Exploring the heat transfer for spherical nanoparticles under electron irradiation

Abstract

To explore the thermal effect of an electron beam irradiation during a scanning electron microscope (SEM) imaging process, a Monte Carlo (MC) method has been used to calculate the spatial distributions of local temperature rise in a spherical gold (Au) nanoparticle (i.e. Au Nano sphere (Au-NS)). The influencesofthe size of the nanoparticle, incident angle of the primary electron (PE) beam, PE energy and the PE beam size on the heat generation were systematically investigated. First of all, this work verified that Au-NSs with various sizes present different heat capacities under the same condition of the electron irradiation. The smaller the sphere, the less heat is accumulated. Besides, the heat in the periphery of a relatively large Au-NS is less than that inside. As the incident angle increases, the distribution regions of the temperature rise gradually expand from the contact surface deep into the interior and its amount rises proportionately. This rule is the same for an Au-NS with the diameter of 40 nm under various PE energies, but is quite opposite for the case of an Au-NS with the diameter of 5 nm. This study next presents that the PE beam size affects the heat generation in a spherical Au nanoparticle significantly. The distribution of temperature rise specifically shows a gradually reduced intensity towards the larger PE beam size. In addition, this work found that the total electron (TE) line-scan profile inversely relates the temperature contour map. The underlying mechanisms of these results were explained in detail primarily with the analysis of the trajectory of electrons as well as the interaction of electron-solid. This work, on the one side, greatly benefits the study of the relationship between the sample structures and the local thermal effect under the electron irradiation. On the other side, this work provides a further understanding and elucidation of the mechanism of electron-beam-induced deposition, compared to those earlier reports only focusing on plane bulks. It is believed that the proceeding of the semiconductor industry would be significantly promoted by this study.