Lane Martin, Scott MacLaren
Gunter Moeller, George Papakonstantopoulos
Neil Thompson, Colin Grant, Nagatha Wijayathunga
Band Excitation (BE) is a new Scanning Probe Microscopy (SPM) technique that has shown great promise in mapping the conservative interactions, nonlinearities, and energy dissipation of materials on the nanoscale.1 The quality factor, Q, of the cantilever vibrating in the vicinity of the surface is a parameter that is inversely proportional to energy dissipation in the tip-surface junction. However, standard single-frequency SPM experiments are incapable of providing this energy transfer information quantitatively, since only two parameters (e.g. amplitude and phase) are measured experimentally, while at least three are required to describe the dynamics of the system. Frequency sweeps using standard lock-in techniques can be performed to determine Q, but the large time requirements are impractical for imaging. Stephen Jesse and Sergei Kalinin at Oak Ridge National Laboratory and their collaborators, including AFM manufacturer Asylum Research, synthesized an excitation signal programmed with a finite amplitude and phase in a predetermined frequency range to drive the cantilever electrically, magnetically, or acoustically and probe the response at multiple frequencies at once. This method extends to energy dissipation measurements since amplitude and phase response can be determined simultaneously over a range of frequencies, even in low Q-factor environments such as liquids. The BE method is a fast and sensitive technique which may be useful for understanding and mitigating energy losses in magnetic, electrical, and electromechanical processes and technologies.
Please contact Dr. Roger Proksch at Asylum Research for further information and to discuss the Band Excitation Technique.
MFP-3D, Cypher, and ARC2 are trademarks of Asylum Research.
Operational principle of the BE method in SPM. The excitation signal is digitally synthesized to have a predefined amplitude and phase in the given frequency window. The cantilever response is detected and Fourier transformed (FFT) at each pixel in an image. The ratio of the fast FFT of response and excitation signals yields the cantilever response (transfer function). Fitting the response to the simple harmonic oscillator yields amplitude, resonance frequency, and Q-factor that are plotted to yield 2D images, or used as feedback signals.1 Reprinted with permission (see reference 1).
Excitation (blue) and response (red) signals in standard SPM techniques in (top left) time domain and (top right) Fourier domain. In BE, the system response is probed in the specified frequency range (e.g. encompassing a resonance), as opposed to a single frequency in conventional SPMs. Reprinted with permission. (See reference 1).