Acoustical Wave Measurements of Thin Films and Aluminum Deposition via Sputtering
Molly James, Vassar College ’17, Mohammed Abdelaziz, Vassar College ’16, Sushant Mahat, Vassar College ’16, Lauren Delgado, Vassar College ’19 and Prof. Brian DalyMany of the nanoscale thin film samples being studied in the ultrafast optics lab are provided by partners at Intel Corp. Although Intel provides some information about them, it is up to us to experimentally determine either their sound velocities or thicknesses. By detecting and recording vibrations caused by the absorption of ultrafast laser pulses, the thicknesses of the sample layers can be measured. Samples are often made from transparent oxide materials that do not absorb light from the lasers; therefore we need to coat them with a nanometer scale aluminum film through a process called sputtering. Sputtering is a type of physical vapor deposition that occurs when an electric field excites particles in a low pressure gas to knock out atoms from a solid target that then coat a sample. This summer, we set up a new sputtering machine, the Desktop Pro manufactured by Denton Vacuum. The Desktop Pro has a large vacuum chamber supported by both a mechanical and a turbomolecular pump. Regular air is pumped out and a small amount of pure argon gas is allowed into the chamber. The argon strikes into a plasma when electricity passes through, and the ions of the plasma eject aluminum atoms from the target that then deposit onto the sample. The thickness of the aluminum topcoat depends on the power applied and the run time of the sputtering machine. We have performed some preliminary laser measurements of the aluminum films prepared in the Desktop Pro.