Comparison between STEM and SEM

Chapter/Index: Introduction | A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z | Appendix

Comparison between STEM and SEM

In general, a low voltage STEM is a hybrid instrument with the features of SEM and TEM with a convergent probe, while a high voltage TEM is a hybrid instrument with the features of TEM with both a parallel beam (for TEM function) and a convergent probe (for STEM function).

	SEM	STEM
	===============================	===============================
Similarity to other techniques		Some are similar to TEM

Signal	Secondary electrons (SEs) and backscattered electrons (BSEs)	Transmitted electrons

Signal intensity	Weak intensity from individual atoms due to limited numbers of secondary electrons (or BSEs) from the individual atoms	Strong intensity from individual atoms due to high transmitted beam intensity

Source of signal	The strongest signal is from the top surface: surface-sensitive	The signal is the integration of the film: probe internal structures directly

Surface-quality-induced contrast effect	Allows us to evaluate the atomic arrangement of the few top layers of the sample including the surface quality and condition; a few angstrom-thick amorphous patches greatly reduce the contrast in a SEM image	Reveals the atomic arrangement of the sample through its entire thickness; a few angstrom-thick amorphous patches do not affect the HAADF image.

Sensitivity to low-Z elements	Higher than HAADF STEM imaging (E.g. lattice fringe of carbon nanotubes is visible in C_s-corrected SEM imaging [2])	Lower than SEM imaging due to the small scattering cross-section of the light elements (E.g. lattice fringe of carbon nanotubes is invisible in C_s-corrected HAADF imaging [2])

Advantages	Is surface-sensitive and can provide depth (3-D) information

Disadvantages		Gives little 3-D information in the direction of the beam's trajectory

Figure 4447a shows the contrast difference of Pd (Palladium) particles on a thin carbon film. The image (a) using SEs as well as BSEs clearly gives rich depth information, or three-dimensional (3-D) information, about the locations of the particles, while the STEM image cannot give such information.

SEM image of Pd STEM image of Pd

Figure 4447a. (a) SEM image of Pd nanoparticles on a carbon support obtained using SEs and BSEs; (b) STEM image obained using transmitted electrons (TEs) with an ADF detector. Adapted from [1].

Figure 4447b shows an example of SEM/STEM images taken from uranium oxide particles on carbon film at atomic resolution in both SEM mode and ADF-STEM mode in C_s-corrected Hitachi HD 2700C. It is clear that the contrast of STEM is much better than that of SEM.

SEM/STEM images taken from uranium oxide particles on carbon film at atomic resolution in SEM mode (a) and ADF-STEM mode(b)

Figure 4447b. SEM/STEM images taken from uranium oxide particles on carbon film at atomic resolution in SEM mode (a) and ADF-STEM mode(b). [2]

Furthermore, the comparison between the EDS measurements in low-energy SEM and high-energy (S)TEM is listed on a table on page4532.

[1] Y. Zhu, H. Inada, K. Nakamura, and J. Wall, Imaging single atoms using secondary electrons with an aberration-corrected electron microscope, Nature Materials, 8 (2009) 808.
[2] H. Inada, D.Su, R. F. Egerton, M.Konno, L.Wu, J.Ciston, J.Wall, Y.Zhu, Atomic imaging using secondary electrons in a scanning transmission electron microscope: Experimental observations and possible mechanisms, Ultramicroscopy 111(2011)865–876.

Practical Electron Microscopy and Database

An Online Book, Second Edition by Dr. Yougui Liao (2006)

Comparison between STEM and SEM