Atomic force microscopy (AFM) has played an increasingly important role in characterizing surface morphology and surface properties of materials. However, the ability to identify and map the surface chemical heterogeneity has remained an unfulfilled opportunity in the field of AFM. Chemical force microscopy (CFM) is a successful approach for enhancing the chemical sensitivity of AFM. However, CFM has usually been conducted in liquid instead of air to eliminate capillary effects. In our study, a well-controlled humidity system is used to enhance the sensitivity of AFM in characterizing surface chemical heterogeneity. The relative humidity (RH) of the tip-sample environment is controlled using a humidity generator and a novel small-volume environmental chamber designed and fabricated at the National Institute of Standards and Technology. The relative humidity in the chamber can be controlled from nearly 0 % RH up to 95 % RH. The effects of RH on AFM image contrast are studied using a patterned SAM sample and polymers with alternating regions of hydrophobic and hydrophilic materials. The results clearly demonstrate that the image contrast between hydrophilic and hydrophobic regions of a surface is substantially increased in elevated relative humidity environments.
Citation: Seeing at the Nanoscale-An international conference
Pub Type: Journals
AFM, chemical heterogeneity, humidity chamber, Nanoscale, phase contrast