Dynamics of the low-energy ion impact on the vander Warls thin films

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The study on the interactions between the low-energy ions and solid surface is of fundamental importance in the field of plasma technology and ion-beam technology. In this study, the dynamics of the low-energy ion impact on the van der Waals thin films were studied in detail. The newly designed reflectron-type TOF mass spectrometer was installed in the ultra-high vacuum chamber. The pulsed ion beam was injected into the van der Waals thin film deposited on the cold head of the cryocooler at 7 K.When the film was bombarded by the He^+ ions, the cluster ions were hardly observed. Instead, fragment ions are formed with strong intensities. This is due to the fact that the kinetic energy of the small-size He^+ ion is mainly dissipated by the electronic excitation in the ion-solid collision events. In contrast, much more efficient momentum transfer takes place in the collision of Ne^+ with the solid films. The efficient momentum transfer in the collision events leads to the shock wave formation in the ion track. This results in the abundant cluster ion formation.In sum, the holes and excitons formed in the matrix play very important roles in the secondary ion formatin.