Noncontact Scanning Force Microscopy – a Computer Simulation of Resolution Limits

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As generally known, in the noncontact mode the changes of effective resonance frequency of a cantilever with the tip-surface distance are used for imaging solid surfaces. For a long time, van der Waals attractive forces between atoms of the tip and surface atoms [1] had been considered to have a decisive influence for making a contrast in images taken by the noncontact mode of SFM. However, very recently the true atomic resolution on several surfaces by means of the noncontact UHV SFM have been obtained (e.g. Si, GaAs, InP, NaCl). This gives rise to questions if the long-range van der Waals forces themselves are capable to provide such an atomic resolution or if some additional short-range forces due to an onset of covalent bonds between atoms of the tip and surface atoms should not be taken into account as well. In [2] the true atomic resolution of the noncontact SFM is explained only by means of the long-range van der Waals forces and by nonlinear oscillations of the cantilever. However, most of the authors [3 – 4] claim that only the addition of short-range forces can provide the true atomic resolution. In our contribution we have studied the influence of attractive and repulsive forces on effective resonance frequency of vibrations of cantilever by numerical simulation. From these studies the principles of noncontact SFM can be understood and its resolution limits estimated.

As generally known, in the noncontact mode the changes of effective resonance frequency of a cantilever with the tip-surface distance are used for imaging solid surfaces. For a long time, van der Waals attractive forces between atoms of the tip and surface atoms [1] had been considered to have a decisive influence for making a contrast in images taken by the noncontact mode of SFM. However, very recently the true atomic resolution on several surfaces by means of the noncontact UHV SFM have been obtained (e.g. Si, GaAs, InP, NaCl). This gives rise to questions if the long-range van der Waals forces themselves are capable to provide such an atomic resolution or if some additional short-range forces due to an onset of covalent bonds between atoms of the tip and surface atoms should not be taken into account as well. In [2] the true atomic resolution of the noncontact SFM is explained only by means of the long-range van der Waals forces and by nonlinear oscillations of the cantilever. However, most of the authors [3 – 4] claim that only the addition of short-range forces can provide the true atomic resolution. In our contribution we have studied the influence of attractive and repulsive forces on effective resonance frequency of vibrations of cantilever by numerical simulation. From these studies the principles of noncontact SFM can be understood and its resolution limits estimated.

AFM, cantiliever vibrations, non-contact mode.

2001

30.09.2001

P. Marcus, A. Galtayries, N. Frémy

Avignon, France

9th European Conference on Applications of Surface and Interface Analysis (ECASIA'01) Book of Abstracts

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