Physicists may have to rewrite their textbooks in future - at least as far as heat transport over extremely small distances in a vacuum is concerned. This is suggested by the results of experiments conducted by Oldenburg scientists.
The fundamentally new findings of the team led by physicists Prof Dr Achim Kittel and PD Dr Svend-Age Biehs have been published in the scientific journal "Nature Communications". The Oldenburg scientists carried out their work together with colleagues from Princeton University in New Jersey, USA.
Using the globally unique near-field scanning thermal microscope developed in Oldenburg, the scientists were able to measure how heat is transferred from a warm source to a cold sample surface via gaps of just a few nanometres in a vacuum. One nanometre corresponds to one millionth of a millimetre; the distances examined corresponded to the size of one to several atoms. The researchers found that this heat transfer was around a thousand times greater than would be expected according to current theories of thermal radiation. Until now, these have referred to distances greater than one micrometre, i.e. one thousandth of a millimetre.
"These investigations are of great interest as they shed light on the energy exchange of nanoscopic systems at very small distances - in the sub-nanometre range," says Kittel. Until now, there have been no experimental investigations in this range of distances, Kittel adds. The new findings could enable scientists to better control the temperature of nanosystems. Such systems are becoming increasingly important for future technologies in electronics, optics and display technology.
The researchers discovered the discrepancy between theory and experiment by comparing their experimental data with the predictions of previously used theories of thermal radiation. Dr Svend-Age Biehs and Prof. Dr Alejandro Rodriguez (Princeton University) carried out calculations based on approximation methods as well as numerically exact calculations. The researchers discovered that there is a new heat transfer mechanism at distances of less than seven nanometres that has not been taken into account in the theory used to date.
In further experiments, the scientists want to investigate the heat flow in this extreme near-field range. They have already discovered that a wafer-thin coating influences the heat transfer. Their aim now is to understand more precisely how the unusual heat transfer actually takes place. The researchers also want to increase the distances that can be analysed. This will enable them to experimentally pinpoint the area in which the previously known theory begins to fail. This requires the development of completely new types of sensors that are a thousand times more sensitive than those used to date.