10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
A Computational Study of Electrostatic Focusing of Aerosol Nanoparticles Using A 3-Electrode Einzel Lens
RAYHAN AHMED, Ranganathan Gopalakrishnan, The University of Memphis
Abstract Number: 857 Working Group: Aerosol Modeling
Abstract The focusing and deflection of electrons and ions using electric fields has been successfully harnessed for many applications and instrumentation development. An adjustable electric field can manipulate the flight path of an electron, ion or a charged particle. This study explores the possibility of focusing charged aerosol nanoparticles, which are much heavier compared to electrons and ions. The study revealed that charged nanoparticles could also be focused towards a focal point by applying an adjustable electrostatic field along the flight path of the same. This study introduces a non-dimensional parameter χe (neΔV/mU2 ), the ratio of electrostatic potential energy to the kinetic energy of an aerosol nanoparticle that greatly affects focusing performance. In the absence of collisions with gas molecules (vacuum), the sum of kinetic and potential energy of a particle remains almost constant, and the applied electrostatic field controls the direction of motion. In this study, the focusing device is a 3-electrode electrostatic lens where the electrostatic field deflects particle trajectories towards the central axis of the lens. The average focal length of the lens is seen to have an inverse power relationship with χe (i.e.) when χe is almost zero the focal length is infinity and decreases with the increasing χe. Multiple focal points appear when electrostatic potential energy is much larger than kinetic energy (χe> 3 in this study). The focusing performance also depends on the electrostatic lens geometry and the attributes of the inlet particles - initial kinetic energy, direction of motion and particle beam radius at the entrance of the electrostatic lens. Similar to electron and ion optics, the focusing performance is limited by spherical aberration and beam divergence. Both χe and initial beam width seems to maintain a cubic relationship with spherical aberration, and the divergence angle has a quadratic relationship with χe which ultimately increases the spherical aberration. From this study, it can be inferred that better focusing performance i.e. a tighter beam of nanoparticles with minimum spherical aberration and small divergence angle could be achievable while χe<1, initial particle motion is parallel to the central axis, and initial beam width is much smaller compared to the diameter of the focusing device. The generation of highly focused beam of nanoparticles is motivated by nano-pattern fabrication research that has numerous applications in electronic and plasmonic devices.