the location of the band edges at the surface of the PZT. The exact position of these edges is determined by the Femi level...

Objective: This paper repositions the challenge of attracting and retaining rural GPs in a marketing context as a new focus for future research and policy development. Design: Case study with mixed design of surveys of GPs and medical students and depth interviews with GPs, medical students, regional-division administrators and GP recruitment agents. Setting: GP recruitment and retention in the Limestone Coast region of South Australia. Participants: Twenty-seven Limestone Coast (LC) GPs; random sample of medical students from Adelaide University, Adelaide University Rural Health Society and Flinders University; snowball sampling two adjacent rural regions (20 GPs); and administrators from LC and adjacent regions and GP recruitment agencies in Adelaide. Main outcome measures: Drawing from marketing theory, creative suggestion of ‘promotion of the practice and not the region’ offers a means of GP recruitment and retention for structured succession planning for rural general practices. Results: Structural attempts to broaden the GP market with overseas recruitment have done little for improving full-time equivalent GP levels. Market segmentation and market orientation offer a new emphasis on value exchange between the corporation (the practice), customer (GPs) and competition (all practices) to influence future mobility. Conclusion: A marketing orientation to the GP challenge emphasises individual's perceptions of value, GP expectations and practice offerings. Failure to acknowledge benefits of this marketing approach means that solutions such as those developed in the Limestone Coast region are unlikely. Research is now required to define GP satisfaction and value for long-term viability of general practices.

In the present day, the information technologies and telecommunications sector continually increase their demand for low cost, low power consumption, high performance electroluminescent devices for display applications. Furthermore, general lighting applications, such as white light and large array colour displays, would also benefit from an increase in the overall efficiency. Several technologies are being investigated to fulfill these needs, such as organic light emitting diodes (OLED), polymeric light emitting diodes (PLED) and field effect emission devices. A new and promising technology is light emitting devices (LEDs) based on nanostructured materials. With organic LEDs (OLEDs) already making an impact on the market in an increasingly large number of applications, hybrid technologies based on organic/inorganic nano-composites are a potential the next step. The incorporation of highefficiency fluorescent semiconductor nanoparticles has been shown to have a beneficial effect on device performance, [1] modify the colour output from the device 2 and provide a simplified route to generation of LED type devices. [3]

Recently there has been much interested on the generation of nanoscale ferroelectric islands to determine the minimum size that ferroelectric material can sustain inherent ferroelectric behaviour. In this paper we report the generation of ferroelectric capacitors with surface areas ranging from 6 × 10−14 m2 to 3 × 10−12 m2 in the form of circular capacitors with lateral diameters between 90 nm and 2 μm. We have shown that these capacitors exhibit piezoelectric behaviour by studying the response to applied electric fields though the technique of piezo-force-response microscopy (PFM). Capacitors show typical ‘butterfly’ type loops to a quasi DC applied field and enhanced displacements consistent with those measured from capacitive structures fabricated from epitaxial lead zirconium titanate (PZT) films [1]. Piezoresponse force microscopy (PFM) was used to measure the piezoresponse of nanocapacitors with lateral diameters between 90 nm to 2 μm incorporating Pb(Ti0.7, Zr0.3)O3 (PZT(30/70). A conductive cantil...

There is much speculation about the origin of fatigue in ferroelectric thin films that have been grown by sol-gel on various substrates. One of the most important substrates for growing thin film ferroelectric materials is native SiO2. After the deposition of suitable electrode, most common are Ti-Pt, a thin film of a ferroelectric material can be grown on the substrate. Procedures to grow thin film lead zirconate titanate (PZT 30-70) have been well publicized and it is now routine that almost 100% [111] orientated PZT with a columnar structure of ca. 100 nm is grown on SiO2 substrates. Recent studies using PFM have shown that it is possible to determine a variation in hysteresis loops with a spatial accuracy of 50 nm on the surface of a ferroelectric material. This study was to determine the variation in d33 for a thin film sample of ferroelectric in terms of a depth profile. It was not suitable to just turn the sample on it's side and analyze the d33 in terms of depth as the continuous back electrode wo...

Here we demonstrate the photochemical reduction of Al 3 + to metallic Al 0 nanoparticles using a ferroelectric material as the photocatalyst, in this case LiNbO 3 . This gives evidence for multi-electron photoreduction reactions and a possible route to the formation of nanostructured metal particles that has high reduction potential cations formed from the dissolution of salts.

iezoforce microscopy (PFM) has been used to determine the domain structure of lead zirconate titanate (PZT) (30/70) on an indium tin oxide (ITO)/glass substrate with a TiO2 boundary layer. The PZT nucleates into the perovskite form in a random crystallographic manner, which leads to a random domain structure in the final film. Using PFM it has been possible to visualize the domain structure of the PZT and determine that the domain structure has features as fine as 8 nm herringbone patterns. The possible impact of these structures for future devices utilizing nanoscale features of PZT and especially FeRAM developments is highlighted.

Atomic polarization in ferroelectric compounds is manipulated to control local electronic structure and influence chemical reactivity. Ferroelectric domains are patterned with electron beams or with probe tips, and electron exchange reactions occur preferentially on positive or negative domains. Using photo reduction from aqueous solution, metal nanoparticles are produced in predefined locations on an oxide substrate. Subsequently, organic molecules are reacted selectively to the particles. The process can be repeated to develop complex structures consisting of nanosized elements of semiconductors, metals, or functional organic molecules.

Recent developments on the use of the piezoelectric effect in ZnO nanorod-based p-n junctions for energy harvesting applications are presented. We describe a hybrid p-n nanostructured ZnO energy device combined with the semiconducting polymer poly(3,4-ethylene-dioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) to produce a kinetic energy harvesting. The load resistance-dependent power output from this p-n junction device is compared with the more common ZnO-PMMA device, which we make from ZnO nanorods manufactured using an identical process. It is shown that the PMMA device generates an open-circuit voltage of 150mV with a maximum power of 0.24μW/cm2 giving 0.03nJ of available energy when on a load resistance of 324 kΩ. The PEDOT:PSS device generates significantly more power, 28.9μW/cm2, when it is matched to a 1.6 kΩ load resistance. The energy output of the PEDOT:PSS device is 2.22nJ. Our results demonstrate the importance of measuring energy delivery to an electrical load to fully understand the output capability of these devices. By analysis of the time-dependent output of the devices the energy can be calculated giving a reasonable estimation as to the available energy and power in any given system.

Recent developments on the use of the piezoelectric effect in ZnO nanorod-based p-n junctions for energy harvesting applications are presented. Two types of junctions are used. The first is a hybrid p-n device combining the semiconducting polymer poly(3,4-ethylene-dioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) with ZnO nanorods. The second type of junction is an all-inorganic junction between n-type ZnO nanorods and p-type CuSCN. It is shown that both these diodes can be produced on flexible plastic substrates, which generate a voltage output when bent. The voltage output of the ZnO/PEDOT:PSS diodes are measured across a range of resistive loads while bending to find a maximum power point of 12 μWcm-2 at 4 kΩ. It is shown that a voltage output is also generated when this structure is vibrated acoustically. The ZnO/CuSCN diode is sensitized to sunlight with a Ru-based dye to form a photovoltaic device. It is shown that the device efficiency can be increased by application of acoustic vibrations. This is attributed to the electric field generated by the piezoelectric effect in ZnO affecting the charge-carrier recombination at the ZnO surface.

We show that a fiber polarimeter can be calibrated in place at a distance of 30km even when the intervening fiber varies in temperature. The calibration accuracy converges after at most 20 random stokes polarizations.

A common procedure performed by many groups in the analysis of neuroimaging data is separating the brain from other tissues. This procedure is often utilized both by volumetric studies as well as functional imaging studies. Regardless of the intent, an accurate, robust method of identifying the brain or cranial vault is imperative. While this is a common requirement, there are relatively few tools to perform this task. Most of these tools require a T1 weighted image and are therefore not able to accurately define a region that includes surface CSF. In this paper, we have developed a novel brain extraction technique termed Maximize Uniformity by Summation Heuristic (MUSH) optimization. The algorithm was designed for extraction of the brain and surface CSF from a multi-modal magnetic resonance (MR) imaging study. The method forms a linear combination of multi-modal MR imaging data to make the signal intensity within the brain as uniform as possible. The resulting image is thresholded and simple morphological operators are utilized to generate the resulting representation of the brain. The resulting method was applied to a sample of 20 MR brain scans and compared to the results generated by 3dSkullStrip, 3dIntracranial, BET, and BET2. The average Jaccard metrics for the twenty subjects was 0.66 (BET), 0.61 (BET2), 0.88 (3dIntracranial), 0.91 (3dSkullStrip), and 0.94 (MUSH).

Colloidal semiconductor nanocrystals are promising luminophores for creating a new generation of electroluminescence devices. Research on semiconductor nanocrystal based light-emitting diodes (LEDs) has made remarkable advances in just one decade: the external quantum efficiency has improved by over two orders of magnitude and highly saturated color emission is now the norm. Although the device efficiencies are still more than an order of magnitude lower than those of the purely organic LEDs there are potential advantages associated with nanocrystal-based devices, such as a spectrally pure emission color, which will certainly merit future research. Further developments of nanocrystal-based LEDs will be improving material stability, understanding and controlling chemical and physical phenomena at the interfaces, and optimizing charge injection and charge transport.

Light emitting devices based on high-efficiency photoluminescence (PL) fluorescent nanocrystals have been investigated in terms of the generation of light from the structure using a variety of deposition methods. An automated modified layer-by-layer (LbL) self-assembly technique has been employed to produce multilayers of thiol-capped red fluorescing CdTe nanocrystals. Indium- tin-oxide (ITO) and aluminium electrodes were used as the electrodes. Morphological characterization was carried out through Schottky field effect (SFEG) SEM and atomic force microscopy (AFM). The structures built presented clear red electroluminescence (EL) to the naked eye. Turn on voltages were found to be in the range of 3-6 volts while the onset current was in the order of tens of microamperes. The role of structure homogeneity, the presence of pinholes and lifetime extension were features addressed during this investigation. Samples with a lifetime of continuous operation in air longer than 60 minutes and highly stable EL spectra were achieved; EL was visible to the unaided eye, although the brightness was still below the commercial standards and has not yet been qualified.

This paper evaluates the improvement in performance of ZnO nanowires energy harvesters using p-type copper thiocyanate (CuSCN) passivation. Two types of p-n junction based devices: ZnO/PEDOT:PSS (poly(3,4-ethylene-dioxythiophene) poly(styrenesulfonate)) and ZnO/CuSCN/PEDOT:PSS were fabricated. It was observed that, the passivation of nanowires using CuSCN improved the performance four times, yielding a peak power density of 303 μWcm−2 for a load of 3.54 kΩ. The results were supported by impedance analysis of each device and it was observed that the piezoelectric voltage output of the device depends on its RC time constant.

Solar cells are produced using solution processing that combine ZnO nanorods with the conjugated polymer poly(3-hexylthiophene) (P3HT). ZnO nanorods have an average length and diameter of 2.7 μm and 81 nm, and are well coated with P3HT. The solar cells have a power conversion efficiency of 1.24 %, which increases to 1.78 % when 10 kHz acoustic vibrations are applied to the device at 75 dB using a loudspeaker. Transient absorption studies demonstrate that the efficiency increase originates from a decrease in the non-geminate recombination rate in the system. It is proposed that electric fields at the ZnO:P3HT interface arising from the piezoelectric effect in ZnO increase the charge-carrier separation, producing this reduction in recombination and associated efficiency increase.

This paper will report on the design, fabrication and testing of a solid-state perovskite enhanced ZnO solar cell. The p-type perovskite material used is bismuth ferrite (BFO) which has an absorption range within the blue range of the visible light spectrum. The solid state solar cell, was sensitized with N719 dye and used a CuSCN hole conductor. A disadvantage of ZnO is its poor chemical stability in acidic and corrosive environments. As chemical solution techniques were used in depositing BFO, a buffer method using an aminosilane ((3-aminopropyltrimethoxysilane or H2N(CH2)3Si(OCH3)3)) coating was used to provide a protective coating on the ZnO nanorods before the BFO film was spin coated onto the ZnO nanorods. The photovoltaic performance of the solar cells were tested using a Keithley 2400 source meter under 100mW/cm2, AM 1.5G simulated sunlight, where improvements in Jsc and efficiency were observed. The BFO was able to harness more electrons and also acted as a buffer from electron recombination.

ZnO nanorods synthesised using an aqueous pH 11 solution are shown to exhibit surface-sensitive morphology post-annealing in oxygen, air, and nitrogen as shown by scanning electron microscopy and transmission electron microscopy analysis. Raman analysis confirms the nanorods were nitrogen-doped and that nitrogen incorporation takes place during the synthesis procedure in the form of N-Hx. A strong green photoluminescence is observed post-annealing for all samples, the intensity of which is dependent on the atmosphere of anneal. This luminescence is linked to zinc vacancies as recent reports have indicated that these defects are energetically favoured with the annealing conditions used herein. ZnO-nanorod/CuSCN diodes are fabricated to examine the effect of material properties on photodetector device performance. The devices exhibit a photocurrent at zero bias, creating a self-powered photodetector. A photocurrent response of 30 μA (at 6 mW cm−2 irradiance) is measured, with a rise time of ∼25 ns, and sensitivity to both UV and visible light (475–525 nm).

Electromechanical energy harvesting converts mechanical energy from the environment, such as vibration or human activity, into electrical energy that can be used to power a low power electronic device. Nanostructured piezoelectric energy harvesting devices, often termed nanogenerators, have rapidly increased in measured output over recent years. With these improvements nanogenerators have the potential to compete with more traditional micro- or macroscopic energy harvesting devices based on piezoelectric ceramics such as lead zirconate titanate (PZT), polymers such as polyvinylidene fluoride (PVDF) or electrostatic, electret or electromagnetic kinetic energy harvesters. Power output from a nanogenerator is most commonly measured through open-circuit voltage and/or short-circuit current, where power may be estimated from the product of these values. Here we show that such measures do not provide a complete picture of the output of these devices, and can be misleading when attempting to compare alternative designs. In order to compare the power output from a nanogenerator, techniques must be improved in line with those used for more established technologies. We compare ZnO nanorod/poly(methyl methacrylate) (PMMA) and ZnO nanorod/poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) devices, and show that despite an open-circuit voltage nearly three times lower the ZnO/PEDOT:PSS device generates 150 times more power on an optimum load. In addition, it is shown that the peak voltage and current output can be increased by straining the device more rapidly and therefore time-averaged power, or time-integrated measures of output such as total energy or total charge should be calculated. Finally, the internal impedance of the devices is characterised to develop an understanding of their behaviour and shows a much higher internal resistance but lower capacitive impedance for the ZnO/PMMA device. It is hoped that by following more rigorous testing procedures the performance of nanostructured piezoelectric devices can be compared more realistically to other energy harvesting technologies and improvements can be rapidly driven by a more complete understanding of their behaviour.

We used controlled bending of a ZnO/poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) diode at known strain rates to measure the mechanical-to-electrical energy conversion efficiency. The mechanical energy input into the nanostructured diode was measured as 330 ± 2 nJ cm−2. The electrical energy output was calculated by integrating the product of the short-circuit current and open-circuit voltage over time. This gives a measured external efficiency of the device at a bending rate of 500 mm/min of 0.0067%. The efficiency increased exponentially with bending rate, though this increase must slow as the mechanical coupling efficiency is approached, which gives a maximum possible efficiency of 23% for ZnO.

ZnO nanorods are coated with a conformal film of CdTe nanoparticles using a layer-by-layer (LbL) process. By increasing the number of CdTe layers the absorption of incident light increases at wavelengths lower than the absorption onset of the nanoparticles (650 nm). At the absorption peak of the nanoparticles, 50 layers of nanoparticles coated onto ZnO nanorods absorb 80% of the incident light. Annealing of the ZnO–CdTe composites leads to a small red-shift in this absorption onset, but does not destroy the quantum confinement of the nanoparticles. Solar cells are produced by filling the CdTe-coated nanorods with CuSCN or PEDOT:PSS, and tested under AM 1.5 illumination. Annealing of the LbL films is essential to reduce the series resistance of the cell. Annealed cells generate an open-circuit voltage of 120 mV and a short-circuit current density of 0.19 mA cm−2.

A blue–green fluorescent organic dye and red-emitting nanoparticles, based on II–VI semiconductors, have been used together in the fabrication of white organic light-emitting devices. In this work, the materials were combined in two different ways: in the form of a blend, and as separate layers deposited on the opposite sides of the substrate. The blended-layer structure provided purer white emission. However, this device also exhibited a number of disadvantages, namely a high drive voltage, a low efficiency and some colour instability. These problems could be avoided by using a device structure that was fabricated using separate dye and nanoparticle layers.

Thiol-capped CdTe nanocrystals were used to fabricate light-emitting diodes, consisting of an emissive nanocrystal multilayer deposited via layer-by-layer, sandwiched between indium-tin-oxide and aluminum electrodes. The emissive and electrical properties of devices with different numbers of nanocrystal layers were studied. The improved structural homogeneity of the nanocrystal multilayer allowed for stable and repeatable current- and electroluminescence-voltage characteristics. These indicate that both current and electroluminescence are electric-field dependent. Devices were operated under ambient conditions and a clear red-light was detected. The best-performing device shows a peak external efficiency of 0.51% and was measured at 0.35mA/cm2 and 3.3V.

We present a performance comparison of polythiophene/fullerene derivative bulk heterojunction solar cells fabricated on fluorinated tin oxide (FTO) and indium tin oxide (ITO) in the presence and absence of the commonly used poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) hole extraction layer. From a potential commercial perspective the performance of cheaper and more readily available FTO compares well with the more expensive ITO in terms of measured device efficiency (FTO:2.8 % and ITO:3.1%). The devices show similar fill factors (FTO:63% and ITO:64%) with the same open circuit voltage of 0.6 V. The short circuit current density is lower for FTO devices at 7.5 mA/cm2 which compares with 8.0 mA/cm2 for ITO; a behaviour that is mainly attributed to the reduced optical transmission of the FTO layer. Importantly, these devices were part fabricated and wholly characterized under atmospheric conditions. The quoted device performance is the best reported for FTO based bulk heterojunction systems in the absence of the highly acidic PEDOT:PSS hole extraction layer, which is believed to degrade conductive oxides.

Extremely thin absorber (eta) solar cells aim to combine the advantages of using very thin, easily and cheaply produced absorber layers on nanostructured substrates with the stability of all-solid-state solar cells using inorganic absorber layers. The concept of using nanostructured substrates originated from the dye-sensitised solar cell, where having a very high surface area allows the use of very thin layers of dye while still absorbing sufficient sunlight. However, both the dye and liquid electrolyte used in these devices demonstrated poor stability, and efforts were made to replace them with very thin inorganic absorber layers and solid state hole collectors respectively. The combination of these concepts – a nanostructured substrate coated with a very thin inorganic absorber and completed with a solid state hole collector – is known as an eta solar cell. This review summarises the development of both the inorganic absorbers and solid state hole collectors in porous TiO2 and ZnO nanorod based...

The layer-by-layer deposition of thin films of CdTe nanoparticles and three different polyelectrolytes has been investigated. Photoluminescence spectra were used to monitor the energy transfer properties within the films. As the number of bilayers in a thin film was increased a decrease in the energy of the light emitted was observed. The wavelength change is a two-stage process. Deposition of the first one to two bi-layers of a thin film produced a sharp energy change (626 nm to 637 nm with the addition of a single bi-layer) whereas deposition of subsequent bi-layers produced a more gradual energy change (642 nm–646 nm with the addition of 5 bi-layers). A space-filling mechanism is suggested to account for these changes; smaller nanoparticles penetrate the earlier levels of a thin film and increase the inter-particle energy transfer opportunities within the layers.