57 Mn Mössbauer collaboration at ISOLDE/CERN Emission Mössbauer spectroscopy of advanced materials for opto- and nano- electronics Spokepersons: Haraldur Páll Gunnlaugsson Sveinn Ólafsson Contact person: Karl Johnston CERN-INTC (INTC-P-275)

57 Mn Mössbauer collaboration at ISOLDE/CERN Mössbauer spectroscopy Valence(/spin) state of probe atom (Fe n+, Sn n+ ) Symmetry of lattice site (V zz ) Diffusion of probe atoms (few jumps ~100 ns) Debye-Waller factors Magnetic interactions Paramagnetic relaxations of Fe 3+ Can usually easily detect up to 5-6 spectral components (substitutional, interstitial, damage, vacancy-defects,…)

57 Mn Mössbauer collaboration at ISOLDE/CERN Work with dilutions (< at.%) not possible with conventional MS Site selective doping with different parents: Make use of ”special” properties - Recoil to create interstitials ( 57 Mn, 119 In) - Observe meta-stable electronic states ( 57 Co) 57 Co (271 d) Radioactive Mössbauer spectroscopy 119m Sn (290 d) 119 Sb (38 h) 119 Sn 119 In (2.1 m) 57 Fe 57 Mn (1.5 m) PAC Use in home laboratories Off-line at ISOLDE

57 Mn Mössbauer collaboration at ISOLDE/CERN This proposal Some basic ideas: –Growing collaboration → Do more Research themes: 1. Paramagnetic relaxations in compound semiconductors (diluted magnetic semiconductors) 2. Vacancy diffusion in group IV semiconductors 3. Doping of Si-nano-particles 4. Investigation of phase change mechanisms in chalcogenides

57 Mn Mössbauer collaboration at ISOLDE/CERN 1. Paramagnetic relaxations in compound semiconductors (diluted magnetic semiconductors) Doping ZnO semiconductors with few percentages of 3d metals make the material magnetic at room temperature (Dietl et al., Science, 287 (2000) 1019) Potential multifunction material or ”Dilute Magnetic Semiconductor (DMS)” with applications in spintronics

57 Mn Mössbauer collaboration at ISOLDE/CERN 1. What can we do at ISOLDE We don’t have to worry about precipitation Can measure spin- lattice relaxation rates Can distinguish between paramagnetism and ferromagnetism

57 Mn Mössbauer collaboration at ISOLDE/CERN 1. Proposed project Determination of the paramagnetic properties of potential DMS and model systems (~10 samples: Mn shifts) Study paramagnetic relaxations with 57 Co (~ 2 samples) : 2 shifts Dynamic properies by making use of 119 In (~ 5 samples) : 4 shifts Understand the 119 In data with 119m Sn (2 samples): 1 shift

57 Mn Mössbauer collaboration at ISOLDE/CERN 2. Vacancy diffusion in group IV semiconductors (Si-SiGe) Understanding diffusion mechanismes in Silicon is of fundamental importance in defect tayloring Vacancy of the more important defects, both intrinsic and formed upon ion implantation However, some gaps in our understanding

57 Mn Mössbauer collaboration at ISOLDE/CERN 2. Vacancy diffusion in silicon

57 Mn Mössbauer collaboration at ISOLDE/CERN 2. What can we do at ISOLDE Make use of the lifetime of 57 Mn and 119 In to perform ”time-delayed” Mössbauer spectroscopy –Implant for short time –Measure time dependent spectra at different T’s –Repeat in different types of materials (Si-Ge, n, p) –7.5× 57 Mn shifts + 4× 119 In shifts + 1× 57 Co, 2× 119m Sn –Do similar studies with emission channeling

57 Mn Mössbauer collaboration at ISOLDE/CERN 2. Time-delayed Mössauer spectroscopy - results from test experiments -

57 Mn Mössbauer collaboration at ISOLDE/CERN 3. Doping of Si-nanoparticles Si nano-particles in SiO 2 matrices have applications in opto- electronics and memory devices. Interest in broadening the application range with tailoring doping Sb is a possible dopant

57 Mn Mössbauer collaboration at ISOLDE/CERN 3. Proposed project Implant with 119 Sb (38 h) and measure 119 Sn Mössbauer spectra -Lattice sites and annealing characteristics -Electronic configuration (Internal pressure and Debye-Waller factors) Need to implant into : Pure Si, Pure SiO 2, at least 3 types of Si Nano-particles (differing sizes). With 2 samples per shift, 2.5 shifts are needed.

57 Mn Mössbauer collaboration at ISOLDE/CERN 4. Investigation of phase change mechanisms in chalcogenides Ge-Sb-Te compounds Amorphous at room temperature Crystallize at 100ºC-150ºC with orders of magnitudes change in resistivity and reflectivity Used in memory applications Very little known about structures and crystallization mechanisms, and optimization through doping with Sn and working with off-stoichiometric compounds of interest. From Wang et al., (2004) For Ge 1.6 Sn 0.4 Sb 2 Te 5

57 Mn Mössbauer collaboration at ISOLDE/CERN 119m Sn (290 d) 4. Site selective doping of Ge-Sb-Te 119 Sb (38 h) 119 Te (4.7 d) 119 Sn -We can enter either Ge and/or Sb sites and monitor the changes in electronic configuration during crystallization -Implant 119 Sb and 119m Sn in at least 5 different types of Ge- Sb-Te compounds (2 samples/shift) : 2.5 shifts for each isotope

57 Mn Mössbauer collaboration at ISOLDE/CERN Project summary

57 Mn Mössbauer collaboration at ISOLDE/CERN Beam time request Ask now for roughly half of the needed shifts Based on previous experience, this will keep us occupied for 2-3 years Then revise the experimental plan, give a status report and propose a addendum to conclude the plan

57 Mn Mössbauer collaboration at ISOLDE/CERN Beam request

57 Mn Mössbauer collaboration at ISOLDE/CERN 2. Proposed project Measure time dependence in ~7 types of materials with 57 Mn (~7 hours/sample + temperature mapping and test experiments) : 7.5 shifts Measure same effects with 119 In with fewer samples: 4 shifts Prepeare two 57 Co samples for comparison (1 sample per shift) : 2 shifts Make 119m Sn samples : 1 shift