November 2014 Archives

A team led by Dr. T. Jach (NIST, USA) and Dr. W. T. Elam (University of Washington, USA) has recently published an interesting theoretical paper discussing the broadening of N K absorption and emission spectra of NH₄NO₃ and NH₄Cl. The authors studied many-body lifetime effects in valence-band X-ray emission. For more information, see the paper, "Origins of extreme broadening mechanisms in near-edge x-ray spectra of nitrogen compounds", J. Vinson et al., Phys. Rev. B90, 205207 (2014).

A German and Austrian group has recently developed a table-top X-ray source based on ultra-short laser pulses. Generation of X-ray pulses by lasers may not be a big surprise for readers (See, for example, "Ultrafast X-ray Pulses from Laser-Produced Plasmas" by M. M. Murnane, Science, 251, 531 (1991), "Microfocus Cu Kα source for femtosecond x-ray science" by N. Zhavoronkov, Opt. Letter, 30, 1737 (2005)). However, so far, the X-ray intensity has not been sufficient for use in practical measurements such as pump-and-probe time resolved X-ray analysis. This time, scientists employed a mid infrared wavelength (3.9 micron) to accelerate electrons from the copper tape target to very high kinetic energy by making use of its comparably long optical period. The pulse width of the laser employed is 80 femto second. It was found that the system gives 10⁹ copper Kα photons per pulse generated with pulses of a peak intensity of 6×10¹⁶ W/cm². This is about 25 times higher than that generated by 800 nm wavelength laser pulses. For more information, see the paper, "High-brightness table-top hard X-ray source driven by sub-100-femtosecond mid-infrared pulses", J. Weisshaupt et al., Nature Photonics, 8, 927 (2014).

Professor A. Adriaens (Ghent University, Belgium) and her colleagues have recently reported on an X-ray-excited optical luminescence microscope using synchrotron light and its applications. The experiments were done at beamlines BM28 and BM26A at the ESRF in Grenoble, France. A broad X-ray beam is used to illuminate large areas of ~4 mm² of the sample, and the resulting optical emission is observed by a specifically designed optical microscope equipped with a CCD camera. By scanning the X-ray energy near the absorption edge, the image can obtain the sensitivity of chemical states. The authors studied copper surfaces with well-defined patterns of different corrosion products (cuprite Cu₂O and nantokite CuCl). For more information, see the paper, "Evaluation of an X-ray Excited Optical Microscope for Chemical Imaging of Metal and Other Surfaces", P-J. Sabbe et al., Anal. Chem., 86, 11789 (2014).