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Optical properties of dielectric nanostructures
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Transcript of Optical properties of dielectric nanostructures
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Applications:› Doped crystals lasers
(radiation-resistant)
› Optical memory
Difficulties of investigation
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DielectricsFluoritesQuantum wellsNanostructures
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DielectricsFluoritesQuantum wellsNanostructures
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Non-conducting substance “dia-electric” from Greek “dia” –
“through” No free charge carriers Wide band gap > 5eV Transparent in visible region Ionic crystals When doped exhibit semiconductor
properties (CdF2)
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DielectricsFluoritesQuantum wellsNanostructures
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- Ca - F
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Main features:› Electron effective
mass is comparable to free electron mass (0,5~1,0 m0)
The valence band:› Maximum is in Г-
point The conduction
band:› Minimum is located
in Г-point
Ion 1s 2s 2p 3s 3p 3d
Ca2+ 2 2 6 2 6
F- 2 2 6
Electronic configuration of ions
The energy bands of CaF2
Energy band formation
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Transitions:
reflectivity
interpretation
Region I
11,2 Г15-Г1
13,9 X’2-X3
15,5 X’5-X3
25,1 Г’25-Г15
Region II
Outermost core state of metal ion
Region III
Interband and ionizing transitions of core e-
I II III
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DielectricsFluoritesQuantum wellsNanostructures
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Eg1 Eg2
Energy levels for infinite well
Selection rule
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DielectricsFluoritesQuantum wellsNanostructures
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Evaporation on to cleaved LiF substarate
Specimens:› SL2: KBr 100A-layer› C-ML: a double
structure of KBr 100A on KCl 200A
› D-ML: a triple structure of KBr 100A sandwiched by two KCl 200A
› E-ML: a 3,5 periods one of KCl 150A – KBr 50A
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Evaporation onto a quartz glass substrate
Specimens:› KI layer is
sandwiched between KBr layer of the same thickness
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Blue shifts:› Quantum
confinement effects
› Interlayer mixed crystallization
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Specimens:› 1: Si-CaF2(30ML)-CaF2
› 2: Si-CaF2-CdF2(10ML)-CaF2
› 3: Si-CaF2-CdF2(30ML)-CaF2
› 4: Si-CaF2-CdF2(90ML)-CaF2
› 5: Si-CaF2-6x[CaF2(5ML)-CdF2(5ML)]-CaF2
› 6: Si-CaF2-14x[CaF2(2,5ML)-CdF2(2ML)]-CaF2
› 7: Si-CaF2-3x[CaF2(10ML)-CdF2(10ML)]-CaF2
Si
Lattice constants:CaF2 5,46 A0
CdF2 5,39 A0
Si 5,43 A0
12.1eV 8eV
CaF2 CdF2
Energy difference atthe interface CaF2/CdF2:
2,9 eV in the conduction band1,2 eV in the valence band
Opposite sing of the fluoride lattice mismatch to Si flavors strain compensation and growth of pseudomorthic superlattices
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To add transitions
CaF2
CaF2-CdF2 10ML
CaF2-CdF2 10ML
CaF2-CdF2 5ML
CaF2-CdF2 2ML
CaF2-CdF2 90ML
CaF2-CdF2 30ML
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- refractive index
- complex dielectric constant
- reflectivity
- reflection coefficient
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Oscillators parameters:
oscillatorresonance
energydumping param
amplitude
0 11,49 0,25 1,24
1 0,5 0,5 1,9
2 0,7 0,7 3,8
3 1,5 1,5 4,4
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Future plans:› To calculate phase of reflective index› To calculate reflectance spectrum from thin
films› To estimate energy level shifts in quantum
well› To estimate interface effects
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1 CaF2 multilayer at 4500C
CaF2 nanoislands stretched along <110> direction
Bare Si surface between CaF2 islands
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6 CaF2 multilayers at 7000C
CaF2 stripes are aligned along <110> direction
Stripes length – several microns, height – 3-6 nm
Formation of wetting layer
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TEMX-Ray diffraction
4ML6ML 10ML T/2
High crystalline quality
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