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In this research work, brass (Cu - 37.2 wt% Zn) and Cu (99.9 wt%) wires having diameters of 200 μm were thermally oxidized in N2 containing 5% O2, at a flow rate of 200 sccm and in the ambient atmosphere respectively, to support the growth of nanowires. The oxidation temperature was varied from 300 to 600 °C and the as-grown nanowires were characterized by field emission scanning electron microscope (FESEM) equipped with energy dispersive X-ray (EDX) spectroscope, and transmission electron microscope (TEM). Results show that ZnO and CuO nanowires are formed on brass and Cu wires, respectively. The ZnO nanowires are branched and CuO nanowires are straight with tapered morphology. ZnO nanowires having hexagonal wurtzite structure grow along the directions whereas, CuO nanowires have monoclinic structure. A diffusion based stress induced model is proposed to explain the growth mechanism of the nanowires. Thermal oxidation process is a suitable platform for synthesizing ZnO and CuO nanowires, which can be used in in-situ device fabrication.

An innovative vibration sensor based on a Fabry-Perot Interferometer (FPI) using Fiber Bragg Grating (FBG) reflectors has been discussed in this work. The sensor has been designed to be compact and easy to fabricate and independent of temperature, to overcome limitations seen in some previous designs, providing an effective correction for temperature effects in FBG-based FPI (FBG-FPI) sensors. In this approach, light from a broadband source in the wavelength range 1500 – 1580 nm has been used to illuminate the FBGs used (having a reflective peak of 1547.42 nm), employing in this way a light source within the FPI optimum wavelength operating range of 1547.15 nm – 1547.80 nm. The sensor developed in this work has been shown able to capture a 3 kHz burst signal from a signal generator, in 1 Hz, 2 Hz, and 3 Hz intervals. In addition, the research carried out has revealed that the sensor could be used to capture sinusoidal signals at frequencies up to 9 kHz, creating a performance comparable with many existing conventional piezoelectric sensors. The ability to operate regardless of any ambient temperature changes (in the range from 26.5°C (room temperature) up until 80°C), opens the way to use such a sensor system over a wide range of engineering applications taking advantage of the next generation of FBG-based FPIs.

The detection of O2 using optical techniques has now become very important and significant progress has been made in this area over the past few years. The measurement of O2 concentration is a key parameter for diverse applications such as in life sciences, environmental monitoring, industry and biological research, and luminescence-based sensors are a valuable tool for measurements of this type. Often commercial sensors are unable to respond within a short time frame and drift over time - this demonstrates the importance of developing and validating a new technological approach. Given that need, a new sensor has been developed, with a specially-formed tip design coated with a very thin Platinum(II) 5,10,15,20-Tetrakis(2,3,4,5,6-pentafluorophenyl)-porphyrin (PtTFPP)-containing a polystyrene layer. The performance and reproducibility of the sensor design has been studied by comparing three identically fabricated sensor probes, showing that the new probe design has extreme fast response times – of a maximum value, Δt90max ≈ 390 ms for increasing and Δt90max ≈ 250 ms for decreasing O2 concentrations. The sensors created had an accuracy of better than ± 0.03 % O2 over the detection range investigated (between 0 % and 20 % O2) and showed a very stable performance over many hours of use. Examining this in detail through extended continuous use, over 12 h in a 0 % O2 solution, the probe stability was confirmed, showing a very low drift of luminescence decay time of ≈ 0.025 %/h (0.01 µs/h). Furthermore, the temperature ‘cross-talk’ has been studied in the important region between 25 °C and 40 °C (so that temperature corrections can be applied) and its mechanical stability, as well as allowing for compensation for any effects seen, has been confirmed. Given the success of the design developed, this work offers both an effective probe design and illustrates many important criteria for the selection of highly effective O2-sensitive coating materials and thus their use as a measurement tool for different quality control (QC) applications in industry.

A new and easy-to-fabricate strain sensor has been developed, based on fiber Bragg grating (FBG) technology embedded into a thermoplastic polyurethane filament using a 3-dimensional (3D) printer. Taking advantage of the flexibility and elastic properties of the thermoplastic polyurethane material, the embedding of the FBG provides durable protection with enhanced flexibility and sensitivity, as compared to the use of a bare FBG. Results of an evaluation of its performance have shown that the FBG sensors embedded in this way can be applied effectively in the measurement of strain, with an average wavelength responsivity of 0.013 5 nm/cm of displacement for tensile strain and −0.014 2 nm/cm for compressive strain, both showing a linearity value of up to 99%. Furthermore, such an embedded FBG-based strain sensor has a sensitivity of ∼1.74 times greater than that of a bare FBG used for strain measurement and is well protected and suitable for in-the-field use. It is also observed that the thermoplastic polyurethane based (TPU-based) FBG strain sensor carries a sensitivity value of ∼2.05 times higher than that of the polylactic acid based (PLA-based) FBG strain sensor proving that TPU material can be made as the material of choice as a “sensing” pad for the FBG.

The electrical characteristics of quad-crescent-shaped silicon nanowire (NW) solar cells (SCs) are numerically analyzed and as a result their performance optimized. The structure discussed consists of four crescents, forming a cavity that permits multiple light scattering with high trapping between the NWs. Additionally, new modes strongly coupled to the incident light are generated along the NWs. As a result, the optical absorption has been increased over a large portion of light wavelengths and hence the power conversion efficiency (PCE) has been improved. The electron–hole (e–h) generation rate in the design reported has been calculated using the 3D finite difference time domain method. Further, the electrical performance of the SC reported has been investigated through the finite element method, using the Lumerical charge software package. In this investigation, the axial and core–shell junctions were analyzed looking at the reported crescent and, as well, conventional NW designs. Additionally, the doping concentration and NW-junction position were studied in this design proposed, as well as the carrier-recombination-and-lifetime effects. This study has revealed that the high back surface field layer used improves the conversion efficiency by $$\sim$$ ∼ 80%. Moreover, conserving the NW radial shell as a low thickness layer can efficiently reduce the NW sidewall recombination effect. The PCE and short circuit current were determined to be equal to 18.5% and 33.8 mA$$/\hbox {cm}^2$$ / cm 2 for the axial junction proposed. However, the core–shell junction shows figures of 19% and 34.9 mA$$/\hbox {cm}^2$$ / cm 2 . The suggested crescent design offers an enhancement of 23% compared to the conventional NW, for both junctions. For a practical surface recombination velocity of $$10^{2}$$ 10 2 cm/s, the PCE of the proposed design, in the axial junction, has been reduced to 16.6%, with a reduction of 11%. However, the core–shell junction achieves PCE of 18.7%, with a slight reduction of 1.6%. Therefore, the optoelectronic performance of the core–shell junction was marginally affected by the NW surface recombination, compared to the axial junction.