Understanding the Strength of the Selenium -- Graphene Interfaces

Abstract: We present a comprehensive first-principles Density Functional Theory (DFT) analyses of the interfacial strength and bonding mechanisms between crystalline and amorphous selenium(Se) with graphene(Gr), a promising duo for energy storage applications. Comparative interface analyses are presented on amorphous silicon(Si) with graphene and crystalline Se with aluminum(Al) substrate. The interface strength of monoclinic Se (0.43 J/m2) and amorphous Si with graphene (0.41 J/m2) is similar in magnitude. While both materials (c-Se, a-Si) are bonded loosely by van der Waals (vdW) forces over graphene, interfacial electron exchange is higher for a-Si/Gr. This is further elaborated by comparing potential energy step and charge transfer (delta q) across the graphene interfaces. The delta q for c-Se/Gr and a-Si/Gr are 0.3119 e-1 and 0.4266 e-1, respectively. However, the interface strength of c-Se on the 3D Al substrate is higher (0.99 J/m2), suggesting stronger adhesion. The amorphous Se with graphene has comparable interface strength (0.34 J/m2), but electron exchange in this system is slightly distinct from monoclinic Se. The electronic characteristics (density of states analysis) and bonding mechanisms are different for monoclinic and amorphous Se with graphene and they activate graphene via surface charge doping divergently. Our findings highlight the complex electrochemical phenomena in Se interfaced with graphene, which may profoundly differ from their 'free' counterparts.