Carbon nanofiber (CNF), grown by plasma-enhanced chemical vapor deposition, is a nanoscale 1D structure with a diameter of 10-300 nm and has been studied for a wide range of applications including electron emitter array, electronic devices, and interconnects for next-generation integrated circuits. In such applications, the interface structure between the CNF and adjacent materials including the underlying substrate, as well as internal structure of the CNF itself, is essential to ensure its high-performance electrical and thermal properties. Scanning electron microscopy (SEM) is one of the powerful tools to investigate such structures. Especially for the carbon-based nanostructures including CNFs, the surface information and internal structure are obtained by using a secondary electron detector and a transmission electron detector, respectively, if the samples are supported on the electron transparent film. To study the interfacial or internal structure of samples on bulk substrate with SEM, however, generally requires sample thinning, which is destructive. We present two new SEM imaging techniques developed for CNF devices fabricated on a thick Si substrate without any sample modification. One is an imaging method for the interface between the CNF and substrate, providing the information whether the CNF is in contact with the substrate using top-down SEM imaging. The other technique enables us to obtain a bright-field scanning transmission electron microscopy (STEM) contrast, providing the internal graphitic layer structure of the CNF without destructive sample thinning. We show that the thermal and electrical transport characteristics of the CNF devices are effectively evaluated with these techniques. Detailed analysis using Monte Carlo simulation shows that the secondary electrons from the substrate and efficient detection of these electrons play a key role in both of these imaging techniques.

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1. Estimation of the Low Voltage BF/DF STEM Image in an UHR FE-SEM