The Role of Electron Beam Induced Heating During 3D Nanoprinting

Focused electron beam induced deposition (FEBID) is a direct-write technique where an electron beam dissociates surface bound precursor molecules at the focal point of the electron beam. FEBID has become a more viable 3D nanoprinting tool due to the sophisticated applications shown recently, such as FEBID simulation [1] that predicts and controls the growth of 3D nanostructures by modeling the dynamic interaction of the electron beam and the precursor molecules, and its accompanying 3D CAD program (3BID) [2]. The ability to fabricate functional deposits such as plasmonic 3D nanostructures [3] and, scaffolds for 3D magnetic nanowires [4] with high degrees of freedom and precision using 3D FEBID show it is a promising additive nanomanufacturing tool. Unfortunately, distortions such as deflections in overhang 3D nanowires where linear growth is prescribed limit the reproduction of 3D FEBID designs. The 3BID program offers a tool to correct the distortions, but these are empirical. A pattern generating algorithm [5] released recently adjusts for proximity effects and compensates for height-dependent precursor coverage. The results show quite good congruence between the prescribed and deposited 3D nanostructures. Here, however, we quantify the mechanism that causes these distortions, paving the way to a more quantitative correction strategy. We will show a combination of experiments, models, and simulations that reveal beam-induced heating as the culprit that constrains the replication of 3D FEBID designs. The electron beam facilitating deposition during nanowire growth also causes Joule heating at the beam interaction region (BIR). The BIR temperature increases gradually during growth as nanowire elongation impedes heat flow. Heat transfer from extended surfaces is used to model the heat flow from the BIR, through the nanowire to the substrate. The temperature gradient in the deposit gives rise to an opposing precursor concentration gradient resulting in a deflected nanowire where otherwise a linear nanowire was specified. This vital role beam-induced heating plays in determining the final deposit shape will be discussed.