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Category: materials – Page 152

Physicists observed a strange new type of behaviour in a magnetic material when it’s heated up. The magnetic spins ‘freeze’ into a static pattern when the temperature rises, a phenomenon that normally occurs when the temperature decreases. They publish their findings in Nature Physics on July 4th.

The researchers discovered the phenomenon in the material neodymium, an element that they described several years ago as a ‘self-induced spin glass’. Spin glasses are typically alloys where iron atoms for example are randomly mixed into a grid of copper atoms. Each iron atom behaves like a small magnet, or a spin. These randomly placed spins point in all kinds of directions.

Unlike conventional spin glasses, where there is random mixing of magnetic materials, neodymium is an element and without significant amounts of any other material, shows glassy behavior in its crystalline form. The spins form patterns that whirl like a helix, and this whirling is random and constantly changes.

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The future may see advancements in claytronics, memory metals, and catoms to allow shapeshifting materials that can take on any form and perform any job — possibly even taking on human form itself.

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Scientists have developed an efficient new way to convert methane into methanol at room temperature. The technique could help reduce greenhouse gas emissions and provide a cleaner way to make key products.

While carbon dioxide gets most of the attention, it’s not the only greenhouse gas changing the Earth’s climate. Methane is emitted in smaller amounts but is 34 times more potent, so reducing its levels remains a priority. Excess methane from industrial processes is often burned off, but that produces CO2.

A commonly sought alternative is to convert methane into methanol, which can be used to make a range of products like fuels, plastics and construction materials. The problem is, the conversion process usually requires high temperatures and pressures, which makes it energy-intensive.

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An international team of researchers, led by scientists at the University of Manchester, has developed a fast and economical method of converting methane, or natural gas, into liquid methanol at ambient temperature and pressure. The method takes place under continuous flow over a photo-catalytic material using visible light to drive the conversion.

To help observe how the process works and how selective it is, the researchers used neutron scattering at the VISION instrument at Oak Ridge National Laboratory’s Spallation Neutron Source.

The method involves a continuous flow of methane/oxygen-saturated water over a novel metal-organic framework (MOF) catalyst. The MOF is porous and contains different components that each have a role in absorbing light, transferring electrons and activating and bringing together methane and oxygen. The liquid methanol is easily extracted from the water. Such a process has commonly been considered “a holy grail of catalysis” and is an area of focus for research supported by the U.S. Department of Energy. Details of the team’s findings, titled “Direct photo-oxidation of methane to methanol over a mono-iron hydroxyl site,” are published in Nature Materials.

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The first logic gate to operate at femtosecond timescales could help usher in an era of information processing at petahertz frequencies – a million times faster than today’s gigahertz-scale computers. The new gate, developed by researchers at the University of Rochester in the US and the Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU) in Germany, is an application of lightwave electronics – essentially, shuffling electrons around with light fields – and harnesses both real and virtual charge carriers.

In lightwave electronics, scientists use laser light to guide the motion of electrons in matter, then exploit this control to create electronic circuit elements. “Since light oscillates so fast (roughly a few hundred million times per second), using light could speed up electronics by a factor of roughly 10 000 as compared to computer chips,” says Tobias Boolakee, a laser physicist in Peter Hommelhoff’s group at the FAU and the first author of a study in Nature on the new gate. “With our present work, we have been able propose the idea for a first light field-driven logic gate (the fundamental building block for any computer architecture) and also demonstrate its working principle experimentally.”

In the work, Boolakee and colleagues prepared tiny graphene-based wires connected to two gold electrodes and illuminated them with a laser pulse lasting a few tens of femtoseconds (10-15 s). This laser pulse excites, or sets in motion, the electrons in graphene and causes them to propagate in a particular direction – so generating a net electrical current.

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“Blinking” behavior of fluorophores, being harmful for the majority of super-resolved techniques, turns into a key property for stochastic optical fluctuation imaging and its modifications, allowing one to look at the fluorophores already used in conventional microscopy, such as graphene quantum dots, from a completely new perspective. Here we discuss fluorescence of aggregated ensembles of graphene quantum dots structured at submicron scale. We study temperature dependence and stochastic character of emission. We show that considered quantum dots ensembles demonstrate rather complicated temperature-dependent intermittent emission, that is, “blinking” with a tendency to shorten “blinking” times with the increase of temperature.

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