Prying apart Ruddlesden-Popper phases: Exfoliation into sheets and nanotubes for assembly of perovskite thin films

Protonated Ruddlesden-Popper tantalates and titanotantalates H₂[A_n-1B_nO_3n+1] (A = Na, Ca, Sr, La; B = Ta, Ti) that have acidic interlayer protons were exfoliated using tetra(n-butyl)ammonium hydroxide (TBA+OH-). H₂CaNaTa₃O₁₀ forms both single sheets and tubular "scrolls" when reacted to make TBA_xH_2-xCaNaTa₃O₁₀ colloids. In contrast, TBA_xH_2-xA₂Ta₂TiO₁₀ and TBA_xH_2-xALaTi₂TaO₁₀ (A = Ca, Sr) form sheets exclusively. The n = 2 tantalate TBA_xH_2-xSrTa₂O₇ forms high aspect ratio scrolls, as well as smaller amounts of sheets. In contrast to the analogous tantalates, the Ruddlesden-Popper titanates and titanoniobates have weakly acidic interlayer protons and exfoliate only to a limited extent. TBA_xH_2-xSrNb₂O₇ forms sheets exclusively, whereas TBA_xH_2-xCa₂Nb₂TiO₁₀ forms both sheets and scrolls. The n = 3 titanate H₂La₂Ti₃O₁₀ exfoliates into sheets using n-butylamine, and N_a2_La₂Ti₃O₁₀· xH₂O forms sheets when exfoliated with TBA⁺OH^-. When reacted with O-(2-aminopropyl)-O′-(2-methoxyethyl) polypropylene glycol 500, H₂La₂Ti₃O₁₀ exfoliates into monodisperse 20 x 100 nm scrolls. The exfoliated tantalates and titanotantalates can be electrostatically adsorbed to a Si/SiO₂/PDDA [PDDA = poly(diallyldimethylammonium chloride)] surface, forming perovskite monolayers. Above pH 9.5, TBA_xH_2-xSrLaTi₂TaO₁₀ sheets tile to densely cover a Si/SiO₂ surface derivatized with 4-aminobutyldimethylmethoxysilane (4-ABDMMS) and two bilayers of poly(sodium styrenesulfonate) (PSS) and poly(allylamine hydrochloride) (PAH). The exfoliated titanates and titanoniobates generally do not adhere to polycationic surfaces.