Takumi Hiasa

Solution–TiO2 Interface Probed by Frequency-Modulation Atomic Force Microscopy

The topography and solvation structure of a solution–TiO2 interface were observed in the dark using highly sensitive, frequency-modulated atomic force microscopy (FM-AFM). The nucleation and growth of an ionic solute, KCl, in this study, were observed in constant frequency-shift topography. The force applied to the tip was determined as a function of tip–surface distance. Modulations were identified on some force curves and were found to be related to the site-specific density of water molecules.

Minitips in Frequency-Modulation Atomic Force Microscopy at Liquid--Solid Interfaces

A frequency-modulation atomic force microscope was operated in liquid using sharpened and cone-shaped tips. The topography of mica and alkanethiol monolayers was obtained with subnanometer resolution, regardless of nominal tip radius, which was either 10 or 250 nm. Force–distance curves determined over a hexadecane–thiol interface showed force modulations caused by liquid layers structured at the interface. The amplitude of force modulation and the layer-to-layer distance were completely insensitive to the nominal tip radius. These results are evidence that minitips smaller than the nominal radius are present on the tip body and function as a force probe.

FM-AFM imaging of a commercial polyethylene film immersed in n-dodecane

The subnanometer topography of a partially crystalline polyethylene film was observed in liquid n-dodecane using a frequency-modulation atomic force microscope. Locally ordered structures were found and assigned to a (100) facet of crystalline domains.

Competitive Adsorption on Graphite Investigated Using Frequency-Modulation Atomic Force Microscopy: Interfacial Liquid Structure Controlled by the Competition of Adsorbed Species

The competitive adsorption of long-chain (C18 and C24) carboxylic acids versus n-decanol on graphite was investigated using frequency-modulation atomic force microscopy. A long-range-ordered monolayer of the solute (stearic acid or lignoceric acid) developed in saturated decanol solution, whereas an ordered decanol monolayer was deposited from dilute solutions. The piconewton-order tip-surface force was observed in solutions as a function of the vertical and lateral coordinates, together with the topography of the monolayers. The tip-surface force was periodically modulated, which was interpreted with a solution structure commensurate with the ordered assembly of adsorbed monolayers. These results show that the solution structure at the interface was controlled by the competitively adsorbed species and thus was sensitive to the composition of the bulk solution.