| AVS 55th International Symposium & Exhibition | |
| Thin Film | Thursday Sessions |
| Session TF-ThM |
| Session: | Evaporation, Pulsed Laser Deposition, and Molecular Beam Epitaxy |
| Presenter: | Y.F. Guan, The University of Tennessee, Knoxville |
| Authors: | Y.F. Guan, The University of Tennessee, Knoxville J.D. Fowlkes, Oak Ridge National Laboratory A.V. Melechko, Oak Ridge National Laboratory M.L. Simpson, Oak Ridge National Laboratory P.D. Rack, The University of Tennessee, Knoxville |
| Correspondent: | Click to Email |
One of the challenges of nanoscience and technology is understanding and controlling bottom up directed assembly of materials. A lot of work has been done studying the assembly of continuous thin polymer and metal films which reveal interesting dewetting phenomenon. While the break-up and pattern formation via dewetting of continuous thin metal and polymer films has been studied in detail, less work has been devoted to the dewetting and pattern formation of confined or patterned thin films. In this work, thin nickel films were patterned into various shapes and treated via nanosecond pulsed laser processing. The short liquid lifetimes offers a unique way to monitor the time dependence of the dewetting process and the subsequent pattern formation. Thin nickel films (30 nm) were evaporated onto electron beam lithography patterned PMMA coated (60 nm) silicon substrates. Thin nickel patterns of a variety of sizes of circles, squares, and triangles were achieved by a conventional lift-off process. The edges and vertices of the patterned shapes act as programmable instabilities which enable directed assembly via dewetting when the laser energy density is above the melting threshold. The pattern formations were monitored as a function of laser pulse and the retraction process was attributed liquid dewetting and a subsequent re-solidification. The calculated retraction velocity (83 m/s) and liquid lifetime (12.3 ns) were consistent with the measured nickel retraction distances. The lateral retraction and pattern formation was correlated to a two step process: 1) initially the surface tension drives the flow of the melted nickel films, and 2) a smaller contraction associated with the density difference between the liquid and solid when the liquid film solidifies. The vertices of the shapes had an initially larger retraction velocity which was attributed to an additional in-plane curvature. The reduced retraction rates at subsequent pulses were attributed to thickening of the front which reduces the curvature and enhances viscous dissipation. Acknowledgements: The authors acknowledge support from the Material Sciences and Engineering Division Program of the DOE Office of Science. And a portion of this research was conducted at the Center for Nanophase Materials Sciences, which is sponsored at Oak Ridge National Laboratory by the Division of Scientific User Facilities, U.S. Department of Energy.