Antognozzi M, Ulcinas A, Picco L, Simpson S H, Heard P J, Szczelkun M D, Brenner B, Miles M J
H H Wills Physics Laboratory, University of Bristol, Tyndall Avenue, Bristol BS8 1TL, UK.
Nanotechnology. 2008 Sep 24;19(38):384002. doi: 10.1088/0957-4484/19/38/384002. Epub 2008 Aug 12.
Detection techniques currently used in scanning force microscopy impose limitations on the geometrical dimensions of the probes and, as a consequence, on their force sensitivity and temporal response. A new technique, based on scattered evanescent electromagnetic waves (SEW), is presented here that can detect the displacement of the extreme end of a vertically mounted cantilever. The resolution of this method is tested using different cantilever sizes and a theoretical model is developed to maximize the detection sensitivity. The applications presented here clearly show that the SEW detection system enables the use of force sensors with sub-micron size, opening new possibilities in the investigation of biomolecular systems and high speed imaging. Two types of cantilevers were successfully tested: a high force sensitivity lever with a spring constant of 0.17 pN nm(-1) and a resonant frequency of 32 kHz; and a high speed lever with a spring constant of 50 pN nm(-1) and a resonant frequency of 1.8 MHz. Both these force sensors were fabricated by modifying commercial microcantilevers in a focused ion beam system. It is important to emphasize that these modified cantilevers could not be detected by the conventional optical detection system used in commercial atomic force microscopes.
目前扫描力显微镜中使用的检测技术对探针的几何尺寸施加了限制，因此也对其力灵敏度和时间响应施加了限制。本文提出了一种基于散射倏逝电磁波（SEW）的新技术，该技术可以检测垂直安装的悬臂梁末端的位移。使用不同尺寸的悬臂梁测试了该方法的分辨率，并建立了一个理论模型以最大化检测灵敏度。本文介绍的应用清楚地表明，SEW检测系统能够使用亚微米尺寸的力传感器，为生物分子系统研究和高速成像开辟了新的可能性。成功测试了两种类型的悬臂梁：一种是弹簧常数为0.17 pN nm⁻¹、共振频率为32 kHz的高力灵敏度悬臂梁；另一种是弹簧常数为50 pN nm⁻¹、共振频率为1.8 MHz的高速悬臂梁。这两种力传感器都是通过在聚焦离子束系统中对商用微悬臂梁进行改性制备的。需要强调的是，商用原子力显微镜中使用的传统光学检测系统无法检测这些改性后的悬臂梁。
