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Understanding the Image Contrast of Material Boundaries in IR Nanoscopy Reaching 5 nm Spatial Resolution
ACS Photonics ( IF 7 ) Pub Date : 2018-07-11 00:00:00 , DOI: 10.1021/acsphotonics.8b00636
Stefan Mastel 1 , Alexander A. Govyadinov 1 , Curdin Maissen 1 , Andrey Chuvilin 1, 2 , Andreas Berger 1 , Rainer Hillenbrand 2, 3
Affiliation  

Scattering-type scanning near-field optical microscopy (s-SNOM) allows for nanoscale-resolved Infrared (IR) and Terahertz (THz) imaging, and thus has manifold applications ranging from materials to biosciences. However, a quantitatively accurate understanding of image contrast formation at materials boundaries, and thus spatial resolution is a surprisingly unexplored terrain. Here we introduce the read/write head of a commercial hard disk drive (HDD) as a most suitable test sample for fundamental studies, given its well-defined sharp material boundaries perpendicular to its ultrasmooth surface. We obtain unprecedented and unexpected insights into the s-SNOM image formation process, free of topography-induced contrasts that often mask and artificially modify the pure near-field optical contrast. Across metal-dielectric boundaries, we observe non-point-symmetric line profiles for both IR and THz illumination, which are fully corroborated by numerical simulations. We explain our findings by a sample-dependent confinement and screening of the near fields at the tip apex, which will be of crucial importance for an accurate understanding and proper interpretation of high-resolution s-SNOM images of nanocomposite materials. We also demonstrate that with ultrasharp tungsten tips the apparent width (resolution) of sharp material boundaries can be reduced to about 5 nm.

中文翻译:

在达到5 nm空间分辨率的IR纳米显微镜中了解材料边界的图像对比度

散射型扫描近场光学显微镜(s-SNOM)可以进行纳米级的红外(IR)和太赫兹(THz)成像,因此具有从材料到生物科学的广泛应用。然而,对材料边界处图像对比度形成的定量准确理解,因此空间分辨率是令人惊讶地未开发的地形。在这里,我们将商业硬盘驱动器(HDD)的读/写头介绍为最适合基础研究的测试样本,因为其垂直于超光滑表面的定义明确的锋利材料边界。我们获得了关于s-SNOM图像形成过程的空前和出乎意料的见解,没有地形诱发的对比度,该对比度通常会掩盖和人为地修改纯近场光学对比度。跨金属介电边界,我们观察到红外和太赫兹照明的非点对称线轮廓,这通过数值模拟得到了充分证实。我们通过样本依赖的封闭和尖端顶端近场的筛选来解释我们的发现,这对于准确理解和正确解释纳米复合材料的高分辨率s-SNOM图像至关重要。我们还证明了使用超锐利的钨尖,尖锐的材料边界的表观宽度(分辨率)可以减小到约5 nm。对于准确理解和正确解释纳米复合材料的高分辨率s-SNOM图像而言,这一点至关重要。我们还证明了使用超锐利的钨尖,尖锐的材料边界的表观宽度(分辨率)可以减小到约5 nm。对于准确理解和正确解释纳米复合材料的高分辨率s-SNOM图像而言,这一点至关重要。我们还证明了使用超锐利的钨尖,尖锐的材料边界的表观宽度(分辨率)可以减小到约5 nm。
更新日期:2018-07-11
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