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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
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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
q lower bonding energies
q Nonbonding electrons on chalcogen atoms
q softer
q lower thermal conductivity, low phonon energy
q higher electrical conductivity (semiconductors, Eg= 0.3 – 3eV), electrical
switching effects, memory materials, phase change, DVD
q lower Tg (<0oC - 600oC), lower Tm, optical and electrical memories, good
model materials
q transparent in the infrared region (~0.8 – 14m for selenides, up to 18 m for
tellurides
q higher refractive index n (~2.2-3.2), matches with Si, GaAs, ZnSe, InSb and
others
q High photoinduced ∆n, waveguides production.
q high non-linearity in n (optical signal processing)
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q intensive luminescence of rare earths RE3+ ions in IR region, Eu, Er,
Nd, Pr, Dy, Sm, …etc., f-f electron transitions,
q Light amplification and generation,
q 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
q 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 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
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14
Luminescence intensity / a.u.
12
10
8
6
4
The luminescence spectrum of
the (Ge30Ga5Se65)99.8(Dy2Se3)0.2
glass pumped by 905 nm light.
2
0
1200 1600 2000 2400 2800 3200
Wavelength / nm
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80
18
70
16
60
14
50
2
12
10
40
8
30
6
4
20
1
10
2
0
1100 1200 1300 1400 1500 1600
Wavelength / nm
Transmittance / %
Luminescence intensity / a.u.
20
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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4
6
8
1
0
1
2
6
F11/2
10
6
F9/2
6
F7/2
6
F5/2
3
Energy / 10 cm
-1
8
6
6
6
6
F1/2, H15/2, F3/2
6
4
2
H13/2
6
H11/2
6
H9/2
6
0
H7/2
H5/2
6
Energy scheme of absorption and luminescent transitions of Sm3+ doped glasses
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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
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Photoinduced changes in amorph. chalcogenides (AC):
Exposure can change
q the structure (without or with phase transition)
q optical transmittivity and reflectivity
q index of refraction
q 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).
q the viscosity
q the isotropy - anisotropic effects can be produced.
q enhance the diffusion or interdiffusion (metals, Ag, Cu, compounds, Bi2Se3 –
Bi2Te3, ..).
q induce chemical reactions inside or on the surface of films (e.g. between Ag
and chalcogenide film, Bi - Se, )
qinduce 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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As38S62 film
97As2S3-3Ga2S3
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)
h i , Ii ,T
2 M  S    M  M

S S
(2)
Simulation and modelling of these processes:
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Models: structural changes: changes of local bonding configuration, overunder – coordinations, photochemical reactions, crystallization,
│As-As│ + │S-S│ = 2│As-S│
(3)

As  S 
 


k
exp
 
As  As S  S 
 kT 
2
K
where ε = 2EAs-S –EAs-As – ES-S
(4)
(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 achalcogenide 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
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
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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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