Perovskite solar cells continue to garner significant attention in the field of photovoltaics. As the optoelectronic properties of the absorbers become better understood, attention has turned to more deeply understanding the contribution of charge transport layers for efficient extraction of carriers. Titanium oxide is known to be an effective electron transport layer (ETL) in planar perovskite solar cells, but it is unlikely to result in the best device performance possible. To investigate the importance of band energy alignment between the electron transport layer and perovskite, we employ numerical modeling as a function of conduction band offset between these layers, interface recombination velocity, and ETL doping levels. Our simulations offer insight into the advantages of energy band alignment and allow us to determine a range of surface recombination velocities and ETL doping densities that will allow us to identify novel high performance ETL materials.

Nuclear fuel debris generated at the Fukushima Daiichi nuclear power plant during the loss of coolant accident in 2011, still resides within the reactor units, constantly cooled by water. Until it is retrieved, the fuel debris will corrode, releasing radioactive elements into the coolant water and the ground surrounding the reactors. To predict the corrosion behaviour of these materials, and to establish parameters for experiments with U-containing and real fuel debris, the corrosion of two surrogate fuel debris materials, with a composition of Ce(1-x)ZrxO2 (x = 0.2 and 0.4), was investigated. Materials were synthesised by a wet chemistry route and pellets were sintered at 1700°C in air atmosphere. Due to the slow corrosion kinetics, aggressive conditions were applied, and corrosion experiments were performed in 9 mol.L-1 HNO3 under static conditions. The incorporation of Zr into the structure of Ce reduced the normalised dissolution rate; from (3.75 ± 0.15) × 10-6 g.m-2.d-1 to (4.96 ± 0.28) × 10-6 g.m-2.d-1 for RL(Ce) of Ce0.8Zr0.2O2 and Ce0.6Zr0.4O2, respectively.

Bentonite is the most widely used foundry binder. Most of the iron castings are made in greensand systems which make use of bentonite as a binder. The bentonite used in greensand moulding is usually activated with sodium carbonate to achieve desirable properties. Activation of bentonite is known to improve mould related properties like giving a high wet tensile strength and improving the durability. The practice of activation is more common with calcium bentonite. A number of bentonite deposits tend to remain unbeneficiated due to their low cation exchange capacity (CEC) which are regarded as low quality commercial grade. The primary characteristic that shows the increased activation is the swelling index of the bentonite. This study investigated the influence of rehydration and activation in improving the quality of low commercial grade sodium bentonite. The bentonite samples were activated with sodium carbonate. Rehydration and activation was seen to improve the CEC and swelling index. The increase in CEC and swelling index was however not consistent with the gains in sodium.

We investigate, from first principles, the electrochemical sodiation mechanism of rutile-type vanadium dioxide as a possible electrode material for sodium-ion batteries. The computed voltages versus sodium metal are low in comparison to current state-of-the-art sodium-ion battery cathodes, which we can relate to the large space demand of sodium ions in the compact rutile structure and the resulting severe lattice deformations compared to other working metals. Due to the same reason large anisotropic unit cell volume changes are predicted during cycling. We furthermore find a change of the preferred reaction mechanism during discharge, with a switching between insertion- and conversion-type reaction at higher degrees of sodiation. The predicted capacities on the other hand are appreciable, making a further consideration of this material as high-potential anode in combination with sodium working metal interesting.

From the present study, vanadium additions up to 6.4% were added to a 14%Cr-3%C white iron, and the effect on the microstructure, hardness and abrasive wear were analysed. The experimental irons were melted in an open induction furnace and cast into sand moulds to obtain bars of 18, 25, and 37 mm thickness. The alloys were characterized by optical and electronic microscopy, and X-ray diffraction. Bulk hardness was measured in the as-cast conditions and after a destabilization heat treatment at 900°C for 45 min. Abrasive wear resistance tests were undertaken for the different irons according to the ASTM G65 standard in both as-cast and heat-treated conditions under a load of 60 N for 1500 m. The results show that, vanadium additions caused a decrease in the carbon content in the alloy and that some carbon is also consumed by forming primary vanadium carbides; thus, decreasing the eutectic M7C3 carbide volume fraction (CVF) from 30% for the base iron to 20% for the iron with 6.4%V;but overall CVF content (M7C3 + VC) is constant at 30%. Wear behaviour was better for the heat-treated alloys and mainly for the 6.4%V iron. Such a behaviour is discussed in terms of the CVF, the amount of vanadium carbides, the amount of martensite/austenite in matrix and the amount of secondary carbides precipitated during the destabilization heat treatment.

Bailey [1] proposed in 1972 that a nanoscale antenna coupled with a rectifier can harvest broad range electromagnetic radiation from visible to infrared. To incorporate this concept in practical systems, there were two main technological bottle necks that have to be overcome: antenna miniaturization and rectification in terahertz frequency. With current technology and equipment [2], we are proposing a third-generation rectenna-based solar cells composed of Ag nanocubes to harvest ambient visible and infrared electromagnetic waves coupled to ferrocene-based molecular diodes [3] capable of switching at terahertz frequency to convert this received energy into DC power. The function of these molecular diodes is two-fold: they rectify and provide an uniform nano-cavity between silver top electrode and gold bottom electrode. These nano-cavities are capable to support gap plasmon modes and absorption of light in both narrow and broad range, depending on the nanocube size and dispersion. A self-assembled monolayer (SAM) of ferrocene alkane-dithiol is deposited in this nano-cavity making it possible to form molecular sized nano-gaps well below the usual 3 nm, and this structure is robust and reproducible [4]. This SAM can be deposited directly or via a two-step click chemistry on the surface to have along with control over the orientation of the molecule. By tuning the orientation and position of the ferrocene moiety, the direction of rectification can be controlled [3]. Hence, the SAM does not only act as a rectifier but also provides mechanical support combining photonic and electrical properties. This paper focuses on studying the electrical and supramolecular structure of these molecular diode based SAMs.

The heterogeneous catalyst HTCMgFe was used in the degradation of the IC, through the heterogeneous photo-fenton treatment, this material in combination with H2O2 and UV light degraded the dye in 30 min at pH 3. As the amount of HTCMgFe increases the degradation it was accelerated because there are more active catalytic sites of Fe2+ on the surface of the material, which generates a greater amount of •OH radicals. The HTCMgFe was characterized by infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and X-ray energy dispersive elemental analysis (EDS). The UV-vis spectrum shows that the absorption bands belonging to the chromophore group of the IC disappear as the treatment time passes, indicating the degradation of the dye.

Silicon telluride (Si2Te3) is a silicon-based 2D chalcogenide with potential applications in optoelectronics. It has a unique crystal structure where Si atoms form Si-Si dimers to occupy the “metal” sites. In this paper, we report an ab initio computational study of its optical dielectric properties using the GW approximation and the Bethe-Salpeter equation (BSE). Strong in-plane optical anisotropy is discovered. The imaginary part of the dielectric constant in the direction parallel to the Si-Si dimers is found to be much lower than that perpendicular to the dimers. The optical measurement of the absorption spectra of 2D Si2Te3 nanoplates shows modulation of the absorption coefficient under 90-degree rotation, confirming the computational results. We show the optical anisotropy originates from the particular compositions of the wavefunctions in the valence and conduction bands. Because it is associated with the Si dimer orientation, the in-plane optical anisotropy can potentially be dynamically controlled by electrical field and strain, which may be useful for new device design. In addition, BSE calculations reduce GW quasiparticle band gap by 0.3 eV in bulk and 0.6 eV in monolayer, indicating a large excitonic effect in Si2Te3. Furthermore, including electron-hole interaction in bulk calculations significantly reduces the imaginary part of the dielectric constant in the out-of-plane direction, suggesting strong interlayer exciton effect in Si2Te3 multilayers.

Laser surface treatment is widely used as an engineering technique due to its special characteristics and several advantages over other surface modification techniques. In the present study, elemental mechanically pre-alloyed powder consisting of Niobium, Titanium and Nickel was deposited onto a grade 5 Titanium alloy substrates to form a high wear resistance coating. This was such that the surface mechanical properties of the base metal can be improved. The fabricated samples were characterised using optical microscopy, scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS), Differential Scanning Calorimeter (DSC), micro hardness tester and wear machine. The deposited coatings were well bonded and consisted of various phases. Hardness was seen decrease with increase in Nb content while wear resistance increasing with increase in niobium content.

The reliability of the plasma etched copper lines with the self-aligned copper oxide passivation layer has been studied with the electromigration stress method. The oxide passivation layer was prepared by plasma oxidation, which covers the entire exposed copper line to prevent the surface oxidation under the ambient condition. The void formation and growth process reflect the line broken mechanism. Voids formed from grain boundary depletion and grain thinning were monitored by optical microscopes. The line failure times with respect to line width and current density were measured. The addition of the oxide passivation layer shortened the lifetime due to the poor heat transfer and copper diffusion, which accelerated the formation and growth of the voids. The narrow line has a longer lifetime than the wide line because of the fewer grain boundaries for flux divergence to form voids. The copper oxide passivation layer was formed self-aligned to the copper line. It also gettered copper atoms diffused from the bulk copper film.

The present research was aimed to study the degradation of 2-Chlorophenol through the use of bismuth molybdate (γ-Bi2MoO6) structures supported on graphene oxide (GO) which is intended to control the recombination of charge carriers. γ-Bi2MoO6/GO systems were doped with nitrogen via chemical reaction, to reduce their energy gap, improving their photocatalytic activity. Structural and physicochemical characterization of the resulting catalysts were performed using X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and UV-Vis. The obtained compounds show good photo catalytic performance when using visible energy to degrade 2-Chlorophenol, obtaining 80% of degradation in 65 min.

A highly ordered cellulose nanocrystal (CNC) film was processed and characterized from a non-aqueous suspension. As a first step, by drawing upon the negative magnetic anisotropy of CNCs, a global order of the nanocrystals is achieved by magnetic field-assisted manipulation of a cholesteric suspension in n-methylformamide (NMF), and then the order is subsequently preserved into a solid-state film. We study the differences between the structures of the 4 T-dried film and the control film dried in the absence of magnetic field. Additionally, we compare the NMF-dried films to those dried from aqueous suspensions with and without magnetic field. Optical microscopy, cross-sectional imaging analysis, and sum frequency generation (SFG) spectroscopy show that the CNC-NMF film dried under magnetic field exhibited a highly ordered layered structure throughout the film, comparable to that observed when films were produced from aqueous suspensions. Extending the potential of the CNC alignment to non-aqueous systems will enable a broad spectrum of applications for CNC-based polymer composites.

Triply Periodic Minimal Surfaces (TPMS) possess locally minimized surface area under the constraint of periodic boundary conditions. Different families of surfaces were obtained with different topologies satisfying such conditions. Examples of such families include Primitive (P), Gyroid (G) and Diamond (D) surfaces. From a purely mathematical subject, TPMS have been recently found in materials science as optimal geometries for structural applications. Proposed by Mackay and Terrones in 1991, schwarzites are 3D crystalline porous carbon nanocrystals exhibiting a TPMS-like surface topology. Although their complex topology poses serious limitations on their synthesis with conventional nanoscale fabrication methods, such as Chemical Vapour Deposition (CVD), schwarzites can be fabricated by Additive Manufacturing (AM) techniques, such as 3D Printing. In this work, we used an optimized atomic model of a schwarzite structure from the D family (D8bal) to generate a surface mesh that was subsequently used for 3D-printing through Fused Deposition Modelling (FDM). This D schwarzite was 3D-printed with thermoplastic PolyLactic Acid (PLA) polymer filaments. Mechanical properties under uniaxial compression were investigated for both the atomic model and the 3D-printed one. Fully atomistic Molecular Dynamics (MD) simulations were also carried out to investigate the uniaxial compression behavior of the D8bal atomic model. Mechanical testings were performed on the 3D-printed schwarzite where the deformation mechanisms were found to be similar to those observed in MD simulations. These results are suggestive of a scale-independent mechanical behavior that is dominated by structural topology.

Dental pulp derived cells are pluripotent stem cells which can be differentiated along odontogenic, osteogenic, adipogenic, or neurogenic lineages. Odontogenic and osteogenic differentiation, in the absence of dexamethasone, have been shown to be highly dependent on substrate morphology and mechanics. Here we focus on neurogenic differentiation, using the protocol described by A. Arthur et al., and its dependence on substrate nature. DPSCs were cultured on PLA, a biodegradable polymer approved for internal use. The upregulation of genetic markers was compared with that of cells plated on standard TCP. The role of substrate morphology was investigated by plating on electrospun fibers approximately 2.0 ± 1.0 μm in diameter and on spin-cast thin films. The influence of graphene was investigated through the addition of 3% and 10% graphene nanoparticles to the films and fibers respectively.

The aspect ratio of the cells was measured using confocal microscopy. Cells grown on graphene containing substrates had larger aspect ratios than their non-graphene counterparts, and cells grown on microfibers were longer than their counterparts on the flat films. But the cell aspect ratio did not necessarily correlate with genetic differentiation. The results after 21 days of incubation indicated that early markers (TBP, β-III tubulin), decreased uniformly on all substrates relative to day 0, with the largest decrease occurring on the PLA flat film with graphene. The late stage marker, NEFM, which indicates differentiation, was upregulated to a significantly larger extent on all PLA substrates. No difference was observed between the fibers and the flat film in the absence of graphene, thus morphology did not play a significant role on this polymer. Addition of graphene did not affect the outcome on the fibers, but significantly suppressed the gene expression on the flat films. These results indicate that PLA is a promising scaffold material for neurogenic differentiation.

There is a need to introduce modern sand binder systems in the South African foundry industry as a means of improving its competiveness through the reduction of scrap castings and compliance to environmental regulations. According to the Industrial Policy Action Plan (IPAP). The foundry industry will play an important role with regards to the economic infrastructure priority advocated in the National Development Plan (NDP) of South Africa. In this study, a new generation water glass binder is introduced in a local foundry for production of cores for export plumbing casting production. The new water glass introduced is unique in that it contains an inorganic breakdown agent. The core making operating parameters including binder content, temperature and cycle time are optimised through core making trials without any alterations on the coremaking machines. Production data was evaluated using an optimization feature of Microsoft excel software. The results provided a set of optimum operating variables to manufacture 80-100% good quality sand cores for casting applications with an environmentally friendly binder. The most favourable binder content is above 2.60%.The most favourable operating temperature range is 160-174 0C. Therefore temperature and related energy costs can be reduced. The shortfall is reduction in cycle time.

The hexagonal boron nitride (h-BN) as a wide bandgap semiconductor is an attractive material for deep ultraviolet (DUV) generation. In this paper we study the prospect of using the stacking hexagonal boron nitride nanosheets (h-BNNS) for generating DUV emission by impact excitation in alternating current driven thin electroluminescence devices (ACTEL) based on BN phosphors having different morphologies. A theoretical approach considered is based on the impact excitation model for generating DUV from stacking h-BNNS under a high electric field. It was found that in the h-BNNS with a thickness of 90 nm biased at 3.33×109 V/m, the quantum yield can reach to 86.8%, and the power conversion efficiency of 1.68%. To achieve the same quantum yield and power conversion efficiency for the ACTEL based on h-BN single crystal, the active phosphor layer should be 2 μm thick when biased at 1.5×108 V/m.

Polyhydroxyalkanoates (PHAs) are degradable (co)polyesters synthesized by microorganisms with a variety of side-chains and co-monomer ratios. PHAs can be efficiently hydrolyzed under alkaline conditions and by PHA depolymerase enzymes, altering their physicochemical properties. Using 2D Langmuir monolayers as model system to study the degradation behavior of macromolecules, we aim to describe the the interdependency between the degradation of two PHAs and the surface potential, which influences material-proteins interaction and cell response. We hypothesize that the mechanism of hydrolysis of the labile ester bonds in (co)polyesters defines the evolution of the surface potential, owing to the rate of accumulation of charged insoluble degradation products. The alkaline hydrolysis and the enzymatically catalyzed hydrolysis of PHAs were previously defined as chain-end scission and random-scission mechanisms, respectively. In this study, these two distinct scenarios are used to validate our model. The surface potential change during the chain-end scission of poly(3-R-hydroxybutyrate) (PHB) under alkaline conditions was compared to that of the enzymatically catalyzed hydrolysis (random-scission) of poly[(3-R-hydroxyoctanoate)-co-(3-R-hydroxyhexanoate)] (PHOHHx), using the Langmuir monolayer technique. In the random-scission mechanism the dissolution of degradation products, measured as a decrease in the area per molecule, was preceded by a substantial change of the surface potential, provoked by the negative charge of the broken ester bonds accumulated in the air-water interface. In contrast, when chains degraded via the chain-ends, the surface potential changed in line with the dissolution of the material, presenting a kinetic dependent on the surface area of the monolayers. These results provide a basis for understanding PHAs degradation mechanism. Future research on (co)polymers with different main-chain lengths might extend the elucidation of the surface potential development of (co)polyesters as Langmuir monolayer.