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(Color online) (a) Schematic picture of measurement set-up in C-AFM, (b) SEM image of platinum wire AFM tip.
(Color online) (a) Optical microscopic image, (b) topological, and (c) conductance AFM images of h-BN flakes on gold-coated mica. The profile lines of (b) and (c) show changes of thickness (nm) and current (nA) along dashed line of (a), respectively. The limit of current which can be measured in C-AFM is 10 nA. Conductance AFM image of (c) was acquired using a tip bias of 1 V. The scale bar is 5 μm.
(Color online) I-V measurements (a) in 3 nm-thick h-BN with various loading forces and (b) in h-BN of various thicknesses (N = layer number) with fixed loading force of 2nN. Inset of (a) shows tunnel conductance in the linear regime of small tip bias with different loading forces. (c) I-V curves of mono-, bi-, and tri-layer h-BN. Inset of (c) shows log-scale tunnel conductance in the linear regime (direct tunneling).
(Color online) (a) ln(I/V2) vs. 1/V curves for fitting of Fowler-Nordheim tunneling model. From linear fitting of curves, barrier height of 3.07 eV (±0.3) for tunneling was calculated. (b) Change of breakdown voltage with thickness of h-BN. The slope of linear fitting in (b) shows dielectric strength of ultrathin h-BN (7.94 MV/cm). Inset of (b) shows log-scale tunnel current curves to determine breakdown voltages for h-BN of various thicknesses, where numbers represent layer of h-BN.
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