It’s a widely spread idea that performing AFM in liquids is a rather complicated research
approach. Actually, many tasks related to the investigation of molecular structures and complexes in a liquid environment claim high demands on the SPM equipment. The picture below shows an AFM scan of surfactant molecules dynamically self-assembled into parallel, hemicylindrical micelles on a hydrophobic graphite surface.

Sample: 10 mM aqueous solution of cetyltrimethylammonium bromide surfactant in contact with HOPG. AFM equipment: NTEGRA Prima, Constant force imaging mode in liquid cell using a very low set point ("so contact mode"– force 100pN). AFM probe: CSG01, 0.03 N/m Author: Hannes Schniepp, College of William and Mary, Williamsburg, VA, USA.

Observation of the dynamically self-assembled molecular structure in this case was a challenge. The imaging mode used is the “soft contact mode” – scanning with constant force using a very low set point. The vertical force of the probe needs to be kept as close as possible to the set point, in this case ~ 100 pN. If the force exceeds this value, the native molecular assembly will be disturbed (the periodicity of the micelles is ~5 nm.). For lower forces, the contrast vanishes. Note that the vertical topography modulation is only 0.1-0.2 nm, but still significantly above the noise level. This example shows also that NTEGRA nanolaboratory provides enough sensitivity and stability to study dynamic molecular structures in an aqueous environment.

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Cetyltrimethylammonium Bromide (CTAB) Length ca 2.4 nm, width 0.4 nm (Mmolecular modeling under AM1 method) Picture from molnet.eu - Polish Molecular Modeling Portal

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Highly Ordered Pyrolytic Graphite or Highly Oriented Pyrolytic Graphite (HOPG) refers to graphite with an angular spread of the between the graphite sheets of less than 1°. This highest-quality synthetic form is used in scientific research.

Name:      Topography of HOPG
SPM principle:     Constant Current mode
Size:     137x135 nm
From: http://www.ntmdt.com

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