a Function of Optical Electronegativity for Semiconducting and Insulating Binary Oxides Kristen Dagenais Chemical Engineering UMBC Matthew Chamberlain Physics and Astronomy James Madison ID: 713703
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Slide1
Energy Band Gap Behavior as a Function of Optical Electronegativity for Semiconducting and Insulating Binary Oxides
Kristen
Dagenais
, Chemical Engineering,
UMBC
Matthew Chamberlain, Physics and Astronomy, James Madison
Unviersity
Dr.
Costel
Constantin
, Physics and Astronomy, James
Madison UniversitySlide2
TopicsEnergy Band GapsElectronegativityCurrent ModelsIonization of Oxygen
Accounting for Band Gap Variation
First Look
Periodic Table
Second Look with Models and TrendsSlide3
Define E
F
as the level below which all electrons fill up the states (little cups).
METALS - Fermi energy level falls at the middle of the allowed band.
INSULATORS and SEMICONDUCTORS - Fermi energy level falls at
the middle of the forbidden gap.
Energy Band GapsSlide4
Semiconducting and Insulating Binary OxidesA big part of electronicsEx. SiO2 used as an insulator in transistorsAs devices get smaller, better materials must be chosen
Band gap is used to justify research
Usually found experimentally
Band gaps models try to replace extra experiment
Usually relate band gap to
electronegativitySlide5
ElectronegativityDifferent ScalesMulliken, Allred-Rochow, Allen etc.
Most Commonly Used Pauling Scale
Optical
Electronegativity
Based on electron transference between atoms
ComparisonOptical Electronegativity is more accurate and preciseSlide6
Accepted Models for EgText Book Model [21]
J.A. Duffy’s Model [2]
*
Di Quarto [20]
Slide7
Duffy ModelDuffy Model [2]Developed based on optical electronegativityModel:
Example:
NaBr
But oxides behave differentlySlide8
Ionization of OxygenOptical electronegativity of oxygen varies with the cation
No fixed value
Duffy’s Oxide Model [2]Slide9
Band Gap VariationBand gap depends on many other factorsDefectsGrowth methodCrystal structure
Temperature
One
cation
may have different oxide forms
Ex. Ytterbium Oxide’s two forms
How do we account/handle these changes?Slide10
Criteria of Choosing a Band GapAt or around room temperature (~300 K)Most stable formMost useful formEx.
Eg
of
YbO
vs
Yb2O3Doesn’t solve the problem of Crystal structureDefectsGrowth methodSlide11
SubstancesReferences [3]-[11]
Compound
Eg (eV)
χ*
BeO
10.5
3.15
B
2
O
3
8.45
3.45
MgO
7.8
2.86
Al
2
O
3
6.96
3.18
Si
2
O
2
9.24
3.38
CaO
6.26
2.26
TiO
2
3.6
3.12
Cr
2
O
3
2.58
3.22
MnO
4
3.13
FeO
3.2
3.33
CoO
3.2
3.37
NiO
2.86
3.38
Cu
2
O
2.04
3.38
ZnO
3.3
3.25
Ga
2
O
3
5.4
3.3
GeO
2
5.35
3.44
Se
2
O
3
5
3.64
SrO
6.5
2.11
MoO
3
2.74
3.51
CdO
2.5
3.24
In
2
O
3
3.55
3.31
SnO
2
3.57
3.41
BaO
5.2
1.9
La
2
O
3
5.5
2.5
CeO
2
3.78
2.54
Pr
2
O
3
3.8
2.56
Nd
2
O
3
4.6
2.58
Sm
2
O
3
5
2.64
Eu
2
O
3
4.3
2.69
Gd
2
O
3
5.4
2.69
Tb
2
O
3
3.8
2.69
Dy
2
O
3
4.9
2.72
Ho
2
O
3
5.3
2.74
Er
2
O
3
5.3
2.76
Tm
2
O
3
5.4
2.77
Yb
2
O
3
4.9
2.5
Lu
2
O
3
5.5
2.8
HgO
2.58
3.43
Tl
2
O
3
2.25
3.19
PbO
2.75
3.57
Bi
2
O
3
2.85
3.44Slide12
Band Gap Error
Compound
First Band Gap, (
eV
)
Second Band Gap, (
eV
)
Average Band Gap
Standard Dev.
Normalized Standard Dev
Average Error
BeO
10.5
5
7.75
3.889
0.5018
0.215
Cr2O3
2.58
3.25
2.92
0.4737
0.1625
ZnO
3.30
3.7
3.5
0.2828
0.08081
GeO2
5.35
6.1
5.73
0.5303
0.09263
CdO
2.50
1.11
1.81
0.9829
0.5445
La2O3
5.50
5.50
5.50
0
0
CeO2
3.78
3.19
3.49
0.4172
0.1197
HgO
2.58
1.9
2.24
0.4808
0.2146
References [12]-[18]Slide13
Final ValuesSlide14
Using the Periodic TableSlide15
With GroupingSlide16
Z Number Model for Alkali Earth Metal OxidesSlide17
Z number Model for Poor Metal OxidesSlide18
Viable ModelsAlkali Earth Metal OxidesElectronegativity model:Z model:
Poor Metal Oxides
Electronegativity
model:
Z model:
Slide19
Transition and Rare Earth Difficulties Transition Metal OxideElectronegativity model: Range of values: 1.82 to 3.82
eV
Rare Earth Oxide
Electronegativity
model:
Range of values: 3.59 to 5.73
eV
Slide20
ResultsAlkali Earth Metal OxidesPoor Metal OxidesRare Earth Oxides
3.59 to 5.73
eV
Transition Metal Oxides
1.82 to 3.82
eVSlide21
Comparison Accepted ModelsSlide22
ConclusionThe behavior of binary oxides’ band gap can be related to the chemical groups on the periodic table Band gap is affected by the presence of a d orbital in the valence band
Band gap behavior can be modeled for individual chemical groups and rows of oxidesSlide23
Questions?
AcknowledgementsSlide24
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