Identifying Vibrational Modes of Thin Film Nanostructures Using Finite Element Modeling
Matteo Bjornsson, Vassar College ’15 and Prof. Brian Daly
Thin films are becoming increasingly essential to a wide variety of technological applications, most notably in microprocessors and computing. One non-destructive technique used to study and measure these structures is the “Pump-Probe” technique. This ultrafast laser technique produces vibrations in a sample that can be measured, providing information about the thickness of the layers and the vibrational modes of the sample. For this experiment we used several thin film structures that contained nanometer scale TiN wires resting on a multiple thin film stack. To better understand the nature of the vibrational modes of these samples, and how the spacing of these wires affected these modes, we modeled their vibration in a finite element modeling program. This investigation took a closer look at the experimentally observed modes of these samples, explored the physical nature of these modes, and sought to explain why our pump-probe technique was only sensitive to certain modes. We simulated models of these samples and observed that for a wider line spacing the material properties of the silicon were most important, but for narrower line spacing the dominant properties were unclear. We also investigated the different types of motion associated with each vibrational mode by making movies of the simulated structure vibrating at an individual frequency.