Dr Michael Ruppert

© 2017 Author(s). The quality (Q) factor is an important parameter of the resonance of the microcantilever as it determines both imaging bandwidth and force sensitivity. The ability to control the Q factor of multiple modes is believed to be of great benefit for atomic force microscopy techniques involving multiple eigenmodes. In this paper, we propose a novel cantilever design employing multiple piezoelectric transducers which are used for separated actuation and sensing, leading to guaranteed collocation of the first eight eigenmodes up to 3 MHz. The design minimizes the feedthrough usually observed with these systems by incorporating a guard trace on the cantilever chip. As a result, a multimode Q controller is demonstrated to be able to modify the quality factor of the first two eigenmodes over up to four orders of magnitude without sacrificing robust stability.

© 2015 IEEE. A fundamental challenge in dynamic mode atomic force microscopy (AFM) is the estimation of the cantilever oscillation amplitude from the deflection signal, which might be distorted by noise and/or high-frequency components. When the cantilever is excited at resonance, its deflection is typically obtained via narrow-band demodulation using a lock-in amplifier (LIA). However, the bandwidth of this measurement technique is ultimately bounded by the low-pass filter, which must be employed after demodulation to attenuate the component at twice the carrier frequency. Furthermore, to measure the amplitude of multiple frequency components, such as higher eigenmodes and/or higher harmonics in multifrequency AFM, multiple LIAs must be employed. In this paper, the authors propose the estimation of amplitude and phase using a linear time-varying Kalman filter that is easily extended to multiple frequencies. Experimental results are obtained using square-modulated sine waves and closed-loop AFM scans, verifying the performance of the proposed Kalman filter.

© 2016 Ruppert and Moheimani; licensee Beilstein-Institut. License and terms: see end of document. Using standard microelectromechanical system (MEMS) processes to coat a microcantilever with a piezoelectric layer results in a versatile transducer with inherent self-sensing capabilities. For applications in multifrequency atomic force microscopy (MF-AFM), we illustrate that a single piezoelectric layer can be simultaneously used for multimode excitation and detection of the cantilever deflection. This is achieved by a charge sensor with a bandwidth of 10 MHz and dual feedthrough cancellation to recover the resonant modes that are heavily buried in feedthrough originating from the piezoelectric capacitance. The setup enables the omission of the commonly used piezoelectric stack actuator and optical beam deflection sensor, alleviating limitations due to distorted frequency responses and instrumentation cost, respectively. The proposed method benefits from a more than two orders of magnitude increase in deflection to strain sensitivity on the fifth eigenmode leading to a remarkable signal-to-noise ratio. Experimental results using bimodal AFM imaging on a two component polymer sample validate that the self-sensing scheme can therefore be used to provide both the feedback signal, for topography imaging on the fundamental mode, and phase imaging on the higher eigenmode.

© 2002-2012 IEEE. We present new insights into the modeling of the microcantilever in dynamic mode atomic force microscopy and outline a novel high-bandwidth tip-sample force estimation technique for the development of high-bandwidth z -axis control. Fundamental to the proposed technique is the assumption that in tapping mode atomic force microscopy, the tip-sample force takes the form of an impulse train. Formulating the estimation problem as a Kalman filter, the tip-sample force is estimated directly; thus, potentially enabling high-bandwidth z-axis control by eliminating the dependence of the control technique on microcantilever dynamics and the amplitude demodulation technique. Application of this technique requires accurate knowledge of the models of the microcantilever; a novel identification method is proposed. Experimental data are used in an offline analysis for verification.

© IFAC. We evaluate two novel reciprocal self-sensing methods for tapping-mode atomic force microscopy (TM-AFM) utilizing charge measurement and charge actuation, respectively. A microcantilever, which can be batch fabricated through a standard microelectromechanical system (MEMS) process, is coated with a single piezoelectric layer and simultaneously used for actuation and deflection sensing. The setup enables the elimination of the optical beam deflection technique which is commonly used to measure the cantilever oscillation amplitude. The voltage to charge and charge to voltage transfer functions reveal a high amount of capacitive feedthrough which degrades the dynamic range of the sensors significantly. A feedforward control technique is employed to cancel the feedthrough and increase the dynamic range from less than 1dB to approximately 30 dB. Experiments show that the conditioned self-sensing schemes achieve an excellent signal-to-noise ratio and can therefore be used to provide the feedback signal for TM-AFM imaging.