Influence of alkylphosphonic acid grafting on the electronic and magnetic properties of La2/3Sr1/3MnO3 surfaces

Self-assembled monolayers (SAMs) are highly promising materials for molecular engineering of electronic and spintronics devices thanks to their surface functionalization properties. In this direction, alkylphosphonic acids have been used to functionalize the most common ferromagnetic electrode in organic spintronics: La2/3Sr1/3MnO3 (LSMO). However, a study on the influence of SAMs grafting on LSMO electronic and magnetic properties is still missing. In this letter, we probe the influence of alkylphosphonic acids-based SAMs on the electronic and magnetic properties of the LSMO surface using different spectroscopies. We observe by X-ray photoemission and X-ray absorption that the grafting of …

Why Bring Organic and Molecular Electronics to Spintronics

Organic spintronics field is an emerging field at the frontier between organic chemistry and spintronics. Exploiting the peculiarity of these two fields, it combines the flexibility, versatility and low production cost of organic materials with the nonvolatility, spin degree of freedom and beyond CMOS capabilities offered by spintronics. Before starting the discussion on the organic spintronics field, in this chapter will be provided a brief introduction on organic and molecular electronics and the specificities of molecules. This will help to understand the advantages that molecular systems can bring to spintronics.

Prussian blue@MoS2 layer composites as highly efficient cathodes for sodium- and potassium-ion batteries

Prussian blue (PB) represents a simple, economical, and eco‐friendly system as cathode material for sodium‐ion batteries (SIBs). However, structural problems usually worsen its experimental performance thus motivating the search for alternative synthetic strategies and the formation of composites that compensate these deficiencies. Herein, a straightforward approach for the preparation of PB/MoS2‐based nanocomposites is presented. MoS2 provides a 2D active support for the homogeneous nucleation of porous PB nanocrystals, which feature superior surface areas than those obtained by other methodologies, giving rise to a compact PB shell covering the full flake. The nanocomposite exhibits an ex…

Self-Assembled Monolayer-Functionalized Half-Metallic Manganite for Molecular Spintronics

(La,Sr)MnO(3) manganite (LSMO) has emerged as the standard ferromagnetic electrode in organic spintronic devices due to its highly spin-polarized character and air stability. Whereas organic semiconductors and polymers have been mainly envisaged to propagate spin information, self-assembled monolayers (SAMs) have been overlooked and should be considered as promising materials for molecular engineering of spintronic devices. Surprisingly, up to now the first key step of SAM grafting protocols over LSMO surface thin films is still missing. We report the grafting of dodecyl (C12P) and octadecyl (C18P) phosphonic acids over the LSMO half-metallic oxide. Alkylphosphonic acids form ordered self-a…

Magneto-Transport Results in SAM Based MTJs

This chapter is dedicated to the description of the magneto-transport results obtained in LSMO/SAM/Co magnetic tunnel nanojunctions fabricated by nanoindentation lithography technique. We started by focusing on the study of LSMO/C12P/Co MTJs. This because C12P is a medium size alkyl chain: long enough to avoid short-circuits in the junction but short enough to give a device resistance in the order of few tens of MO and thus easier to measure. Next, we started to tune the molecule thickness from C10P to C18P (from 10 carbon atoms in the alkyl chain to 18). This allowed on one hand to validate our system by comparing the exponential increase of the junction resistance to the one reported in t…

Monolayer-to-Mesoscale Modulation of the Optical Properties in 2D CrI3 Mapped by Hyperspectral Microscopy

Correction: Effect of nanostructuration on the spin crossover transition in crystalline ultrathin films

Correction for ‘Effect of nanostructuration on the spin crossover transition in crystalline ultrathin films’ by Víctor Rubio-Giménez et al., Chem. Sci., 2019, DOI: 10.1039/c8sc04935a.

Spinterface: Crafting spintronics at the molecular scale

A number of studies have suggested that molecular materials could offer similar performance as, or even potentially supersede, those of inorganic materials in spintronics devices. Radically new spintronics functionalities, unavailable with conventional inorganic materials, could stem from the interface between ferromagnetic (FM) and molecular materials, giving rise to the so-called “spinterface” field. In this article, we review the fundamental concepts, recent experiments, and perspectives in this fast rising field, where the functionality is brought from the bulk to the ultimate downscaled device: the interface. The article shows how spin-dependent hybridization at the FM metal/molecule i…

Path to Overcome Material and Fundamental Obstacles in Spin Valves Based on Mo S 2 and Other Transition-Metal Dichalcogenides

International audience; Experimental studies on spin valves with exfoliated 2D materials face the main technological issue of ferromagnetic electrode oxidation during the 2Ds integration process. As a twofold outcome, magne-toresistance (MR) signals are very difficult to obtain and, when they finally are, they are often far from expectations. We propose a fabrication method to circumvent this key issue for 2D-based spintronics devices. We report on the fabrication of NiFe/MoS 2 /Co spin valves with mechanically exfoliated mul-tilayer MoS 2 using an in situ fabrication protocol that allows high-quality nonoxidized interfaces to be maintained between the ferromagnetic electrodes and the 2D la…

State of the Art in Organic and Molecular Spintronics

Organic spintronics field was born in 2002 with the pioneer work presented by the group of C. Taliani and A. V. Dediu. While molecules are easily tailored by chemical synthesis compared to inorganic materials, organics were initially seen as the ultimate media for spintronics devices due to their expected very long spin lifetime. Only very recently it was also unveiled that radically new spintronics functionalities, unavailable with conventional inorganic materials, could stem from the interface between ferromagnetic (FM) and molecular materials, giving rise to the so-called “spinterface” field. This chapter will present a general state of the art in organic and molecular spintronics fields…

Spin filtering by proximity effects at hybridized interfaces in spin-valves with 2D graphene barriers

We report on spin transport in state-of-the-art epitaxial monolayer graphene based 2D-magnetic tunnel junctions (2D-MTJs). In our measurements, supported by ab-initio calculations, the strength of interaction between ferromagnetic electrodes and graphene monolayers is shown to fundamentally control the resulting spin signal. In particular, by switching the graphene/ferromagnet interaction, spin transport reveals magneto-resistance signal MR > 80% in junctions with low resistance × area products. Descriptions based only on a simple K-point filtering picture (i.e. MR increase with the number of layers) are not sufficient to predict the behavior of our devices. We emphasize that hybridization …

Magneto-Transport Results in Alq3 Based OSVs

The achievement of good magnetoresistance signal at room temperature is an important requirement for the possible future development of organic devices for applications. However, until now only few works reported room temperature MR effect in organic spin valves (OSVs). In this regard, this chapter is dedicated to the investigation of Alq3-based OSVs where Alq3 molecule was chosen since it is a standard material in the field. A systematic study on Co/Alq3/Co OSVs will be presented showing room temperature MR results. Moreover, inelastic electron tunneling spectroscopy (IETS) technique will be used to prove spin injection into the organic layer. Finally, an insulating oxide barrier (Al2O3 or…

Field dependence of the vortex core size probed by scanning tunneling microscopy

We study the spatial distribution of the density of states (DOS) at zero bias N(r) in the mixed state of single and multigap superconductors. We provide an analytic expression for N(r) based on deGennes' relationship between DOS and the order parameter that reproduces well scanning tunneling microscopy (STM) data in several superconducting materials. In the single gap superconductor β-Bi2Pd, we find that N(r) is governed by a length scale ξH=φ0/2πH, which decreases in rising fields. The vortex core size C, defined via the slope of the order parameter at the vortex center, C (dΔ/dr|r→0)-1, differs from ξH by a material dependent numerical factor. The new data on the tunneling conductance and…

Reinforced Room-Temperature Spin Filtering in Chiral Paramagnetic Metallopeptides

Chirality-induced spin selectivity (CISS), whereby helical molecules polarize the spin of electrical current, is an intriguing effect with potential applications in nanospintronics. In this nascent field, the study of the CISS effect using paramagnetic chiral molecules, which could introduce another degree of freedom in controlling the spin transport, remains so far unexplored. To address this challenge, herein we propose the use of self-assembled monolayers (SAMs) of helical lanthanide-binding peptides. To elucidate the effect of the paramagnetic nuclei, monolayers of the peptide coordinating paramagnetic or diamagnetic ions are prepared. By means of spin-dependent electrochemistry, the CI…

Introduction to Spintronics

Spintronics was born in 1988 with the discovery of GMR provided simultaneously by A. Fert and P. Grunberg and rewarded in 2007 with the Nobel Prize in Physics. This field has since been largely exploited on the market, for example it has been at the base of every hard disk read head. Spintronics field is extremely active and interesting from both a fundamental point of view and for technological applications. Currently, with the aim at new functionalities, there is an increased activity from materials research perspective to understand and develop spintronics devices using materials with new properties like carbon nanotubes, graphene, topological insulators and molecules. This chapter will …

Wrapping up Metal-Organic Framework Crystals with Carbon Nanotubes

The presence of tetrazine units in the organic nodes of UiO- 68-TZCD controls the formation of ultrathin coatings of single wall nanotubes that decorate the surface of the crystal. These crystal hybrids can be prepared straightforwardly in one step and are extraordinarily respectful with the properties of the framework for combination of mesoporosity and surface areas near 4.000 m·g-1 ,with excellent stability in water, and conductivities at room temperature of 4·10-2 S·cm-1 even at very low carbon weight contents (2.3 wt%).

State of the Art in Alq3-Based Spintronic Devices

Since the first observation of a magnetoresistance signal in a vertical organic spin valve in 2004, tris (8-hydroxyquinoline) aluminium (Alq3) molecule has become a standard material for organic spintronics devices. This chapter will briefly present the state of the art on Alq3-based spintronic devices and the different approaches applied through the years to try to optimize these systems. It will be remarked that, despite extensively investigated, many fundamental questions regarding the spin injection and transport mechanisms through the organic layer are still unclear. The chapter will also present some of the most controversial topics in the organic spintronic area and it will highlight…

Path to Overcome Material and Fundamental Obstacles in Spin Valves Based on MoS2 and Other Transition-Metal Dichalcogenides

The recent introduction of two-dimensional materials into magnetic tunnel junctions (2D MTJs) offers very promising properties for spintronics, such as atomically defined interfaces, spin filtering, perpendicular anisotropy, and modulation of spin-orbit torque. Nevertheless, the difficulty of integrating exfoliated 2D materials into spintronic devices has limited exploration. Here the authors find a fabrication process leading to superior performance in MTJs based on transition-metal dichalcogenides, and further suggest a path to alleviate basic issues of technology and physics for 2D MTJs.

Path to Overcome Material and Fundamental Obstacles in Spin Valves Based on MoS2 and Other Transition-Metal Dichalcogenides

Experimental studies on spin valves with exfoliated 2D materials face the main technological issue of ferromagnetic electrode oxidation during the 2Ds integration process. As a twofold outcome, magnetoresistance (MR) signals are very difficult to obtain and, when they finally are, they are often far from expectations. We propose a fabrication method to circumvent this key issue for 2D-based spintronics devices. We report on the fabrication of NiFe/MoS2/Co spin valves with mechanically exfoliated multilayer MoS2 using an in situ fabrication protocol that allows high-quality nonoxidized interfaces to be maintained between the ferromagnetic electrodes and the 2D layer. Devices display a large …

Effect of nanostructuration on the spin crossover transition in crystalline ultrathin films† †Electronic supplementary information (ESI) available: Materials and methods, supplementary figures and tables. See DOI: 10.1039/c8sc04935a

Film thickness and microstructure critically affect the spin crossover transition of a 2D coordination polymer.

WS2 2D Semiconductor Down to Monolayers by Pulsed-Laser Deposition for Large-Scale Integration in Electronics and Spintronics Circuits

International audience; We report on the achievement of a large-scale tungsten disulfide (WS2) 2D semiconducting platform derived by pulsed-laser deposition (PLD) on both insulating substrates (SrTiO3), as required for in-plane semiconductor circuit definition, and ferromagnetic spin sources (Ni), as required for spintronics applications. We show thickness and phase control, with highly homogeneous wafer-scale monolayers observed under certain conditions, as demonstrated by X-ray photoelectron spectroscopy and Raman spectroscopy mappings. Interestingly, growth appears to be dependent on the substrate selection, with a dramatically increased growth rate on Ni substrates. We show that this 2D…

Introduction to Self-Assembled Monolayers

One of the most exciting targets of molecular spintronics field is to go towards multifunctional devices where the properties can be accurately controlled and actively changed. Spin dependent hybridization at the metal/molecule interface could thus be used in the tailoring of the resistive and magnetoresistive response of spintronic devices exploiting chemistry versatility. In this new direction, Self-Assembled Monolayers (SAMs) appear as highly promising candidates since each part and function of this system can be modulated independently (like a molecular LEGO building unit). Despite highly promising, they are still scarcely investigated in the literature probably due to the difficulties …

Ultrathin Films of 2D Hofmann-Type Coordination Polymers: Influence of Pillaring Linkers on Structural Flexibility and Vertical Charge Transport

Searching for novel materials and controlling their nanostructuration into electronic devices is a challenging task ahead of chemists and chemical engineers. Even more so when this new application requires an exquisite control over the morphology, crystallinity, roughness and orientation of the films produced. In this context, it is of critical importance to analyze the influence of the chemical composition of perspective materials on their properties at the nanoscale. We report the fabrication of ultrathin films (thickness < 30 nm) of a family of FeII Hofmann-like coordination polymers by using an optimized liquid phase epitaxy (LPE) set-up. The series [Fe(L)2{Pt(CN)4}] (L = pyridine, pyri…

Direct Visualization of Pyrrole Reactivity upon Confinement within a Cyclodextrin Metal–Organic Framework

Metal&ndash;organic frameworks can be used as porous templates to exert control over polymerization reactions. Shown here are the possibilities offered by these crystalline, porous nanoreactors to capture highly-reactive intermediates for a better understanding of the mechanism of polymerization reactions. By using a cyclodextrin framework the polymerization of pyrrole is restricted, capturing the formation of terpyrrole cationic intermediates. Single-crystal X-ray diffraction is used to provide definite information on the supramolecular interactions that induce the formation and stabilization of a conductive array of cationic complexes.

SAMs Based Device Fabrication and Characterization

Despite the high potentiality of SAMs for spintronics, not many results exist at the moment in the literature. This lack of results is mainly due to the difficulty to fabricate the devices. The two main technological problems consist in the ferromagnetic electrodes compatibility issues with wet chemistry and the short-circuit formation during top electrode deposition. A part of this thesis has been committed to overcome these technological problems. This chapter will explain the steps that led us to the development of SAMs-based magnetic tunnel nanojunctions.

Very Long Term Stabilization of a 2D Magnet down to the Monolayer for Device Integration

2D materials have recently demonstrated a strong potential for spintronic applications. This has been further reinforced by the discovery of ferromagnetic 2D layers. Nevertheless, the fragility of ...

Self-assembled monolayers based spintronics: from ferromagnetic surface functionalization to spin-dependent transport.

Chemically functionalized surfaces are studied for a wide range of applications going from medicine to electronics. Whereas non-magnetic surfaces have been widely studied, functionalization of magnetic surfaces is much less common and has almost never been used for spintronics applications. In this article we present the functionalization of La2/3Sr1/3MnO3, a ferromagnetic oxide, with self-assembled monolayers for spintronics. La2/3Sr1/3MnO3 is the prototypical half-metallic manganite used in spintronics studies. First, we show that La2/3Sr1/3MnO3 can be functionalized by alkylphosphonic acid molecules. We then emphasize the use of these functionalized surfaces in spintronics devices such a…

Origin of the Chemiresistive Response of Ultrathin Films of Conductive Metal–Organic Frameworks

Conductive metal-organic frameworks are opening new perspectives for the use of these porous materials for applications traditionally limited to more classical inorganic materials, such as their integration into electronic devices. This has enabled the development of chemiresistive sensors capable of transducing the presence of specific guests into an electrical response with good selectivity and sensitivity. By combining experimental data with computational modelling, a possible origin for the underlying mechanism of this phenomenon in ultrathin films (ca. 30 nm) of Cu-CAT-1 is described. ispartof: ANGEWANDTE CHEMIE-INTERNATIONAL EDITION vol:57 issue:46 pages:15086-15090 ispartof: location…

Bottom‐Up Fabrication of Semiconductive Metal-Organic Framework Ultrathin Films

Though generally considered insulating, recent progress on the discovery of conductive porous metal-organic frameworks (MOFs) offers new opportunities for their integration as electroactive components in electronic devices. Compared to classical semiconductors, these metal-organic hybrids combine the crystallinity of inorganic materials with easier chemical functionalization and processability. Still, future development depends on the ability to produce high-quality films with fine control over their orientation, crystallinity, homogeneity, and thickness. Here self-assembled monolayer substrate modification and bottom-up techniques are used to produce preferentially oriented, ultrathin, con…

Monolayer-to-mesoscale modulation of the optical properties in 2D CrI3 mapped by hyperspectral microscopy

Magnetic 2D materials hold promise to change the miniaturization paradigm of unidirectional photonic components. However, the integration of these materials in devices hinges on the accurate determination of the optical properties down to the monolayer limit, which is still missing. By using hyperspectral wide-field imaging at room temperature, we reveal a nonmonotonic thickness dependence of the complex optical dielectric function in the archetypal magnetic 2D material CrI3 extending across different length scales: onsetting at the mesoscale, peaking at the nanoscale, and decreasing again down to the single layer. These results portray a modification of the electronic properties of the mat…

Raman Spectra of ZrS2 and ZrSe2 from Bulk to Atomically Thin Layers

In the race towards two-dimensional electronic and optoelectronic devices, semiconducting transition metal dichalcogenides (TMDCs) from group VIB have been intensively studied in recent years due to the indirect to direct band-gap transition from bulk to the monolayer. However, new materials still need to be explored. For example, semiconducting TMDCs from group IVB have been predicted to have larger mobilities than their counterparts from group VIB in the monolayer limit. In this work we report the mechanical exfoliation of ZrX2 (X = S, Se) from bulk down to the monolayer and we study the dimensionality dependence of the Raman spectra in ambient conditions. We observe Raman signal from bul…

A perpendicular graphene/ferromagnet electrode for spintronics

We report on the large-scale integration of graphene layers over a FePd perpendicular magnetic anisotropy (PMA) platform, targeting further downscaling of spin circuits. An L10 FePd ordered alloy showing both high magneto-crystalline anisotropy and a low magnetic damping constant, is deposited by magnetron sputtering. The graphene layer is then grown on top of it by large-scale chemical vapor deposition. A step-by-step study, including structural and magnetic analyses by x-ray diffraction and Kerr microscopy, shows that the measured FePd properties are preserved after the graphene deposition process. This scheme provides a graphene protected perpendicular spin electrode showing resistance t…

Direct visualization of pyrrole reactivity by confined oxidation in a Cyclodextrin Metal‐Organic Framework

Metal-organic frameworks can be used as porous templates to exert control over polymerization reactions. Shown here are the possibilities offered by these crystalline, porous nanoreactors to capture highly‐reactive intermediates for a better understanding of the mechanism of polymerization reactions. By using a cyclodextrin framework the polymerization of pyrrole is restricted, capturing the formation of terpyrrole cationic intermediates. Single‐crystal X‐ray diffraction is used to provide definite information on the supramolecular interactions that induce the formation and stabilization of a conductive array of cationic complexes.

Smart molecular/MoS2 Heterostructures Featuring Light and Thermally-Induced Strain Driven by Spin Switching

In this work we exploit the ability of spin-crossover molecules to switch between two spin states, upon the application of external stimuli, to prepare smart molecular/2D heterostructures. Through the chemical design of the hybrid interface, that involves a covalent grafting between the two components, we obtain a hybrid heterostructure formed by spin-crossover nanoparticles anchored on chemically functionalized monolayers of semiconducting MoS2. In the resulting hybrid, the strain generated by the molecular system over the MoS2 layer, as a consequence of a thermal or light-induced spin switching, results in a dramatic and reversible change of its electrical and optical properties. This nov…

A Local Study of the Transport Mechanisms in MoS2 Layers for Magnetic Tunnel Junctions

MoS2-based vertical spintronic devices have attracted an increasing interest thanks to theoretical predictions of large magnetoresistance signals. However, experimental performances are still far from expectations. Here, we carry out the local electrical characterization of thin MoS2 flakes in a Co/Al2O3/MoS2 structure through conductive tip AFM measurements. We show that thin MoS2 presents a metallic behavior with a strong lateral transport contribution that hinders the direct tunnelling through thin layers. Indeed, no resistance dependence is observed with the flake thickness. These findings reveal a spin depolarization source in the MoS2-based spin valves, thus pointing to possible solut…

Spin-crossover nanoparticles anchored on MoS2 layers for heterostructures with tunable strain driven by thermal or light-induced spin switching

In the past few years, the effect of strain on the optical and electronic properties of MoS2 layers has attracted particular attention as it can improve the performance of optoelectronic and spintronic devices. Although several approaches have been explored, strain is typically externally applied on the two-dimensional material. In this work, we describe the preparation of a reversible ‘self-strainable’ system in which the strain is generated at the molecular level by one component of a MoS2-based composite material. Spin-crossover nanoparticles were covalently grafted onto functionalized layers of semiconducting MoS2 to form a hybrid heterostructure. Their ability to switch between two spi…

CCDC 1893564: Experimental Crystal Structure Determination

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CCDC 1910991: Experimental Crystal Structure Determination

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CCDC 1910989: Experimental Crystal Structure Determination

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