Oral Exam Announcement: Karthik Vijayraghavan

EE Department Oral Defense

Title: High Bandwidth AFM Imaging in Fluid Using Interdigitated Probes

Speaker: Karthik Vijayraghavan
Advisor: Olav Solgaard

Date: Monday, November 12, 2012
Time: 3:30 pm (refreshments at 3:15 pm)
Location: Packard 101

Abstract:

High speed imaging of local material properties of soft materials such as cells using the Atomic Force Microscope (AFM) is an area of active research. An understanding of nanomechanical properties and local adhesive forces of cells would greatly improve our understanding of fundamental cellular processes. Traditionally, these properties have been obtained quantitatively using "force-distance" curves which are slow to obtain and not amenable to high speed imaging. Alternatively, qualitative mapping of these properties has been performed using phase imaging in AC mode AFM where an AFM probe is oscillated close to its fundamental resonance frequency and concurrently scanned over a sample surface to make intermittent contact with the sample surface. The interaction force between the probe tip and the sample surface contains rich information about the properties of the sample. However, due to the limited bandwidth of traditional AFM cantilevers, a significant portion of this rich information is lost. Interdigitated AFM probes overcome this limitation by incorporating a high bandwidth diffraction grating based force sensor on the cantilever to measure the time-varying interaction forces with adequately high bandwidth.

In the first part of this talk, I will describe the mechanical and optical design of interdigitated AFM probes and present a simplified analytical model to calculate the mechanical frequency response of the probes. I will then describe the fabrication of these probes using MEMS fabrication techniques and demonstrate the characterization of these probes. In the second part of this talk, I will describe signal processing methods that were developed to obtain physical properties of samples scanned with these probes. Finally, I will present representative results from imaging a sputtered gold surface, a polymer sample, and a cell sample, in fluid, thereby demonstrating the ability of these interdigitated probes to image multiple physical properties of a wide range of samples.