Liu Hao, Ahmed Zuned, Vranjkovic Sasa, Parschau Manfred, Mandru Andrada-Oana, Hug Hans J
Empa, Swiss Federal Laboratories for Materials Science and Technology, CH-8600 Dübendorf, Switzerland.
Department of Physics, University of Basel, CH-4056 Basel, Switzerland.
Beilstein J Nanotechnol. 2022 Oct 11;13:1120-1140. doi: 10.3762/bjnano.13.95. eCollection 2022.
Cantilever-based atomic force microscopy (AFM) performed under ambient conditions has become an important tool to characterize new material systems as well as devices. Current instruments permit robust scanning over large areas, atomic-scale lateral resolution, and the characterization of various sample properties using multifrequency and multimodal AFM operation modes. Research of new quantum materials and devices, however, often requires low temperatures and ultrahigh vacuum (UHV) conditions and, more specifically, AFM instrumentation providing atomic resolution. For this, AFM instrumentation based on a tuning fork force sensor became increasingly popular. In comparison to microfabricated cantilevers, the more macroscopic tuning forks, however, lack sensitivity, which limits the measurement bandwidth. Moreover, multimodal and multifrequency techniques, such as those available in cantilever-based AFM carried out under ambient conditions, are challenging to implement. In this article, we describe a cantilever-based low-temperature UHV AFM setup that allows one to transfer the versatile AFM techniques developed for ambient conditions to UHV and low-temperature conditions. We demonstrate that such a cantilever-based AFM offers experimental flexibility by permitting multimodal or multifrequency operations with superior force derivative sensitivities and bandwidths. Our instrument has a sub-picometer gap stability and can simultaneously map not only vertical and lateral forces with atomic-scale resolution, but also perform rapid overview scans with the tip kept at larger tip-sample distances for robust imaging.
在环境条件下进行的基于悬臂的原子力显微镜（AFM）已成为表征新材料系统以及器件的重要工具。当前的仪器允许在大面积上进行稳健扫描、实现原子尺度的横向分辨率，并使用多频和多模态AFM操作模式来表征各种样品特性。然而，新型量子材料和器件的研究通常需要低温和超高真空（UHV）条件，更具体地说，需要提供原子分辨率的AFM仪器。为此，基于音叉力传感器的AFM仪器越来越受欢迎。然而，与微加工悬臂相比，更为宏观的音叉缺乏灵敏度，这限制了测量带宽。此外，多模态和多频技术，如在环境条件下基于悬臂的AFM中可用的技术，实施起来具有挑战性。在本文中，我们描述了一种基于悬臂的低温超高真空AFM装置，它允许将为环境条件开发的通用AFM技术转移到超高真空和低温条件下。我们证明，这种基于悬臂的AFM通过允许具有卓越力导数灵敏度和带宽的多模态或多频操作，提供了实验灵活性。我们的仪器具有亚皮米级的间隙稳定性，不仅可以以原子尺度分辨率同时绘制垂直力和横向力，还可以在保持针尖与样品距离较大的情况下进行快速全景扫描，以实现稳健成像。
