Sputtered lead-free piezoelectric materials like potassium sodium niobate (K1-xNaxNbO3 or KNN) have received significant technological interest in recent years in light of several reports of piezoelectric constants comparable to lead zirconium titanate (PZT). Potential applications include self-powered sensors, actuators, and low acoustic impedance transducers. For large area printed applications, it is vital to develop low-temperature solution processed deposition methods. In this work, sol-gel synthesis of K-rich (70:30) KNN was carried out under an argon atmosphere, using acetate precursors, followed by precipitation of white KNN powder upon careful drying. Powder X-ray diffraction (XRD) scans of the product with a Cu Kα source after calcination revealed a dominant (110) peak, accompanied by smaller (100) and (010) peaks, in agreement with published standard KNN data. The composition of K-rich phase was confirmed using energy dispersive X-ray spectroscopy (EDX). To produce thin films, the sol was spin coated on a surface-treated Au-coated Si substrate, followed by slow annealing to obtain low surface roughness films (RMS roughness ﹤∼10 nm) of thickness ∼200 nm after solvent removal. Atomic force microscopy (AFM) scans revealed an unremarkable amorphous film. However, deposition of the sol on the Au-coated backside of Si wafer under similar processing conditions revealed limited polycrystalline film formation observed using optical profilometry. Thin film XRD measurements of the deposited film reveal orthorhombic phase growth of KNN, though the unannealed film was more amorphous than the calcined KNN film. Preliminary piezoresponse force microscopy (PFM) scans were used to estimate a piezoelectric constant (d33) ∼ 2.7 pC/N, consistent with the general expectation of lower piezoelectric constants for thin sol-gel films. The highest processing temperature used at any step during the deposition process was 90°C, consistent with the applications involving flexible polyimide substrates. This low-temperature thin-film growth suggests a potential route towards integration of large area piezoelectric generators for environmentally-friendly autonomous flexible sensor applications, with better control of phase and composition during the solution-phase deposition of KNN.

The structural integrity of nuclear fission and fusion power plant components is the focus of this research. The state of the art is using micro scale specimens milled with a focussed ion beam (FIB). Because of their very low volume such specimens can be lab tested, even when irradiated to low or medium level of activity. This offers a possibility of testing multiple specimens to investigate stochastic effects, e.g. effects of irradiation on the shift of the ductile to brittle transition. However, FIB milled specimens suffer from Ga contamination, to the degree that the validity of fracture data obtained on such specimens is questionable. We propose to use nano-additive manufacturing as an alternative to FIB for making micro scale fracture specimens. A combination of two-photon polymerization and electrodeposition and sputtering was used to manufacture micro-scale Brazilian disk fracture specimens (CBD), which are free from Ga and thus better suited for the study of irradiation effects on structural integrity. In this study Ni CBD specimens were made with 30 µm diameter and up to 13 µm thickness. The slot width varied between 1 µm to 2.9 µm width the corresponding slot length of between 7.5 µm and 8 µm. Consecutive FIB characterization shows that the specimens have polycrystalline microstructure with sub-µm grains. The work is ongoing making W CBD specimens and on reducing the slot width and using chemical vapor deposition fabrication.

With the rising interest in oceanic monitoring, climate awareness and surveillance, the scientific community need for developing autonomous, self-sustaining Unmanned Underwater Vehicles (UUVs) increased as well. Limitations on the size, maneuverability, power consumption, and available on-site maintenance of these UUVs make a number of proposed technologies to power them harder to implement than others; solar energy harvesting stands as one of the more promising candidates to address the need for a long-term energy supply for UUVs due to its relatively small size and ease of deployment. Studies show research groups focusing on the use of Si cells (amorphous and crystalline), InGaP, and more recently Organic Photovoltaics to convert the attenuated solar spectrum under shallow depths (no deeper than 9.1 m) into electrical energy used or stored by the UUV’s power management system (P. P. Jenkins et al. 2014; Walters et al. 2015). In our study, we consider the ternary compound In1-xTlxP that allows for varying the quantum efficiency of the cell, and by extension the overall harvesting efficiency of the system by altering the Tl content (x) in the compound. In1-xTlxP on InP is a low strain system since the compound exhibits very little change in its lattice constant with changing Tl content due to the comparable atomic size and forces of In and Tl allowing for relatively easy growth on InP substrates. The study focuses on studying the spectral response and comparing the performance of an optimized single junction In1-xTlxP cells to In1-yGayP cells while accounting for the optical losses of the solar irradiance underwater for various depths.

Magnesium (Mg) and its alloys have showed a promising potential for medical implant applications due to their attractive biocompatibility and mechanical strength. Despite these promising properties, the critical challenge with Mg-based implants is rapid degradation in physiological environment that results in early loss of mechanical strength and hydrogen gas accumulation at the local site. Hydroxyapatite (HA) coatings provide a sound solution for controlling Mg degradation at the bone interface. In this paper, HA coatings with different particle sizes, namely, microHA (mHA) and nanoHA (nHA), were deposited on Mg plates and rods with two different pressures using N2 Biomedical’s proprietary deposition process called IonTiteTM. Surface characterization of the deposited layers showed mHA coated Mg prepared at high pressure had more homogeneous HA particles distribution with less defects.

Bacterial cultures exposed to iron-doped apatite nanoparticles (IDANPs) prior to the introduction of antagonistic viruses experience up to 2.3 times the bacterial destruction observed in control cultures. Maximum antibacterial activity of these bacteria-specific viruses, or phage, occurs after bacterial cultures have been exposed to IDANPs for 1 hr prior to phage introduction, demonstrating that IDANP-assisted phage therapy would not be straight forward, but would instead require controlled time release of IDANPs and phage. These findings motivated the design of an electrospun nanofiber mesh treatment delivery system that allows burst release of IDANPs, followed by slow, consistent release of phage for treatment of topical bacterial infections. IDANPs resemble hydroxyapatite, a biocompatible mineral analogous to the inorganic constituent of mammalian bone, which has been approved by the Food and Drug Administration for many biomedical purposes. The composite nanofiber mesh was designed for IDANP-assisted phage therapy treatment of topical wounds and consists of a superficial, rapid release layer of polyethylene oxide (PEO) fibers doped with IDANPs, followed by inner, coaxial polycaprolactone / polyethylene glycol (PCL/PEG) blended polymer fiber layer for slower phage delivery. Our investigations have established that IDANP-doped PEO fibers are effective vehicles for dissemination of IDANPs for bacterial exposure and resultant increased bacterial death by phage. In this work, slower delivery of the phage behind IDANPs was accomplished using coaxial, electrospun fibers composed of PCL/PEG polymer blend.

Amorphous TiO2 and SnO2 electron transport layers (ETLs) were deposited by low-temperature atomic layer deposition (ALD). Surface morphology and x-ray photoelectron spectroscopy (XPS) indicate uniform and pinhole free coverage of these ALD hole blocking layers. Both mesoporous and planar perovskite solar cells were fabricated based on these thin films with aperture areas of 1.04 cm2 for TiO2 and 0.09 cm2 and 0.70 cm2 for SnO2. The resulting cell performance of 18.3 % power conversion efficiency (PCE) using planar SnO2 on 0.09 cm2 and 15.3 % PCE using mesoporous TiO2 on 1.04 cm2 active areas are discussed in conjunction with the significance of growth parameters and ETL composition.

Soiling in solar power generation will be a significant obstacle to its growth if a water free method cannot be found. Demand for water in arid regions will increase as more solar power generation is built, requiring more water to clean the optical surface, in turn increasing the price of water. This will lead to increased operating costs for solar power generation, and potentially disputes in locations where water is scarce. The electrodynamic screen (EDS) can reduce soiling and contribute to restoring the optical surface without the use of water. Periodic cleaning will still be required, but at reduced frequency, leading to a significant reduction in the consumption of water. In this model, it was found that a 250 MW concentrated solar power plant would have a 74% reduction in water given current laboratory production uncertainties. This indicates that EDS technology could decrease both the operating cost and the water use for solar generation plants.

Synthesis and characterization of cassava bark nanoparticles (CBNPs) was carried out using ball milling at 36, 48, 60 and 72 hours. The morphology study was done using SEM and the Gwyddion software was used to determine the particle sizes from the SEM images. The particle distribution for the un-milled cassava bark (CB) was between 1.25 + 0.06 to 19.92 + 1.00 µm, while after milling for 36, 48, 60 and 72 hours the average particle size were 4.07 + 0.20, 4.00 + 0.20 µm, 80.90 + 4.05, 74.50 + 3.73 nm respectively. 13.68 + 0.68 nm was obtained by XRD using Scherrer equation after milling for 72 hours and the XRD results revealed the presence of compounds such as SiO2, CaCO3 and KAlSi3O8. TEM was used to determine nanoparticle size distribution after milling for 72 hours and the particle size ranged from 9.73 + 0.49 to 114.60 + 5.73 nm for cassava bark nanoparticles (CBNPs), EDX results showed trace element of Si, Ca, K, Fe, Al, O in the CB milled for 72hours.

New routes in additive devices fabrication techniques and advances in printable materials are required to meet the ever increasing demands for low-cost and large-area flexible electronics. In particular, perovskite-based materials have gained an appeal due to their unique optoelectronics and ferroelectrics properties, which may replace p-n junction in semiconductor devices. Metal-organic methylammonium lead trihalide perovskite formulations have been extensively studied in the last few years as promising materials for use in printed electronics, which do not require high temperatures or vacuum environment, contrary to conventional semiconductor fabrication techniques. In this work, digital inkjet-printing in ambient atmosphere is proposed as a deposition pathway for the fabrication of perovskite active layers in photodetector and thin-film photovoltaic device architectures. The device architecture containing a printed perovskite active layer sandwiched between TiO2 and Spiro-OMeTAD as electron and hole transport layers, respectively, as well as layer-on-layer fabrication and responsivity spectra of the perovskite-based device are presented.

Materials science is arguably the most important discipline in the physical sciences that should be developed in Africa given its rich resources of minerals, energy and biological diversity. Developing materials science should therefore be an important goal for Africa with important opportunities for economic benefits and quality people development. There are already many successful materials science activities that are underway in Africa. This needs to gain wider international attention and should become contact points for international collaborations. The African School for Electronic Structure Methods and Applications (ASESMA)[1,2,3,4] is one such successful initiative that has been in existence for the past decade. ASESMA has shown that it is possible to build a network across sub-Saharan Africa with world-class research with a relatively low budget. The greatest asset is the commitment of the lecturers and mentors, the team-work of the local organisers and the idealism of the participants who rank amongst the brightest of young minds from Africa, many of whom come from impoverished backgrounds but still dare to reach for the stars.

Due to its excellent optical properties, gold nanomaterials with anisotropic morphology are playing an important role in biomedical applications, specifically in the use of Surface Enhanced Raman Spectroscopy (SERS) technique for biological assays. In this work, we verified the behavior of the star shape nanoparticle peaks obtained by chemical synthesis (precursor reactant: HAuCl4, cationic surfactant: CTAB) and whose peaks were formed from the different concentrations of gold seeds (55, 65, 75 and 85 ul) which were added to the total solution (5.275 ml). The shape and size of the nanoparticles was verified with a Hitachi S-5500 microscope with a BF & DF SEM / STEM detector, and for the diameter distribution (hydrodynamic) was carried out by the dynamic light distribution technique with a Malvern DLS system Zetasizer Nano ZS. Particle sizes (peak-to-peak considering) were obtained with variations from 107 to 166 nm. The results suggest adding 75 ul of gold seeds to obtain uniform nanostars with well defined peaks. These gold nano-stars could be applied for identification of specific membrane markers for the study of different types of cancer by the SERS technique.

Tungsten oxide based micro and nanostructures as well as their 2-D integrated counterparts with appropriate surface modifications such as sensitization, coating of other semiconductors or growth of functional groups have been examined to enhance supercapacitance and sensing capabilities. With the goal of investigation of these changes, the electrochemical capacitance behavior of newly prepared nano and micro-structured tungsten oxide coated substrates were examined. The utilization of WO3 based sensors to differentiate edible colorant and toxic pigments, was also explored. The systematic electrochemical analysis and comparative study of selected colorants was done in order to establish a roadmap to detect model organic compounds for better preventive action.

Application of lead-halide perovskite nanostructures for photovoltaic and light emitting applications depends on fashion of the surface termination. The reasonable choice of surface ligands for perovskite nanostructures prevent formation of trap states and contribute to chemical stability, wide opening of the bandgap, and intensity of absorption and photoluminescence of perovskite nanostructures. This work provides atomistic arguments for dual ligand protocol of surface passivation of fully inorganic perovskite quantum dots with fully organic ligands being a mix of cations (ethyl-ammonium) and anions (acetic) in nearly equal proportions. Computed binding energies of either individual ligands or anion-cation pairs demonstrate high stability in comparison to thermal energy and are concluded to be favourable choice in synthesis of colloidal perovskite quantum dots for light emitting applications.

Vanadium carbide has outstanding tribological behaviour, superior to other similar carbides in Groups IVB and VB, except TiC. Most research on vanadium carbide uses it as an additive to enhance wear performance, inhibit grain growth and decrease density, and it has also been used as a partial replacement for WC in WC-Co. This work is on alloys of VC-Ni to provide potential lighter and more corrosion-resistant materials, and VC-Ni alloys were made by this method for the first time, and evaluated. Three alloys of compositions VC-4Ni, VC-10Ni and VC-22.1Ni (at.%) were produced by spark plasma sintering (SPS). The mixed powders were sintered at different temperatures and pressures to optimize the sintered density and hardness of the alloys. The best alloy was VC-10Ni (at.%), which had the highest density and the highest hardness.

We investigate the insertion energetics of Ca at low concentrations in four promising vanadium oxide phases (α and δ vanadium pentoxide (V2O5) polymorphs as well as rutile- (R) and bronze-type (B) vanadium dioxide (VO2)) using density functional theory (DFT). We find α-V2O5 to be the most suitable material for an application as cathode, driven by a stable coordinative environment, while VO2(R) does not exhibit a stable low-concentration CaxVO2 phase due to severe distortions of the host lattice due to the large calcium ion. The results provide insight into the possibility of employing these phases as active cathode materials of Ca-ion batteries.

The search for new materials with low density and superior mechanical properties is a very intense and stimulating investigation area. These new materials could provide potential application for ballistic protection. Recent experiments and simulations revealed graphene possesses exceptional energy absorption properties. In this work, we analysed through fully atomistic molecular dynamics simulations the ballistic performance of a carbon-based material recently proposed named penta-graphene. Our results show that the fracture pattern is more spherical (no petals formation like observed for graphene). The estimated penetration energy for single-layer penta-graphene structures obtained here was d1penta ∼ 37.7 MJ/kg, and is comparable with recently results obtained for graphene: d1graphene ∼ 29.0 MJ/kg and d1graphene ∼ 40.8 MJ/kg under similar conditions. These preliminary results are suggestive that penta-graphene could be an excellent material for ballistic applications.

In battery systems, a solid electrolyte interphase (SEI) is formed through electrolyte reaction on an electrode surface. The formation of SEI can have both positive and negative effects on electrochemistry. The initial formation of the layer protects the electrode from further reactivity, which can improve both shelf and cycle life. However, if the layer continues to form, it can impede charge transfer, which increases cell resistance and limits cycle life. The role of SEI is particularly important when studying conversion electrodes, since phase transformations which unveil new electroactive surfaces during reduction/oxidation can facilitate electrolyte decomposition. This manuscript highlights recent developments in the understanding and control of SEI formation for magnetite (Fe3O4) conversion electrodes through electrolyte and electrode modification.

The Supercontainer (SC) is the reference concept for the post-conditioning of vitrified high-level nuclear waste and spent fuel in Belgium. It comprises a prefabricated concrete buffer that completely surrounds a carbon steel overpack. Welding is being considered as a final closure technique of the carbon steel overpack in order to ensure its water tightness. Welding is known to induce residual stresses near the weld zone, which may lead to an increased susceptibility to stress corrosion cracking (SCC). In this study, slow strain rate tests were conducted to study the SCC behavior of plain and welded P355 QL2 grade carbon steel exposed to an artificial concrete pore water solution that is representative of the SC concrete buffer environment. The tests were performed at 140°C, a constant strain rate of 5 × 10-7 s-1 and at open circuit potential under anoxic conditions. The effect of thiosulfate on the SCC behavior was investigated up to levels of 600 mg/L S2O32-.

Mechanical properties similar to natural bone and good biocompatibility make magnesium a great option for its use as biodegradable implant material. The use of castings as fabrication technique brings inherent problems, such as segregation and void formation. Also, the architecture of the specimens created by using these techniques is limited. This study shows the implementation of WAAM for the fabrication of elements made out of AZ91D magnesium alloy (9% aluminium and 1% zinc). The results demonstrate that porosity or cracking only appears at the surface of the individual printed lines, while the central sections presents a void-less structure composed by an HCP magnesium matrix and a high density of well dispersed aluminium-zinc rich precipitates. EDS mapping confirms the presence of orthorhombic Al5Mg11Zn4 phase. Also, the relationship between the heat present in the system and the morphology of the lines is analysed.

In this work, we report on fabrication of the thin-films of silicon oxide dielectric layers on silicon with back-side contact and utilization of the structure to study the detection of human Troponin antigen (cTnI) molecules: the cardiac biomarkers for the early diagnosis of acute myocardial infraction. Aptamers are selectively bound to the target molecules and can block the binding epitope for further reaction like immobilization or interaction to any other molecules. In contrast to antibodies, the aptamers are smaller in size, which allows target molecules to be brought closer to the surface of the biosensor and, therefore, to enhance the molecular signal. The target molecule in this work is cTnI, which is located in the cardiac muscle tissue. As a reliable indicator of heart failure and injury, it is specifically considered for the diagnosis of myocardial infarctions. The solutions of Troponin molecules were studied in different concentrations range from 10 pg/μL to 1 ng/μL. For the electrical detection of cTnI, we used the field-effect capacitive electrolyte-insulator-semiconductor (EIS) technique, which is a robust method for the quantitative characterization of molecular layers. The measured values of capacitances and flat band voltages were used to acquire information about the properties of the molecular layers obtained using solutions with different troponin concentrations. It was shown that this method demonstrates high sensitivity to target cardiac biomolecules and opens up new perspectives for highly selective and sensitive cardiac biosensors developed on the basis of silicon nanowire structures.