Crystal Channeling for Large Colliders: Machine and Physics Applications
22 -23 March 2007, CERN Geneva1A. Vomiero
Characterization of crystalsCharacterization of crystalsfor relativistic channelingfor 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 Applications
22 -23 March 2007, CERN Geneva2A. Vomiero
OutlineOutline
Surface defects & noise effectsSurface defects & noise effects Shape of deflected beamShape of deflected beam Extraction efficiencyExtraction efficiency Edge effectEdge effect
Surface preparation & analytical techniquesSurface preparation & analytical techniques Preliminary characterisationsPreliminary characterisations Definition of analytical protocolDefinition of analytical protocol
Silicon crystals devoted to CERN-SPS experiment in H8 Silicon crystals devoted to CERN-SPS experiment in H8 beam line (September 2006)beam line (September 2006)
New materials: Germanium crystalsNew materials: Germanium crystals
ConclusionsConclusions
Crystal Channeling for Large Colliders: Machine and Physics Applications
22 -23 March 2007, CERN Geneva3A. Vomiero
Surface treatment proved useful to improve the Surface treatment proved useful to improve the quality of the extracted beamquality of the extracted beam
Images of the 70 GeV protons deflected through mechanically Images of the 70 GeV protons deflected through mechanically treated and chemically polished crystals (U70 @ IHEP)treated and chemically polished crystals (U70 @ IHEP)
Byriukov et al.
Crystal Channeling for Large Colliders: Machine and Physics Applications
22 -23 March 2007, CERN Geneva4A. Vomiero
What is the best crystal for channeling?What is the best crystal for channeling?
AS-cutAS-cut Chemical etchingChemical etching
Mechanical polishingMechanical polishing
Crystal Channeling for Large Colliders: Machine and Physics Applications
22 -23 March 2007, CERN Geneva5A. Vomiero
Extraction efficiency: theoretical calculations and Extraction efficiency: theoretical calculations and experimental resultsexperimental 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 Applications
22 -23 March 2007, CERN Geneva6A. Vomiero
Surface imperfection & channeling degradationSurface imperfection & channeling degradationRole of the edges (“Septum width effect”)Role of the edges (“Septum width effect”)
Elsener et al.
Crystal Channeling for Large Colliders: Machine and Physics Applications
22 -23 March 2007, CERN Geneva7A. Vomiero
Surface preparation & analytical techniquesSurface preparation & analytical techniques
Crystal Channeling for Large Colliders: Machine and Physics Applications
22 -23 March 2007, CERN Geneva8A. Vomiero
Surface preparation / Analytical techniquesSurface preparation / Analytical techniques
Rutherford backscattering channeling (c-RBS)Rutherford backscattering channeling (c-RBS) The same effect as high energy channeling Depth profile of lattice perfection
Scanning electron microscopy (SEM)Scanning electron microscopy (SEM) Surface morphology (qualitative)
Atomic force microscopy (AFM)Atomic force microscopy (AFM) Surface morphology Roughness (quantitative)
Crystal cutCrystal cut Mechanical polishingMechanical polishing
Chemical etchingChemical etching
As cutAs cut
Refined preparation methodology Refined preparation methodology for experiment at H8 CERN-SPS for experiment at H8 CERN-SPS
(September 2006)(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.
CharacterisationCharacterisationofof
Final crystalsFinal crystals
Crystal Channeling for Large Colliders: Machine and Physics Applications
22 -23 March 2007, CERN Geneva9A. Vomiero
Rutherford backscatteringRutherford backscattering
surface
surface
m, E0
M
IN
OUTCoulombscattering
100 200 300 400
Channel
0
5
10
15
20
25
30
35
Nor
mal
ized
Yie
ld
0.5 1.0 1.5
Energy (MeV)
Si, KSiE0
m, E0
M
Main parameter:min
Crystal Channeling for Large Colliders: Machine and Physics Applications
22 -23 March 2007, CERN Geneva10A. Vomiero
c-RBS spectrum of silicon (c-RBS spectrum of silicon (44HeHe++ beam) beam)
depth scale
Surface peak
44HeHe++, E, E00=2.0 MeV=2.0 MeV
Analised depth Analised depth ~~1 1 mmmkeV
dx
dEmkeV
dx
dE
OUTIN
/300 , /230
Energy loss
Crystal Channeling for Large Colliders: Machine and Physics Applications
22 -23 March 2007, CERN Geneva11A. Vomiero
c-RBS spectrum of silicon (c-RBS spectrum of silicon (11HH++ beam) beam)
mkeVdx
dEmkeV
dx
dE
OUTIN
/50 , /25
Energy loss
11HH++, E, E00=2.0 MeV=2.0 MeV
Analised depth Analised depth ~~10 10 mm
Reduced energy loss with respect to 4He+
Reduced depth resolution
Lack of surface peak
Crystal Channeling for Large Colliders: Machine and Physics Applications
22 -23 March 2007, CERN Geneva12A. Vomiero
Preliminary tests: SEM (*)Preliminary tests: SEM (*)
AS-cutAS-cut Chemical etchingChemical etching
Mechanical polishingMechanical polishing
(*) Guidi (*) Guidi et al.et al. NIM B (2005) NIM B (2005)
Crystal Channeling for Large Colliders: Machine and Physics Applications
22 -23 March 2007, CERN Geneva13A. Vomiero
Preliminary tests: AFMPreliminary tests: AFM
As-cutAs-cut Chemical etchingChemical etching Mechanical polishingMechanical polishing
Crystal Channeling for Large Colliders: Machine and Physics Applications
22 -23 March 2007, CERN Geneva14A. Vomiero
CharacterisationCharacterisation / AFM (2)AFM (2)
RoughnessRoughness
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
Crystal Channeling for Large Colliders: Machine and Physics Applications
22 -23 March 2007, CERN Geneva15A. Vomiero
Preliminary tests: c-RBS (*)Preliminary tests: c-RBS (*)
(*) Baricordi et al. APL (2005)
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
Crystal Channeling for Large Colliders: Machine and Physics Applications
22 -23 March 2007, CERN Geneva16A. Vomiero
The best crystal for channeling:The best crystal for channeling:
AS-cutAS-cut Chemical etchingChemical etching
Mechanical polishingMechanical polishing
HOWEVER:HOWEVER:roughnessroughness
must be reducedmust be reduced
Crystal Channeling for Large Colliders: Machine and Physics Applications
22 -23 March 2007, CERN Geneva17A. Vomiero
Silicon crystals for the H8-SPS experimentSilicon crystals for the H8-SPS experiment
Crystal Channeling for Large Colliders: Machine and Physics Applications
22 -23 March 2007, CERN Geneva18A. Vomiero
AFM (1)AFM (1)
As-cutAs-cut Chemical etchingChemical etching Mechanical polishingMechanical polishing
Crystal Channeling for Large Colliders: Machine and Physics Applications
22 -23 March 2007, CERN Geneva19A. Vomiero
AFM (2)AFM (2)
OLD
NEW
Crystal Channeling for Large Colliders: Machine and Physics Applications
22 -23 March 2007, CERN Geneva20A. Vomiero
c-RBS / chemical etchingc-RBS / chemical etching
<011> <111>
1H+
4He+
Crystal Channeling for Large Colliders: Machine and Physics Applications
22 -23 March 2007, CERN Geneva21A. Vomiero
c-RBS / mechanical polishingc-RBS / mechanical polishing
min, <011> = 0.16 OLD preparation methodology
min, <011> = 0.03 NEW preparation methodology
New method of mechanical polishing seems being very promising since allows:
1. Low Ra
2. Low lattice defects
Crystal Channeling for Large Colliders: Machine and Physics Applications
22 -23 March 2007, CERN Geneva22A. Vomiero
SummarySummary
AFMAFM c-RBSc-RBS
Crystal Channeling for Large Colliders: Machine and Physics Applications
22 -23 March 2007, CERN Geneva23A. Vomiero
What about the egde?What about the egde?
200 m 20 m
Old methodology - mechanicalOld methodology - mechanical
Crystal face ║ to beam direction:
Ra= 1.6 nm
Crystal Channeling for Large Colliders: Machine and Physics Applications
22 -23 March 2007, CERN Geneva24A. Vomiero
Germanium Crystals
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°
http://www.webelements.com/webelements/elements/text/Ge/xtal-pdb.html
http://www.webelements.com/webelements/elements/text/Si/xtal-pdb.html
Ge Si
Crystal Channeling for Large Colliders: Machine and Physics Applications
22 -23 March 2007, CERN Geneva25A. Vomiero
AFMAFM
As cut Chemical etching
Crystal Channeling for Large Colliders: Machine and Physics Applications
22 -23 March 2007, CERN Geneva26A. Vomiero
c-RBSc-RBS
Crystal Channeling for Large Colliders: Machine and Physics Applications
22 -23 March 2007, CERN Geneva27A. Vomiero
SummarySummary
Sample AFM c-RBS
Ra (nm) min
As-cut 26±8 0.31
Mechanical polishing / 0.75
Chemical etching 1’ 13±2 0.03
Chemical etching 4’ 11±3 0.03
Crystal Channeling for Large Colliders: Machine and Physics Applications
22 -23 March 2007, CERN Geneva28A. Vomiero
ConclusionsConclusions
Surface analytical techniques successfully applied for the characterisation Surface analytical techniques successfully applied for the characterisation of silicon crystals designed for high-energy-channeling experimentsof silicon crystals designed for high-energy-channeling experiments
Results on morphological & structural investigation can give account for Results on morphological & structural investigation can give account for enhanced channeling efficiencyenhanced channeling efficiency
Application of analytical protocol can be useful benchmark before high-Application of analytical protocol can be useful benchmark before high-energy runsenergy runs
Crystals devoted to CERN-SPS experiment in H8 beam line (September Crystals devoted to CERN-SPS experiment in H8 beam line (September 2006)2006)
New materials: GermaniumNew materials: Germanium
Investigation on crystal edgesInvestigation on crystal edges