Probing the adsorption of weak acids on graphite using amplitude modulation-frequency modulation atomic force...

Area of Science:

• Surface Science
• Materials Chemistry
• Nanotechnology

Background:

• Adsorption of self-assembled layers (SAL) on carbon surfaces is crucial for various applications.
• Previous studies attributed SAL adsorption to negatively charged hydrogen bonding (-CAHB), but direct visualization was lacking.

Purpose of the Study:

• To directly visualize and characterize the adsorption behavior of decanoic acid (DA) on highly ordered pyrolytic graphite (HOPG).
• To investigate the role of -CAHB in SAL formation on HOPG.
• To explore the effect of surface functionalization on DA adsorption.

Main Methods:

• Amplitude Modulation-Frequency Modulation Atomic Force Microscopy (AM-FM AFM) for high-resolution imaging.
• Thermodynamics calculations and adsorption isotherms to understand adsorption driving forces.
• Water-plasma treatment to modify HOPG surface properties.

Main Results:

• AM-FM AFM successfully visualized DA adsorption on HOPG, confirming SAL formation.
• Adsorption was driven by -CAHB between DA and negatively charged functional groups on HOPG.
• Multilayer adsorption and aggregate formation were observed on HOPG-functionalized steps.
• Water-plasma treatment resulted in uniform DA adsorption over the entire HOPG surface.

Conclusions:

• Direct visualization confirms -CAHB as the primary mechanism for DA SAL adsorption on HOPG.
• Surface functionalization significantly influences the adsorption pattern and uniformity of DA.
• AM-FM AFM is a powerful tool for characterizing molecular adsorption at the nanoscale.