Slide1: Amorphous and glassy chalcogenides – perspective HIGH–TECH MATERIALS with many applications in electronics, optoelectronics, optics, medicine, chemistry and ecology (FIBERS, MEMORIES, SENSORS, OPTICAL SIGNAL PROCESSING, …) Miloslav Frumar, Tomas Wagner, Bozena Frumarova1 and Petr Nemec, and collaborators, MSc and PhD students   Research Center and Dep. of General and Inorg. Chemistry, University of Pardubice, 1Joint Laboratory of Solid State Chemistry of Acad. Sci. of Czech Rep. and University of Pardubice, Czech Republic    Frumar Brussels 11 2005 1


Slide2: Large interest: q               electrical and photoelectrical properties: photoconductivity, photovoltaics,          switching effects (treshold and memory) - electrical memories (phase change, ionic) bateries, sensors (optical and electrical) q              optics, optoelectronics infrared optics, optical transmission up to IR (18µm), optical signal processing, memories, IR luminescence, sensors q              photoinduced phenomena Photoinduced effects, optical waveguides, optical gratings, microlenses, planar optical circuits and devices, memories Frumar Brussels 11 2005 2


Slide3: Properties – chalcogenide vs. oxide glasses lower bonding energies Nonbonding electrons on chalcogen atoms softer lower thermal conductivity, low phonon energy higher electrical conductivity (semiconductors, Eg= 0.3 – 3eV), electrical switching effects, memory materials, phase change, DVD lower Tg (<0oC - 600oC), lower Tm, optical and electrical memories, good model materials transparent in the infrared region (~0.8 – 14m for selenides, up to 18 m for tellurides higher refractive index n (~2.2-3.2), matches with Si, GaAs, ZnSe, InSb and others High photoinduced ∆n, waveguides production. high non-linearity in n (optical signal processing) Frumar Brussels 11 2005 3


Slide4: Frumar Brussels 11 2005 4 intensive luminescence of rare earths RE3+ ions in IR  region, Eu, Er, Nd, Pr, Dy, Sm, …etc., f-f electron transitions, Light amplification and generation, IR lasers for tissue coagulation, cutting without bleeding, for tissue excission, removal of arterial plaque, cutting bone and drilling teeth, eye-safe lasers (radar) at wavelength of ~ 2 μm chemical sensing and environmental monitoring light up-conversion, signal couplers, frequency mixing,


Slide5: High non-linear index of refraction, The (3) are high in chalcogenides As2S3 glass: (3) = (1.48 – 2.2) x10-12 esu GeS2 glass, (3) = 1x10-12 esu, SiO2 glass, (3) = 2.8x10-14 (esu) for λ= 1900 nm. larger (3)  lower necessary power and shorter the interaction lengths  possibilty of fully optical signal processing and, optical computing !!?? If successful: many orders increase of computors speed Frumar Brussels 11 2005 5


Slide6: The luminescence spectrum of the (Ge30Ga5Se65)99.8(Dy2Se3)0.2 glass pumped by 905 nm light. Frumar Brussels 11 2005 6


Slide7: The room temperature luminescence spectra of the (Ge30Ga5Se65)99.9(Sm2Se3) 0.1 glass, excited by 980 nm light (1). The transmittance spectrum is also given (2). Frumar Brussels 11 2005 7


Slide8:   Energy scheme of absorption and luminescent transitions of Sm3+ doped glasses Frumar Brussels 11 2005 8


Slide9: UNIVERSITY of Pardubice, Czech republic: chalcogenides: > 30 years, >400 papers, 20 patents Many aspects: - Synthesis - Structure: X ray, Raman, IR, XPS, UPS – Intrinsic defects (non-stoichiometry, broken bonds, coordination defects, “wrong” bonds, ESR, Raman) - Extrinsic defects, transition metals, RE3+ ions Bi, Ag, halides,… - Thin films – vacuum evaporation, spin coating, laser ablation, magnetron sputtering - Properties: thermal, electrical, optical (VIS, IR), bulk glasses, thin films Photoinduced changes RE3+ doped glasses Pulsed laser ablation APPLICATION OF GLASSES AND FILMS Frumar Brussels 11 2005 9


Slide10: Photoinduced changes in amorph. chalcogenides (AC): Exposure can change the structure (without or with phase transition) optical transmittivity and reflectivity index of refraction reactivity of the films, the rate of dissolution in chemical solvents production of holographic gratings, very large-resolution lithography (photo-resists for features with size < 0.1 m, optical circuits). the viscosity the isotropy - anisotropic effects can be produced. enhance the diffusion or interdiffusion (metals, Ag, Cu, compounds, Bi2Se3 – Bi2Te3, ..). induce chemical reactions inside or on the surface of films (e.g. between Ag and chalcogenide film, Bi - Se, ) induce phase changes, e.g.: amorphous-crystalline state Optical and electrical data storage, DVD, etc. Frumar Brussels 11 2005 10


Slide11: many materials studied, e.g. a-Se, As-S, Sb-S, As-Se, As-Te, Sb-Te, Bi-Te, As-S-Te, Ge-Sb-S, Ge-Ga-S, Ge-Sb-Se, Ge-Sb-Te, Ge-In-Te, Ge-Bi-Te, Pb-Sb-Se, Pb-Sb-Te, Pb-Bi-Te, etc., all pure and doped, stoichiometric, non- stoichiometric, thin films, bulk glasses, glassy powders Thin films - much more disordered more intensive changes Frumar Brussels 11 2005 11


Slide12: The mechanisms of isotropic irreversible photoinduced changes is relatively well understood Frumar Brussels 11 2005 12


Slide13: Exposure or heating increases the rates of chemical reactions among fragments, the film is polymerized and closer to thermodynamic equilibrium. As4S4 + S2  2As2S3 (1)   simultaneously photolytic reaction (2) (2) Simulation and modelling of these processes: Frumar Brussels 11 2005 13


Slide14: Models: structural changes: changes of local bonding configuration, over- under – coordinations, photochemical reactions, crystallization, │As-As│ + │S-S│ = 2│As-S│ (3) where ε = 2EAs-S –EAs-As – ES-S (5) (4) Frumar Brussels 11 2005 14


Slide15: The exposure changes also the volume and surface profile  microlenses or microlens arrays can be applied in CCD cameras, imaging machines, optical communication very high resolution ( 30nm, 5000-10000 lines/mm can be obtained. Exposure also for holographic recording Frumar Brussels 11 2005 15


Slide16: Optically induced dissolution and diffusion of metals in a-chalcogenide films. The physicochemical processes behind the photodoping were studied. The changes of optical parameters and chemical reactivity are higher than those of undoped glasses and films. The photodoped films applied as solid state batteries, ionic sensors Frumar Brussels 11 2005 16


Diffraction gratings: Diffraction gratings Frumar Brussels 11 2005 17


Selective optically-induced diffusion and dissolution of silver in a-chalcogenides (no etching): Selective optically-induced diffusion and dissolution of silver in a-chalcogenides (no etching) Frumar Brussels 11 2005 18


Slide19: INTENSIVE infrared LUMINESCENCE For high quantum efficiency of luminescence: low phonon-energies of the glassy matrix: the number of phonons to bridge the energy , between electron levels of RE3+ ions, is large → multiphonon relaxation rate is low ! High index of refraction → higher values of spontaneous emission probabilities and → larger emission cross-sections of radiative electron transitions between energy levels of RE3+ ions → intensive luminescence Frumar Brussels 11 2005 19


Slide20: For many applications: thin films are necessary (planar waveguides, planar circuits, amplifiers, generators) Laser ablation and the sputtering - the composition is not practically changed – all parts of the glass (volatile and non-volatile) are evaporated together rare–earths elements - less volatile than chalcogenide matrix glasses → Thin films can not be prepared by classical vacuum evaporation – similar (identical) Raman spectra = structure similar (identical) luminescence spectra Frumar Brussels 11 2005 20


Slide21: -     For IR gratings, deep etching is necessary. Sharp edges with height up to 5-10m were obtained   The optically induced crystallization or amorphization can be observed in many binary, ternary, more complex, or eutectic compositions Optical imaging and storage: commercial devices: ternary tellurides are already applied (the change from amorphous to crystalline state and vice versa, 30 nm, DVD - experimentally hundreds of Gb/DVD Frumar Brussels 11 2005 21


Slide22: Resently at Pardubice university: large attention to nonvolatile phase change memories, multilevel nano-size memories 6FP [IST-NMP-3] IST-2004-017406 CHalcogenide MEmory with multiLevel Storage, CAMELS, with Tech. Univ. Aachen, Politech. Milano, Umicore Lichtenstein, STMicroelectronics Milano Frumar Brussels 11 2005 22


Slide23:   CONCLUSION Chalcogenide glasses and films many present and potential applications: IR, fibers, sensors, bateries, optoelectronics, optical storage and signal processing, memories, optical computers !? eye-safe lasers telecommunications, chemistry, environment, biology, medicine: e.g. IR lasers for tissue coagulation, cutting without bleeding, for tissue excision, removal of arterial plaque, cutting bone and drilling teeth, Chalcogenides - promising candidates for many applications   Frumar Brussels 11 2005 23


Slide24: Thank you for invitation and for your kind attention !!! Frumar Brussels 11 2005 24