Structural and Electronic Properties of Benzyl Isothiocyanate Films

Benzyl isothiocyanate (BITC) is an aromatic isothiocyanate that exhibits antimicrobial effects, shows promise as an antivirulence compound, and can be encapsulated in nanoparticles for drug delivery. Despite the use of BITC in the condensed phase for biological applications, little structural or electronic information is understood for BITC films nor are the optimal parameters for forming well-ordered BITC self-assembled monolayers (SAMs) on Au surfaces clearly defined. In this work, we employed a novel amplitude-modulated atomic force microscopy (AM-AFM) technique to rapidly screen BITC SAMs by following various preparation protocols. Optimal BITC SAMs formed following the incubation of Au(111)/mica for at least 65 h in a 20 mM ethanolic BITC solution under ambient conditions. AM-AFM findings were corroborated with ultrahigh-vacuum scanning tunneling microscopy and spectroscopy (UHV STM/STS) analysis, confirming the formation of striped domains of BITC across the Au(111) surface. The density of states indicates significant hybridization of electronic states in the BITC and the Au(111) support. Density functional theory (DFT) calculations verified the experimentally observed packing structure for BITC/Au(111) and revealed a large work function attenuation following the adsorption of BITC on Au(111) surfaces. These results validate the use of AM-AFM to rapidly and with high precision characterize complex thin film surfaces for subsequent analysis using STM/STS and highlight the unique structural and electronic properties of BITC films when used in the condensed phase.