| 1. |
- Afanasiev, Sergey V., et al.
(author)
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Experimental apparatus to study crystal channeling in an external SPS beamline
- 2007
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In: Proceedings of SPIE, the International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. ; 6634
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Journal article (peer-reviewed)abstract
- For the new generation of high intensity hadronic machines as, for instance, LHC, halo collimation is a necessary issue for the accelerator to operate at the highest possible luminosity and to prevent the damage of superconductor magnets.1 We propose an experiment aimed to systematic study of the channeling phenomenology and of the newly observed "volume reflection" effect. This experiment will be performed for an external SPS beamline and will make use of a primary proton beam with 400 GeV/c momentum and very small (∼ 3 μrad) divergence. The advantage of a proposed experiment is precise tracking of particles that interacted with a crystal, so that to determine the single-pass efficiency for all the processes involved. For this purpose, a telescope equipped with high-resolution silicon microstrip detectors will be used. New generation silicon crystals and an extra-precise goniometer are mandatory issues. Main goal of the experiment is to get the precise information on channeling of relativistic particles and, ultimately, on the feasibility of such technique for halo collimation at LHC. In this contribution we review the status of the setting-up of experimental apparatus and its future development in sight of the planned run in September 2006.
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| 2. |
- Boscarino, Diego, et al.
(author)
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Deposition of silica-silver nanocomposites by magnetron cosputtering
- 2005
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In: Journal of Vacuum Science & Technology B. - : American Vacuum Society. - 1071-1023 .- 1520-8567. ; 23:1, s. 11-19
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Journal article (peer-reviewed)abstract
- Thin films have been grown on silicon and silica substrates by cosputtering of silica and silver in Ar, Ar+2.5% O2, and Ar+5% O2 gas mixtures. Rutherford backscattering spectrometry showed that the films have Ag atomic fractions xAg in the range of ∼1 to ∼10 at. %, and, by valence considerations, that the fraction of oxidized Ag in the films deposited in presence of oxygen is limited. Transmission electron microscopy images revealed the presence of Ag nanoclusters, with a mean size diameter not larger than 5 nm. The clusters are preferentially arranged along columns. It is suggested that the columns are regions with diameter in the nanometer range in which the density of the dielectric matrix is lower, thus favoring the formation of metal clusters. In presence of O2, the clusters were observed to have a more regular spherical shape. The optical absorption spectra of films grown in presence of O2 are distinguished from those grown in Ar by specific features, which are attributed to oxidation at the cluster surface. © 2005 American Vacuum Society.
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| 3. |
- Comini, Elisabetta, et al.
(author)
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Effects of Ta/Nb-doping on titania-based thin films for gas-sensing
- 2005
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In: Sensors and actuators. B, Chemical. - : Elsevier BV. - 0925-4005 .- 1873-3077. ; 108:1-2 SPEC. ISS., s. 21-28
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Journal article (peer-reviewed)abstract
- Thin films of titania with the addition of niobium and tantalum have been achieved by reactive sputtering process. Structural and morphological studies have been carried out by means of XRD, RBS, TEM and AFM in order to correlate the microstructural features to the sensing performance of the layers. The films proved sensitive to ethanol and carbon monoxide and ammonia. In the case of niobium addition, it was shown that annealing temperature and niobium content strongly influence the gas response of the films converting a n-type response, which is typical of pure TiO2 and of most of metal-oxide sensors, to a p-type response; this peculiarity is crucial for the discrimination of different gases. In the case of tantalum addition, the annealing treatment at 800 °C led only to a phase transformation that reduced the sensing performance of the layer. High sensitivity to CO is achieved with anatase or mixed anatase and rutile phases, while the rutile phase only exhibit a low gas sensitivity. © 2005 Elsevier B.V. All rights reserved.
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| 4. |
- Guidi, Vincenzo, et al.
(author)
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Selective sublimation processing of thin films for gas sensing
- 2005
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In: Sensors and actuators. B, Chemical. - : Elsevier BV. - 0925-4005 .- 1873-3077. ; 108:1-2 SPEC. ISS., s. 15-20
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Journal article (peer-reviewed)abstract
- The selective sublimation processing (SSP) is a useful and easy method for production of semiconducting thin films via reactive sputtering for gas sensing. We have investigated the mechanism of film growth and processing for an insight into the main parameters that control the preparation methodology. A model based on diffusion equation, in the framework of a linear theory, has been proposed and compared to experimental evidences. Rutherford backscattering spectrometry has been extensively used as a tool for determination of concentration profiles in the layers. The model allowed a deeper understanding of film preparation with a physical description of the processes involved, which would open up the design of innovative nanostructured materials that rely on SSP. Titania thin films produced by this methodology and proved capable of sensing target gases of interest for many applications. © 2004 Elsevier B.V. All rights reserved.
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| 5. |
- Maggioni, Gianluigi, et al.
(author)
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Effects of heat treatments on the properties of copper phthalocyanine films deposited by glow-discharge-induced sublimation
- 2006
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In: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 18:17, s. 4195-4204
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Journal article (peer-reviewed)abstract
- Copper phthalocyanine films have been deposited by glow-discharge-induced sublimation. The films have undergone postdeposition heat treatments in air at 250 and 290°C for different times, ranging from 30 min to 14 h. The properties of as-deposited and heated films have been investigated by different techniques in order to determine the effects of heat treatments on the film properties. Fourier transform infrared analysis and UV-visible optical absorption analysis point out a gradual evolution of the film structure from a mixture of α and β polymorphs to the only β polymorph in the sample heated at 290°C for 14 h. A pronounced decrease of carbon and nitrogen atomic percentages against an oxygen increase in the heated films are shown by ion beam analyses (Rutherford backscattering spectrometry and nuclear reaction analysis) and X-ray photoelectron spectroscopy (XPS). X-ray absorption spectroscopy and XPS indicate that part of the copper phthalocyanine molecules decompose during heat treatments and the formation of copper oxide takes place. The replacement of copper phthalocyanine by copper oxide in the heated films accounts for the change of their surface electrical conductance and of their electrical response to NO 2. © 2006 American Chemical Society.
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| 6. |
- Maggioni, Gianluigi, et al.
(author)
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Production and characterization of thin film materials for indoor optical gas sensing applications
- 2006
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In: Journal of Physics, Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 41:1, s. 531-534
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Journal article (peer-reviewed)abstract
- Pure and Nile-Red-doped polyimide and porphyrin films have been deposited and their optical response to different organic vapours has been tested. Polyimide films were obtained by spin coating a solution containing 4, 4'-4, 4'-(hexafluoroisopropylidene) diphthalic anhydride and 2, 3, 5, 6-tetramethyl-1, 4-phenylenediamine. Free, cobalt and iron chloride 5, 10, 15, 20 meso-tetraphenyl porphyrin films were deposited by spin coating and by high vacuum evaporation. Exposure to water, ethanol and isopropanol vapours produce reversible changes of the fluorescence features of both pure and doped polyimide films. Exposure to methanol, ethanol and isopropanol vapours gives rise to changes of the optical absorption of porphyrin films. The results of the optical measurements point out that the synthesized films can be used for the detection of volatile organic compounds. © 2006 IOP Publishing Ltd.
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| 7. |
- Rupertus, Volker, et al.
(author)
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Thickness of thin films on glass : A round robin test
- 2005
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In: Glass Science and Technology. - : Verlag der Deutschen Glas Technischen Gesellschaft. - 0946-7475. ; 78:5, s. 212-217
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Journal article (peer-reviewed)abstract
- The film thicknesses of five different layer systems on glass substrates were analyzed and determined in a multi-method approach by eight different university and industrial laboratories. The total coating thicknesses varied between a few nm up to some 100 nm. The measurements give information about the chemical composition and cover a wide spectrum of typical coating application on glasses. The results of the different laboratories and methods are compared and the challenges and limits of the various analytical techniques are discussed.
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| 8. |
- Scandale, Walter, et al.
(author)
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Apparatus to study crystal channeling and volume reflection phenomena at the SPS H8 beamline
- 2008
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In: Review of Scientific Instruments. - : AIP Publishing. - 0034-6748 .- 1089-7623. ; 79:2
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Journal article (peer-reviewed)abstract
- A high performance apparatus has been designed and built by the H8-RD22 collaboration for the study of channeling and volume reflection phenomena in the interaction of 400 GeVc protons with bent silicon crystals, during the 2006 data taking in the external beamline H8 of the CERN SPS. High-quality silicon short crystals were bent by either anticlastic or quasimosaic effects. Alignment with the highly parallel (8 μrad divergence) proton beam was guaranteed through a submicroradian goniometric system equipped with both rotational and translational stages. Particle tracking was possible by a series of silicon microstrip detectors with high-resolution and a parallel plate gas chamber, triggered by various scintillating detectors located along the beamline. Experimental observation of volume reflection with 400 GeVc protons proved true with a deflection angle of (10.4±0.5) μrad with respect to the unperturbed beam, with a silicon crystal whose (111) planes were parallel to the beam. © 2008 American Institute of Physics.
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| 9. |
- Scandale, Walter, et al.
(author)
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Deflection of 400GeV/c proton beam with bent silicon crystals at the CERN Super Proton Synchrotron
- 2008
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In: Physical Review Special Topics - Accelerators and Beams. - 1098-4402. ; 11:6
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Journal article (peer-reviewed)abstract
- This paper presents a detailed study of the deflection phenomena of a 400GeV/c proton beam impinging on a new generation of bent silicon crystals; the tests have been performed at the CERN Super Proton Synchrotron H8 beam line. Channeling and volume reflection angles are measured with an extremely precise goniometer and with high resolution silicon microstrip detectors. Volume reflection has been observed and measured for the first time at this energy, with a single-pass efficiency as large as 98%, in good agreement with the simulation results. This efficiency makes volume reflection a possible candidate for collimation with bent crystals at the CERN Large Hadron Collider. © 2008 The American Physical Society.
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| 10. |
- Scandale, W., et al.
(author)
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Deflection of high-energy negative particles in a bent crystal through axial channeling and multiple volume reflection stimulated by doughnut scattering
- 2010
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In: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 693:5, s. 545-550
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Journal article (peer-reviewed)abstract
- Different kinds of deflection in a silicon crystal bent along the 〈111〉 axis was observed for 150 GeV/. c negative particles, mainly π- mesons, at one of the secondary beams of the CERN SPS. The whole beam was deflected to one side in quasi-bound states of doughnut scattering (DSB) by atomic strings with the efficiency (95.4 ± 0.2)% and with the peak position close to the bend crystal angle, α=185 μrad. It was observed volume capture of π- mesons into the DSB states with a probability higher than 7%. A beam deflection opposite to the crystal bend was observed for some orientations of the crystal axis due to doughnut scattering and subsequent multiple volume reflections of π- mesons by different bent planes crossing the axis. © 2010 Elsevier B.V.
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| 11. |
- Scandale, Walter, et al.
(author)
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Double volume reflection of a proton beam by a sequence of two bent crystals
- 2008
-
In: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 658:4, s. 109-111
-
Journal article (peer-reviewed)abstract
- The doubling of the angle of beam deflection due to volume reflection of protons by a sequence of two bent silicon crystals was experimentally observed at the 400 GeV proton beam of the CERN SPS. A similar sequence of short bent crystals can be used as an efficient primary collimator for the Large Hadron Collider.
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| 12. |
- Scandale, W., et al.
(author)
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First observation of multiple volume reflection by different planes in one bent silicon crystal for high-energy protons
- 2009
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In: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 682:3, s. 274-277
-
Journal article (peer-reviewed)abstract
- Multiple volume reflection by different planes in a bent silicon crystal with its 〈111〉 axis orientation close to the beam direction was observed for the first time for 400 GeV/c protons at the CERN SPS. The proton beam was deflected to the side opposite to the crystal bend by an angle of about 67 μrad, which is five times larger than in a single volume reflection by the (110) bent planes. The registered efficiency of one side deflection was about 84%. It was shown that multiple volume reflection transforms to a single volume reflection when the orientation angle of the 〈111〉 axis relative to the beam direction is increased. © 2009 Elsevier B.V. All rights reserved.
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| 13. |
- Scandale, W., et al.
(author)
-
High-efficiency deflection of high-energy negative particles through axial channeling in a bent crystal
- 2009
-
In: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 680:4, s. 301-304
-
Journal article (peer-reviewed)abstract
- Deflection due to axial channeling in a silicon crystal bent along the 〈111〉 axis was observed for 150 GeV/c negative particles, mainly π- mesons, at one of the secondary beams of the CERN SPS. The whole beam was deflected to one side with the efficiency of about 90% and with the peak position at the bend crystal angle α = 43 μrad. The deflection occurs mainly due to doughnut scattering of above-barrier particles by the atomic strings of the crystal. However, due to a high probability of particle recapture into bound states with the atomic strings their contribution to the deflection should be about 15% for our case according to simulation results. © 2009 Elsevier B.V. All rights reserved.
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| 14. |
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| 15. |
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| 16. |
- Scandale, W., et al.
(author)
-
Multiple volume reflections of high-energy protons in a sequence of bent silicon crystals assisted by volume capture
- 2010
-
In: Physics Letters B. - : Elsevier. - 0370-2693 .- 1873-2445. ; 688:4-5, s. 284-288
-
Journal article (peer-reviewed)abstract
- Multiple volume reflections of the 400 GeV / c proton beam by the sequence of fourteen bent silicon strips has been studied at the CERN SPS. The sequence is close to be parallel that is the spread of the strip orientation angles is much smaller than their bend angle and eleven strips working coherently in the regime of volume reflections deflected the beam by 110 μrad with the efficiency 88%, which is significantly larger than the estimation based on independent reflections. The mechanism giving the efficiency increase has been studied by simulation. It appears that many particles volume captured in one of the strips take part in volume reflections in the subsequent ones. Such a crystal multi reflector can be successfully used as a primary collimator for the beam halo collimation of high-energy accelerators.
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| 17. |
- Scandale, W., et al.
(author)
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Observation of channeling and volume reflection in bent crystals for high-energy negative particles
- 2009
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In: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 681:3, s. 233-236
-
Journal article (peer-reviewed)abstract
- Deflection due to planar channeling and volume reflection in short bent silicon crystals was observed for the first time for 150 GeV / c negative particles, π- mesons, at one of the secondary beams of the CERN SPS. The deflection efficiency was about 30% for channeling and higher than 80% for volume reflection. Volume reflection occurs, in spite of the attractive character of the forces acting between the particles and the crystal planes, in a wide angular range of the crystal orientations determined by the crystal bend angle. © 2009 Elsevier B.V. All rights reserved.
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| 18. |
- Scandale, W., et al.
(author)
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Observation of nuclear dechanneling for high-energy protons in crystals
- 2009
-
In: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 680:2, s. 129-132
-
Journal article (peer-reviewed)abstract
- Channeling in a short bent silicon crystal was investigated at the CERN SPS using 400-GeV/c protons with an angular spread much narrower than the critical channeling angle. Particle dechanneling due to multiple scattering on the atomic nuclei of the crystal was observed and its dechanneling length was measured to be about 1.5 mm. For a crystal with length comparable to such dechanneling length, an efficiency of 83.4% was recorded, which is close to the maximum value expected for a parallel beam and exceeds the previously known limitation of deflection efficiency for long crystals. © 2009 Elsevier B.V. All rights reserved.
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| 19. |
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| 20. |
- Vomiero, Alberto, et al.
(author)
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Effects of thermal annealing on the structural properties of sputtered W-Si-N diffusion barriers
- 2004
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In: Materials Science in Semiconductor Processing. - : Elsevier BV. - 1369-8001 .- 1873-4081. ; 7:4-6 SPEC. ISS., s. 325-330
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Journal article (peer-reviewed)abstract
- W-Si-N thin films were deposited via rf-magnetron sputtering from a W 5Si3 target in Ar/N2 reactive gas mixtures over a large range of compositions, obtained by varying the partial flow of nitrogen within the reaction chamber. The samples of each set were then thermally annealed in vacuum at different temperatures up to 980°C. Film composition was determined by Rutherford backscattering spectrometry (RBS), surface film morphology by scanning electron microscopy (SEM), micro-structure by transmission electron microscopy (TEM), vibrational properties by FT-IR absorption and Raman scattering spectroscopy, and electrical resistivity by four-point probe measurements. Independently of the deposition conditions, all the as-deposited films have an amorphous structure, while their composition varies, showing an increase of Si/W ratio from 0.1 up to 0.55 when the nitrogen concentration in the films increases from 0 to 60 at%. Thermal treatments in vacuum induce an important loss of nitrogen in the nitrogen-rich samples, especially at temperatures higher than 600°C. Samples with high nitrogen content preserve their amorphous structure even at the highest annealing temperature, despite the chemical bonding ordering observed by means of FTIR measurements. Raman spectroscopy of as-deposited films rich in nitrogen suggests the presence of an important amorphous silicon nitride component, but fails to detect any structural rearrangement either within the composite matrix of film or within silicon nitride component. Segregation of metallic tungsten was detected by TEM in the annealed sample with lowest nitrogen content (W 58Si21N21). Finally, the resistivity of the films increases with the N content, while the loss of nitrogen accompanies the decrease of resistivity especially of samples with high nitrogen content. © 2004 Elsevier Ltd. All rights reserved.
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| 21. |
- Vomiero, Alberto, et al.
(author)
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Structural and functional characterization of W-Si-N sputtered thin films for copper metallizations
- 2004
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In: Materials Research Society Symposium Proceedings. - 0272-9172 .- 1946-4274. ; 812, s. 153-158
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Journal article (peer-reviewed)abstract
- Ternary W-Si-N thin films have been reactively sputter-deposited from a W5Si3 target at different nitrogen partial pressures. The composition has been determined by 2.2 MeV 4He+ beam, the structure by x-ray diffraction and transmission electron microscope, the chemical bonds by Fourier transform - infrared spectroscopy and the surface morphology by scanning electron microscopy. Electrical resistivity was measured by four point probe technique on the as grown films. The film as-deposited is amorphous with the Si/W ratio increasing from about 0.1 up to 0.55 with the nitrogen content going from 0 to 60 at%. The heat treatments up to 980°C induce a loss of nitrogen in the nitrogen rich samples. Segregation of metallic tungsten occurs in the sample with low nitrogen content (W58Si 21N21). Samples with high nitrogen content preserve the amorphous structure, despite of the precipitation of a more ordered phase inferred by FT-IR absorbance spectrum of the layer treated at highest temperature. The surface morphology depends upon the nitrogen content; the loss of nitrogen induces the formation of blistering and in the most nitrogen rich sample the formation of holes. Electrical resistivity preliminary results on the as grown layers range between 500 and 4750 μΩcm passing from the lowest to the highest N concentration.
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| 22. |
- Vomiero, Alberto, et al.
(author)
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Structure and morphology of surface of silicon crystals to be applied for channeling at relativistic energies
- 2006
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In: Nuclear Instruments and Methods in Physics Research Section B. - : Elsevier BV. - 0168-583X .- 1872-9584. ; 249:1-2 SPEC. ISS., s. 903-906
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Journal article (peer-reviewed)abstract
- Bent crystals can be successfully applied for extraction/collimation of relativistic particles. A crucial feature to obtain high extraction efficiencies is the treatment of the surfaces being encountered by the beam, since mechanical operations induce considerable lattice imperfections. In order to remove the superficial damaged layer a planar etching can be applied on the surface exposed to the beam. This work presents a systematic study of the morphology and the crystalline perfection of the surface of the samples that have been used in accelerators with high efficiency. Crystals with different surface treatments have been investigated. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were applied on the characterisation of surface morphology. Low energy backscattering channeling of 2-MeV α particles or protons was used as a probe for the crystalline structure. The presence of a superficial damaged layer in the samples just after mechanical treatment was unveiled, while, in contrast, chemical etching leaves a surface with high crystalline perfection that can be related to the record efficiency. © 2006 Elsevier B.V. All rights reserved.
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