X-ray beam monitoring and wavelength calibration using four-beam diffraction

Rigorous dynamical theory calculations show that four-beam diffraction (4BD) can be activated only by a unique photon energy and a unique incidence direction. Thus, 4BD may be used to precisely calibrate X-ray photon energies and beam positions. Based on the principles that the forbidden-reflection 4BD pattern, which is typically an X-shaped cross, can be generated by instant imaging using the divergent beam from a point source without rocking the crystal, a detailed real-time high-resolution beam (and source) position monitoring scheme is illustrated for monitoring two-dimensional beam positions and directions of modern synchrotron light sources, X-ray free-electron lasers and nano-focused X-ray sources.

Particle size and convergent electron diffraction patterns of triangular prismatic gold nanoparticles

Convergent beam diffraction (CBED) patterns of nanoparticles are possible. CBED of triangular prismatic shaped Au nanoparticle with focus on diffraction pattern symmetry and forbidden reflections observed along [111] and [112] zone axes are reported in this work. It is well known that the CBED patterns of nanoparticles of 30 nm or less in size only show bright kinematical discs. The dynamic contrast with Kikuchi and sharp HOLZ lines within the bright discs, as observed in CBED of volumetric materials, is well observed in particles larger of 500 nm in size. In addition, it is shown that the 1/3[422] and 1/2[311] weak forbidden reflections observed in the [111] and [112] electron diffraction patterns of these particles do not modify the symmetry of the CBED patterns, but they disappear as the size of the particle increases. The symmetry of the CBED patterns are always observed in concordance with the space group Fm3m (No. 225) of the Au unit cell. The possible explanations for observing forbidden reflections are the incomplete ABC stacking due to surface termination and the stacking faults in the fcc structure.

Effect of Ge Concentration on the On-Current Boosting of Logic P-Type MOSFET with Sigma-Shaped Source/Drain

Silicon german ium (SiGe) has attracted significant attention for applications in the source/drain (S/D) regions of p-type metal-oxide-semiconductor field-effect transistors (p-MOSFETs). However, in SiGe, as the Ge concentration increases, high-density defects are generated, which limit its applications. Therefore, several techniques have been developed to minimize defects; however, these techniques require relatively thick epitaxial layers and are not suitable for gate-all-around FETs. This study examined the effect of Ge concentration on the embedded SiGe source/drain region of a logic p-MOSFET. The strain was calculated through nano-beam diffraction and predictions through a simulation were compared to understand the effects of stress relaxation on the change in strain applied to the Si channel. When the device performance was evaluated, the drain saturation current was approximately 710 µA/µm at an off current of 100 nA/µm with a drain voltage of 1 V, indicating that the current was enhanced by 58% when the Ge concentration was optimized.

A polarization-switch effect of silicon crystals under multiple-beam diffraction geometry

On the basis of rigorous dynamical-theory calculations, a complete X-ray polarization-switch effect of silicon crystals at the exact multiple-beam diffraction condition is demonstrated. The underlying physical mechanism of this unique phenomenon can be revealed using a simple multiple-wave propagation and interference model. The constructive and destructive interference of the multiple detoured-diffraction beams along the direction of the primary diffracted beam directly leads to the complete polarization switch. This phenomenon can be realized using both synchrotron and laboratory X-ray sources at many discrete wavelengths, and used to design a novel crystal-based polarizer to achieve a 90° polarization rotation.

Effect of X-ray free-electron laser-induced shockwaves on haemoglobin microcrystals delivered in a liquid jet

X-ray free-electron lasers (XFELs) enable obtaining novel insights in structural biology. The recently available MHz repetition rate XFELs allow full data sets to be collected in shorter time and can also decrease sample consumption. However, the microsecond spacing of MHz XFEL pulses raises new challenges, including possible sample damage induced by shock waves that are launched by preceding pulses in the sample-carrying jet. We explored this matter with an X-ray-pump/X-ray-probe experiment employing haemoglobin microcrystals transported via a liquid jet into the XFEL beam. Diffraction data were collected using a shock-wave-free single-pulse scheme as well as the dual-pulse pump-probe scheme. The latter, relative to the former, reveals significant degradation of crystal hit rate, diffraction resolution and data quality. Crystal structures extracted from the two data sets also differ. Since our pump-probe attributes were chosen to emulate EuXFEL operation at its 4.5 MHz maximum pulse rate, this prompts concern about such data collection.