characterization of crystals for relativistic channeling

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



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



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.



What is the best crystal for channeling?What is the best crystal for channeling?

AS-cutAS-cut Chemical etchingChemical etching

Mechanical polishingMechanical polishing



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.



Surface imperfection & channeling degradationSurface imperfection & channeling degradationRole of the edges (“Septum width effect”)Role of the edges (“Septum width effect”)

Elsener et al.



Surface preparation & analytical techniquesSurface preparation & analytical techniques



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



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



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



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



Preliminary tests: SEM (*)Preliminary tests: SEM (*)



(*) Guidi (*) Guidi et al.et al. NIM B (2005) NIM B (2005)



Preliminary tests: AFMPreliminary tests: AFM

As-cutAs-cut Chemical etchingChemical etching Mechanical polishingMechanical polishing



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



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



The best crystal for channeling:The best crystal for channeling:



HOWEVER:HOWEVER:roughnessroughness

must be reducedmust be reduced



Silicon crystals for the H8-SPS experimentSilicon crystals for the H8-SPS experiment



AFM (1)AFM (1)

As-cutAs-cut Chemical etchingChemical etching Mechanical polishingMechanical polishing



AFM (2)AFM (2)

OLD

NEW



c-RBS / chemical etchingc-RBS / chemical etching

<011> <111>

1H+

4He+



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



SummarySummary

AFMAFM c-RBSc-RBS



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



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



AFMAFM

As cut Chemical etching



c-RBSc-RBS



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



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

characterization of crystals for relativistic channeling

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