Compensation of thermal drift effects in atomic force microscopy using probabilistic state estimation

二十多年来，原子力显微镜（AFM）在生命科学、生物学、材料科学、半导体工业以及一般的微米和纳米技术等各个学科中都是必不可少的仪器。它通过提供微观、纳米和原子尺度结构的高分辨率可视化，彻底改变了表面分析。虽然AFM最初仅用于对样品的形貌进行成像，但随着时间的推移，不同的操作模式逐渐发展，包括电，磁和化学测量。对提供比常规光刻工艺更高的分辨率并且能够处理新材料（例如生物材料）的新颖光刻方法的需求已经激发了基于AFM的光刻领域中的研究。也进行了激烈的研究，对个别微/纳米实体与AFM针尖的操作。这种基于AFM的组件的有前途的潜在应用是例如基于纳米材料（例如CNT、DNA、单石墨烯层、纳米线等）的新型纳米电子器件和系统的原型设计。影响AFM的几乎每个应用领域的问题是引起的热漂移的存在。热漂移源于温度的微小变化和AFM（或一般SPM）不同组件的热膨胀系数差异。这导致探针相对于样品在所有三个维度上的未知的时变位移。这种运动通常是缓慢的，但它会导致图像和光刻过程中的失真，伪造光谱结果，并损害纳米操纵的成功。在拟议的项目中，我们的主要目标是开发一种灵活的漂移补偿系统，适用于成像，光谱学以及纳米操纵任务。所开发的方法应允许在图像采集和实时操作过程中对热漂移进行主动补偿，而无需任何样品性质或漂移状态的先验知识。此外，它应该在所有三个维度上补偿漂移，从而不限制应用领域。为了达到这些目标的概率算法将开发结合非光栅扫描方法，一般有效的模型描述AFM形貌数据以及描述漂移的概率模型。该算法将以贝叶斯过滤为基础，以纳入不准确模型带来的不确定性。该系统将在不同的系统上进行实验验证，使用定制的AFM控制架构，在基于AFM的自动操作不同的纳米物体的背景下。

Since more than two decades, the atomic force microscope (AFM) represents an essential instrument in various disciplines covering life science, biology, material science, semiconductor industries, and micro- and nanotechnology in general. It has revolutionized surface analysis by providing high-resolution visualization of structures at micro-, nano-, and atomic scales. While AFM was first only used for imaging the topography of a sample, different operation modes evolved over time including electrical, magnetic, and chemical measurements. The need for novel lithographic methods providing higher resolution than conventional lithographic processes and enabling to process new materials (e.g. biomaterials) have motivated research in the domain of AFM-based lithography. Intense research has also been carried out on the manipulation of individual micro-/nanoentities with the AFM tip. Promising potential applications of such AFM-based assembly are e.g. prototyping of novel nanoelectronic devices and systems based on nanomaterials such as CNTs, DNA, single-graphene layers, nanowires, etc. A problem that is affecting almost every application area of AFM is the presence of thermal drift induced. Thermal drift originates from small changes in temperature and differences in the coefficient of thermal expansion of the different components of the AFM (or SPM in general). This results in an unknown, time-variant displacement of the probe relative to the sample in all three dimensions. This motion is generally slow, but it is causing distortions in images and lithographic processes, falsifying spectroscopy results, and compromising the success of nanomanipulations. In the proposed project our major objective is the development of a flexible drift compensation system applicable in the context of imaging, spectroscopy as well as nanomanipulation tasks. The developed methods should allow for an active compensation of thermal drift during image acquisition and manipulation in real-time without any prior knowledge of the sample properties or drift state. Moreover, it should compensate drift in all three dimensions thus not limiting the field of application. To reach these objectives a probabilistic algorithm will be developed incorporating non-raster scanning methods, generally valid models describing AFM topography data as well as a probabilistic model describing drift. The algorithm will be based on Bayesian filtering to incorporate the uncertainties introduced by inaccurate models. The system will be experimentally validated on different systems using a custom-made AFM control architecture in the context of AFM-based automated manipulation of different nanoobjects.