title: Fast amplitude modulation detector for scanning force microscopy with high Q factor.
abstract: Amplitude modulation (AM) scanning force microscopy (SFM) is superior to frequency modulation SFM in simplicity, sensitivity, and stability, but is still replaced by the latter because it is too slow when the Q factor is high (bandwidth < 0.5 Hz for Q > 50,000 and resonant frequency ω0 < 50 kHz). We report a close-loop AM detector that has an 18 Hz bandwidth, better than 1 mHz frequency resolution and excellent response to step frequency changes even for Q ∼ 60,000 and ω0 ∼ 32 kHz. Its superiority is well shown by the comparison of magnetic force microscope images taken under the new and old AM detection modes with the tip and scan area (videotape sample) being unchanged. Also important is that shifting the driving frequency from near the resonance peak to further away from the peak does not decrease the frequency resolution as much as we expect (but can increase the response speed).
authors.affiliation: Hefei National Laboratory for Physical Sciences at Microscale, University of Science and Technology of China, Hefei, Anhui 230026, People's Republic of China.
authors.forename: Yizhi
authors.initials: Y
authors.lastname: Shi
authors.forename: Qingyou
authors.initials: Q
authors.lastname: Lu