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Mahdavi, Mohammad

Publications and source records attributed to Mahdavi, Mohammad.

7 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Cantilever with a collocated piezoelectric actuator-sensor pair

Illustrative embodiments provide an apparatus comprising a substrate comprising a cantilever, a bottom electrode on the substrate, a bottom piezoelectric transducer on the bottom electrode such that the bottom electrode is between the substrate and the bottom piezoelectric transducer, a middle electrode on the bottom piezoelectric transducer such that the bottom piezoelectric transducer is between the bottom electrode and the middle electrode, a top piezoelectric transducer on the middle electrode such that the middle electrode is between the bottom piezoelectric transducer and the top piezoelectric transducer, and a top electrode on the top piezoelectric transducer, such that the top piezoelectric transducer is between the middle electrode and the top electrode. Illustrative embodiments also provide a method of making the apparatus and a method of using the apparatus for atomic force microscopy.

Moheimani, Seyed Omid Reza↗
DOE OSTI2022

High resolution atomic force microscopy with an active piezoelectric microcantilever

Active microcantilevers with on-chip sensing and actuation provide significant advantages in tapping mode Atomic Force Microscopy (AFM). Collocated transduction allows for effective manipulation of cantilever dynamics through feedback control, enabling higher scan rates. However, the adjacency of the sensing and actuation electrodes is known to result in a high level of feedthrough, leading to a low imaging resolution. Readout circuit noise further deteriorates the imaging precision. Here, we investigate the noise sources that affect AFM microcantilevers with collocated aluminum nitride (AlN) actuator–sensor pairs. We reported these cantilevers in earlier work and demonstrated that they display a very low level of feedthrough between the actuation and sensing electrodes. We present a high signal-to-noise ratio (SNR) sensing method that enables us to demonstrate high-resolution AFM on a calibration grating with nm-step silicon carbide (SiC) terraces. In conclusion, measuring the Lorentzian response of the cantilever’s Brownian motion with the on-chip active sensor at resonance enables us to calibrate the dynamic stiffness at the first fundamental resonance mode, without utilizing an optical sensor.

47 OTHER INSTRUMENTATION↗
DOE OSTI2020

AFM Microcantilever With a Collocated AlN Sensor-Actuator Pair: Enabling Efficient Q-Control for Dynamic Imaging

This manuscript presents a novel microcantilever with an embedded piezoelectric sensor-actuator pair for dynamic atomic force microscopy (AFM). The transducer pair is constructed from a two-layered AlN stack. Stacking the piezoelectric transducers in this manner leads to a minimal feedthrough from actuation to sense electrode, granting a high dynamic range frequency response for dynamic mode AFM. The cantilever's design allows for dual mode operation at 1 st and 2 nd resonance modes. High resolution tapping mode imaging results are reported, while the cantilever is operated at these modes. A feedback control loop is used to modify quality factor of the 1 st mode of the cantilever, using a positive position feedback (PPF) controller. Here, a faster response time is achieved by reducing the Q-factor, enabling the cantilever to track the topography at a higher scan rate. Results of bimodal AFM imaging are reported, using amplitude changes of the 1 st mode for surface topography, while material properties are encoded in phase changes of the 2 nd mode.

47 OTHER INSTRUMENTATION↗
DOE OSTI2020

High Dynamic Range AFM Cantilever With a Collocated Piezoelectric Actuator-Sensor Pair

We present a novel approach to fundamentally eliminate electrical feedthrough (cross-talk) signal in self-sensing piezoelectric microcantilevers, used in dynamic mode atomic force microscopy (AFM). The probe is an Si microcantilever on which a two-layer piezoelectric stack transducer is microfabricated. The top transducer in the stack functions as an actuator, while the bottom transducer is used as a deflection sensor. This arrangement leads to a collocated actuator-sensor pair that co-exist on the same surface area. We report experimental results that establish the sensor's ability to capture the full dynamic range of the cantilever with minimal feedthrough from the actuator.

42 ENGINEERING↗
DOE OSTI2019

SOI-MEMS Bulk Piezoresistive Displacement Sensor: A Comparative Study of Readout Circuits

Performance of several readout circuits, when applied to a MEMS-based bulk piezoresistive displacement sensor is compared in this study. The sensor comprises a pair of tilted clamped-guided silicon beams whose bulk piezoresistivity is used for displacement sensing. Wheatstone half-bridge, constant-voltage, and constant-current circuits are implemented to measure resistance changes of this sensor. We report full characterization of the sensor with these circuits and explore the sensor’s important characteristics such as linearity, bandwidth, and noise. The results reveal that the constant-current circuit provides the highest sensitivity at equal-power bias condition. Here, we find that the resolution of the sensor is degraded from 1.6 nm with the Wheatstone half-bridge and constant-voltage circuits to about 4.2 nm with the constant-current configuration. In the frequency domain, the sensor captures the full dynamics of the MEMS nanopositioner up to 20 kHz with all readout circuits.

42 ENGINEERING↗