Atomically Defined Templates for Epitaxial Growth of Complex Oxide Thin Films

Abstract

Atomically defined substrate surfaces are prerequisite for the epitaxial growth of complex oxide thin films. In this protocol, two approaches to obtain such surfaces are described. The first approach is the preparation of single terminated perovskite SrTiO 3 (001) and DyScO 3 (110) substrates. Wet etching was used to selectively remove one of the two possible surface terminations, while an annealing step was used to increase the smoothness of the surface. The resulting single terminated surfaces allow for the heteroepitaxial growth of perovskite oxide thin films with high crystalline quality and well-defined interfaces between substrate and film. In the second approach, seed layers for epitaxial film growth on arbitrary substrates were created by Langmuir-Blodgett (LB) deposition of nanosheets. As model system Ca 2 Nb 3 O 10 -nanosheets were used, prepared by delamination of their layered parent compound HCa 2 Nb 3 O 10 . A key advantage of creating seed layers with nanosheets is that relatively expensive and size-limited single crystalline substrates can be replaced by virtually any substrate material.

Film transfer enabled by nanosheet seed layers on arbitrary sacrificial substrates

“…Ca 2 Nb 3 O 10 nanosheets were prepared and deposited as a seed layer by Langmuir-Blodgett (LB) deposition 15 following the procedure described elsewhere. 13,16 In short, the layered parent compound HCa 2 Nb 3 O 10 was dispersed in demi-water and tetra-n-butyl ammonium hydroxide was added as an exfoliation agent to separate the crystals into discrete nanosheets. Monolayers of these nanosheets were deposited onto freshly cleaved phlogopite mica substrates by LB deposition.…”

Water sensitivity and microporosity in organosilica glasses

“…This generally results in a denser packing, strong surface hydrophobicity and easy access to functional groups. [1][2][3] Organic groups in bridging positions (Si-R-Si) are part of the network backbone and are more encapsulated by the surrounding siloxane bonds, affecting the micropore structure by acting as spacers. [4][5][6] Such molecular design in combination with the tunability of sol-gel syntheses enables the development of tailored organosilica materials for a variety of applications in e.g.…”

“…This results in denser packing, easy access to functional groups and strong surface hydrophobicity. [1][2][3] Organic groups in bridging positions (Si-R-Si) are part of the network backbone and are more encapsulated by the surrounding siloxane bonds, affecting the micropore structure by acting as spacers. [4][5][6][7] An important advantage of bridged organosilicas is their superior hydrothermal stability as compared to terminal methylated silica and inorganic silica (amorphous SiO2).…”

“…An extensively studied example of hybrid organosilica is the ethylene-bridged network, usually derived from the precursor 1,2-bis(triethoxysilyl)ethane (BTESE). The introduction of these ethylene bridges between Si atoms improves the fracture resistance of the material as compared to both pure silica and silica with organic terminal groups 1,2 and a high Young's modulus is maintained at high porosities. 1 The ethylene bridge tends to enhance the average micropore size as compared to pure silica, [3][4][5][6] but despite the addition of hydrophobic organic segments the material keeps on having a significant affinity for water.…”

“…The introduction of these ethylene bridges between Si atoms improves the fracture resistance of the material as compared to both pure silica and silica with organic terminal groups 1,2 and a high Young's modulus is maintained at high porosities. 1 The ethylene bridge tends to enhance the average micropore size as compared to pure silica, [3][4][5][6] but despite the addition of hydrophobic organic segments the material keeps on having a significant affinity for water. [6][7][8][9][10] Ethylene-bridged organosilica in mesoporous architectures is particularly interesting as low-k material, 1,11 is UV-responsive upon metal doping 12 and has been used in chiral thermochromic composites.…”