Zurich Instruments Launches Dedicated AFM Features

Zurich Instruments offers support for additional high-end atomic force microscopy modes

Zurich Instruments the technology leader for lock-in amplifiers and phase-locked loops (PLL) has improved its application support for Atomic Force Microscopy, based on its world-class HF2 Series. Zurich Instruments has now added automatic gain control (AGC), Q-Control, and Kelvin probe feedback (KPF) support. Considering the large number of users publishing about these modes at low frequencies, Zurich Instruments offers new perspectives for the high-frequency range. Whereas existing AFM controllers are limited to a few MHz of frequency, the Zurich Instruments HF2PLL phase-locked loop provides AGC, KPF, and Q-Control for frequencies up to 50 MHz. This major step up in performance as a basis of new materials research, is available today for shipping and only from Zurich Instruments.

Automatic gain control permits closed-loop operation with constant amplitude, and is therefore useful for all applications that require a stable amplitude of the external resonator (e.g. MEMS, AFM cantilevers). The damping of resonators can vary significantly and this can cause uncontrolled excitation to lead to undesirable amplitudes, which may then result in unstable conditions. In order to avoid such conditions, the excitation signal must be controlled to keep the resonators at a defined amplitude. Implemented with a fully configurable proportional integral derivative (PID) controller inside the new HF2LI-PID Quad-PID option, the automatic gain control algorithm is preconfigured for optimal performance.

Kelvin probe feedback is used to simultaneously measure and compensate the electrostatic interaction between the cantilever tip and a conducting substrate with the topography scan. This permits the automatic cancellation of electrostatically induced height errors. This is obtained by modulating a voltage between the cantilever and the substrate, typically at a frequency well above the cut-off frequency of the Z-feedback controller, and therefore does not influence topography scanning. Technically this is performed by adding a controlled DC offset to the AC component. The DC offset is a direct measure of the work function and contact potential. KPF is supported by the HF2LI-PID Quad-PID option, which is equipped with 4 independent configurable PID controllers, capable of accommodating KPF mode at the same time as with 3 other control loops.

Q-Control allows the tuning of the effective Q-factor of a resonator driven by the HF2LI. Q-Increase introduces a positive feedback to the resonator, which reduces the damping of cantilevers and thus increases the effective quality factor. Particularly when operated in air or liquids, Q-control increases the resolution of imaging obtained in AFM tapping mode, it improves the sensitivity in MFM (magnetic force microscopy) and EFM (electrostatic force microscopy) modes while at the same time reducing the contact forces exerted on the sample. Q-Increase allows the imaging of sensitive structures and prevents their damage. Q-Decrease increases the damping of the cantilever by the introduction of a negative feedback. Particularly in high-vacuum conditions with very high Q this effect increases the maximum scanning speed, as the cantilever is less prone to continue oscillating in previously excited frequencies. Q-Control is going to be added to the existing HF2LI-PLL Dual PLL option. Existing PLL customers of Zurich Instruments will be automatically upgraded.

Technology leader Zurich Instruments (ZI) designs and manufactures high performance dynamic signal analysis instruments for advanced scientific research and high-end industrial applications. ZI products include lock-in amplifiers, phase-locked loops, instruments for electrical impedance spectroscopy, and application specific pre-amplifiers. Headquartered in Zurich, Switzerland, ZI was established in 2008. ZI customers are scientists and engineers in leading research labs and organizations worldwide. Zurich Instruments: Your Application. Measured

call +41 44 515 04 10
or leave us a message.

To help with your request and to comply with data protection legislation we will need to confirm that you agree for us to collect and use your personal data:

See here for details of the data that we hold on our customers and what we do with it. If you have any questions please contact privacy@zhinst.com