Approaching Charge Compensation Limit for Promoting Magnetoresistance in 2D Nonlayered MoO2 via Surface Hydrogen Passivation

Large non-saturated magnetoresistances of semimetals are dominated by charge compensation due to their unique electronic structure. However, the dramatic magnetoresistance deteriorations are often observed in low-dimensional system resulting from high-density surface defects, where the suppression of charge scattering or concentration unbalance with highly maintained magnetoresistance is still challenging. Herein, a hydrogen annealing strategy is developed for surface defects passivation of 2D MoO 2 nanoflakes. Systematical characterization for H-MoO 2 nanoflakes reveals the formation of hydrogen chemical bonds that reduce surface defect density and slightly change Fermi level with unchanged bulk structures. An obviously enhanced magnetoresistance of 9.2% is demonstrated for H-MoO 2 nanoflakes compared to Ar-MoO 2 of 3.9% at 10 K and 9 T. The analysis of the nonlinearity Hall resistivity unravels the concentration of electrons and holes in H-MoO 2 approaches a more balanced equilibrium, which is attributed to surface defects passivation resulting in the suppression of self-doping effects for enhanced magnetoresistance rather than the reduced charge scattering with slightly enhanced carrier mobility. The research not only provides a universal surface passivation strategy on 2D nonlayered semimetals for approaching the charge compensation limit with the preserved magnetoresistance but also underscores the significance of surface passivation in tuning electronic structures of 2D nonlayered materials.