Thin film deposition of BaO by molecular beam epitaxy

Growth and Characterization of Barium Oxide Nanoclusters on YSZ(111)

“…During and following the growth under UHV, we found the BaO clusters remained in single phase as shown by the in situ RHEED pattern. Previous studies showed that BaO is in a highly unstable phase under ambient conditions. − This is indeed found to be the case for most attempts of the BaO growth in our experiments as well. When BaO clusters are exposed to ambient conditions, the clusters transformed to BaCO 3 and/or Ba(OH) 2 H 2 O as determined by GIXRD measurements.…”

“…The lattice constant determined from the XRD pattern of BaO clusters is 0.5418(1) nm. This value is ∼2% lower than the lattice constant of 0.55 nm reported previously for epitaxial cubic BaO(001) on SrTiO 3 (001) with a SrTiO 3 capped layer. − A decrease in the lattice constant is probably from the formation of BaO clusters, which are expected to be fully relaxed, unlike the previous study where BaO forms an epitaxial layer over a SrTiO 3 single-crystal substrate in which there could be strain because of substrate influence. − The average crystallite size determined from full-width at half-maximum (fwhm) of diffraction patterns using the Scherrer equation is found to be ∼25 nm. Exposing the single-phase BaO clusters in air resulted in the formation of Ba(OH) 2 H 2 O. Temperature-dependent X-ray diffraction measurements under rough vacuum (3.0 × 10 −3 Torr) showed that Ba(OH) 2 H 2 O formed from BaO clusters at room temperature converted to BaCO 3 at ∼200 °C followed by decomposition of BaCO 3 at ∼500 °C.…”

Phase Separation at the Nanoscale: Structural Properties of BaO Segregates on MgO-Based Nanoparticles

“…Given the broad distribution of sizes and particle qualities inside the composite nanoparticle powder, we assume that the XRD active Ba(OH) 2 xH 2 O phase has not been covered by our TEM measurements, and that the total number of supported BaO structures characterized along with Figures and is below the detection limit of XRD and therefore escapes detection. On the other hand, BaO is a highly unstable phase under ambient conditions and transforms readily to Ba(OH) 2 xH 2 O. − During sample transfer from the vacuum activation cell into the vacuum of the TEM – an unavoidable procedure which typically takes less than 5 min - the BaO segregates most likely undergo surface hydroxylation. Whether adsorption induced morphology transformation from cubic BaO segregates into rounded surface structures would occur at room temperature during particle powder exposure to air remains open at this point.…”