Abstract
ABSTRACTMany vapor-deposited metal-on-insulator films exhibit a morphological progression with increasing thickness consisting of several distinct stages: (1) nucleation of 3-dimensional na-nocrystalline islands; (2) elongation of the islands; (3) film percolation. Here we report a study of this progression during Pulsed Laser Deposition (PLD), a technique for film deposition that differs from thermal deposition in that the depositing species arrive in short energetic bursts, leading to instantaneous deposition fluxes orders of magnitude higher than can be achieved in thermal growth. Atomic Force Microscopy reveals that advancement through this same morphological progression occurs at lower thickness in PLD films relative to films grown under comparable conditions by thermal deposition, with PLD films having lower RMS roughness at a given thickness. We also observe that for a constant amount deposited per pulse, films deposited at higher laser pulse frequency are further advanced in morphological state. Kinetic Monte Carlo simulations reveal that PLD nucleation behavior differs from that of thermally deposited films, and this can account for the observed differences. Simulations also reveal a scaling of the percolation thickness with pulse frequency that is consistent with experiment.
Highlights
Metal-on-insulator thin films typically grow according to the Volmer-Weber growth mode, in which atoms grow in 3D islands on the surface.[1,2,3,4,5] As the islands grow larger, they impinge upon other islands
For the purposes of this paper, we primarily consider the effect of (1), leaving (2) for future work. We study this phenomenon using a combination of experiments and Kinetic Monte Carlo simulations
Pulsed Laser Deposition (PLD) films were grown at 3 Hz, and these were compared with films grown at roughly the same time-averaged deposition rate by Baski and Fuchs by Molecular Beam Epitaxy (MBE) deposition.[2]
Summary
Metal-on-insulator thin films typically grow according to the Volmer-Weber growth mode, in which atoms grow in 3D islands on the surface.[1,2,3,4,5] As the islands grow larger, they impinge upon other islands When this occurs, the islands may begin to coalesce, with atoms being exchanged between them, driving them to become a single island. To reproduce the Volmer-Weber film growth geometry, islands are assumed to remain hemispherical, with a contact angle of 90° This is accomplished by immediately relocating an impinging atom to the nearest vacant site to the projected center of mass of the island.
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