Determination of the transport levels in thin films of organic semiconductors [Elektronische Ressource] / vorgelegt von Stefan Krause

Stefan Krause

Sujets

• Physik

Informations

• Publié par: julius-maximilians-universitat_wurzburg
• Publié le: 01 janvier 2009
• Nombre de lectures: 123
• Langue: Deutsch
• Poids de l'ouvrage: 31 Mo

Extrait

Determination of the transport levels
in thin films of organic
semiconductors
Dissertation zur Erlangung des
naturwissenschaftlichen Doktorgrades
der Bayerischen Julius - Maximilians - Universität Würzburg
vorgelegt von
Stefan Krause
aus Jena
Würzburg 2009Eingereicht am: 29.6.2009
bei der Fakultät für Physik und Astronomie
1. Gutachter: Prof. Dr. E. Umbach
2.hter: Prof. Dr. J. Pflaum
der Dissertation.
1. Prüfer: Prof. Dr. E. Umbach
2. Prof. Dr. J. Pflaum
3. Prüfer: Prof. Dr. C. Honerkamp
im Promotionskolloquium
Tag des Promotionskolloquiums: 27.7.2009
Doktorurkunde ausgehändigt am:Eidesstattliche Erklärung
Ich versichere hiermit an Eides statt, dass ich die vorliegende Dissertation eigenständig,
d. h. insbesondere selbständig und ohne Hilfe eines kommerziellen Promotionsberaters
angefertigt und keine anderen als die angegebenen Quellen und Hilfsmittel verwendet
habe.
Stefan Krause, Las Vegas, den 23.6.2009Contents
Eidesstattliche Erklärung III
List of Figures VII
List of Tables XIII
List of Abbreviations XIV
1. Introduction 1
2. Influences on the energetic position of the transport levels 3
2.1. Polarization . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1.1. Gas phase vs. solid state . . . . . . . . . . . . . . 8
2.1.2. Differences between surface and bulk . . . . . . . 10
2.1.3. Conclusions on polarization induced intermolecu-
lar screening . . . . . . . . . . . . . . . . . . . . . 12
2.2. Film morphology and thickness . . . . . . . . . . . . . . . 13
2.2.1. Mor information from spectroscopic data . 14
2.2.2. Growth mode of PTCDA . . . . . . . . . . . . . . . 16
2.2.3. Growth mode of Alq3 . . . . . . . . . . . . . . . . 18
2.2.4. Growth mode of CuPc . . . . . . . . . . . . . . . . 19
2.2.5. Growth mode of DIP . . . . . . . . . . . . . . . . . 20
2.2.6. Growth mode of PBI-H4 . . . . . . . . . . . . . . . 25
2.2.7. Conclusions on growth modes . . . . . . . . . . . 26
2.3. Band alignment . . . . . . . . . . . . . . . . . . . . . . . . 27
2.3.1. Vacuum level vs. Fermi level alignment . . . . . . 27
2.3.2. Interface dipoles . . . . . . . . . . . . . . . . . . . 29
2.3.3. Experimental results . . . . . . . . . . . . . . . . . 31
IV2.4. Band bending . . . . . . . . . . . . . . . . . . . . . . . . . 31
2.4.1. Theory of band bending . . . . . . . . . . . . . . . 32
2.4.2. Experimental results . . . . . . . . . . . . . . . . . 33
2.5. Diindenoperylene - Different geometric film structures for
one molecule . . . . . . . . . . . . . . . . . . . . . . . . . 38
2.5.1. Dependence of geometric structure on sample prepa-
ration . . . . . . . . . . . . . . . . . . . . . . . . . 38
2.6. How geometric structure influences the UPS/IPS - spec-
trum: Diindenoperylene . . . . . . . . . . . . . . . . . . . 61
2.6.1. DFT calculations . . . . . . . . . . . . . . . . . . . 61
2.6.2. The DIP-metal interface (monolayer investigation) 66
2.6.3. Comparison of the multilayer phases . . . . . . . . 71
2.6.4. How structural changes cause IP changes . . . . . 77
2.6.5. Multilayer phase transition in the UPS . . . . . . . 79
2.6.6. HREELS of the different phases . . . . . . . . . . 80
2.6.7. Summary and Conclusions . . . . . . . . . . . . . 85
2.7. Summary and Conclusions . . . . . . . . . . . . . . . . . 87
3. Peak broadening mechanisms 89
3.1. Lifetime . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
3.2. Experimental resolution . . . . . . . . . . . . . . . . . . . 91
3.3. Band dispersion and bending . . . . . . . . . . . . . . . . 92
3.4. Structural inhomogeneities . . . . . . . . . . . . . . . . . 94
3.5. Vibration and phonon coupling . . . . . . . . . . . . . . . 96
3.6. Static and dynamic screening . . . . . . . . . . . . . . . . 98
3.7. Summary and conclusions . . . . . . . . . . . . . . . . . . 100
4. Determination of the transport levels and their gap 102
4.1. Inorganic semiconductors . . . . . . . . . . . . . . . . . . 102
4.1.1. Si(001) and its preparation . . . . . . . . . . . . . 103
4.1.2. Positioning in the Brillouin zone . . . . . . . . . . . 104
4.1.3. Influence of surface states . . . . . . . . . . . . . . 108
4.1.4. Position of the transport levels in the spectrum . . 116
4.2. Organic semiconductors . . . . . . . . . . . . . . . . . . . 119
4.2.1. Position of the transport levels in the spectrum . . 120
4.2.2. Determination of exciton binding energies . . . . . 125
V4.3. Summary and Conclusions . . . . . . . . . . . . . . . . . 128
5. Summary 130
6. Zusammenfassung 133
Bibliography 137
A. IPS radiation damage for organic semiconductors 150
B. Most intense infrared active modes 152
VIList of Figures
2.1. Relaxation during the process of photoemission. . . . . . . . . 4
2.2. Polaron formation . . . . . . . . . . . . . . . . . . . . . . . . 6
2.3. Comparison of ionization potentials for solid state and gas
phase of naphthalene determined by UPS . . . . . . . . . . . 8
2.4. Comparison of the UPS of PTCDA in gas phase and of a
multilayer film on Ag(111) . . . . . . . . . . . . . . . . . . . 9
2.5. Sketchofthedifferentsurroundingsofmoleculesatthesurface
and in the bulk of a polarizable medium . . . . . . . . . . . . 10
2.6. Comparison of the HOMO of Anthracene in gas phase and
the two angles (20 and 80 ) of the solid state sample . . . . . 12
2.7. Attenuation behavior of the substrate XPS signal with grow-
ing film thickness for the three growth modes . . . . . . . . . 15
2.8. Chemical structure of Perylene - 3,4,9,10 - Tetracarboxylic
Dianhydride. . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
2.9. Chemical structure of Aluminum Tris(8-Hydroxyquinoline). . 17
2.10.Thickness dependent attenuation of the Ag 3d intensity for
Alq . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183
2.11.Chemical structure of (29H, 31H-Phthalocyaninato(2-)-N29,
N30, N31, N32)Copper. . . . . . . . . . . . . . . . . . . . . . 19
2.12.Attenuation of the silver substrate with increasing CuPc cov-
erage for T <200K . . . . . . . . . . . . . . . . . . . . 19Substrate
2.13.Chemical structure of Diindeno-Perylene. . . . . . . . . . . . 20
2.14.Thickness dependent attenuation of the Ag 3d intensity for
DIP prepared at substrate temperatures below 150K. . . . . . 21
2.15.Photograph of the Ag(111) crystal . . . . . . . . . . . . . . . 22
2.16.Thickness dependent attenuation of the Ag 3d intensity for
DIP prepared at substrate temperatures of about 210K. . . . 22
2.17.Growth mode for DIP on Ag(111) at T = 210K . . . . 23Substrate
VII2.18.Photograph of a DIP film prepared at 210K and the same film
after 30 minutes at 350K . . . . . . . . . . . . . . . . . . . . 24
2.19.Thickness dependent attenuation of the Ag 3d intensity for
DIP prepared at substrate temperatures above 350K. . . . . . 24
2.20.Growth behavior for DIP at T = 350K if the layersSubstrate
are prepared in more than one step. . . . . . . . . . . . . . . 25
2.21.ChemicalstructureofN,N’-Di(2,2,3,3,4,4,4-Heptafluorobutyl)
- 3,4,9,10. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
2.22.Sketch of the two possible types of band alignment between
metal substrate and organic semiconductors. . . . . . . . . . 28
2.23.Overview about the mechanisms that form and influence the
interface dipole between metal and organic film. . . . . . . . . 29
2.24.Overviewofthepossibletypesofabandbendingwithgrowing
film thickness in thin films of organic semiconductors. . . . . 33
2.25.Thickness dependent position of the frontier orbitals and the
vacuum level for PTCDA . . . . . . . . . . . . . . . . . . . . 35
2.26.Thickness dependent position of the frontier orbitals and the
vacuum level for CuPc . . . . . . . . . . . . . . . . . . . . . 35
2.27.Thickness dependent position of the frontier orbitals and the
vacuum level for Alq . . . . . . . . . . . . . . . . . . . . . . 363
2.28.Thickness dependent position of the frontier orbitals and the
vacuum level for DIP grown below 150K substrate temperature 36
2.29.Thickness dependent position of the frontier orbitals and the
vacuum level for DIP grown at 210K substrate temperature . 37
2.30.Thickness dependent position of the frontier orbitals and the
vacuum level for DIP grown above 350K substrate temperature 37
2.31.Series of LEED patterns of the DIP monolayer on Ag(111) . . 40
2.32.SPALEED diffractogram of a monolayer DIP on . . . 40
2.33.Series of diffractograms showing the monolayer of DIP on
Ag(111) for different temperatures . . . . . . . . . . . . . . . 41
2.34.Series of SPALEED line scans (300 K to 370 K) for a mono-
layer DIP on Ag(111) . . . . . . . . . . . . . . . . . . . . . . 42
2.35.Diffractogram of the monolayer DIP on Ag(111) . . . . . . . 43
2.36.Line scan through the (0,0) - spot of the monolayer DIP and
one scan perpendicular to the first . . . . . . . . . . . . . . . 44
VIII2.37.Model of the arrangement of the DIP molecules on the silver
surface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
2.38.LEED pattern of a 5 - 6 layer thick DIP film on Ag(111). The
substrate temperature during deposition was 125 K. E =kin
26 eV . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
2.39.SPALEED Pattern for a DIP multilayer (5 - 6 layers) grown
at 117 K. E = 35 eV . . . . . .