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P.P. Murmu NZIP 2011  Wellington, New Zealand Investigation of structural, electronic and magnetic properties of Gd implan...
ZnO applications
<ul><li>II-VI compound semiconductor </li></ul><ul><li>Direct band gap semiconductor,  E B  ~  3.37eV </li></ul><ul><li>Tr...
Dilute Magnetic Semiconductors (DMSs) <ul><li>Semiconductor doped with magnetic elements (e.g. GaAs:Mn, GaN:Mn, GaN:Gd, Ti...
ZnO- Rare earth (RE) doping <ul><li>Large magnetic moments e.g. 7.94 μ B  for Gd  </li></ul><ul><li>Very high magnetic mom...
GNS ion implanter – New Zealand unique facility Gd depth profiles calculated with DYNAMIC-TRIM for Gd implanted at 40 keV ...
Rutherford Backscattering spectrometry (RBS) E. Rutherford,  Philos. Mag.  6, vol. 21 (1911) p. 669-688 He ++ He ++ H. Gei...
Rutherford Backscattering spectrometry (RBS) <ul><li>Elastic interaction:  RBS, channeling, recoiling ions </li></ul><ul><...
Rutherford Backscattering spectrometry (RBS) <ul><li>RBS performed with 2 MeV He + </li></ul><ul><li>Rutherford Universal ...
RBS-Channeling Random and <0001>-aligned RBS spectra of 3.9x10 15  Gd cm -2  implanted and annealed ZnO (magnified Gd peak...
RBS-Channeling Angular scan around <0001> for 3.9x10 15  Gd cm -2  (a) as-implanted and (b) annealed ZnO  <ul><li>Angular ...
Raman Spectroscopy <ul><li>Raman effect:  inelastic scattering of light (provides information about vibrational modes in a...
SQUID results <ul><li>Diagmagnetic response observed in unimplanted and as-implanted ZnO </li></ul><ul><li>Annealing enhan...
SQUID results <ul><li>For  3.0x10 16  Gd cm -2  implanted and annealed  ZnO v ery small ferromagnetic ordering (even at 5 ...
XANES results <ul><li>O K-edge (~ 538 eV) observed due to electronic transition from O 2p states to conduction band </li><...
Conclusion <ul><li>RBS channeling along <0001> show ~60% Gd occupation in Zn sub-lattices  </li></ul><ul><li>A small fract...
<ul><li>Ministry of Science and Innovation </li></ul><ul><li>MacDiarmid scholarship </li></ul><ul><li>GNS Science scholars...
Thanks for your attention
RBS and channeling (a) Random (b) planar and (c) axial
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16.40 o5 p murmu

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Research 4: P Murmu

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16.40 o5 p murmu

  1. 1. P.P. Murmu NZIP 2011 Wellington, New Zealand Investigation of structural, electronic and magnetic properties of Gd implanted ZnO single crystals
  2. 2. ZnO applications
  3. 3. <ul><li>II-VI compound semiconductor </li></ul><ul><li>Direct band gap semiconductor, E B ~ 3.37eV </li></ul><ul><li>Transparent c onducting o xide </li></ul><ul><li>Has n-type conductivity, due to zinc-interstitials and oxygen vacancies </li></ul><ul><li>Availability of high quality bulk substrate (low defect densities) for homo-epitaxial film growth </li></ul><ul><li>Suitable host material for spintronic applications ? </li></ul><ul><li>ZnO based dilute magnetic semiconductors </li></ul>ZnO properties Spintronics cartoon courtesy to T. Jungwirth c a Oxygen Zinc
  4. 4. Dilute Magnetic Semiconductors (DMSs) <ul><li>Semiconductor doped with magnetic elements (e.g. GaAs:Mn, GaN:Mn, GaN:Gd, TiO 2 :Co) </li></ul><ul><li>Applications: Magnetic RAM, </li></ul><ul><li>Spin FET, Spin LED etc. </li></ul><ul><li>Room temperature ferromagnetism </li></ul><ul><li>Origin: Metallic clusters / secondary phases ?? </li></ul><ul><li>Highly sensitive to defects </li></ul>Magnetic ions Cation Anion H. Toyosaki et al. Nat. Mater. 3, 221 (2004) Datta and Das, APL 56, 665 (1990)
  5. 5. ZnO- Rare earth (RE) doping <ul><li>Large magnetic moments e.g. 7.94 μ B for Gd </li></ul><ul><li>Very high magnetic moment (4000 μ B / Gd) in GaN:Gd * </li></ul><ul><li>Aim : to investigate the electronic and magnetic properties of ZnO:Gd prepared by ion implantation </li></ul><ul><li>* Dhar et al. PRL 94, 037205 (2005) </li></ul>Calculated and measured effective Bohr magneton for rare-earth ions
  6. 6. GNS ion implanter – New Zealand unique facility Gd depth profiles calculated with DYNAMIC-TRIM for Gd implanted at 40 keV into ZnO in the fluence range from 6.7x10 14 to 3.0x10 16 ions.cm -2 Implantation parameters: Energy: up to 100 keV Ions: 12 C + , 13 C + , 14 N + , 15 N + , & Vacuum: < 2x10 -7 mbar
  7. 7. Rutherford Backscattering spectrometry (RBS) E. Rutherford, Philos. Mag. 6, vol. 21 (1911) p. 669-688 He ++ He ++ H. Geiger (left) and E. Rutherford (right) Au-foil &quot; The making of the Rutherford documentary &quot; by Dr John Campbell , 10.45 am Wed 19 th Oct
  8. 8. Rutherford Backscattering spectrometry (RBS) <ul><li>Elastic interaction: RBS, channeling, recoiling ions </li></ul><ul><li>Inelastic interaction: X-rays, visible-UV photons, Nuclear reaction </li></ul><ul><li>RBS: kinematic factor, K α mass </li></ul><ul><ul><ul><li>cross section, σ α yield </li></ul></ul></ul><ul><ul><ul><li>energy loss, Δ E α depth </li></ul></ul></ul><ul><li>RBS and channeling: drastic reduction </li></ul><ul><ul><ul><li>in backscattered particles </li></ul></ul></ul>Schematic illustration of RBS mechanism High energy light ion interaction with target atoms
  9. 9. Rutherford Backscattering spectrometry (RBS) <ul><li>RBS performed with 2 MeV He + </li></ul><ul><li>Rutherford Universal Manipulation Program (RUMP) used to retrieve the composition, depth profile etc. </li></ul><ul><li>For the 1x10 16 Gd cm -2 and higher fluence implantation, preferential sputtering occurs </li></ul><ul><li>Leads to a slightly lower retained dose for the implantation at higher fluences </li></ul>Zn Gd O surface 3 MeV Particle Accelerator at GNS Science, Lower Hutt RBS spectrum and RUMP fitting Fluence vs. retained dose
  10. 10. RBS-Channeling Random and <0001>-aligned RBS spectra of 3.9x10 15 Gd cm -2 implanted and annealed ZnO (magnified Gd peaks in inset) <ul><li>RBS/C along <0001> </li></ul><ul><li>Zn minimum yield ( Zn X min ) of ~7% indicates the high crystalline quality of un-doped ZnO </li></ul><ul><li>For 3.9x10 15 Gd.cm -2 , Zn X min in as implanted ZnO is ~ 27%, which suggests the implantation causes only moderate structural damages </li></ul><ul><li>Vacuum annealing at 650 o C, the X min for Zn goes down to ~ 22%, which implies the annealing helps to regain the crystalline quality </li></ul>
  11. 11. RBS-Channeling Angular scan around <0001> for 3.9x10 15 Gd cm -2 (a) as-implanted and (b) annealed ZnO <ul><li>Angular scans around <0001> </li></ul><ul><li>Zn and Gd scans followed same trend, suggests both subjected to similar disorders </li></ul><ul><li>Split between the scans implies some of Gd atoms at random sites </li></ul><ul><li>Using, Gd Zn = (1- Gd X min ) / (1- Zn X min ), around 60% Gd atoms estimated to occupy the substitutional lattice sites </li></ul><ul><li>A small fraction of interstitial Gd atoms align with <0001> (a shadow-effect) </li></ul><ul><li>Gd Zn reduces to 47 % up on annealing, possibly due to the diffusion of Gd atoms </li></ul>
  12. 12. Raman Spectroscopy <ul><li>Raman effect: inelastic scattering of light (provides information about vibrational modes in a material) </li></ul><ul><li>Discovered by C.V. Raman in 1928 </li></ul><ul><li>E 2 (high) and E 2 (low) modes from O and Zn vibrations </li></ul><ul><li>575 cm -1 attributed to the A 1 (LO) mode of ZnO </li></ul><ul><li>A 1 (LO) mode primarily observed due to implantation induced disorder </li></ul><ul><li>also correlated to the structural defects such as oxygen vacancies (V o ) and zinc interstitials (Zn i ) or their complexes </li></ul>C.V. Raman demonstrating his Nobel Prize (1930) winning spectrometer Raman spectra of unimplanted, 3.9x10 15 Gd cm -2 implanted and annealed ZnO
  13. 13. SQUID results <ul><li>Diagmagnetic response observed in unimplanted and as-implanted ZnO </li></ul><ul><li>Annealing enhanced the ferromagnetism in low fluence Gd implanted and annealed ZnO </li></ul><ul><li>Ferromagnetism at room temperature !! </li></ul><ul><li>FC curve shows combination of ferromagnetic and paramagnetic ordering </li></ul><ul><li>Clustering or secondary phases ?? </li></ul><ul><li>Zero field-cooled (ZFC) magnetisation curve suggests contribution from super-paramagnetic particles </li></ul>Hysteresis loop of 3.9x10 15 Gd cm -2 implanted and annealed ZnO at 5 K & 300 K FC and ZFC magnetisation curves of 3.9x10 15 Gd cm -2 implanted and annealed ZnO at 100 Oe
  14. 14. SQUID results <ul><li>For 3.0x10 16 Gd cm -2 implanted and annealed ZnO v ery small ferromagnetic ordering (even at 5 K) </li></ul><ul><li>Ferromagnetism decreases at higher fluences </li></ul><ul><li>Ferromagnetic interaction depends on the ions separation, and can have ferromagnetic or antiferromagnetic coupling </li></ul><ul><li>Antiferromagnetic interaction among Gd atoms at high concentration may be responsible </li></ul>(b) FC and ZFC magnetisation curves of 3.0x10 16 Gd cm -2 implanted and annealed ZnO (a) Hysteresis loops of 3.9x10 15 & 3.0x10 16 Gd cm -2 implanted and annealed ZnO at 5K
  15. 15. XANES results <ul><li>O K-edge (~ 538 eV) observed due to electronic transition from O 2p states to conduction band </li></ul><ul><li>A pre-edge feature appears in ZnO thin film </li></ul><ul><li>Usually assigned to intrinsic defects such as oxygen vacancies and zinc interstitials </li></ul><ul><li>Gd atoms in 3+ state </li></ul>(a) O K-edge for as-deposited ZnO film, un-implanted and Gd-implanted ZnO single crystals (b) Gd M-edge for Gd-metal and Gd-implanted ZnO single crystals
  16. 16. Conclusion <ul><li>RBS channeling along <0001> show ~60% Gd occupation in Zn sub-lattices </li></ul><ul><li>A small fraction of the ions may be at interstitialy shadowed region aligned with <0001> </li></ul><ul><li>Radiation damages related A 1 (LO) peak observed in Gd implanted ZnO </li></ul><ul><li>Ferromagnetic ordering at room temperature </li></ul><ul><li>Moment decreases at higher temperatures </li></ul><ul><li>FC/ZFC curves suggest presence of small clusters </li></ul><ul><li>O K-edge shows intrinsic defect related pre-edge feature </li></ul><ul><li>Gd valency: 3+ </li></ul>
  17. 17. <ul><li>Ministry of Science and Innovation </li></ul><ul><li>MacDiarmid scholarship </li></ul><ul><li>GNS Science scholarship </li></ul><ul><li>Australian synchrotron </li></ul>Acknowledgement Funding Supervisors <ul><li>Dr A. Markwitz (GNS, New Zealand) </li></ul><ul><li>Dr G.V.M. Williams (VUW, New Zealand) </li></ul><ul><li>Dr S. Grenville (IRL, New Zealand) </li></ul><ul><li>Dr S. Rubanov (University of Melbourne, Australia) </li></ul><ul><li>Dr A. Suvorova (UWA, Australia) </li></ul>Collaborators <ul><li>Dr B.J. Ruck (VUW, New Zealand) </li></ul><ul><li>Dr J. Kennedy (GNS, New Zealand) </li></ul>
  18. 18. Thanks for your attention
  19. 19. RBS and channeling (a) Random (b) planar and (c) axial

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