Tag: Science and Technology of Advanced Materials

Devices that can see shortwave infrared light, which is invisible to the naked eye, could soon become cheaper and more accessible to a broader consumer base.

Scientists in Europe have designed an organic dye-based device that can see light waves in the shortwave infrared (SWIR) range. The device is easy to make using cheap materials, and is stable at high temperatures.

The findings, published in the journal Science and Technology of Advanced Materials, could lead to more widespread use of inexpensive consumer SWIR imaging and sensing devices.

The human eye can only detect a very narrow segment of the electromagnetic spectrum, from around 400 to 700 nanometers. The SWIR region, on the other hand, extends from 1,000 to 2,500 nanometers. Specially designed cameras can take images of objects that reflect waves in the SWIR region. They are used for improving night vision, in airborne remote sensing, and deep tissue imaging. The cameras also help assess the composition and quality of silicon wafers, building structures and even food produce.

“These cameras are typically difficult to manufacture and are quite expensive, as they are made of inorganic semiconductor photodiode arrays interconnected with read-out integrated circuitry,” says Roland Hany of the Swiss Federal Laboratories for Materials Science and Technology.

Hany worked with colleagues in Switzerland and Italy to design an organic dye-based ‘SWIR upconversion device’ that efficiently converts shortwave infrared light to visible light.

The device uses organic (materials made with carbon) components: a squaraine dye-coated flexible substrate combined with a fluorescent organic light-emitting diode (OLED). When the dye absorbs SWIR waves, an electric current is generated and directly converted into a visible image by the OLED.

The team had to play with the molecular composition of several squaraine dyes to get them to absorb specific wavelengths. Ultimately, they synthesized squaraine dyes that absorb SWIR light beyond 1,200 nanometers and remained stable up to 200 degrees Celsius. The finished dye-based device performed stably for several weeks under normal laboratory conditions.

“All-organic upconverters could lead to applications that can’t be realized with current technology. For example, invisible night vision devices can be directly integrated into car windscreens without affecting the visual field,” explains Hany.

The team is now working on shifting the dye’s absorption further into the SWIR range. They are also using machine learning techniques to find new dye molecules capable of sensing SWIR waves. Finally, the team aims to improve device stability and sensitivity.

Further information
Roland Hany
Empa, Swiss Federal Laboratories for Materials Science and Technology
Email: roland.hany@empa.ch

About Science and Technology of Advanced Materials Journal
Open access journal STAM publishes outstanding research articles across all aspects of materials science, including functional and structural materials, theoretical analyses, and properties of materials.

Dr. Yoshikazu Shinohara
STAM Publishing Director
Email: SHINOHARA.Yoshikazu@nims.go.jp

Press release distributed by ResearchSEA for Science and Technology of Advanced Materials.

A review on the latest research of the various types of Heusler alloys summarizes the field’s main achievements up to 2020.

A study published in the journal Science and Technology of Advanced Materials summarizes the major achievements made to-date in Heusler alloy research. “Our review article can serve as an ideal reference for researchers in magnetic materials,” says Atsufumi Hirohata of the University of York, UK, who specializes in spintronics.

Spintronics, also known as spin electronics, is a field of applied physics that studies the use of electron spins, instead of their charge, to carry information in solid-state devices, with reduction in power consumption and improvements in memory and processing capabilities.

A category of materials showing great promise in this area is Heusler alloys: materials formed of one or two parts metal X, one part metal Y, and one part metal Z, each coming from a distinct part of the periodic table of elements. The interesting thing about these alloys is that individually, the metals are not magnetic, but when combined, they become magnetic.

A major advantage of Heusler alloys for spintronic devices is the ability to control their unique electrical and magnetic properties, which result directly from electron spins, by making changes to their crystalline structures. But this requires very high temperatures, which researchers want to reduce.

Over the last few decades, scientists have been working on approaches to grow Heusler alloy films at room temperature on special substrates with crystal lattices that are similar to the alloy’s. The interaction between the two lattices can lead to the development of half-metallicity in the Heusler alloy, where only electrons spinning in one orientation are conducted through the material whereas those spinning in another are not.

Researchers need to be able to measure the properties of materials in order to conduct their investigations. The atomic structure of Heusler alloys can be directly observed by X-ray diffraction and indirectly measured through examining the relationship between the material’s resistance to an electric current and temperature changes. Other techniques are also available for measuring their magnetic properties.

Hirohata and his colleagues are currently working on fabricating a metallic magnetic junction made of Heusler alloy films. These junctions are made from two ferromagnets separated by a thin insulator. When the insulating layer is thin enough, electrons are able to tunnel from one ferromagnet to the other. There is low resistance to electron movement as long as an external magnetic field is applied, but as soon as it is removed, the material becomes highly resistant to electron movement. “These devices are expected to replace currently used memory cells and magnetic sensors,” says Hirohata. The team hopes to develop metallic magnetic junctions with much larger magnetoresistance than the current record at room temperature, realising a next-generation memory for a sustainable society.

Research paper: https://www.tandfonline.com/doi/full/10.1080/14686996.2020.1812364

Further information
Atsufumi Hirohata
University of York
Email: atsufumi.hirohata@york.ac.uk

About Science and Technology of Advanced Materials Journal
Open access journal STAM publishes outstanding research articles across all aspects of materials science, including functional and structural materials, theoretical analyses, and properties of materials.

Chikashi Nishimura
STAM Publishing Director
Email: NISHIMURA.Chikashi@nims.go.jp

Press release distributed by ResearchSEA for Science and Technology of Advanced Materials.

Materials inspired by the colour changes in a peacock’s feather could lead to anti-counterfeit and sensing applications.

Melanin-like compounds can be precisely designed and arranged to colour materials using a mechanism similar to that found in a peacock’s feathers. Chemist Michinari Kohri of Chiba University in Japan reviewed the latest research on these ‘melanin-mimetic materials’ and their potential applications for the journal Science and Technology of Advanced Materials.

Melanin is a dark pigment that gives hair and skin its colour. It is also essential for the bright colours we see in some organisms. When light interacts with the structures of feathers, wings and shells of many organisms, like peacocks, butterflies and jewel beetles, it is scattered, appearing white. But when melanin is interspersed within these structures, some of the scattered light is absorbed, producing various colours. Scientists are looking for ways to mimic these so-called ‘structural colour’ changes of living organisms in synthetic materials.

“Vivid structural colours can be obtained by constructing microstructures containing a light-absorbing black material made of natural or artificial melanin,” says Kohri. “Research in this area is progressing rapidly worldwide.”

A leading contender is a compound called polydopamine. It is made of a material naturally found in the body, so it is biocompatible. It is also dark, so it absorbs light like melanin. Scientists found they could control polydopamine’s iridescence – how much the colour changes as the angle of light hitting it shifts, similar to a peacock’s feather. They achieved this by altering the particle size or by adding compounds that react to a magnetic field.

Scientists are also investigating particles formed of a polystyrene core and a polydopamine shell. Changing the diameter of the inner core, for example, leads to different colours. Making the polydopamine shell thicker causes the particles to be less closely packed, leading to non-iridescent structural colour, which remains the same regardless of the light angle.

Scientists have also toyed with controlling colour and angle-dependence by changing the shapes of polystyrene/polydopamine particles, making them hollow on the inside, and adding multiple coatings to the external shell.

Polydopamine particles are showing potential for a variety of applications. For example, they can be used as inks to dye fabrics or in cosmetics. They could help prove a product is real versus counterfeit by shifting colour with strong light, wetting, or temperature changes. Finally, scientists have found that adding these particles to rubber causes it to change colour when stretched or relaxed, which could be useful for sensing local stress and strain in bridges.

Further information
Michinari Kohri
Chiba University
Email: kohri@faculty.chiba-u.jp

About Science and Technology of Advanced Materials Journal
Open access journal STAM publishes outstanding research articles across all aspects of materials science, including functional and structural materials, theoretical analyses, and properties of materials.

Chikashi Nishimura
STAM Publishing Director
NISHIMURA.Chikashi@nims.go.jp

Press release distributed by ResearchSEA for Science and Technology of Advanced Materials.

Accurate measurements of crystalline deformation should help engineer stronger components for more energy-efficient turbines.

Metals containing niobium silicide are promising materials that can withstand high temperatures and improve efficiency of gas turbines in power plants and aircraft. But it has been difficult to accurately determine their mechanical properties due to their complex crystal structures. Now, scientists at Kyoto University in Japan have measured what happens at the micro-level when pressure is applied on tiny samples of these materials. The approach, published in the journal Science and Technology of Advanced Materials, could help scientists obtain the accurate measurements needed to understand the atomic-level behaviour of complex crystals to develop more heat-tolerant components in gas turbines.