This study addresses high electric field transport in multilayer black phosphorus (BP) field effect transistors (FETs) with self-heating and thermal spreading by dielectric engineering.Interestingly, we found that multilayer BP device on a SiO 2 substrate exhibited a maximum current density of 3.310 10 A/m 2 at an electric field of 5.58 MV/m, several times higher than multilayer MoS 2 . Our breakdown thermometry analysis revealed that self-heating was impeded along BP-dielectric interface, resulting in a thermal plateau inside the channel and eventual Joule breakdown. Using a size-dependent electro-thermal transport model, we extracted an interfacial thermal conductance of 1~10 MW/m 2 •K for the BP-dielectric interfaces. By using hBN as a dielectric material for BP instead of thermally resistive SiO 2 (κ ~ 1.4 W/m•K), we observed a 3 fold increase in breakdown power density and a relatively higher electric field endurance together with efficient and homogenous thermal spreading because hBN had superior structural and thermal compatibility with BP. We further confirmed our results based on micro-Raman spectroscopy and atomic force microscopy, and observed that BP devices on hBN exhibited centrally localized hotspots with a breakdown temperature of 600K, while the BP device on SiO 2 exhibited a hotspot in the vicinity of the electrode at 520K.

In situ small-angle X-ray scattering (SAXS) is used to show that iron oxide nanoparticles (NPs) of a range of sizes form hexagonally ordered monolayers (MLs) on a diethylene glycol liquid surface, after drop-casting the NPs in hexane and subsequent hexane evaporation. The formation of the ordered NP ML is followed in real time by SAXS when using a heptane solvent. During drying, the NPs remain in the hexane or heptane layer, and an ordered structure is not formed then. After drying, the NPs are farther apart than expected from only van der Waals attraction between the NP cores and Brownian motion considerations, which suggests the importance of ligand attraction in binding the NPs.

No abstract