Electron transport nonlocality in monolayer graphene modified with hydrogen silsesquioxane polymerization

A number of practical and fundamental applications of graphene requires modification of some of its properties. In this paper we study the effect of polymerization of a hydrogen silsesquioxane film on top of monolayer graphene with the intent to increase the strength of the spin-orbit interaction. The measured nonlocal resistances R-NL were found to be up to 700 Omega, significantly exceeding the expected contribution from conventional Ohmic currents. The RNL dependence on the channel length resembles exponential decay with a characteristic length of lambda similar or equal to 500 nm that is close to the spin-relaxation length in graphene reported elsewhere. The sensitivity of the measured effect to the electron-beam exposure was shown to decrease with an increased level of the surface contamination. However, no modulation of the effect is observed when an in-plane magnetic field is applied. This implies that a spin Hall model fails to explain the observed phenomenon and an alternative interpretation is required.