Defining Approaches and Philosophy: Signals, Controls, Multidimensionality, and Multimodality for Advancing Nanoscale Imaging and Spectroscopy
Signals to and from the Nanoscale
Our group has a rich history of advancing the field of scanning probe microscopy by developing new and innovative driving signals to probe material properties. We strive to improve AFM detection schemes by replacing standard driving signals with novel ones, which can help us overcome challenges related to distinguishing multiple signal sources, spurious signals from the ones we are interested in, and for calibration.
The tip-surface interaction, to put in plainly, is where the rubber meets the road in SPM, and our goal is to gather the most reliable and noise-free information from this region as possible. In AFM, the cantilever's complex dynamics are effectively the lens of this particular microscope through which any signal generated at the tip-surface junction must pass to be detected and understood. The cantilever and its modes of motion can and do modify and amplify information. Therefore, we devote significant effort to capturing and understanding the cantilever's mechanical motion and behavior while performing imaging and spectroscopy.
Band Excitation
The use of multifrequency signals allow us a direct means to quickly and reliably capture many salient aspects of AFM cantilever dynamics. Band Excitation (BE) is a technique developed at the CNMS in which many frequencies within a “band” are generated together to drive the motion of the cantilever in a particular way. The response of the cantilever is captured at all of these same frequencies, thus giving a much better, wider, and more detailed picture of the cantilever motion.
The bands of frequencies in Band Excitation are focused on the resonant modes of the cantilever. Notably, the position, height, width, and general shape of the resonant peaks (as seen in the Fourier domain) Are strongly affected by properties and motion of the tip surface junction. Band excitation allows us to monitor the resonance peaks continuously while scanning therefore allowing us direct access to material behavior and response to stimuli with maximal amplification. Notably, the single frequency methods that standard AFM uses cannot provide reliable information about the cantilever dynamics – there are just to many variables in flux for one information channel to capture or describe.
Multifrequency signals provide a direct and reliable means of capturing important aspects of AFM cantilever dynamics. Band Excitation (BE), a technique developed at CNMS, generates multiple frequencies within a "band" to drive the cantilever's motion in a specific way. By capturing the cantilever's response at these same frequencies, BE provides a wider and more detailed picture of the cantilever's motion.
The frequencies in BE are focused on one or more of the resonant modes of the cantilever. The position, height, width, and shape of the resonant peaks in the Fourier domain are strongly influenced by and in large part describe the properties and motion of the tip-surface junction. BE enables continuous monitoring of these resonance peaks while scanning and while performing spectroscopy, providing direct access to material behavior and response to stimuli with maximum amplification.
Notably, standard AFM techniques use single-frequency methods and cannot reliably capture information about cantilever dynamics due to the large number of variables at play. BE overcomes this limitation by using multiple frequencies and capturing a more comprehensive picture of the cantilever's resonances and motion.
Functionalities
We focus on several areas of material functionality for our research and development and in the capabilities we provide to the user community. In many cases, we integrate approaches described above to enhance our measurements. The primary areas of interest are described below:
Dielectric and Conductive properties
Nano electromechanical properties
Nanoscale Thermal characterization
Fluid FM
List of Instrumentation
Contacts
Section Head
Senior R&D Staff Scientist
R&D Staff Scientist
R&D Staff Scientist
R&D Staff Scientist
R&D Staff Scientist