Golovko Dmytro S, Haschke Thomas, Wiechert Wolfgang, Bonaccurso Elmar
Max Planck Institute for Polymer Research, Ackermannweg 10, Mainz, Germany.
Rev Sci Instrum. 2007 Apr;78(4):043705. doi: 10.1063/1.2720727.
We present here an experimental setup and suggest an extension to the long existing added-mass method for the calibration of the spring constant of atomic force microscope cantilevers. Instead of measuring the resonance frequency shift that results from attaching particles of known masses to the end of cantilevers, we load them with water microdrops generated by a commercial inkjet dispenser. Such a device is capable of generating drops, and thus masses, of extremely reproducible size. This makes it an ideal tool for calibration tasks. Moreover, the major advantage of water microdrops is that they allow for a nearly contactless calibration: no mechanical micromanipulation of particles on cantilevers is required, neither for their deposition nor for removal. After some seconds the water drop is completely evaporated, and no residues are left on the cantilever surface or tip. We present two variants: we vary the size of the drops and deposit them at the free end of the cantilever, or we keep the size of the drops constant and vary their position along the cantilever. For the second variant, we implemented also numerical simulations. Spring constants measured by this method are comparable to results obtained by the thermal noise method, as we demonstrate for six different cantilevers.
我们在此展示一种实验装置，并建议对长期存在的用于校准原子力显微镜悬臂弹簧常数的附加质量法进行扩展。我们不是测量因将已知质量的颗粒附着到悬臂末端而导致的共振频率偏移，而是用商用喷墨打印机喷头产生的水微滴加载悬臂。这样的装置能够产生尺寸极具可重复性的液滴，进而产生质量极具可重复性的物体。这使其成为校准任务的理想工具。此外，水微滴的主要优点在于它们允许进行几乎无接触的校准：无论是液滴的沉积还是去除，都无需对悬臂上的颗粒进行机械微操作。几秒钟后，水滴完全蒸发，悬臂表面或尖端不会留下任何残留物。我们展示了两种变体：我们改变液滴大小并将它们沉积在悬臂的自由端，或者我们保持液滴大小不变并改变它们在悬臂上的位置。对于第二种变体，我们还进行了数值模拟。正如我们对六种不同悬臂所展示的那样，用这种方法测量的弹簧常数与通过热噪声法获得的结果相当。
