A simple method for the determination of qPlus sensor spring constants

John Melcher, Julian Stirling, Gordon A Shaw

Research output: Contribution to journalArticlepeer-review

14 Citations (SciVal)


qPlus sensors are widely used to measure forces at the atomic scale, however, confidence in these measurements is limited by inconsistent reports of the spring constant of the sensor and complications from finite tip heights. Here we combine a numerical investigation of the force reconstruction with an experimental characterization of the flexural mechanics of the qPlus sensor. Numerical studies reveal significant errors in reconstructed force for tip heights exceeding 400 μm or one sixth of the cantilever length. Experimental results with a calibrated nanoindenter reveal excellent agreement with an Euler–Bernoulli beam model for the sensor. Prior to the attachment of a tip, measured spring constants of 1902 ± 29 N/m are found to be in agreement with theoretical predictions for the geometry and material properties of the sensor once a peaked ridge in the beam cross section is included. We further develop a correction necessary to adjust the spring constant for the size and placement of the tip.
Original languageEnglish
Pages (from-to)1733
Number of pages1
JournalBeilstein Journal of Nanotechnology
Publication statusPublished - 14 Aug 2015


  • atomic force microscopy
  • calibration
  • non-contact atomic force microscopy


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