The TRAPS Apparatus: Enhancing Target Density of Nanoparticle Beams in Vacuum for X-ray and Optical Spectroscopy

Abstract

We present an experimental setup that allows the injection of charged nanoparticles in a diameter range of 3-15 nm into a vacuum chamber and their storage there in an electrodynamic cage. The nanoparticle density in the trap is limited by space charge and can be several orders of magnitude higher than in a free nanoparticle beam. The setup provides for the first time a tool for the application of advanced techniques of spectroscopy to free nanoparticles in this size range. It consists of a combination of (1) a plasma discharge nanoparticle source that generates a high density of nanoparticles of various composition suspended in helium carrier gas at a pressure of about 10-150 mbar, (2) an aerodynamic lens optimized for small particles (diameter 3-15 nm) that forms a well-collimated beam of charged nanoparticles and focuses it into (3) an octopole ion trap operated at low frequencies and filled with helium buffer gas at 10 −2 mbar in order to moderate and store the nanoparticles at densities of more than 10 7 cm −3 .

Core level photoionization on free sub-10-nm nanoparticles using synchrotron radiation

“…Details of this device have been given earlier. 13,14 The particle diameter produced by the MPPS can be tuned from 3 to 15 nm diameter, depending on the reactor pressure, which is typically operated between 60 and 150 mbar. The particle number density directly 25 mm downstream from the reaction zone is 10 11 cm −3 and the fraction of singly charged particles of negative charge is 25%.…”

“…We have recently reported an optimized design of a tunable ADL for nanoparticles of different materials in the diameter range from 3 to 15 nm. 13 This ADL was used for the present experiments. It consisted of two focusing orifices ͑diameter: 2.20 and 2.40 mm͒ and an acceleration nozzle ͑diameter: 2.10 mm͒ separated by 40 mm from each other in a tube of 40 mm diameter.…”

“…The particle size was determined by using of the TRAPS-TOF setup, as outlined in the previous work. 13 The gas/particle stream propagated through an ISO-KF16 flexible metal hose and entered the ADL through a flow limiting orifice of 1.0 mm diameter.…”

“…spectrometer ͑TRAPS͒. 13 We will demonstrate in this work the applicability of this inlet system to XPS on free nanoparticles in the sub-10-nm regime.…”

The vapor pressure over nano-crystalline ice

“…The molecular flow ice cell within the trapped reactive atmospheric particle spectrometer (MICE-TRAPS; Duft et al, 2015;Meinen et al, 2010) has been used previously to investigate the adsorption and nucleation of CO 2 on levitated small metal-oxide nanoparticles at low temperatures (Nachbar et al, 2016). In this work, we expose the nanoparticles to a flow of water molecules originated from temperature-controlled ice-covered sample surfaces.…”