Electrosprayed Heavy Ion and Nanodrop Beams for Surface Engineering and Electrical Propulsion.

摘要

In this project we have investigated the generation, interaction and energetic impact of electrosprayed nanodroplets and molecular ions, covering continuously the projectile size range from 1 nm up to hundreds of nm. The 1-20 nm size range is of great interest to achieve variable specific impulse (Isp) from 100 s to >1000 s in drop-based electrical propulsion, while pure molecular ion emission enables higher Isp. The resulting knowledge is directly applicable to electrospray thrusters/electric propulsion (achievement of improved and variable Isp, maximization of thrust, power density and propulsive efficiency, quantification of the lifetime of electrospray thrusters), and will lead to new opportunities in other fields such as MEMS and IC fabrication (broad-beam and focused-beam nanodroplet and ion sources for high speed beam milling and microfabrication, reactive nanodroplet and ion etching, polishing of large and curved mirrors), surface processing (patterning of crystalline surfaces with amorphous layers, patterning of a textured surface with controllable roughness, strengthening of materials for increased thruster life, microscopy), and secondary ion mass spectrometry (SIMS) of organic surfaces. The goals of this project were to gain a detailed, first-principles understanding of the production of nanoprojectiles, the extraction of their beams, their interaction with surfaces, and the investigation of the propulsive and surface processing applications outlined above. The specific research problems tackle during this projects and accomplishments include: the development of a basic electrospray beam model, and measurements of the spreading of the beam at varying temperture; the experimental characterization and typical thruster surfaces bombarded by electrosprayed nanodroplets, and a molecular dynamics study of the physics of nanodroplet impact; the extension of the minimum size of electrosprayed nanodroplets, and the exploration of energetic propellants for propulsion and sputtering; and molecular dynamics simulations of the fragmentation and emission of ions from ionic liquids.