Fighting f-factors and implantation damage in emission Mössbauer spectroscopy Haraldur Páll Gunnlaugsson* The Mössbauer collaboration at ISOLDE CERN The ISOLDE collabroation *Aarhus University → KU Leuven → CERN

Acknowledgements 2 The Mössbauer collaboration at ISOLDE/CERN, >30 active members with new members (2014) from China, Russia, Bulgaria, Austria, Spain: Three experiments (IS501, IS576, IS578) Existing members New members 2014

Outline Emission Mössbauer spectroscopy Damage and f-factor Annealing/quenching experiments Preliminary results from 2014 Future prospective 3

Emission Mössbauer spectroscopy 4 Implanted propes: 57 Mn (1.5 min.) → 57M Fe (100 ns) → 57 Fe 119 In (2.4 min.) → 119M Sn (23 ns) → 119 Sn Sample     Major benefits:  E (  ) ~ neV → Hyperfine interactions Measure dilute (~10 -4 at.%) Chemistry of Mn/In Recoil  E R  ~ 40 eV ( 57 Mn → 57M Fe)  E R  ~ 8 eV ( 119 In → 119M Sn) → Interstitial defects

Experimental setup 5 MS drive and detector Beam Chamber

Damage (point defects) 6 V’s; I’s Increase temperature, determine mobility and/or activation energies E a  T A Mn S -V O → Mn S E a = 1.6 eV Mn S -V O → Mn S E a = 1.6 eV V Ti mobile at 300 K Example: Mn/Fe in TiO 2

Damage (amorphos zones) 7 Each ion creates a small, spatially isolated amorphous zone - First step in amorphization of the material - Few nm across - Anneal (disappear) at K (silicon) while >1100 K is needed to recrystallize amorphous layers HR-TEM of amorphous zones in Ge (Jenčič & Robertson, Mat. Sci Semicon. Proc. 3 (2000) 311.)

The f-factor 8 There are limits to eMS measurements due to the Debye Waller factor E  : transition energy  x 2  : mean square displacement of the nucleus  x 2  evaluated in the Debye approximation

Physics and damage 9 In some cases: The interesting physics are at ”low” temperatures Damage annealing at ”high” temperatures Examples: Magnetic interactions: MnGa, MnSi & Heusler alloys (IS578) (Al, Ga)N:Mn (IS576) Diffusion of interstital Fe Si & oxides (IS501) Re-invention of ”quenching” experiments AmorphousPoint-defectsAnnealed

Annealing of 119In implanted samples, G. Weyer 1980’s 10 Implantation of 119 In (T ½ = 2.4 min) at RT -Measurements at RT/LN show complicated spectrum with at least 4 spectral components -Measurements at LN after annealing at 340ºC reveal a much simpler spectrum where effects of damage have disappeared -Great deal of running involved… -Repeated in different types of materials with great sucess

Quenching experiments 11 1.Implant (and measure) at elevated temperatures (RT-1000 K) 2.Remove the sample from vacuum, quench in LN, measure off-line Implantation chamber On-line measurement Off-line measurement in LN bath Samples

Quenching experiments 12 1.Implant (and measure) at elevated temperatures (RT-1000 K) 2.Remove the sample from vacuum, quench in LN, measure off-line

Quenching experiments 13 1.Implant (and measure) at elevated temperatures (RT-1000 K) 2.Remove the sample from vacuum, quench in LN, measure off-line

Quenching experiments 14 1.Implant (and measure) at elevated temperatures (RT-1000 K) 2.Remove the sample from vacuum, quench in LN, measure off-line

Quenching experiments 15 1.Implant (and measure) at elevated temperatures (RT-1000 K) 2.Remove the sample from vacuum, quench in LN, measure off-line

Quenching equipment 16 Tested/set up and used at the 2014 beam-time Considerable problems but evaluable lessons learned

Results from 2014: 57 Mn in silicon Physics of 3d metals in Si Probe native defects (IS501) Apparent inconsistency with EC 17 Quenching from 670 K If Fe S and Fe I :  Mn N weakly bound defect generated with fast <100 ns V capture of recoiling Fe If Fe S and Fe N :  Mn N stable defect  Fe N = Fe I -V

Conclusions/outlook Quenching experiments performed again after >20 years New possibilities in the physics program With sample out of vacuum system, many new experimental situations are possible  Quenching  External magnetic field  Laser light illumination  Sample orientation  Mechanical strain  External electical field  …. 18 Workshop on the Applications of Emission Mössbauer spectroscopy (WEMS2015) 4-6 March 2015 Johannes Kepler University Linz, Austria