UC San Diego

Small particle interactions with surfaces dominate processes from industrial manufacturing to micrometeorite impacts in space. For particles that are optically visible a wide range of modeling and studies exist to characterize the mechanical behavior and material properties that govern these interactions. The properties of materials at smaller scales, below microns in size, can differ from bulk measurements and the body of literature examining these smaller interactions lacks the same variety of experimental data. Presented herein is a new tool, the Aerosol Impact Spectrometer (AIS), for the characterization of submicron particles impacting on surfaces.

The AIS is composed of a particles source, particle mass spectrometer, linear accelerator, impact target, and post impact detectors. Highly charged particles are generated using an electrospray ionization source before being injected into vacuum through an aerodynamic lens. A subset of the particle beam is selected using a quadrupole deflector and individual particles are injected into a linear electrostatic trap. As particles oscillate in the trap charge detection mass spectrometry is performed to determine individual particle mass and charge before being ejection into a linear accelerator. A series of high voltage elements either accelerates or decelerates each particle to a select final energy before impacting a target surface. The subsequent behavior of the particle is examined with a variety of charge sensitive detectors including measurements of particle sticking and rebound velocity.

The rebound velocities over a wide range of initial energies has been demonstrated using polystyrene latex spheres, tin metal particles, and frozen water-ice. The behavior of each species is distinct and further analysis of the tin metal particles shows behavior consistent with non-bulk material properties of the metal. Evidence for water ice melting and fragmentation have also been observed with high impact energies. Finally, the techniques employed to examine particle behavior after impact have also been applied to examine durability in freestanding ultrathin films under particle bombardment and measure the efficacy of large particle detection using a microchannel plate detector.