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Nanoparticle superlattice films that form at the solid-liquid interface are important for mesoscale materials but are challenging to analyze on the onset of formation at a solid-liquid interface. In a new report on Science Advances, E. Cepeda-Perez and a research team in materials, physics and chemistry in Germany studied the early stages of nanoparticle assembly at solid-liquid interfaces using liquid-phase electron microscopy. They observed oleylamine-stabilized gold nanoparticles to spontaneously form thin layers on a silicon nitride membrane window of the liquid enclosure. In the first monolayer, the assembly maintained dense packings of hexagonal symmetry independent of the nonpolar solvent type. The second layer displayed geometries ranging from dense packing in a hexagonal honeycomb structure to quasi-crystalline particle arrangements—based on the dielectric constant of the liquid. The complex structures made of weaker interactions remained preserved, while the surface remained immersed in liquid. By fine-tuning the properties of materials involved in nanoparticle superlattice formation, Cepeda-Perez et al. controlled the three-dimensional (3D) geometry of a superlattice, including quasi-crystals (a new state of matter).

Nanoparticles that are densely packed into two or three dimensions can form regular arrays of nanoparticle superlattices. For example, semiconductor particle superlattices can act as “meta” semiconductors when doped with particles to form new mesoscale materials, while plasmonic particles in dense superlattices can couple to form collective modes with angle-dependent and tunable wavelength responses. Large electric fields can occur between such particles for surface-enhanced Raman spectroscopy. Superlattices can be developed at liquid-liquid, gas-liquid and solid-liquid interfaces, where static and dynamic interactions between particle-substrate, particle-particle and particle-liquid interactions can dictate the structure of superlattices. However, it remains difficult to predict such structures in advance. For example, simulating the assembly of superlattices at multiple stages is not yet possible, with very little in-lab real-space data available for modeling.

Just as a literature buff might explore a novel for recurring themes, physicists and mathematicians search for repeating structures present throughout nature.

For example, a certain geometrical structure of knots, which scientists call a Hopfion, manifests itself in unexpected corners of the universe, ranging from particle physics, to biology, to cosmology. Like the Fibonacci spiral and the golden ratio, the Hopfion pattern unites different scientific fields, and deeper understanding of its structure and influence will help scientists to develop transformative technologies.

Continue reading “Novel insight reveals topological tangle in unexpected corner of the universe” »

Scientific Reports volume 10, Article number: 2222 (2020) Cite this article.

Cesium atoms and laser traps offer a more robust type of quantum computer.

Acoustofluidics is the fusion of acoustics and fluid mechanics which provides a contact-free, rapid and effective manipulation of fluids and suspended particles. The applied acoustic wave can produce a non-zero time-averaged pressure field to exert an acoustic radiation force on particles suspended in a microfluidic channel. However, for particles below a critical size the viscous drag force dominates over the acoustic radiation forces due to the strong acoustic streaming resulting from the acoustic energy dissipation in the fluid. Thus, particle size acts as a key limiting factor in the use of acoustic fields for manipulation and sorting applications that would otherwise be useful in fields including sensing (plasmonic nanoparticles), biology (small bioparticle enrichment) and optics (micro-lenses).

Although acoustic nanoparticle manipulation has been demonstrated, terahertz (THz) or gigahertz (GHz) frequencies are usually required to create nanoscale wavelengths, in which the fabrication of very small feature sizes of SAW transducers is challenging. In addition, single nanoparticle positioning into discrete traps has not been demonstrated in nanoacoustic fields. Hence, there is a pressing need to develop a fast, precise and scalable method for individual nano- and submicron scale manipulation in acoustic fields using megahertz (MHz) frequencies.

An interdisciplinary research team led by Associate Professor Ye Ai from Singapore University of Technology and Design (SUTD) and Dr. David Collins from University of Melbourne, in collaboration with Professor Jongyoon Han from MIT and Associate Professor Hong Yee Low from SUTD, developed a novel acoustofluidic technology for massively multiplexed submicron particle trapping within nanocavities at the single-particle level.

Here’s a new chapter in the story of the miniaturization of machines: researchers in a laboratory in Singapore have shown that a single atom can function as either an engine or a fridge. Such a device could be engineered into future computers and fuel cells to control energy flows.” Think about how your computer or laptop has a lot of things inside it that heat up. Today you cool that with a fan that blows air. In nanomachines or quantum computers, small devices that do cooling could be something useful,” says Dario Poletti from the Singapore University of Technology and Design (SUTD).

This work gives new insight into the mechanics of such devices. The work is a collaboration involving researchers at the Centre for Quantum Technologies (CQT) and Department of Physics at the National University of Singapore (NUS), SUTD and at the University of Augsburg in Germany. The results were published in the peer-reviewed journal npj Quantum Information on 1 May.

Engines and refrigerators are both machines described by thermodynamics, a branch of science that tells us how energy moves within a system and how we can extract useful work. A classical engine turns energy into useful work. A refrigerator does work to transfer heat, reducing the local temperature. They are, in some sense, opposites.

A team of researchers from the University of Lille, CNRS, Centrale Lille, University of Artois, in France, and Keele University in the U.K has developed a way to produce ethane from methane using a photochemical looping strategy. In their paper published in the journal Nature Energy, the group describes their process. Fumiaki Amano with the University of Kitakyushu in Japan has published a News & Views piece on the work done by the team in the same journal issue.

Over the past several years, methane has become important for the production of fuels and other chemicals. But due to its stability, converting methane to desired products requires high temperatures and results in less-than-desired selectivity. Developing a way to carry out such conversions without the need for energy intensive heat production has been a goal of chemists in the field for several years. Prior research has suggested that methane coupling is an attractive option due to the ease with which it can be dehydrogenated to ethylene. In this new effort, the researchers followed up on such suggestions, and in so doing, have developed a way to produce ethane from methane that overcomes prior problems.

Amano suggests the success factor used by the researchers centered around the development of a three-part nanocomposite material—by adding phosphotungstic acid and silver cations to a traditional TiO₂ photocatalyst. The resulting Ag–HPW/TiO₂ nanocomposites induced methane coupling which resulted in the production of ethane—and also small amounts of propane and CO₂. The final result was a two-stage looping process that was based on photochemical conversions. Amano notes that the process resulted in silver cation reduction to a metallic, which was followed up by reoxidization of a metallic silver species using oxygen that was irradiated with ultraviolet light. He also points out that the HPW coating that was used on the particles was a major factor in improving selectivity, and suggests that the looping redox cycle is similar in some ways to the reactions that happen in rechargeable batteries.

Education Saturday with Space Time.

This episode of space time is brought to you by the information flowing through an impossibly complex network of quantum entanglement, that just happens to mutually agree that you and I exist inside it. Oh, and Schrodinger’s cat is in here too.

Continue reading “How Do Quantum States Manifest In The Classical World?” »

Magnesium dimer (Mg₂) is a fragile molecule consisting of two weakly interacting atoms held together by the laws of quantum mechanics. It has recently emerged as a potential probe for understanding fundamental phenomena at the intersection of chemistry and ultracold physics, but its use has been thwarted by a half-century-old enigma—five high-lying vibrational states that hold the key to understanding how the magnesium atoms interact but have eluded detection for 50 years.

The lowest fourteen Mg₂ vibrational states were discovered in the 1970s, but both early and recent experiments should have observed a total of nineteen states. Like a quantum cold case, experimental efforts to find the last five failed, and Mg₂ was almost forgotten. Until now.

Piotr Piecuch, Michigan State University Distinguished Professor and MSU Foundation Professor of chemistry, along with College of Natural Science Department of Chemistry graduate students Stephen H. Yuwono and Ilias Magoulas, developed new, computationally derived evidence that not only made a quantum leap in first-principles quantum chemistry, but finally solved the 50-year-old Mg₂ mystery.