Prying Apart Ruddlesden−Popper Phases:  Exfoliation into Sheets and Nanotubes for Assembly of Perovskite Thin Films

Abstract

Protonated Ruddlesden−Popper tantalates and titanotantalates H 2 [A n - 1 B n O 3 n +1 ] (A = Na, Ca, Sr, La; B = Ta, Ti) that have acidic interlayer protons were exfoliated using tetra( n -butyl)ammonium hydroxide (TBA + OH - ). H 2 CaNaTa 3 O 10 forms both single sheets and tubular “scrolls” when reacted to make TBA x H 2 - x CaNaTa 3 O 10 colloids. In contrast, TBA x H 2 - x A 2 Ta 2 TiO 10 and TBA x H 2 - x ALaTi 2 TaO 10 (A = Ca, Sr) form sheets exclusively. The n = 2 tantalate TBA x H 2 - x SrTa 2 O 7 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 x H 2 - x SrNb 2 O 7 forms sheets exclusively, whereas TBA x H 2 - x Ca 2 Nb 2 TiO 10 forms both sheets and scrolls. The n = 3 titanate H 2 La 2 Ti 3 O 10 exfoliates into sheets using n -butylamine, and Na 2 La 2 Ti 3 O 10 · x H 2 O forms sheets when exfoliated with TBA + OH - . When reacted with O -(2-aminopropyl)- O ‘ -(2-methoxyethyl) polypropylene glycol 500, H 2 La 2 Ti 3 O 10 exfoliates into monodisperse 20 × 100 nm scrolls. The exfoliated tantalates and titanotantalates can be electrostatically adsorbed to a Si/SiO 2 /PDDA [PDDA = poly(diallyldimethylammonium chloride)] surface, forming perovskite monolayers. Above pH 9.5, TBA x H 2 - x SrLaTi 2 TaO 10 sheets tile to densely cover a Si/SiO 2 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.