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Papers by Alberto Riminucci
ACS Applied Electronic Materials
ACS Applied Materials & Interfaces, Feb 5, 2019
The understanding of magnetoresistance (MR) in organic spin valves (OSVs) based on molecular semi... more The understanding of magnetoresistance (MR) in organic spin valves (OSVs) based on molecular semiconductors is still incomplete after its demonstration more than a decade ago. While carrier concentration may play an essential role in spin transport in these devices, direct experimental evidence of its importance is lacking. We probed the role of charge carrier concentration by studying the interplay between MR and multilevel resistive switching in OSVs. The present work demonstrates that all salient features of these devices, particularly the intimate correlation between MR and resistance, can be accounted for by the impurity band model, based on oxygen migration. Finally, we highlight the critical 2 importance of carrier concentration in determining spin transport and MR in OSVs and the role of interface-mediated oxygen migration in controlling the OSVs response.
The Journal of Physical Chemistry C, 2021
The inorganic/molecular spinterface is an ideal platform for generating extraordinary spin effect... more The inorganic/molecular spinterface is an ideal platform for generating extraordinary spin effects. Understanding and controlling these spin-related effects is mandatory for the exploitation of such interfaces in devices. For this purpose, we have investigated the adsorption of α-sexithiophene (α-6T) on La 0.7 Sr 0.3 MnO 3 (LSMO), as one of the prototypical material combinations used in organic spintronic devices. Atomic force microscopy, confocal photoluminescence, Xray photoelectron spectroscopy, and metastable de-excitation spectroscopy unraveled the structure and electronic configuration of 6T for various surface coverages. This data set allowed the determination of characteristic features of occupied states, the band diagram and the work function. Finally, density functional theory enabled us to establish that the spin polarization in 6T molecular orbitals critically depends on the termination layer of LSMO. We believe that this research provides important hints for a comprehensive understanding of spinterface effects in general and provides key suggestions for further engineering of LSMO/6T-based devices. INTRODUCTION: Hybridization at the interface between molecular entities and ferromagnetic metals leads to drastic changes of the properties of both layers [1,2]. Notably, an increase of spin polarization of states around the Fermi level [2], modulation of the magnetic anisotropy [3] and spin reorientation transitions were observed in ferromagnetic layers as well as the appearance of spin polarized states in the molecular material [5]. Such new hybrid interfaces with unexpected spin functionality, named after the seminal paper by Sanvito as "spinterfaces" [6], act as a key element at the molecular level for engineering the properties and the performance of spin-devices. Among the plethora of spinterfaces, those including half-metallic ferromagnetic oxides such as La 0.7 Sr 0.3 MnO 3 (LSMO) are of special interest. LSMO has been coupled to a variety of organic molecules and successfully used in spintronic devices [7,8], even showing the inversion of the sign of the polarization upon the deposition of an organic molecule [9]. Nonetheless, the variability of the composition of the termination layer of LSMO [10-12] hindered a reliable investigation of its interface with organic molecules. In this paper we focus on the coupling between a π-conjugated oligothiophene, 6T (sexithiophene), and LSMO; one of the first hybrid interfaces used in spin injection devices [13]. 6T is a rodlike model organic molecule [14] which contains six thiophene rings linked together; it can be easily sublimated in ultrahigh vacuum (UHV), a prerequisite for the control and reproducibility of interfacial states, and it is also known to form ordered thin layers on solid surfaces. Here, the growth process of 6T on
ACS Applied Materials & Interfaces, 2018
Scientific reports, Jan 10, 2014
The outgrowth formation in inorganic thin films is a dramatic problem that has limited the techno... more The outgrowth formation in inorganic thin films is a dramatic problem that has limited the technological impact of many techniques and materials. Outgrowths are often themselves part of the films, but are detrimental for vertical junctions since they cause short-circuits or work as defects, compromising the reproducibility and in some cases the operation of the corresponding devices. The problem of outgrowth is particularly relevant in ablation-based methods and in some complex oxides, but is present in a large variety of systems and techniques. Here we propose an efficient local electrochemical method to selectively decompose the outgrowths of conductive oxide thin films by electrochemical decomposition, without altering the properties of the background film. The process is carried out using the same set-up as for local oxidation nanolithography, except for the sign of the voltage bias and it works at the nanoscale both as serial method using a scanning probe and as parallel method...
Applied Physics Letters, 2013
We investigate spin precession (Hanle effect) in the prototypical organic spintronic giant magnet... more We investigate spin precession (Hanle effect) in the prototypical organic spintronic giant magnetoresistance (GMR) device La 0.7 Sr 0.3 MnO 3 (LSMO)/tris(8-hydroxyquinoline)(Alq3)/AlOx/Co. The Hanle effect is not observed in measurements taken by sweeping a magnetic field at different angles from the plane of the device. As possible explanations we discuss the tilting out of plane of the magnetization of the electrodes, exceptionally high mobility or hot spots. Our results call for a greater understanding of spin injection and transport in such devices.
Information and communication technology (ICT) is calling for solutions enabling lower power cons... more Information and communication technology (ICT) is calling for solutions enabling lower power consumption, further miniaturization and multi-functionality requiring the development of new device concepts and new materials. A fertile approach to meet such demands is the introduction of the spin degree of freedom into electronics devices, an approach commonly known as spintronics. This already lead to a revolution in the information storage (GMR read heads) in the last decades. Nowadays, the challenge is to bring spintronics also into devices dedicated to logics, communications and storage within the same material technology [1]. In this context the electric control of the magnetoresistance represents one of the most promising issues enabling both further miniaturization and multifunctional operation of spintronic devices. We will discuss the multi-functionality as an intrinsic characteristics of organic based spintronic devices [2] leading to conceptually new device paradigms. We will...
Journal of Colloid and Interface Science
The possible influence of internal barrier dynamics on spin, charge transport and their fluctuati... more The possible influence of internal barrier dynamics on spin, charge transport and their fluctuations in organic spintronics remains poorly understood. Here we present investigation of the electron transport and low frequency noise at temperatures down to 0.3K in magnetic tunnel junctions with an organic PTCDA barriers with thickness up to 5 nm in the tunneling regime and with 200 nm thick Alq3 barrier in the hopping regime. We observed high tunneling magnetoresistance at low temperatures (15-40%) and spin dependent superpoissonian shot noise in organic magnetic tunnel junctions (OMTJs) with PTCDA. The Fano factor exceeds 1.5-2 values which could be caused by interfacial states controlled by spin dependent bunching in the tunneling events through the molecules. The bias dependence of the low frequency noise in OMTJs with PTCDA barriers which includes both 1/f and random telegraph noise activated at specific biases will also be discussed. On the other hand, the organic junctions with ...
arXiv: Mesoscale and Nanoscale Physics, 2016
Molecular spintronics has successfully crossed its first decade of life becoming an important pla... more Molecular spintronics has successfully crossed its first decade of life becoming an important player in the race towards the fabrication of next generation spintronic devices. The development and fabrication of spin OLEDs represents one of the key challenges in this area. Indeed, combining spin polarised injection with light emission is expected to establish a quantum control over the statistics of singlet and triplet excitons in the emitting material, enabling a magneto electro optical multifunctionality. This may represent a new route for the increase of light emitting efficiency and, on the other hand, may embody a powerful tool for the investigation of spintronics effects in organic materials. In spite of numerous steps made in this direction, a convincing demonstration of this magnetic quantum control of the light emission has not been accomplished so far. Here, by tailoring the energy level alignment between the frontier orbitals of the organic semiconductor and the electrode ...
J. Phys. Chem. C, 2021
The inorganic/molecular spinterface is an ideal platform for generating 7 extraordinary spin effe... more The inorganic/molecular spinterface is an ideal platform for generating 7 extraordinary spin effects. Understanding and controlling these spin-related effects is 8 mandatory for the exploitation of such interfaces in devices. For this purpose we have 9 investigated the adsorption of α-sexithiophene (α-6T) on La 0.7 Sr 0.3 MnO 3 (LSMO) as one of 10 the prototypical material combinations used in organic spintronic devices. Atomic force 11 microscopy (AFM) confocal photoluminescence X-ray photoelectron spectroscopy and 12 metastable de-excitation spectroscopy unraveled the structure and the electronic 13 configuration of 6T for various surface coverages. This data set allowed the determination 14 of the characteristic features of occupied states: the band diagram and the work function. 15 Finally density functional theory enabled us to establish that the spin polarization in 6T 16 molecular orbitals critically depends on the termination layer of LSMO, showing a 17 substantial effect on...
![Research paper thumbnail of Publisher's Note: “Low intrinsic carrier density LSMO/Alq3/AlOx/Co organic spintronic devices” [Appl. Phys. Lett. 112, 142401 (2018)]](https://attachments.academia-assets.com/79627345/thumbnails/1.jpg)
](Applied Physics Letters, May 14, 2018
ACS Applied Materials & Interfaces
The understanding of magnetoresistance (MR) in organic spin valves (OSVs) based on molecular semi... more The understanding of magnetoresistance (MR) in organic spin valves (OSVs) based on molecular semiconductors is still incomplete after its demonstration more than a decade ago. While carrier concentration may play an essential role in spin transport in these devices, direct experimental evidence of its importance is lacking. We probed the role of charge carrier concentration by studying the interplay between MR and multilevel resistive switching in OSVs. The present work demonstrates that all salient features of these devices, particularly the intimate correlation between MR and resistance, can be accounted for by the impurity band model, based on oxygen migration. Finally, we highlight the critical 2 importance of carrier concentration in determining spin transport and MR in OSVs and the role of interface-mediated oxygen migration in controlling the OSVs response.
Applied Physics Letters
The understanding of spin injection and transport in organic spintronic devices is still incomple... more The understanding of spin injection and transport in organic spintronic devices is still incomplete, with some experiments showing magnetoresistance and others not detecting it. We have investigated the transport properties of a large number of tris-(8-hydroxyquinoline)aluminum-based organic spintronic devices with an electrical resistance greater than 5 MΩ that did not show magnetoresistance. Their transport properties could be described satisfactorily by known models for organic semiconductors. At high voltages (>2 V), the results followed the model of space charge limited current with a Poole-Frenkel mobility. At low voltages (∼0.1 V), that are those at which the spin valve behavior is usually observed, the charge transport was modelled by nearest neighbor hopping in intra-gap impurity levels, with a charge carrier density of n0 = (1.44 ± 0.21) × 1015 cm−3 at room temperature. Such a low carrier density can explain why no magnetoresistance was observed.
ACS applied materials & interfaces, Jan 23, 2018
One promising route toward encoding information is to utilize the two stable electronic states of... more One promising route toward encoding information is to utilize the two stable electronic states of a spin crossover molecule. While this property is clearly manifested in transport across single molecule junctions, evidence linking charge transport across a solid-state device to the molecular film's spin state has thus far remained indirect. To establish this link, we deploy materials-centric and device-centric operando experiments involving X-ray absorption spectroscopy. We find a correlation between the temperature dependencies of the junction resistance and the Fe spin state within the device's [Fe(H2B(pz)2)2(NH2-phen)] molecular film. We also factually observe that the Fe molecular site mediates charge transport. Our dual operando studies reveal that transport involves a subset of molecules within an electronically heterogeneous spin crossover film. Our work confers an insight that substantially improves the state-of-the-art regarding spin crossover-based devices, thanks ...
![Research paper thumbnail of Erratum: “Seed layer technique for high quality epitaxial manganite films” [AIP Advances 6, 085109 (2016)]](https://attachments.academia-assets.com/79627339/thumbnails/1.jpg)
](
ACS Applied Electronic Materials
ACS Applied Materials & Interfaces, Feb 5, 2019
The understanding of magnetoresistance (MR) in organic spin valves (OSVs) based on molecular semi... more The understanding of magnetoresistance (MR) in organic spin valves (OSVs) based on molecular semiconductors is still incomplete after its demonstration more than a decade ago. While carrier concentration may play an essential role in spin transport in these devices, direct experimental evidence of its importance is lacking. We probed the role of charge carrier concentration by studying the interplay between MR and multilevel resistive switching in OSVs. The present work demonstrates that all salient features of these devices, particularly the intimate correlation between MR and resistance, can be accounted for by the impurity band model, based on oxygen migration. Finally, we highlight the critical 2 importance of carrier concentration in determining spin transport and MR in OSVs and the role of interface-mediated oxygen migration in controlling the OSVs response.
The Journal of Physical Chemistry C, 2021
The inorganic/molecular spinterface is an ideal platform for generating extraordinary spin effect... more The inorganic/molecular spinterface is an ideal platform for generating extraordinary spin effects. Understanding and controlling these spin-related effects is mandatory for the exploitation of such interfaces in devices. For this purpose, we have investigated the adsorption of α-sexithiophene (α-6T) on La 0.7 Sr 0.3 MnO 3 (LSMO), as one of the prototypical material combinations used in organic spintronic devices. Atomic force microscopy, confocal photoluminescence, Xray photoelectron spectroscopy, and metastable de-excitation spectroscopy unraveled the structure and electronic configuration of 6T for various surface coverages. This data set allowed the determination of characteristic features of occupied states, the band diagram and the work function. Finally, density functional theory enabled us to establish that the spin polarization in 6T molecular orbitals critically depends on the termination layer of LSMO. We believe that this research provides important hints for a comprehensive understanding of spinterface effects in general and provides key suggestions for further engineering of LSMO/6T-based devices. INTRODUCTION: Hybridization at the interface between molecular entities and ferromagnetic metals leads to drastic changes of the properties of both layers [1,2]. Notably, an increase of spin polarization of states around the Fermi level [2], modulation of the magnetic anisotropy [3] and spin reorientation transitions were observed in ferromagnetic layers as well as the appearance of spin polarized states in the molecular material [5]. Such new hybrid interfaces with unexpected spin functionality, named after the seminal paper by Sanvito as "spinterfaces" [6], act as a key element at the molecular level for engineering the properties and the performance of spin-devices. Among the plethora of spinterfaces, those including half-metallic ferromagnetic oxides such as La 0.7 Sr 0.3 MnO 3 (LSMO) are of special interest. LSMO has been coupled to a variety of organic molecules and successfully used in spintronic devices [7,8], even showing the inversion of the sign of the polarization upon the deposition of an organic molecule [9]. Nonetheless, the variability of the composition of the termination layer of LSMO [10-12] hindered a reliable investigation of its interface with organic molecules. In this paper we focus on the coupling between a π-conjugated oligothiophene, 6T (sexithiophene), and LSMO; one of the first hybrid interfaces used in spin injection devices [13]. 6T is a rodlike model organic molecule [14] which contains six thiophene rings linked together; it can be easily sublimated in ultrahigh vacuum (UHV), a prerequisite for the control and reproducibility of interfacial states, and it is also known to form ordered thin layers on solid surfaces. Here, the growth process of 6T on
ACS Applied Materials & Interfaces, 2018
Scientific reports, Jan 10, 2014
The outgrowth formation in inorganic thin films is a dramatic problem that has limited the techno... more The outgrowth formation in inorganic thin films is a dramatic problem that has limited the technological impact of many techniques and materials. Outgrowths are often themselves part of the films, but are detrimental for vertical junctions since they cause short-circuits or work as defects, compromising the reproducibility and in some cases the operation of the corresponding devices. The problem of outgrowth is particularly relevant in ablation-based methods and in some complex oxides, but is present in a large variety of systems and techniques. Here we propose an efficient local electrochemical method to selectively decompose the outgrowths of conductive oxide thin films by electrochemical decomposition, without altering the properties of the background film. The process is carried out using the same set-up as for local oxidation nanolithography, except for the sign of the voltage bias and it works at the nanoscale both as serial method using a scanning probe and as parallel method...
Applied Physics Letters, 2013
We investigate spin precession (Hanle effect) in the prototypical organic spintronic giant magnet... more We investigate spin precession (Hanle effect) in the prototypical organic spintronic giant magnetoresistance (GMR) device La 0.7 Sr 0.3 MnO 3 (LSMO)/tris(8-hydroxyquinoline)(Alq3)/AlOx/Co. The Hanle effect is not observed in measurements taken by sweeping a magnetic field at different angles from the plane of the device. As possible explanations we discuss the tilting out of plane of the magnetization of the electrodes, exceptionally high mobility or hot spots. Our results call for a greater understanding of spin injection and transport in such devices.
Information and communication technology (ICT) is calling for solutions enabling lower power cons... more Information and communication technology (ICT) is calling for solutions enabling lower power consumption, further miniaturization and multi-functionality requiring the development of new device concepts and new materials. A fertile approach to meet such demands is the introduction of the spin degree of freedom into electronics devices, an approach commonly known as spintronics. This already lead to a revolution in the information storage (GMR read heads) in the last decades. Nowadays, the challenge is to bring spintronics also into devices dedicated to logics, communications and storage within the same material technology [1]. In this context the electric control of the magnetoresistance represents one of the most promising issues enabling both further miniaturization and multifunctional operation of spintronic devices. We will discuss the multi-functionality as an intrinsic characteristics of organic based spintronic devices [2] leading to conceptually new device paradigms. We will...
Journal of Colloid and Interface Science
The possible influence of internal barrier dynamics on spin, charge transport and their fluctuati... more The possible influence of internal barrier dynamics on spin, charge transport and their fluctuations in organic spintronics remains poorly understood. Here we present investigation of the electron transport and low frequency noise at temperatures down to 0.3K in magnetic tunnel junctions with an organic PTCDA barriers with thickness up to 5 nm in the tunneling regime and with 200 nm thick Alq3 barrier in the hopping regime. We observed high tunneling magnetoresistance at low temperatures (15-40%) and spin dependent superpoissonian shot noise in organic magnetic tunnel junctions (OMTJs) with PTCDA. The Fano factor exceeds 1.5-2 values which could be caused by interfacial states controlled by spin dependent bunching in the tunneling events through the molecules. The bias dependence of the low frequency noise in OMTJs with PTCDA barriers which includes both 1/f and random telegraph noise activated at specific biases will also be discussed. On the other hand, the organic junctions with ...
arXiv: Mesoscale and Nanoscale Physics, 2016
Molecular spintronics has successfully crossed its first decade of life becoming an important pla... more Molecular spintronics has successfully crossed its first decade of life becoming an important player in the race towards the fabrication of next generation spintronic devices. The development and fabrication of spin OLEDs represents one of the key challenges in this area. Indeed, combining spin polarised injection with light emission is expected to establish a quantum control over the statistics of singlet and triplet excitons in the emitting material, enabling a magneto electro optical multifunctionality. This may represent a new route for the increase of light emitting efficiency and, on the other hand, may embody a powerful tool for the investigation of spintronics effects in organic materials. In spite of numerous steps made in this direction, a convincing demonstration of this magnetic quantum control of the light emission has not been accomplished so far. Here, by tailoring the energy level alignment between the frontier orbitals of the organic semiconductor and the electrode ...
J. Phys. Chem. C, 2021
The inorganic/molecular spinterface is an ideal platform for generating 7 extraordinary spin effe... more The inorganic/molecular spinterface is an ideal platform for generating 7 extraordinary spin effects. Understanding and controlling these spin-related effects is 8 mandatory for the exploitation of such interfaces in devices. For this purpose we have 9 investigated the adsorption of α-sexithiophene (α-6T) on La 0.7 Sr 0.3 MnO 3 (LSMO) as one of 10 the prototypical material combinations used in organic spintronic devices. Atomic force 11 microscopy (AFM) confocal photoluminescence X-ray photoelectron spectroscopy and 12 metastable de-excitation spectroscopy unraveled the structure and the electronic 13 configuration of 6T for various surface coverages. This data set allowed the determination 14 of the characteristic features of occupied states: the band diagram and the work function. 15 Finally density functional theory enabled us to establish that the spin polarization in 6T 16 molecular orbitals critically depends on the termination layer of LSMO, showing a 17 substantial effect on...
Applied Physics Letters, May 14, 2018
ACS Applied Materials & Interfaces
The understanding of magnetoresistance (MR) in organic spin valves (OSVs) based on molecular semi... more The understanding of magnetoresistance (MR) in organic spin valves (OSVs) based on molecular semiconductors is still incomplete after its demonstration more than a decade ago. While carrier concentration may play an essential role in spin transport in these devices, direct experimental evidence of its importance is lacking. We probed the role of charge carrier concentration by studying the interplay between MR and multilevel resistive switching in OSVs. The present work demonstrates that all salient features of these devices, particularly the intimate correlation between MR and resistance, can be accounted for by the impurity band model, based on oxygen migration. Finally, we highlight the critical 2 importance of carrier concentration in determining spin transport and MR in OSVs and the role of interface-mediated oxygen migration in controlling the OSVs response.
Applied Physics Letters
The understanding of spin injection and transport in organic spintronic devices is still incomple... more The understanding of spin injection and transport in organic spintronic devices is still incomplete, with some experiments showing magnetoresistance and others not detecting it. We have investigated the transport properties of a large number of tris-(8-hydroxyquinoline)aluminum-based organic spintronic devices with an electrical resistance greater than 5 MΩ that did not show magnetoresistance. Their transport properties could be described satisfactorily by known models for organic semiconductors. At high voltages (>2 V), the results followed the model of space charge limited current with a Poole-Frenkel mobility. At low voltages (∼0.1 V), that are those at which the spin valve behavior is usually observed, the charge transport was modelled by nearest neighbor hopping in intra-gap impurity levels, with a charge carrier density of n0 = (1.44 ± 0.21) × 1015 cm−3 at room temperature. Such a low carrier density can explain why no magnetoresistance was observed.
ACS applied materials & interfaces, Jan 23, 2018
One promising route toward encoding information is to utilize the two stable electronic states of... more One promising route toward encoding information is to utilize the two stable electronic states of a spin crossover molecule. While this property is clearly manifested in transport across single molecule junctions, evidence linking charge transport across a solid-state device to the molecular film's spin state has thus far remained indirect. To establish this link, we deploy materials-centric and device-centric operando experiments involving X-ray absorption spectroscopy. We find a correlation between the temperature dependencies of the junction resistance and the Fe spin state within the device's [Fe(H2B(pz)2)2(NH2-phen)] molecular film. We also factually observe that the Fe molecular site mediates charge transport. Our dual operando studies reveal that transport involves a subset of molecules within an electronically heterogeneous spin crossover film. Our work confers an insight that substantially improves the state-of-the-art regarding spin crossover-based devices, thanks ...