xps, optical propertiessusi.theochem.tuwien.ac.at/events/ws2019/blaha_xps...criteria colors harmony...
TRANSCRIPT
XPS, Optical properties
Peter BlahaInstitute of Materials Chemistry, TU Wien
(Xavier Rocquefelte)University of Rennes
Photoemission spectroscopy, PES
Energyconservation: ħ + Ekin + Eb
: work function Ekin: kinetic E of e-
Eb: bindingenergy of e-
UPS: UV (He-light, 21.1 und 40.4 eV), for valence-electrons XPS, ESCA: X-rays (Al 1486 eV), for core and valence-electrons Synchrotronradiation: UV or X-rays of “any” wavelength
•Illuminate sample with light of knownenergy, measure kinetic E of emittedelectrons e-
core-e-, Valence-DOS
Work function
potential
bulk
Surface
EF
Work-function
Vacuum
supercell
WF= :VZERO - :FER (check convergence with vacuum)
binding energy of oneparticular state
XPS, core-level shifts
Ionizationpotential of core-e-, IP= Etot(N) – Etot(N-1) gives information on charge state of the atom
core-eigenvalues i are NOT a good approximation: i=dE/dn Slater’s “transition state”: core-eigenvalues i for half occupancy
-SCF-calculation with and without core-hole: Etot(N) – Etot(N-1) supercells to reduce hole-hole interaction
C,N 1s exp.(eV) i -SCF
TiC 281.5 264.7 281.9
Ti4C4 281.5 263.3 281.1
TiN 397.0 377.5 397.1
E
E
n
tangent at N ≠ E
tangent at N-½ ~ secant ~ E
N-1 N-½ N
valence e-: bandstructure via ARPES
Surface stated-bandsp-band
valence PES: usually explained by DOS
a single DOS cannot explain the E-dependency of PES
, ,, Na,l = Partial DOS a,l = atomic cross section
O1s
2s2p
SiO2 valence band XPS
Total DOS gives 5 peaks, but wrong intensities
Cross section modulated PDOS gives better intensities
Renormalized PDOS * gives perfect intensities renormalization according to the inverse
charge fraction of an orbital within the atomic sphere + removal of interstitalDOS: ∑ ,,
PbO2 at 3 different energies
56eV: O-2p PDOS explains the spectrum
1486 eV: all orbitals contribute
7700 eV: O-2p not important
PBO2 at very low BE
56 eV: almost no intensity till -1 eV
7700eV: strong contribution from antibonding Pb-6s
1 – MULTIPLE FACETS OF COLOURED MATTER
2 – ELECTRONIC STRUCTURE OF A SOLID
3 – UNDERSTANDING OF COLORS FROM BANDS
4 – LIGHT‐MATTER INTERACTION
5 – OPTICAL PROPERTIES: WHICH TREATMENT?
6 – ILLUSTRATIONS
Modelling the Optical Properties of Inorganic Materials
1 – MULTIPLE FACETS OF COLOURED MATTER
DiffusionAbsorption
Coloring and pigments
Sky and clouds Others diffusingSystems …
Intermediate cases
Photons in interactionwith matter
Light‐Matter interaction
Zone ofinterferences
RefractioncolorsRainbow
Diffractioncolors
Interferentialcolor
Waves intransparentmedium
DiffusionAbsorptionLight‐Matter interaction
Coloring and pigments
Sky and clouds Others diffusingSystems …
Intermediate cases
Photons in interactionwith matter
1 – MULTIPLE FACETS OF COLOURED MATTER
Zone ofinterferences
RefractioncolorsRainbow
Diffractioncolors
Interferentialcolor
Waves intransparentmedium
DiffusionAbsorptionLight‐Matter interaction
Coloring and pigments
Sky and clouds Others diffusingSystems …
Intermediate cases
Photons in interactionwith matter
Eye
Brain Colored shadowCriteria colorsharmony
Colorimetry Color mixing
Light‐Matter interactionRetinal
in interactionwith photons
Nervoussignal
1 – MULTIPLE FACETS OF COLOURED MATTER
Interaction between the electromagnetic field and matter
Physical color
Diffusion et interferencesDispersion / Reflection et Refraction / Scattering
Transparent matter
1 – MULTIPLE FACETS OF COLOURED MATTER
Interaction between the electromagnetic field and matter
Physical color Chemical color
Diffusion et interferencesDispersion / Reflection et Refraction / Scattering
AbsorptionEnergy dissipation
Transparent matter Opaque matter
1 – MULTIPLE FACETS OF COLOURED MATTER
Chemical colors
AbsorptionEnergy dissipation
Opaque Matter
Acceptor electron levels Dissipative absorption
h
VB
CB
Gap
VB
CB
VB
CBUV
IR0
E (eV)
1.65
3.26
Chemical color « Inelastic diffusion »
From insulator to semiconductor to metal systems
1 – MULTIPLE FACETS OF COLOURED MATTER
2 – ELECTRONIC STRUCTURE OF A SOLID
p
s
From the atom to the molecule and to the solidEnergy
AtomAtomicOrbitals
p
s
*LCAO : Linear Combination of Atomic Orbitals
MoleculeLCAO*
MolecularOrbitals
From the atom to the molecule and to the solid
AtomAtomicOrbitals
Energy
2 – ELECTRONIC STRUCTURE OF A SOLID
SolidDispersion
Eg
CB
BV
ConductionBand
ValenceBand
BandGap
Bloch Orbitals= Bands
p
s
*LCAO : Linear Combination of Atomic Orbitals
MoleculeLCAO*
MolecularOrbitals
AtomAtomicOrbitals
Energy
From the atom to the molecule and to the solid
2 – ELECTRONIC STRUCTURE OF A SOLID
h
BV
CB
UV
IR
E (eV)
0
1
2
3
4
5
6
h
VB
UV
IR
E (eV)
0
1
2
3
4
5
6 Color of a SC* with 1 gap
*SC : Semiconductor
3 – UNDERSTANDING OF COLORS FROM BANDS
GAP
Abs
orpt
ion
(a.u
.)
Energy (eV)0 1 2 3 4 5 6
Transmittedlight
Color of thecompound
BV
CB
BV
CB
VB VB
Gap
0 1 2 3 4 5 6
hUV
IR
E (eV)
0
1
2
3
4
5
6
hUV
IR
E (eV)
0
1
2
3
4
5
6
Color of thecompound
Color of a SC* with 1 gap
Abs
orpt
ion
(a.u
.)
Energy (eV)
Transmittedlight
*SC : Semiconductor
3 – UNDERSTANDING OF COLORS FROM BANDS
BV
CB
BV
CB
BV
CB
VB VB VB
BI
Abs
orpt
ion
(a.u
.)
Energy (eV)0 1 2 3 4 5 6
No transmittedlight
*SC : Semiconductor
hUV
IR
E (eV)
0
1
2
3
4
5
6
hUV
IR
E (eV)
0
1
2
3
4
5
6
Color of thecompound
Color of a SC* with 1 gap
3 – UNDERSTANDING OF COLORS FROM BANDS
0 1 2 3 4 5 6BV
CB
VB
TransmittedLight
Energy (eV)
Abs
orpt
ion
(a.u
.)
EnergyColor of a SC* with several gaps
*SC : Semiconductor
3 – UNDERSTANDING OF COLORS FROM BANDS
*SC : Semi‐conducteur – BI : Bande interdite
0 1 2 3 4 5 6Energy (eV)
Abs
orpt
ion
(a.u
.)Transmitted
Light
BV
CB
VB
EnergyColor of a SC* with several gaps
3 – UNDERSTANDING OF COLORS FROM BANDS
Powder sample of TiO2 (rutile)
Charge transfercolor
TiO2
3 – UNDERSTANDING OF COLORS FROM BANDS
‐10
0
10
Energy (eV)
‐5
5
2 O2‐ (2p6)
Ti4+ (3d0)
“t2g”
“eg”
Eg 3 eV
TiO2
O Ti
Powder sample of TiO2 (rutile)
Charge transfercolor
3 – UNDERSTANDING OF COLORS FROM BANDS
‐10
0
10
Energy (eV)
‐5
5
2 O2‐ (2p6)
Ti4+ (3d0)
“t2g”
“eg”
Eg 3 eV
TiO2
O Ti
Absorption (a.u.)
Energy (eV)0 1 2 3 4 5 6
UV
Charge transfercolor
3 – UNDERSTANDING OF COLORS FROM BANDS
‐10
0
10
Energy (eV)
‐5
5
2 O2‐ (2p6)
Ti4+ (3d0)
“t2g”
“eg”
h> 3 eV
TiO2
Absorption (a.u.)
Energy (eV)0 1 2 3 4 5 6
UV
O Ti
Charge transfercolor
3 – UNDERSTANDING OF COLORS FROM BANDS
TiCl3in solution
6 O2‐ (2p6)
Ti3+ (3d1)“t2g”
“eg”
h> 3 eV
h 2,5 eV
Ti[H2O]3+
d‐d transition color
3 – UNDERSTANDING OF COLORS FROM BANDS
Ti[H2O]3+
6 O2‐ (2p6)
Ti4+ (3d1)“t2g”
“eg”
h> 3 eV
h 2,5 eV
Absorption (a.u.)
Energy (eV)0 1 2 3 4 5 6
UV
Rq. : For dn with n > 1 Interelectronic correlations must be taken into accountTanabe‐Sugano diagrams(spectroscopic terms)
d‐d transition color
3 – UNDERSTANDING OF COLORS FROM BANDS
Aluminecorindon(Al2O3)
BV
CB
VB
EnergieAbsorption (a.u.)
Energy (eV)0 1 2 3 4 9
UV
10 11 12
3 – UNDERSTANDING OF COLORS FROM BANDS
Aluminecorindon(Al2O3)
Syntheticrubis
(Al2O3:1%Cr3+)
+ 1% Cr3+
Absorption (a.u.)
Energy (eV)0 1 2 3 4 9
UV
10 11
Absorption (a.u.)
Energy (eV)0 1 2 3 4
3 – UNDERSTANDING OF COLORS FROM BANDS
Impurity (d‐d) color
Rubis (Al2O3:1%Cr3+)
Cr3+ : electronic conf. d3 Interelectronic correlations must be taken into accountTanabe‐Sugano diagrams(spectroscopic terms)
3 – UNDERSTANDING OF COLORS FROM BANDS
Multiplicity of spin
Cr3+ : elect. conf. d3
2S+1X
Energy
4F0
4P
2G
2F
No CF*
Rubis (Al2O3:1%Cr3+)
Free ion: we define the spectroscopic terms :
4Fml +2 +1 0 ‐1 ‐2
L = +3
S = 3/2
*CF : Cristal Field
Impurity (d‐d) color
3 – UNDERSTANDING OF COLORS FROM BANDS
Energy
4F0
4P
2G
2F
2E2T1
2T2
4A2 (t23e0)
4T2 (t22e1)
4T1 (t21e2)
2A1
No CF* With CF*
Rubis (Al2O3:1%Cr3+)
Degeneracy lifting due to the octahedralcrystal field effect created by the ligands
Cr3+ : conf. eq d3
t23
e0
t22
e1
t21
e2
Excited States
Fundamental state
Impurity (d‐d) color
*CF : Cristal Field
3 – UNDERSTANDING OF COLORS FROM BANDS
Energy
4F0
4P
2G
2F
2E2T1
2T2
2A1
No CF* With CF**CC : Champ Cristallin
Rubis (Al2O3:1%Cr3+)
Energy (eV)0 1 2 3 4 5
Red color+
Slightly blue
Abs. (a.u.)
4A2 (t23e0)
4T2 (t22e1)
4T1 (t21e2)
Impurity (d‐d) color
Cr3+ : electronic conf. d3 Interelectronic correlations must be taken into accountTanabe‐Sugano diagrams(spectroscopic terms)
3 – UNDERSTANDING OF COLORS FROM BANDS
nvac. = 1
v = c/n
c
Example of a prism
Physical color « Elastic diffusion »
n : index of refraction
Propagation speed is changed
4 – LIGHT‐MATTER INTERACTION
Example of a prism
Oscillating field
Without applied field
Electronic density
re .Dipole moment
nvac. = 1
v = c/n
c
Physical color « Elastic diffusion »
Elastic diffusion mechanismat the electronic level
Succession of absorption and emission
: Inductive dipole moment Receiver‐transmitter antenna
Oscillating Electric Field polarize
4 – LIGHT‐MATTER INTERACTION
0 5 10 15 200.0
0.5
1.0
1.5
2.0
Energy (eV)0 5 10 15 20
0.0
0.5
1.0
1.5
Energy (eV)
n k
Diffusion Absorption
Kramers‐Kronig
Complex index of refraction: N = n + i k
4 – LIGHT‐MATTER INTERACTION
0 5 10 15 200.0
1.0
2.0
3.0
4.0
Energy (eV)0 5 10 15 20
0.0
1.0
2.0
1.5
4.0
Energy (eV)
1 2Complex dielectric function: = 1 + i 2
1 = n2 – k2
2 = 2nk
0 5 10 15 200.0
0.5
1.0
1.5
2.0
Energy (eV)0 5 10 15 20
0.0
0.5
1.0
1.5
Energy (eV)
n k
Diffusion Absorption
Kramers‐Kronig
Complex index of refraction: N = n + i k
4 – LIGHT‐MATTER INTERACTION
0 5 10 15 200.0
1.0
2.0
3.0
4.0
Energy (eV)
0 5 10 15 200.0
0.5
1.0
1.5
2.0
Energy (eV)
n
1
Diffusion in the case of a prism
n(blue) > n(red)
0 5
1.5
2.0
4 – LIGHT‐MATTER INTERACTION
0 5 10 15 200.0
0.5
1.0
1.5
2.0
Energy (eV)
nk
Index of vacuum
Vacuum
0 5 10 15 200.0
0.5
1.0
1.5
2.0
Energy (eV)
nk
0 5 10 15 200.0
0.5
1.0
1.5
2.0
Energy (eV)
nk
0 5 10 15 200.0
0.5
1.0
1.5
2.0
Energy (eV)
nk
Insulator Semi‐conductor Metal
Electron more and more free
Absorption band is displaced towards low energies
Directly related to the oscillator strength
4 – LIGHT‐MATTER INTERACTION
5 – OPTICAL PROPERTIES: WHICH TREATMENT?
Band structure
VB
CB
Eg
1
The different steps to calculate the optical properties:
Imaginary part of the dielectric function: 2
Dipolartransitions
2
Band structure
VB
CB
Eg
1
The different steps to calculate the optical properties:
5 – OPTICAL PROPERTIES: WHICH TREATMENT?
Real part of the dielectric
function : 1
Kramers-Kronigtransformation3
Imaginary part of the dielectric function: 2
Dipolartransitions
2
Band structure
VB
CB
Eg
1
The different steps to calculate the optical properties:
5 – OPTICAL PROPERTIES: WHICH TREATMENT?
4
1 = n2 – k2
2 = 2nk
Determination ofn = f(E) & k = f(E)
Real part of the dielectric
function : 1
Kramers-Krönigtransformation3
Imaginary part of the dielectric function: 2
Dipolartransitions
2
Band structure
VB
CB
Eg
1
The different steps to calculate the optical properties:
5 – OPTICAL PROPERTIES: WHICH TREATMENT?
0 5 10
BiVO4-mono atom 0 size 0.70
Γ A Z M L V Γ
E F
Ener
gy (
eV)
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
-1.0
-2.0
-3.0
-4.0
-5.0
-6.0
Ener
gy (e
V)
0 2 4 6 8 10 12 140
5
10
Energy (eV)
2
Band structure DOS
Gap 2.3 eV
Band structure calculation1 Determination of 22
Gap 2.3 eV
Optical properties of m-BiVO4 and z-BiVO4 phases
Example of BiVO4
5 – OPTICAL PROPERTIES: WHICH TREATMENT?
Determination of 13 4 Determination ofn = f(E) & k = f(E)
0
1
2
3
4
0
1
2
3
kn
Energy (eV)0 2 4 6 8 10 12 14
0
5
10
21
-5
0
5
10
Energy (eV)0 2 4 6 8 10 12 14
Example of BiVO4
5 – OPTICAL PROPERTIES: WHICH TREATMENT?
Journées communications – 15/01/09
5 – OPTICAL PROPERTIES SIMULATION IN WIEN2k
Interband contributions(based on IPA*)
Intraband contributions(using a Drude‐like term)
EF EF
In WIEN2k, two types of contributions to the dielectric function( = 1 + i.2) could be estimated:
h h
Dielectric tensor / Optical conductivity / Refractive index / Reflectivity / Absorption coefficient / Loss function (EELS)
*IPA: Independant Particle Approximation
Journées communications – 15/01/09
5 – OPTICAL PROPERTIES SIMULATION IN WIEN2k
Interband contributions(based on IPA*)
EF
In WIEN2k, two types of contributions to the dielectric function( = 1 + i.2) could be estimated:
h h
*IPA: Independant Particle Approximation
Sum over all valence and conduction bands
Im(ij())
Journées communications – 15/01/09
5 – INTERPRETATION: Intraband transitions (for metals)
Plasma frequency: (longitudinal oscillations of the electron gas)
Intraband contributions(using a Drude‐like term)
EF
Journées communications – 15/01/09
5 – OPTICAL PROPERTIES SIMULATION IN WIEN2kOptical functions:
Journées communications – 15/01/09
5 – OPTICAL PROPERTIES SIMULATION IN WIEN2k
Symmetry of the dielectric tensor
cubic
monoclinic (, = 90°) orthorhombic
tetragonal, hexagonal
triclinic
Journées communications – 15/01/09
5 – OPTICAL PROPERTIES SIMULATION IN WIEN2k
Convergence with k‐mesh (expl.: Al)
‐30
‐20
‐10
0
10
Energy (eV)
EF
3p Ti
2s O
2p O
3d Ti
Example of the rutile phase
Atomicstructure
Electronicstructure
Dielectricfunction
Journées communications – 15/01/09
6 – ILLUSTRATIONS: TiO2 series
‐30
‐20
‐10
0
10
Energy (eV)
EF
3p Ti
2s O
2p O
3d Ti
0 5 10 15 20 25 300
2
4
6
8
10
12
14
Energie (eV)
2EELS experiments
Journées communications – 15/01/09
Example of the rutile phase
Atomicstructure
Electronicstructure
Dielectricfunction
6 – ILLUSTRATIONS: TiO2 series
‐30
‐20
‐10
0
10
Energy (eV)
EF
3p Ti
2s O
2p O
3d Ti
0 5 10 15 20 25 300
2
4
6
8
10
12
14
Energie (eV)
2EELS experimentsDFT simulation
Journées communications – 15/01/09
Example of the rutile phase
Atomicstructure
Electronicstructure
Dielectricfunction
GGA (PBE)+ gap correction of 0.6 eV
6 – ILLUSTRATIONS: TiO2 series
Journées communications – 15/01/09
6 – OPTICS IN WIEN2k
x joint Im ij() ,(case.joint) (JDOS*symmat)
x kram Re ij(), other optical funct.,broadening, scissor operator
opticplot
5
6
7
and high Emax
Journées communications – 15/01/09
6 – SOME ADDITIONAL DETAILS
Journées communications – 15/01/09
6 – ILLUSTRATIONS: TiO2 series
TiO2-RUT.inop2000 1 number of k‐points, first k‐point ‐5.0 5.0 Emin, Emax in Ry for matrix elements2 number of choices (columns in *outmat)1 Re xx3 Re zzOFF write unsymmetrized matrix elements to file?
Choices:1......Re <x><x>2......Re <y><y>3......Re <z><z>4......Re <x><y>5......Re <x><z>6......Re <y><z>7......Im <x><y>8......Im <x><z>
Journées communications – 15/01/09
6 – ILLUSTRATIONS: TiO2 series
TiO2-RUT.injoint1 261 LOWER AND UPPER BANDINDEX0.0000 0.00100 10.0000 EMIN DE EMAX FOR ENERGYGRID IN rydeV output units eV / ryd / cm‐14 SWITCH 2 NUMBER OF COLUMNS0.1 0.1 0.3 BROADENING (FOR DRUDE MODEL ‐ switch 6,7 ‐ONLY)
SWITCH:
0...JOINTDOS FOR EACH BAND COMBINATION 1...JOINTDOS AS SUM OVER ALL BAND COMBINATIONS2...DOS FOR EACH BAND 3...DOS AS SUM OVER ALL BANDS4...Im(EPSILON) 5...Im(EPSILON) for each band combination6...INTRABAND contributions7...INTRABAND contributions including band analysis
TiO2-RUT.inkram0.1 Gamma: broadening of interband spectrum0.6 energy shift (scissors operator)0 add intraband contributions? yes/no: 1/012.60 plasma frequencies (from joint, opt 6)0.20 Gammas for Drude terms
Journées communications – 15/01/09
6 – ILLUSTRATIONS: TiO2 series
Files generated by:x optic TiO2-RUT.symmat
TiO2-RUT.mommat
x joint TiO2-RUT.joint
x kram TiO2-RUT.epsilon
TiO2-RUT.sigmak
TiO2-RUT.refraction
TiO2-RUT.absorption
TiO2-RUT.eloss
I(є2) V
1.8
1.9
2.0
2.1
2.2
2.3
2.4
2.5
2.6
2.7
2.8
2.9
3.0
1500 2000 2500 3000 3500 4000 4500
CdTe
CdSe
CdS
ZnTe
ZnSe
ZnS
ZnO
1.8
1.9
2.0
2.1
2.2
2.3
2.4
2.5
2.6
2.7
2.8
2.9
3.0
52 54 56 58 60 62 64 66 68
Blende structure Wurtzite structure
CdTe
CdSe
CdS
ZnTe
ZnSe
ZnS
ZnO
I(є2)
Refractive index (n)
0 5 10 15 20 250
10
20
30
40
50
2
Energy (eV)
EELS exp.DFT calc.(gap correction)
ZnO Blende ZnS
ZnSe
ZnTe
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 200.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.51.61.82.02.22.42.62.83.03.23.43.63.84.04.24.4
Ref
ract
ive
inde
x
Photon Energy (eV)
Ref
ract
ive
inde
x (n
)
Energy (eV)
nCdO 1.95
ZnOZnS
ZnSeZnTe
ZnS
6 –ILLUSTRATIONS: MQ series (M = Zn, Cd & Q = O, S, Se, Te)
Refractive index (n)
Refractive index (n)
Journées communications – 15/01/09
7 – Limitations:
The band gap problem Necessity to go beyond DFT
Energy Energy
Electro‐affinity: N+1(N+1) = ‐AIonization energy: N(N) = ‐I
Eg = N+1(N+1) – N(N) = I – A
Energy
Eg = N+1(N) – N(N)
Eg = N+1(2N) – N(2N) + N+1(2N+1) – N+1(2N)
NN‐1
N+1
NN‐1
N+1
NN‐1
N+1
Eg = g + xc
g
with xc: Scissor Operator/mBJ/hybrid/GW…
5 – OPTICAL PROPERTIES SIMULATION IN WIEN2k
Fundamental gap: electronic gap optical gapDeduced from the band structure Dipolar transitions
E
O(2p) Ti(3d)
DO
S
g(1)
2
0 2 4 6 8 10 12 140
2
4
6
8
10
12
5 – OPTICAL PROPERTIES SIMULATION IN WIEN2k
If excitonic effects: we should go beyond(TDDFT / BSE)
Fundamental gap: electronic gap optical gapDeduced from the band structure Dipolar transitions
E
O(2p) Ti(3d)
DO
S
g(1)
2
0 2 4 6 8 10 12 140
2
4
6
8
10
12
Energy Energy
NN‐1
N+1
NN‐1
N+1Opticalexcitation
7 – Some limitations of DFT simulation of optical properties
‐ Kohn‐Sham eigenstates interpreted as excited states
‐ Independent‐particle approximation (no e‐—h+ interaction)
‐ LDA/GGA are not exact
Use of Bethe‐Salpeter Equation (BSE) – Time‐dependent DFT
Use of hybrid DFT, effective potentialsUse of DFT+U, LDA+DMFT, GW…