#pyroelectric

Record-breaking photodetector captures light in just 125 picoseconds

Record-breaking ultrathin photodetector captures light across the entire spectrum in just 125 picoseconds, opening the door to powerful new imaging technologies.

Electrical engineers at Duke University have created the fastest pyroelectric photodetector ever demonstrated, a device that detects light by sensing the tiny amount of heat it produces when absorbed. The ultrathin sensor can capture light across the entire electromagnetic spectrum. It operates at room temperature, requires no external power source, and can be integrated directly into on-chip systems. The technology could eventually enable a new generation of multispectral cameras with applications in areas such as skin cancer detection, food safety monitoring, and large scale agriculture. The findings were reported in the journal Advanced Functional Materials.

Tinzenite

The rare mineral group known as axinite grows in beautiful bladed axe like crystals that are named after the Greek for axe. The colours of this calcium iron/magnesium/manganese borosilicate vary from violet to reddish brown or yellow, and its hardness of 6-7 on Mohs scale means that it is sometimes faceted for gem collectors (though the perfect cleavage along lines of weaker bonding within the structure makes this difficult, as entire layers of the crystal can separate off when polishing it on the wheel). Like some members of the garnet group, the three elements separated above by slashes form what is called a solid solution series, in which these elements are mixed, and the type of axinite depends on the proportions of the mixture between them in the crystal structure. This version is Tinzenite, usually yellow to orange in colour and hued by manganese.

Most axinite forms when the heat from granitic magma rising and cooling in the Earth bakes the rocks it pushes through, a process known as contact metamorphism, though a related process called metasomatism, in which hot element rich fluids circulate between the two kinds of juxtaposed rock. Axinite, like demantoid garnet (see http://tinyurl.com/kqop7lh), only forms when the granites intrude limestones forming a type of rocks (that often host mineral deposits) called skarns. It also occurs more rarely in certain kinds of silica poor mafic volcanic rocks and the Tinzenite variety is usually found here, in association with ophiolites, chunks of oceanic crust and upper mantle that have been pushed onto continents in collisions or similar rocks post metamorphism.

Inclusion free specimens are rare, as is common with many metamorphic gems, in which elements that do not enter the crystal structure of the gem in question crystalise as different minerals within the structure of the gem. Axinite displays very strong pleochroism (see our post on Alexandrite for an explanation at http://bit.ly/1PvWSE5), a phenomenon in which the crystal appears differently coloured depending on the direction from which it is viewed. This happens because the crystal structure separates light into different rays, each travelling through the crystal through separate pathways, and having some of their wavelengths absorbed on the way. The different light pathways are not absorbed in the same way, leaving three separate residual colours visible in the crystal.

It is one of the rare minerals with electrical properties, called pyro and piezo electricity. When rapidly heated or cooled, or stresses with pressure, the structure generates an electrical current. Tourmaline is another such mineral, and gems in shop windows often attract dust due to the currents generated during the day/night cycle. It also fluoresces reddish orange in UV light (for an explanation of how minerals do this see our past post on glowing diamonds at http://bit.ly/2uLwzXv). Axinite is found in France, Russia, Brazil, Paistan and Tanzania. It is not treated, and should not be exposed to harsh chemicals, detergents or ultrasonic cleaners. The 2.1 x 2.0 x 0.7 cm specimen in the photo comes from the Kalahari Manganese Field in South Africa.

Loz

Image credit: Rob Lavinsky/iRocks.com

https://www.mindat.org/min-3972.html http://bit.ly/2vTyxVW

MIT engineers have developed a technique to grow and peel ultrathin "skins" of electronic material. The method could pave the way for new classes of electronic devices, such as ultrathin wearable sensors, flexible transistors and computing elements, and highly sensitive and compact imaging devices. As a demonstration, the team fabricated a thin membrane of pyroelectric material -- a class of heat-sensing material that produces an electric current in response to changes in temperature. The thinner the pyroelectric material, the better it is at sensing subtle thermal variations. With their new method, the team fabricated the thinnest pyroelectric membrane yet, measuring 10 nanometers thick, and demonstrated that the film is highly sensitive to heat and radiation across the far-infrared spectrum.

Thermal vision of snakes inspires soft pyroelectric materials

Converting heat into electricity is a property thought to be reserved only for stiff materials like crystals. However, researchers—inspired by the infrared (IR) vision of snakes—developed a mathematical model for converting soft, organic structures into so-called "pyroelectric" materials. The study, appearing October 21 in the journal Matter, proves that soft and flexible matter can be transformed into a pyroelectric material and potentially solves a long-held mystery surrounding the mechanism of IR vision in snakes.

When a material can convert heat into an electric impulse it is called "pyroelectric," a property typically only found in hard, inflexible substances. The mystery is how IR sensing snakes can achieve this heat-to-electricity conversion despite having naturally soft anatomy.

"People thought we could explain the IR sensing of snakes if there was a hard, pyroelectric material in their pit organ, but nobody ever found one," says Pradeep Sharma, the M.D. Anderson Professor and Chair of Mechanical Engineering at the University of Houston. "So, we wondered whether just as we are trying to make these soft materials pyroelectric, maybe nature is doing the same thing."

Gold-plated crystals set new standard for natural gas detectors

Materials scientists and engineers have developed a sensor that is fast, sensitive and efficient enough to detect specific wavelengths of electromagnetic energy while on the move. The technology could actively scan areas for methane or natural gas leaks, monitor the health of vast fields of crops or quickly sort plastics for recycling.

Working closely with the optoelectronic materials company SRICO, engineers from Duke University have built a prototype detector that beats the existing competition in size, weight, power, speed and, most importantly, cost.

The new technology relies on metamaterials—engineered structures made of carefully designed repeating cells that can interact with electromagnetic waves in unnatural ways. By combining seemingly simple patterns of metal with extremely thin slices of perfect crystals, the engineers created a streamlined device able to detect invisible infrared signatures emitted by various kinds of gasses, plastics and other sources.

Material can turn sunlight, heat and movement into electricity—all at once

Many forms of energy surround you: sunlight, the heat in your room and even your own movements. All that energy—normally wasted—can potentially help power your portable and wearable gadgets, from biometric sensors to smart watches. Now, researchers from the University of Oulu in Finland have found that a mineral with the perovskite crystal structure has the right properties to extract energy from multiple sources at the same time.

Perovskites are a family of minerals, many of which have shown promise for harvesting one or two types of energy at a time—but not simultaneously. One family member may be good for solar cells, with the right properties for efficiently converting solar energy into electricity. Meanwhile, another is adept at harnessing energy from changes in temperature and pressure, which can arise from motion, making them so-called pyroelectric and piezoelectric materials, respectively.

Sometimes, however, just one type of energy isn't enough. A given form of energy isn't always available—maybe it's cloudy or you're in a meeting and can't get up to move around. Other researchers have developed devices that can harness multiple forms of energy, but they require multiple materials, adding bulk to what's supposed to be a small and portable device.

Ultrahigh sensitivity graphene infrared detectors for imaging and spectroscopy

Researcher from the Graphene Flagship have developed a novel graphene-based infrared (IR) detector demonstrating record high sensitivity for thermal detection. Graphene's unique attributes pave the way for high-performance IR imaging and spectroscopy.

Graphene's benefits are opening possibilities in high-performance IR imaging and spectroscopy. Researchers from the Graphene Flagship, working at the University of Cambridge (UK), Emberion Ltd. (UK), the Institute of Photonic Sciences (ICFO; Spain), Nokia UK, and the University of Ioannina (Greece) have developed a graphene-based pyroelectric bolometer that detects infrared (IR) radiation by measuring tiny temperature changes with an ultra-high level of accuracy. The work, published in Nature Communications, demonstrates the highest reported temperature sensitivity for graphene-based uncooled thermal detectors, capable of resolving temperature changes down to a few tens of µK. Only a few nano-Watts of IR radiation power are required to produce such a small temperature variation in isolated devices, about 1000 times smaller than the IR power delivered to the detector by a human hand in close proximity.