Research and monitoring of surface
properties with nano-scale resolution

FEATURES

Main features of NanoScan

NanoScan is a scanning force microscope that works in a regime of rigid contact and does not require vacuum. The main characteristic feature of NanoScan is the use of piezoresonance probe having high bending stiffness of the cantilever (patented). Use of the regime of resonance oscillations permits to perform checking of contact between the probe tip and the surface on two parameters: change of amplitude A and frequency F of the probe oscillations. This makes it possible to discriminate correspondingly viscous and elastic components of the tip-surface interaction, and distinguish an elastic surface and a viscous contamination layer on it, appearing inevitably in an open space, as well as to measure mechanical properties of surfaces. High bending stiffness of the cantilever permits to go through the viscous layer and contact the elastic surface, making an indentation. The probe construction allows to use various tips, such as standard tips for SPM, and unusual for SPM diamond indenters of various types. Our company offers tips made of ultrahard fullerite C₆₀ (patented) which is harder than diamond. The hardness measurements of superhard materials, including diamond, are possible with use of these tips. The listed above functional capabilities present dramatic distinctions between NanoScan and the presently existing commercial apparatus.

Operation modes of NanoScan

NanoScan Measurement System allows to carry out the Topography measurements and the Measurements of maps of surface mechanical properties at the same surface area. It gives a possibility to find the correspondence between topography and distribution of mechanical properties. Moreover, NanoScan allows to execute loading and scratching of the surface by the probe tip and make Hardness measurements (Indentation and Sclerometry).

1.1 Topography measurements
Topography measurements are carried out by line-to-line scanning of a surface area with recording of a feedback signal. Two quantities serve as the measured signals: A presents the difference between the amplitude of free oscillations A₀ of the probe and the amplitude of stationary oscillations while the contact with the surface A_c; and F presents the difference between the frequencies F₀ and F_c of the same two kinds of oscillations (Fig. 1). The given values of the measured signals A or F, accordingly A_ref or F_ref, are kept constant by the feedback. With feedback based on different A or F quantities, the obtained images of the same area of surface have different meanings (Fig. 2). The viscous surface relief is scanned with feedback on A. The elastic surface relief is scanned with feedback on F. The scanning mode with feedback on F is especially effective when scanning very dirty surfaces. An increase of A_ref and F_ref makes the tip-surface contact stronger and decreases the influence of the surface pollution on the measured topography. A decrease of A_ref and F_ref makes the strength applied to the surface to diminish and lowers the probability of its destruction.

Fig. 1

Fig. 2

1.2 Measurement of maps of surface mechanical properties
This measurement is performed by line-to-line scanning of the surface area with feedback on one of the parameters and recording the other one.

Fig. 3 illustrates the scanning with feedback on A and recording the F signal. The local elasticity E_A of the area of the tip-surface interaction at point A is greater than E_B at point B, hence, the value F_A of the frequency shift signal F at point A is less than F_B (the signal at point B).

Fig. 3

- the volume of material having local elasticity E_A, involved into interaction with the probe tip.

Fig. 4 illustrates scanning with feedback on F and recording the A signal. The local elasticity h_A of the tip-surface interaction area at point A is less than the value h_B at point B, hence, the value A_A of the signal amplitude at point A is less than A_B (the value at point B).

Fig. 4

- the volume of material having viscosity h involved into interaction with the probe tip.

The described above examples of measurement of mechanical property maps are used to evaluate the mutual disposition of viscous material (e.g. dirt) and an elastic surface.

Another variant of measurement of mechanical property maps which is described below serves to investigate the structure of a surface whose mechanical properties (moduli of elasticity and of viscosity) vary from point to point.

Fig. 5 illustrates scanning with feedback on A and recording the F signal. Here the given feedback reference value A_ref is enough for the tip to reach the elastic surface through the viscous layer. The local elasticity x_A of the tip-surface interaction area at point A is less than the values x_B and x_C at points B and C. Hence, the values of the frequency shift signal F at points B and C (F_B and F_C) are greater than F_A (the F value at point A).

Fig. 5

- The surface area having greater elasticity.

This measurement regime permits to distinguish the surface areas with different mechanical properties, e.g. in the case of heterophasic materials.

1.3 Hardness measurements (Indentation and sclerometry)
Due to high bend stiffness of the probe cantilever and use of tips of hard materials, NanoScan gives a possibility to scratch and to indent the surface. Indentation is performed by means of increasing the load on the tip at certain point of the surface (Fig. 6). For scratching, analogous loading is performed, and then the indenter is horizontally moved under the load. The size of the print or scratch is determined by means of scanning of the relief before and after indentation.

Fig. 6

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