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Amorphous and glassy chalcogenides perspective
HIGHTECH 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   

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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
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• 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 (lt0oC - 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)

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• 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,

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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 ? 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

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The luminescence spectrum of the
(Ge30Ga5Se65)99.8(Dy2Se3)0.2 glass pumped by 905
nm light.
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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).
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Energy scheme of absorption and luminescent
transitions of Sm3 doped glasses
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UNIVERSITY of Pardubice, Czech
republic chalcogenides gt 30 years, gt400 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
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• 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 lt 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.

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• 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
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The mechanisms of isotropic irreversible
photoinduced changes is relatively well
understood
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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

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Models structural changes changes of local
bonding configuration, over- under
coordinations, photochemical reactions,
crystallization,
As-As S-S 2As-S (3)
(4)
where e 2EAs-S EAs-As ES-S

(5)
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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
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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
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Diffraction gratings
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Selective optically-induced diffusion and
dissolution of silver in a-chalcogenides (no
etching)
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• 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

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• 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
• rareearths 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

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-     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
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• 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

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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  
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• Thank you for invitation
• and for your kind attention !!!

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