An easy-to-use non-optical shear-force distance control for near-field optical microscopes

Abstract

We present an easy-to-use non-optical shear-force detection system for tip–sample distance control in scanning near-field optical microscopes. The fibre tip is fixed in a four-segmented piezo-tube by a polymer, Polyisobutylene, which couples the tip stiffly to the piezo at frequencies of 10 kHz or more at room temperature. One segment of the piezo-tube excites the fibre tip in resonance, while the other three segments detect the tip vibration in the manner of a piezo-microphone. When the tip is damped by shear forces the induced voltage at the three segments changes and can easily be detected with a lock-in amplifier. Further our method allows a fast and reproducible tip exchange with minor adjustments of mechanical or electrical components. We demonstrate the performance of our distance control on a holographically fabricated line pattern with 417 nm lattice spacing and 10 nm height. A height resolution of better than 1 nm is demonstrated.

Friction and Molecular Deformation in the Tensile Regime

“…The fiber typically has a mechanical resonance at 25-50 kHz, depending on the length, a typical Q factor of 100, and a lateral motion amplitude determined by A piezo Q, where A piezo is the sinusoidal piezodrive amplitude [11]. Detection of fiber motion is accomplished by monitoring induced voltages on the drive piezo [12]. Although tip amplitudes ø1 nm can be detected, we use ϳ12 nm.…”

Tuning fork shear-force feedback

“…These techniques have the disadvantage that additional stray light is brought into the vicinity of the aperture, disturbing the measurement of the near-field optical signal; moreover, accurate alignment of the external optics with respect to the probe is necessary. An alternative method is to use piezoelectric materials which generate a piezoelectric voltage proportional to the amplitude of the oscillation [4][5][6][7]. Based on this idea, the use of crystalline quartz tuning forks for detecting the probe's amplitude was demonstrated recently by Karraı¨ [4].…”

Optical Microscopy via Spectral Modifications of a Nanoantenna

“…This sample was placed on a 3D piezoelectric scanner, mounted on an inverted microscope. A home-made SNOM stage was used to position the tip and to stabilize its distance from the sample to about 5-10 nm via shear-force feedback [13]. Figure 2a shows the shear-force topography image recorded when the sample was scanned under the gold nanoparticle probe, whereas the inset displays a cross section along cut (ii) (see Fig.…”