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MSR in Diamond

MSR in Diamond. SH Connell, K Bharuth-Ram, S Cox. University of Johannesburg, Univ. of KwaZulu-Natal, Rutherford Appleton Lab. Natural diamond Synthetic Diamond Synchrotron characterisation Muon Spin Rotation studies Coherence.

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MSR in Diamond

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  1. MSR in Diamond SH Connell, K Bharuth-Ram, S Cox University of Johannesburg, Univ. of KwaZulu-Natal, Rutherford Appleton Lab • Natural diamond • Synthetic Diamond • Synchrotron characterisation • Muon Spin Rotation studies • Coherence

  2. "…. It seems, indeed, to be a general truth, that there are comparatively few diamonds without cavities and flaws and that this mineral is a fouler stone than any other used in jewelry …." Sir David Brewster 1862 5 mm Courtesy J Hansen - Hansen Future Materials

  3. The Star of Africa ~ 50 ct This is all changing ……. … diamond for high tech applications CLEO diamond tracker - OSU “ … the dawn of diamond electronics has arrived …" Element Six MD, Christian Hultner 24-02-2005 “… a crucial new role for diamond in an ultra-high technology area is emerging …” SYNCHROTRON RADIATION NEWS, Vol. 18, No. 1, 2005 Bent diamond ESRF

  4. Diamond IR Spectra P1 nitrogen peak at 1130 cm-1 HPHT and SC-CVD (many HPHT and SC-CVD) Consider absorption, luminescence and EPR centres Very complex …..

  5. CVD diamond Electronic grade SC-CVD(~100 GBP /mm3) Optical grade PC-CVD(~25 GBP /mm3) Nano diamond(~1 $ /cm3) • Properties (at best) • Substitutional N, B < few ppb • CCD ~ 1mm • Combined mobility ~ theoretical • Best case : Residual strain ~ 10-6 • Plates 5 – 10 mm sides

  6. HPHT diamond • Properties (at best) • Substitutional N, B ~ few ppb • Best case : Residual strain ~ 10-8 • Plates 5 – 10 mm sides Low Strain IIa HPHT (~1000 €/mm3)

  7. “Electronic" diamond Combined Mobility (cm2/Vs) Bandgap (eV) t > 2 ms, CCD > Dxmaterial • Intrinsic • p-type ? … n-type mc high combined mobility, eg wide band gap, Eb high breakdown field, W high resistivity s high thermal conductivity, Dl broad spectral band, er low relative permeability nv very radiation hard • Study • Charge carrier dynamics • Near surface defects • Contacts • Electrically active defects FoM (various) Diamond >> Si 8000 x

  8. “Optical” Diamond Eg. Monochromator for Synchrotron X-rays • high thermal conductivity, m low linear X-ray absorption, • low thermal expansion PRB42(1990)1104 – T Anthony et al For Silicon : liquid N2 cooling works up to 400 W/mm2 For FEL’s: 10-100 GW/pulse (tpulse = 100fs) Response to transients important

  9. Improvements in Diamond Synthesis Increasing quality UV luminescence White beam topograph Optical microscope

  10. 30/11/05 Courtesy J Hansen - Hansen Future Materials

  11. AboveWireframe of growth sectors, schematic BelowPhoto, UV Luminescence 1-3 Images from Growth program of the DTC middle bottom top

  12. Clockwise Visible image Birefringence image UV - luminescence WB X-ray Topograph

  13. HPHT vs CVD • Techniques are complimentary – both are necessary • CVD growth conditions cold for diamond – allow better control of impurities however, defects can freeze in.Leads to purer diamond (c<1ppb), but residual strain is compromised (bundles of dislocations emanating from defects in substrate, maybe more still Dq>10-6).Niche is Electronic Applications • HPHT growth conditions hotter, and in the pressure capsule its more difficult to control impurities, growth is in “annealing” conditions.Leads to low strain diamond Dq~10-8, but more impurities, c<10ppb.Niche is Optical Applications Situation evolves HPHT CVD DRM17(2008)262 White Beam Topographs - In each case illustrative samples (not the best available)

  14. Si (975), |b|  40 ESRF/ID18 Si (111), |b|  18.3 Si (975), |b|  40 Si (111) detector CRL Ge (331) Si (111) diamond (400) High-resolution diffractometry set-up E = 14.413 keV Δλ/λ 10-8 ( 0.0023”)   0.18”

  15. WHITE BEAM TOPOGRAPHY and Rocking Curve Broadening HPHT with inclusion - theo * app - exp ● exp - fit FWHM 0.07 ’’ FW20%M 0.14 ’’ FW2%M 0.48 ’’ footprint = 1 x 0.4 mm arcsecs h 1 mm fit after convolution “defects broadening” “defects broadening” function Δd/d = 1.2 x 10-5 arcsecs arcsecs

  16. position width height width height position

  17. Bendable Monochromator 2.5o x 10-3 f(FWHM) 0.5o x 10-3 3 x 104 f(R) in a.u. 0 x 104 +4o x 10-3 Micrometer scaled resolved X-ray diffraction image of diamond f(q) -4o x 10-3

  18. Quantification of strain at the 10-8 level Eg =12 keV Si (444) C* (115) Working point on the non-dispersive double crystal reflectivity curve arc secs

  19. dislocations Increasing strain sensitivity WBT Laue case MPWT Bragg MPWT Bragg 1 mm scratches 12keV, Si [444] C* [115] Δd/d >  4 10-8 20keV, Si [800] C* [800] Δd/d >  1.2 10-8 Also with this very high strain sensitivity a rather homogenous zone is present, there crystal quality close to that of silicon ESRF Newsletter 45(2007))27

  20. 1 mm

  21. Dislocation free -220 and 220-reflections sample dimension 4x4 mm2 The crystal quality seen with the strain sensitivity of white beam topography is very good! No macroscopic defects like dislocations are visible. White beam topographs in transmission

  22. Quantum Diamond

  23. Why study Muonium ? • Mu chemically similar to H • Dynamics are different • Reconcile Mu, H studies • Study quantum diffusion e- e- p+ m+

  24. Focus on Hydrogen in diamond • Observations • Diamonds are always contaminated with H in some form • Passivates acceptors and dopants • Compensates deep recombination centres • Possibly a mechanism to generate extended defects. • H role in surface conductivity • Possible role in shallowing of donor states – Hn-X complexes • “MSR only unambiguous probe” – MA Stoneham in “The Properties of Diamond” • Traps at the NV centre  NVH

  25. The search for shallow donors in diamond • Elemental : • N- Ed ~ 1700 meV, also deep • P- Ed ~ 550 meV, me ~ 200 cm2/V, probably attracts defects • Molecular : • Many theoretical suggestions • Bond compression shallows state • N-B-N • N-H-N • N-O • Hn-X

  26. HBC Diamond E HT H2* di-HBC HBC H2* Dislocation dipole H4* 0 H4*

  27. Typical MSR in Diamond CN ~ 10 ppb CN ~ 1 ppm CN ~ 1 ppm CN ~ 1 ppm CN ~ 1 ppm CN ~ 100 ppm

  28. TF MSR for Tetrahedral Muonium - MuT l(T) Beating of the two closely spaced precession frequencies n12 and n23 Note the damping of the oscillations Extract the depolarisation rate l(T)

  29. Four measurements of the Muonium Diffusion • TF Methods • Ensemble dephases by different arrival times at traps. • Boron Impurities • Vacancies • Ensemble dephases due to motion against a background of randomly oriented moments • 13C enriched diamond • LF Methods • Depolarisation by spin-lattice relaxation • 13C enriched diamond

  30. Wave-like motion

  31. Assume deep trapping at B after rapid diffusion • Observation of passivation • Observation of fast motion, then power law transition to slower hop rates(T-2)

  32. Assume deep trapping at V after rapid diffusion • Observation of fast motion, then power law transition to slower hop rates (T-2)

  33. Assume deep trapping at V after rapid diffusion • Observation of fast motion, then power law transition to slower hop rates (T-1)

  34. TF MSR in a 13C diamond • Motional narrowing for inhomogeneous background of randomly oriented nuclear spins • Observation of fast motion, then power law transition to slower hop rates (T1.3)

  35. LF MSR in a 13C diamond

  36. LF MSR in a 13C diamond Fit this expression to all Time Differential LF spectra at all temperatures simultaneously, and extract the nuclear hyperfine constantand hop rate. Data Analysis by Redfield Method

  37. LF MSR in a 13C diamond

  38. LF MSR in a 13C diamond DMu ~ 2.4 x 10-6 cm2/s c.f. DH ~10-12 cm2/s

  39. LF MSR in a 13C diamond

  40. LF MSR in a 13C diamond • Conclusions • The spin relaxation rate, T1-1, does have a power law behaviour, but this is due to a change in the nuclear hyperfine constant rather than the hop rate. As the temperature increases, the muonium localises. This could be the onset of the MuT MuBC transition. • The hop rate is very high : 6 x 1010s-1. It is also almost constant in temperature over the range studied. This is consistent with previous conclusion of quantum diffusion. • Apart from this general agreement, the results of the LF measurements do not fully reconcile with the TF measurements.

  41. Possible MuBC thermal ionisation MuT MuBC MuBC+

  42. Possible MuBC thermal ionisation • Conclusions • MuT MuBC transition observed in LF for the first time with the correct activation energy of 0.476eV. • The transition MuT MuBC occurs faster than the trapping of MuT at nitrogen centres at high temperatures. This supports the idea that MuT must first localise before it can convert. • If MuBC is ionising, its rate is faster than 2 x 108s-1. • This would also imply the level of MuBC in the gap is 0.60 – 1.80 eV (dependant on data analysis model) • There is still the possibility (very small) that MuBC has become mobile, accounting for its depolarisation. (Recent measurement to higher T to check this).

  43. MSR in Diamond SH Connell, K Bharuth-Ram, S Cox University of Johannesburg, Univ. of KwaZulu-Natal, Rutherford Appleton Lab Electronic Optical Quantum

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