A dynamic double layer as the origin of the mass-dependent ion acceleration in laser-induced plasmas
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The kinetic energies of the plasma plume species and their control are critical to ensure the high quality of thin films grown by pulsed laser deposition. The maximum kinetic energies of ionic plasma species from different multicomponent materials, CaTiO3, EuAlO3, La0.4Ca0.6MnO3, La0.4Ca0.6Mn0.9Ru0.1O3, and YBa2Cu3O7, have been analysed, revealing a wide range of energies of 100–700 eV. A direct relationship between the maximum kinetic energies and atomic masses has been found: the larger is the mass of an ion, the higher is its energy. This dependence varies with the kind of the ablated material and its slope is changing with laser fluence. The results are explained by the generation of a self-consistent ambipolar electric field in front of the expanding laser plume. The concept of a dynamic double layer has been considered, when heavier ions remain in the ambipolar field for a longer time as compared to lighter ions, thus resulting in stronger acceleration of heavy ions.
Financial supports from the Paul Scherrer Institute and the Swiss National Science Foundation (SNF/Project 00021_143665) are gratefully acknowledged. NMB and AVB acknowledge financial support from the European Regional Development Fund and the state budget of the Czech Republic (Project BIATRI: CZ.02.1.01/0.0/0.0/15_003/0000445), from the Ministry of Education, Youth and Sports (Programs NPU I-Project no. LO1602), and from the Russian Science Foundation (Project 16-19-10506).
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