Activating deformation twinning in cubic boron nitride
Related Articles
Edge states with hidden topology in spinner lattices
Symmetries – whether explicit, latent, or hidden – are fundamental to understanding topological materials. This work introduces a prototypical spring-mass model that extends beyond established canonical models, revealing topological edge states with distinct profiles at opposite edges. These edge states originate from hidden symmetries that become apparent only in deformation coordinates, as opposed to the conventional displacement coordinates used for bulk-boundary correspondence. Our model, realized through the intricate connectivity of a spinner chain, demonstrates experimentally distinct edge states at opposite ends. By extending this framework to two dimensions, we explore the conditions required for such edge waves and their hidden symmetry in deformation coordinates. We also show that these edge states are robust against disorders that respect the hidden symmetry. This research paves the way for advanced material designs with tailored boundary conditions and edge state profiles, offering potential applications in fields such as photonics, acoustics, and mechanical metamaterials.
Boron nitride for applications in microelectronics
In this Perspective, we survey recent research on boron nitride (BN) including synthesis, integration and simulation aspects from the material engineering perspective for applications in microelectronics industry. First, we discuss the BN history and its process development milestones, with an emphasis on amorphous BN and hexagonal BN deposition process, highlighting the need for deep understanding of precursor and surface chemistry as well as integration issues. Next, we summarize recent material synthesis simulation progress for BN in the context of tackling complex amorphous material network formation mechanisms and discuss new methodology development needs to address current challenges. We propose future research directions towards the co-development between experimental and modelling approaches to further accelerate discovery of additional material property improvements. Finally, overall trends in microelectronic applications of BN and perspectives are presented and categorized into two main directions.
Resolving the fundamentals of the J-integral concept by multi-method in situ nanoscale stress-strain mapping
The integrity of structural materials is oftentimes defined by their resistance against catastrophic failure through dissipative plastic processes at the crack tip, commonly quantified by the J-integral concept. However, to date the experimental stress and strain fields necessary to quantify the J-integral associated with local crack propagation in its original integral form were inaccessible. Here, we present a multi-method nanoscale strain- and stress-mapping surrounding a growing crack tip in two identical miniaturized fracture specimens made from a nanocrystalline FeCrMnNiCo high-entropy alloy. The respective samples were tested in situ in a scanning electron microscope and a synchrotron X-ray nanodiffraction setup, with detailed analyzes of loading states during elastic loading, crack tip blunting and general yielding, corroborated by a detailed elastic-plastic finite element model. This complementary in situ methodology uniquely enabled a detailed quantification of the J-integral along different integration paths from experimental nanoscale stress and strain fields. We find that conventional linear-elastic and elastic-plastic models, typically used to interpret fracture phenomena, have limited applicability at micron to nanoscale distances from propagating cracks. This for the first time unravels a limit to the path-independence of the J-integral, which has significant implications in the development and assessment of modern damage-tolerant materials and microstructures.
Rapid rise in atmospheric CO2 marked the end of the Late Palaeozoic Ice Age
Atmospheric CO2 is thought to play a fundamental role in Earth’s climate regulation. Yet, for much of Earth’s geological past, atmospheric CO2 has been poorly constrained, hindering our understanding of transitions between cool and warm climates. Beginning ~370 million years ago in the Late Devonian and ending ~260 million years ago in the Permian, the Late Palaeozoic Ice Age was the last major glaciation preceding the current Late Cenozoic Ice Age and possibly the most intense glaciation witnessed by complex lifeforms. From the onset of the main phase of the Late Palaeozoic Ice Age in the mid-Mississippian ~330 million years ago, the Earth is thought to have sustained glacial conditions, with continental ice accumulating in high to mid-latitudes. Here we present an 80-million-year-long boron isotope record within a proxy framework for robust quantification of CO2. Our record reveals that the main phase of the Late Palaeozoic Ice Age glaciation was maintained by prolonged low CO2, unprecedented in Earth’s history. About 294 million years ago, atmospheric CO2 rose abruptly (4-fold), releasing the Earth from its penultimate ice age and transforming the Early Permian into a warmer world.
Improving the thermoelectric performance of scandium nitride thin films by implanting helium ions
Ion implantation is a widely used technique to introduce defects in low-dimensional materials and tune their properties. Here, we investigate the thermoelectric properties of scandium nitride thin films implanted with helium ions, revealing a positive impact of defect engineering on thermoelectric performance. Transport properties modeling and electron microscopy provide insights on the defect distribution in the films. The electrical resistivity and Seebeck coefficient increase significantly in absolute values after implantation and partially recover upon annealing as some of the implantation-induced defects heal. The thermal conductivity decreases by 46 % post- implantation due to the formation of extended defects and nanocavities. Consequently, the thermoelectric figure of merit zT doubles for the sample annealed at 673 K. These findings highlight the potential of controlled ion implantation to enhance thermoelectric properties in thin films, paving the way for further optimization through defect engineering.
Responses