Electron transport nonlocality in monolayer graphene modified with hydrogen silsesquioxane polymerization

Abstract

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 $700\phantom{\rule{0.28em}{0ex}}\ensuremath{\Omega}$, significantly exceeding the expected contribution from conventional Ohmic currents. The ${R}_{NL}$ dependence on the channel length resembles exponential decay with a characteristic length of $\ensuremath{\lambda}\ensuremath{\simeq}500\phantom{\rule{0.28em}{0ex}}\mathrm{nm}$ 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.