Correlative SEM / AFM Microscopy - Combining Two High-Performance Methods for Nanoscale Measurements

The combination of different analytical methods for the qualitative and quantitative evaluation of material properties has become an essential part of today's characterization methods. In this context, the field of correlative microscopy represents an important technique for the simultaneous acquisition of complementary information. In particular, the combination of two of the most powerful microscopy techniques – scanning electron microscopy (SEM) and atomic force microscopy (AFM) – provides completely new insights into the micro- and nano-world to investigate even the smallest features of a sample with the highest resolution.[1-2] However, combining these two methods is not easy and remains challenging in terms of the instrumentation required. In most cases, both methods are used separately, and the obtained results cannot be truly spatially correlated. In this work, we present a unique inspection device that seamlessly combines SEM and AFM for characterization and process control of micro- and nanostructures. Due to the self-sensing piezoresistive cantilever technology used for the AFM scanner, the cantilever deflection signal can be measured completely electrically,[3] and a joint coordinate system between SEM and AFM allows the simultaneous acquisition of data directly at the region of interest. We will present a series of novel case studies to illustrate the advantages of this new tool for the interactive, correlative <i>in-situ</i> characterization of various materials and nanostructures at the nanoscale.<br/><br/>The first results focus on semiconducting ceramics based on BaTiO₃ with a positive temperature coefficient of resistance (PTCR). These materials, widely used in the field of self-regulating heating elements or temperature sensors, offer a wide range of applications in the energy sector. In this context, electrostatic force microscopy (EFM) combined with SEM shows that an accurate colocalized analysis of the grain boundary potential barriers of various BaTiO₃-based samples can be performed within nanometer resolution. The grain boundaries were localized using backscattered electron (BSE) detection and subsequently measured using the <i>in-situ</i> EFM technique demonstrating the influence of SiO₂ as a sintering agent on the barriers. Moreover, these results can be directly correlated with electron backscatter diffraction (EBSD) measurements to link the AFM and SEM data to the crystallographic microstructure of the samples.[4]<br/><br/>We will also present results for the <i>in-situ</i> characterization of nanowires, 2-D thin film materials, and multilayer samples to characterize their electrical, magnetic, topographic, and mechanical properties. The SEM allows the easy localization of single or multiple surface features, while the <i>in-situ</i> AFM allows the characterization of various "visible" and "hidden" surface and bulk properties. In this context, some aspects of advanced tip fabrication techniques such as focused electron beam induced deposition (FEBID) will also be briefly outlined to give an impression of how the fine-tuning of tip properties can be beneficial for correlated measurements.[5]<br/><br/>Due to the wide range of applications in inspection and process control of various materials and components, we expect this new inspection device to be one of the future key characterization tools for correlative SEM and AFM analysis. <br/> <br/>[1] D. Yablon, et al., Microscopy and Analysis – EMEA, <b>29</b>, 14-18 (2017).<br/>[2] S. H. Andany, et al., Beilstein Journal of Nanotechnology, <b>11</b>, 1272-1279 (2020).<br/>[3] M. Dukic, et al., Scientific Reports, <b>5 </b>(1), 16393 (2015).<br/>[4] J. M. Prohinig, et al., Scripta Materialia, <b>214</b>, 114646 (2022).<br/>[5] L. M. Seewald, et al., Nanomaterials, <b>12 </b>(24), 4477 (2022).