| RESEARCH HIGHLIGHTS |


based on a simple spherical nanoparticle model, and observed the fluorescence enhancement in an air and water environ- ment. This allowed them to observe the different physical confinement characteristics for each material.


“Our results show that in air the


dielectric is better, but in water the metals perform better,” says Bai. “This provided us with knowledge to explore new materials and structures that could combine the advantages of


both materials, with the potential for more-sensitive technologies.”


1. Sun, S., Wu, L., Bai, P. & Png, C. E. Fluorescence enhancement in visible light: Dielectric or noble metal? Physical Chemistry Chemical Physics 18, 19324–19335 (2016).


Materials


STANENE’S THERMAL SURPRISE


ELECTRONS PLAY A KEY ROLE IN HEAT TRANSPORT THROUGH 2D TIN SHEETS


Heat travels through atom-thin sheets of tin in a very unusual way, A*STAR researchers have found1. The discovery could help develop applications for the material, including ther- moelectric refrigeration or power generation. Graphene, a layer of carbon just one


atom thick, was first isolated in 2004. Since


then, researchers have created a plethora of other ‘2D’ analogs of graphene using different atoms. Stanene, with its tin atoms arranged in a slightly corrugated hexagonal pattern (see image), arrived in 2015. Hangbo Zhou and colleagues at the A*STAR Institute of High Performance Computing have


now studied how this cousin of graphene conducts heat. In solid materials, heat is generally carried


by electrons or through vibrations between atoms. As these vibrations travel through the material, they behave rather like a particle, known as a phonon. At room temperature, graphene mostly conducts heat with phonons, whereas metals largely rely on electrons. But in stanene, the balance between these two mechanisms was unknown. The A*STAR team calculated the


phonon and electron thermal conduction in stanene at various temperatures and found that stanene has a much lower phonon thermal conduction than graphene. Indeed, at room temperature, electron thermal conduction in stanene is roughly the same as its phonon conduction.


"THE VIOLATION OF THE LAW MAY PROVIDE AN ALTERNATIVE ROUTE TO ACHIEVING HIGH-EFFI- CIENCY THERMOELECTRIC MATERIALS."


They also found that stanene deviates from


Stanene is a hexagonal lattice of tin atoms


just one-atom thick (right), which is slightly corrugated (left).


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the Wiedemann–Franz law, which states that electron thermal conduction depends on the temperature and the electrical conductivity of the material. In stanene, however, the contribution of electron thermal conduction to overall heat transfer also depends on the material’s ‘chemical potential’— a measure of how much energy is required to add one more electron to the material. Crucially, the researchers found that chemical potential also affects electron thermal transport in graphene and some other 2D materials. The surprising findings could make


stanene useful in thermoelectric devices, in which a temperature gradient creates a voltage between two parts of a material, or vice versa.


A*STAR RESEARCH 17


Adapted with permission from Ref. 1. Copyrighted by the American Physical Society.


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