Periodic Reporting for period 2 - Mol-2D (Molecule-induced control over 2D Materials)
Berichtszeitraum: 2020-04-01 bis 2021-09-30
Materials formed by atomic thin layers constitute a common topic of interest in physics, chemistry and materials science, with van der Waals heterostructures playing a central role as they afford the opportunity for both studying fundamental physical phenomena and developing applied research towards the design of novel materials and devices. In Mol-2D we propose to create a new class of heterostructures by combining functional molecules with 2D materials –exhibiting in particular superconductivity or magnetism– with the aim of tuning/improving the properties of the “all surface” 2D material through the interactions established with the functional molecular system. As molecular systems we will concentrate on bistable magnetic molecules able to switch between two spin states upon the application of an external stimulus (temperature, light, pressure, electrical field, etc.). The driving idea will be that of tuning the properties of the 2D material through an active control the hybrid interface. This concept provides an entire new class of smart molecular/2D heterostructures of interest that may give rise to a novel generation of hybrid materials and devices of direct application in highly topical fields like electronics, spintronics, molecular sensing and energy storage.
MOL-2D addresses major challenges in different 2D areas: i) in 2D physics, we will investigate the magnetic properties of magnets in the 2D limit and the new properties that should appear in heterostructures formed by truly 2D superconductors in contact with 2D magnets or magnetic molecules; ii) in 2D electronics, we will explore the possibility of tuning the properties of a 2D material by applying an external stimulus, or to design smart electronic/spintronic devices that respond to physical or chemical stimuli; iii) in 2D composite materials, a general goal will be that of designing hybrid molecular/2D materials with improved properties with respect to the pure 2D material to be used, for example, as active components of hybrid supercapacitors or electrocatalysts.
MOL-2D addresses major challenges in different 2D areas: i) in 2D physics, we will investigate the magnetic properties of magnets in the 2D limit and the new properties that should appear in heterostructures formed by truly 2D superconductors in contact with 2D magnets or magnetic molecules; ii) in 2D electronics, we will explore the possibility of tuning the properties of a 2D material by applying an external stimulus, or to design smart electronic/spintronic devices that respond to physical or chemical stimuli; iii) in 2D composite materials, a general goal will be that of designing hybrid molecular/2D materials with improved properties with respect to the pure 2D material to be used, for example, as active components of hybrid supercapacitors or electrocatalysts.
The work performed in Mol-2D can be grouped around three classes of materials/heterostructures: i) 2D superconductors and magnets and related vdW heterostructures; ii) Hybrid molecular/2D heterostructures; iii) 2D composite materials.
In the first class of materials, a major achievement has been the magnetic characterization in the 2D limit of the family of antiferromagnets MPS3 (M= Mn, Fe, Ni). In contrast to ferromagnets, the detection of the magnetic ordering in a 2D antiferromagnet constitutes a formidable experimental challenge since, due to the lack of a net magnetic moment in the ordered state, conventional techniques such as magneto-optical Kerr effect or Magnetic Force Microscopy, are not useful. Here, we demonstrated that using nanomechanical resonators this problem can be solved. Even more, this technique, which so far was used for sensing molecules in suspended membranes of 2D materials, has shown to be also sensitive to the structural changes induced in the lattice by applying an electrostatic strain, opening a way of tuning the magnetism. A second key achievement has been the preparation of novel vdW heterostructures incorporating a quantum spin liquid (1T-TaS2) or 2D superconductors (NbSe2). Electronic devices based on these heterostructures have provided the opportunity of studying for the first time the 2D physics that emerges in such cases.
In the second class of materials, a breakthrough has been the report the first example of a 2D molecular-based magnet based on a vdW coordination Fe polymer bridged by benzimidazole ligands. On mechanical exfoliation, crystalline single-layers are obtained that retain their long- range structural order and exhibit good mechanical properties. Compared with the inorganic 2D magnets, our results have shown that these molecular magnets present some unique features: i) the layers can be functionalized at will without altering the magnetic properties. ii) this coordination chemistry approach allows us to isolate chemically stable layers where, by changing either the metal or the benzimidazole ligand, novel 2D materials with tunable magnetic or topological properties can be designed. From a physical point of view, the unusual mechanical robustness exhibited by thin membranes of these 2D magnets can allow us to study their magnetic properties by using mechanical resonators. A second key result has been the report on the first example of smart molecular/2D heterostructure. This was obtained by covalently linking spin-crossover (SCO) nanoparticles on a MoS2 semiconducting layer. In this heterostructure the transport and optical properties of MoS2 can be tuned by the spin transition, induced thermally or by light. For the first time we have demonstrated that the SCO can be sensed optically taking advantage of the luminescent properties of the MoS2 monolayer. Further, we have shown that a reversible strain in the MoS2 layer can be induced by the molecular SCO system, which undergoes a significant change in volume upon the spin transition. These ground-breaking discoveries have shown the power of chemistry to design unprecedented classes of 2D materials and molecular/2D heterostructures of potential interest in 2D electronics and spintronics.
In the third class of materials (2D composites), a major achievement has been the preparation, using a molecular approach, of nanocomposites formed by graphene and magnetic nanoparticles exhibiting unprecedented features in the capacitance properties. An interesting discovery was the strong response of these composites upon the applying external stimuli such as magnetic fields or electron beams. This sensitivity, which results in a giant enhancement of the capacitance, has been exploited for the fabrication of high-efficient supercapacitors showing very competitive values.
In the first class of materials, a major achievement has been the magnetic characterization in the 2D limit of the family of antiferromagnets MPS3 (M= Mn, Fe, Ni). In contrast to ferromagnets, the detection of the magnetic ordering in a 2D antiferromagnet constitutes a formidable experimental challenge since, due to the lack of a net magnetic moment in the ordered state, conventional techniques such as magneto-optical Kerr effect or Magnetic Force Microscopy, are not useful. Here, we demonstrated that using nanomechanical resonators this problem can be solved. Even more, this technique, which so far was used for sensing molecules in suspended membranes of 2D materials, has shown to be also sensitive to the structural changes induced in the lattice by applying an electrostatic strain, opening a way of tuning the magnetism. A second key achievement has been the preparation of novel vdW heterostructures incorporating a quantum spin liquid (1T-TaS2) or 2D superconductors (NbSe2). Electronic devices based on these heterostructures have provided the opportunity of studying for the first time the 2D physics that emerges in such cases.
In the second class of materials, a breakthrough has been the report the first example of a 2D molecular-based magnet based on a vdW coordination Fe polymer bridged by benzimidazole ligands. On mechanical exfoliation, crystalline single-layers are obtained that retain their long- range structural order and exhibit good mechanical properties. Compared with the inorganic 2D magnets, our results have shown that these molecular magnets present some unique features: i) the layers can be functionalized at will without altering the magnetic properties. ii) this coordination chemistry approach allows us to isolate chemically stable layers where, by changing either the metal or the benzimidazole ligand, novel 2D materials with tunable magnetic or topological properties can be designed. From a physical point of view, the unusual mechanical robustness exhibited by thin membranes of these 2D magnets can allow us to study their magnetic properties by using mechanical resonators. A second key result has been the report on the first example of smart molecular/2D heterostructure. This was obtained by covalently linking spin-crossover (SCO) nanoparticles on a MoS2 semiconducting layer. In this heterostructure the transport and optical properties of MoS2 can be tuned by the spin transition, induced thermally or by light. For the first time we have demonstrated that the SCO can be sensed optically taking advantage of the luminescent properties of the MoS2 monolayer. Further, we have shown that a reversible strain in the MoS2 layer can be induced by the molecular SCO system, which undergoes a significant change in volume upon the spin transition. These ground-breaking discoveries have shown the power of chemistry to design unprecedented classes of 2D materials and molecular/2D heterostructures of potential interest in 2D electronics and spintronics.
In the third class of materials (2D composites), a major achievement has been the preparation, using a molecular approach, of nanocomposites formed by graphene and magnetic nanoparticles exhibiting unprecedented features in the capacitance properties. An interesting discovery was the strong response of these composites upon the applying external stimuli such as magnetic fields or electron beams. This sensitivity, which results in a giant enhancement of the capacitance, has been exploited for the fabrication of high-efficient supercapacitors showing very competitive values.
Most of the results obtained in Mol-2D so far are beyond the current state-of-the-art. Just to mention a few, we can consider i) fabrication of vdWs heterostructures based on 2D superconductors or ultrathin layers of quantum spin liquids; ii) magnetic characterization of a 2D antiferromagnet both inorgnic as well as molecular-based, using micromechanical resonators; iii) isolation of monolayers of molecular-based magnets; iv) design of smart molecular/2D heterostructures using a chemical approach; v) the preparation of 2D magnetic nanocomposites that respond to a magnetic stimulus to enhance their supercapacitive properties.
Until the end of the project, we expect to extend these results with the final goals of i) studying the emergent properties that should appear in a magnet in the 2D limit; ii) developing an electronics based on 2D superconductors; iii) Extending the types of 2D molecule-based magnets to other coordination compounds, with emphasis on the isolation of 2D ferromagnets; iv) Search for novel smart molecular/2D heterostructures using spin crossover systems of different dimensionalities (from single-molecules to 2D networks); v) Integrate these hybrid heterostructures in electronic/spintronic devices; vi) Prepare and process novel 2D magnetic nanocomposites to be integrated in hybrid supercapacitors with the final aim of developing real applications in the area of energy storage; vii) Develop 2D materials and hybrid hemostructures for electrocatalysis applications
Until the end of the project, we expect to extend these results with the final goals of i) studying the emergent properties that should appear in a magnet in the 2D limit; ii) developing an electronics based on 2D superconductors; iii) Extending the types of 2D molecule-based magnets to other coordination compounds, with emphasis on the isolation of 2D ferromagnets; iv) Search for novel smart molecular/2D heterostructures using spin crossover systems of different dimensionalities (from single-molecules to 2D networks); v) Integrate these hybrid heterostructures in electronic/spintronic devices; vi) Prepare and process novel 2D magnetic nanocomposites to be integrated in hybrid supercapacitors with the final aim of developing real applications in the area of energy storage; vii) Develop 2D materials and hybrid hemostructures for electrocatalysis applications