1,721,122 research outputs found
Charge-carrier dynamics in organic LEDs
Full text linkAnyone who decides to buy a new mobile phone today is likely to buy a screen made from organic light-emitting diodes (OLEDs). OLEDs are a relatively new display technology and will probably account for the largest market share in the upcoming years. This is due to their brilliant colors, high achievable display resolution, and comparably simple processing. Since they are not based on the rigid crystal structure of classical semiconductors and can be produced as planar thin-film modules, they also enable the fabrication of large-area lamps on flexible substrates – an attractive scenario for future lighting systems. Despite these promising properties, the breakthrough of OLED lighting technology is still pending and requires further research.
The charge-carrier dynamics in an OLED determine its device functionality and, therefore, enable the understanding of fundamental physical concepts and phenomena.
From the description of charge-carrier dynamics, this work derives experimental methods and device concepts to optimize the efficiency and stability of OLEDs. OLEDs feature an electric current of charge carriers (electrons and holes) that are intended to recombine under the emission of light. This process is preceded by charge-carrier injection and their transport to the emission layer. These three aspects are discussed together in this work. First, a method is presented that quantifies injection resistances using a simple experiment. It provides a valuable opportunity to better understand and optimize injection layers. Subsequently, the charge carrier transport at high electrical currents, as required for OLEDs as bright lighting elements, will be investigated. Here, electro-thermal effects are presented that form physical limits for the design and function of OLED modules and explain their sudden failure. Finally, the dynamics and recombination of electro-statically bound charge carrier pairs, so-called excitons, are examined. Various options are presented for manipulating exciton dynamics in such a way that the emission behavior of the OLED can be adjusted according to specific requirements.:List of publications . . . . . . . . . . . . . . . . . v
List of abbreviations . . . . . . . . . . . . . . . . . ix
1 Introduction . . . . . . . . . . . . . . . . . 1
2 Fundamentals . . . . . . . . . . . . . . . . . 5
2.1 Light sources and the human society . . . . . . . . . . . . . . . . . 5
2.1.1 Human light perception . . . . . . . . . . . . . . . . . . . . 8
2.1.2 Physical light quantification . . . . . . . . . . . . . . . . . . 10
2.1.3 Non-visual light impact . . . . . . . . . . . . . . . . . . . . . 13
2.1.4 Implications for modern light sources . . . . . . . . . . . . . 15
2.2 Organic semiconductors . . . . . . . . . . . . . . . . . . . . . . . . 17
2.2.1 Molecular energy states . . . . . . . . . . . . . . . . . . . . . 18
2.2.2 Intramolecular state transitions . . . . . . . . . . . . . . . . 24
2.2.3 Molecular films . . . . . . . . . . . . . . . . . . . . . . . . . 31
2.2.4 Electrical doping . . . . . . . . . . . . . . . . . . . . . . . . 34
2.2.5 Charge-carrier transport . . . . . . . . . . . . . . . . . . . . 36
2.2.6 Exciton formation and recombination . . . . . . . . . . . . . 38
2.2.7 Exciton transfer . . . . . . . . . . . . . . . . . . . . . . . . . 41
2.3 Organic light-emitting diodes . . . . . . . . . . . . . . . . . . . . . 44
2.3.1 Structure and operation principle . . . . . . . . . . . . . . . 44
2.3.2 Metal-semiconductor interfaces . . . . . . . . . . . . . . . . 47
2.3.3 Typical operation characteristics . . . . . . . . . . . . . . . . 49
2.4 Colloidal nanocrystal emitters . . . . . . . . . . . . . . . . . . . . . 52
2.4.1 Terminology: Nanocrystals and quantum dots . . . . . . . . 52
2.4.2 The particle-in-a-box model . . . . . . . . . . . . . . . . . . 54
2.4.3 Surface passivation . . . . . . . . . . . . . . . . . . . . . . . 55
3 Materials and methods . . . . . . . . . . . . . . . . . 57
3.1 Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
3.1.1 OLED materials . . . . . . . . . . . . . . . . . . . . . . . . . 57
3.1.2 Materials for photoluminescence . . . . . . . . . . . . . . . . 60
3.2 Sample preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
3.2.1 Thermal evaporation . . . . . . . . . . . . . . . . . . . . . . 62
3.2.2 Solution processing . . . . . . . . . . . . . . . . . . . . . . . 64
3.3 Spectroscopy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
3.3.1 Absorbance spectroscopy . . . . . . . . . . . . . . . . . . . . 66
3.3.2 Photoluminescence quantum yield . . . . . . . . . . . . . . . 66
3.3.3 Excitation sources . . . . . . . . . . . . . . . . . . . . . . . 67
3.3.4 Sensitive EQE for absorber materials . . . . . . . . . . . . . 68
3.4 Exciton-lifetime analysis . . . . . . . . . . . . . . . . . . . . . . . . 69
3.4.1 Triplet lifetime . . . . . . . . . . . . . . . . . . . . . . . . . 69
3.4.2 Singlet-state lifetime . . . . . . . . . . . . . . . . . . . . . . 70
3.4.3 Lifetime extraction . . . . . . . . . . . . . . . . . . . . . . . 70
3.5 OLED characterization . . . . . . . . . . . . . . . . . . . . . . . . . 73
3.5.1 Current-voltage-luminance and quantum efficiency . . . . . . 73
3.5.2 Temperature-controlled evaluation . . . . . . . . . . . . . . . 74
4 Charge-carrier injection into doped organic films . . . . . . . . . . . . . . . . . 77
4.1 Ohmic injection contacts . . . . . . . . . . . . . . . . . . . . . . . . 79
4.2 Device architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
4.2.1 Conception . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
4.2.2 Device symmetry . . . . . . . . . . . . . . . . . . . . . . . . 80
4.2.3 Device homogeneity . . . . . . . . . . . . . . . . . . . . . . . 83
4.3 Resistance characteristics . . . . . . . . . . . . . . . . . . . . . . . . 84
4.3.1 Experimental results . . . . . . . . . . . . . . . . . . . . . . 84
4.3.2 Equivalent-circuit development . . . . . . . . . . . . . . . . 85
4.4 Impedance spectroscopy . . . . . . . . . . . . . . . . . . . . . . . . 92
4.4.1 Measurement fundamentals . . . . . . . . . . . . . . . . . . 92
4.4.2 Thickness dependence . . . . . . . . . . . . . . . . . . . . . 93
4.4.3 Temperature dependence . . . . . . . . . . . . . . . . . . . . 95
4.5 Depletion zone variation . . . . . . . . . . . . . . . . . . . . . . . . 97
4.6 Molybdenum oxide as a case study . . . . . . . . . . . . . . . . . . 99
5 Charge-carrier transport and self-heating in OLED lighting . . . . . . . . . . . . . . . . .101
5.1 Joule self-heating in OLEDs . . . . . . . . . . . . . . . . . . . . . . 104
5.1.1 Electrothermal feedback . . . . . . . . . . . . . . . . . . . . 104
5.1.2 Thermistors . . . . . . . . . . . . . . . . . . . . . . . . . . . 105
5.1.3 Cooling strategies . . . . . . . . . . . . . . . . . . . . . . . . 106
5.2 Self-heating causes lateral luminance inhomogeneities in OLEDs . . 108
5.2.1 The influence of transparent electrodes . . . . . . . . . . . . 108
5.2.2 Luminance inhomogeneities in large OLED panels . . . . . . 110
5.3 Electrothermal OLED models . . . . . . . . . . . . . . . . . . . . . 112
5.3.1 Perceiving an OLED as thermistor array . . . . . . . . . . . 112
5.3.2 The OLED as a single three-layer thermistor . . . . . . . . . 114
5.3.3 A numerical 3D model of heat and current flow . . . . . . . 116
5.4 OLED stack and experimental conception . . . . . . . . . . . . . . 118
5.5 The Switch-back effect in planar light sources . . . . . . . . . . . . 120
5.5.1 Predictions from numerical 3D modeling . . . . . . . . . . . 121
5.5.2 Experimental proof . . . . . . . . . . . . . . . . . . . . . . . 124
5.5.3 Variation of vertical heat flux . . . . . . . . . . . . . . . . . 127
5.5.4 Variation of the OLED area . . . . . . . . . . . . . . . . . . 131
5.6 Electrothermal tristabilities in OLEDs . . . . . . . . . . . . . . . . 133
5.6.1 Observing different burn-in schematics . . . . . . . . . . . . 133
5.6.2 Bistability and tristability in organic semiconductors . . . . 134
5.6.3 Experimental indications for attempted branch hopping . . . 138
5.6.4 Saving bright OLEDs from burning in . . . . . . . . . . . . 144
5.6.5 Taking another view onto the camera pictures . . . . . . . . 145
6 Charge-carrier recombination and exciton management . . . . . . . . . . . . . . . . .147
6.1 Optical down conversion . . . . . . . . . . . . . . . . . . . . . . . . 149
6.1.1 Spectral reshaping of visible OLEDs . . . . . . . . . . . . . 149
6.1.2 Infrared-emitting OLEDs . . . . . . . . . . . . . . . . . . . . 155
6.2 Dual-state Förster transfer . . . . . . . . . . . . . . . . . . . . . . . 158
6.2.1 Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . . 158
6.2.2 Verification . . . . . . . . . . . . . . . . . . . . . . . . . . . 159
6.3 Singlet fission and triplet fusion in rubrene . . . . . . . . . . . . . . 161
6.3.1 Photoluminescence of pure and doped rubrene films . . . . . 163
6.3.2 Electroluminescence transients of rubrene OLEDs . . . . . . 172
6.4 Charge transfer-state tuning by electric fields . . . . . . . . . . . . . 177
6.4.1 CT-state tuning via doping variation . . . . . . . . . . . . . 177
6.4.2 CT-state tuning via voltage . . . . . . . . . . . . . . . . . . 180
6.5 Excursus: Exciton-spin mixing for wavelength identification . . . . 183
6.5.1 Characteristics of the active film . . . . . . . . . . . . . . . . 184
6.5.2 Conception . . . . . . . . . . . . . . . . . . . . . . . . . . . 186
6.5.3 Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187
6.5.4 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 188
6.5.5 Application demonstrations . . . . . . . . . . . . . . . . . . 192
6.5.6 All-organic device . . . . . . . . . . . . . . . . . . . . . . . . 195
6.5.7 Device limitations and prospects . . . . . . . . . . . . . . . . 198
7 Conclusion and outlook . . . . . . . . . . . . . . . . . 207
7.1 Charge-carrier injection into doped films . . . . . . . . . . . . . . . 207
7.2 Charge-carrier transport in hot OLEDs . . . . . . . . . . . . . . . . 208
7.2.1 Prospects for OLED lighting facing tristable behavior . . . . 209
7.2.2 Outlook: Accessing the hidden PDR 2 region . . . . . . . . . 210
7.3 Charge-carrier recombination and spin mixing . . . . . . . . . . . . 211
7.3.1 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . 211
7.3.2 Outlook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 211
Bibliography. . . . . . . . . . . . . . . . . 215
Acknowledgements . . . . . . . . . . . . . . . . . 249Wer sich heute für ein neues Mobiltelefon entscheidet, kauft damit wahrscheinlich einen Bildschirm aus organischen Leuchtdioden (OLEDs). Durch ihre brillanten Farben, die hohe erreichbare Auflösung und eine vergleichsweise einfache Prozessierung werden OLEDs als relativ neue Bildschirmtechnologie in den nächsten Jahren wohl den größten Marktanteil ausmachen. Da sie nicht auf der starren Kristallstruktur klassischer Halbleiter beruhen und als planare Dünnschichtmodule produziert werden können, ermöglichen sie außerdem die Fertigung großer Flächenstrahler auf flexiblen Substraten – ein sehr attraktives Szenario für zukünftige Beleuchtungssysteme. Trotz dieser vielversprechenden Eigenschaften steht der Durchbruch der OLED-Technologie als Leuchtmittel noch aus und erfordert weitere Forschung. Die Dynamik der Ladungsträger (Elektronen und Löcher) in einer OLED charakterisiert wichtige Teile der Bauteilfunktion und ermöglicht daher das Verständnis grundlegender physikalischer Konzepte und Phänomene. Diese Arbeit leitet anhand dieser Beschreibung experimentelle Methoden und Bauteilkonzepte ab, um die Effizienz und Stabilität von OLEDs zu optimieren.
OLEDs zeichnen sich dadurch aus, dass ein elektrischer Strom aus Ladungsträgern (Elektronen und Löchern) möglichst effizient unter Aussendung von Licht rekombiniert. Diesem Prozess geht eine Ladungsträgerinjektion und deren Transport zur Emissionsschicht voraus. Diese drei Aspekte werden in dieser Arbeit zusammenhängend diskutiert. Als erstes wird eine Methode vorgestellt, die Injektionswiderstände anhand eines einfachen Experimentes quantifiziert. Sie bildet eine wertvolle Möglichkeit, Injektionsschichten besser zu verstehen und zu optimieren. Anschließend wird der Ladungsträgertransport bei hohen elektrischen Strömen untersucht, wie sie für OLEDs als helle Beleuchtungselemente nötig sind. Hier werden elektro-thermische Effekte vorgestellt, die physikalische Grenzen für das Design und die Funktion von OLED Modulen bilden und deren plötzliches Versagen erklären. Abschließend wird die Dynamik der stark elektrostatisch gebundenen Ladungsträgerpaare, sogenannter Exzitonen, kurz vor deren Rekombination untersucht. Es werden verschiedene Möglichkeiten vorgestellt sie so zu manipulieren, dass sich das Abstrahlverhalten der OLED anhand bestimmter Anforderungen einstellen lässt.:List of publications . . . . . . . . . . . . . . . . . v
List of abbreviations . . . . . . . . . . . . . . . . . ix
1 Introduction . . . . . . . . . . . . . . . . . 1
2 Fundamentals . . . . . . . . . . . . . . . . . 5
2.1 Light sources and the human society . . . . . . . . . . . . . . . . . 5
2.1.1 Human light perception . . . . . . . . . . . . . . . . . . . . 8
2.1.2 Physical light quantification . . . . . . . . . . . . . . . . . . 10
2.1.3 Non-visual light impact . . . . . . . . . . . . . . . . . . . . . 13
2.1.4 Implications for modern light sources . . . . . . . . . . . . . 15
2.2 Organic semiconductors . . . . . . . . . . . . . . . . . . . . . . . . 17
2.2.1 Molecular energy states . . . . . . . . . . . . . . . . . . . . . 18
2.2.2 Intramolecular state transitions . . . . . . . . . . . . . . . . 24
2.2.3 Molecular films . . . . . . . . . . . . . . . . . . . . . . . . . 31
2.2.4 Electrical doping . . . . . . . . . . . . . . . . . . . . . . . . 34
2.2.5 Charge-carrier transport . . . . . . . . . . . . . . . . . . . . 36
2.2.6 Exciton formation and recombination . . . . . . . . . . . . . 38
2.2.7 Exciton transfer . . . . . . . . . . . . . . . . . . . . . . . . . 41
2.3 Organic light-emitting diodes . . . . . . . . . . . . . . . . . . . . . 44
2.3.1 Structure and operation principle . . . . . . . . . . . . . . . 44
2.3.2 Metal-semiconductor interfaces . . . . . . . . . . . . . . . . 47
2.3.3 Typical operation characteristics . . . . . . . . . . . . . . . . 49
2.4 Colloidal nanocrystal emitters . . . . . . . . . . . . . . . . . . . . . 52
2.4.1 Terminology: Nanocrystals and quantum dots . . . . . . . . 52
2.4.2 The particle-in-a-box model . . . . . . . . . . . . . . . . . . 54
2.4.3 Surface passivation . . . . . . . . . . . . . . . . . . . . . . . 55
3 Materials and methods . . . . . . . . . . . . . . . . . 57
3.1 Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
3.1.1 OLED materials . . . . . . . . . . . . . . . . . . . . . . . . . 57
3.1.2 Materials for photoluminescence . . . . . . . . . . . . . . . . 60
3.2 Sample preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
3.2.1 Thermal evaporation . . . . . . . . . . . . . . . . . . . . . . 62
3.2.2 Solution processing . . . . . . . . . . . . . . . . . . . . . . . 64
3.3 Spectroscopy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
3.3.1 Absorbance spectroscopy . . . . . . . . . . . . . . . . . . . . 66
3.3.2 Photoluminescence quantum yield . . . . . . . . . . . . . . . 66
3.3.3 Excitation sources . . . . . . . . . . . . . . . . . . . . . . . 67
3.3.4 Sensitive EQE for absorber materials . . . . . . . . . . . . . 68
3.4 Exciton-lifetime analysis . . . . . . . . . . . . . . . . . . . . . . . . 69
3.4.1 Triplet lifetime . . . . . . . . . . . . . . . . . . . . . . . . . 69
3.4.2 Singlet-state lifetime . . . . . . . . . . . . . . . . . . . . . . 70
3.4.3 Lifetime extraction . . . . . . . . . . . . . . . . . . . . . . . 70
3.5 OLED characterization . . . . . . . . . . . . . . . . . . . . . . . . . 73
3.5.1 Current-voltage-luminance and quantum efficiency . . . . . . 73
3.5.2 Temperature-controlled evaluation . . . . . . . . . . . . . . . 74
4 Charge-carrier injection into doped organic films . . . . . . . . . . . . . . . . . 77
4.1 Ohmic injection contacts . . . . . . . . . . . . . . . . . . . . . . . . 79
4.2 Device architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
4.2.1 Conception . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
4.2.2 Device symmetry . . . . . . . . . . . . . . . . . . . . . . . . 80
4.2.3 Device homogeneity . . . . . . . . . . . . . . . . . . . . . . . 83
4.3 Resistance characteristics . . . . . . . . . . . . . . . . . . . . . . . . 84
4.3.1 Experimental results . . . . . . . . . . . . . . . . . . . . . . 84
4.3.2 Equivalent-circuit development . . . . . . . . . . . . . . . . 85
4.4 Impedance spectroscopy . . . . . . . . . . . . . . . . . . . . . . . . 92
4.4.1 Measurement fundamentals . . . . . . . . . . . . . . . . . . 92
4.4.2 Thickness dependence . . . . . . . . . . . . . . . . . . . . . 93
4.4.3 Temperature dependence . . . . . . . . . . . . . . . . . . . . 95
4.5 Depletion zone variation . . . . . . . . . . . . . . . . . . . . . . . . 97
4.6 Molybdenum oxide as a case study . . . . . . . . . . . . . . . . . . 99
5 Charge-carrier transport and self-heating in OLED lighting . . . . . . . . . . . . . . . . .101
5.1 Joule self-heating in OLEDs . . . . . . . . . . . . . . . . . . . . . . 104
5.1.1 Electrothermal feedback . . . . . . . . . . . . . . . . . . . . 104
5.1.2 Thermistors . . . . . . . . . . . . . . . . . . . . . . . . . . . 105
5.1.3 Cooling strategies . . . . . . . . . . . . . . . . . . . . . . . . 106
5.2 Self-heating causes lateral luminance inhomogeneities in OLEDs . . 108
5.2.1 The influence of transparent electrodes . . . . . . . . . . . . 108
5.2.2 Luminance inhomogeneities in large OLED panels . . . . . . 110
5.3 Electrothermal OLED models . . . . . . . . . . . . . . . . . . . . . 112
5.3.1 Perceiving an OLED as thermistor array . . . . . . . . . . . 112
5.3.2 The OLED as a single three-layer thermistor . . . . . . . . . 114
5.3.3 A numerical 3D model of heat and current flow . . . . . . . 116
5.4 OLED stack and experimental conception . . . . . . . . . . . . . . 118
5.5 The Switch-back effect in planar light sources . . . . . . . . . . . . 120
5.5.1 Predictions from numerical 3D modeling . . . . . . . . . . . 121
5.5.2 Experimental proof . . . . . . . . . . . . . . . . . . . . . . . 124
5.5.3 Variation of vertical heat flux . . . . . . . . . . . . . . . . . 127
5.5.4 Variation of the OLED area . . . . . . . . . . . . . . . . . . 131
5.6 Electrothermal tristabilities in OLEDs . . . . . . . . . . . . . . . . 133
5.6.1 Observing different burn-in schematics . . . . . . . . . . . . 133
5.6.2 Bistability and tristability in organic semiconductors . . . . 134
5.6.3 Experimental indications for attempted branch hopping . . . 138
5.6.4 Saving bright OLEDs from burning in . . . . . . . . . . . . 144
5.6.5 Taking another view onto the camera pictures . . . . . . . . 145
6 Charge-carrier recombination and exciton management . . . . . . . . . . . . . . . . .147
6.1 Optical down conversion . . . . . . . . . . . . . . . . . . . . . . . . 149
6.1.1 Spectral reshaping of visible OLEDs . . . . . . . . . . . . . 149
6.1.2 Infrared-emitting OLEDs . . . . . . . . . . . . . . . . . . . . 155
6.2 Dual-state Förster transfer . . . . . . . . . . . . . . . . . . . . . . . 158
6.2.1 Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . . 158
6.2.2 Verification . . . . . . . . . . . . . . . . . . . . . . . . . . . 159
6.3 Singlet fission and triplet fusion in rubrene . . . . . . . . . . . . . . 161
6.3.1 Photoluminescence of pure and doped rubrene films . . . . . 163
6.3.2 Electroluminescence transients of rubrene OLEDs . . . . . . 172
6.4 Charge transfer-state tuning by electric fields . . . . . . . . . . . . . 177
6.4.1 CT-state tuning via doping variation . . . . . . . . . . . . . 177
6.4.2 CT-state tuning via voltage . . . . . . . . . . . . . . . . . . 180
6.5 Excursus: Exciton-spin mixing for wavelength identification . . . . 183
6.5.1 Characteristics of the active film . . . . . . . . . . . . . . . . 184
6.5.2 Conception . . . . . . . . . . . . . . . . . . . . . . . . . . . 186
6.5.3 Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187
6.5.4 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 188
6.5.5 Application demonstrations . . . . . . . . . . . . . . . . . . 192
6.5.6 All-organic device . . . . . . . . . . . . . . . . . . . . . . . . 195
6.5.7 Device limitations and prospects . . . . . . . . . . . . . . . . 198
7 Conclusion and outlook . . . . . . . . . . . . . . . . . 207
7.1 Charge-carrier injection into doped films . . . . . . . . . . . . . . . 207
7.2 Charge-carrier transport in hot OLEDs . . . . . . . . . . . . . . . . 208
7.2.1 Prospects for OLED lighting facing tristable behavior . . . . 209
7.2.2 Outlook: Accessing the hidden PDR 2 region . . . . . . . . . 210
7.3 Charge-carrier recombination and spin mixing . . . . . . . . . . . . 211
7.3.1 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . 211
7.3.2 Outlook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 211
Bibliography. . . . . . . . . . . . . . . . . 215
Acknowledgements . . . . . . . . . . . . . . . . . 24
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Bringing Light to Solid-State Electrolytes: The Polymer Light-Emitting Electrochemical Cell
No full textDispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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