An alternative method to determining optical lever sensitivity in atomic force microscopy without tip-sample contact

Abstract

Force studies using atomic force microscopy generally require knowledge of the cantilever spring constants and the optical lever sensitivity. The traditional method of evaluating the optical lever sensitivity by pressing the tip against a hard surface can damage the tip, especially sharp ones. Here a method is shown to calculate the sensitivity without having to bring the tip into contact. Instead a sharpened tungsten wire is used to cause a point contact directly onto the cantilever and cause cantilever bending. Using beam theory, the sensitivity thus found can be converted to the equivalent sensitivity that would be obtained using the tip location. A comparison is presented between sensitivity values obtained from the conventional tip contact method and those derived from the wire-based technique for a range of cantilevers in air. It was found that the difference between the calculated sensitivity from the wire-based technique and the sensitivity obtained conventionally was less than 12%. These measurements indicate the presented method offers a simple alternative approach to obtain optical lever sensitivity without compromising the tip shape. KeywordsTungsten, Atomic force microscopy, Atomic force microscopes, Point contacts, Calibration, Bending, Materials analysis, Optical microscopes, Nanomaterials, Nanotechnology DisciplinesMechanical Engineering | Nanoscience and Nanotechnology CommentsThe following article appeared in Review of Scientific Instruments 81 (2010) Force studies using atomic force microscopy generally require knowledge of the cantilever spring constants and the optical lever sensitivity. The traditional method of evaluating the optical lever sensitivity by pressing the tip against a hard surface can damage the tip, especially sharp ones. Here a method is shown to calculate the sensitivity without having to bring the tip into contact. Instead a sharpened tungsten wire is used to cause a point contact directly onto the cantilever and cause cantilever bending. Using beam theory, the sensitivity thus found can be converted to the equivalent sensitivity that would be obtained using the tip location. A comparison is presented between sensitivity values obtained from the conventional tip contact method and those derived from the wire-based technique for a range of cantilevers in air. It was found that the difference between the calculated sensitivity from the wire-based technique and the sensitivity obtained conventionally was less than 12%. These measurements indicate the presented method offers a simple alternative approach to obtain optical lever sensitivity without compromising the tip shape.

Application of Ion Beam Processes to Scanning Probe Microscopy

“…The main disadvantage to this approach is that the tip must contact a hard surface, which often results in tip damage to some extent. There have been several methods reported in literature to eliminate the problem of tip-surface contact during deflection sensitivity measurements, although often at the cost of additional uncertainty [17,[20][21][22].…”

The Effect of Surface Inclination on AFM Force-Curve Calibration and Evaluation

“…1, right) [1]. Since it can damage the tip several efforts have been made to replace it with non-destructive methods [2][3][4], but these methods requires special tools.…”

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

“…The procedure bases on pressing the tip against rigid surface, while the response of the detector is acquired. Tourek et al presented the solution, basing on the sharpened tungsten wire, allowing to avoid the contact of the tip with the surface [134]. One has to be aware, that the changes of the support point of the cantilever has an impact on its bending, therefore the sensitivity at the location of the tip S a can be calculated from following formula:…”