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.

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.

Phase Contrast Imaging in Atomic Force Microscopy

1997 ◽  
Vol 3 (S2) ◽  
pp. 1275-1276
Author(s):  
Sergei Magonov
Keyword(s):  
Atomic Force Microscopy ◽  
Phase Contrast ◽  
Phase Changes ◽  
Phase Imaging ◽  
Phase Detection ◽  
Contrast Imaging ◽  
Force Microscopy ◽  
Atomic Force ◽  
Resonance Frequencies ◽  
Soft Samples

Phase detection in TappingMode™ enhances capabilities of Atomic Force Microscopy (AFM) for soft samples (polymers and biological materials). Changes of amplitude and phase changes of a fast oscillating probe are caused by tip-sample force interactions. Height images reflect the amplitude changes, and in most cases they present a sample topography. Phase images show local differences between phases of free-oscillating probe and of probe interacting with a sample surface. These differences are related to the change of the resonance frequency of the probe either by attractive or repulsive tip-sample forces. Therefore phase detection helps to choose attractive or repulsive force regime for surface imaging and to minimize tip-sample force. For heterogeneous materials the phase imaging allows to distinguish individual components and to visualize their distribution due to differences in phase contrast. This is typically achieved in moderate tapping, when set-point amplitude, Asp, is about half of the amplitude of free-oscillating cantilever, Ao. In contrast, light tapping with Asp close to Ao is best suited for recording a true topography of the topmost surface layer of soft samples. Examples of phase imaging of polymers obtained with a scanning probe microscope Nanoscope® IIIa (Digital Instruments). Si probes (225 μk long, resonance frequencies 150-200 kHz) were used.

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.

Fault Isolation of MOL and FEOL Buried Defects Using Conductive Atomic Force Microscopy as a Complement to Passive Voltage Contrast Imaging

2017 ◽  
Author(s):  
Lucile C. Teague Sheridan ◽  
Linda Conohan ◽  
Chong Khiam Oh
Keyword(s):  
Atomic Force Microscopy ◽  
Cmos Technology ◽  
Fault Isolation ◽  
Contrast Imaging ◽  
Conductive Atomic Force Microscopy ◽  
Isolation Technique ◽  
Conductive Afm ◽  
Force Microscopy ◽  
Atomic Force ◽  
Voltage Contrast

Abstract Atomic force microscopy (AFM) methods have provided a wealth of knowledge into the topographic, electrical, mechanical, magnetic, and electrochemical properties of surfaces and materials at the micro- and nanoscale over the last several decades. More specifically, the application of conductive AFM (CAFM) techniques for failure analysis can provide a simultaneous view of the conductivity and topographic properties of the patterned features. As CMOS technology progresses to smaller and smaller devices, the benefits of CAFM techniques have become apparent [1-3]. Herein, we review several cases in which CAFM has been utilized as a fault-isolation technique to detect middle of line (MOL) and front end of line (FEOL) buried defects in 20nm technologies and beyond.

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