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Quantum mechanics, literally: the schematic diagram illustrates how a mechanical stress develops in aluminium nanofilms of five and seven atomic layers thick due to quantum effects. The electron energy, represented in the decaying oscillation, depends on the film thickness. To reach an electron energy minimum, the film thickness must change. A film of five atomic layers thick is forced to compress perpendicular to the surface, where in contrast, a seven-atomic layer film relaxes perpendicular to the surface. Parallel to the film the system wants to simultaneously expand or contract, respectively. However, this is impossible because the aluminium atoms are fixed on the substrate. Therefore a compressive or tensile stress develops that is shown by the yellow arrows. They signify the force that develops to prevent the respective expansion or contraction. © David Flötotto / MPI for Intelligent Systems

Quantum stress in nanofilms

Electrons confined in an aluminium film of a few atomic layers thick create mechanical stress equivalent to up to one thousand times the standard atmospheric pressures

  • 12 September 2012

Read heads in hard drives, lasers in DVD players, transistors on computer chips, and many other components all contain ultrathin films of metal or semiconductor materials. Stresses arise in thin films during their manufacture. These influence the optical and magnetic properties of the components, but also cause defects in crystal lattices, and in the end, lead to component failure. As researchers in the department of Eric Mittemeijer at the Max Planck Institute for Intelligent Systems in Stuttgart have now established, enormous stresses in the films are created by a quantum-mechanical mechanism that has been unknown until now, based on an effect by the name of quantum confinement. This effect can cause stresses equivalent to one thousand times standard atmospheric pressure, dependent of thickness. Knowledge of this could be helpful in controlling the optical and mechanical properties of thin-film systems and increase their mechanical stability. Additionally, very sensitive sensors might also be developed on the basis of this knowledge.