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AFM-in-SEM


Figure 7: C-CPEM and I/V curves. The same sample area imaged by SEM (a) showing the insulated areas (highlighted by arrows) that failed to be visualized in the C-AFM conductivity map (b), but are clearly visible by C-CPEM (c) using the SEM electron beam as a bias source. (d) The I/V curves characterize differences in conduc- tivity on a sample containing graphene oxide, graphene, and EtaG identified by SEM (images show the conductive AFM tip in contact with the corresponding material).


Te detailed 3D AFM view shows indentation in the matrix with the amount of material pushed out of the indent (the black arrows in Figures 6c and 6d).


Measurement of Electrical Properties Te measurement of electrical properties can also be car-


ried out. Tis category includes conductive AFM (C-AFM), conductive CPEM (C-CPEM), Kelvin probe force microscopy (KPFM), probe force microscopy PFM, and spectroscopy regimes (Table 1). Technical advancement, especially in the semiconductor and solar industries, places increasing demand on the measurement of current distribution (conductivity) over the sample surface with nanometer precision. Conduc- tive AFM represents a common technique where a bias voltage is applied between the conductive cantilever and the sample, and the resulting current (as well as topography) is measured as the tip scans the sample surface. Clearly, this approach can- not work in insulated areas (Figure 7a), as depicted in Figure 7b. However, this C-AFM limitation can be overcome by the AFM-in-SEM approach combined with C-CPEM technology (Figure 7c), where the electron beam at the constant distance from the tip replaces the need for an applied bias in the mea- sured area, and the tip-sample bias can still be simultaneously applied. During scanning, the tip-sample current flow is mea- sured in contact AFM mode. Tis means that during a single measurement, information about the sample topography in


2020 May • www.microscopy-today.com


contact mode, SE and BSE images, and a conductivity map can be acquired. For a detailed local investigation of the surface electri-


cal properties, AFM-in-SEM can be used to measure current- voltage characteristics (I/V curves) by applying a bias of -10V to 10V. Figure 7d demonstrates the use of I/V curves for con- ductivity measurement of a sample containing graphene oxide, graphene, and 4-ethynylaniline graphene derivative (EtaG). Te SEM enables precise identification and navigation of the conductive tip to the respective material. Te investigation revealed that graphene oxide is non-conductive, EtaG more conductive, and graphene the most conductive material [18].


Conclusion Tis article provides insight into the AFM-in-SEM tech-


nology. Te LiteScope is a compact, yet powerful, AFM that fits into a large variety of SEM systems in a plug-and-play fashion. It provides complex sample surface analysis by sup- porting multiple techniques measuring structural, electri- cal, magnetic, and mechanical properties. Te unique CPEM technology allows a number of AFM and SEM signals to be simultaneously measured and automatically correlated into one detailed 3D image while maintaining the same pixel size and coordinate system. Te described technology enables com- plex sample analysis that was either impossible or extremely tedious/expensive when measured by separate instruments.


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