Formation of Stable Singularities in Mixed Monolayers of Porphyrins and Tetracosanoic Acid upon SFM Tapping

Abstract

Langmuir films of tetracosanoic acid have been transferred at 10 mN/m from water to mica surfaces and were characterized by scanning force microscopy (SFM) in the tapping mode at first as a smooth monolayer. Then, upon repeated tapping cycles, many singularities appeared in form of 2.5 nm high pairs of peaks in a plane, which stretched only 1.8 nm above the mica subphase. These peaks are attributed to islands of upright-standing molecules in a layer of molecules tilted at an angle of 35°. Transferring the films thus results first in a nonequilibrated film on mica, which undergoes relaxation upon tapping to a nonhomogeneous equilibrium phase. The same phenomenon was observed in films made of rigid porphyrin and tetracosanoic acid domains at 20 mN/m. The formation of fluid fatty acid structures at pressures where strong ordering prevails in pure fatty acid films was related to a reorientation in the rigid porphyrin domains after the transfer to mica. SFM phase shift images were applied to different hard and soft parts of the mixed monolayer, and scanning near-field optical microscopy was used to confirm the assignment of the porphyrin domains on the basis of their fluorescence.

Growth Mechanisms of Octadecylphosphonic Acid Self-Assembled Monolayers on Sapphire (Corundum): Evidence for a Quasi-equilibrium Triple Point

“…According to the theory of phase imaging, harder parts of the sample have greater phase shifts, under the light tapping conditions employed here, and thus appear lighter in color. This has been verified for polymers, mixed Langmuir−Blodgett films, and bilayers of amphiphiles b there is a smaller phase shift (consistent with a softer film) for the parts of the sample covered by the continuous phase (meaning they appear dark in the image) than for the low regions surrounding the islands.…”

Monolayer Fibers on Solid Surfaces Made of a Quinone Sulfonate

“…To check whether the quinone 1 film adhered to the porphyrin 2 film without removing it and to investigate how the quinone film rearranged upon transfer, we applied atomic force microscopy (AFM) again. Figure b shows the characteristic stripes of the underlying porphyrin layer (pH 2.5), which have been characterized before . Without quinone, the upright-standing porphyrin stripes have a height of 1.7 ± 0.1 nm, and the surrounding porphyrin dimers are 0.7 ± 0.1 nm high.…”

“…We then formed a photoactive, bilayered LB-film system using fibers made of 1 as an electron acceptor and β-tetraethyl-β-tetrapyridinyl porphyrin ( 2 ) monolayers as donors. ,,, At pH = 2.5, the porphyrin 2 forms LB-films on mica, containing upright-standing stripes surrounded by flat-lying porphyrin dimers . The upright-standing porphyrins fluoresce at 660 nm, and the flat-lying dimers fluoresce at 645 nm.…”

Starre Lipidmembranen und Nanometerlücken – Motive zur Gestaltung molekularer Landschaften

“…Bei mehrmaligem Tapping der fluiden/starren Monoschicht richteten sich viele Eicosansäuremoleküle steil auf und bildeten 30 Å hohe Spitzen (Singularitäten) in der 24‐Å‐Ebene (Abbildung 26). Die Singularitäten sind sehr langlebig (>7 Tage), obwohl sie im fluiden Bereich der Monoschicht stehen 95…”