Figure 2: Preparation of BP nanoribbons and nanoribbon-bridged micro-devices.

(a–e) Illustration of the fabrication process. (a) Exfoliation of BP flakes onto a SiO₂ substrate. Crystal directions are identified by Raman analysis. (b) Formation of PMMA stripes on the BP flake by the first electron beam lithography (EBL). (c) Removal of the exposed BP by dry etching, and removal of the PMMA protecting stripes with acetone, to form BP nanoribbons (NRs). (d) Opening up the contact area via the second EBL, Ar⁺ milling of the exposed contact area and electron beam deposition of Ti/Au and lift-off. The Ti/Au layer offers good thermal/electrical contact with BP nanoribbon. Inset shows optical image of BP nanoribbons coated with four Ti/Au contacts resting on the SiO₂ substrate. (e) Dry transfer of a BP nanoribbon onto the micro-device to bridge two suspended pads, and connection of the Ti/Au to the metal electrodes on the pads using FIB Pt bonding. (f) Plot of total thermal resistance (1/K) at room temperature multiplied by cross-sectional area (A) as a function of the nanoribbon length. Error bars include the errors (∼8%) from thermal conductance and sample size measurements. These ribbons have similar thicknesses. The linear relationship extrapolating to nearly zero indicates negligible thermal contact resistance for both ZZ and AC oriented nanoribbons. (g) Linear electrical current–voltage curves of the ZZ and AC oriented nanoribbons, measured on the micro-devices. All the measured devices (six devices) show linear I–V curves.