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A D V A N C E D M A T E R I A L S & P R O C E S S E S | M A Y / J U N E 2 0 1 8 1 3 THIN FILM HELPS MANAGE HEAT FLOW Researchers at Purdue University, West Lafayette, Ind., demonstrated the ability of a thin film to conduct heat on just its surfaces, identifying a potential solution to overheating in electronic devices such as smartphones and com- puters. The material is a topological insulator, which supports the flow of electrons on its surface but not in its interior. No study had yet tested wheth- er the same were true for heat. Past re- search speculated that topological in- sulators could be useful for developing spintronic devices, which encode infor- mation through the spins of electrons as opposed to the electrical charge in today’s electronics. Researchers found that the thin- ner the film is, the higher the heat con- ductivity. They also discovered that the ratio of thermal conductivity to electrical conductivity at the surface of the topological insulator materials can be more than 10 times higher than the Sommerfeld value, the value known for most metals and semiconductors de- termined by the Weidemann-Franz law. By conducting heat on just its surfaces rather than across the entire film, this material could prevent parts of a device from heating up or redirect heat. Now, having identified this characteristic of heat transfer in topological insulators, the next step is to figure out how to use them for manipulating heat flow. purdue.edu . TRANSPARENT DEVICE ENABLES INVISIBLE DISPLAYS University of California, Berkeley engineers built a bright-light emitting device that is millimeters wide and fully transparent when turned off. The light emitting material in this device is a monolayer semiconductor, just three atoms thick. The device opens the door to invisible displays on walls and win- dows—displays that would be bright when turned on but see-through when turned off—or in futuristic applications such as light emitting tattoos, say re- searchers. Commercial LEDs consist of a semiconductor material that is electri- cally injectedwith positive and negative charges, which produce light when they Probes inject positive and negative charges in the light emitting device, which is transparent under the campanile outline, producing bright light. Courtesy of Javey lab. EMERGING TECHNOLOGY Carpenter Technology Corp., Philadelphia, will invest $100 million in soft magnetics capabilities and a new, preci- sion strip hot rolling mill at its Reading, Pa., facility to help meet increasing demand. Soft magnetics, materials that can be easily magnetized and demagnetized, are indispensable in modern electrical engineering and electronics applications. The new mill will offer greater flexibility in processing alloys for specialized applications in aerospace, consumer electronics, and electric vehicles. cartech.com . BRIEF meet. Typically, two contact points are used in such a device—one for injecting negatively charged particles and one for positively charged particles. Mak- ing contacts that can efficiently inject these charges is a fundamental issue for LEDs, and it is particularly challenging for monolayer semiconductors because there is so little material to work with. The new device only requires one contact on the semiconductor to pro- duce light. By laying the semiconductor monolayer on an insulator and placing electrodes on the monolayer and un- derneath the insulator, the researchers could apply an AC signal across the in- sulator. When the AC signal switches polarity from positive to negative, and vice versa, both positive and negative charges are present at the same time in the semiconductor, creating light. The novel device is a proof of concept and its efficiency needs improvement: Researchers estimate 1% efficiency for the new device, while commercial LEDs feature efficiencies of around 25-30%. berkeley.edu. Researchers discovered a characteristic of this thin film that could help control heat flow in electronics. Courtesy of Jared Pike.