Abstract
Imaging nanometer- or molecule-scale topography has been achieved by dynamic atomic force microscopy (AFM) when a solid object of interest is damaged by vacuum exposure or electron irradiation. Imaging in a liquid offers a means to remove contaminations from the surface scanned using the microscope tip when the object is soluble to the surrounding liquid, typically water. In the present study, we attempted to take topographic images of crystalline sucrose. A problem arose due to the high solubility of this compound to water. Cantilever oscillation could not be excited in the saturated, viscous aqueous solution. By using n-hexanol instead of water, the solubility in the solvent and thus viscosity of the solution were reduced sufficiently to excite cantilever oscillation. Single-height steps and sucrose molecules were recognized in the images and thereby recorded on the (001)-oriented facets of sucrose crystals. Furthermore, two-dimensional distribution of liquid-induced force pushing or pulling the tip was mapped on planes perpendicular to the hexanol–sucrose interface. Observed uneven force distributions indicated liquid hexanol structured on the corrugated surface of sucrose. The viscosity tuning demonstrated here, which is not limited to hexanol instead of water, extends the range of liquid–solid interfaces to be probed by dynamic AFM.
Highlights
Structure determination of solid surfaces is a fundamental task in chemistry and physics at interfaces
The imaging liquid should be less viscous than water when saturated with sucrose, harmless to an operator since our liquid cell is open to the laboratory air, and inert on metals and adhesives of the cantilever assembly
A sucrose (001) surface was cleaved in the air and imaged with frequency-modulation atomic force microscopy (AFM) in n-hexanol, n-butanol, and noctanol
Summary
Structure determination of solid surfaces is a fundamental task in chemistry and physics at interfaces. Atomic force microscopy (AFM) is used for visualizing nanometer-scale and even molecule-scale topography of organic materials. Even if the surface is contaminated prior to immersion, the contaminated layers are spontaneously removed By applying this simple and efficient means, molecule- or atomscale alkali imhaalgidinegs12o−f144-nhiatsroabneielninea,2c,h3 ieCvaeCd Oin3,4−aq10ueMougsCOso3l,u11tioannsd. The imaging liquid should be less viscous than water when saturated with sucrose, harmless to an operator since our liquid cell is open to the laboratory air, and inert on metals and adhesives of the cantilever assembly.
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