The novel approach to correlative microscopy of AFM-in-SEM using CPEM technology
Scanning electron microscopy (SEM) and atomic force microscopy (AFM) are two of the most used, complementary techniques for surface analysis at the nanoscale. Thus, combining them by integrating a compact AFM into SEM brings novel possibilities for true correlative microscopy and advanced multi-modal sample characterization that would be often unfeasible using each imaging modality separately.
LiteScope™ (Figure 1a) produced by the NenoVision company represents a compact AFM, which is directly integrable into a large variety of SEMs in a plug-and-play manner. In general, the strength of the AFM-in-SEM hybrid system lies in combining the AFM modes (3D topography, electrical, mechanical and magnetic measurements) with SEM capabilities (fast imaging with wide resolution range, chemical analysis, surface modification, etc.). Further benefits include precise AFM tip navigation by SEM, roughness evaluation and in-situ measurement, which is essential for sensitive samples prone to oxidation. Uniquely, LiteScope design enables simultaneous acquisition and correlation of AFM and SEM data by a technique called Correlative Probe and Electron Microscopy (CPEM).
CPEM functionates in a way that the electron beam and AFM probe keep a constant offset and remain static during the image acquisition (Figure 1b). The scanning movement is conducted by a piezo scanner that carries the sample. This ensures simultaneous data collection in the same coordinate system and with identical pixel size. The resulting 3D CPEM view can combine multiple channels, both AFM and SEM (Figure 1c), enabling thorough analysis for specific applications.
Above mentioned advantages are demonstrated in Figure 2, showing structural analysis of multilayered WSe2 flakes on Si nanopillars, where a certain shape of the WSe2 monolayer over the nanopillars creates a single-photon emitter. A monolayer of WSe2 is barely visible in the SEM image, but it’s clearly distinguishable on the AFM topography. Also, the AFM-in-SEM system enabled to quickly localize the structure of interest and the 3D CPEM view allowed unmistakable data interpretation.
In conclusion, the AFM-in-SEM strategy benefits from the complementarity of both techniques alongside significant savings both in time and resources. Also, it opens completely new possibilities for advanced data correlation and measurements, e.g. in the field of surface modification, semiconductor or spectroscopy.
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|Extended Abstract||Figure 1||Figure 1: (a) AFM LiteScope, (b) CPEM principle and (c) 3D CPEM view of tungsten alloy consisting of multiple channels (topography, SEM SE and BSE).||4 MB||Download|
|Extended Abstract||Figure 2||Figure 2: Exfoliated WSe2 flakes on Si nanopillars: SEM overview of the sample and fast AFM probe navigation. The signal from secondary electrons detector (SE), AFM topography with height profile, and resulting 3D CPEM view of merged AFM topography and SE signal.||1 MB||Download|