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Our activities on ABO 3 oxides Our activities on ABO 3 oxides Some information about DFAV Some information about DFAV Brief summary on the activities of.

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Presentation on theme: "Our activities on ABO 3 oxides Our activities on ABO 3 oxides Some information about DFAV Some information about DFAV Brief summary on the activities of."— Presentation transcript:

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

2 Survey on activities on ABO 3 oxides University of Pavia Dipartimento di Fisica “A. Volta” LiNbO 3  Characterization of LN substrates Characterization of structural and photoinduced defects Microstructures in LN by means of fs laser pulses Staff and experimental facilities Materials and Collaborations Basic physical problems of interest KTO/KLTN/BCT Charge transport and trapping in KTO Doping in KTO Examples Kiev 2005, February 2 nd – P. Galinetto DFAV University of Pavia

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

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

5 Materials LiNbO 3 K 1-x Li x Ta 1-y Nb y O 3 Ba 0.77 Ca 0.23 TiO 3 LiNbO 3 /LiTaO 3 KTaO 3 BaTiO 3 KNbO 3 SrTiO 3 LiTaO 3 Fe Cr Mg Cu Hf V … Single crystals thin films Nano-particles diluted in silica glass Nanosized grains ceramics Kiev 2005, February 2 nd – P. Galinetto DFAV University of Pavia

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

7 Main Basic Physical Phenomena Phase transitions (PT) in pure and mixed oxides based on ABO 3 (KTO, STO, BTO, etc) compounds Structural, electronic and optical properties of intrinsic and impurities defects in ABO 3 related materials Study of the transport phenomena and charge localization due to optical irradiation in ABO 3 compounds Kiev 2005, February 2 nd – P. Galinetto DFAV University of Pavia

8 Study of self-ordering and of new phase transitions in soft matrices containing interacting degrees of freedom of impurities and Jahn-Teller polarons 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. Phase transitions in mixed oxides….. Prof. Blinc, Opening talk EMF Cambridge 2003 Kiev 2005, February 2 nd – P. Galinetto DFAV University of Pavia

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

10 Isovalent substitution Ba 2+  Ca 2+ Ca has smaller ionic radius (Ba= 1.35Å vs Ca= 0.99Å) Influence on Curie temperature Source of structural disorder Congruently grown barium calcium titanate, Ba 0.77 Ca 0.23 TiO 3 (BCT77/23) can be fabricated as high optical quality single 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 77/23 holographic sensitivity making it excellent candidate for various photorefraction based applications Kiev 2005, February 2 nd – P. Galinetto DFAV University of Pavia

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

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 Photo-induced transport phenomena and charge localization of ABO 3 compounds (PC + PL) vs T TL TSC + EPR + photo-EPR Kiev 2005, February 2 nd – P. Galinetto DFAV University of Pavia

14 Cu centres in KTO ……impurities defects in ABO 3 Kiev 2005, February 2 nd – P. Galinetto DFAV University of Pavia  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 EPR+PhotoEPR +Abs

15 Characterization of structural, optical and electronic properties of LiNbO 3 crystals and substrates in connection with different growth processes and different doping Study of the transport phenomena and charge localization due to optical irradiation of LiNbO 3 (or other ABO 3 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 LiNbO 3 (or other ferroelectric oxides) crystalline substrates by means of femtosecond laser irradiation in the transparent spectral region Keypoints of activities on LiNbO 3 Crystalline quality 123 Kiev 2005, February 2 nd – P. Galinetto DFAV University of Pavia

16 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 * Kiev 2005, February 2 nd – P. Galinetto DFAV University of Pavia

17 Lattice of ideal, defect-free LN crystal coupling and mutual influence of intrinsic and extrinsic defects decrease of the intrinsic defect concentration 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) 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 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 2 nd – P. Galinetto DFAV University of Pavia

18 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%) Kiev 2005, February 2 nd – P. Galinetto DFAV University of Pavia

19 Raman in LiNbO 3 In crystals, Raman spectrum depends on the direction and polarization state of the incident and scattered light with respect to the cristallographic axes  Porto notation: k i (e i,e d )k d The crystal structure of pure LiNbO 3 has Rc3 space group symmetry and 4A 1 + 9E Raman-active modes are predicted by factor-group analysis Kiev 2005, February 2 nd – P. Galinetto DFAV University of Pavia

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

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

22 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. 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 (   Raman), allows a 3D determination of the sample stoichiometry. Kiev 2005, February 2 nd – P. Galinetto DFAV University of Pavia

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  Non-destructive structural tool  Micron-scale spatial resolution  Presence of a structurally disordered layer  Effectiveness of damage removal method  Control on optical surface finishing  Raman for surface quality analysis after wafering process: Kiev 2005, February 2 nd – 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 Study of the transport phenomena and charge localization due to optical irradiation of LiNbO 3 (or other ABO 3 compounds, eventually doped) and of the irradiation effects on the linear and nonlinear optical properties 2 Photovoltaic current, photoconductivity, Photo-EPR vs %, doping,  T Kiev 2005, February 2 nd – P. Galinetto DFAV University of Pavia

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 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 to different 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. Experimental VIS-UV UV Charge transport and trapping phenomena Photovoltaic and Photocurrent Raman scattering, optical absorption, EPR Foto-EPR

28 Raman spectroscopy

29 Optical absorption Shift in the ”optical edge” Absorption Band at ~ 2.6 eV,  Fe 2+ Mg doping: decrease in the polaron induced abs band antisites Nb Li Absorption Band at ~ 1.5 eV  polarons

30 EPR B  c-axis 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 SFe e CFe hanno stechiometria in accordo con quella nominale, paragonabile quantità di Fe 3+ 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. Appl. Phys. A 56, 103-108 (1993) Fe 3+ : presente in tracce anche nei campioni nominalmente puri, non rilevato solo in CMg. Cfe: righe più larghe e asimmetriche.  B CFe è circa 3 volte  B SFe (valori in accordo coi risultati di ΔB vs. x c di letteratura).

31 Photovoltaic current and Photoconductivity VISIBLE UV

32 2.7250.10.17CFM - UV 2.370.130.044-CFM – 514 nm 0.581.553.4SFe - UV 0.160.023.6-SFe – 514 nm 0.040.0310.79CFe - UV 0.036L 0.054H 3.02-CFe - 514 nm J DARK (10 -6 A/m 2 )J PHC (10 -6 A/m 2 )J PHV (10 -6 A/m 2 ) J phv is proportional to the number of Fe 2+, while J phc is proportional to the [Fe 2+ ]/[Fe 3+ ] ratio This one-center model was refined, adding to the scheme the intrinsic defects Nb Li, which can take part in the charge transport as shallow electron traps, lowering the n-type J phc Campo applicato: 60kV/m. Contatti normali all’asse ottico (asse c).

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

34 Femto-writing e femto-sculpture Advantage of the method: i 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 2 nd – P. Galinetto DFAV University of Pavia

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

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

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

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

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

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42  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 Experimental set-up conventional Labram Dilor JYHoriba (mod. 010) 60 cm

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

44 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).

45 other research activities Colossal Magnetoresistive Material (La 1-x A x MnO 3  A = Ca, Na) CaCu 3 Ti 4 O 12 (CCTO): high-k material Li 3 VO 4 :Cr,Mg  ionic transport, SHG Ultrafast spin dynamics in ferromagnetic thin films  transient MOKE Kiev 2005, February 2 nd – P. Galinetto DFAV University of Pavia

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

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

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

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

50 MAGNETISM AND SUPERCONDUCTIVITY 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 Kiev 2005, February 2 nd – P. Galinetto DFAV University of Pavia

51 Motions and structure of flux lines lattice in superconductors Diamagnetic fluctuations above T C in BCS superconductors (MgB 2 ) Quantum Phase transitions (Quantum Critical Point) CeCu 6-x Au x Low-dimensional quantum antiferromagnets (S=1/2) La 2 CuO 4 SrCu 2 O 3 Sr 2 CuO 3 Cu 8

52 Negligible intermolecular interactions  molecular nanomagnets Molecular nanomagnets Fe 8 crystal Easy-axis (magnetization) Fe (3+) s=5/2 ground state S=10 (giant spin) Quantum tunneling of the magnetization (QTM)

53 Optical Spectroscopy & Laser-Matter Interaction Optical Spectroscopy Laboratory M. Galli, D. Bajoni, M. Patrini, M. Belotti, G. Guizzetti, F. Marabelli Nonlinear Optics Laboratory A.M. Malvezzi, M. Patrini, G. Vecchi, C. Comaschi Electronic and photonic nanostructures: theory D. Gerace, M. Liscidini, M. Agio, A. Balestrieri, L.C. Andreani Kiev 2005, February 2 nd – P. Galinetto DFAV University of Pavia

54 Optical Techniques Linear: angle-resolved reflectance & transmittance spectroscopic ellipsometry modulation spectroscopies (photo-, electro- and thermo- reflectance). Nonlinear : Raman scattering luminescence and second-harmonic generation time-resolved spectroscopy Kiev 2005, February 2 nd – P. Galinetto DFAV University of Pavia

55 Optical Spectroscopy Laboratory Facilities FFT-IR spectrometer, 20-5000 cm -1, with accessories for reflectance and transmittance measurements, cryostat for T= 4-300 K, micro-reflectance apparatus and optical microscope for high spatial resolution FT-Step Scan, with spectral extension up to the visible (20 – 50000 cm -1 ) for phase- sensitive detection and time-resolved spectroscopy (> 1  s) in reflectance and transmittance. Spectrophotometer 200-3300 nm, with cryostat for T = 12 - 300 K, and accessories for transmittance and reflectance in the specular and diffuse configurations (250-2500 nm). Spectroscopic ellipsometer (250 - 900 nm), with macro- and micro- probe (minimum spot size 100 microns). Micro - Raman apparatus with He-Ne laser source, microprobe (down to 1 micron) and stage for mapping, CCD camera detector. Atomic Force microscope

56 Laser Matter Interaction Laboratory Facilities CW picosecond laser system 80 MHz, 40 ps, > 10 W @1.053 µm, ­ 1.5 W @ 0.53 µm, THG and FHG CW femtosecond laser system, ­130 fs, 760 - 840 nm, 2 W CW femtosecond OPO, 80 MHz, 1.4 - 2 µm Detection facilities from UV to IR, lock-in, average, photon counting Nonlinear measurements, 2 nd and 3 rd harmonic generation

57 Photonic crystals and waveguides Metallic and semiconducting nanoparticles in dielectric matrices SiGe Q-dots for integrated optics Si-compatible Q-dots InAs/InGaAs for laser @ 1.3 – 1.55 micron III-V structures for photovoltaic applications Research activities Si SiO 2  – X (  = 0°)

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59 In any case…

60 Thanks!


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