Structural Studies of 2D Perovskites for Catalyst Support Applications by Environmental Transmission Electron Microscopy

Two-dimensional perovskites materials gained traction for applications in various optoelectronic and sensor devices. Another potential application for this class of the material is a catalyst support, as epitaxial relationships between catalyst and support can be utilized to gain control over catalyst active sites in catalyst activity studies. Nanosheets of Sr₂Nb₃O₁₀(SNO) with thicknesses down to 1.8 nm were synthesized by liquid exfoliation technique. Palladium film of a nominal thickness of 1.0 nm was deposited by electron beam evaporation to form Pd particles supported on SNO, which was picked up as a model system. Structural characterization was done in the column of C_s-corrected environmental FEI Titan scanning transmission electron microscope (ETEM). Bright field (BF) and dark field (DF) imaging revealed nanosheets of sizes of few squared micrometers. SNO flakes show contrast revealing strain and deviation from the exact [001] zone axis across the nanosheet. A perfect orientation down to the [001] zone axis was limited to a few hundred square nanometers. DF images of the SNO flakes acquired in several two-beam conditions show contrast from grain boundaries of misoriented grains. Planar defects (PD) running at an angle to the imaging plane reveal alternating contrast. Some areas show defected structure on HREM images, which also reveals itself by additional diffraction spots on the FFT in comparison with the perfect perovskites structure. In addition to vacuum environment, deposited films were also studied in the presence of Hydrogen in environmental regime of the same Titan (S)TEM. The sample was heated to 900C in the presence of 80mTorr Hydrogen. Nanoparticles supported on SNO exhibit faceted nature compared to those supported on amorphous SiN support, which potentially opens a way to controllable studies of catalyst’s active sites. This research used the Electron Microscopy facility of the Center for Functional Nanomaterials (CFN), which is a U.S. Department of Energy Office of Science User Facility, at Brookhaven National Laboratory under Contract No. DESC0012704.