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The ITER-oriented JET research program brings new requirements for the low-Z impurity monitoring, in particular for the Be-the future main wall component of JET and ITER. Monitoring based on Bragg spectroscopy requires an absolute sensitivity calibration, which is challenging for large tokamaks. This paper describes both 'component-by-component' and 'continua' calibration methods used for the Be IV channel (75.9 Å) of the Bragg rotor spectrometer deployed on JET. The calibration techniques presented here rely on multiorder reflectivity calculations and measurements of continuum radiation emitted from helium plasmas. These offer excellent conditions for the absolute photon flux calibration due to their low level of impurities. It was found that the component-by-component method gives results that are four times higher than those obtained by means of the continua method. A better understanding of this discrepancy requires further investigations. [ABSTRACT FROM AUTHOR]

The fabrication procedure of efficient surface enhanced Raman scattering (SERS) platforms is demonstrated based on reproducibly photo-etched GaN epitaxial layers covered by a thin Au-Ag layer and subjected to partial de-alloying. Using a gold-rich Au57Ag43 alloy (70/30 wt. %), it is possible to preserve about 19 at. % of silver in the layer, even after etching in nitric acid for up to 24 h. A large enhancement of the Raman signal from the test 4-mercaptobenzoic acid molecules attached to such porous Au-Ag metal layer is obtained due to the presence of a high percentage of Ag. For the optimal etching time, in the range of 6-24 h, an enhancement factor (EF) greater than 107 was obtained. The contribution of different features of our SERS platforms such as the size of pores, nano-roughness, and the chemical composition of the metal layer for the EF parameter are critically discussed. [ABSTRACT FROM AUTHOR]

In this communication, we show that chemical modifications of etched GaN (with different morphological features) through treatment with trichlorododecylsilane or sputtering nano-Au films followed by covalent binding of 1-dodecanethiol strongly affect surface water repellency characteristics. Binding of 1-dodecanethiol to Au-coated whiskers results in GaN crystals becoming superhydrophobic with the contact angles approaching 150°. For a single type of surface morphology, a pairwise comparison of contact angle values of trichlorododecylsilane- and Au/1-dodecanethiol-modified surfaces provides an insight into relative abundance of -OH groups on GaN's Ga-polar side, which mediate and control binding of the hydrophobic silane compound, but not of thiols. [ABSTRACT FROM AUTHOR]