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Pristine and vanadium-doped nickel ferrite (NiFe2O4) nanoparticles (NPs) were prepared by a chemical co-precipitation method. They were characterized by X-ray diffraction, scanning electron microscopy and X-ray photoelectron spectroscopy to explore their crystallinity, morphology and chemical states. Dielectric constant and dielectric loss properties were studied as a function of frequency and temperature and it was found that V-doping resulted in the enhancement of the dielectric properties. Both pristine and V-doped ferrites showed superparamagnetic nature and zero coercivity and retentivity. However, the saturation magnetization was decreased after V-doping, suggesting presence of superexchange interaction between A–B sites. Both pristine and V-doped NiFe2O4 NPs were also used for NO sensing studies and it was revealed that V-doped gas sensor revealed a better sensing performance (response of 5 s and sensitivity of 43 to 200 ppm NO gas) than pristine one (response of 9 s and sensitivity of 37 to 200 ppm NO gas).

Herein, we report the chemiresistive gas and humidity sensing properties of pristine and nickel-doped tin oxide (Ni-SnO2) gas sensors prepared by a microwave-assisted wet chemical method. The structural and optical properties are characterised using X-ray diffraction, scanning electron microscopy, scanning transmission electron microscopy, ultraviolet spectroscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The structural elucidation and morphology analyses confirm a particle size of 32–46 nm, tetragonal rutile crystal structure and small cauliflower-type surface appearance. Nickel doping can tune the structure of NPs and morphology. The tested carbon dioxide gas and humidity sensing properties reveal a rapid sensing performance with high-to-moderate sensitivity. Also, the materials favour gas sensing because their sensitivity is enhanced with the increase in nickel concentration. The sensing results suggest that nickel is a vibrant metal additive to increase the gas sensitivity of the sensor. However, nickel doping decreases the electron density and increases the oxygen vacancies. Ultimately, the gas sensor produces highly rapid sensing with a response time of 4 s.

Capabilities of the Attenuated Total Reflection (ATR) at THz wavelengths for increased sub-surface depth characterisation of (bio-)materials is presented. The penetration depth of a THz evanescent wave in biological samples is dependent on the wavelength and temperature and can reach 0.1-0.5 mm depth due to strong refractive index change ∼0.4 of the ice-water transition; this is quite significant and important when studying biological samples. Technical challenges are discussed when using ATR for uneven, heterogeneous, high refractive index samples with possibility of frustrated total internal reflection (a breakdown of the ATR reflection-mode into transmission-mode). Local field enhancements at the interface are discussed with numerical/analytical examples. Maxwell’s scaling was used to model behaviour of absorber-scatterer inside materials at the interface with ATR prism for realistic complex refractive indices of bio-materials. Modality of ATR with polarisation analysis is proposed and its principle illustrated, opening an invitation for its experimental validation. The sensitivity of the polarised ATR mode to the refractive index between the sample and ATR prism is revealed. Design principles of polarisation active optical elements and spectral filters are outlined. The results and concepts are based on experiments carried out at the THz beamline of the Australian Synchrotron.

Infrared (IR) microspectroscopy is a powerful molecular fingerprinting tool widely used for the identification of structural and functional composition of biological and chemical samples. The IR microspectroscopy beamline at the Australian Synchrotron can be operated either with a single-point narrow-band mercury cadmium telluride (MCT) detector or a focal plane array (FPA) imaging detector with 64 × 64 pixels. For the implementation of indirect nonscanning imaging technology, the system was operated with the FPA detector. In this study, we propose an indirect IR imaging technique based on the principles of correlation optics using diffractive optical elements such as random pinhole array (RPA) and Fresnel zone plate (FZP). The spatial and spectral variations of point spread functions (PSFs) of the RPA and FZP were simulated for the synchrotron configuration. Intensity responses for 2D objects were simulated using the same simulation conditions and reconstructed using Lucy-Richardson algorithm. Fabrication of diffractive elements for IR wavelengths is often a challenging task as the IR transparent material substrates, such as barium fluoride and calcium fluoride, are highly susceptible to thermal shocks and brittle by nature. The diffractive elements were fabricated by ablating directly on a 100 nm thick gold coated substrate using femtosecond laser pulses. The simulation results and the fabrication outcomes demonstrate the feasibility of indirect imaging at the synchrotron IR beamline.

A five-dimensional imaging technique to resolve objects in three-dimensional space, spectrum and time has been developed using a single diffractive optical element consisting of a quasi-random array of pinholes. The object space and spectrum were sampled by axially scanning a point object with different wavelengths along the optical axis and recording the corresponding spatio-spectral signatures. The recorded spatio-spectral signatures were catalogued and stored in a library. A thick object emitting light at different wavelengths was placed in the object space within the axial boundaries of the library and illuminated by light sources within the spectral boundaries of the spatio-spectral library and a single object intensity pattern was recorded. The spatio-spectral images of the object were reconstructed by processing the object intensity pattern and the spatio-spectral library in the computer. Depth-wavelength reciprocity was exploited to see colour from depth and depth from colour. A computational approach utilizing the scaling factors in image formation was used to synthesize the spatio-spectral signatures. The application of depth-wavelength reciprocity and the synthesis of spatio-spectral signatures accelerated the training procedure leading to a faster multidimensional multispectral imaging technology in comparison to the existing coded aperture holography techniques. The developed technology was implemented for spatio-spectral-temporal imaging of a fast transient event such as a spark with a temporal resolution of 40 μs. A single camera shot of the spark recorded by a monochrome high-speed camera was converted into intensity cube data along depth for different wavelengths.

Fresnel incoherent correlation holography (FINCH) is a super-resolution incoherent imaging technique built on the principle of self-interference. In FINCH, the object wave is split into two, modulated by diffractive lenses with different focal distances and interfered to generate the hologram. At least three holograms with different phase-shifts between the two object waves were recorded and combined to synthesize a complex hologram. The different planes of the object were reconstructed by numerically propagating the complex hologram to one of the focal planes of the diffractive lenses. FINCH, in general, has a higher lateral resolution but lower axial and temporal resolutions than direct imaging. A new approach inspired by guide-star holography techniques is applied to FINCH. In this study, two diffractive lens functions with different focal lengths have been spatially multiplexed into one using a binary quasi-random function and fabricated using electron beam lithography. In the first step, the point spread hologram library was recorded by axially scanning a point object along the optical axis. In the next step, an object hologram was recorded. The three-dimensional image of the object was reconstructed using a cross-correlation between the point spread hologram library and the object hologram. The modified approach increased the time resolution of FINCH by three times, improved the axial resolving power and enabled the development of the most compact version of FINCH. We believe that FINCH can be applied for monitoring bacterial cell shape during contact with mechanically biocidal nanotextured surface and light matter interactions.

Metasurfaces of gold (Au) nanoparticles on a SiO2-Si substrate were fabricated for the enhancement of second harmonic generation (SHG) using electron beam lithography and lift-off. Triangular Au nanoprisms which are non-centro-symmetric and support second-order nonlinearity were examined for SHG. The thickness of the SiO2 spacer is shown to be an effective parameter to tune for maximising SHG. Electrical field enhancement at the fundamental wavelength was shown to define the SHG intensity. Numerical modeling of light enhancement was verified by experimental measurements of SHG and reflectivity spectra at the normal incidence. At the plasmonic resonance, SHG is enhanced up to &sim, 3.5 &times, 103 times for the optimised conditions.

The thermal properties of novel nanomaterials play a significant role in determining the performance of the material in technological applications. Herein, direct measurement of the temperature diffusivity of cellulose nanocomposite films was carried out by the micro-contact method. Polymer films containing up to 2%wt. of nanocellulose were synthesised by a simple chemical process. Films of a high optical transmittance T ≈ 80 % (for a 200- μ m-thick film), which were up to 44% crystalline, were characterised. Two different modalities of temperature diffusivity based on: 1) a resistance change and 2) micro-thermocouple detected modulation of a heat wave, were used for the polymer films with cross-sections of ∼ 100 μ m thickness. Twice different in-plane α ‖ and out-of-plane α ⊥ temperature diffusivities were directly determined with high fidelity: α ‖ = 2 . 12 × 10 − 7 m 2 /s and α ⊥ = 1 . 13 × 10 − 7 m 2 /s. An amorphous polyethylene terephthalate (PET) fiber was measured for comparison α ‖ = 1 . 15 × 10 − 7 m 2 /s. This work provides an example of a direct contact measurement of thermal properties of nanocellulose composite films. The thermal diffusivity, which is usually high in strongly interconnected networks and crystals, was investigated for the first time in this composite.

The thermal properties of novel nanomaterials play a significant role in determining the performance of the material in technological applications. Herein, direct measurement of the temperature diffusivity of nanocellulose-doped starch&ndash, polyurethane nanocomposite films was carried out by the micro-contact method. Polymer films containing up to 2 wt%. of nanocellulose were synthesised by a simple chemical process and are biodegradable. Films of a high optical transmittance T&asymp, 80% (for a 200 &mu, m thick film), which were up to 44% crystalline, were characterised. Two different modalities of temperature diffusivity based on (1) a resistance change and (2) micro-thermocouple detected voltage modulation caused by the heat wave, were used for the polymer films with cross sections of &sim, 100 &mu, m thickness. Twice different in-plane &alpha, ‖ and out-of-plane &alpha, &perp, temperature diffusivities were directly determined with high fidelity: &alpha, ‖=2.12&times, 10&minus, 7 m2/s and &alpha, =1.13&times, 7 m2/s. This work provides an example of a direct contact measurement of thermal properties of nanocellulose composite biodegradable polymer films. The thermal diffusivity, which is usually high in strongly interconnected networks and crystals, was investigated for the first time in this polymer nanocomposite.

We demonstrate a concept and fabrication of lithography-free layered metal-SiO2 thin-film structures which have reduced reflectivity (black appearance), to as low as 0.9%, with 4.9% broadband reflectance (8.9% for soda lime) in the 500&ndash, 1400 nm range. The multi-layered (four layers) thin-film metamaterial is designed so that optical impedance matching produces minimal reflectance and transmittance within the visible and infra-red (IR) spectral region for a range of incident angles. The structure has enhanced absorbance and is easily tuned for reduced minimal transmission and reflection. This approach should allow for novel anti-reflection surfaces by impedance matching to be realized.

Capabilities of the attenuated total reflection (ATR) at THz wavelengths for increased sub-surface depth characterisation of (bio-)materials are presented. The penetration depth of a THz evanescent wave in biological samples is dependent on the wavelength and temperature and can reach 0.1–0.5 mm depth, due to the strong refractive index change ∼0.4 of the ice-water transition; this is quite significant and important when studying biological samples. Technical challenges are discussed when using ATR for uneven, heterogeneous, high refractive index samples with the possibility of frustrated total internal reflection (a breakdown of the ATR reflection mode into transmission mode). Local field enhancements at the interface are discussed with numerical/analytical examples. Maxwell’s scaling is used to model the behaviour of absorber–scatterer inside the materials at the interface with the ATR prism for realistic complex refractive indices of bio-materials. The modality of ATR with a polarisation analysis is proposed, and its principle is illustrated, opening an invitation for its experimental validation. The sensitivity of the polarised ATR mode to the refractive index between the sample and ATR prism is numerically modelled and experimentally verified for background (air) spectra. The design principles of polarisation active optical elements and spectral filters are outlined. The results and proposed concepts are based on experimental conditions at the THz beamline of the Australian Synchrotron.

Light harvesting using photonic crystal (PhC) surface patterns provides an opportunity to surpass the ray-optics defined light trapping and to approach thermodynamic ShockleyQueisser limit of solar cell efficiency, which for a single junction Si solar cell is ~ 32%. For an industry amenable nano-patterning of Si solar cells, we used laser direct write and stepper lithography based approaches for defining a large area (1 cm2) light trapping PhC patterns on silicon. Nanoholes of ~ 500 nm in diameter were fabricated by direct laser writing in a thin layer of chromium to act as a mask for subsequent reactive plasma etching to fabricate the nanostructures forming a PhC surface over a square centimeter. Surface area fabrication throughput was improved by more than order of magnitude as compared with electron beam lithography required to achieve sub-1 μm resolution.

We describe the optical and electrical analysis of a micro-explosion of silicon and micro-thermite micro-bridges with a spectral temporal resolution within a 2 ms time range. The intensity of peaks and their mean lifetimes are calculated to identify the contributing atomic and molecular species. Singly ionised atoms and molecules were the main contributor to spectroscopic signature of emission. It is shown that micro-bridges can be used to characterise small (safe) &lt, 10 mg amounts of energetic materials. Use of ions at low ionisation numbers of Si as well as Cu-oxides with different metal-to-oxygen ratios allows the thermal conditions for micro-explosions and a higher temperature of the discharge plasma to be engineered. Temperatures of 5000&nbsp, ±&nbsp, 500 K (the black-body radiation fit) were achieved with simple micro-bridge junctions of 10–30 Ω resistance initiated with 100–250 V (triggered capacitor discharge). The demonstrated approach can be applied in material science research concerning ultra-fast melting, phase transitions, and detailed steps leading towards detonation (exponentially growing exothermic chemical reactions).

Neodymium-doped iron oxide (Nd–Fe2O3) nanoparticles (NPs), synthesized via chemical co-precipitation method where particle size is reduced due to the neodymium doping. The addition of neodymium doping, the applied thermal energy of Fe2O3 changes the dielectric constant and loss. At this juncture, the dielectric constant increases due to the elevation of neodymium concentration and thermal energy which eventually reduces the dielectric value. On comparison of dielectric performance, the pristine Fe2O3 endows a high dielectric constant and loss in comparison to Nd–Fe2O3. Neodymium induces the transition from antiferromagnetic to superparamagnetic. The as-fabricated sensors confirm humidity sensing at different ranges. Fascinatingly, the sensitivity of the sensor has increased owing to the increase of neodymium substitution and decrease of particle size while the response time is decreased. The sensors confirm outstanding performance in corrosive environment and their response and sensitivity time values are respectively 5s and 85%.

Fresnel incoherent correlation holography (FINCH) is a self-interference based super-resolution three-dimensional imaging technique. FINCH in inline configuration requires an active phase modulator and at least three camera shots to reconstruct objects without the twin image and bias terms. In this study, FINCH is realized using a randomly multiplexed bifocal binary Fresnel zone lenses fabricated using electron beam lithography. A modified hologram reconstruction mechanism is presented which introduces the single shot capability in FINCH. A point spread hologram library was recorded using a point object located at different axial locations and an object hologram was recorded. The image of the object at different planes were reconstructed using decorrelation of the object hologram by the point spread hologram library. Application potential including bio-medical optics is discussed., Comment: 25 pages, 13 figures

Fast fabrication of micro-optical elements for generation of optical vortex beams based on the q-plate design is demonstrated by femtosecond (fs) laser ablation of gold film on glass. Q-plates with diameter of ~0.5 mm were made in ~1 min using galvanometric scanners with writing speed of 5 mm/s. Period of gratings of 0.8 micrometers and groove width of 250 nm were achieved using fs-laser ablation at 343 nm wavelength. Phase and intensity analysis of optical vortex generators was carried out at 633 nm wavelength and confirmed the designed performance. Efficiency of spin-orbital conversion of the q-plates made by ablation of 50-nm-thick film of gold was ~3%. Such gratings can withstand thermal annealing up to 800C. They can be used as optical vortex generators using post-selection of polarisation., 6 figures (additional 3 in a supplement)

Nano-texturing of surface by self-organised ablation ripples as well as modifications of internal volume of materials, transparent at the wavelength of laser irradiation, is gaining interest due to simplicity of direct laser writing/printing. With ultra-short laser pulses (τp < 1 ps) a wider range of structuring morphologies is accessible, namely, sub-wavelength ripples. The surface wave formed on the plasma-dielectric (air or substrate) explains difference of the formed pattern. These corresponding front- and back-side (in respect to the incoming laser beam) modes of laser structuring accounts for the ripple formation inside transparent materials, where a skin-layer plasma is formed. Emerging applications of nano-textured surfaces for bio-medical field are discussed.

Primers are used to reliably initiate a secondary explosive in a wide range of industrial and defence applications. However, established primer technologies pose both direct and indirect risks to health and safety. This review analyses a new generation of primer materials and ignition control mechanisms that have been developed to address these risks in firearms. Electrically or optically initiated metal, oxide and semiconductor-based devices show promise as alternatives for heavy metal percussive primers. The prospects for wider use of low-cost, safe, reliable and non-toxic primers are discussed in view of these developments.