Contrast and resolution versus specimen thickness in low energy scanning transmission electron microscopy

Journal Article · Fri Jun 01 04:00:00 EDT 2007 · Journal of Applied Physics

DOI:https://doi.org/10.1063/1.2745333· OSTI ID:20979430

Morandi, Vittorio; Merli, Pier Giorgio ^[1]

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1. CNR-IMM, Sezione di Bologna, via Gobetti 101, 40126 Bologna (Italy)

A theoretical and experimental investigation of contrast and resolution versus specimen thickness in scanning transmission electron microscopy at low energy is reported. Due to absence of postspecimen imaging lenses it is possible to have images with a resolution defined by the probe size using very wide collection angles and independent of the energy loss of the transmitted electrons. The fundamental limitation in observable specimen thickness is represented by the signal to noise ratio, i.e., the intensity of the beam current. The investigated specimens are semiconductor multilayers and Sb precipitates in a Si implanted specimen. The observations of layers crossing the whole specimens parallel to the electron beam point out that only a small portion of them, the one close to the surface, causes the image contrast, while the portion below, where the probe diameter, as a consequence of the broadening, is larger than the layer itself, reduces the contrast. A similarity with recent results, achieved in scanning transmission electron microscopy at high energy, where the layers are represented by atomic columns, is pointed out. The image contrast depends on the angular distribution of the transmitted electrons, and for thick specimens it is always of bright field type, independent of the collection angle of the transmitted electrons. The observation of Sb precipitates, distributed along the specimen thickness, evidences the role of beam broadening on the resolution and contrast.

• OSTI ID: 20979430
• Journal Information: Journal of Applied Physics, Journal Name: Journal of Applied Physics Journal Issue: 11 Vol. 101; ISSN JAPIAU; ISSN 0021-8979
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ALUMINIUM COMPOUNDS
ANGULAR DISTRIBUTION
ANTIMONY
BEAM CURRENTS
ELECTRON BEAMS
ELECTRONS
ENERGY LOSSES
IMAGES
LAYERS
PRECIPITATION
RESOLUTION
SEMICONDUCTOR MATERIALS
SIGNAL-TO-NOISE RATIO
THICKNESS
TRANSMISSION ELECTRON MICROSCOPY