Continetti Group

Machine AIM - the Aerosol Impact Spectrometer (AIS)

The goal of this project is to use hypervelocity impact of single mass- and charge-selected nanoparticles and atmospheric aerosols as a probe of the composition, radial structure and solid phase of the particles. The major components of the apparatus allow for the trapping of particles, measurement of the mass and charge of a single particle, acceleration of that particle to a high velocity and finally, impact of the particle on an inert surface with mass- and charge-selective detection of the chemical products of the impact. Particle ensembles are initially trapped in an RF quadrupole ion trap (QIT), where they can be accumulated and, if desired, chemically or photochemically modified. Single particles are then injected into the image-charge-detection mass spectrometer (ICDMS) that we now refer to as the nanoparticle electrostatic trap (NET). In the NET, the mass and charge of a single particle will be measured. Once this quantity has been determined to the desired precision, the particle will be injected into the linear accelerator (LINAC), accelerated to a final impact velocity and will impinge on an inert surface (a single crystal diamond surface in the initial measurements. Charged and neutral desorption products, and their product angular distributions, will be measured by coupling VUV photoionization with velocity map imaging and time-of-flight mass spectrometry. This technique will provide a new approach to understanding the composition of particles, including radial density gradients, by varying the impact energy and thus the extent of vaporization of the particle. Product angular distributions will provide a way to examine the solid-phase of the particle, by analysis of how the fragments recoil relative to the incident trajectory using ion imaging techniques. The ultimate goal is the demonstration of an new analytical technique that will provide for aerosols and nanoparticles information of the type that secondary ion mass spectrometry (SIMS) now provides for unknown surfaces using known incident particles to vaporize the substrate.

A critical aspect of the AIS will be the ability to extract in a serial fashion single aerosol particles from a trapped ensemble. Using an extractor electrode we call the 'Snorkel', we have demonstrated this capability as shown in this quicktime movie captured with a high-speed CCD camera of CaCO3 particles in the 1 micron range irradiated by a CW 532 nm laser. Warning - video may not play in all browsers.