2023-10-18 11:00:04
Researchers have shown that on the surface of a pure silicon solid subjected to a temperature gradient, the atoms migrate preferentially towards cold zones, at exceptionally slow speeds…
The dissipation of electrical energy into heat (In common language, the words heat and temperature often have an equivalent meaning:…), also known as the “Joule effect (The Joule effect is the thermal manifestation of electrical resistance. It occurs during…)”, is inevitable in any electrical device, and in particular in our computers and our mobile phones. This phenomenon causes hot spots in electronic components and connections which have harmful consequences on their operation and lifespan. Indeed, local variations in temperature (Temperature is a physical quantity measured using a thermometer and…) lead to transport (Transport is the act of carrying something, or someone, of one place to another, the more…) of surface matter by a phenomenon called thermomigration. This transport of material leads to the progressive modification of the performance of the components and can even induce the breakdown of electrical connections, inducing breakdowns in our devices. Furthermore, on a fundamental level, this physical process is very difficult to quantify experimentally and to understand theoretically.
In a recent experimental study, researchers from the Nanoscience Center of Marseille (Interdisciplinary work integrates concepts from different disciplines.)CINaM, University (A university is a higher education establishment whose objective is…) Aix-Marseille / CNRS) proposed an original method to precisely quantify thermomigration, using silicon (Silicon is an element chemical from the family of crystallogens, with the symbol Si…), which for this phenomenon behaves like a model material. The exceptional crystalline quality of the silicon surface makes it possible to precisely describe the elementary thermomigration processes.
The silicon sample, a square surface with a side of 9 millimeters, was subjected to a thermal gradient of 10⁰C per millimeter and at an average temperature of 830°C and was observed in real time by slow electron microscopy. With this technique, the displacement ( In geometry, a displacement is a similarity which preserves distances and angles…) of atoms cannot be followed individually, but it might nevertheless be inferred by following the displacement of surface defects, depressions of monatomic thickness which act as sources and sinks for the surface migration of atoms.
Left: two successive images by slow electron microscopy, time shifted by 1200s, show the displacement of a circular depression of atomic height on the silicon surface.
Right: schematic diagram of the thermomigration process: silicon atoms leave the hot edge of the depression and join the opposite cold edge because of a bias in the diffusive process with each atomic movement.
This process is also favored by a lower rate of atom dropout on the cold edge than on the hot edge.
© Frédéric Leroy.
The researchers not only showed that the atoms move towards the cold areas of the surface, but even measured their speed, of the order of 2 nanometers per second, an extremely low value compared to the typical speeds linked to the thermal agitation. They were also able to deduce the average value of the force responsible for thermomigration.
This pioneering experimental work will undoubtedly serve as a reference for future experimental and theoretical studies in this area. The results obtained also make it possible to consider using thermomigration to control the surface movement of atoms and therefore to produce controlled atomic assemblies using, for example, local laser heating. These results are published in Physical Review Letters.
References
Determination of the Thermomigration Force on Adatoms,
Frédéric Leroy, A. El Barraj, Fabien Cheynis, Pierre Müller, Stefano Curiotto,
Physical Review Letters, published September 15, 2023.
Doi: 10.1103/PhysRevLett.131.116202
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#Atoms #prefer #cold
