Increase of probability of particle capture into the channeling regime

1. Increase of probability of particle capture into the channeling regime 4th Crystal Channeling Workshop 2009 Vincenzo Guidi, Andrea Mazzolari, University of Ferrara and INFN - ItalyAlberto Carnera, Davide De Salvador, University of Padova and INFN - Italy and Victor Тikhоmirоv RINP, Minsk CERN, March 26, 2009

2. Outlook • Super acceptance channeling • SIMOX structure • Channeling in SIMOX structure • SIMOX structure channeling experiments • SIMOX structure-transmitted energy distribution • SIMOX structure-transmitted angular distribution • SIMOX structure-experiment at high energies • Conclusions

3. z2 z1 Super-acceptance channeling I With a silicon lens it is possibile to reduce the number of dechanneled particles by focusing the proton beam onto the center of the potential well, with a precise cut in the crystal potential. z1~λ/12÷ λ/8 z1-z2 ~λ/8÷ λ/6 λ: channeling oscillation period

4. Super-acceptance channeling II • The cut decreases dechanneling probability to 1-2% • Crystal can be realized using standard silicon micromachining tecniques

5. SIMOX structure I Substrate heated at 650 °C and oxygen ions implantation Thermal anneling at 1320 °C in O2/Ar atmosphere Thermal annealing

6. SIMOX structure II Implementation of the method of the cut through a buried SiO2 layer. Si (device) SiO2 (BOX) Si (Bulk) • Thermal annealing restores silicon cristalline quality and creates a buried SiO2 layer. • Interfaces between Si and SiO2 are well terminated. • Misalignment between silicon layers in available SIMOX structures: less than 0.7 Å/mm

7. Channeling in SIMOX structure I Focusing effect of BOX layer

8. Channeling in SIMOX structure II Above: nonchanneling probability behind the BOX layers in a SIMOX structure (thick) and behind the entry face of a crystal (thin) vs proton energy simulated at xc = 0.15Å (dashed) and 0.20Å (solid). Below: optimal BOX layer coordinates vs proton energy.

9. SIMOX structure chanelling experiments Si thickness: 231 nm BOX thickness: 377 nm SIMOX thickness: 500 μm • RBS-channeling experiments with 6.1 MeV protons • Divergence less than 0.01° (half angle) χ Crystal depth (μm)

10. SIMOX structure-transmitted energy distribution Si Simox Transmitted energy distribution after a SIMOX 10 μm thin

11. SIMOX structure-transmitted angular distribution Transmitted angular distributions with (dashed) and without (solid) a BOX layer Left: for 400 MeV and z1,2= 150 nm, 560 nm, SIMOX thickness: 20 μm Right: for 7 MeV and z1,2,3 =20nm, 60nm, SIMOX thickness: 3 μm.

12. SIMOX structure experiment at high energies I Beam • Maximum z1 and z2 values for available SIMOX structures are respectively about 200 and 400 nm. (110) planes • It is possible to use SIMOX crystal at high energies (400GeV) orienting the crystal at grazing incidence with respect to the beam

13. SIMOX structure experiment at high energies II dN/dΘ (mrad) Θ (mrad) Si thickness: 231 nm BOX thickness: 377 nm SIMOX thickness: 500 μm Grazing incidence angle: 3° E = 400 GeV

14. Conclusions • Crystal with cut may lead to deflection efficiency through planar channeling close to 100% • SIMOX crystal experiment at high or low energy is a good way to check the principle of crystal with cut.