Brent Grocholski

Hearing a volcanic plume

Volcanology![Figure][1] CREDIT: ASSOCIATED PRESS, COLT SNAPP Monitoring remote eruptions—such as that of Pavlof Volcano, Alaska, in 2016—is challenging. Fee et al. found that the height of the ash plume during the Pavlof eruption could be inferred from sound waves detected by distant

Natural and engineered perovskites

Perovskite is an unremarkable calcium titanium oxide mineral discovered in 1839 with an extremely versatile crystal structure. The compact crystal structure marks the transition to Earths lower mantle as silicate perovskite becomes stable. Silicate perovskites make up the bulk of the lower mantle

Lower symmetry for higher performance

Thermoelectrics Thermoelectric materials interchange heat and electricity. Lowering thermal conductivity while maintaining electrical conductivity is important for developing promising thermoelectric materials. Li et al. depart from the usual strategy of using high-symmetry materials by moving from

Blowing by the blackbody limit

Thermal Transport The blackbody limit tells us the maximum amount of heat that can be emitted from an object. However, this limit is known to be no limit at all when the spacing between objects is small enough. Thompson et al. show that the blackbody limit can be circumvented when the emitting objects themselves are small. More importantly, they demonstrate a massive, hundredfold enhancement relative to the classical blackbody limit using nanoscale membranes. This opens the door to tailoring nanoscale materials for enhanced thermal absorption and emission applications. Nature 561 , 216 (2018).

Moving the heat aside with BAs

Thermal Conductivity Thermal management becomes increasingly important as we decrease device size and increase computing power. Engineering materials with high thermal conductivity, such as boron arsenide (BAs), is hard because it is essential to avoid defects and impurities during synthesis, which would stop heat flow. Three different research groups have synthesized BAs with a thermal conductivity around 1000 watts per meter-kelvin: Kang et al. , Li et al. , and Tian et al. succeeded in synthesizing high-purity BAs with conductivities half that of diamond but more than double that of conventional metals (see the Perspective by Dames). The advance validates the search for high-thermal-conductivity materials and provides a new material that may be more easily integrated into semiconducting devices. Science , this issue p. [575][1], p. [579][2], p. [582][3]; see also p. [549][4] [1]: /lookup/doi/10.1126/science.aat5522 [2]: /lookup/doi/10.1126/science.aat8982 [3]: /lookup/doi/10.1126/science.aat7932 [4]: /lookup/doi/10.1126/science.aau4793

Measuring martian organics and methane

Planetary Science The Curiosity rover has been sampling on Mars for the past 5 years (see the Perspective by ten Kate). Eigenbrode et al. used two instruments in the SAM (Sample Analysis at Mars) suite to catch traces of complex organics preserved in 3-billion-year-old sediments. Heating the sediments released an array of organics and volatiles reminiscent of organic-rich sedimentary rock found on Earth. Most methane on Earth is produced by biological sources, but numerous abiotic processes have been proposed to explain martian methane. Webster et al. report atmospheric measurements of methane covering 3 martian years and found that the background level varies with the local seasons. The seasonal variation provides an important clue for determining the origin of martian methane. Science , this issue p. [1096][1], p. [1093][2]; see also p. [1068][3] [1]: /lookup/doi/10.1126/science.aas9185 [2]: /lookup/doi/10.1126/science.aaq0131 [3]: /lookup/doi/10.1126/science.aat2662

Nanoparticle synthesis gets a shock

Nanomaterials Nanoparticles are useful in a wide range of applications such as catalysis, imaging, and energy storage. Yao et al. developed a method for making nanoparticles with up to eight different elements (see the Perspective by Skrabalak). The method relies on shocking metal salt–covered

Giving a hand to metamaterials

Metamaterials Auxetic materials expand in an unusual way: perpendicular to the direction in which they are stretched. Lipton et al. engineered a type of auxetic material that also has handedness. When this material is sheared, it twists either to the right or the left. By tiling the underlying

Smaller but more thermally stable

Metallurgy Synthesizing metals with extremely small (nanoscale) grain sizes makes for much stronger materials. However, very small–grained materials start to coarsen at relatively low temperatures, wiping out their most desirable properties. Zhou et al. discovered a way to avoid this problem by mechanically grinding copper and nickel at liquid nitrogen temperatures. The processing method creates low-angle grain boundaries between the nanograins, which promotes thermal stability. Science , this issue p. [526][1] [1]: /lookup/doi/10.1126/science.aar6941

Silicon sheds its harmonicity

Materials Science The widespread technological uses for silicon make understanding this elements physical properties very important. Kim et al. performed inelastic neutron scattering experiments on single crystals of silicon to measure the vibrational properties up to 1500 K. Silicon has some odd thermal properties at certain temperatures, and these experiments show the need to account for a number of factors to explain the unusual thermal expansion behavior. This in-depth look at silicon helps refine theoretical models and provides a better understanding of this technologically important material. Proc. Natl. Acad. Sci. U.S.A. 10.1073/pnas.1707745115 (2018).