Connectivity in metallic nanowire networks with resistive junctions is manipulated by applying an electric field to create materials with tunable electrical conductivity. In situ electron microscope and electrical measurements visualize the activation and evolution of connectivity within these networks. Modeling nanowire networks, having a distribution of junction breakdown voltages, reveals universal scaling behavior applicable to all network materials. We demonstrate how local connectivity within these networks can be programmed and discuss material and device applications.

Type of publicationArticle (peer-reviewed) Microscopy (TEM) cross-sectional analysis, which showed hemispeherical-shaped surface blisters that are amorphous in nature approximately 180-240 nm tall and 420-540 nm wide, after 5 months of air exposure, as well as surface deformation in regions between these structures, related to surface oxidation. An X-ray photoelectron spectroscopy (XPS) study of atmosphere exposed HfSe2 was conducted over various time scales which indicated the Hf undergoes preferential reaction with oxygen as compared to the Se. Energy-Dispersive XRay Spectroscopy (EDX) showed that the blisters are Se-rich, thus it is theorised that HfO2 forms when the HfSe2 reacts in ambient, which in turn causes the Se atoms to be aggregated at the surface in the form of blisters. Overall it is evident that air contact drastically affects the structural properties of TMD materials. This issue poses one of the biggest challenges for future TMD-based devices and technologies.2

A comprehensive nanoscale understanding of layered double hydroxide (LDH) thermal evolution is critical for their current and future applications as catalysts, flame retardants and oxygen evolution performers. In this report, we applied in situ transmission electron microscopy (TEM) to extensively characterise the thermal progressions of nickel-iron containing (Ni-Fe) LDH nanomaterials. The combinative approach of TEM and selected area electron diffraction (SAED) yielded both a morphological and crystallographic understanding of such processes. As the Ni-Fe LDH nanomaterials are heated in situ, an amorphization occurred at 250°C, followed by a transition to a heterogeneous structure of NiO particles embedded throughout a NiFe 2 O 4 matrix at 850°C, confirmed by highresolution TEM and scanning TEM. Further electron microscopy characterisation methodologies of energy-filtered TEM were utilised to directly observe these mechanistic behaviours in real time, showing an evolution and nucleation to an array of spherical NiO nanoparticles on the platelet surfaces. The versatility of this characterisation approach was verified by the analogous behaviours of Ni-Fe LDH materials heated ex situ as well as parallel in situ TEM and SAED comparisons to that of an akin magnesium-aluminium containing (Mg-Al) LDH structure. The in situ TEM work hereby discussed allows for a state-of-the-art understanding of the Ni-Fe material thermal evolution. This is an important first, which reveals pivotal information, especially when considering LDH applications as catalysts and flame retardants.

Electrical connectivity in networks of nanoscale junctions must be better understood if nanowire devices are to be scaled up from single wires to functional material systems. We show that the natural connectivity behaviour found in random nanowire networks presents a new paradigm for creating multifunctional, programmable materials. In devices made from networks of Ni/NiO core-shell nanowires at different length scales, we discover the emergence of distinct behavioural regimes when networks are electrically stressed. We show that a small network, with few nanowire-nanowire junctions, acts as a unipolar resistive switch, demonstrating very high ON/OFF current ratios (>10 5 ). However, large networks of nanowires distribute an applied bias across a large number of junctions, and thus respond not by switching but instead by evolving connectivity. We demonstrate that these emergent properties lead to fault-tolerant materials whose resistance may be tuned, and which are capable of adaptively reconfiguring under stress. By combining these two behavioural regimes, we demonstrate that the same nanowire network may be programmed to act both as a metallic interconnect, and a resistive switch device with high ON/OFF ratio. These results enable the fabrication of programmable, multi-functional materials from random nanowire networks.

In this article, we present a comprehensive investigation of the photothermal properties of plasmonic nanowire networks. We measure the local steady-state temperature increase, heat source density, and absorption in Ag, Au, and Ni metallic nanowire networks under optical illumination. This allows direct experimental confirmation of increased heat generation at the junction between two metallic nanowires and stacking-dependent absorption of polarized light. Due to thermal collective effects, the local temperature distribution in a network is shown to be completely delocalized on a micrometer scale, despite the nanoscale features in the heat source density. Comparison of the experimental temperature profile with numerical simulation allows an upper limit for the effective thermal conductivity of a Ag nanowire network to be established at 43 Wm(-1) K(-1) (0.1 κbulk).

ABSTRACT. Networks comprised of randomly oriented overlapping nanowires offer the possibility of simple fabrication on a variety of substrates, in contrast with the precise placement required for devices with single or aligned nanowires. Metal nanowires typically have a coating of surfactant or oxide that prevents aggregation, but also prevents electrical connection.Prohibitively high voltages can be required to electrically activate nanowire networks, and even after activation many nanowire junctions remain non-conducting. Non-electrical activation methods can enhance conductivity but destroy the memristive behavior of the junctions that

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Additive manufacturing is being increasingly used in the fabrication of Ti-6Al-4V parts to combine excellent mechanical properties and biocompatibility with high precision. Unfortunately, due to the build-up of thermal residual stresses and the formation of martensitic structure across a wide range of typical processing conditions, it is generally necessary to use a post-thermal treatment to achieve superior mechanical performance. This investigation aims to obtain a deeper understanding of the micro/nanostructural evolution (a 0 martensite phase decomposition), accounting for the kinetics of phase transformation during the heat treatment of 3D-printed Ti-6Al-4V alloy. As the mechanism of phase transformation and stress relaxation is still ambiguous, in this study the changes in crystal lattice, phase, composition and lattice strain were investigated up to 1000°C using both in situ high temperature X-ray diffraction (XRD) and transmission electron microscopy (TEM). Based on the result a mechanism of phase transformation is proposed, via the accommodation/substitution of Al, V and Ti atoms in the crystal lattice. The proposed mechanism is supported based on elemental concentration changes during heat treatment, in combination with changes in crystal structure observed using the high temperature XRD and TEM measurements. This study provides a deeper understanding on the mechanism of phase transformation through martensitic decomposition, as well as a deeper understanding of the influence of post-thermal treatment conditions on the alloy's crystal structure.