Applications:› Doped crystals lasers

(radiation-resistant)

› Optical memory

Difficulties of investigation

DielectricsFluoritesQuantum wellsNanostructures

DielectricsFluoritesQuantum wellsNanostructures

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)

DielectricsFluoritesQuantum wellsNanostructures

- Ca - F

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

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

DielectricsFluoritesQuantum wellsNanostructures

Eg1 Eg2

Energy levels for infinite well

Selection rule

DielectricsFluoritesQuantum wellsNanostructures

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

Evaporation onto a quartz glass substrate

Specimens:› KI layer is

sandwiched between KBr layer of the same thickness

Blue shifts:› Quantum

confinement effects

› Interlayer mixed crystallization

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

To add transitions

CaF2

CaF2-CdF2 10ML

CaF2-CdF2 10ML

CaF2-CdF2 5ML

CaF2-CdF2 2ML

CaF2-CdF2 90ML

CaF2-CdF2 30ML

- refractive index

- complex dielectric constant

- reflectivity

- reflection coefficient

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

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

1 CaF2 multilayer at 4500C

CaF2 nanoislands stretched along <110> direction

Bare Si surface between CaF2 islands

6 CaF2 multilayers at 7000C

CaF2 stripes are aligned along <110> direction

Stripes length – several microns, height – 3-6 nm

Formation of wetting layer

TEMX-Ray diffraction

4ML6ML 10ML T/2

High crystalline quality