Centres Científics i Tecnològics UB

News

26.07.2018

Publication of the article “Quasi-parallel precession diffraction: Alignment method for scanning transmission electron microscopes.”

PhD. Joaquim Portillo, responsible of the TEM Applied to Materials technology of the CCiTUB, have published the article: “Quasi-parallel precession diffraction: Alignment method for scanning transmission electron microscopes” in the journal Ultramicroscopy. The article has been made possible thanks to the collaboration with the researchers: PhD. Francesca Peiró, PhD. Sònia Estradé and Mr. Sergi Plana of the Engineering Department of the Universitat de Barcelona, PhD. Ute Kolb of the Johannes Gutenberg-Universität Mainz and the PhD. S.Nicolopoulos of NanoMEGAS SPRL.

Once more, the article is the result of the collaboration between University-Company and, in this prticular case, in the framework of the agreement between the company NanoMEGAS SPRL and the CCiTUB.

The summary of the article is:

"A general method to set illuminating conditions for selectable beam convergence and probe size is presented in this work for Transmission Electron Microscopes (TEM) fitted with µs/pixel fast beam scanning control, (S)TEM, and an annular dark field detector. The case of interest of beam convergence and probe size, which enables diffraction pattern indexation, is then used as a starting point in this work to add 100Hz precession to the beam while imaging the specimen at a fast rate and keeping the projector system in diffraction mode. The described systematic alignment method for the adjustment of beam precession on the specimen plane while scanning at fast rates is mainly based on the sharpness of the precessed STEM image. The complete alignment method for parallel condition and precession, Quasi-Parallel PED-STEM, is presented in block diagram scheme, as it has been tested on a variety of instruments. The immediate application of this methodology is that it renders the TEM column ready for the acquisition of Precessed Electron Diffraction Tomographies (EDT) as well as for the acquisition of slow Precessed Scanning Nanometer Electron Diffraction (SNED). Examples of the quality of the Precessed Electron Diffraction (PED) patterns and PED-STEM alignment images are presented with corresponding probe sizes and convergence angles".

More information is available at the following link: [+].