Atomic Force Microscopy Imaging of Crystalline Sucrose in Alcohols

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.

Tip Charge Dependence of Three-Dimensional AFM Mapping of Concentrated Ionic Solutions

“…Three-dimensional AFM has been applied to image the local water density distribution on proteins [6], DNA [21,22], lipid bilayers [23], and nanoparticles [24]. The robustness of the method has enabled the 3D molecular mapping of the interfacial structure of organic solvents [25][26][27][28][29], concentrated electrolyte solutions [30], and ionic liquids [31][32][33]. In particular, it provided high spatial resolution images of the electric double layer of an ionic liquid on an electrode surface [32].…”

Predicting hydration layers on surfaces using deep learning

“…3 Atomic force microscopy (AFM) 4 is being developed to image these critical atomic interactions at high speed-commensurate to the molecular-diffusion timescales-and atomic-scale resolution. [5][6][7][8][9][10][11][12][13][14] However, the interpretation of the AFM images at such resolutions still remains a massive challenge. The measured force between an AFM tip and the surface hydration layers in the solution comprises tipsurface-solvent interactions and entropic effects, and linking this to the image-contrast mechanism requires an intensive modelling approach for reliable understanding.…”

Generalised deep-learning workflow for the prediction of hydration layers over surfaces

“…The nature of the complex hydration structures formed at solid-liquid interfaces plays a key role in many macroscopic surface phenomena [1,2], that drive various natural and technological processes [3]. Amongst many complementary techniques to characterise solid-liquid interfaces at the nanoscale, Atomic force microscopy (AFM) [4] has emerged as a leading method to image systems in solution at high speed with molecular resolution [5][6][7][8][9][10][11][12][13][14]. However, the convolution of tip-surface-solvent interactions and entropic effects in the measured force at high resolution means that it remains a challenge to provide comprehensive understanding and interpretation of the results -requiring extensive free energy simulations [15][16][17][18].…”