Quantitative analytical atomic force microscopy: a cantilever reference device for easy and accurate AFM spring-constant calibration

Abstract

Calibration of atomic force microscope (AFM) cantilevers is necessary for the measurement of nanonewton and piconewton forces, which are critical to analytical applications of AFM in the analysis of polymer surfaces, biological structures and organic molecules. We have developed a compact and easy-to-use reference artefact for this calibration by bulk micromachining of silicon, which we call a cantilever microfabricated array of reference springs (C-MARS). Two separate reference cantilever structures, each nominally 3 µm thick, are fabricated from a single crystal silicon membrane. A binary code of surface oxide squares (easily visible in light, electron and atomic force microscopy) makes it easy to locate the position of the AFM tip along the length of the cantilevers. Uncertainty in location is the main source of error when calibrating an AFM using reference cantilevers, especially for those having spring constants greater than around 10 N m −1. This error is effectively eliminated in our new design. The C-MARS device spans the range of spring constants from 25 N m −1 down to 0.03 N m −1 important in AFM, allowing almost any contact-mode AFM cantilever to be calibrated easily and rapidly.

SI-Traceable Spring Constant Calibration of Microfabricated Cantilevers for Small Force Measurement

“…The cantilever under test was the cantilever microfabricated array of reference springs (CMARS) [15]. Designed specifically for the purpose of spring constant calibration, it was fabricated from polycrystalline silicon and is approximately 1,600-2m long, 150-2m wide and 3-2m thick.…”

“…Typically, the passive transducer is an auxiliary cantilever with a known spring constant. If a test cantilever is pressed against a reference cantilever, measuring the deflection signal of the test cantilever allows the determination of its k [15,16]. Generally, the cantilever under test is displaced in a direction normal to the surface of the reference cantilever, and its deflection is monitored with the optical lever configuration typical of AFM.…”

Atomic force microscope probe calibration by use of a commercial precision balance

“…Therefore, more convenient, non-destructive, and fast methods have been introduced by using artifacts (or references) for force calibration. Precalibrated cantilevers [6][7][8] and specially designed reference springs [9][10] give not only ease-of-use but also high calibration accuracy. However these methods need "reference" or "precalibrated artifacts."…”

Quantitative Normal Force Measurements by Means of Atomic Force Microscopy Towards the Accurate and Easy Spring Constant Determination

“…Cumpson et al developed the 1.6 mm long and 150 µm wide cantilever designed specifically for the standard transfer [133]. The specific features of C-MARS (cantilever microfabricated array of reference springs) allowed to place calibrated probe at specific positions due to the presence of binary markers along the C-MARS.…”