Electrons in graphene follow various spiraling paths when they flow around a circular barrier under the influence of a magnetic field.
Category: nanotechnology
Reshaping gold leads to new electronic and optical properties
By changing the physical structure of gold at the nanoscale, researchers can drastically change how the material interacts with light—and, as a result, its electronic and optical properties. This is shown by a study from Umeå University published in Nature Communications.
Gold plays a crucial role in modern advanced technology thanks to its unique properties. New research now demonstrates that changing the material’s physical structure—its morphology—can fundamentally enhance both its electronic behavior and its ability to interact with light.
“This might make it possible to improve the efficiency of chemical reactions such as those used in hydrogen production or carbon capture,” says Tlek Tapani, one of the leading researchers behind the study and doctoral student at the Department of Physics.
A New Probe of Nanoparticle Melting
Understanding nanoparticles is important in astrophysics and atmospheric physics and for applications like catalysts. These particles are tough to characterize, but now Vitaly Kresin of the University of Southern California and his colleagues have determined one elusive property with high accuracy. They inferred the melting point of sodium and potassium nanoparticles 7–9 nm in diameter with an accuracy of 1% [1]. They found that the melting point is about 100 K lower than in bulk samples, in agreement with less-precise data on other types of nanoparticles of this size and with theoretical predictions. The technique could potentially provide a new way to probe other properties of nanoparticles having a wide range of sizes.
Metal nanoparticles are known to melt at lower temperatures than bulk samples, but the theory needed to predict the melting point has significant uncertainties. Experiments also face various challenges, such as the tendency of electron microscopes to melt nanoparticles. Kresin and his colleagues suspected that the work function—the energy required to remove an electron from a surface or a nanoparticle—might show some notable changes when a nanoparticle melts, given the major structural rearrangements involved.
Their recently developed setup [2] uses a beam of temperature-controlled nanoparticles targeted by an adjustable-wavelength, monochromatic light source. When the photons eject electrons, the team detects the charged particles. For both sodium and potassium, the work function-versus-temperature data show a clear discontinuity and change in slope at the melting point.
How Hair Cells in the Ear Actively Respond to Sound
Tiny hair cells located in the inner ear help us hear and maintain balance. On top of each hair cell is a hair bundle, a sensory organelle that converts mechanical input from sound or movement into electrical output, which is then passed on to the brain. Previous research has shown that hair bundles aren’t simply passive entities. They actively oscillate to amplify weak audio signals or to tune into specific frequencies. Biologists have also observed bundles oscillating in the absence of stimuli. Models have tried to capture this bundle behavior, but the connection between active oscillation and the audio response has not been made clear. A new thermodynamic model of energy flow within hair bundles suggests that they work like tiny machines [1]. Depending on the stimulus, the bundles either extract power from incoming sound waves or inject power into them—corresponding, respectively, to sensing or amplifying a stimulus.
In the inner ear, an active process called cochlear amplification helps humans (and other mammals) hear the faintest of sounds. When a faint whisper enters the ear, for example, the outer rows of hair cells respond to the weak signal by moving in a way that amplifies the sound waves for the inner hair cells, which are the ones that send a message to the brain. Molecular motors propel the movement or twisting of hair bundles required for these functions.
Previous work has explored how much energy a hair cell consumes to drive bundle oscillations, but the resulting models have typically assumed that bundles are moving spontaneously—that is, in the absence of external stimuli. Roman Belousov from the European Molecular Biology Laboratory in Germany and his colleagues have developed a stochastic thermodynamic model that includes an energy input from sound waves. “Instead of just looking at how a hair bundle moves on its own, we wanted to add what happens when it interacts with sound,” Belousov says.
Chiral metasurfaces guide twisted light into free space
Light can carry angular momentum in two distinct ways. One comes from polarization, which describes how the electric field rotates. The other comes from the shape of the wavefront itself, which can twist like a corkscrew as it travels. This second form, known as orbital angular momentum, has attracted wide interest because it allows light to encode information, interact with matter in new ways, and probe physical and biological systems. Despite this promise, producing well-defined twisted light in free space remains technically challenging, especially when the light originates from small or localized sources.
Recent research reported in Advanced Photonics Nexus demonstrates a route to generating twisted light beams by combining a dielectric multilayer with a patterned metallic surface. The work shows that surface-bound light waves can be converted into free-space beams with controlled angular momentum and polarization. Importantly, the approach avoids several limitations of earlier designs and points toward future integration with single-photon emitters.
Many existing methods for generating orbital angular momentum rely on reshaping a laser beam using holograms, liquid-crystal plates, or patterned films known as metasurfaces. While effective for large, externally illuminated beams, these approaches struggle when light must be generated directly on a chip or from nanoscale emitters such as quantum dots or single molecules. Such sources cannot uniformly illuminate a structure or arrive at a precisely defined angle, making efficient beam shaping difficult.
Quantum researchers engineer extremely precise phonon lasers
When lasers were invented in the 1960s, they opened new avenues for scientific discovery and everyday applications, from scanners at the grocery store to corrective eye surgery. Conventional lasers control photons—individual particles of light—but over the past 20 years, scientists have invented lasers that control other fundamental particles, including phonons—individual particles of vibration or sound. Controlling phonons could open even more possibilities with lasers, such as taking advantage of unique quantum properties like entanglement.
A new squeezed phonon laser developed by researchers at the University of Rochester and Rochester Institute of Technology provides precise control over phonons at the nanoscale level. This could give new insights into the nature of gravity, particle acceleration, and quantum physics.
In a paper in Nature Communications, the researchers describe how they coax these individual particles of mechanical motion to behave like a laser.
Aerosol jet printing creates durable, low-power transistors for next-generation tech
Tiny electronic devices, called microelectronics, may one day be printed as easily as words on a page, thanks to new research from scientists at the U.S. Department of Energy’s (DOE) Argonne National Laboratory. Building on years of progress in printed electronics, the team has shown how to create durable, low-power electronic switches, called transistors, by combining custom inks and a specialized printing process.
These switches, which control the flow of electrical current to turn circuits on and off, use very little power, are built to last and show new behaviors not seen in earlier printed devices. This research could help create flexible sensors, smart windows and other new technologies that need reliable, energy-saving electronics. The work is published in Advanced Materials Technologies.
How aerosol jet printing works The scientists used a method called aerosol jet printing, which works like an inkjet printer. But instead of regular ink, it uses specially formulated ink made from nanoparticles. The printer turns the ink into a fine mist and sprays it onto a surface, building up layers to form electronic parts.
Fieldoscopy reveals femtosecond optical switching in 15 nm indium tin oxide nanocrystals
Just as an antenna interacts with radio waves, light interacts with metallic nanostructures. Therefore, understanding how a structure influences field oscillations provides valuable insights into the structure’s physical properties. An international research team, including scientists from the Max Planck Institute for the Science of Light (MPL), is investigating the changes in field oscillations that occur when light interacts with indium tin oxide (ITO) nanocrystals. This will deepen our understanding of how the interaction between light and these nanocrystals depends on time.
Precise and high-speed control of light is crucial to optical communication. It opens up the possibility to transmit data more quickly and efficiently in the future. Optical switches, which can activate or deactivate light pulses selectively, are a key component in achieving this.
To ensure optimal performance and prevent delays caused by switching times, the switches must respond very fast. Ideally, they also have the highest possible modulation depth. This refers to the difference in brightness between the light transmitted in the “on” and “off” states. Additionally, a suitable switch exhibits the same predictable behavior each time it is used.