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Our activities on ABO 3 oxides Some information about DFAV

University of Pavia. Dipartimento di Fisica “A. Volta” DFAV. Our activities on ABO 3 oxides Some information about DFAV Brief summary on the activities of other groups or DFAV. University of Pavia Dipartimento di Fisica “A. Volta”.

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Our activities on ABO 3 oxides Some information about DFAV

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  1. University of Pavia Dipartimento di Fisica “A. Volta” DFAV • Our activities on ABO3 oxides • Some information about DFAV • Brief summary on the activities of other groups or DFAV

  2. University of Pavia Dipartimento di Fisica “A. Volta” Kiev 2005, February 2nd – P. Galinetto DFAV University of Pavia Survey on activities on ABO3 oxides Staff and experimental facilities Materials and Collaborations Basic physical problems of interest Examples • KTO/KLTN/BCT • Charge transport and trapping in KTO • Doping in KTO LiNbO3 Characterization of LN substrates Characterization of structural and photoinduced defects Microstructures in LN by means of fs laser pulses

  3. Kiev 2005, February 2nd – P. Galinetto DFAV University of Pavia Staff members: Giorgio Samoggia Full Professor Carlo Bruno Azzoni Associate Professor H. of D. Pietro Galinetto Researcher Enrico Giulotto Researcher Daniela Grando * Researcher Maria Cristina Mozzati Contract Researcher Francesco Rossella Ph.D. Student Dorino Maghini Technician Massimo Marinone Graduate Student Virginia Stasi Graduate Student Massimiliano Rossi Graduate Student (USA LBL) *Electronics Department e-mail : lastname@fisicavolta.unipv.it

  4. Kiev 2005, February 2nd – P. Galinetto DFAV University of Pavia Experimental facilities • Raman and micro-Raman spectroscopy • Optical absorption, PL, TL, PC, TSC • Hall, Photo-Hall and magneto-optical spectroscopy • EPR spectroscopy and Photo-EPR • Static magnetization measurements • Electro-optical characterization • Femto-second laser sources • Dielectric permittivity spectroscopy

  5. Kiev 2005, February 2nd – P. Galinetto DFAV University of Pavia Materials Fe Cr Mg Cu Hf V … LiNbO3 LiTaO3 K1-xLixTa1-yNbyO3 Ba0.77Ca0.23TiO3 LiNbO3/LiTaO3 BaTiO3 SrTiO3 KNbO3 KTaO3 Single crystals thin films Nano-particles diluted in silica glass Nanosized grains ceramics

  6. Kiev 2005, February 2nd – P. Galinetto DFAV University of Pavia Collaborations UniCatt. Physics Dept- Brescia INOA Firenze C.n.r. IMM Bologna Dip. Fisica - Padova C.n.r. Ist. di Cibernetica Napoli Saes Getter S.p.a. Avanex 2 Co. Materials physics department – UA Madrid - E Dept of Mat. Science, Ukrainian Acad.of Sciences, Kiev, Uk Institute of Physics, AS CR, Prague RC Fachbereich Physik, University of Osnabrueck - DE A.F. Ioffe Physical & Technical Institute – S.Petersburg – RU

  7. Kiev 2005, February 2nd – P. Galinetto DFAV University of Pavia Main Basic Physical Phenomena • Phase transitions (PT) in pure and mixed oxides based on ABO3 (KTO, STO, BTO, etc) compounds • Structural, electronic and optical properties of intrinsic and impurities defects in ABO3 related materials • Study of the transport phenomena and charge localization due to optical irradiation in ABO3 compounds

  8. Doped KTO, KLT, KLTN PT temperature ranging from LT to RT and more complex interplay between Li-dipoles and Nb-dipoles character of soft-mode and relaxation order-disorder PT, magnitude of dielectric susceptibility, and very interesting new matrix and impurity mode coupling effects,new PT and related phenomena. Kiev 2005, February 2nd – P. Galinetto DFAV University of Pavia Phase transitions in mixed oxides….. Study of self-ordering and of new phase transitions in soft matrices containing interacting degrees of freedom of impurities and Jahn-Teller polarons Prof. Blinc, Opening talk EMF Cambridge 2003

  9. Kiev 2005, February 2nd – P. Galinetto DFAV University of Pavia Investigations of PT in KLTN combining Raman and dielectric spectroscopy KLTN 0.14/1.2 KLTN 0.4/3.1 KLTN 0.6/17.3 + Cu, V

  10. Congruently grown barium calcium titanate,Ba0.77Ca0.23TiO3(BCT77/23) can be fabricated as high optical qualitysingle crystals, possess large electro-optic coefficients. Another great advantage of BCT is that the tetragonal-ortorhombic phase transition, which is destructive in BaTiO3, is depressed in BCT 77/23holographic sensitivity making it excellent candidate for various photorefraction based applications Isovalent substitution Ba2+ Ca2+ Ca has smaller ionic radius (Ba= 1.35Å vs Ca= 0.99Å) Influence on Curie temperature Source of structural disorder Kiev 2005, February 2nd – P. Galinetto DFAV University of Pavia

  11. Lowering the temperature... FWHM, integrated intensity and energy for the mode at 300 cm-1 The E-mode softens FWHM, integrated intensity and energy for the mode at 40 cm-1 The A-mode hardens

  12. PHOTO-INDUCED EFFECTS ON PT IN KTO, STO • ?Nano-materials?: effect of nanometric scaling on the occurrence and the nature of phase transition in BTO, KTO and STO

  13. TL + EPR + photo-EPR TSC Kiev 2005, February 2nd – P. Galinetto DFAV University of Pavia Photo-induced transport phenomena and charge localization of ABO3 compounds (PC + PL) vs T

  14. Kiev 2005, February 2nd – P. Galinetto DFAV University of Pavia ……impurities defects in ABO3 Cu centres in KTO EPR+PhotoEPR +Abs • Characterization of Cu centres in KTO • Other dopants like Be, Co, Ni • Absorption due to polarons in KTO:Be • LT Absorption, EPR, PhotoEPR, Phototransport, PL, TL, TSC

  15. 1 2 3 Kiev 2005, February 2nd – P. Galinetto DFAV University of Pavia Keypoints of activities on LiNbO3 Characterization of structural, optical and electronic properties of LiNbO3 crystals and substrates in connection with different growth processes and different doping Crystalline quality Study of the transport phenomena and charge localization due to optical irradiation of LiNbO3(or other ABO3 compounds, eventually doped) and of the irradiation effects on the linear and nonlinear optical properties Study of the feasibility of 1D, 2D and 3D periodical structures, waveguides and microstructures on LiNbO3 (or other ferroelectric oxides) crystalline substrates by means of femtosecond laser irradiation in the transparent spectral region

  16. Kiev 2005, February 2nd – P. Galinetto DFAV University of Pavia How we study crystalline quality? • Raman and micro-Raman spectroscopy • Optical absorption, PL, TL, PC, TSC • Hall, Photo-Hall and magneto-optical spectroscopy • Ellipsometry • Electron Paramagnetic Resonance (EPR)and Photo-EPR • Static magnetization measurements • Electro-optical characterization • Femto-second laser sources *

  17. strong increase of the spectrum resolution due to line narrowing • changes of some LN properties • appearance of new impurity centers EPR Raman Kiev 2005, February 2nd – P. Galinetto DFAV University of Pavia Due to the Li-deficiency the conventional congruent crystals have high concentration of intrinsic (non-stoichiometric) defects, which can easily compensate a high concentration of extrinsic defects (for instance, optically or acoustically active impurities) coupling and mutual influence of intrinsic and extrinsic defects decrease of the intrinsic defect concentration Possibility to vary both the [Li]/[Nb] ratio and [O] contents (in addition to the modification by dopants!) is a very powerful tool for the optimisation of crystal parameters Lattice of ideal, defect-free LN crystal

  18. Kiev 2005, February 2nd – P. Galinetto DFAV University of Pavia • EPR spectroscopy : • Control of the material quality: • check of purity of growth processes • detection of defects and/or unwanted EPR active magnetic impurities • information about structural disorder • Evaluation of the oxidation state of the transition ions • Information about site symmetry from the EPR signal angular dependence Fe3+ EPR lines (BIc) in CLN (LN:Fe 0.1%) …in quasi-st LN (LN:Fe 0.1%)

  19. In crystals, Raman spectrum depends on the direction and polarization state of the incident and scattered light with respect to the cristallographic axes Kiev 2005, February 2nd – P. Galinetto DFAV University of Pavia Raman in LiNbO3 • Porto notation: ki(ei,ed)kd The crystal structure of pure LiNbO3 has Rc3 space group symmetry and 4A1+ 9E Raman-active modes are predicted by factor-group analysis

  20. Kiev 2005, February 2nd – P. Galinetto DFAV University of Pavia RS is strongly sensitive to orientation Elight| c Elight // c m-Raman to check disorientation, multidomains…

  21. Kiev 2005, February 2nd – P. Galinetto DFAV University of Pavia RS is sensitive to the deformation of the lattice and to the presence of point defects, becoming a powerful tool to deal with the problem of stoichiometry The mode at 880 cm-1 is the vibration, parallel to the c axis, of the oxygen ions which consists basically in the stretching of the Nb–O and Li–O bonds. When a Nb ion sits at a Li site its oxygen first neighbors increase their bonding forces respective to the perfect crystal situation because of the stronger electrostatic interaction.

  22. The fact that the linewidth of some Raman modes scale with the composition xc = [Li]/([Li] + [Nb])of LN crystals, together with the use of a confocal microscope ( mRaman), allows a 3D determination of the sample stoichiometry. Kiev 2005, February 2nd – P. Galinetto DFAV University of Pavia Can be used to check the stoichiometry (Li/Nb ratio) monitoring the changes of linewidth of some Raman modes. FWHM changes are greater than peak shift.

  23. Scan at 10 microns depth in a 10 mm long plate Depth profile Li/Nb changes ˜ 0.08 % good homogeneity of Li/Nb ratio(changes less than 0.3 cm-1)

  24. mRaman for surface quality analysis after wafering process: • Non-destructive structural tool • Micron-scale spatial resolution • Presence of a structurally disordered layer • Effectiveness of damage removal method • Control on optical surface finishing Kiev 2005, February 2nd – P. Galinetto DFAV University of Pavia

  25. Important complete characterization of: stoichiometry, nature and content of impurities, degree of structural disorder before starting with investigation of charge trapping mechanisms and phenomena related to photo-induced defects 2 Kiev 2005, February 2nd – P. Galinetto DFAV University of Pavia • Photovoltaic current, photoconductivity, • Photo-EPR • vs %, doping, l, T Study of the transport phenomena and charge localization due to optical irradiation of LiNbO3(or other ABO3 compounds, eventually doped) and of the irradiation effects on the linear and nonlinear optical properties

  26. complementary techniques (Raman microscopy, Electron Paramagnetic Resonance, optical absorption, photo-voltaic current and photo-conductivity measurements) were used to detect intrinsic and extrinsic defects, charge trapping and recombination processes, and the related photo-refractive behaviour in lithium niobate single crystals, with congruent and stoichiometric composition, containing Fe and Mg dopant. The role of UV and visible irradiation was investigated. Comprehension and control of the photocarrier localization mechanisms in connection with preparation methods and treatment of the materials.

  27. Characterization of structural and photoinduced defects in pure and doped lithium niobate Experimental RT The properties of LN crystals are not simply ruled by the stoichiometry (Li/Nb ratio) and by intentional or accidental impurities: interrelations of intrinsic and extrinsic defects ever exist, leading todifferent phenomena in samples with apparent similar composition. In this frame it is important to perform experiments in crystals well characterized in terms of stoichiometry, impurity content and degree of structural disorder. Raman scattering, optical absorption, EPR l Photovoltaic and Photocurrent l Charge transport and trapping phenomena VIS-UV Foto-EPR l UV

  28. Raman spectroscopy

  29. Shift in the ”optical edge” Absorption Band at ~ 2.6 eV,  Fe2+ Absorption Band at ~ 1.5 eV polarons antisites NbLi Optical absorption Mg doping: decrease in the polaron induced abs band

  30. EPR B  c-axis Fe3+: presente in tracce anche nei campioni nominalmente puri, non rilevato solo in CMg. Sfe: componenti a 380 G e 1440 G, più intense, con la minore larghezza di riga (ΔB) e forma quasi simmetrica, in accordo con stechiometria nominale Cfe: righe più larghe e asimmetriche. BCFe è circa 3 volte BSFe (valori in accordo coi risultati di ΔB vs. xc di letteratura). Appl. Phys. A 56, 103-108 (1993) SFe e CFe hanno stechiometria in accordo con quella nominale, paragonabile quantità di Fe3+ e, in particolare SFe, buona qualità del cristallo CMF: transizione –½  +½, indipendente dalla simmetria puntuale, è la più intensa  alto grado di disordine nei siti reticolari di Fe, indotto dal drogaggio di Mg, porta allo “spread” e quindi all’allargamento e alla scomparsa delle componenti a bassi campi di risonanza.

  31. Photovoltaic current and Photoconductivity VISIBLE UV

  32. Campo applicato: 60kV/m. Contatti normali all’asse ottico (asse c). JPHV (10-6A/m2) JPHC (10-6A/m2) JDARK (10-6A/m2) -CFe - 514 nm H 3.02 L 0.054 0.036 CFe - UV 0.79 0.031 0.04 -SFe – 514 nm 3.6 0.02 0.16 SFe - UV 3.4 1.55 0.58 -CFM – 514 nm 0.044 0.13 2.37 CFM - UV 0.17 0.1 2.725 Jphv is proportional to the number of Fe2+, while Jphc is proportional to the [Fe2+]/[Fe3+] ratio This one-center model was refined, adding to the scheme the intrinsic defects NbLi, which can take part in the charge transport as shallow electron traps, lowering the n-type Jphc

  33. “MICROSTRUCTURAL MODIFICATION OF LINBO3 CRYSTALS INDUCED BY FEMTOSECOND LASER IRRADIATION” Appl. Surf. Science in press 3 Kiev 2005, February 2nd – P. Galinetto DFAV University of Pavia Study of the feasibility of 1D, 2D and 3D periodical structures, waveguides and microstructures on LiNbO3 (or other ferroelectric oxides) crystalline substrates by means of femtosecond laser irradiation in the transparent spectral region

  34. Advantage of the method: irradiation in the transparence region  higher penetration length very high peak intensity  multiphoton absorption  cascade ionization the energy transfer is confined in the focal volume Possible effects: • Refraction index changes due to photorefractive/stresses/structural changes • Ablation – optical breakdown Kiev 2005, February 2nd – P. Galinetto DFAV University of Pavia Femto-writing e femto-sculpture

  35. Gratings written by means of ultrashort pulses (100fs) with interferential method in glasses Applied Surface Science 197 (2002) 688, M. Hirano et al. Wave-guide laser writing in transverse and longitudinal geometry

  36. Ti:Sapphire oscillator 25 nJ-130 fs-82 MHz Ti:Sapphire amplifier 1 mJ-130 fs-1 kHz At the LaserLab of Electronics Dept in situ monitoring Kiev 2005, February 2nd – P. Galinetto DFAV University of Pavia Experimental Set-up = 810 nm mirror /2 sheet isolatore shutter /2 sheet Dichroic mirror Monitoring channel objective Commercial z-cut congruent LN substrates. Sample on motor controlled xyz stage filters CCD camera polarizer mirror

  37. Formation of large ablated regions (>10 mm) triggered by the presence of crystal defects, surface scratches or accumulation centers. At the focus region either refractive index changes or material removal were observed at variance of irradiation conditions. Ti:Sapphire oscillator, LE + HRR The main effect of the irradiation in this regime was the formation of refractive index microstructures, visible at the polarizing microscope.

  38. Raman shift (cm-1) Oscillator ablation Amplifier ablation

  39. Kiev 2005, February 2nd – P. Galinetto DFAV University of Pavia AFM

  40. Kiev 2005, February 2nd – P. Galinetto DFAV University of Pavia 3μm-step grating Efficiency: 10% - 1st order (red light) 10μm Grating diffraction spots

  41. Experimental set-upconventional Labram Dilor JYHoriba (mod. 010) 60 cm • laser source (He-Ne): 20 mW , λ = 632.8 nm • Integrated Optical microscope Olimpus Spot diameter 10 µm÷ 1 µm depending on the objectives (10X, 50X, 100X), autofocus by means of piezoelectric driver • Back-scattering geometry • Spectrometer focal length = 300 mm, 2 holographic gratings (1800 gg/mm or 600 gg/mm). Resolution 0.2 cm-1 • Holographic notch filter • CCD 256 X 1024 pixels (pixel = 27 µn, 16 bit dinamical range), Peltier cooled system

  42. EPR spectrometer Kiev 2005, February 2nd – P. Galinetto DFAV University of Pavia

  43. Apparato di misura: MAGNETOMETRO SQUID Cosa misura: momento magnetico“m” di un campione, da cui si determinano suscettività magnetica e magnetizzazione Unità di misura: emu (erg/G) Range di misura di “m”: 10-8 2 emu (condizioni standard) Errore di misura: in genere < 2% Come misura: Sonda bobina superconduttrice connessa a uno SQUID che rileva la variazione del flusso magnetico provocata dal movimento del campione attraverso la bobina stessa (tecnica a estrazione).

  44. Kiev 2005, February 2nd – P. Galinetto DFAV University of Pavia other research activities Colossal Magnetoresistive Material (La1-xAxMnO3 A = Ca, Na) CaCu3Ti4O12 (CCTO): high-k material Li3VO4:Cr,Mg  ionic transport, SHG Ultrafast spin dynamics in ferromagnetic thin films  transient MOKE

  45. Kiev 2005, February 2nd – P. Galinetto DFAV University of Pavia Dipartimento di Fisica “A. Volta” 12 full professors 18 associate professors 10 researchers 15 technicians 30 post graduate, PhD and fellowship students

  46. Kiev 2005, February 2nd – P. Galinetto DFAV University of Pavia Sources of budget (~)

  47. Kiev 2005, February 2nd – P. Galinetto DFAV University of Pavia Research activities of other groups • Physics education and physics history • Quantum information theory • Optical spectroscopy & laser-matter interaction in semiconductors • Magnetism and superconductivity

  48. Kiev 2005, February 2nd – P. Galinetto DFAV University of Pavia PHYSICS EDUCATION and PHYSICS HISTORY Group Staff: G. Bonera, L. Borghi, A. De Ambrosis, L. Falomo, L. Mascheretti, M.C. Garbarino, L. Cardinali *Identification of tools and strategies to support the Physics teaching/learning process *Historical comprehension of the developments of different physical branches, taking into account not only the technical aspects but also the global cultural and social context. • QUANTUM INFORMATION THEORY GROUP • Staff: GM D’Ariano, C. Macchiavello, M. Sacchi, P. Lo Presti, R. Buscemi, E. Chiribella, P. Perinotti • Quantum Measuring Devices for Photonics and Quantum Information • Entanglement Assisted High Precision Measurements • Quantum Teleportation and Quantum Cloning by the optical parametric squeezing process • Quantum Properties of Distributed Systems

  49. Kiev 2005, February 2nd – P. Galinetto DFAV University of Pavia MAGNETISM AND SUPERCONDUCTIVITY Dipartimento di Fisica “A. Volta”, Universita’ di Pavia and INFM, Via Bassi 6 , I-27100 Pavia (Italy) Techniques : Nuclear Magnetic Resonance (NMR, mainly in Solids) Muon Spin Rotation (MUSR) Susceptibility and magnetization (SQUID) Specific heat Magnetic Resonance Imaging (collaborations) Team : Prof. A. Rigamonti, Prof. F. Borsa, Prof. P. Carretta, Prof. M. Corti, Dr. A. Lascialfari, p.i. S. Aldrovandi Post-doc : J. Lago PhD and graduate students : I. Zucca, L. Spanu, E. Micotti, N. Papinutto, M. Filibian, M. Mariani

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