In the oil and gas industry, carbon steel is widely used in the construction of infrastructure, such as pipelines and tanks, for the transmission and storage of crude oil as well as petroleum products. This is due to its excellent mechanical properties, ease to work with, and low cost. However, it is vulnerable to corrosion. Ionic surfactant type of corrosion inhibitors have been widely applied against pipeline corrosion due to their high mitigation efficiency at low applied concentrations. Corrosion inhibition efficiency is closely related to the inhibitor adsorption mechanism. However, past corrosion inhibition research has generally focused on the electrochemical mechanisms of inhibition processes and associated corrosion rate reductions. In this current work, in situ tapping mode AFM phase imaging and contact mode AFM nano-scratching techniques have been applied to investigate the influence of different tetradecylbenzyldimethylammonium (BDA-C14) concentrations on inhibitor adsorption morphology and inhibition mechanisms. Analysis of tapping mode topography and phase images on mica show that multiple small holes/defects were present in the uniform inhibitor film at 50 and 100 ppm, which are above the surface saturation concentration. While at 25 ppm (below the surface saturation concentration), a non-uniform inhibitor film with different sizes of holes was detected. At 5 ppm, discontinuous inhibitor aggregates were observed. The contact mode AFM scratching technique was used to obtain the inhibitor film thickness at each concentration, which was consistent with the corresponding depth of holes measured by tapping mode topography. The molecular orientations and inhibitor film structures at each concentration are postulated based on the measured inhibitor film thickness. Observed adsorption morphologies on mica are connected with the corrosion inhibition behavior observed on UNS G1018 steel at each concentration.