The properties of electrical steels and their coatings

Grain oriented steels containing 3 % silicon are widely used as stacks of thin laminations in transformers and other electrical devices. Phosphate coatings are applied to these laminations in order in insulate between the sheets and hold them under tension, reducing the electrical energy losses and making the transformers more efficient. This thesis explores the properties of aluminium and magnesium phosphate, two commonly used coating materials. Using model phosphate coatings it has been shown that an excess of phosphoric acid is required to cause the condensation reaction that produces the metaphosphate, thought to be the cause of the increased tension imparted on the steel. The addition of chromium oxide was found to prevent this transformation by reacting with the excess acid to form chromium pyrophosphate, which lead to a more stable coating which imparted a greater tension upon the steel substrate. XPS has been shown to be a useful technique for the characterisation of model phosphate coatings, however it cannot be used to quantitatively analyse the systems (unlike other phosphate systems) possibly due to the higher number of phases present within the samples

Rationalization of the X-ray photoelectron spectroscopy of aluminium phosphates synthesized from different precursors

The aim of this paper is to clarify the assignments of X-ray photoelectron spectra of aluminium phosphate materials prepared from the reaction of phosphoric acid with three different aluminium precursors [Al(OH)3, Al(NO3)3 and AlCl3] at different annealing temperatures. The materials prepared have been studied by X-ray photoelectron spectroscopy (XPS), powder X-ray diffraction (XRD), infrared spectroscopy and high-resolution solid-state 31P NMR spectroscopy. A progressive polymerization from orthophosphate to metaphosphates is observed by XRD, ATR-FTIR and solid state 31P NMR, and on this basis the oxygen states observed in the XP spectra at 532.3 eV and 533.7 eV are assigned to P–O–Al and P–O–P environments, respectively. The presence of cyclic polyphosphates at the surface of the samples is also evident

An Electroactive Oligo-EDOT Platform for Neural Tissue Engineering

The unique electrochemical properties of the conductive polymer poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) make it an attractive material for use in neural tissue engineering applications. However, inadequate mechanical properties, and difficulties in processing and lack of biodegradability have hindered progress in this field. Here, the functionality of PEDOT:PSS for neural tissue engineering is improved by incorporating 3,4-ethylenedioxythiophene (EDOT) oligomers, synthesized using a novel end-capping strategy, into block co-polymers. By exploiting end-functionalized oligoEDOT constructs as macroinitiators for the polymerization of poly(caprolactone), a block co-polymer is produced that is electroactive, processable, and bio-compatible. By combining these properties, electroactive fibrous mats are produced for neuronal culture via solution electrospinning and melt electrospinning writing. Importantly, it is also shown that neurite length and branching of neural stem cells can be enhanced on the materials under electrical stimulation, demonstrating the promise of these scaffolds for neural tissue engineering

Functionalizing DNA Origami by Triplex-Directed Site-Specific Photo- Crosslinking

Here we present a universal method to introduce functionality and improve the structural integrity of DNA origami in a one-pot reaction. Our strategy involves adding nucleotide sequences to adjacent staple strands so that, upon origami assembly, the add-on sequences form short hairpin duplexes targetable by psoralen-labelled triplex-forming oligonucleotides (pso-TFOs) bearing other functionality. Subsequent irradiation with UVA light generates psoralen adducts with one or both hairpin staples leading to site-specific attachment of the pso-TFO to the origami with >80% efficiency. Bis-adduct formation between strands in proximal hairpins further tethers the TFO to the structure and generates ‘super-staples’ that improve the structural integrity of the complex. We also show that crosslinking reduces the sensitivity of the functionalized origami to thermal denaturation and disassembly by T7 RNA polymerase. Our strategy is scalable and cost-effective as it works with existing DNA origami structures, does not require scaffold redesign, and can be achieved with just one psoralen- modified oligonucleotide. It is also non-damaging to the origami scaffold, as well as to introduced fluorescent functionalities

Functionalizing DNA Origami by Triplex-Directed Site-Specific Photo-Cross-Linking

Here, we present a cross-linking approach to covalently functionalize and stabilize DNA origami structures in a one-pot reaction. Our strategy involves adding nucleotide sequences to adjacent staple strands, so that, upon assembly of the origami structure, the extensions form short hairpin duplexes targetable by psoralen-labeled triplex-forming oligonucleotides bearing other functional groups (pso-TFOs). Subsequent irradiation with UVA light generates psoralen adducts with one or both hairpin staples leading to site-specific attachment of the pso-TFO (and attached group) to the origami with ca. 80% efficiency. Bis-adduct formation between strands in proximal hairpins further tethers the TFO to the structure and generates "superstaples" that improve the structural integrity of the functionalized complex. We show that directing cross-linking to regions outside of the origami core dramatically reduces sensitivity of the structures to thermal denaturation and disassembly by T7 RNA polymerase. We also show that the underlying duplex regions of the origami core are digested by DNase I and thus remain accessible to read-out by DNA-binding proteins. Our strategy is scalable and cost-effective, as it works with existing DNA origami structures, does not require scaffold redesign, and can be achieved with just one psoralen-modified oligonucleotide.</p

Thickness-Dependent Characterization of Chemically Exfoliated TiS₂ Nanosheets

Monolayer TiS₂ is the lightest member of the transition metal dichalcogenide family with promising applications in energy storage and conversion systems. The use of TiS₂ has been limited by the lack of rapid characterization of layer numbers via Raman spectroscopy and its easy oxidation in wet environment. Here, we demonstrate the layer-number-dependent Raman modes for TiS₂. 1T TiS₂ presents two characteristics of the Raman active modes, A_1g (out-of-plane) and E_g (in-plane). We identified a characteristic peak frequency shift of the E_g mode with the layer number and an unexplored Raman mode at 372 cm^–1 whose intensity changes relative to the A_1g mode with the thickness of the TiS₂ sheets. These two characteristic features of Raman spectra allow the determination of layer numbers between 1 and 5 in exfoliated TiS₂. Further, we develop a method to produce oxidation-resistant inks of micron-sized mono- and few-layered TiS₂ nanosheets at concentrations up to 1 mg/mL. These TiS₂ inks can be deposited to form thin films with controllable thickness and nanosheet density over square centimeter areas. This opens up pathways for a wider utilization of exfoliated TiS₂ toward a range of applications

Realization of ground state in artificial kagome spin ice via topological defect-driven magnetic writing

Arrays of non-interacting nanomagnets are widespread in data storage and processing. As current technologies approach fundamental limits on size and thermal stability, enhancing functionality through embracing the strong interactions present at high array densities becomes attractive. In this respect, artificial spin ices are geometrically frustrated magnetic metamaterials that offer vast untapped potential due to their unique microstate landscapes, with intriguing prospects in applications from reconfigurable logic to magnonic devices or hardware neural networks. However, progress in such systems is impeded by the inability to access more than a fraction of the total microstate space. Here, we demonstrate that topological defect-driven magnetic writing-a scanning probe technique-provides access to all of the possible microstates in artificial spin ices and related arrays of nanomagnets. We create previously elusive configurations such as the spin-crystal ground state of artificial kagome dipolar spin ices and high-energy, low-entropy 'monopole-chain' states that exhibit negative effective temperatures