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Characterization of crystals for relativistic channeling

This article discusses the characterization of crystals for relativistic channeling in large colliders. It includes surface treatment techniques, extraction efficiency, edge effects, and analytical protocols. Silicon and Germanium crystals are examined, and the role of surface imperfections in channeling degradation is explored.

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Characterization of crystals for relativistic channeling

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  1. Characterization of crystalsfor relativistic channeling A. Carnera, G. Della Mea, D. De Salvador,R. Milan, A. Sambo, A. Vomiero S. Baricordi, V. Guidi, G. Martinelli, A. Mazzolari, E. Milan Crystal Channeling for Large Colliders: Machine and Physics Applications22 -23 March 2007, CERN Geneva

  2. Surface defects & noise effects Shape of deflected beam Extraction efficiency Edge effect Surface preparation & analytical techniques Preliminary characterisations Definition of analytical protocol Silicon crystals devoted to CERN-SPS experiment in H8 beam line (September 2006) New materials: Germanium crystals Conclusions Outline Crystal Channeling for Large Colliders: Machine and Physics Applications22 -23 March 2007, CERN Geneva

  3. Surface treatment proved useful to improve the quality of the extracted beam Images of the 70 GeV protons deflected through mechanically treated and chemically polished crystals (U70 @ IHEP) Byriukov et al. Crystal Channeling for Large Colliders: Machine and Physics Applications22 -23 March 2007, CERN Geneva

  4. What is the best crystal for channeling? AS-cut Chemical etching Mechanical polishing Crystal Channeling for Large Colliders: Machine and Physics Applications22 -23 March 2007, CERN Geneva

  5. Extraction efficiency: theoretical calculations and experimental results V.M.Biryukov, A.I.Drozhdin, N.V.Mokhov. PAC 1999 Proceedings (New York), pp. 1234-1236. FERMILAB-Conf-99-072 (1999). V.I.Kotov et al. EPAC 2000 Proceedings (Vienna), p.364. CERN-LHC-2000-007-MMS. Crystal Channeling for Large Colliders: Machine and Physics Applications22 -23 March 2007, CERN Geneva

  6. Surface imperfection & channeling degradationRole of the edges (“Septum width effect”) Elsener et al. Crystal Channeling for Large Colliders: Machine and Physics Applications22 -23 March 2007, CERN Geneva

  7. Surface preparation & analytical techniques Crystal Channeling for Large Colliders: Machine and Physics Applications22 -23 March 2007, CERN Geneva

  8. Rutherford backscattering channeling (c-RBS) The same effect as high energy channeling Depth profile of lattice perfection Scanning electron microscopy (SEM) Surface morphology (qualitative) Atomic force microscopy (AFM) Surface morphology Roughness (quantitative) As cut Crystal cut Mechanical polishing Chemical etching Surface preparation / Analytical techniques Characterisation of Final crystals Refined preparation methodology for experiment at H8 CERN-SPS (September 2006) S. Baricordi et al. Appl. Phys. Lett. 87 (2005) 094102. V. Guidi et al. Nucl. Inst. Meth. B 234 (2005) 40. A. Vomiero et al. Nucl. Instr. Meth. B 249 (2006) 903. Crystal Channeling for Large Colliders: Machine and Physics Applications22 -23 March 2007, CERN Geneva

  9. Si, KSiE0 eIN eOUT Coulomb scattering Rutherford backscattering M surface m, E0 M surface Main parameter: cmin m, E0 Crystal Channeling for Large Colliders: Machine and Physics Applications22 -23 March 2007, CERN Geneva

  10. depth scale c-RBS spectrum of silicon (4He+ beam) Surface peak Energy loss 4He+, E0=2.0 MeV Analised depth ~1 mm Crystal Channeling for Large Colliders: Machine and Physics Applications22 -23 March 2007, CERN Geneva

  11. Reduced energy loss with respect to 4He+ Reduced depth resolution Lack of surface peak c-RBS spectrum of silicon (1H+ beam) Energy loss 1H+, E0=2.0 MeV Analised depth ~10 mm Crystal Channeling for Large Colliders: Machine and Physics Applications22 -23 March 2007, CERN Geneva

  12. Preliminary tests: SEM (*) Chemical etching AS-cut Mechanical polishing (*) Guidi et al. NIM B (2005) Crystal Channeling for Large Colliders: Machine and Physics Applications22 -23 March 2007, CERN Geneva

  13. As-cut Chemical etching Mechanical polishing Preliminary tests: AFM Crystal Channeling for Large Colliders: Machine and Physics Applications22 -23 March 2007, CERN Geneva

  14. Roughness Ra=4.4 nm Rq=5.7 nm Rz=34.8 nm full area selected area Roughness Ra=0.8 nm Rq=1.1 nm Rz=5.3 nm Characterisation/ AFM (2) Crystal Channeling for Large Colliders: Machine and Physics Applications22 -23 March 2007, CERN Geneva

  15. Preliminary tests: c-RBS (*) The spectrum of chemically etched sample overlaps the aligned reference silicon. The spectrum of mechanical polishing and as-cut is 5 times higher than the reference: highly defected surface region. Regular shape: homogeneous in-depth distribution of defects, responsible for de-channeling events. c-RBS highly effective for discriminating high quality crystals for high-energy channeling experiments (*) Baricordi et al. APL (2005) Crystal Channeling for Large Colliders: Machine and Physics Applications22 -23 March 2007, CERN Geneva

  16. The best crystal for channeling: AS-cut Chemical etching HOWEVER:roughnessmust be reduced Mechanical polishing Crystal Channeling for Large Colliders: Machine and Physics Applications22 -23 March 2007, CERN Geneva

  17. Silicon crystals for the H8-SPS experiment Crystal Channeling for Large Colliders: Machine and Physics Applications22 -23 March 2007, CERN Geneva

  18. As-cut Chemical etching Mechanical polishing AFM (1) Crystal Channeling for Large Colliders: Machine and Physics Applications22 -23 March 2007, CERN Geneva

  19. AFM (2) OLD NEW Crystal Channeling for Large Colliders: Machine and Physics Applications22 -23 March 2007, CERN Geneva

  20. c-RBS / chemical etching <011> <111> 1H+ 4He+ Crystal Channeling for Large Colliders: Machine and Physics Applications22 -23 March 2007, CERN Geneva

  21. c-RBS / mechanical polishing • New method of mechanical polishing seems being very promising since allows: • Low Ra • Low lattice defects cmin, <011> = 0.16 OLD preparation methodology cmin, <011> = 0.03 NEW preparation methodology Crystal Channeling for Large Colliders: Machine and Physics Applications22 -23 March 2007, CERN Geneva

  22. Summary AFM c-RBS Crystal Channeling for Large Colliders: Machine and Physics Applications22 -23 March 2007, CERN Geneva

  23. 200 mm 20 mm Old methodology - mechanical What about the egde? Crystal face ║ to beam direction: Ra= 1.6 nm Crystal Channeling for Large Colliders: Machine and Physics Applications22 -23 March 2007, CERN Geneva

  24. Germanium Crystals Ge Si http://www.webelements.com/webelements/elements/text/Ge/xtal-pdb.html http://www.webelements.com/webelements/elements/text/Si/xtal-pdb.html • Space group: Fm-3m (Space group number: 225) • Structure: ccp (cubic close-packed) • Cell parameters: • a: 565.75 pm • b: 565.75 pm • c: 565.75 pm • α: 90.000° • β: 90.000° • γ: 90.000° • Space group: Fd-3m (Space group number: 227) • Structure: diamond • Cell parameters: • a: 543.09 pm • b: 543.09 pm • c: 543.09 pm • α: 90.000° • β: 90.000° • γ: 90.000° Crystal Channeling for Large Colliders: Machine and Physics Applications22 -23 March 2007, CERN Geneva

  25. AFM As cut Chemical etching Crystal Channeling for Large Colliders: Machine and Physics Applications22 -23 March 2007, CERN Geneva

  26. c-RBS Crystal Channeling for Large Colliders: Machine and Physics Applications22 -23 March 2007, CERN Geneva

  27. Summary Crystal Channeling for Large Colliders: Machine and Physics Applications22 -23 March 2007, CERN Geneva

  28. Conclusions • Surface analytical techniques successfully applied for the characterisation of silicon crystals designed for high-energy-channeling experiments • Results on morphological & structural investigation can give account for enhanced channeling efficiency • Application of analytical protocol can be useful benchmark before high-energy runs • Crystals devoted to CERN-SPS experiment in H8 beam line (September 2006) • New materials: Germanium • Investigation on crystal edges Crystal Channeling for Large Colliders: Machine and Physics Applications22 -23 March 2007, CERN Geneva

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