Far-field background suppression in tip-modulated apertureless near-field optical microscopy
Far-field background suppression in tip-modulated apertureless near-field optical microscopy
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DOI：
10.1063/1.2208527
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发表时间：
2006-06-15
影响因子：
3.2
通讯作者：
Bachelier, Guillaume
中科院分区：
文献类型：
--
作者：
Gucciardi, Pietro Giuseppe;Bachelier, Guillaume
在无孔径近场光学显微镜中，与高次谐波（n > 1）处的解调相关联的尖端的垂直抖动允许我们抑制远场背景，从而提供无伪影的弹性散射图像。本文分析，从理论和实验上，在不同的谐波背景信号的物理起源和其拒绝的传播场照明的一般情况下的机制。我们表明，背景的傅立叶分量必须在每个谐波，证明为什么在高次谐波解调是不是一个固有的背景免费的技术，并评估实验条件，它成为这样的。特别地，我们提出了谐波阶数和尖端振幅在背景抑制机制中的基本作用。此外，我们概述了如何锁定检测的信号幅度可以提高非线性依赖的背景上的尖端样本的距离。这种效应提供了更微妙的形貌伪影来源，因为光学图变得与形貌对应物在质量上不相关，需要升级标准以评估光学图中是否存在伪影。
In apertureless near-field optical microscopy the vertical dithering of the tip, associated with demodulation at higher harmonics (n > 1), allows us to suppress the far-field background, providing artifact free elastic scattering images. This paper analyzes, both theoretically and experimentally, the physical origin of the background signal at the different harmonics and the mechanisms underlying its rejection for the general case of propagative-field illumination. We show that Fourier components of the background must be expected at every harmonic, evidencing why demodulation at higher harmonics is not an inherently background-free technique, and assessing the experimental conditions in which it becomes like that. In particular, we put forward the fundamental roles of both the harmonic order and the tip oscillation amplitude in the background suppression mechanisms. Furthermore, we outline how the lock-in detection of the signals amplitude can enhance the nonlinear dependence of the background on the tip-sample distance. Such effect provides a more subtle source of topography artifacts since the optical maps become qualitatively uncorrelated from the topographic counterpart, requiring an upgrade of the criteria to assess the absence of artifacts from the optical maps.