AFM-based techniques that rely on the excitation of surface ultrasonic vibration have already demonstrated their ability to render information about nanoscale dynamic materials properties such as elasticity, viscoelasticity, adhesion and friction [1]. In addition, the use of ultrasound may be advantageous in AFM-based nanofabrication procedures [2]. In Ultrasonic Force Microscopy (UFM), normal surface ultrasonic vibration is detected via the mechanical-diode effect [3]. Recently, the technique of Mechanical-Diode mode Ultrasonic Friction Force Microscopy (MD-UFFM) has been proposed based in the detection of a lateral mechanical-diode response when a tip in contact with a sample surface is scanning at low frequencies in the presence of shear ultrasonic vibration at the tip-sample contact [4]. The feasibility of implementing UFM in liquids was first reported in [5]. Recent experiments in our lab confirm the detection of ultrasonic-induced mechanical diode cantilever responses in liquid environments. Moreover, we have obtained reasonable UFM image contrast on samples of biological interest such as lipid bilayers [6]. In mechanical-diode mode ultrasonic AFM approaches, the cantilever motion does not follow the high-frequency excitation signal, but reacts to the time-averaged net-forces that actuate upon the tip when in contact with a vibrating sample surface. In the poster I will present our experimental data, analyze the main differences between ultrasonic-induced mechanical diode cantilever responses detected in air and liquid environments, and discuss the opportunities of the development of nanoscale ultrasonics in liquid media.
[1] "Nanoscale Friction and Ultrasonics", M. T. Cuberes in "Fundamentals of friction and wear on the nanoscale", E. Gnecco and E. Meyer (editors), Springer (2007).
[2] M. T. Cuberes, J. of Physics: Conf. Ser., Proceedings of ICN+T06 (May, 2007).
[3] O. Kolosov and K. Yamanaka, Jpn. J. Appl. Phys. 32, L1095 (1993).
[4] M. T. Cuberes and J. J. Martínez, J. of Physics: Conf. Ser., Proceedings of ICN+T07 (May, 2007).
[5] O. Kolosov, SXM3 Conference in Basel, Switzerland (14-17 September, 1998).
[6] Prepared in collaboration with M. Vélez, Instituto de Ciencia de Materiales Nicolás Cabrera, UAM, Spain.
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