14 articles · sorted by date
A material only a few dozen nanometres thick can change dramatically in less time than a blink. In this paper, graphene oxide was reduced by a single near-infrared laser pulse, but only after electron-beam irradiation had primed it first. Using a dynamic transmission electron microscope and time-resolved electron energy-loss spectroscopy, the team tracked oxygen leaving the film in real time and measured an oxygen diffusivity of 1.6 ± 0.4 × 10^-8 m2/s. That rate corresponds to 90% reduction of a 46-nm-thick film within 960 ns. The electron beam also changed how strongly graphene oxide absorbed near-infrared light, and simulations reproduced the heating cycle caused by the laser pulse. Electron microscopy and diffraction then showed local restoration of sp2 bonding, along with turbostatic disorder in the reduced material. The results point to a simple but powerful mechanism: electron-beam-created defects and vacancies make the material absorb the infrared pulse more efficiently and let oxygen move out normal to the layers faster.
In a quantum dot photocell, the same quantum trick can be a helper or a hindrance. That matters because photo-generated carriers have to move through the device efficiently if light is to become electricity. This paper studies a quantum dot photocell with two intermediate bands, where carriers can travel through different charge-transport channels. The authors find that increasing the transition rates does not produce one simple trend: the photoelectric conversion efficiency first rises, then falls, and then falls monotonically. They also show that quantum coherence generated by the upper transition rates increases conversion efficiency because the interference is robust. By contrast, quantum interference induced by the two lower-transition rates reduces conversion efficiency, because it shortens the population lifetime in the intermediate bands. The takeaway is sharply practical for this narrow device model: quantum interference is not automatically beneficial. In a quantum dot photocell with multiple intermediate bands, the effect depends on which transitions create the interference.
When a material is squeezed to the extreme pressures inside a diamond anvil cell, even its magnetism can change. Iron is the test case here. The team used an ensemble of nitrogen-vacancy (NV) centers—tiny defects in diamond that act as magnetic sensors—fabricated directly on the anvil surface to image iron’s stray magnetic field under pressure. That setup let them make precise magnetic measurements up to 30 GPa, a range where magnetometry has been hard to do. With those measurements, they observed iron’s α-ε transition, the magnetic change between two pressure-driven phases of the metal. The result shows that diamond quantum sensors can measure magnetic behavior in the same tiny, high-pressure space where the sample is being squeezed. That matters because diamond anvil cells can reach ultrahigh pressures, but the sample chamber is very small, so conventional probes struggle to fit and still work reliably.
A single laser spot may now reveal signals from regions tens of micrometers away, instead of only the exact place it hits. That matters for layered materials, where the signal from one interface can be buried under others. The paper reports direct observation of delocalized second-harmonic generation, a nonlinear optical process that turns two photons at one color into one photon at twice the frequency. On monocrystalline gold surfaces and structures, the team generated second-harmonic light up to 35 µm from the excitation spot, and even detected signal from atomically flat surfaces where no fundamental excitation beam was present in the same region. The authors trace the effect to two counter-propagating surface plasmon polaritons interacting with each other, a process they say has not been seen at this scale before. The emitted light kept the same polarization dependence as localized second-harmonic generation and came out as a collimated beam perpendicular to the sample surface. Because the signal was strong enough, the team captured it on a CMOS camera with 1 s exposure, no gain, and an industrial-grade pulsed laser. They say this could help probe wide-area multilayer samples with one excitation beam for energy, catalysis, and single-particle surface sensing.
If you want gallium nitride devices on cheap silicon wafers, the usual buffer layers have been the bottleneck. They block current and make vertical designs harder to use in practice. This paper reports a sputtering-based strategy that forms an in-situ silicide-based template only about 0.5 nanometers thick, then uses rapid thermal annealing to turn it into a base for high-quality GaN growth on Si(111). The approach worked across 25 different metallic species and produced GaN films with very low vertical resistance, ohmic behavior, and strong thermal stability. Scanning transmission electron microscopy showed a unique amorphous-like interlayer that absorbs lattice mismatch and relaxes epitaxial strain. The same template also served as a strong platform for MOCVD overgrowth, which matters because it links low-cost fabrication with device-grade vertical performance for power electronics and high-resolution micro-LEDs.
If you were hoping ultra-thin solar cells could squeeze extra power from wasted heat, this paper puts hard limits on that dream. The study looks at transition-metal dichalcogenides, a class of materials prized for strong light absorption and flexible device designs. It shows that carrier multiplication, where one energetic photon creates more than one electron, and hot-carrier extraction both pull from the same above-gap energy pool. That means carrier multiplication does not lift the reversible hot-carrier thermodynamic ceiling. The model folds in thickness-dependent absorptance, monolayer exciton effects, a carrier-multiplication quantum-yield limit of 0.97, and finite cooling leakage. For thick TMD absorbers under AM1.5G sunlight, the Shockley–Queisser optimum sits near a 1.3 eV band gap, while the carrier-multiplication and hot-carrier-friendly envelope shifts toward 1.0 eV and can exceed 50% reversible efficiency. But for monolayer WSe2 with a 1.63 eV gap, only about 3.7% of above-gap photons have enough energy for multiplication, so the ideal short-circuit-current gain is only about 0.6%. The takeaway is sharp: high-gap monolayer TMDs are poor one-sun carrier-multiplication candidates, while narrow-gap bulk-like TMDs only look promising if energy-selective extraction and suppressed cooling can be achieved together.
A high-capacity battery is useless if its anode cracks apart after repeated charging. This paper tackles that problem in germanium, a promising next-generation anode material, by adding trace amounts of different metals. The standout result came from large atoms, especially ytterbium: the germanium anode kept its initial capacity and lasted about three times longer in cycling tests when doped appropriately. The reason was not that the material became stronger. It became softer. Structural and electrochemical tests showed that this mechanical softening reduced lithiation damage, including cracking and delamination as lithium moved in and out of the film. Nanoindentation measurements backed that up: larger dopant atoms were linked to lower film hardness. The trade-off was real. Ytterbium doping reduced rate capability at high C-rates, meaning fast charging performance suffered. Even so, the work points to a new design rule for alloy anodes: instead of only trying to suppress volume change, engineers may need to tune mechanical compliance at the atomic scale.
Imagine steering microwave signals inside a chip without converting them into electric charge. This paper shows that spin waves — tiny ripples of magnetization — can be chained into programmable circuits instead of staying as isolated parts. The team used a single-step direct laser writing process in yttrium iron garnet to build waveguides, coupled waveguides, and phase shifters on the same platform. With magneto-optical Kerr effect microscopy, they saw spin waves travel with preserved phase coherence for hundreds of wavelengths. In coupled waveguides, power moved back and forth completely and periodically over several coupling lengths, and the phase shifters produced arbitrary, tunable phase delays. By combining these building blocks, they made programmable splitters, frequency demultiplexers, and phase-controlled 2x2 routers, where output power and relative phase could be set on demand with external fields. They then extended this into interferometric meshes with up to six inputs and outputs and seven cascaded stages, without intermediate amplification. The result is a path toward larger magnonic circuits for classical and quantum processing.
A tiny squeeze can rewrite how a crystal’s internal regions line up, which matters for devices that rely on strain and domain walls. In single-crystal LaAlO3, the team showed that in-situ uniaxial strain continuously and reversibly changes the ferroelastic domain structure, where ferroelastic domains are regions that settle into different strain-related shapes. Using atomic force microscopy, X-ray diffraction, Raman spectroscopy, and first-principles calculations, they tracked the twin domain population as the crystal moved from its rhombohedral R3c ground state toward the predicted orthorhombic Fmmm phase. Strains below 0.5% caused pronounced surface flattening and large-scale domain reorganisation. The result makes uniaxial strain a practical control knob for engineering domain patterns in LaAlO3. The paper says that could enable active, real-time programming of LaAlO3-based heterostructures, with implications for strain-tunable superconducting interfaces, nanoscale phonon-polariton optics, and ultrafast lattice control.
Blood and other body fluids can hide weak biomarker signals the way salt blurs a tiny charge in a crowded room. This paper shows a way to coax those signals back out using silicon nanowire field-effect transistors and radiofrequency fields. The radio waves create strain gradients in the nanowires, which generate flexoelectric polarization and become stronger at resonant frequencies. In tests with C-reactive protein, the sensor produced a 62% conductance increase with radiofrequency modulation, compared with 30% without it — about an order-of-magnitude improvement in detection sensitivity. The high-frequency field also disturbed the electrical double layer, which helped reduce Debye screening in high-ionic-strength conditions. That mattered because it allowed direct biomarker detection without diluting the sample first. The paper argues that flexoelectric resonance could be a general strategy for improving nanoscale biosensing in physiologically relevant fluids.
A tiny superconducting switch can now do more than one job, and it can change roles without extra hardware. That matters because cryogenic computers need logic parts that are fast, compact, and easy to wire together. The paper presents a dual-input multilayered heater nanocryotron, or hTron, that adds two-input operation and reconfigurable logic in a single device. The device can switch between logic operations dynamically, instead of relying on separate components for each function. The authors also show that these devices can, in principle, drive one another, which points toward larger integrated circuits. Because the same hardware can be reused for different logic tasks, the design reduces circuit area and simplifies cryogenic and biasing requirements. The result is a practical step toward scalable superconducting computing systems. Superconducting electronics already offer ultralow-loss operation at cryogenic temperatures, and this work pushes that platform toward more flexible on-chip computation and signal handling.
If you want to move single electrons with the precision quantum devices need, you need a tiny traveling conveyor belt. Surface acoustic waves, or SAWs, provide that moving electrical potential, and this paper shows they can run on LaAlO3/SrTiO3 at room temperature. The team observed SAW modes up to 2.2 GHz with very low propagation loss, about 10^-3 dB per wavelength. To see the wave forms directly, they used atomic acoustic force microscopy and achieved sub-micron resolution imaging. Their measurements point to a shear horizontal-type mode, which can couple to in-plane degrees of freedom. That matters because the LAO/STO interface hosts a gate-tunable superconducting two-dimensional electron gas that can be programmed into devices such as ballistic electron waveguides and quantum dots. The work also sheds light on how SAWs are generated in strontium titanate, a widely used and commercially available substrate, and suggests a route for coupling SAWs to materials grown or transferred onto it.
If you try to judge depth from two viewpoints, tiny measurement losses can blur the result fast. This paper tackles that problem in passive triangulation, where a point source is located from angular disparity between two laterally spaced detectors. The key idea is simple: keep the analog signal alive longer and reject common-mode noise instead of throwing away information in the measurement pipeline. The authors also review the Cramér-Rao bound, a standard limit on how precisely angle sensing can work, and build a monolithic camera/balanced detector system with a doubly layered analog voltage differential system. In experiments, they report nanometer-scale depth precision at a 1.42 meter standoff using only a 10 centimeter baseline. That is still about two orders of magnitude above the shot noise limit, but it is several orders of magnitude better than current camera-only or other position-sensitive detector systems. The result shows that careful system design can push triangulation much closer to its fundamental limit, with even more improvement possible through vibration and turbulence mitigation.
What if one of the world’s biggest particle colliders could also act like a giant atomic trap and beam factory? That is the idea behind CERN’s Gamma Factory proposal. It would store highly relativistic partially stripped ions in the LHC, then use laser photons to excite their internal states. In this scheme, laser light stored in Fabry–Perot cavities interacts with the circulating ions to produce high-energy, highly collimated, and polarised secondary gamma-ray beams. The paper says these beams could be far stronger than today’s gamma-ray sources, by several orders of magnitude. Those photons could then help generate tertiary beams of polarised electrons, positrons, muons, neutrons, radioactive ions, and flavour- or CP-tagged neutrinos. The authors argue that this could turn existing CERN infrastructure and state-of-the-art lasers into a cost-effective bridge between the HL-LHC era and the future FCC era.
