In this study, the use of flexographic printing was investigated for low cost, high volume production of devices incorporating nanowires through the printing of zinc acetate precursors on a substrate used to form zinc oxide (ZnO) seeds for the growth of nanowires using a hydrothermal growth technique. The printing of precursors allows the selective area growth of ZnO nanowires, which has implications in high-yield production of devices incorporating ZnO nanowires. The work presented here achieved printed line widths of <60 μm with low edge distortion (<3 μm) using a printing plate with a line width of 50 μm. The hydrothermally grown ZnO nanowires show uniform density of growth over the printed area with nanowire diameters between 40 and 60 nm on both silicon and polyimide substrates. Energy-dispersive x-ray spectra showed contamination-free crystals with a 1:1 (zinc to oxygen) stoichiometry. Crystal orientation is along the c-axis with high quality crystalline structure shown using x-ray diffraction spectroscopy and high resolution transmission electron microscopy. A ZnO nanowire gas sensor, fabricated using the flexographic printing technique, is demonstrated. Such a printing-assisted fabrication offers low cost, high volume production of devices incorporating ZnO nanowires, ranging from gas sensors to field emission devices.

In this paper, we have presented the use of flexographic printing techniques in the selective patterning of gold nanoparticles (AuNPs) onto a substrate. Highly uniform coverage of AuNPs was selectively patterned on the substrate surface, which was subsequently used in the development of a glucose sensor. These AuNPs provide a biocompatible site for the attachment of enzymes and offer high sensitivity in the detection of glucose due to their large surface to volume ratio. The average size of the printed AuNPs is less than 60 nm. Glucose sensing tests were performed using printed carbon-AuNP electrodes functionalized with glucose oxidase (GOx). The results showed a high sensitivity of 5.52 μA mM−1 cm−2 with a detection limit of 26 μM. We have demonstrated the fabrication of AuNP-based biosensors using flexographic printing, which is ideal for low-cost, high-volume production of the devices.Electronic supplementary materialThe online version of this article (doi:10.1186/s11671-015-0835-1) contains supplementary material, which is available to authorized users.

A three electrode electrochemical enzymatic biosensor consisting of ZnO nanowires was successfully fabricated using flexographic printing technique. The incorporation of ZnO nanowires at the working electrode provides advantages such as simple functionalization and high surface area for enhanced sensitivity. The flexographic printing technique allows ultra-high throughput and low cost mass production of devices due to the roll-to-roll nature of the technique. Therefore, the techniques developed here are prudent to the development of technologies capable of meeting the vast market demand for biosensing. Carbon electrodes, silver/silver chloride reference electrodes and ZnO seed layer precursors were directly printed onto a flexible plastic substrate through flexographic printing. The printing process was optimised to allow a suitable seed layer to be formed on the porous printed-carbon electrode to allow selective growth of ZnO nanowires using a hydrothermal growth method. The ZnO nanowires were subsequently functionalised with glucose oxidase, which was used in this work to form a glucose sensor as an exemplary use of the device. The fabricated nanowire electrochemical biosensing devices showed a typical sensitivity of 1.2 ± 0.2 µA mM-1 cm-2 with a linear response to the addition of glucose over a concentration range of 0.1 mM to 3.6 mM.

The optimisation of the interface between back contact and absorber is one of the main challenges to improve the electrical behaviour and further enhance the efficiencies of Cu 2 ZnSn(S,Se) 4 (CZTS(e)) solar cell devices. In this work, Mo/Si x N y thin films with various film thicknesses were introduced as an interfacial layer to explore its influence on opto-electronic properties of the pure sulphide CZTS thin film solar cells. The Si x N y was deposited through plasma enhanced chemical vapour deposition (PECVD). The film thickness and stress of the Mo/Si x N y films were controlled to improve the adhesion of the CZTS layer and reduce the chances of cracking the deposited films. Energy dispersive X-Ray spectroscopy (EDS) mapping measurements performed directly on the cross-section of Mo/Si x N y /CZTS/Mo films indicate that the Si x N y intermediate layer can effectively inhibit the formation of a highly resistive MoS 2 layer and decomposition of CZTS at the CZTS/Molybdenum (Mo) interface region. A reduced efficiency was obtained with a Si x N y modified back contact compared with the devices without this layer. This could be due to the increased recombination and poor hole extraction stemming from the very low valance band maximum of Si x N y obtained from ultraviolet photoelectron spectroscopy (UPS) measurements. Temperature dependent current density-voltage (T-JV) and temperature dependent transient photovoltage (T-TPV) measurements were used to uncover insights into the internal recombination dynamics of the charge carriers.

High-entropy alloys (HEAs) are single-phase systems prepared from equimolar or near-equimolar concentrations of at least five principal elements. The combination of high mixing entropy, severe lattice distortion, sluggish diffusion and cocktail effect favours the formation of simple phases-usually a bcc or fcc matrix with minor inclusions of ordered binary intermetallics. HEAs have been proposed for applications in which high temperature stability (including mechanical and chemical stability under high temperature and high mechanical impact) is required. On the other hand, the major challenge to overcome for HEAs to become commercially attractive is the achievement of lightweight alloys of extreme hardness and low brittleness. The multicomponent AlCrCuScTi alloy was prepared and characterized using powder X-ray diffraction (PXRD), scanning-electron microscope (SEM) and atomic-force microscope equipped with scanning Kelvin probe (AFM/SKP) techniques. Results show that the formation of complex multicomponent ternary intermetallic compounds upon heating plays a key role in phase evolution. The formation and degradation of W-phase, Al 2 Cu 3 Sc, in the AlCrCuScTi alloy plays a crucial role in its properties and stability. Analysis of as-melted and annealed alloy suggests that the W-phase is favoured kinetically, but thermodynamically unstable. The disruption of the W-phase in the alloy matrix has a positive effect on hardness (890 HV), density (4.83 g¨cm´3) and crack propagation. The hardness/density ratio obtained for this alloy shows a record value in comparison with ordinary heavy refractory HEAs.