查看更多>>摘要：Knowledge of the actual temperature of nanoparticles under electron beam irradiation is of growing demand for in situ TEM studies. In this work, we addressed the problem with an experimental study of the temperature increment of single AuGe nanoparticles in a TEM and a STEM. The two-phase hemispherical AuGe nanoparticles were formed by the dewetting of an Au/Ge film on a SiNx substrate. The nanoparticles were thermally cycled in an electron microscope in the 293–653 K temperature range, under a wide range of electron beam currents. The jump-like change of the morphology of the AuGe nanoparticles at melting was used as a temperature label. The melting-crystallization process in binary alloy nanoparticles is fully reversible, with a large temperature hysteresis. It could be repeated on the same nanoparticle, providing a simple and robust way to measure the local temperature increment induced by the electron beam. It was shown that the temperature of the AuGe nanoparticles rose linearly with the e-beam current density J, and the temperature increment reached 25 K at J ～ 1.8 × 106 A/m2 in the TEM. Given a fully known specimen geometry, the temperature increment was calculated when using theoretical approaches and compared with the experimental observations. As a result, recommendations for the assessment of real temperature in similar configurations were provided. In the STEM mode, no change in the temperature of the nanoparticles was registered at conventional parameters of the electron beam and the raster scans, which makes this mode preferable for in situ studies of metal and alloy nanoparticles.
查看更多>>摘要：Blade-Like Field Emitters (BFE), as defined here, are emitters expanded in one direction, forming a sharp emitting edge instead of a sharp tip. These structures have four main advantages compared to their needle counterparts, i.e., they are mechanically firmer, are better electrical and thermal conductors, and provide a larger emission area. We focus on the optimization of the last of these. We evaluate the emission properties of three types of BFEs, which we short-named hSoC-blade, HCP-blade and Elli-blade. Each is built from the expansion of a hemisphere-on-a-cone (hSoC), hemisphere-on-a-cylindrical-post (HCP) and an ellipsoidal (Elli) emitter, respectively. The characteristics of the field enhancement factor, the local electrostatic field distribution on each blades’ edges and their notional area (An) of emission as a function of the expansion length are described. Finally, we point out how to improve the edge of the HCP-blade to obtain the optimal profile, which yield the largest An.
NSTL
Elsevier