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February 2015 • SMT Magazine 45 induced by surface plasmon polariton excita- tions. This technique could be used for con- trolled growth of metal nanowires of desirable parameters on metal surfaces. 4) Applications to modern large area thin film photovoltaic technology where whiskers can shunt through the device, thereby causing significant reliability concerns (which has not been sufficiently addressed yet). Properly re- placing those device metal contacts or surface treatments mitigating whisker growth can im- prove the device reliability and stability with respect to shunting. acknowledgement The author is grateful to D. Shvydka, A. Vasko, G. Davy, S. Smith, B. Rollins, J. Brusse, A. Kostic, and the entire tin whisker teleconfer- ence group for useful discussions. The NASA Electronic Parts and Packaging (NEPP) Program is greatly appreciated. SMT references 1. V. G. Karpov, Electrostatic Theory of Met- al Whiskers, Physical Review Applied, 1, 044001 (2014). 2. Private communication, October 2014, slightly abridged here. 3. G. A. Mesyats, Explosive Electron Emis- sion, URO Press, Ekaterinburg, (1998); p.29 Victor Karpov is professor of physics at the university of Toledo. He has published about 200 papers on condensed mat- ter, physical chemistry, photovol- taics, and device physics. eLeCTrOSTaTIC MeCHaNISM OF NuCLeaTION aNd GrOWTH OF MeTaL WHISKerS continues rice university scientists advanced their recent development of laser-induced graphene (lig) by producing and testing stacked, three-dimensional supercapacitors, energy-storage devices that are im- portant for portable, flexible electronics. The rice lab of chemist James Tour discovered last year that firing a laser at an inexpensive poly- mer burned off other elements and left a film of po- rous graphene, the much-studied atom-thick lattice of carbon. The researchers viewed the porous, con- ductive material as a perfect electrode for superca- pacitors or electronic circuits. Members of the Tour group have since extended their work to make vertically aligned supercapacitors with laser-induced graphene on both sides of a poly- mer sheet. The sections are then stacked with solid electrolytes in between for a multi- layer sandwich with multiple microsu- percapacitors. The flexible stacks show excellent energy-storage capacity and power potential and can be scaled up for commercial applications. liG can be made in air at ambient temperature, perhaps in industrial quantities through roll-to- roll processes, Tour said. The research was reported this week in applied Materials and interfaces. liG supercapacitors appear able to do everything capacitors can do, with the added benefits of flex- ibility and scalability. The flexibility ensures they can easily conform to varied packages—they can be rolled within a cylinder, for instance—without giving up any of the device's performance. "What we've made are comparable to microsu- percapacitors being commercialized now, but our ability to put devices into a 3-D configuration allows us to pack a lot of them into a very small area," Tour said. "We simply stack them up. "The other key is that we're doing this very sim- ply. nothing about the process requires a clean room. it's done on a commercial laser system, as found in routine machine shops, in the open air." ripples, wrinkles and sub-10-nanometer pores in the surface and atomic-level imperfections give liG its ability to store a lot of energy. but the graphene retains its ability to move electrons quickly and gives it the quick charge-and-release characteris - tics of a supercapacitor. in testing, the researchers charged and discharged the devices for thousands of cycles with almost no loss of capacitance. Laser-induced Graphene Vital for Flex Electronics Feature

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