{"id":6013,"date":"2012-07-18T22:26:23","date_gmt":"2012-07-18T22:26:23","guid":{"rendered":"https:\/\/mtlsites.mit.edu\/annual_reports\/2012\/?p=6013"},"modified":"2012-08-01T18:36:27","modified_gmt":"2012-08-01T18:36:27","slug":"measuring-ion-energy-distribution-using-batch-microfabricated-rpas","status":"publish","type":"post","link":"https:\/\/mtlsites.mit.edu\/annual_reports\/2012\/measuring-ion-energy-distribution-using-batch-microfabricated-rpas\/","title":{"rendered":"Measuring Ion Energy Distribution Using Batch-microfabricated RPAs"},"content":{"rendered":"

The need to measure particle energies arises in many applications, from calibrating electron sources for electron guns in precision microscopes to determining the efficiency of space-based ion beam thrusters.\u00a0 Retarding potential analyzers (RPAs) are capable of filtering particles based on their energy and have been used as early as the late 1950s and early 1960s for such purposes [1<\/a>] <\/sup>.\u00a0 However, these devices maintain limited application due to stringent dimensional constraints driven by plasma Debye length.\u00a0 Cold dense plasmas require minute apertures and tight spacing tolerances between biasing grids that are difficult to enforce using conventional means.\u00a0 We suggest microelectromechanical system (MEMS) batch-fabrication techniques in order to achieve unprecedented alignment accuracy of successive electrodes while incorporating the necessary micron-scale features.\u00a0 Assembly to a precision of a few tens of microns has been demonstrated with a hybrid RPA (see Figure 1a) [2<\/a>] <\/sup>.\u00a0 Figure 1b shows the fully MEMS-fabricated sensor inspired by in-plane assembly of high-voltage devices, which will have tolerances on the order of 1\u03bcm [3<\/a>] <\/sup>.<\/p>\n

Augmenting the optical transparency of RPAs provides a more direct path for particles to the collector plate.\u00a0 Signal strength is thus improved as the effective collection area is increased.\u00a0 Preliminary results and comparisons between MEMS-fabricated electrodes and conventional stainless steel mesh have revealed an ameliorated signal quality.\u00a0 Figure 2 shows a greater than two-fold improvement in peak signal strength with the micromachined grids over the conventional RPA [2<\/a>] <\/sup>.\u00a0 Currents captured by the various grids and simulations suggest the possibility of ion beam focusing and interception of ions prior to reaching the collector.\u00a0 Alteration of the internal dynamics of the sensor provides a cleaner signal that may lead to a better interpretation of the measurements than with models that incorporated the stochastic behavior of charged species through randomly oriented electrode apertures.<\/p>\n\n\t\t