Nion STEM takes nanoscale temperatures
Image: ORNL researchers, Andrew Lupini (left) and Juan Carlos Idrobo (right), with the Nion HERMES.
Researchers from the Oak Ridge National Laboratory and Nion have used a HERMES STEM to directly measure the temperature of boron nitride at the nanoscale.
The Nion HERMES - High Energy Resolution Monochromated Electron energy-loss spectroscopy STEM - with its high energy resolution and narrow electron beam, combines electron energy gain and loss spectroscopy to determine local temperature in nanoenvironments.
Physicist, Juan Carlos Idrobo, from the Center for Nanophase Materials Sciences at ORNL, and colleagues used the instrument to measure the temperature of semiconducting hexagonal boron nitride, directly observing the atomic vibrations that corresponded to heat, within the material.
As Idrobo points out, the experimenter only needs to know the energy and intensity of an atomic vibration within a material to determine temperature at the nanoscale.
Using the HERMES STEM to directly probe phonons in boron nitride, the researchers measured the loss and gain peaks that corresponded to an optical-phonon mode in the material as temperature increased from room temperature to around 1600 K.
"Both loss and gain peaks exhibit a shift towards lower energies as the sample is heated up," writes Idrobo and colleagues in Physical Review Letters. "First-principle calculations of these temperature-induced phonon frequency shifts provided insights into the origin of this effect and confirmed experimental data."
"The ability to probe such exquisite physical phenomena at these tiny scales is why ORNL purchased the HERMES," adds Idrobo.
Pioneered by Ondrej Krivanek, co-founder of Nion, and colleagues, the STEM was introduced several years ago, and uses a monochromator to boost the attainable energy resolution of EELS in a STEM.
Nanoscale resolution is crucial to characterising local temperatures during phase transitions in materials.
HERMES spectroscopy could be useful for studying devices working across a wide range of temperatures from electronics operating under ambient conditions to vehicle catalysts that perform at temperatures greater than 300ºC.
Research is published in Physical Review Letters.