Enhanced quality factors and force sensitivity by attaching magnetic beads to cantilevers for atomic force microscopy in liquid

TL;DR

Attaching magnetic beads to AFM cantilevers in liquid significantly enhances their quality factor and force sensitivity, enabling better performance in dynamic-mode atomic force microscopy despite increased mass and lowered resonance frequency.

Contribution

This work demonstrates a simple method to improve AFM performance in liquid by attaching magnetic beads, increasing quality factor without compromising force sensitivity.

Findings

High-quality resonance (Q>20) achieved in liquid with attached beads

Force sensitivity remains nearly unchanged despite increased mass

Enhanced signal-to-noise ratio due to reduced detector noise impact

Abstract

Dynamic-mode atomic force microscopy (AFM) in liquid remains complicated due to the strong viscous damping of the cantilever resonance. Here we show that a high-quality resonance (Q>20) can be achieved in aqueous solution by attaching a microgram-bead at the end of the nanogram-cantilever. The resulting increase in cantilever mass causes the resonance frequency to drop significantly. However, the force sensitivity --- as expressed via the minimum detectable force gradient --- is hardly affected, because of the enhanced quality factor. Via the enhancement of the quality factor, the attached bead also reduces the relative importance of noise in the deflection detector. It can thus yield an improved signal-to-noise ratio when this detector noise is significant. We describe and analyze these effects for a set-up which includes magnetic actuation of the cantilevers and which can be easily implemented in any AFM system that is compatible with an inverted optical microscope.