Improved burst pressure of LPCVD Si3N4 membranes by nanometer thick compressive adlayers

Si3N4 is a material widely used in MEMS technology. Its high mechanical strength makes Si3N4 attractive for applications where there is a need for ultrathin, yet robust, freestanding films, such as nanometer thick X-ray windows and support films for TEM. In this work, mechanical properties of Si3N4 and B-coated Si3N4 membranes were studied using a bulge test method. Burst pressure and corresponding membrane stress in Si3N4 layers were found to be significantly increased when a 3nm thick B layer was deposited on the top side of 25nm thick Si3N4 membranes, whereas a B layer applied to the bottom side of the membranes did not have an effect on the membrane strength. Using FEM simulations, we show that the B layer deposited at the top side decreases the maximum tensile stress in Si3N4 near the membrane edge, where a significant contribution to the total stress comes from bending. From this, we conclude that failure in single layer Si3N4 membranes during bulge test is dominated by fracture at the edge. The burst pressure of B-coated Si3N4 membranes was found to be higher for membranes with lower (more compressive) residual stress in B, which indicates that failure of bilayer membranes is caused by fracture initiated in the B layer. Please click Additional Files below to see the full abstract

Oxidation of thin film binary entropy alloys

In recent years, material science has put significant effort into understanding the behavior of multiple principle element alloys (MPEAs), notably the category high entropy alloys (HEAs). Most of these studies have been conducted on the micro to macro scales, yet the nanoscale remains relatively unexplored. Additionally, investigating the structural changes caused by amorphous oxidation for thin film MPEAs is particularly new, with no fundamental theory having been found. By studying ambient oxidation of thin film binary entropy alloys, we show how the Hume-Rothery rules affect the oxide formation and in particular the requirement of an increased temperature prior to the formation of polycrystalline oxides for these systems, compared to their single metal counterparts

Crystal surface characterization

Characterization of the structure of the crystal surface is essential for next generation electronics devices. Such as spin injection structures and topological insulators, to name a few. We have studied the advantages of characterization of the crystal surface based on the analysis of modulations of specular X-ray reflection occurred during the azimuthal scan in grazing incidence X-ray diffraction (GID) geometry