Martin-Jimenez Daniel, Ruppert Michael G, Ihle Alexander, Ahles Sebastian, Wegner Hermann A, Schirmeisen André, Ebeling Daniel
Institute of Applied Physics (IAP), Justus Liebig University Giessen, Heinrich-Buff-Ring 16, Giessen 35392, Germany.
Center for Materials Research (LaMa), Justus Liebig University Giessen, Heinrich-Buff-Ring 16, Giessen 35392, Germany.
Nanoscale. 2022 Apr 7;14(14):5329-5339. doi: 10.1039/d2nr01062c.
Non-contact atomic force microscopy (AFM) with CO-functionalized tips allows visualization of the chemical structure of adsorbed molecules and identify individual inter- and intramolecular bonds. This technique enables in-depth studies of on-surface reactions and self-assembly processes. Herein, we analyze the suitability of qPlus sensors, which are commonly used for such studies, for the application of modern multifrequency AFM techniques. Two different qPlus sensors were tested for submolecular resolution imaging actuating torsional and flexural higher eigenmodes and bimodal AFM. The torsional eigenmode of one of our sensors is perfectly suited for performing lateral force microscopy (LFM) with single bond resolution. The obtained LFM images agree well with images from the literature, which were scanned with customized qPlus sensors that were specifically designed for LFM. The advantage of using a torsional eigenmode is that the same molecule can be imaged either with a vertically or laterally oscillating tip without replacing the sensor simply by actuating a different eigenmode. Submolecular resolution is also achieved by actuating the 2 flexural eigenmode of our second sensor. In this case, we observe particular contrast features that only appear in the AFM images of the 2 flexural eigenmode but not for the fundamental eigenmode. With complementary laser Doppler vibrometry measurements and AFM simulations we can rationalize that these contrast features are caused by a diagonal ( in-phase vertical and lateral) oscillation of the AFM tip.
采用一氧化碳功能化探针的非接触原子力显微镜（AFM）能够可视化吸附分子的化学结构，并识别分子间和分子内的单个化学键。该技术能够深入研究表面反应和自组装过程。在此，我们分析了常用于此类研究的qPlus传感器对于现代多频AFM技术应用的适用性。测试了两种不同的qPlus传感器用于亚分子分辨率成像，驱动扭转和弯曲高阶本征模以及双峰AFM。我们其中一个传感器的扭转本征模非常适合以单键分辨率进行侧向力显微镜（LFM）操作。所获得的LFM图像与文献中的图像吻合良好，文献中的图像是用专门为LFM设计的定制qPlus传感器扫描得到的。使用扭转本征模的优势在于，无需更换传感器，只需驱动不同的本征模，就可以用垂直或侧向振荡的探针成像相同的分子。通过驱动我们第二个传感器的二阶弯曲本征模也实现了亚分子分辨率。在这种情况下，我们观察到特定的对比度特征，这些特征仅出现在二阶弯曲本征模的AFM图像中，而在基模图像中则没有。通过互补的激光多普勒振动测量和AFM模拟，我们可以推断出这些对比度特征是由AFM探针的对角（同相垂直和侧向）振荡引起的。
