Characterizing gas flow from aerosol particle injectors

A novel methodology for measuring gas flow from small orifices or nozzles into vacuum is presented. It utilizes a high-intensity femtosecond laser pulse to create a plasma within the gas plume produced by the nozzle, which is imaged by a microscope. Calibration of the imaging system allows for the extraction of absolute number densities. We show detection down to helium densities of $4\times10^{16}$~cm$^{-3}$ with a spatial resolution of a few micrometer. The technique is used to characterize the gas flow from a convergent-nozzle aerosol injector [Struct.\ Dyn.~2, 041717 (2015)] as used in single-particle diffractive imaging experiments at free-electron laser sources. Based on the measured gas-density profile we estimate the scattering background signal under typical operating conditions of single-particle imaging experiments and estimate that fewer than 50 photons per shot can be expected on the detector

Helium-Electrospray: an improved sample delivery system for single-particle imaging with X-ray lasers

Imaging the structure and observing the dynamics of isolated proteins using single-particle X-ray diffractive imaging (SPI) is one of the potential applications of X-ray free-electron lasers (XFELs). Currently, SPI experiments on isolated proteins are limited by three factors: low signal strength, limited data and high background from gas scattering. The last two factors are largely due to the shortcomings of the aerosol sample delivery methods in use. Here we present our modified electrospray ionization (ESI) source, which we dubbed Helium-ESI (He-ESI). With it, we increased particle delivery into the interaction region by a factor of 10, for 26 nm-sized biological particles, and decreased the gas load in the interaction chamber corresponding to an 80% reduction in gas scattering when compared to the original ESI. These improvements will lead to a significant increase in the quality and quantity of SPI diffraction patterns in future experiments using He-ESI, resulting in higher-resolution structures

Generation of ultrashort UV pulses and R2PI measurements of deflected molecules

This thesis is about the generation and characterization of ultrashort ultraviolet (UV) laser pulses, resonance-enhanced two photon ionization (R2PI) measurements of indole and the electrostatic deflection of indole.UV pulses are generated from a 39 fs Ti:Sapphire Laser with a central wavelength of 800 nm and a bandwidth of 60 nm. To generate UV pulses, the nonlinear process of harmonic generation in a beta-barium-borate (BBO)-crystal is used. A prism compressor ensures group velocity dispersion (GVD) compensation and a cross cor- relation is used to measure the pulse duration of the generated UV pulses. An energy conversion efficiency of up to 6 % of the fundamental energy is achieved to produce UV pulses and the generated pulses have a theoretical minimum pulse duration of 35 fs due to the spectrum.R2PI measurements are used to identify the fragmentation of indole (C8H7N) at UV pulses in comparison to the fragmentation at IR pulses. Additionally, the spatial deflection of indole due to an electric field is measured.The time of flight mass spectra (TOF MS) of indole show great differences when the molecule is ionized by IR or UV pulses, respectively. With UV pulses it is possible to ionize the molecule almost without fragments or background

Les Hollandais et les Antilles françaises (XVIIe-XVIIIe siècles)

Jusqu’à l’application de l’Édit de Fontainebleau portant révocation de l’édit de Nantes dans les Antilles françaises en 1687, l’influence hollandaise se manifestait à tous les niveaux dans les activités politiques, sociales, agro-industrielles et commerciales. Il faut dire que la communauté d’origine hollandaise se confondait avec les protestants d’origine française et que leurs sorts étaient liés. Avant d’arriver à cette rupture, rappelons que la puissance des Pays-Bas fut prépondérante dans..

Controlled beams of shock-frozen, isolated, biological and artificial nanoparticles

X-ray free-electron lasers (XFELs) promise the diffractive imaging of single molecules and nanoparticles with atomic spatial resolution. This relies on the averaging of millions of diffraction patterns of identical particles, which should ideally be isolated in the gas phase and preserved in their native structure. Here, we demonstrated that polystyrene nanospheres and Cydia pomonella granulovirus can be transferred into the gas phase, isolated, and very quickly shockfrozen, i. e., cooled to 4 K within microseconds in a helium-buffer-gas cell, much faster than state-of-the-art approaches. Nanoparticle beams emerging from the cell were characterized using particle-localization microscopy with light-sheet illumination, which allowed for the full reconstruction of the particle beams, focused to < 100 μm, as well as for the determination of particle flux and number density. The experimental results were quantitatively reproduced and rationalized through particle-trajectory simulations. We propose an optimized setup with cooling rates for few-nanometers particles on nanoseconds timescales. The produced beams of shockfrozen isolated nanoparticles provide a breakthrough in sample delivery, e. g., for diffractive imaging and microscopy or low-temperature nanoscience

Charge-State Distribution of Aerosolized Nanoparticles

In single-particle imaging experiments, beams of individual nanoparticles are exposed to intense pulses of X-rays from free-electron lasers to record diffraction patterns of single, isolated molecules. The reconstruction for structure determination relies on signals from many identical particles. Therefore, well-defined-sample delivery conditions are desired in order to achieve sample uniformity, including avoidance of charge polydispersity. We have observed charging of 220 nm polystyrene particles in an aerosol beam created by a gas-dynamic virtual nozzle focusing technique, without intentional charging of the nanoparticles. Here, we present a deflection method for detecting and characterizing the charge states of a beam of aerosolized nanoparticles. Our analysis of the observed charge-state distribution using optical light-sheet localization microscopy and quantitative particle trajectory simulations is consistent with previous descriptions of skewed charging probabilities of triboelectrically charged nanoparticles

Charge-State Distribution of Aerosolized Nanoparticles

In single-particle imaging experiments, beams of individual nanoparticles are exposed to intense pulses of X-rays from free-electron lasers to record diffraction patterns of single, isolated molecules. The reconstruction for structure determination relies on signals from many identical particles. Therefore, well-defined-sample delivery conditions are desired in order to achieve sample uniformity, including avoidance of charge polydispersity. We have observed charging of 220 nm polystyrene particles in an aerosol beam created by a gas-dynamic virtual nozzle focusing technique, without intentional charging of the nanoparticles. Here, we present a deflection method for detecting and characterizing the charge states of a beam of aerosolized nanoparticles. Our analysis of the observed charge-state distribution using optical light-sheet localization microscopy and quantitative particle trajectory simulations is consistent with previous descriptions of skewed charging probabilities of triboelectrically charged nanoparticles

Optimizing the geometry of aerodynamic lens injectors for single-particle coherent diffractive imaging of gold nanoparticles

Single-particle x-ray diffractive imaging (SPI) of small (bio-)nanoparticles (NPs) requires optimized injectors to collect sufficient diffraction patterns to reconstruct the NP structure with high resolution. Typically, aerodynamic-lens-stack injectors are used for single NP injection. However, current injectors were developed for larger NPs (100 nm) and their ability to generate high-density NP beams suffers with decreasing NP size. Here, an aerodynamic-lens-stack injector with variable geometry and the geometry-optimization procedure are presented. The optimization for 50 nmgold NP (AuNP) injection using a numerical simulation infrastructure capable of calculating the carrier gas flow and the particle trajectories through the injector is introduced. The simulations are experimentally validated using spherical AuNPs and sucrose NPs. In addition, the optimized injector is compared to the standard-installation “Uppsala-injector” for AuNPs and results for these heavy particles show a shift in the particle-beam focus position rather than a change in beam size, which results in a lower gas background for the optimized injector. Optimized aerodynamic-lens stack injectors will allow to increase NP beam density, reduce the gas background, discover the limits of current injectors, and contribute to structure determination of small NPs using SPI