Cumpson Peter J, Hedley John
Centre for Optical and Analytical Measurement (COAM), National Physical Laboratory, Teddington TW11 0LW, UK.
Nanotechnology. 2003 Dec;14(12):1279-88. doi: 10.1088/0957-4484/14/12/009. Epub 2003 Oct 28.
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 at nanoscale lateral resolution. We have developed a compact and easy-to-use reference artefact for this calibration, using a method that allows traceability to the SI (Système International). Traceability is crucial to ensure that force measurements by AFM are comparable to those made by optical tweezers and other methods. The new non-contact calibration method measures the spring constant of these artefacts, by a combination of electrical measurements and Doppler velocimetry. The device was fabricated by silicon surface micromachining. The device allows AFM cantilevers to be calibrated quite easily by the 'cantilever-on-reference' method, with our reference device having a spring constant uncertainty of around ± 5% at one standard deviation. A simple substitution of the analogue velocimeter used in this work with a digital model should reduce this uncertainty to around ± 2%. Both are significant improvements on current practice, and allow traceability to the SI for the first time at these nanonewton levels.
校准原子力显微镜（AFM）悬臂对于测量纳牛顿和皮牛顿力是必要的，这对于AFM在纳米级横向分辨率下分析聚合物表面、生物结构和有机分子的分析应用至关重要。我们已经开发出一种紧凑且易于使用的参考标准件用于这种校准，采用了一种能够溯源至国际单位制（SI）的方法。溯源对于确保AFM的力测量结果与光镊及其他方法所测得的结果具有可比性至关重要。这种新的非接触校准方法通过电学测量和多普勒测速法相结合来测量这些标准件的弹簧常数。该器件通过硅表面微加工制造而成。该器件能够通过“悬臂置于参考标准件上”的方法非常轻松地校准AFM悬臂，我们的参考标准件在一个标准偏差下弹簧常数的不确定度约为±5%。用数字模型简单替换本工作中使用的模拟测速仪应可将这种不确定度降低至约±2%。这两者都是对当前做法的重大改进，并且首次在这些纳牛顿量级上实现了溯源至国际单位制。
