JILA, National Institute of Standards and Technology and University of Colorado, Boulder, Colorado 80309, United States.
Nano Lett. 2012 Jul 11;12(7):3557-61. doi: 10.1021/nl301166w. Epub 2012 Jun 15.
Force drift is a significant, yet unresolved, problem in atomic force microscopy (AFM). We show that the primary source of force drift for a popular class of cantilevers is their gold coating, even though they are coated on both sides to minimize drift. Drift of the zero-force position of the cantilever was reduced from 900 nm for gold-coated cantilevers to 70 nm (N = 10; rms) for uncoated cantilevers over the first 2 h after wetting the tip; a majority of these uncoated cantilevers (60%) showed significantly less drift (12 nm, rms). Removing the gold also led to ∼10-fold reduction in reflected light, yet short-term (0.1-10 s) force precision improved. Moreover, improved force precision did not require extended settling; most of the cantilevers tested (9 out of 15) achieved sub-pN force precision (0.54 ± 0.02 pN) over a broad bandwidth (0.01-10 Hz) just 30 min after loading. Finally, this precision was maintained while stretching DNA. Hence, removing gold enables both routine and timely access to sub-pN force precision in liquid over extended periods (100 s). We expect that many current and future applications of AFM can immediately benefit from these improvements in force stability and precision.
力漂移是原子力显微镜（AFM）中一个重要但尚未解决的问题。我们表明，对于一类流行的悬臂梁，力漂移的主要来源是它们的金涂层，尽管它们的两面都涂有涂层以最小化漂移。在润湿尖端后的头 2 小时内，金涂层悬臂梁的零力位置漂移从 900nm 降低到 70nm（N=10；rms）；大多数未涂层的悬臂梁（60%）显示出明显更小的漂移（12nm，rms）。去除金涂层还导致反射光减少了约 10 倍，但短期（0.1-10 秒）力精度提高了。此外，力精度的提高并不需要延长稳定时间；大多数测试的悬臂梁（15 个中的 9 个）在加载后 30 分钟内实现了亚皮牛（0.54±0.02pN）的力精度（0.54±0.02pN），在较宽的带宽（0.01-10Hz）内。最后，在拉伸 DNA 时保持了这种精度。因此，去除金可以在较长时间内（100 秒）在液体中实现常规且及时的亚皮牛力精度。我们预计，AFM 的许多当前和未来应用将立即受益于这些力稳定性和精度的改进。
