ISSN 2056-6727 (Print) The CRUCIBLE The magazine of the Minor Metals Trade Association Clean fuels and EVs Tungsten: the path of least resistance Thinking about... Responsible Sourcing 10th Edition 2017/Nov-Dec 1 THE MMTA’S INTERNATIONAL MINOR METALS CONFERENCE 2018 Organised by Metal Events Ltd The Queen Elizabeth Hotel, Montreal, Canada, 11-13 April EXCELLENT MEMBERS’ AND NON-MEMBERS’ EARLY-BIRD RATES AVAILABLE Register by 11 January: MMTA members £750 and non-members £1050 Platinum Sponsor Gold Sponsor Who attends the Conference? 2 Re-cap: 44th Anniversary Dinner INSIDE THIS ISSUE The MMTA welcomed over 200 guests to the impressive ballroom of 1 Great George Street during LME week for good food and great company. Tesla announcement 3 Tungsten: no resistance 4 Dr Robin Gleek was able to bring a refreshing , Clean tech update 6-7 first-hand report of the work and progress made in the mining community of Mufulira, Zambia. Letter from N. America 8-9 Brussels Raw Materials Week 10 A record amount was raised by the raffle to benefit Mufulira with the final total of £3283 (EUR 85). Metallic glass 12 Snowflakes & Stibnites 14 Thank you for your generosity, this brings us closer Responsible Sourcing Launch 15 to reaching the goal of purchasing an ultrasound machine to benefit Mufulira’s hospital and it’s patients. The MMTA would like thank RC Inspection for their kind sponsorship which helped to make this such a successful event. The MMTA promotes essential elements that add Birgit Bender, RC Inspection quality, safety and enjoyment to our lives. The MMTA is the world's Tesla have announced a ‘semi-truck’ and sports car leading minor metals industry Elon Musk unveiled Tesla’s first electric semi-truck last week that also included the surprise reveal of a organisation. new Tesla sports car. The new Roadster emerged from the back of one of the trucks at the end of a presentation that focused largely on the economic and performance needs of truck drivers. While the sports car provided a jolt of excitement for Tesla enthusiasts, much of the event focused on Contact Us: pitching the truck to truck drivers – customers with very different concerns than the average Tesla owner. Address: MMTA, Suite 53, 3 Whitehall Court, London, SW1A 2EL, UK Musk had hyped the truck on Twitter throughout the week. He reported that the Tesla truck cost of Tel: +44 (0)207 833 0237 ownership will be 20% less per mile compared with diesel trucks. Among them: faster acceleration, better Email: [email protected] uphill performance, a 500-mile (805km) range at maximum weight at highway speed, and “thermonuclear explosion-proof glass” in the windshield. 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Other companies working on electric it, nor is it intended to endorse any views expressed, accuracy of material, products or services offered or trucks include Volkswagen, Cummins and Nikola. other information made available via the link. 3 Tungsten offers nano-interconnects a path of least resistance As microchips become ever smaller, and therefore faster, the shrinking size of their copper interconnects leads to increased electrical resistivity at the nanoscale. Finding a solution to this impending technical bottleneck is a major problem for the semiconductor industry. One promising possibility involves reducing the resistivity size effect by altering the crystalline orientation of interconnect materials. Researchers from Rensselaer Polytechnic Institute conducted electron transport measurements in epitaxial single-crystal layers of tungsten (W) as one such potential interconnect solution. They performed first-principles simulations, finding a definite orientation- dependent effect. The anisotropic resistivity effect they found was most marked between layers with two particular orientations of the lattice structure, namely W(001) and W(110). The work is published in the Journal of Applied Physics. Author Pengyuan Zheng noted that both the 2013 and 2015 International Technology Roadmap for Semiconductors (ITRS) called for new materials to replace copper as interconnect material to limit resistance increase at reduced scale and minimize both power consumption and signal delay. In their study, Zheng and co-author Daniel Gall chose tungsten because of its asymmetric Fermi surface—its electron energy structure. This made it a good candidate to demonstrate the anisotropic resistivity effect at the small scales of interest. "The bulk material is completely isotropic, so the resistivity is the same in all directions," Gall said. "But if we have thin films, then the resistivity varies considerably." To test the most promising orientations, the researchers grew epitaxial W(001) and W(110) films on substrates and conducted resistivity measurements of both while immersed in liquid nitrogen at 77 Kelvin (about -196 degrees Celsius) and at room temperature, or 295 Kelvin. "We had roughly a factor of 2 difference in the resistivity between the 001 oriented tungsten and 110 oriented tungsten," Gall said, but they found considerably smaller resistivity in the W(011) layers. Although the measured anisotropic resistance effect was in good agreement with what they expected from calculations, the effective mean free path—the average distance electrons can move before scattering against a boundary—in the thin film experiments was much larger than the theoretical value for bulk tungsten. "An electron travels through a wire on a diagonal, it hits a surface, gets scattered, and then continues traveling until it hits something else, maybe the other side of the wire or a lattice vibration," Gall said. "But this model looks wrong for small wires." The experimenters believe this may be explained by quantum mechanical processes of the electrons that arise at these limited scales. Electrons may be simultaneously touching both sides of the wire or experiencing increased electron-phonon (lattice vibrations) coupling as the layer thickness decreases, phenomena that could affect the search for another metal to replace copper interconnects. "The envisioned conductivity advantages of rhodium, iridium, and nickel may be smaller than predicted," said Zheng. Findings like these will prove increasingly important as quantum mechanical scales become more commonplace for the demands of interconnects. The research team is continuing to explore the anisotropic size effect in other metals with nonspherical Fermi surfaces, such as molybdenum. They found that the orientation of the surface relative to the layer orientation and transport direction is vital, as it determines the actual increase in resistivity at these reduced dimensions. "The results presented in this paper clearly demonstrate that the correct choice of crystalline orientation has the potential to reduce nanowire resistance," said Zheng. The importance of the work extends beyond current nanoelectronics to new and developing technologies, including transparent flexible conductors, thermoelectrics and memristors that can potentially store information. "It's the problem that defines what you can do in the next technology," Gall said. Read more at: https://phys.org/news/2017-10-tungsten-nano-interconnects-path-resistance.html#jCp