Taking 2-D materials’ temperature at the nanoscale

As the number of two-dimensional materials continues to grow quickly, so does the number of proposed applications. Many of them fall in the area of microelectronics, where using atomically thin circuit components can lead to extremely miniature and ultrafast transistors and other devices. For these devices to function reliably, engineers need to know how hot the 2-D materials get when the device is switched on, how much they expand, and how fast heat dissipates—all at the nanoscale. A few methods can measure some of those parameters, but they have shortcomings. In scanning probe techniques, for example, the size of the cantilever tip limits the resolution, and the specimen sits on a support that affects the measurement. So Robert F. Klie and Amin Salehi-Khojin of the University of Illinois, Chicago, and coworkers developed a new high-resolution thermometry method by combining scanning transmission electron microscopy with electron energy-loss spectroscopy (Phys. Rev. Lett. 2018, DOI: 10.1103/PhysRevLett.120.055902). The team used the technique to generate maps with few-nanometer resolution of the temperature and thermal expansion coefficients of freestanding samples of several 2-D materials, including graphene, MoS₂, MoSe₂, WS₂, and WSe₂.