Diffraction Properties of Periodic Lattices under Free Electron Laser Radiation

In this Letter, we report the pioneering use of free electron laser radiation for the investigation of periodic crystalline structures. The diffraction properties of silver behenate single nanocrystals (5.8 nm periodicity) with the dimensions of $20\mathrm{nm}\times 20\mathrm{nm}\times 20\mu \mathrm{m}$ and as powder with grain sizes smaller than 200 nm were investigated with 8 nm free electron laser radiation in single-shot modus with 30 fs long free electron laser pulses. This work emphasizes the possibility of using soft x-ray free electron laser radiation for these crystallographic studies on a nanometer scale.

Figure 1

Experimental setup for the diffraction experiments with FEL radiation. The whole setup is rotated for 20° around the $x$ axis, and the incoming beam is polarized horizontally in the direction of the $y$ axis. (a) The needlelike morphology of a polycrystalline silver behenate sample has been revealed by scanning electron microscopy. The crystal planes are oriented parallel to the sample surface. (b) FLASH pulses (30 fs, 8 nm, 5 Hz) are arriving at the sample at an incident angle of 45°. (c) The x-ray camera is positioned at a 90° angle to the incident beam, for recording the (100) diffraction peak. (d) Nanoperiodic structure of silver behenate.

Figure 2

(a) (100) Bragg diffraction peak of silver behenate investigated by single-shot FEL radiation. (b) Part of the (100) silver behenate powder diffraction ring. Accumulation of 4–10 shots was required to gain a sufficient signal-to-noise ratio. (c) One-dimensional cut through reflection profile [intensity in arbitrary units (a.u.)]. (d) One-dimensional cut through powder diffraction profile. Both cuts were made through the dashed lines shown in (a) and (b).

Figure 3

(a) Comparison of the radial intensity distribution of the powder diffraction ring (in arbitrary units) with the position of the diffraction spots of various single crystals as a function of FLASH energy. (b) Horizontal FWHM (in number of pixels) and intensities of the Bragg reflections (in photon units) as a function of FLASH energy (8 nm radiation). Note that for the intensity the symbol size has been chosen to reflect the error bar.