Hits: 1687075

Advances in microscopy: in situ electron microscopy and scanning probe microscopy

The actual coupling between the microstructure studied by microscopy on one hand and the property of a material is almost elusive. The reason is that these properties are determined by the collective dynamic behavior of defects rather than by the behavior of an individual static defect. However, the situation is not hopeless and we argue that for a more quantitative evaluation of the structure-property relationship emphasis on in-situ measurements is necessary.

High-resolution transmission electron microscopy (HRTEM) plays a predominant role in the research program. Notably the method of HRTEM founds its origin in the technique of phase contrast microscopy that was introduced by Frits Zernike of this very same University of Groningen for optical microscopy. High-resolution TEM imaging is based on the same principles and phase contrast imaging derives contrast from the phase differences among the different beams scattered by the specimen, causing addition and subtraction of amplitude from the forward-scattered beam. In reality a HRTEM is not a perfect phase contrast microscope and electron beams at different angles with the optical axis obtain different phase shifts. As a consequence applications of the concept of resolution in high-resolution transmission electron microscopy are still not without pitfalls, and a thorough understanding of image formation is essential for a reliable interpretation.


APPLIED PHYSICS LETTERS Volume: 86 Issue: 11 Article Number: 113113 Published: MAR 14 2005

Besides electron microscopy scanning probe techniques are employed to study the influence of roughness quantified with AFM on the force fields detected with our VEECO Pico force instrument. These force fields are relevant in the field of metal based NEMS/MEMS. Focused ion beam methods play an important role in the preparation of nano-objects as is illustrated in the following highlight.

movie1 (In-situ TEM indentation - Adobe Flash movie)
Microscopy and Microanalysis 8 (4)  274-287 (2002), Appl. Phys. Lett. 90, 181924 (2007)

ACTA MATERIALIA Volume: 58 Issue: 1 Pages: 189-200 Published: JAN 2010

Quantitative bending and compression tests on micropillars made of two different amorphous alloys, with tip diameters ranging from 93 to 645 nm, are performed in situ in a transmission electron microscope (TEM). Under microcompression each pillar shows an intermittent plastic flow accommodated by inhomogeneous shear banding. However, the individual shear banding events are strongly size dependent, i.e. in larger pillars the deformation is controlled by nucleation of shear bands, but in smaller pillars it becomes propagation controlled. On the other hand, the yield stress is essentially size-independent. Microbending tests show further advantages by amplifying size effects and minimizing artifacts. An interesting finding is that by microbending, a switch from highly inhomogeneous to fully homogeneous deformation is observed at an experimentally accessible size regime near 200 nm, whereas it is not accessible under microcompression, even at a sub-100 nm scale. These size effects are well interpreted by a micromechanical model, leading to a deformation map in the stress-size space. A physical picture of nanoscale shear localization process is also provided.


movie1 (Amorphous Nanopillar Deformation - Adobe Flash movie)

Ref: Acta Materialia 58 (1) 189-200 (2010)