scholarly journals A review of demodulation techniques for amplitude-modulation atomic force microscopy

2017 ◽  
Vol 8 ◽  
pp. 1407-1426 ◽  
Author(s):  
Michael G Ruppert ◽  
David M Harcombe ◽  
Michael R P Ragazzon ◽  
S O Reza Moheimani ◽  
Andrew J Fleming
Keyword(s):  
Atomic Force Microscopy ◽  
Amplitude Modulation ◽  
High Speed ◽  
Performance Metrics ◽  
Processing System ◽  
Digital Processing ◽  
Cantilever Deflection ◽  
Force Microscopy ◽  
Atomic Force ◽  
Frequency Components

In this review paper, traditional and novel demodulation methods applicable to amplitude-modulation atomic force microscopy are implemented on a widely used digital processing system. As a crucial bandwidth-limiting component in the z-axis feedback loop of an atomic force microscope, the purpose of the demodulator is to obtain estimates of amplitude and phase of the cantilever deflection signal in the presence of sensor noise or additional distinct frequency components. Specifically for modern multifrequency techniques, where higher harmonic and/or higher eigenmode contributions are present in the oscillation signal, the fidelity of the estimates obtained from some demodulation techniques is not guaranteed. To enable a rigorous comparison, the performance metrics tracking bandwidth, implementation complexity and sensitivity to other frequency components are experimentally evaluated for each method. Finally, the significance of an adequate demodulator bandwidth is highlighted during high-speed tapping-mode atomic force microscopy experiments in constant-height mode.

scholarly journals High-resolution dynamic atomic force microscopy in liquids with different feedback architectures

2013 ◽  
Vol 4 ◽  
pp. 153-163 ◽  
Author(s):  
John Melcher ◽  
David Martínez-Martín ◽  
Miriam Jaafar ◽  
Julio Gómez-Herrero ◽  
Arvind Raman
Keyword(s):  
Atomic Force Microscopy ◽  
High Resolution ◽  
Amplitude Modulation ◽  
Performance Metrics ◽  
Operating Conditions ◽  
Atomic Resolution ◽  
Quality Factors ◽  
Liquid Media ◽  
Force Microscopy ◽  
Atomic Force

The recent achievement of atomic resolution with dynamic atomic force microscopy (dAFM) [Fukuma et al., Appl. Phys. Lett. 2005, 87, 034101], where quality factors of the oscillating probe are inherently low, challenges some accepted beliefs concerning sensitivity and resolution in dAFM imaging modes. Through analysis and experiment we study the performance metrics for high-resolution imaging with dAFM in liquid media with amplitude modulation (AM), frequency modulation (FM) and drive-amplitude modulation (DAM) imaging modes. We find that while the quality factors of dAFM probes may deviate by several orders of magnitude between vacuum and liquid media, their sensitivity to tip–sample forces can be remarkable similar. Furthermore, the reduction in noncontact forces and quality factors in liquids diminishes the role of feedback control in achieving high-resolution images. The theoretical findings are supported by atomic-resolution images of mica in water acquired with AM, FM and DAM under similar operating conditions.

scholarly journals Lyapunov estimation for high-speed demodulation in multifrequency atomic force microscopy

2018 ◽  
Vol 9 ◽  
pp. 490-498 ◽  
Author(s):  
David M Harcombe ◽  
Michael G Ruppert ◽  
Michael R P Ragazzon ◽  
Andrew J Fleming
Keyword(s):  
Atomic Force Microscopy ◽  
High Speed ◽  
Harmonic Amplitude ◽  
Phase Imaging ◽  
Contrast Imaging ◽  
Force Microscopy ◽  
Atomic Force ◽  
Field Programmable ◽  
Frequency Components ◽  
Lock In

An important issue in the emerging field of multifrequency atomic force microscopy (MF-AFM) is the accurate and fast demodulation of the cantilever-tip deflection signal. As this signal consists of multiple frequency components and noise processes, a lock-in amplifier is typically employed for its narrowband response. However, this demodulator suffers inherent bandwidth limitations as high-frequency mixing products must be filtered out and several must be operated in parallel. Many MF-AFM methods require amplitude and phase demodulation at multiple frequencies of interest, enabling both z-axis feedback and phase contrast imaging to be achieved. This article proposes a model-based multifrequency Lyapunov filter implemented on a field-programmable gate array (FPGA) for high-speed MF-AFM demodulation. System descriptions and simulations are verified by experimental results demonstrating high tracking bandwidths, strong off-mode rejection and minor sensitivity to cross-coupling effects. Additionally, a five-frequency system operating at 3.5 MHz is implemented for higher harmonic amplitude and phase imaging up to 1 MHz.

Visualization of molecular binding sites at the nanoscale in the lift-up mode by amplitude-modulation atomic force microscopy

Nanoscale ◽  
2021 ◽  
Vol 13 (7) ◽  
pp. 4213-4220
Author(s):  
Tatsuhiro Maekawa ◽  
Takashi Nyu ◽  
Evan Angelo Quimada Mondarte ◽  
Hiroyuki Tahara ◽  
Kasinan Suthiwanich ◽  
...  
Keyword(s):  
Atomic Force Microscopy ◽  
Molecular Recognition ◽  
Amplitude Modulation ◽  
Binding Sites ◽  
Local Distribution ◽  
New Approach ◽  
Molecular Binding ◽  
Force Microscopy ◽  
Atomic Force ◽  
Recognition Sites

We report a new approach to visualize the local distribution of molecular recognition sites with nanoscale resolution by amplitude-modulation atomic force microscopy.

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