Novel amplitude and frequency demodulation algorithm for a virtual dynamic atomic force microscope

Frequency-modulated atomic force microscopy (FM-AFM; also called non-contact atomic force microscopy) is the prevailing operation mode in (sub-)atomic resolution vacuum applications. A major obstacle that prohibits a wider application range is the low frame capture rate. The speed of FM-AFM is limited by the low bandwidth of the automatic gain control (AGC) and frequency demodulation loops. In this work we describe a novel algorithm that can be used to overcome these weaknesses. We analysed the settling times of the proposed loops and that of the complete system, and we found that an approximately 70-fold improvement can be achieved over the existing real and virtual atomic force microscopes. We show that proportional-integral-differential controllers perform better in the frequency demodulation loop than conventional proportional-integral controllers. We demonstrate that the signal to noise ratio of the proposed system is 5.7 × 10(-5), which agrees with that of the conventional systems; thus, the new algorithm would improve the performance of FM-AFMs without compromising the resolution.

[1]  T. Ando,et al.  A high-speed atomic force microscope for studying biological macromolecules , 2001, Proceedings of the National Academy of Sciences of the United States of America.

[2]  T. Ando,et al.  A high-speed atomic force microscope for studying biological macromolecules in action. , 2003, Chemphyschem : a European journal of chemical physics and physical chemistry.

[3]  Zoltan L. Horvath,et al.  Dynamical properties of the Q-controlled atomic force microscope , 2004 .

[4]  B. Gotsmann,et al.  Determination of tip-sample interaction forces from measured dynamic force spectroscopy curves , 1999 .

[5]  Javier Tamayo,et al.  Active quality factor control in liquids for force spectroscopy , 2000 .

[6]  Jerome Mertz,et al.  Regulation of a microcantilever response by force feedback , 1993 .

[7]  J. Salardenne,et al.  A virtual non contact-atomic force microscope (NC-AFM): Simulation and comparison with analytical models , 2001 .

[8]  B. Gotsmann,et al.  Measurement of conservative and dissipative tip-sample interaction forces with a dynamic force microscope using the frequency modulation technique , 2001 .

[9]  Michel Gauthier,et al.  Interplay between nonlinearity, scan speed, damping, and electronics in frequency modulation atomic-force microscopy. , 2002, Physical review letters.

[10]  Sébastien Gauthier,et al.  A virtual dynamic atomic force microscope for image calculations , 2005 .

[11]  D. Rugar,et al.  Frequency modulation detection using high‐Q cantilevers for enhanced force microscope sensitivity , 1991 .

[12]  Seizo Morita,et al.  Mechanical vertical manipulation of selected single atoms by soft nanoindentation using near contact atomic force microscopy. , 2003, Physical review letters.

[13]  M. Stark,et al.  Fast low-cost phase detection setup for tapping-mode atomic force microscopy , 1999 .

[14]  Dynamics of the cantilever in noncontact dynamic force microscopy: The steady-state approximation and beyond , 2001 .

[15]  H. Güntherodt,et al.  Quantitative Measurement of Short-Range Chemical Bonding Forces , 2001, Science.

[16]  A. Shluger,et al.  Unambiguous interpretation of atomically resolved force microscopy images of an insulator. , 2001, Physical review letters.

[17]  Franz J. Giessibl,et al.  Advances in atomic force microscopy , 2003, cond-mat/0305119.

[18]  L. Nony,et al.  Nonlinear dynamical properties of an oscillating tip–cantilever system in the tapping mode , 1999, physics/0510099.