CC-2007 - 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
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)
Silicon strip: fabrication
Samples are fabricated by
dicing of a high-quality Si
wafers
Miscut angle < 0,5 mrad
TTV < 3 m
Dimensions (mm)
(111) orientation
(110) orientation
W
L
H
70
2
0.2
70
2
0.5
70
2
0.9
70
1
0.2
70
3
0.9
Chemical etching
Isotropic wet-chemical etching
• planar etching
HF + HNO3 + CH3COOH
• etching = about 2 m
RBS-channeling spectra
before chemical etching
after chemical etching
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
Observation of volume reflection
be
a
m
Successful observation of VR
with strip-like crystals with
(110) orientation
crystals sizes: 0.9 x 70 x 3 mm3
Germanium: sample fabrication
Dimensions (mm)
W
L
H
70
2
0.5
Samples with (111) and
(110) orientation
Miscut angle < 0,5 mrad
TTV < 3 m
Reconsideration of chemical
etching due to different
reactivity of Germanium vs.
Silicon
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
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 3764.4 mm
Deflection angle: 500 µrad
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
0.2
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
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)
Investigation on complex crystals II
Energy (MeV)
1.0
3000
1.4
1.6
1.8
Reduced backscattering
yield in channeled beam
geometry in old sample
zeolite Random
zeolite Allineato
2500
Normalized Yield
1.2
O
2000
1500
Si
1000
Ca
500
0
200
250
300
350
400
450
Channel
New samples ready to be prepared
and characterized with
RBS channeling
Direction of channels
2 cm
Configuration for multiple
volume reflection
θref
Ideally a series of strips would multiply the
reflection at each individual strip
θref
At 400 GeV it holds:
θref
 ref  14.5 rad
θref
 bend  170 rad
θref
θacc
 ref   bend
A series of parallel strips
appears to be affordable
θref
Configuration for multiple
volume reflection
θref
Ideally a series of strips would multiply the
reflection at each individual strip
θref
At 400 GeV it holds:
θref
 ref  14.5 rad
θref
 bend  170 rad
θref
θref
θacc
 ref   bend
A series of parallel strips
appears to be affordable
How to do it?
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)
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)
Undulator I
θref
θref
Undulator I
θref
θref
200-2000 μm
θref
θref
An undulator would be
a compact “multi-strip”
with millimetric or submillimetric period
Technology developed
in a previous study
PRL 90 (2003) 034801
Easy to compensate for the
shift of the tangency point
with a global curvature
(non-parallel configuration)
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
3"
0.3mm
0.1mm
10"
10"
0.1mm
10"
10"
The bending of crystal from one
groove is ~80 rad for grain size 4060 m and ~20 rad for grain size
4-6 m with 300 m samples
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
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) 114107
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