AVS 59th Annual International Symposium and Exhibition
    Exhibitor Technology Spotlight Tuesday Sessions
       Session EW-TuM

Paper EW-TuM8
AM-FM and Loss Tangent Imaging–Two New Tools for Quantitative Nanomechanical Properties

Tuesday, October 30, 2012, 10:20 am, Room West Hall

Session: Exhibitor Technology Spotlight
Presenter: K. Jones, Asylum Research
Authors: R. Proksch, Asylum Research
I. Revenko, Asylum Research
S. Hohlbauch, Asylum Research
J. Cleveland, Asylum Research
N. Geisse, Asylum Research
A. Moshar, Asylum Research
J. Bemis, Asylum Research
C. Callahan, Asylum Research
K. Jones, Asylum Research
Correspondent: Click to Email
Amplitude-modulated Atomic Force Microscopy (AM-AFM), also known as tapping mode, is a reliable and gentle imaging method with widespread applications. Previously, the contrast in AM-AFM has been difficult to quantify. In this work, we introduce two new techniques that allow unambiguous interpretation of material properties. AM-FM imaging combines the features and benefits of normal tapping mode with quantitative and high sensitivity of frequency modulated (FM) mode. Briefly, the topographic feedback operates in AM mode while the second resonant mode drive frequency is adjusted to keep the phase at 90 degrees, on resonance. With this approach, frequency feedback on the second resonant mode and topographic feedback on the first are decoupled, allowing stable, robust operation. The FM image returns a quantitative value of the frequency shift that in turn depends on the sample stiffness and can be applied to a variety of physical models. Loss tangent imaging is a recently introduced quantitative technique that recasts phase imaging into a term that includes both the dissipated and stored energy of the tip sample interactions. Quantifying the loss tangent depends solely on the measurement of cantilever parameters as a reference position. These two quantitative techniques can be performed simultaneously. To illustrate this, we will present an example of a micro-cryotomed, cross-sectioned area of a coffee bag packaging material that has been imaged. The loss tangent image shows the highly lossy "tie" layers connecting the low loss metal layer with two vapor-barrier polymer layers. The AM-FM image shows the relative stiffness of the five layers, with the metal layer being the stiffest and the tie layers the softest. As a second example, we imaged graphene deposited onto SiO2, where the softer graphene layer showed a lowered resonance and the loss tangent imaging revealed a dissipative region between SiO2 and graphene.