A team of scientists from the Department of Energy’s Oak Ridge National Laboratory has developed a new method that can take the local temperature using a material that is a billionth of a meter wide and 100,000 times thinner than a human hair.
This new development could lead researchers to further understand the physical and chemical behaviors that happen at the nanoscale level. This new development is helpful for microelectronic devices, semiconducting materials and other techs that depends on mapping atomic-scale vibrations from heat in these electronics.
The study used electron energy gain spectroscopy with a specialized instrument that can produce images with high spatial resolution and great spectral detail. The instrument is named High Energy Resolution Monochromated Electron energy-loss spectroscopy-Scanning transmission electron microscope, nicknamed HERMES. HERMES is 13 feet tall — matching its incredibly long name.
Scientists used HERMES to measure the temperature of semiconducting hexagonal boron nitride. To do this they observed the atomic vibrations that go along with the heat in the material.
While other thermometers need calibration to operate properly, HERMES doesn’t require temperature calibration. This speeds up the process and operations significantly. Instead of having to figure out how much mercury is in the thermometer to make the temperature marks on the thermometer, HERMES gives a direct measurement of nanoscale temperature.
In order to get a temperature, there are two features that are depicted as peaks. These peaks are used to calculate an energy gain and loss ratio. The team didn’t need any other information about a material before they can find a temperature.
The ORNL team took a concept from a 1966 paper by H. Boersch, J. Geiger and W. Stickel on electron energy gain spectroscopy that was published in Physical Review Letters and theorized that they should be able to measure the nanomaterial’s temperature with an electron microscope. The key is that the electron microscope must have an electron beam that is monochromated within a narrow range.
In order to perform the electron energy gain and loss experiments, the researchers put a sample material in the microscope. The microscope’s electron beam went through the sample with minimal interaction between the electrons and the beam. In electron energy loss spectroscopy, the beam loses energy when it passes through the sample and in energy gain spectroscopy the electrons gain energy from interaction with the sample.
"The new HERMES lets us look at very tiny energy losses and even very small amounts of energy gain by the sample, which are even harder to observe because they are less likely to happen," Idrobo said. "The key to our experiment is that statistical physical principles tell us that it is more likely to observe energy gain when the sample is heated. That is precisely what allowed us to measure the temperature of the boron nitride. The monochromated electron microscope enables this from nanoscale volumes. The ability to probe such exquisite physical phenomena at these tiny scales is why ORNL purchased the HERMES."
The researchers are always trying to push the capabilities of electron microscopes to create new ways of conducting research. They hope to use HERMES whenever they can to further develop this.
The nanoscale resolution makes it possible to characterize phase transition local temperature. This technique is impossible without HERMES and HERMES could be used over a wide range of temperatures.
The paper on this research was published in Physical Review Letters.