scholarly journals Publisher’s Note: “A constant-frequency feedback loop for non-contact frequency-modulated atomic force microscopy via root locus: Implemented on a single-board field-programmable gate array device” [Rev. Sci. Instrum. 91, 113702 (2020)]

2020 ◽  
Vol 91 (12) ◽  
pp. 129901
Author(s):  
Solomon Davis ◽  
Tal Obstbaum ◽  
Gil Ben Ari ◽  
Uri Sivan
Keyword(s):  
Atomic Force Microscopy ◽  
Field Programmable Gate Array ◽  
Feedback Loop ◽  
Root Locus ◽  
Constant Frequency ◽  
Force Microscopy ◽  
Atomic Force ◽  
Contact Frequency ◽  
Field Programmable ◽  
Gate Array

scholarly journals A review of demodulation techniques for multifrequency atomic force microscopy

2020 ◽  
Vol 11 ◽  
pp. 76-91 ◽  
Author(s):  
David M Harcombe ◽  
Michael G Ruppert ◽  
Andrew J Fleming
Keyword(s):  
Atomic Force Microscopy ◽  
Sampling Rate ◽  
Microscopy Imaging ◽  
Force Microscopy ◽  
Atomic Force ◽  
Direct Design ◽  
Field Programmable ◽  
Frequency Components ◽  
Atomic Force Microscopy Imaging ◽  
Lock In

This article compares the performance of traditional and recently proposed demodulators for multifrequency atomic force microscopy. The compared methods include the lock-in amplifier, coherent demodulator, Kalman filter, Lyapunov filter, and direct-design demodulator. Each method is implemented on a field-programmable gate array (FPGA) with a sampling rate of 1.5 MHz. The metrics for comparison include the sensitivity to other frequency components and the magnitude of demodulation artifacts for a range of demodulator bandwidths. Performance differences are demonstrated through higher harmonic atomic force microscopy imaging.

scholarly journals Quantitative comparison of wideband low-latency phase-locked loop circuit designs for high-speed frequency modulation atomic force microscopy

2018 ◽  
Vol 9 ◽  
pp. 1844-1855 ◽  
Author(s):  
Kazuki Miyata ◽  
Takeshi Fukuma
Keyword(s):  
Atomic Force Microscopy ◽  
Frequency Modulation ◽  
High Speed ◽  
Feedback Loop ◽  
Response Speed ◽  
Low Latency ◽  
Pass Filter ◽  
Force Microscopy ◽  
Atomic Force ◽  
Afm Imaging

A phase-locked loop (PLL) circuit is the central component of frequency modulation atomic force microscopy (FM-AFM). However, its response speed is often insufficient, and limits the FM-AFM imaging speed. To overcome this issue, we propose a PLL design that enables high-speed FM-AFM. We discuss the main problems with the conventional PLL design and their possible solutions. In the conventional design, a low-pass filter with relatively high latency is used in the phase feedback loop, leading to a slow response of the PLL. In the proposed design, a phase detector with a low-latency high-pass filter is located outside the phase feedback loop, while a subtraction-based phase comparator with negligible latency is located inside the loop. This design minimizes the latency within the phase feedback loop and significantly improves the PLL response speed. In addition, we implemented PLLs with the conventional and proposed designs in the same field programmable gate array chip and quantitatively compared their performances. The results demonstrate that the performance of the proposed PLL is superior to that of the conventional PLL: 165 kHz bandwidth and 3.2 μs latency in water. Using this setup, we performed FM-AFM imaging of calcite dissolution in water at 0.5 s/frame with true atomic resolution. The high-speed and high-resolution imaging capabilities of the proposed design will enable a wide range of studies to be conducted on various atomic-scale dynamic phenomena at solid–liquid interfaces.

Identification and Analysis of Artifacts in Amplitude Modulated Atomic Force Microscopy Array Operation

2017 ◽  
Vol 12 (5) ◽  
Author(s):  
Samuel Jackson ◽  
Stefanie Gutschmidt
Keyword(s):  
Atomic Force Microscopy ◽  
Separation Distance ◽  
Constant Frequency ◽  
Single Beam ◽  
Force Microscopy ◽  
Atomic Force ◽  
Close Proximity ◽  
Output Amplitude ◽  
Sample Separation ◽  
The Relationship

To increase measurement throughput of atomic force microscopy (AFM), multiple cantilevers can be placed in close proximity to form an array for parallel throughput. In this paper, we have measured the relationship between amplitude and tip-sample separation distance for an array of AFM cantilevers on a shared base actuated at a constant frequency and amplitude. The data show that discontinuous jumps in output amplitude occur within the response of individual beams. This is a phenomenon that does not occur for a standard, single beam system. To gain a better understanding of the coupled array response, a macroscale experiment and mathematical model are used to determine how parameter space alters the measured amplitude. The results demonstrate that a cusp catastrophe bifurcation occurs due to changes in individual beam resonant frequency, as well as significant zero-frequency coupling at the point of jump-to-contact. Both of these phenomena are shown to account for the amplitude jumps observed in the AFM array.

scholarly journals Bimodal atomic force microscopy driving the higher eigenmode in frequency-modulation mode: Implementation, advantages, disadvantages and comparison to the open-loop case

2013 ◽  
Vol 4 ◽  
pp. 198-207 ◽  
Author(s):  
Daniel Ebeling ◽  
Santiago D Solares
Keyword(s):  
Atomic Force Microscopy ◽  
Frequency Modulation ◽  
Operation Mode ◽  
Excitation Amplitude ◽  
Open Loop ◽  
Constant Frequency ◽  
Force Microscopy ◽  
Advantages And Disadvantages ◽  
Atomic Force ◽  
Modulation Mode

We present an overview of the bimodal amplitude–frequency-modulation (AM-FM) imaging mode of atomic force microscopy (AFM), whereby the fundamental eigenmode is driven by using the amplitude-modulation technique (AM-AFM) while a higher eigenmode is driven by using either the constant-excitation or the constant-amplitude variant of the frequency-modulation (FM-AFM) technique. We also offer a comparison to the original bimodal AFM method, in which the higher eigenmode is driven with constant frequency and constant excitation amplitude. General as well as particular characteristics of the different driving schemes are highlighted from theoretical and experimental points of view, revealing the advantages and disadvantages of each. This study provides information and guidelines that can be useful in selecting the most appropriate operation mode to characterize different samples in the most efficient and reliable way.

Analysis of a Bi-Harmonic Tapping Mode for Atomic Force Microscopy

2013 ◽  
Author(s):  
Muthukumaran Loganathan ◽  
Douglas A. Bristow
Keyword(s):  
Atomic Force Microscopy ◽  
Feedback Loop ◽  
Mechanical Sensitivity ◽  
Tapping Mode ◽  
Force Microscopy ◽  
Atomic Force ◽  
Imaging Mode ◽  
Trajectory Dynamics ◽  
Mode Tm

The tapping mode (TM) is a popularly used imaging mode in atomic force microscopy (AFM). A feedback loop regulates the amplitude of the tapping cantilever by adjusting the offset between the probe and sample; the image is generated from the control action. This paper explores the role of the trajectory of the tapping cantilever in the accuracy of the acquired image. This paper demonstrates that reshaping the cantilever trajectory alters the amplitude response to changes in surface topography, effectively altering the mechanical sensitivity of the instrument. Trajectory dynamics are analyzed to determine the effect on mechanical sensitivity and analysis of the feedback loop is used to determine the effect on image accuracy. Experimental results validate the analysis, demonstrating better than 30% improvement in mechanical sensitivity using certain trajectories. Images obtained using these trajectories exhibit improved sharpness and surface tracking, especially at high scan speeds.

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.

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