Development of liquid-environment frequency modulation atomic force microscope with low noise deflection sensor for cantilevers of various dimensions

TLDR

An accurate equation for the theoretical limit of optical beam deflection in air and liquid is presented. The study develops a liquid‑environment FM‑AFM with a low‑noise deflection sensor for cantilevers of various dimensions. The system uses replaceable objective lenses for high‑magnification optical detection and a ~10 µm laser spot, and the sensor is designed from the theoretical limit equation. The sensor achieves deflection noise densities below 11 fm/Hz in air and 16 fm/Hz in water across cantilevers 35–125 µm, reaching a minimum of 5.7 fm/Hz in air and 7.3 fm/Hz in water for a 50 µm cantilever, and enables true atomic resolution imaging of mica in water.

Abstract

We have developed a liquid-environment frequency modulation atomic force microscope (FM-AFM) with a low noise deflection sensor for a wide range of cantilevers with different dimensions. A simple yet accurate equation describing the theoretical limit of the optical beam deflection method in air and liquid is presented. Based on the equation, we have designed a low noise deflection sensor. Replaceable microscope objective lenses are utilized for providing a high magnification optical view (resolution: <3μm) as well as for focusing a laser beam (laser spot size: ∼10μm). Even for a broad range of cantilevers with lengths from 35to125μm, the sensor provides deflection noise densities of less than 11fm∕Hz in air and 16fm∕Hz in water. In particular, a cantilever with a length of 50μm gives the minimum deflection noise density of 5.7fm∕Hz in air and 7.3fm∕Hz in water. True atomic resolution of the developed FM-AFM is demonstrated by imaging mica in water.