Tip lenght influence on the shear force imaging in liquids

Valentinas Snitka 1Gediminas Seniunas 1Kestutis Nemciauskas 1Vida Mizariene 1Ingrida Bruzaite 2

1. Kaunas University of Technology, Research Center for Microsystems and Nanotechnology (RCMN KTU), Studentu 65 - 203, Kaunas 3031, Lithuania
2. Kaunas University of Technology, Deparment of Inorganic Chemistry, Radvilenu 19, Kaunas LT-50254, Lithuania

Abstract

Shear force near-field microscopy in liquid environment loses considerable sensitivity and resolution as a result of liquid viscous damping. The Q-control technique allows to increase significantly a quality factor (Q -factor) in water, without changing its intrinsic resonance frequency and spring constant. However, Q-control technique is quite expensive and complicated to incorporate into commercial instrumentation. In this work, we investigate the possibility to use a tuning-fork with a long (4mm ) tungsten tip to operate in liquid environments. We have investigated the damping of the tip oscillation as a function of its shape and as a function of its depth under the liquid surface. The degradation of the quality factor from 1300 in air down to 400 in contact with liquid was observed with a tip with diameter of 130 microns and the lenght 0.4 mm and down to 980 with the tip length 1.4 mm at the conventional 32.768 kHz tuning fork first overtone resonant frequency of ~ 190 kHz.The shear force between a glass, a biological cells sample and approaching near-field probe using tuning fork detection is studied in detail. The tuning-fork and a tip oscillation amplitude-frequency dependence in air and a tip in contact with surface were investigated using Finite Element Modelling and good agreement between experiment and theory have shown. Shear force imaging of silicon calibration gratings in liquid with a 1.2 mm long tip and a tuning-fork Q -factor of 460 have shown a high imaging sensitivity (30 nm) and stability. The tip diameter and the length variations allows to control the stiffness of the tip. To test whether the interaction forces are low enough to image soft biological material, a sample containing fixed MH22 hepatoma cells was prepared. The shear force image is comparable to an image obtained using tapping mode AFM in liquid with a silicon nitride cantilever with a spring constant of 0.10 N/m and a resonance frequency of 28 kHz at a similar scanning speed.

 

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Presentation: Poster at E-MRS Fall Meeting 2007, Symposium J, by Valentinas Snitka
See On-line Journal of E-MRS Fall Meeting 2007

Submitted: 2007-05-13 19:09
Revised:   2009-06-07 00:44