Raphael Pfattner - Academia.edu (original) (raw)

Papers by Raphael Pfattner

Research paper thumbnail of CCDC 2097176: Experimental Crystal Structure Determination

The Cambridge Structural Database, 2022

Research paper thumbnail of Polymer Field-Effect Transistors – Stability

Research paper thumbnail of Air-stable Active Layer Materials for Organic Field-Effect Transistors

Research paper thumbnail of 本質的に伸縮可能な薄膜トランジスタへの応用のためのゴム誘電体の静電容量特性化【Powered by NICT】

Advanced Functional Materials, 2016

Research paper thumbnail of Stability Issues of Organic Thin-Film Transistors

Research paper thumbnail of Stability Issues of Organic Field-Effect Transistors

Research paper thumbnail of Organic electronics based on tetrathiafulvalene-derivatives: organic field-effect transistors and sensors

Nowadays, organic electronics has become a popular topic which is discussed all around with an in... more Nowadays, organic electronics has become a popular topic which is discussed all around with an increasing appearance of potential real applications on the market. This has been possible due to the pioneering work performed by scientists to study and understand the working mechanisms of those materials to be able to transfer this technology to easy, low-cost but nevertheless high performing device fabrication techniques. This thesis starts with a general introduction to the field of organic electronics keeping their inorganic counterparts in mind. Specially low-cost, light weight and flexibility are key features, that motivate the transfer of the outstanding properties of organic active materials towards device fabrication and technology on large areas (OLAE - Organic Large Area Electronics). Organic Field-Effect Transistors (OFETs) are one important potential application where organic active materials can be found. The main working mechanisms, including simple charge transport models, as well as the main device parameters of such devices are introduced and discussed. Tetrathiafulvalenes (TTFs), which exhibit two reversible oxidation processes, are an important family of organic donor molecules, that have a key impact on the world of organic electronics. The main characteristics of these molecules, which can form conducting charge transfer salts and can also work as organic semiconductors in their neutral state, are described. Further the potential of employing TTFs in devices, is highlighted. Two polymorphic forms of dithiophene-tetrathiafulvalene (DTTTF), i.e. alpha- and beta-DT-TTF were studied by means of confocal Raman spectroscopy and X-ray diffraction and employed as active material in different Organic Field-Effect Transistor (OFET) architectures. Both polymorphs exhibited excellent device performance, although the -phase revealed mobilities between two and ten times higher in accordance to the closer stacking of the molecules. Additionally, the OFET properties of three TTF families bearing electron-withdrawing groups were investigated, since it is known that the incorporation of such substituents to the organic semiconductor core can improve the device stability and give rise to electron transport. High p-channel OFET mobilities of up to 0.44 cm2/Vs were achieved for some of these materials and even some hints of electron transport were observed in one of them. A new technique, Electrical Time of Flight (EToF) measurements in devices with OFET structures, revealed ambipolar behavior in some TTF-derivatives. Moreover an easy, solution-based technology, zone casting, was used for the preparation of highly crystalline layers of different TTF-derivatives on flexible substrates and extended over large areas. An important issue to improve device performance in Organic Field-Effect Transistors (OFETs) is to minimize the contact resistance (RC) (i.e. enhance charge injection) which is mainly determined by the material used as source-drain electrodes as well as by the device configuration. In case of p-channel OFETs, for instance, the Fermi level of these electrodes should be close to the Highest Occupied Molecular Orbital (HOMO) level of the active material. Here we report a novel approach to grow organic source and drain contacts in organic single crystals of alpha-dithiophene-tetrathiafulvalene (DT-TTF) which leads to very high performing field-effect transistors (maximum muFE = 6.15 cm2/Vs). The investigation of the organic semiconductor/organic metal interface by means of Atomic Force Microscopy (AFM), Focused Ion Beam - Scanning Electron Microscopy (FIBSEM), Raman analysis and gated four probe measurements shows that the crystallization of DT-TTF on the electrodes does not damage the materials but causes a blending of them improving the contact. This work elucidates the larger versatility of organic metals in contrast to the inorganic ones, and highlights the importance of the contacts in OFETs not only in terms of the energy levels alignment but also with respect to the interface morphology. In a further study the temperature dependence of the best performing single crystal OFET was measured in both the linear and the saturation regime which allowed the estimation of the Density Of States (DOS) in the band gap. Ultra strain sensitive all-organic flexible thin-Films composed by a thin topmost conducting layer of Ion-Radical Salts (IRSs) based on tetrathiafulvalene (TTF)-derivatives embedded in a polymeric matrix, called also Bilayer (BL)-Films. Four BL-Films based on different IRS were studied in more detail, namely alpha-(BEDT-TTF)2I3, beta-(BEDT-TTF)2I3, (BET-TTF)2IxBr3-x and bet-(BET-TTF)2I3, by means of Energy-Dispersive X-ray spectroscopy (EDX), Scanning Electron Microscopy (SEM), X-ray and Electronic Paramagnetic Resonance (EPR). All samples exhibited a sheet resistance (RSHEET) of the order of 10 kOmega. To study the influence of strain on the change of the electrical resistance, an…

Research paper thumbnail of Polymer Field-Effect Transistors – Air Stability and Fabricational Issues

Semianual ISOTEC Meeting, Jul 6, 2006

Research paper thumbnail of CCDC 1460869: Experimental Crystal Structure Determination

An entry from the Cambridge Structural Database, the world's repository for small molecule cr... more An entry from the Cambridge Structural Database, the world's repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Research paper thumbnail of CCDC 737356: Experimental Crystal Structure Determination

An entry from the Cambridge Structural Database, the world's repository for small molecule cr... more An entry from the Cambridge Structural Database, the world's repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Research paper thumbnail of CCDC 974980: Experimental Crystal Structure Determination

An entry from the Cambridge Structural Database, the world's repository for small molecule cr... more An entry from the Cambridge Structural Database, the world's repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Research paper thumbnail of CCDC 812334: Experimental Crystal Structure Determination

An entry from the Cambridge Structural Database, the world's repository for small molecule cr... more An entry from the Cambridge Structural Database, the world's repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Research paper thumbnail of Stability Issues of Organic Thin-Film Transistors

Research paper thumbnail of TetramethylbenzidineTetrafluoroTCNQ (TMBTCNQF4): A Narrow-Gap Semiconducting Salt with Room-Temperature Relaxor Ferroelectric Behavior

Research paper thumbnail of Stability Issues of Organic Field-Effect Transistors

Research paper thumbnail of Structural and electronic characterisation of π-extended tetrathiafulvalene derivatives as active components in field-effect transistors

CrystEngComm, 2016

The electronic and structural properties of two tetrathiafulvalene derivatives bearing aromatic b... more The electronic and structural properties of two tetrathiafulvalene derivatives bearing aromatic benzene rings are reported. Thin film transistors of these materials show p-type characteristics with comparable mobility values. It is found that the rigidification of the molecule is beneficial for reducing the reorganisation energy but also has an unfavorable impact on the electronic structure dimensionality.

Research paper thumbnail of A bioinspired flexible organic artificial afferent nerve

Science, Jun 1, 2018

The distributed network of receptors, neurons, and synapses in the somatosensory system efficient... more The distributed network of receptors, neurons, and synapses in the somatosensory system efficiently processes complex tactile information. We used flexible organic electronics to mimic the functions of a sensory nerve. Our artificial afferent nerve collects pressure information (1 to 80 kilopascals) from clusters of pressure sensors, converts the pressure information into action potentials (0 to 100 hertz) by using ring oscillators, and integrates the action potentials from multiple ring oscillators with a synaptic transistor. Biomimetic hierarchical structures can detect movement of an object, combine simultaneous pressure inputs, and distinguish braille characters. Furthermore, we connected our artificial afferent nerve to motor nerves to construct a hybrid bioelectronic reflex arc to actuate muscles. Our system has potential applications in neurorobotics and neuroprosthetics.

Research paper thumbnail of Low-voltage polymer transistors on hydrophobic dielectrics and surfaces

JPhys materials, Mar 2, 2023

A set of unique features, including large-area solution processing on flexible and stretchable su... more A set of unique features, including large-area solution processing on flexible and stretchable substrates, make polymer semiconductors a promising material choice for a range of state-of-the-art applications in electronics, optoelectronics and sensing. Yet, an inherent weakness of polymer semiconductors remains their low dielectric constants, increasing their susceptibility toward unscreened dipoles. These dipoles are particularly prevalent at polymer-dielectric interfaces with high-k dielectrics, which are essential for the operation of devices such as low-voltage field-effect transistors. This shortcoming can be addressed by using self-assembled monolayers (SAMs) to passivate surfaces that impact charge transport. However, SAM-treatment also increases the hydrophobicity of surfaces and therefore poses a challenge for subsequent solution processing steps and complex packaging of devices. Here, we report low-voltage polymer transistors processed by spin coating of the polymer semiconductors on highly hydrophobic SAM-treated aluminum and hafnium oxide dielectrics (contact angles >100) through fine-tuning of the interfacial tension at the polymer-dielectric interface. This approach enables the processing and detailed characterization of near-amorphous (indacenodithiophene-cobenzothiadiazole) as well as semicrystalline (poly(2,5-bis(2-octyldodecyl)-3,6-di(thiophen-2-yl)diketopyrrolo[3,4-c]pyrrole-1,4-dione-alt-thieno[3,2-b]thiophen)) polymer semiconductors. We demonstrate polymer transistors that exhibit high on-currents and field-independent, charge carrier mobilities of 0.8 cm2 V−1s−1 at low operating voltages (<3 V).

Research paper thumbnail of CCDC 737358: Experimental Crystal Structure Determination

Related Article: F.Oton, R.Pfattner, N.S.Oxtoby, M.Mas-Torrent, K.Wurst, X.Fontrodona, Y.Olivier,... more Related Article: F.Oton, R.Pfattner, N.S.Oxtoby, M.Mas-Torrent, K.Wurst, X.Fontrodona, Y.Olivier, J.Cornil, J.Veciana, C.Rovira|2011|J.Org.Chem.|76|154|doi:10.1021/jo101817j

Research paper thumbnail of Selection of the two enantiotropic polymorphs of diF-TES-ADT in solution sheared thin film transistors

Journal of Materials Chemistry C, 2020

We report the effect of solution shearing speed on the performances of diF-TES-ADT-based OFETs. X... more We report the effect of solution shearing speed on the performances of diF-TES-ADT-based OFETs. X-ray diffraction reveals that the low-temperature phase is predominant at low shearing speed, while, upon increasing the speed, the high-tempertature phase prevails. The effect of polymorph composition on the electrical performances is reported with the best mobilities found in a mixture of the two polymorphs.

Research paper thumbnail of CCDC 2097176: Experimental Crystal Structure Determination

The Cambridge Structural Database, 2022

Research paper thumbnail of Polymer Field-Effect Transistors – Stability

Research paper thumbnail of Air-stable Active Layer Materials for Organic Field-Effect Transistors

Research paper thumbnail of 本質的に伸縮可能な薄膜トランジスタへの応用のためのゴム誘電体の静電容量特性化【Powered by NICT】

Advanced Functional Materials, 2016

Research paper thumbnail of Stability Issues of Organic Thin-Film Transistors

Research paper thumbnail of Stability Issues of Organic Field-Effect Transistors

Research paper thumbnail of Organic electronics based on tetrathiafulvalene-derivatives: organic field-effect transistors and sensors

Nowadays, organic electronics has become a popular topic which is discussed all around with an in... more Nowadays, organic electronics has become a popular topic which is discussed all around with an increasing appearance of potential real applications on the market. This has been possible due to the pioneering work performed by scientists to study and understand the working mechanisms of those materials to be able to transfer this technology to easy, low-cost but nevertheless high performing device fabrication techniques. This thesis starts with a general introduction to the field of organic electronics keeping their inorganic counterparts in mind. Specially low-cost, light weight and flexibility are key features, that motivate the transfer of the outstanding properties of organic active materials towards device fabrication and technology on large areas (OLAE - Organic Large Area Electronics). Organic Field-Effect Transistors (OFETs) are one important potential application where organic active materials can be found. The main working mechanisms, including simple charge transport models, as well as the main device parameters of such devices are introduced and discussed. Tetrathiafulvalenes (TTFs), which exhibit two reversible oxidation processes, are an important family of organic donor molecules, that have a key impact on the world of organic electronics. The main characteristics of these molecules, which can form conducting charge transfer salts and can also work as organic semiconductors in their neutral state, are described. Further the potential of employing TTFs in devices, is highlighted. Two polymorphic forms of dithiophene-tetrathiafulvalene (DTTTF), i.e. alpha- and beta-DT-TTF were studied by means of confocal Raman spectroscopy and X-ray diffraction and employed as active material in different Organic Field-Effect Transistor (OFET) architectures. Both polymorphs exhibited excellent device performance, although the -phase revealed mobilities between two and ten times higher in accordance to the closer stacking of the molecules. Additionally, the OFET properties of three TTF families bearing electron-withdrawing groups were investigated, since it is known that the incorporation of such substituents to the organic semiconductor core can improve the device stability and give rise to electron transport. High p-channel OFET mobilities of up to 0.44 cm2/Vs were achieved for some of these materials and even some hints of electron transport were observed in one of them. A new technique, Electrical Time of Flight (EToF) measurements in devices with OFET structures, revealed ambipolar behavior in some TTF-derivatives. Moreover an easy, solution-based technology, zone casting, was used for the preparation of highly crystalline layers of different TTF-derivatives on flexible substrates and extended over large areas. An important issue to improve device performance in Organic Field-Effect Transistors (OFETs) is to minimize the contact resistance (RC) (i.e. enhance charge injection) which is mainly determined by the material used as source-drain electrodes as well as by the device configuration. In case of p-channel OFETs, for instance, the Fermi level of these electrodes should be close to the Highest Occupied Molecular Orbital (HOMO) level of the active material. Here we report a novel approach to grow organic source and drain contacts in organic single crystals of alpha-dithiophene-tetrathiafulvalene (DT-TTF) which leads to very high performing field-effect transistors (maximum muFE = 6.15 cm2/Vs). The investigation of the organic semiconductor/organic metal interface by means of Atomic Force Microscopy (AFM), Focused Ion Beam - Scanning Electron Microscopy (FIBSEM), Raman analysis and gated four probe measurements shows that the crystallization of DT-TTF on the electrodes does not damage the materials but causes a blending of them improving the contact. This work elucidates the larger versatility of organic metals in contrast to the inorganic ones, and highlights the importance of the contacts in OFETs not only in terms of the energy levels alignment but also with respect to the interface morphology. In a further study the temperature dependence of the best performing single crystal OFET was measured in both the linear and the saturation regime which allowed the estimation of the Density Of States (DOS) in the band gap. Ultra strain sensitive all-organic flexible thin-Films composed by a thin topmost conducting layer of Ion-Radical Salts (IRSs) based on tetrathiafulvalene (TTF)-derivatives embedded in a polymeric matrix, called also Bilayer (BL)-Films. Four BL-Films based on different IRS were studied in more detail, namely alpha-(BEDT-TTF)2I3, beta-(BEDT-TTF)2I3, (BET-TTF)2IxBr3-x and bet-(BET-TTF)2I3, by means of Energy-Dispersive X-ray spectroscopy (EDX), Scanning Electron Microscopy (SEM), X-ray and Electronic Paramagnetic Resonance (EPR). All samples exhibited a sheet resistance (RSHEET) of the order of 10 kOmega. To study the influence of strain on the change of the electrical resistance, an…

Research paper thumbnail of Polymer Field-Effect Transistors – Air Stability and Fabricational Issues

Semianual ISOTEC Meeting, Jul 6, 2006

Research paper thumbnail of CCDC 1460869: Experimental Crystal Structure Determination

An entry from the Cambridge Structural Database, the world's repository for small molecule cr... more An entry from the Cambridge Structural Database, the world's repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Research paper thumbnail of CCDC 737356: Experimental Crystal Structure Determination

An entry from the Cambridge Structural Database, the world's repository for small molecule cr... more An entry from the Cambridge Structural Database, the world's repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Research paper thumbnail of CCDC 974980: Experimental Crystal Structure Determination

An entry from the Cambridge Structural Database, the world's repository for small molecule cr... more An entry from the Cambridge Structural Database, the world's repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Research paper thumbnail of CCDC 812334: Experimental Crystal Structure Determination

An entry from the Cambridge Structural Database, the world's repository for small molecule cr... more An entry from the Cambridge Structural Database, the world's repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Research paper thumbnail of Stability Issues of Organic Thin-Film Transistors

Research paper thumbnail of TetramethylbenzidineTetrafluoroTCNQ (TMBTCNQF4): A Narrow-Gap Semiconducting Salt with Room-Temperature Relaxor Ferroelectric Behavior

Research paper thumbnail of Stability Issues of Organic Field-Effect Transistors

Research paper thumbnail of Structural and electronic characterisation of π-extended tetrathiafulvalene derivatives as active components in field-effect transistors

CrystEngComm, 2016

The electronic and structural properties of two tetrathiafulvalene derivatives bearing aromatic b... more The electronic and structural properties of two tetrathiafulvalene derivatives bearing aromatic benzene rings are reported. Thin film transistors of these materials show p-type characteristics with comparable mobility values. It is found that the rigidification of the molecule is beneficial for reducing the reorganisation energy but also has an unfavorable impact on the electronic structure dimensionality.

Research paper thumbnail of A bioinspired flexible organic artificial afferent nerve

Science, Jun 1, 2018

The distributed network of receptors, neurons, and synapses in the somatosensory system efficient... more The distributed network of receptors, neurons, and synapses in the somatosensory system efficiently processes complex tactile information. We used flexible organic electronics to mimic the functions of a sensory nerve. Our artificial afferent nerve collects pressure information (1 to 80 kilopascals) from clusters of pressure sensors, converts the pressure information into action potentials (0 to 100 hertz) by using ring oscillators, and integrates the action potentials from multiple ring oscillators with a synaptic transistor. Biomimetic hierarchical structures can detect movement of an object, combine simultaneous pressure inputs, and distinguish braille characters. Furthermore, we connected our artificial afferent nerve to motor nerves to construct a hybrid bioelectronic reflex arc to actuate muscles. Our system has potential applications in neurorobotics and neuroprosthetics.

Research paper thumbnail of Low-voltage polymer transistors on hydrophobic dielectrics and surfaces

JPhys materials, Mar 2, 2023

A set of unique features, including large-area solution processing on flexible and stretchable su... more A set of unique features, including large-area solution processing on flexible and stretchable substrates, make polymer semiconductors a promising material choice for a range of state-of-the-art applications in electronics, optoelectronics and sensing. Yet, an inherent weakness of polymer semiconductors remains their low dielectric constants, increasing their susceptibility toward unscreened dipoles. These dipoles are particularly prevalent at polymer-dielectric interfaces with high-k dielectrics, which are essential for the operation of devices such as low-voltage field-effect transistors. This shortcoming can be addressed by using self-assembled monolayers (SAMs) to passivate surfaces that impact charge transport. However, SAM-treatment also increases the hydrophobicity of surfaces and therefore poses a challenge for subsequent solution processing steps and complex packaging of devices. Here, we report low-voltage polymer transistors processed by spin coating of the polymer semiconductors on highly hydrophobic SAM-treated aluminum and hafnium oxide dielectrics (contact angles >100) through fine-tuning of the interfacial tension at the polymer-dielectric interface. This approach enables the processing and detailed characterization of near-amorphous (indacenodithiophene-cobenzothiadiazole) as well as semicrystalline (poly(2,5-bis(2-octyldodecyl)-3,6-di(thiophen-2-yl)diketopyrrolo[3,4-c]pyrrole-1,4-dione-alt-thieno[3,2-b]thiophen)) polymer semiconductors. We demonstrate polymer transistors that exhibit high on-currents and field-independent, charge carrier mobilities of 0.8 cm2 V−1s−1 at low operating voltages (<3 V).

Research paper thumbnail of CCDC 737358: Experimental Crystal Structure Determination

Related Article: F.Oton, R.Pfattner, N.S.Oxtoby, M.Mas-Torrent, K.Wurst, X.Fontrodona, Y.Olivier,... more Related Article: F.Oton, R.Pfattner, N.S.Oxtoby, M.Mas-Torrent, K.Wurst, X.Fontrodona, Y.Olivier, J.Cornil, J.Veciana, C.Rovira|2011|J.Org.Chem.|76|154|doi:10.1021/jo101817j

Research paper thumbnail of Selection of the two enantiotropic polymorphs of diF-TES-ADT in solution sheared thin film transistors

Journal of Materials Chemistry C, 2020

We report the effect of solution shearing speed on the performances of diF-TES-ADT-based OFETs. X... more We report the effect of solution shearing speed on the performances of diF-TES-ADT-based OFETs. X-ray diffraction reveals that the low-temperature phase is predominant at low shearing speed, while, upon increasing the speed, the high-tempertature phase prevails. The effect of polymorph composition on the electrical performances is reported with the best mobilities found in a mixture of the two polymorphs.