Science 347, 629–632 (2015)

Nanoscale electronic devices dissipate heat in a non-homogeneous way, and local variations in temperature can substantially affect the performance of a device. Various approaches have been explored in the past to efficiently map the temperature of devices with high spatial resolution. However, methods based on contact thermometry can disturb the temperature of a device, and non-contact spectroscopic methods cannot achieve spatial resolution better than several tens of nanometres. Matthew Mecklenburg and colleagues at the University of California, Los Angeles and Lawrence Berkeley National Laboratory have now performed temperature mapping of an operating aluminium electronic device using a technique they term plasmon energy expansion thermometry.

The technique is based on a scanning transmission electron microscope operated in electron energy-loss spectroscopy mode. By using the microscope to measure the energy needed to excite a plasmon (a collective electron mode) in the aluminium, it is possible to extract the local density. From this, the thermal expansion can be determined and hence the local temperature. With the technique, Mecklenburg and colleagues produce thermal maps of serpentine aluminium nanowire devices that had temperature gradients on a nanometre length scale (see image; the hottest regions are shown in yellow and the coldest in green; the diameter of the nanowire is around 100 nm).