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- Guidi, V., et al.
(author)
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Characterization of crystals for steering of protons through channelling in hadronic accelerators
- 2006
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In: EPAC 2006. - Edinburgh : European Physical Society Accelerator Group (EPS-AG). - 9290832797 ; , s. 1523-1525
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Conference paper (peer-reviewed)abstract
- Channeling of relativistic particles through a crystal may be useful for many applications in accelerators, and particularly for collimation in hadronic colliders. Efficiency proved to be dependent on the state of the crystal surface and hence on the method used for preparation. We investigated the morphology and structure of the surface of the samples that have been used in accelerators with high efficiency. We found that crystal fabrication by only mechanical methods (dicing, lapping, and others) leads to a superficial damaged layer, which is correlated to performance limitation in accelerators. A planar chemical etching was studied and applied in order to remove the superficial damaged layer. RBS channeling analysis with low-energy protons and 4He + highlighted better crystal perfection at surface, as a result of the etching. A protocol for preparation and characterization of crystal for channelling has been developed, which may be of interest for reliable operation with crystals in accelerators.
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- Vomiero, Alberto, et al.
(author)
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Structural properties of reactively sputtered W-Si-N thin films
- 2007
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In: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 102:3
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Journal article (peer-reviewed)abstract
- Tungsten-silicon-nitrogen, W-Si-N, ternary thin films have been reactively sputter deposited from W5 Si3 and W Si2 targets using several nitrogen partial pressures. The films have been thermal annealed in the 600-1000 °C temperature range and a wide region of the W-Si-N ternary phase diagram has been explored by changing the N2 Ar ratio during the deposition. Multitechnique approach was adopted for the analysis of the samples. Composition has been determined via ion beam analysis; chemical states were investigated using x-ray photoelectron spectroscopy (XPS); crystalline structure was studied using transmission electron microscopy (TEM) and x-ray diffraction (XRD) and surface morphology by scanning electron microscope. The films deposited in pure argon atmosphere are tungsten rich and approach the target contents as N2 Ar ratio is varied during deposition. Tungsten enrichment in the films is caused by resputtering of silicon which can be inhibited by the formation of silicon nitride, allowing films with SiW ratio closer to the target compositions. The higher capability to form nitrides with silicon than with tungsten favors enhancement of nitrogen content in samples deposited from the silicon rich target (W Si2). The samples with excess nitrogen content have shown losses of this element after thermal treatment. XPS measurements show a break of W-N bonds caused by thermal instability of tungsten nitrides. TEM and XRD revealed the segregation of tungsten in form of metallic or silicide nanoclusters in samples with low nitrogen content (W58 Si21 N21 and W24 Si42 N34). High amounts of nitrogen were revealed to be highly effective in inhibiting metallic cluster coalescence. Measurements of electrical resistivity of as deposited films were performed using four point probe technique. They were found to lie in the range between 0.4 and 79 m cm depending on sample composition. © 2007 American Institute of Physics.
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