Preserving the 7x7 surface reconstruction of clean Si(111) by graphene adsorption

We employ room-temperature ultrahigh vacuum scanning tunneling microscopy (UHV STM) and {em ab-initio} calculations to study graphene flakes that were adsorbed onto the Si(111)$-$7$times$7 surface. The characteristic 7$times$7 reconstruction of this semiconductor substrate can be resolved through graphene at all scanning biases, thus indicating that the atomistic configuration of the semiconducting substrate is not altered upon graphene adsorption. Large-scale {em ab-initio} calculations confirm these experimental observations and point to a lack of chemical bonding among interfacial graphene and silicon atoms. Our work provides insight into atomic-scale chemistry between graphene and highly-reactive surfaces, directing future passivation and chemical interaction work in graphene-based heterostructures.