Simple convergent-nozzle aerosol injector for single-particle diffractive imaging with X-ray free-electron lasers.

Richard A Kirian ,H Fleckenstein,Jochen Küpper ,Max O Wiedorn ,D Oberthüer ,Andrei Rode ,Tokushi Sato ,Markus Metz ,Niko Eckerskorn ,Saša Bajt ,J Knoška ,Michaël Heymann ,Nils Roth ,Luigi Adriano ,M Domaracký ,Kenneth R Beyerlein ,P Lourdu Xavier ,Miriam Barthelmeß ,Andrew J Morgan ,Oleksandr Yefanov ,Daniel A Horke ,Richard Bean ,Leonard M G Chavas ,Salah Awel ,Henry N Chapman

doi:10.1063/1.4922648

Abstract

A major challenge in high-resolution x-ray free-electron laser-based coherent diffractive imaging is the development of aerosol injectors that can efficiently deliver particles to the peak intensity of the focused X-ray beam. Here, we consider the use of a simple convergent-orifice nozzle for producing tightly focused beams of particles. Through optical imaging we show that 0.5 μm particles can be focused to a full-width at half maximum diameter of 4.2 μm, and we demonstrate the use of such a nozzle for injecting viruses into a micro-focused soft-X-ray FEL beam.

Highlights

X-ray free-electron lasers (XFELs) offer a compelling new approach to imaging a wide variety of aerosolized particles at high resolution and under conditions that are not accessible through cryogenic electron microscopy or synchrotron-based X-ray microscopy
Two dimensional sub-nanometer-resolution images should be achievable from single-shot diffraction patterns of irreproducible targets such as living cells and aerosol particles, and three-dimensional atomic-resolution structure determination should be possible by assembling many patterns from reproducible targets such as proteins and viruses a)R
While we observed a large fraction of aggregated particle clusters, we note that the mechanism for generating and conditioning the initial aerosol particle suspension is largely independent of the particle focusing mechanism that we describe here

Summary

INTRODUCTION

X-ray free-electron lasers (XFELs) offer a compelling new approach to imaging a wide variety of aerosolized particles at high resolution and under conditions that are not accessible through cryogenic electron microscopy or synchrotron-based X-ray microscopy. X-ray focal spot diameters are typically in the range of 0.1–5 lm, and the rate at which X-rays intercept targets is of extreme importance since XFELs are costly large-scale facilities based on linear accelerators that are typically available to only one user group at a time To this end, most femtosecond single-particle imaging experiments have utilized aerodynamic lens stacks (Murphy and Sears, 1964; Liu et al, 1995; and Bogan et al, 2008) in order to concentrate and inject particles into the vacuum environment of experimental end stations. Convergent nozzles are convenient due to their compact size (in our case, only about 1 mm in diameter and 20 mm long), are simple to fabricate and operate, and can maintain targets at atmospheric pressure until they rapidly exit into vacuum in less than 1 ls Such injectors can produce tightly focused beams of sub-lm particles, with focal spots of about 5-lm diameter. Our experiments performed with a 1-lm diameter soft-X-ray FEL beam suggest the basic feasibility of utilizing such injectors for coherent diffractive imaging work

INJECTOR DESIGN AND OPERATIONAL CONCEPT

OPTICAL IMAGING AND INJECTOR PERFORMANCE

FEL DIFFRACTION EXPERIMENTS

Findings

DISCUSSION AND CONCLUSIONS