Propulsion and assembly of remotely powered p-type silicon microparticles

In this letter, we discuss how to prepare millions of uniform p-type silicon (Si) microparticles using top-down fabrication processes and how to remotely control their dynamics when they are suspended in water and powered by external alternating current (AC) electric fields. These microparticles present positively charged carrier types (majority carriers from boron atom doping in the intrinsic Si) and negatively charged carrier types (minority carriers from the free electrons in the Si lattice), which electrostatically affects their negatively charged surfaces and enables a variety of programmable behaviors, such as directional assembly and propulsion. At high AC electric field frequencies ( f > 10 kHz), the microparticles assemble by attractive dielectrophoretic polarization forces. At low electric field frequencies ( f ≤ 10 kHz), the microparticles propel by induced-charge electrophoretic flows. The ability to manipulate the electrostatic potential distribution within and around the microparticles (i.e., by controlling electronic carrier types through doping) is useful for designing a number of new dynamic systems and devices with precise control over their behaviors.