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Rapid reconstruction of a strong nonlinear property by a multiple lock-in technique

机译:通过多重锁定技术快速重建强非线性特性

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摘要

We propose and discuss a rapid reconstruction procedure for strongly nonlinear signals and validate it for dynamic force microscopy. Harmonics of the cantilever resonance frequency shift, generated by a low-frequency modulation of the tip-sample distance, are detected by a phase-locked loop followed by 12 lock-in amplifiers. The distance dependence of the frequency shift can be reconstructed by summing up the sampled Fourier components with judiciously assigned phase shifts. Following a successful test with a model potential, we report a measurement of the frequency shifts induced by the force field above a KBr(001) surface at room temperature in ultrahigh vacuum. Experimental spectra justify the neglect of harmonics beyond tenth order in the range where clear atomic-scale contrast appears in images of the lower harmonic intensities. A high-resolution three-dimensional frequency shift dataset was measured in 400 s. The method can in general be applied to any single-valued physical quantity with a smooth nonlinear dependence on a control variable.
机译:我们提出并讨论了针对强非线性信号的快速重建程序,并对其进行了动态力显微镜验证。尖端采样距离的低频调制产生的悬臂共振频率偏移的谐波,由锁相环和12个锁相放大器检测。频移的距离相关性可以通过将采样的傅立叶分量与经过明智分配的相移相加而重建。在成功进行了模型电位测试之后,我们报告了在室温下超高真空下KBr(001)表面上方的力场引起的频移测量结果。实验光谱证明,在较低谐波强度的图像中出现清晰的原子级对比度的范围内,忽略了超过十阶的谐波。在400 s内测量了高分辨率的三维频移数据集。该方法通常可以应用于对控制变量具有平滑非线性依赖关系的任何单值物理量。

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