A new mapping procedure for polycrystals using neutron Bragg-dip transmission is presented. This is expected to be useful as a new materials characterization tool which can simultaneously map the crystallographic direction of grains parallel to the incident beam. The method potentially has a higher spatial resolution than neutron diffraction imaging. As a demonstration, a Bragg-dip neutron transmission experiment was conducted at J-PARC on beamline MLF BL10 NOBORU. A large-grained Si-steel plate was used. Since this specimen included multiple grains along the neutron beam transmission path, it was a challenging task for existing methods to analyse the direction of the crystal lattice of each grain. A new data-analysis method for Bragg-dip transmission measurements was developed based on database matching. As a result, the number of grains and their crystallographic direction along the neutron transmission path have been determined.

Abstract

We succeeded the observation of microstructures in bulk-sized specimens of over 10µm in thickness by employing a technique that combines transmission electron microscopy (TEM) with energy-filtered imaging based on electron energy-loss spectroscopy (EELS). This method is unique in that it incorporates the inelastically scattered electrons into the imaging process. Using this technique, bright and sharp images of dislocations in crystalline silicon specimens as thick as 10µm were obtained. A calibration curve to determine foil thickness of such a thick specimen was also derived. This method simply extends the observable thickness range in TEM. If combined with tilt series of observation over a significant range of angle, it will disclose three dimensional nanostructures in a µm-order block of a specimen, promoting our understanding of the controlling mechanisms behind various bulky material properties.

No abstract

Crack tip dislocations in silicon single crystals were observed by combining high-voltage electron microscopy and electron tomography. Cracks were introduced by an indentation method and dislocations were introduced around the crack tip by keeping the indented sample at high temperatures for several hours. The number of dislocations emitted from the crack tip was controlled by changing the holding time of the indented specimen at high temperatures. The dislocations observed were characterized in detail. It was found that primary emitted dislocations all had the same Burgers vectors and that some dislocation segments cross-slipped around the crack. The local stress intensity factor due to dislocations was calculated, basing on the dislocation character obtained in this study, indicating that emitted dislocations shields mode I, II and III stress intensity at the crack tip. After the emission of the number of those dislocations, dislocations with another Burgers vector were emitted around the crack. It was found that those dislocations accommodate mode II and III stress components which are the excess shielding fields due to the dislocations primary emitted from the crack tip.