Self-assembled graphene oxide/polyethyleneimine films as high-performance quartz crystal microbalance humidity sensors

As humidity is one of the most widely demanded environmental parameters, the precision of its detection is significant. An advanced humidity sensor will improve the validity of the humidity monitoring system. In this study, a facile chemical layer-by-layer self-assembly (CLS) method was developed for fabricating graphene oxide (GO)/polyethyleneimine (PEI) multilayer films. Owing to the chemical bonding between the PEI and GO, and the intrinsic stickiness of the PEI, layered films with different numbers of layers were successfully prepared using the CLS method and confirmed through ultraviolet–visible (UV–Vis) spectroscopy and the mass loading of quartz crystal microbalance (QCM). Morphological measurements revealed that the roughness and thickness of the films increased exponentially with the number of bilayers. The GO/PEI films were deposited on QCM electrodes using the CLS method to produce the humidity sensors. The humidity measurement results showed a high sensitivity (37.84 Hz/%RH) and rapid response/recovery (