Comparison of force sensors for atomic force microscopy based on quartz tuning forks and length-extensional resonators
Comparison of force sensors for atomic force microscopy based on quartz tuning forks and length-extensional resonators
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DOI：
10.1103/physrevb.84.125409
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发表时间：
2011-09-06
影响因子：
3.7
通讯作者：
Hasegawa, Yukio
中科院分区：
文献类型：
--
作者：
Giessibl, Franz J.;Pielmeier, Florian;Hasegawa, Yukio
力传感器是影响原子力显微镜（AFM）性能的关键。如今，大多数原子力显微镜使用由硅制成的微机械力传感器，但压电石英传感器的应用率越来越高，主要是在真空中。这些自感知力传感器允许相对容易地将扫描隧道显微镜升级为组合的扫描隧道/原子力显微镜。两种完全不同类型的石英传感器已经实现了原子分辨率：基于长度延伸谐振器的“针传感器”和基于音叉的“qPlus传感器”。在这里，我们计算和测量这些传感器的噪声特性。我们发现四个噪声源：偏转探测器噪声，热噪声，振荡器噪声，和热漂移噪声。我们计算这些噪声源作为传感器刚度，带宽和振荡幅度的一个因素的影响。我们发现，对于自感知石英传感器，偏转检测器的噪声是独立的传感器刚度，而其余三个噪声源增加强烈与传感器刚度。偏转检测器噪声随带宽增加到1.5次幂，而热噪声和振荡器噪声与带宽的平方根成比例。然而，热漂移噪声与带宽成反比。前三个噪声源与幅度成反比，而热漂移噪声与幅度无关。因此，我们表明，早期的发现，引用了一个最佳的信号-噪声比的振荡幅度类似的范围内的力量仍然是正确的，当考虑所有四个频率的噪声贡献。最后，我们提出了如何进一步提高传感器的信噪比，我们简要讨论了安装提示的挑战，我们比较了自感知石英传感器和光学检测的硅晶体管的噪声性能。
The force sensor is key to the performance of atomic force microscopy (AFM). Nowadays, most atomic force microscopes use micromachined force sensors made from silicon, but piezoelectric quartz sensors are being applied at an increasing rate, mainly in vacuum. These self-sensing force sensors allow a relatively easy upgrade of a scanning tunneling microscope to a combined scanning tunneling/atomic force microscope. Two fundamentally different types of quartz sensors have achieved atomic resolution: the "needle sensor," which is based on a length-extensional resonator, and the "qPlus sensor," which is based on a tuning fork. Here, we calculate and measure the noise characteristics of these sensors. We find four noise sources: deflection detector noise, thermal noise, oscillator noise, and thermal drift noise. We calculate the effect of these noise sources as a factor of sensor stiffness, bandwidth, and oscillation amplitude. We find that for self-sensing quartz sensors, the deflection detector noise is independent of sensor stiffness, while the remaining three noise sources increase strongly with sensor stiffness. Deflection detector noise increases with bandwidth to the power of 1.5, while thermal noise and oscillator noise are proportional to the square root of the bandwidth. Thermal drift noise, however, is inversely proportional to bandwidth. The first three noise sources are inversely proportional to amplitude while thermal drift noise is independent of the amplitude. Thus, we show that the earlier finding that quoted an optimal signal-to-noise ratio for oscillation amplitudes similar to the range of the forces is still correct when considering all four frequency noise contributions. Finally, we suggest how the signal-to-noise ratio of the sensors can be improved further, we briefly discuss the challenges of mounting tips, and we compare the noise performance of self-sensing quartz sensors and optically detected Si cantilevers.