Noncontact Atomic Force Microscopy - Yale School of Engineering ...

Small amplitude atomic resolution NC-AFM imaging and force
spectroscopy experiments using a stiff piezoelectric force sensor
Stefan Torbrügge 1 , Jörg Rychen 2 , Oliver Schaff 1
1 SPECS GmbH, Voltastrasse 5, 13355 Berlin, Germany
2 SPECS Zurich GmbH, Technoparkstrasse 1, 8005 Zurich, Switzerland
Fr-0920
We present the design of the recently introduced KolibriSensor TM and its application to
frequency modulation atomic force microscopy. The KolibriSensor TM , schematically
shown in Fig. 1(a), is a new type of piezoelectric force sensor based on a quartz length
extension resonator (LER) [1]. Key features of the KolibriSensor TM are a high spring
constant (k~540,000 N/m), avoiding snap into contact when operated at small amplitudes,
and a large Q-factor exceeding 10,000 at room temperature. Its high resonance frequency
(fres~1 MHz) enables fast scanning and an excellent signal-to-noise ratio necessary for
stable operation at sub-nanometer oscillation amplitudes. In-situ sputtering enables
repeated sharpening of the separately contacted tungsten tip. Switching between AFM,
STM, or combined feedback modes is possible on the fly during measurement.
We demonstrate atomic resolution measurements on Si(111)-(7x7) and insulating
KBr(001), see Fig. 1(b), with oscillation amplitudes down to 30 pm at room temperature
and scanning speeds of several lines/s. Furthermore the performance of the sensor in
force spectroscopy experiments is evaluated by acquisition of two-dimensional force
maps measured on KBr(001) (see Fig. 1 (c)).
Figure 1: (a) Schematic drawing of the KolibriSensor TM . (b) Topographic atomic resolution NC-
AFM image of the KBr(001) surface recorded at room temperature. (c) Vertical tip-sample force
map F(x,z) derived from 20 Δf(z) curves taken along the line in the insert image in (c).
[1] T. An, et al. Appl. Phys. Lett., 88, 149903 (2006); T. An, et al., Rev. Sci. Instrum., 79, 033703 (2008)
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