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.

异硫氰酸苄酯（Benzyl isothiocyanate, BITC）是一类芳香族异硫氰酸酯。它兼具抗菌活性，作为抗毒力化合物展现出良好的应用潜力，还可被包封于纳米颗粒中用于药物递送。尽管BITC已在凝聚态生物应用中得到使用，但目前学界对其薄膜的结构与电子性质仍缺乏足够认知，且在金（Au）表面制备有序度优异的BITC自组装单层膜（self-assembled monolayers, SAMs）的最优参数也尚未明确。本研究采用一种新型调幅原子力显微镜（amplitude-modulated atomic force microscopy, AM-AFM）技术，通过遵循多种制备方案对BITC SAMs进行快速筛选。实验结果显示，将Au(111)/云母基底置于20 mM的BITC乙醇溶液中，在环境条件下孵育至少65小时后，可得到最优的BITC SAMs。该实验发现通过超高真空扫描隧道显微镜与光谱学（ultrahigh-vacuum scanning tunneling microscopy and spectroscopy, UHV STM/STS）分析得到了验证，证实BITC在Au(111)表面形成了条纹状畴结构。态密度分析表明，BITC与Au(111)基底的电子态发生了显著杂化。密度泛函理论（density functional theory, DFT）计算验证了实验中观测到的BITC/Au(111)堆积结构，并揭示出BITC吸附于Au(111)表面后，体系功函数出现大幅衰减。上述结果证实了AM-AFM可用于快速且高精度地表征复杂薄膜表面，为后续采用STM/STS开展相关分析提供了可靠支撑，同时也凸显了凝聚态BITC薄膜独特的结构与电子性质。