Rapid imaging of nanotubes on insulating substrates

Abstract

We demonstrate the use of field-emission scanning electron microscopy for rapid imaging of small-diameter carbon nanotubes on insulating SiO 2 substrates. The image contrast stems from local potential differences between the nanotube and substrate and is insensitive to surface roughness and defects. This technique may also be used as a probe of the electrical connectivity of small structures without external leads.

High contrast imaging and thickness determination of graphene with in-column secondary electron microscopy

“…3d). If we ignore the interaction of SLG with SE, the brightness of graphene images at low E p can be explained in a manner similar to the case of carbon nanotubes 23,24 . In this regime (E p < 2 kV) differential surface charging due to the flow of EBIC from graphene to SiO 2 which results in an enhanced SE emission from the graphene-covered region of the substrate making it appear brighter.…”

“…Experiments using an outer SE detector (often an Everhart-Thornley detector) generally yield relatively poor contrast, making a quantitative analysis less reliable. Instead, an in-column SE detector (in-lens) in a field-emission SEM (FESEM), which generally responds to lower electron energies (∼ few tens of eV), has been known to produce images of very sharp contrast for carbon nanotubes on insulating substrates 23,24 . Since it is assumed that the interaction between the SE emitted from the substrate and the nanotube is negligible, the physical mechanism behind this contrast is under debate, and both voltage contrast due to differential surface charging 23 and electron beam induced current (EBIC) processes 24 have been suggested.…”

“…Instead, an in-column SE detector (in-lens) in a field-emission SEM (FESEM), which generally responds to lower electron energies (∼ few tens of eV), has been known to produce images of very sharp contrast for carbon nanotubes on insulating substrates 23,24 . Since it is assumed that the interaction between the SE emitted from the substrate and the nanotube is negligible, the physical mechanism behind this contrast is under debate, and both voltage contrast due to differential surface charging 23 and electron beam induced current (EBIC) processes 24 have been suggested. Here we show that low-energy SE imaging using the in-lens detector of a FESEM provides a sharp thickness-dependent contrast of graphene on insulating substrates over a wide range of primary electron energies, E p .…”

Split gate and asymmetric contact carbon nanotube optical devices

“…As the CNTs in our devices are encapsulated beneath 40 nm of Al 2 O 3 , it is unlikely that the SEM images are derived purely from secondary electrons; we propose that the contrast mechanism observed in the image results from charge build up in the nanotube and its metal contacts, leading to enhanced secondary electron yield directly above the CNT. A similar contrast mechanism is thought to occur with bare CNTs on insulating substrates [22]. EL measurements were taken in air by collecting the EL with a 50x objective with a focal length of ~1cm, the EL was then dispersed by a monochromator and detected using a liquid nitrogen cooled InGaS detector array.…”

Carbon Nanotube Electron Sources: From Electron Beams to Energy Conversion and Optophononics

“…Of course, image formation and contrast mechanisms in an SEM are complex phenomena, influenced by artifacts such as charging and contamination [5,6]. Certainly, charging and voltage contrast appear to play an important role in scanning electron microscopy of carbon nanotubes [123][124][125]. Electron-beaminduced current has also been reported to play a part [126].…”