Nanowerk July 26, 2023 The photosensitivity of silicon is inherently very low in the visible electromagnetic spectrum, and it drops rapidly beyond 800 nm in near-infrared wavelengths. Utilizing photon-trapping surface structures a team of researchers in the US (UC Davis, UC Santa Barbara, industry) demonstrated photoabsorption improvement in 1-μm-thin silicon, surpassing the inherent absorption efficiency of gallium arsenide for a broad spectrum. The photon-trapping structures allowed the bending of normally incident light by almost 90 deg to transform into laterally propagating modes along the silicon plane. The propagation length of light increased, contributing to more than one order of magnitude […]
Extraordinarily strong, lightweight material combines DNA and glass
Nanowerk July 25, 2023 Continuous nanolattices are an emerging class of mechanical metamaterials that are highly attractive due to their superior strength-to-weight ratios, which originate from their spatial architectures and nanoscale-sized elements possessing near-theoretical strength. Rational design of frameworks remains challenging below 50 nm because of limited methods to arrange small elements into complex architectures. A team of researchers in the US (Columbia University, Brookhaven National Laboratory, University of Connecticut) fabricated silica frameworks with ∼4- to 20-nm-thick elements using self-assembly and silica templating of DNA origami nanolattices and performed in situ micro-compression testing to examine the mechanical properties. They observed […]
Self-healing plastic becomes biodegradable
Science Daily July 27, 2023 Mineral plastics are a promising class of bio-inspired materials that have properties, like self-heal ability, stretchability, hardness, and non-flammability, they can be reshaped easily. However, current mineral plastics are hardly biodegradable, and thus persistent in nature. Researchers in Germany have developed the next generation of mineral plastics, which are bio-based and biodegradable. Physically cross-linked (poly)glutamic-acid (PGlu)-based mineral plastics using various alcohol-water mixtures, metal ion ratios and molecular weights. The rheological properties were easily adjusted using these parameters. The general procedure involved addition of equimolar solution of CaCl2 to PGlu in equal volumes followed by addition […]
Gloomy climate calculation: Scientists predict a collapse of the Atlantic Ocean current to happen mid-century
Science Daily July 25, 2023 The Atlantic meridional overturning circulation (AMOC) is a major tipping element in the climate system and its collapse would have severe impacts on climate in the North Atlantic region. In recent years weakening in circulation has been reported, but assessments by the Intergovernmental Panel on Climate Change (IPCC), based on the Climate Model Intercomparison Project (CMIP) model simulations suggest that a full collapse is unlikely within the 21st century. Tipping to an undesired state in the climate is a growing concern with increasing greenhouse gas concentrations. Predictions based on observations rely on detecting early-warning signals, […]
MIT engineers create an energy-storing supercapacitor from ancient materials
MIT News July 31, 2023 A team of researchers in the US (MIT, Harvard University) investigated using cement, water, and carbon black as chemical precursors for energy storage. Texture analysis revealed that the hydration reactions of cement in the presence of carbon generates a fractal-like electron-conducting carbon network that permeates the load-bearing cement-based matrix. The energy storage capacity of this space-filling carbon black network of the high specific surface area accessible to charge storage was shown to be an intensive quantity, whereas the high-rate capability of the carbon-cement electrodes exhibited self-similarity due to the hydration porosity available for charge transport. […]
‘Quantum avalanche’ explains how nonconductors turn into conductors
Phys.org July 24, 2023 The significant discrepancy observed between the predicted and experimental switching fields in correlated insulators under a DC electric field far-from-equilibrium necessitates a reevaluation of current microscopic understanding. An international team of researchers (USA – SUNY Buffalo, France, South Korea) has shown that an electron avalanche can occur in the bulk limit of such insulators at arbitrarily small electric field by introducing a generic model of electrons coupled to an inelastic medium of phonons. The quantum avalanche arose because of the generation of a ladder of in-gap states, created by a multi-phonon emission process. Hot-phonons in the […]
Research team takes neuromorphic computing a step forward
Phys.org July 24, 2023 Magnons undergo nonlinear multimode scattering processes at large input powers. In experiments and simulations, an international team of researchers (Germany, France) showed that the interaction between magnon modes of a confined magnetic vortex could be harnessed for pattern recognition. They studied the magnetic response to signals comprising sine wave pulses with frequencies corresponding to radial mode excitations. The amplitudes of three-magnon scattering results in the excitation of different azimuthal modes depended strongly on the input sequences. They showed that recognition rates as high as 99.4% could be attained for four-symbol sequences using the scattered modes, with […]
Researchers create class of tiny polarization structures called solitons
Phys.org July 26, 2023 Ferroelectric solitons represent a new class of materials with promise for beyond-CMOS technologies due to their ultrafine size and sensitivity to external stimuli. Such polarization textures have scarcely been demonstrated in multiferroics. Using a special arrangement an international team of researchers (Australia, USA – University of Arkansas) presented evidence of solitons in bismuth ferrite and strontium titanate superlattice. High-resolution scanning transmission electron microscopy revealed a zoo of topologies, and polarization displacement mapping of planar specimens revealed center-convergent/divergent topological defects as small as 3 nm. Phase-field simulations verified that some of these structures could be classed as bimerons […]
Scientists develop a broadband quantum-dot frequency-modulated comb laser
Phys.org July 27, 2023 The formation of a broadband optical frequency comb relies on careful engineering of the group velocity dispersion (GVD) of the waveguide, which is challenging for platforms where the GVD is mainly determined by the material. An international team of researchers (USA – UC Santa Barbara, Egypt) has generated a 60 GHz quantum-dot (QD) mode-locked laser in which both the amplitude-modulated (AM) and the frequency-modulated (FM) comb could be generated independently. The high four-wave-modulated (FWM) efficiency of –5 dB allowed the QD laser to generate FM comb efficiently. They demonstrated that the Kerr nonlinearity could be practically engineered to […]
Some alloys don’t change size when heated, and we now know why
Phys.org July 31, 2023 The low thermal expansion of Fe–Ni Invar has long been associated with magnetism, but to date, the microscopic underpinnings of the Invar behaviour have eluded both theory and experiment. An international team of researchers (USA – Caltech, Boston College, Argonne National Laboratory, Israel) applied thermodynamic Maxwell relation to nuclear resonant X-ray scattering measurements of the phonon and magnetic entropies under pressure to obtain the separate phonon and magnetic contributions to thermal expansion. They found that the Invar behaviour stems from a competition between phonons and spins. In particular, the phonon contribution to thermal expansion cancelled the […]