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

Protonated Ruddlesden-Popper tantalates and titanotantalates H-2[A(n-1)B(n)O(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(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 H2La2Ti3O10 exfoliates into sheets using n-butylamine, and Na2La2Ti3O10. xH(2)O 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(x)Ha(2-x)SrLaTi(2)TaO(10) sheets the 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.