1. Fabrication of strip-like crystals for channeling
CC  CARE-HHH-APD mini-Workshop on
Crystal Channeling for Large Colliders: Machine and Physics Applications
Fabrication of strip-like crystals for channeling
Vincenzo Guidi
on behalf of the Sensors and Semiconductors group
at University of Ferrara and INFN
CERN, March 22nd 2007

2. Outline Preparation of Si strip-like crystals (2006)
Preparation of Ge strip-like crystals (2007)
Preparation of thin Si strip-like crystals (2007)
Investigation on complex crystals (2007)
Configurations for multiple volume reflection (2007)

3. Silicon strip: fabrication
Samples are fabricated by dicing of a high-quality Si wafers
Miscut angle < 0,5 mrad
TTV < 3 m
Dimensions (mm) W L H 70 2
0.2
0.5
0.9 1 3
(111) orientation
(110) orientation

4. RBS-channeling spectra
Chemical etching
Isotropic wet-chemical etching
planar etching
HF + HNO3 + CH3COOH
etching = about 2 m
after chemical etching
before chemical etching
RBS-channeling spectra

5. Bending of the strip
Deflection is provided by anticlastic forces though externally imparted mechanical forces
At H8-SPS bending angle was fixed at about 150 μrad

6. Observation of volume reflection
beam
Successful observation of VR with strip-like crystals with
(110) orientation
crystals sizes: 0.9 x 70 x 3 mm3

7. Germanium: sample fabrication
Miscut angle < 0,5 mrad
TTV < 3 m
Dimensions (mm) W L H 70 2
0.5
Samples with (111) and
(110) orientation
Reconsideration of chemical etching due to different reactivity of Germanium vs. Silicon

8. Germanium: characterization
Characterization of the samples
via RBS-channeling (courtesy of A. Vomiero)
Samples delivered to IHEP for
experiments with 70 GeV protons and available for the H8 RD22 runs

9. Germanium: bending Courtesy of D. Vincenzi
Interferometric measurements made with a Zygo Fizeau-type interferometer
strip
Wafer orientation: (110)
Strip size: 2x0.2x70 mm3
Main radius of curvature: -631 mm
Anticlastic radius of curvature mm
Deflection angle: 500 µrad

10. Thin strips I
New fabrication methodology to prepare thin strips (achieved by both fully chemical and mechanical methods)
Dimensions (mm) W L H 70
0.2

11. Thin strips II
Recent observation of channeling with 450 MeV positrons at the BTF at LNF
Ideal crystal for extraction in machines for adrotherapy
Peak of channeling
Courtesy of M. Prest

12. Investigation on complex crystals I
Natural and artificial zeolites offer high acceptance for
channeling
Calculation of potential and electric field in zeolites (courtesy of V.A. Maisheev)

13. Investigation on complex crystals IICa
Reduced backscattering yield in channeled beam geometry in old sample
2 cm
Direction of channels
New samples ready to be prepared
and characterized with
RBS channeling

14. Configuration for multiple volume reflection
Ideally a series of strips would multiply the reflection at each individual strip
θref
θacc
At 400 GeV it holds:
A series of parallel strips appears to be affordable

15. Configuration for multiple volume reflection
Ideally a series of strips would multiply the reflection at each individual strip
θref
θacc
At 400 GeV it holds:
A series of parallel strips appears to be affordable
How to do it?

16. Silicon multi-strip
Fabrication of a preliminary sample of a multi-strip with (111) silicon by mechanical dicing
Technology to achieve multi-strips through fully chemical methods (110)

17. Silicon multi-strip
Fabrication of a preliminary sample of a multi-strip with (111) silicon by mechanical dicing
Technology to achieve multi-strips through fully chemical methods (110)

18. Undulator I
θref
θref

19. Undulator I
θref
An undulator would be a compact “multi-strip” with millimetric or sub-millimetric period
θref
Technology developed in a previous study
θref μm
PRL 90 (2003)
Easy to compensate for the shift of the tangency point with a global curvature
(non-parallel configuration)

20. Undulator II
The method of grooves proved the possibility to implement a crystalline undulator with proper parameters
Courtesy of Y. Ivanov
Sample produced in Ferrara
The bending of crystal from one groove is ~80 rad for grain size m and ~20 rad for grain size 4-6 m with 300 m samples

21. Undulator III
Alternative method to generate a periodic structure within a crystal: deposition of an alternate tensile coating
It allows exploitation of the full cross section of the crystal featuring quasi-sinusoidal deformation field

22. Undulator III
Alternative method to generate a periodic structure within a crystal: deposition of an alternate tensile coating
It allows exploitation of the full cross section of the crystal featuring quasi-sinusoidal deformation field
APL 90 (2007)

23. Conclusions Production of Ge samples for H8
Optical characterization of curvature
Investigation on zeolites
Production of thin Si crystal
Realization of a Si multi-strip
Undulator as a multi-strip