#thin films

Superconductivity switched on in material once thought only magnetic

Superconductivity—the ability of a material to conduct electricity without any energy loss to heat—enables highly efficient, ultra-fast electronics essential for advanced technologies such as magnetic resonance imaging (MRI) machines, particle accelerators and, potentially, quantum computers. New research has now revealed that iron telluride (FeTe), a compound composed of the chemical elements iron and tellurium and long thought to be an ordinary magnetic metal, is in fact a superconductor. The researchers found that hidden excess iron atoms induce the material's magnetism, and removing these atoms allows electricity to flow with zero resistance.

Fire Obsidian is an iridescent variety of obsidian from Glass Buttes, Oregon.

James Miller, a geologist in Redmond, Washington, is an avid “knapper,” meaning he chips stone to make tools, the very old-fashioned way. During a search for material, he came across some obsidian that shimmered colorfully in direct light. It didn’t look like striped rainbow obsidian, but instead hosted flame-like patterns in the glass. Wanting to know more, he sent a few samples to George Rossman and Chi Ma for their spectroscopic studies.

Under bright light, fire obsidian reflects brilliantly colored streaks resembling an iridescent oil slick. When thinned to a translucent blade, dark, wispy flames can be seen through the glass. Rossman suspected the layers of “fire” were made of tiny particles that increased the refractive index in the layer, giving rise to another manifestation of thin-film interference. “Out of curiosity, we said, ‘Well, let’s take a look at it and find out what it is,’” he recalls. At 100,000 times magnification, they found their answer—a wave of white, snowflake-like nanoparticles were suspended in the glass.   Electron back-scatter diffraction (EBSD) analyses revealed that these flakes were the mineral magnetite, an iron oxide.

--The Secret Lives of Minerals, Elizabeth Nadin

The black obsidian without thin layers from Glass Buttes contains evenly distributed inclusions of magnetite. The darker the black obsidian, the more numerous the magnetite crystals or the larger the crystals are in size. Where the magnetite inclusions concentrate to form thin layers of a submicrometric thickness, the “fire” coloration may appear. Measurements of the layer thickness and the estimated index of refraction indicate that some of the layers are of an appropriate thickness to cause thin-film interference. The layers have both a higher calculated index of refraction than the host obsidian and have a thickness slightly less than the wavelength of visible light. Such conditions are ideally suited to giving interference colors similar to those from a thin slick of oil on water.

Fabricating transparent ceramics: Four studies provide a glimpse into several different systems

Opacity is traditionally a hallmark characteristic of ceramics, as their polycrystalline structure prevents light from passing cleanly through. But starting in the mid-20th century, scientists discovered that when ceramics are specially processed to reduce pores and secondary phases, it is possible for ceramics to achieve high levels of light transmission—even achieving optical-grade levels of performance. The combination of optical clarity, durability, and heat resistance offered by transparent ceramics makes them a desirable material for various optical, energy, and defense applications. As such, the market is expected to experience rapid growth in the coming years and reach a value of nearly $2 billion by the end of 2030.

Laser beam flips a ferromagnet's polarity without heating the material

Researchers at the University of Basel and the ETH in Zurich have succeeded in changing the polarity of a special ferromagnet using a laser beam. In the future, this method could be used to create adaptable electronic circuits with light. In a ferromagnet, combined forces are at work. In order for a compass needle to point north or a fridge magnet to stick to the fridge door, countless electrons spin inside them, each of which only creates a tiny magnetic field, all need to line up in the same direction. This happens through interactions between the spins, which have to be stronger than the disordered thermal motion inside the ferromagnet. If the temperature of the material is below a critical value, it becomes ferromagnetic. Conversely, to change the polarity of a ferromagnet, one usually needs to first heat it up above its critical temperature. The electron spins can then reorient themselves, and after cooling down, the magnetic field of the ferromagnet eventually points in a different direction.

Chiral carbon nanotube films deliver giant light-conversion effect

A sheet of twisted carbon nanotubes has revealed a hidden talent scientists suspected for decades but had never managed to measure. Researchers at Rice University have created large, highly ordered films of chiral carbon nanotubes (CNTs), hollow cylinders of carbon atoms with either a left- or a right-handed twist. Measurements showed the crystalline films can convert the color of light at a rate two to three orders of magnitude greater than conventional materials. The findings, reported in ACS Nano, confirm a long-standing theoretical prediction and point toward a future in which ultrathin carbon nanotube films could help power faster optical communications, flexible photonic chips and light-based computing systems that today exist mostly as prototypes.

Cracking the secret of Kanazawa gold leaf's brilliant texture

Kanazawa gold leaf is a traditional Japanese material known for its remarkable thinness, just 100 nanometers—about 1/1,000 the diameter of a human hair—and its brilliant shine. Made using the entsuke technique, a manual process of packing and hammering at room temperature, this ultra-thin foil is commonly used to decorate temples, shrines, crafts, and historical objects. While the skill of Kanazawa artisans has gained global recognition, including UNESCO's designation as an Intangible Cultural Heritage in 2020, the scientific reason behind its unique thinness has remained unclear. Now, researchers from the Japan Advanced Institute of Science and Technology (JAIST), led by Professor Yoshifumi Oshima, in collaboration with Doctoral Course Student Yuanzhe Xu; Senior Lecturer Kohei Aso; Prof. Hideyuki Murata at JAIST, and Specially Appointed Professor Satoshi Ichikawa at the University of Osaka, have uncovered the deformation processes that give Kanazawa gold leaf its special qualities.