Ebook: Organic Nanostructures: Science and Applications

Organic nanostructures have been studied extensively during the last five-ten years and this field is constantly growing both in view of technological applications and of the basic scientific interest for new physical phenomena. For instance, on the one hand, multicolour organic light-emitting diodes are in the stage of industrial production, organic-based lasers and field effect transistors have been demonstrated, and various molecular optoelectronic devices proposed. On the other hand, many important mechanisms both in photophysics and transport are still not completely understood, as mentioned in the Introductory lecture by the Nobel Laureate Alan Heeger.

In this “Enrico Fermi” School, the first one dedicated to advanced organic materials, the main research results and open problems in science and technology of organic nanostructures have been discussed; in particular, growth techniques, electronic and optical properties, device applications. The necessary background material has been covered and interdisciplinary aspects have been emphasized with the aim of a unified approach to the basic physical phenomena bridging the gap between standard graduate courses and the state of the art in the field.

The lecturers have provided authoritative and comprehensive tutorial reviews of the main issues involved in the science and technology of organic materials and their nanostructures. In particular, the following topics have been specifically addressed: charge carrier mobility and transport properties, electrical conductivity of conjugated polymers, charge transfer states in organics, photorefractivity in organics, energy transfer processes in organics, photophysics and fast spectroscopy, technology of polymer electronics and light-emitting devices.

Besides tutorial presentations, both lecturers and seminar speakers addressed the state of the art in the field of organic-based advanced materials. In particular, new results of great scientific relevance among the many discussed ones are, for instance: the realization of single-crystal organic devices of very high mobility, the demonstration of the strong-coupling regime in organic-based microcavities, the controlled n- and p-type doping of organic semiconductors, the use of single-molecule spectroscopy for fundamental molecular physics and quantum optics studies as well as a nanoprobe of the surrounding ambient, the development of nanomechanics based on nanotubes, the control of interfaces and thin-film properties in organic molecular deposition.

We would like to thank here all the lecturers and seminar speakers for their participation. Apart from the formal presentations, both senior scientists and young students have been involved in many lively discussions, we thank them all for their personal contributions. Both the tutorial and the research presentation are collected in the present volume of the “Enrico Fermi” School Proceedings Series. The course has been attended by the young scientists of today who will determine the development of this topical area in the future, we hope that through the present book many more students and scholars will have access to the contributions of the leading scientists of the field present in Varenna.

We thank the Italian Physical Society both for the financial support and the perfect organization. In particular, we thank all the Italian Physical Society staff that took care with personal dedication of all the participants and, later, helped us in editing the present volume.

Finally, we wish to thank also the sponsors that, apart from the Italian Physical Society, have contributed to the School: the EUROPEAN COMMUNITY, THE NATIONAL COUNCIL OF RESEARCH, THE UNESCO UVO-ROSTE OFFICE AND THE UNIVERSITY OF SALERNO.

V. M. AGRANOVICH AND G. C. LA ROCCA

Theoretical description of charge-transfer states is presented on the example of one-component organic molecular crystals. The classical approach where the charges are envisaged as localized is used as a starting point for discussing the quantum delocalization effects. General experience-based suggestions for constructing the model Hamiltonians are discussed, and the problems of parameter estimation are highlighted. The misleading aspects of the quantum description are given particular attention in relation to experimental data (photocurrent and electro-absorption). Crucial points are illustrated on the results of the past and of the very recent calculations. Wherever possible, the general context of the calculations is emphasized.

1. Introduction

2. Experimental observation of CT states

3. Theoretical description of CT states

4. Model Hamiltonian

5. Parametrization

6. Conceptual subtleties and pitfalls

7. Experimental verification

8. Intuitive conclusions

9. Concluding remarks

1. Introduction to organic photo- and semiconductors

2. Measurement techniques for charge carrier mobility

3. Charge carrier mobility in pure and perfect single crystals, experimental results

4. Charge carrier transport in polycrystalline thin films

5. Concluding remarks

1. Introduction

2. Production of charge carriers by light

3. Production of carriers by doping

4. Carrier injection at contacts

5. Transport in pristine conducting polymers

6. Theory of soliton and polaron dynamics in pristine polymers

7. Insulator-metal transition

1. Introduction

2. Molecular physics, nonlinear and quantum optics with single molecules

3. Probing solid-state dynamics with single molecules

4. Summary and outlook

1. Introduction

2. A mini-course on molecular optical response

3. Optical response of dimers

4. Pauli operators for Frenkel excitons

5. Linear optical properties of linear J-aggregates

6. Nonlinear optical properties of linear J-aggregates

7. Other aspects

8. Aggregates of other geometries

9. Conclusions

1. Introduction

2. Electronic excitations in organic solids

3. Oligomeric thin films: growth and properties

4. Two-dimensional patterning of organic thin films

5. Three-dimensional patterning

6. Organic electronics

7. Conclusions

In this contribution we present some aspects of why interfaces are important, how interfaces of organic thin films on inorganic substrates can be prepared under optimum conditions, how interfaces can decisively determine the properties of thin films, and how interfaces can be characterized under all relevant aspects. We concentrate on well-defined systems, i.e. model molecules on single-crystal substrates, prepared under optimised conditions in ultrahigh vacuum by sublimation techniques. We will briefly discuss a number of useful surface/interface characterization techniques and how these can contribute to a deeper understanding of the various properties. By means of a few examples we present results, experience, basic understanding, and some general conclusions which actually were derived from a much larger bulk of experiments and data. The main aspects concern the chemical bonding at the interface, the molecular orientation, the interface dipole and band offset, the interface ordering, and the growth properties of thin films.

1. Introduction and motivation

2. Substrates, molecular materials, and preparation techniques

3. Experimental methods for interface studies

4. Chemical bonding at organic/inorganic interfaces

5. Orientation

6. Work function, interface dipole, and band offset tuning

7. Interface ordering

8. Growth of thin organic films

9. Concluding remarks

1. Introduction

2. Experiment

3. Investigations on the doping mechanism

4. UPS/XPS investigation of interfaces of doped organic layers

5. Low-voltage organic light-emitting diodes

6. Conclusions

1. Photoinduced IRAV: ultrafast photogeneration of charged polarons

2. Electric-field--induced ionization of the exciton in PPV

3. Conclusion

1. Introduction and goals

2. Experimental procedures

3. Phenomenology of MEH-PPV solution and film photophysics

4. Aggregation effects on spectroscopy: the two-species model

5. Independent proof of the two-species model

6. Structural nature of the two species

7. Photoexcitation dynamics and origin of aggregation quenching

8. Overview and conclusions

1. Introduction

2. Electronic devices based on organic materials

3. Integrated device technology

4. Electronic properties of devices based on organic semiconductors

5. Challenges

6. Applications of organic electronics

7. Conclusions

1. Introduction

2. Comparison of display technologies and polymer OLED

3. Polymer light-emitting device technology

4. Ink jet printing

5. Conclusions and outlook

1. Introduction

2. Crystal growth and transistor preparation

3. Devices

4. Basic science

5. Conclusions

1. Introduction

2. Experimental details

3. Film growth, morphology, and structure

4. Optical properties

5. Conclusions

1. Introduction

2. Stokes shift in crystalline PTCDA

3. Displaced harmonic oscillator

4. Resonant Raman spectra of epitaxial films

5. Monomer absorption

6. Exciton transfer

7. k-space dispersion and low-temperature photoluminescence

8. Time-dependent density functional calculations for dimers

9. Heterostructures

10. Conclusion

1. Introduction

2. Materials and microcavity structures

3. Reflectivity measurements

4. Resonant excitation of strongly coupled microcavities

5. Optical hybridization of organic excitons

1. Energy transfer: an introductory discussion

2. Semiclassical description of the transfer

3. Modeling a specific structure

4. Results

5. Review of relevant experiments

6. Conclusions

1. Introduction

2. Fabrication of metallic nanostructures

3. Results and discussion

4. Summary and conclusions

1. Prologue

2. Introduction

3. The pump-probe experiment

4. Excited-state kinetics

5. Excited-states processes

6. Conclusion

1. Introduction

2. Origin of photorefractive effect

3. Light amplification in two-beam--coupling experiments

4. Materials

5. Hybrid photoconducting polymer liquid-crystal structures (HPCPLCS)

6. Performances of HPCPLCS

7. Applications

8. Conclusions

1. Introduction

2. Inorganic-organic perovskites

3. Modification of optical properties due to grating substrates

4. Conclusion

1. Introduction

2. Model

3. Optical absorption

4. Energy transfer

5. Concluding remarks

1. Introduction

2. Mixing of Frenkel and charge-transfer excitons in a finite molecular chain

3. Surface and bulk states in a finite molecular chain with mixing of Frenkel and charge-transfer excitons

4. Quantum confinement

5. Concluding remarks