1) Instituto Tecnológico e Nuclear, Sacavém, Portugal 2) Centro de Física Nuclear da Universidade de Lisboa, Portugal 3) II. Physikalisches Institut, Universität Göttingen, Germany 4) Instituut voor Kern- en Stralingsfysica, Katholieke Universiteit Leuven, Belgium 5) University of KwaZulu Natal, Durban, South Africa 6) Departamento Física, Universidade do Porto, Porto, Portugal 7) CERN-PH, Geneva, Switzerland Emission Channeling Lattice Location Experiments with Short-Lived Isotopes The EC-SLI collaboration L. Amorim 4, J.P. Araújo 6, K. Bharuth-Ram 5, J.G. Correia 1,2,7, M.R. da Silva 2, S. Decoster 4, H. Hofsäss 3, M. Nagl 3, L. Pereira 1,4,6, A. Vantomme 4, U. Vetter 3, and U. Wahl 1,2 spokesperson: U. Wahl contact person: J.G. Correia LEUVEN Status report and addendum

Motivation and outline of our 10/2006 proposal We would like to extend emission channeling experiments to... short-lived isotopes (t 1/2 < 6 h) isotopes emitting low energy electrons (E < 40 keV) New equipment to be used: Position-sensitive self-triggered Si pad detectors (for count rates > 1 kHz) Position-sensitive CCD detector for low-energy electrons (  E  1 keV below 40 keV) new on-line emission channeling setups from Lisbon and Göttingen Physics cases: lattice location of transition metals in semiconductors lattice location of Mg in GaN lattice location of Li in ZnO exploring the possibilities for Auger electron emission channeling INTC granted 20 of 36 requested shifts, asked for status report

Motivation and outline of our 10/2006 proposal We would like to extend emission channeling experiments to... short-lived isotopes (t 1/2 < 6 h) isotopes emitting low energy electrons (E < 40 keV) New equipment to be used: Position-sensitive self-triggered Si pad detectors (for count rates > 1 kHz) Position-sensitive CCD detector for low-energy electrons (  E  1 keV below 40 keV) new on-line emission channeling setups from Lisbon and Göttingen Physics cases: lattice location of transition metals in semiconductors lattice location of Mg in GaN lattice location of Li in ZnO exploring the possibilities for Auger electron emission channeling INTC granted 20 of 36 requested shifts, asked for status report postponed not yet achieved manufacturer repair required post- poned

Emission channeling: basic principle 3  3 cm 2 Si pad detector 22  22 pixels of 1.3  1.3 mm 2 new system: max. 3.5 kHz

EC-SLI on-line setup coupled to GHM beam line Since 2007: On-line setup available and used during Mn beam times at LA1 or LA2 Equipped with fast position-sensitive Si pad detector that allows for data taking rates up to 3.5 kHz Aug. 2009: Setup moved to GHM (space that was available following the removal of the PHOENIX ECRIS) Sept. 2009: First 27 Mg beam time, reduced to ~2.5 shifts only, due to Booster vacuum problems

Physics case 1: Lattice location of transition metals in semiconductors Our two main motivations to study transition metals (TMs): TM-doped ZnO, GaN and GaAs are dilute magnetic semiconductors showing room-temperature ferromagnetism (  spintronics) TMs are most-feared deep-level contaminants in Si and Ge processing  Knowledge on the lattice location of TMs is crucial for understanding their properties in these materials Within this experiment (IS453) we have so far obtained results on 56 Mn (1.5 h) in ZnO, GaN, p + -GaAs, Ge, Si 61 Co (1.6 h) in ZnO, GaN 59 Fe (45 d) in Ge, si-GaAs, p + -GaAs, n + -GaAs, SrTiO 3, KTaO 3 Examples: 61 Co in ZnO, 56 Mn in GaN, 56 Mn in p + -GaAs Future experiments: 56 Mn in Si and Ge (in parallel with 57 Mn Mössbauer experiments!) 61 Co in Si 65 Ni (2.5 h) in ZnO, GaN, Si

  emission channeling patterns from 61 Co in ZnO 61 Mn implanted (~10 13 cm  2 ) wait 25 min + anneal emission channeling patterns measured from 61 Co   particles fit results: ~100% 61 Co on substitutional Zn sites T A =800°C

  emission channeling patterns from 56 Mn in GaN 56 Mn implanted directly emission channeling patterns measured from 56 Mn   particles qualitative result: 56 Mn on substitutional Ga sites T A =900°C

  emission channeling patterns from 56 Mn in p + -GaAs Fit result: 56 Mn on 70% substitutional Ga sites S Ga 30% tetrahedral interstitial T As sites T A =300°C

56 Mn in p + -GaAs as function of annealing temperature 56 Mn on tetrahedral interstitial T As sites converted to substitutional Ga sites above 400°C  activation energy for diffusion of Mn(T As ) E A  eV direct evidence for interstitial Mn and its stability, of relevance for Ga 1-x Mn x As dilute magnetic semiconductor (amount of interstitial Mn limits achievable Curie temperature T c )

Physics case 2: Lattice location of Mg in nitride semiconductors GaN is base material for blue LEDs + lasers Mg is the only technologically relevant p-type dopant in GaN Mg (group II) supposed to occupy substitutional Ga (group III) sites However, large fractions of Mg are electrically inactive Why? Are there other Mg lattice sites?  Lattice location of (implanted) Mg will help to answer this question With the EC-SLI on-line setup it is now feasible to use short-lived 27 Mg (9.5 min)  , the only suitable Mg isotope for emission channeling  Investigate lattice sites of 27 Mg in GaN, AlN (first results for RT implantation available) Future experiments:implantation temperatures up to 900°C, also include InN

Major Problem with mass 27 beams: 27 Al contamination 27 Al thermally released contamination of target material SiC Target at 2000°C: 27 Al : 27 Mg  5 nA : 5 pA Reduce outdiffusion of Al by running the target under relatively cool conditions, with less severe losses for Mg  Target at °C: 27 Al : 27 Mg  3 pA : 0.3 pA Proposed measures to reduce Al contamination (Th. Stora): –Use of highly pure SiC target material –GdB 6 cavities as ionizer –Use neutron converter and 30 Si(n,  ) 27 Mg reaction to produce 27 Mg

  emission channeling patterns from 27 Mg in GaN 27 Mg +little 27 Na + 27 Al implanted beam off  emission channeling patterns measured from 27 Mg   particles only preliminary fit results (not corrected for background, inaccurate depth profile): ~30% 27 Mg on substitutional Ga sites, possible Mg interstitial fraction 5-10% on hexagonal H or O sites Relatively high   endpoint energy of 27 Mg causes quite narrow channeling effects, improved angular resolution would help T A =RT as-implanted

Physics case 3: Lattice location of Li in ZnO ZnO promising “new” wide band gap semiconductor similar to GaN Li Ga is being discussed as possible p-type dopant However, Li is probably amphoteric: Li Ga acceptors vs Li i donors Lattice location of Li can be studied using 8 Li (838 ms)   2  (alpha emission channeling) Previously obtained results (IS-342 up till 2000) on 8 Li in (Si, Ge, SiC, diamond) GaAs, AlGaAs, GaP, InP, InSb, AlN, GaN, ZnSe, ZnTe, CdTe - have proven Li to be amphoteric in compound semiconductors - were able to study microscopic diffusion of Li  Proposed lattice location studies of 8 Li in ZnO (50 K < T < 800 K) should unambiguously establish Li i, identify its exact lattice site and probe its diffusion behaviour

73 As and 75 Se requested for tests of TimePix PSD detectors Since 2007 support of MediPix collaboration In 2009 first successful tests of a 3  3 cm  512 pixel (pixel size 59  m) TimePix detector Energy resolution by means of time- over-threshold method (ToT) so far achieved 6.5 keV at 42 keV Conversion electron emitters 73 As (80 d) 75 Se (120 d) requested for detector tests First   emission channeling results with TimePix: 89 Sr in SrTiO 3

Beam request Total requested shifts: 22 All standard ISOLDE targets, however, target development is requested for reducing 27 Al contamination from SiC targets isotopeshiftstargetion sourceyield [at/s/  A] 56 Mn (1.5 h)3UC 2 -WRILIS Mn 5  Mn (4.6 s)  61 Fe (6 min)  61 Co (1.6 h) 1UC 2 -WRILIS Mn 2  Mn (0.71 s)  59 Fe (45 d) 1UC 2 -WRILIS Mn Ni (2.5 h)4UC 2 -WRILIS Ni 5  Mg (9.5 min)8SiCRILIS Mg 5  Li (838 ms)3TaW surface ionization As (80 d) 75 Se (120 d) 2ZrO 2 or Nb foilHot Plasma10 8