Abstract
This article presents a focused electrospray beam source and discusses its potential for microfabrication. Its main elements are an electrospray emitter electrode (a point source of charged nanodroplets), an extractor electrode, a skimmer electrode, and an Einzel electrostatic lens. The focusing parameters of the source are calculated by integrating the equations of motion of the charged droplets in the axisymmetric electrostatic field generated by the electrodes. The results of the model are validated with a laboratory source replica by characterizing the sputtered region produced by the focused beam on a silicon target and comparing it with the image obtained with the model. In the experiments, the size of the focused beam at the image plane is at least 20 times smaller than that of the unfocused beam, despite the presence of aberrations that have a negative effect on the ability to concentrate the beam. In a well aligned source, the sputtered area is close to a disk, and spherical and chromatic aberrations are the most significant nonidealities making the size of the image larger than the ideal one. When the emitter is deliberately misaligned, spherical and chromatic aberrations continue increasing the size of the image, while astigmatism distorts its circular shape. All aberrations are reduced by increasing the strength of the focusing electrostatic field while maintaining the net acceleration potential of the beam. The focusing column increases the particle density of the beam and advances the development of electrosprayed nanodroplet beams as a tool for surface engineering.
Highlights
The use of atomic and cluster ion beams in the form of broad ion sources and the focused ion beam (FIB) has contributed to the creation and improvement of surface modification techniques such as physical sputtering, doping, and thin-film deposition.1–5 These processes rely on the transfer of the kinetic energy of the beam particles to the target, which is intense enough to alter its atomic arrangement, leading, for example, to surface amorphization6,7 and sputtering.8–10 The size of the projectile is a major factor determining the outcome of the impact
Beams of electrosprayed droplets are amenable to strong electrostatic focusing
The analysis of a simple focusing column composed by an emitter, an extractor, a skimmer, and an Einzel lens suggests that spherical and chromatic aberrations are the main factors limiting the minimum beam spot size in an actual implementation
Summary
The use of atomic and cluster ion beams in the form of broad ion sources and the focused ion beam (FIB) has contributed to the creation and improvement of surface modification techniques such as physical sputtering, doping, and thin-film deposition. These processes rely on the transfer of the kinetic energy of the beam particles to the target, which is intense enough to alter its atomic arrangement, leading, for example, to surface amorphization and sputtering. The size of the projectile is a major factor determining the outcome of the impact. The use of atomic and cluster ion beams in the form of broad ion sources and the focused ion beam (FIB) has contributed to the creation and improvement of surface modification techniques such as physical sputtering, doping, and thin-film deposition.. The use of atomic and cluster ion beams in the form of broad ion sources and the focused ion beam (FIB) has contributed to the creation and improvement of surface modification techniques such as physical sputtering, doping, and thin-film deposition.1–5 These processes rely on the transfer of the kinetic energy of the beam particles to the target, which is intense enough to alter its atomic arrangement, leading, for example, to surface amorphization and sputtering.. The diameter D of electrosprayed droplets can be controlled from a few nanometers to tens of micrometers, while their chargeto-mass ratio q/m scales more favorably than that of cluster ions (q/m ∝ D−3/2 vs q/m ∝ D−3) This makes it easier to electrostatically accelerate them into the hypervelocity range typical of particle beams. At lower impact velocities, electrosprayed droplets have been used for molecular-level etching of native silicon scitation.org/journal/adv oxide on surface, surface cleaning and smoothing, and surface analysis by secondary ion mass spectrometry.
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