How important are calibration samples? How frequently should we use them?
Atomic Force Microscopy (AFM) is a versatile technique that allows researchers to explore and characterize surfaces at the nanoscale. However, to ensure accurate and reliable results, calibration of the AFM system is crucial. Calibration samples play a vital role in both troubleshooting unexpected imaging issues and achieving precise measurements. In this article, we discuss the significance of calibration samples, their various types, and the frequency of calibration.
Troubleshooting and System Validation
Calibration samples serve as valuable tools for troubleshooting unexpected results or imaging issues in AFM. By comparing the obtained imaging results with the known structure of calibration samples, researchers can identify if the problem lies with the sample preparation or the AFM system itself. Calibration gratings with well-defined structures are particularly useful for this purpose. Any deviations observed in the imaging results can indicate for example a system malfunction or miscalibration, prompting further investigation and adjustments.
Precise Measurements and Accuracy
Accurate calibration is essential for obtaining precise measurements in AFM. Various types of calibration samples are available, including some with certified dimensions. While certified calibration samples are more expensive, they offer higher accuracy and are well-suited for applications that demand the utmost precision. These samples provide a reliable reference to ensure the accuracy of the dimensions measured in AFM images.
During system calibration at the factory, certified calibration samples are typically used to directly calibrate the AFM scanner or to cross-validate the calibration obtained from interferometric measurements.
The frequency of system re-calibration depends on the AFM system and its design. For systems equipped with electromagnetic scanners, like Nanosurf’s FlexAFM, linearity is inherent, and aging effects are minimal. Such systems hardly require calibration in the field. Additionally, systems equipped with position sensors such as Nanosurf’s DriveAFM typically do not require calibration as the position feedback ensures accuracy.
However, AFM systems with open-loop piezo scanners may be susceptible to aging effects of the piezo material over time. In such cases, more frequent calibration or regular checks of calibration are recommended to maintain measurement accuracy. Understanding the specific requirements of your AFM system and consulting the manufacturer's guidelines will help determine the appropriate calibration frequency.
In summary, calibration samples play a critical role in AFM imaging and measurement accuracy. They provide valuable insights to troubleshoot unexpected results and serve as a benchmark for validating the performance of the AFM system. Calibration samples with certified dimensions offer higher accuracy, but whether or not to use them depends on the specific needs of the application in question.
For a deep dive on calibration, check out Session 6 of the Nanosurf AFM Master Class.
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