(a) Scheme of the standard A-Probe: two discrete resonators, quartz TF, and U-shaped microfabricated cantilever are combined and form an oscillatory force sensor. The piezoelectricity of the quartz TF enables self-sensing and self-actuating of the probe. The spring constant of the A-Probe is determined by the cantilever. (b) A simplified model of the A-Probe. Two resonators are serially coupled. (c) The working principle. In-plane movements of the TF prongs are translated into the vertical motion of the silicon cantilever.
Micrograph of fabricated Si cantilevers before assembly with TFs. The inset sketches the conception of assembly. The TFs are individually placed in alignment grooves.
SEM pictures: (a) side view of the tip and (b) front view of the cantilever after the assembly.
(a) Top view of the assembled A-Probe. The dotted lines show the outlines of the metal pieces and the TF, respectively, (b) close up view of the cantilever, and (c) developed probe substrate (left), which can be plugged onto the kinematic mount of receptacle (right). It is kept in place by means of the small magnet, visible in the center of the receptacle.
Special holder with incorporated preamplifier electronics for mounting the A-Probe on a commercial AFM.
Electrical setup for dynamic mode AFM in the FM detection. The A-Probe is self-oscillated at its resonance. Changes in frequency are tracked by the PLL working in a passive mode. The electronics in the square with dotted lines is implemented on the special holder.
Characterization of the tip dynamics. (a) Optical measurement: tip vibration amplitude as a function of driving frequency from 10 kHz to 1 MHz and (b) optical (solid line) and electrical measurements (dashed and dotted lines) around the first resonance (in-phase peak) of A-Probe.
Approach-withdraw curves onto freshly cleaved HOPG surface: (top) optical measurement of the tip vibration during the approach phase, (middle) electronically measured frequency shift of the A-Probe and (bottom) normalized dissipation. The region between A and B indicates the periodic contact phase.
Frequency and amplitude response of the A-Probe to an applied small vibration of varying frequency (solid lines). The bare performance of the PLL (dotted lines) is also included for comparison. It can be seen that the performance of the probe is limited by the PLL.
Experimental setup for measuring an averaged effective loading force between the tip of an A-Probe and a sample in the periodic contact operation. A standard Si cantilever is “tapped” by the A-Probe mounted on the tube scanner of a standard AFM. From the deflection of the sensing cantilever, the loading force was estimated.
AFM images taken at ambient conditions in frequency detection mode: (a) electronic chip, (b) compact disk stamper, (c) carbon nanotubes, and (d) Si beads.
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