Abstract
A new apparatus designed to accelerate/decelerate and study the surface impact phenomena of charged aerosols and nanoparticles over a wide range of mass-to-charge (m/z) ratios and final velocities is described. A nanoparticle ion source coupled with a linear electrostatic trap configured as an image charge detection (ICD) mass spectrometer allows determination of the mass-to-charge ratio and the absolute charge and mass of single nanoparticles. A nine-stage linear accelerator/decelerator is used to fix the final velocity of the nanoparticles, and in the results reported here the coefficient of restitution for polystyrene latex spheres (PSLs) impacting on silicon is measured using ICD techniques. To enable this apparatus to study a wide range of m/z, the data acquisition system uses a transient digitizer interfaced to a field-programmable gate array module that allows real time calculation of m/z and determination of the pulse sequence for the linear accelerator/decelerator. Electrospray ionization of a colloidal suspension of PSL spheres of 510 and 990 nm has been used to demonstrate acceleration and deceleration of charged nanoparticles and the resolution of the apparatus. Measurements of the coefficient of restitution for PSLs on silicon over the range 10-400 m/s are consistent with previous studies.
Highlights
As interest in the characterization of nanoparticles, aerosols and dusts increases, the need for the development of new tools for the manipulation and analysis of single particles continues to grow [1]
The initial results obtained with the Aerosol Impact Spectrometer (AIS) will be presented, showing the measurement of charge/mass distributions, acceleration and deceleration of single charged polystyrene latex spheres (PSLs) spheres, and measurements of impact inelasticity of single particles with a silicon substrate. These results show that the AIS will have great utility for measuring the reflection of nanoparticles from surfaces, yielding quantitative information on the coefficient of restitution that describes the inelasticity of such collisions [29, 30]
The Field programmable gate array (FPGA) releases the particle from the trap by lowering the exit mirror and triggers the two high voltage (HV) switches connected to the linear accelerator (LINAC) at the times required to accelerate/decelerate the particle to a final energy that depends on the number of elements used and the potential applied to each element
Summary
As interest in the characterization of nanoparticles, aerosols and dusts increases, the need for the development of new tools for the manipulation and analysis of single particles continues to grow [1]. In the present work the development of a versatile new nanoparticle mass spectrometer/accelerator/decelerator, the Aerosol Impact Spectrometer (AIS), is described with a demonstration of its capabilities using polystyrene latex (PSL) spheres, including studies of collision inelasticity on silicon wafers by determination of incident and scattered velocities in measurements of the coefficient of restitution.
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